Browse Topic: Ignition timing

Items (1,082)

3D Computational Fluid Dynamics Analysis of the Performance and Emissions of an Off-Highway Port Fuel Injection Hydrogen Engine

03-19-04-0018

7/27/2026

To fulfil the global aspiration of achieving net-zero emissions, hydrogen as a fuel seems to be one of the promising candidates. High energy density per unit mass and zero carbonaceous emissions are the two salient advantages that hydrogen offers. In the present study, a set of detailed chemistry-based 3D CFD combustion simulation has been carried on a 3-cylinder turbocharged, water-cooled port fuel injection SI Hydrogen engine to understand its optimum air–fuel ratio, compression ratio, spark timing and combustion chamber geometry. The simulations have been conducted at the full load of the rated power and maximum torque engine rpms. During simulation, the λ zone for study is restricted between 2.1 and 2.7. Two different bowl geometries (spherical and cylindrical), with two compression ratio options (12 and 14) are explored in the simulations. While the spherical bowl seems to accommodate flame front better than the cylindrical bowl, the compression ratio of 12 is a safer choice to control the maximum rate of pressure rise (dp/dθ). At full load and rated speed, the indicated thermal efficiency drops by 7.7% as the λ swings from 2.1 to 2.7, whereas the indicated specific NOx and dp/dθ drop by 99% and 81%, respectively. Similarly, at full load and maximum torque RPM, the indicated thermal efficiency drops by 6.4% with λ swing from 2.1 to 2.7, whereas the indicated specific NOx and dp/dθ drop by 99% and 91%, respectively. Beyond λ = 2.4 NOx reaches almost to zero, however, at a compromise of the thermal efficiency. The dp/dθ remains well within the acceptable limit under this scenario. To account this trade-off between the performance and emission parameters, optimum λ zone has been found out to be between 2.3 and 2.5.

Satre, Santosh Dadasaheb, Mukherjee, Nalini Kanta, Kumar, Sanjeev, Nene, Devendra

Study on Diesel-Methanol Non-Premixed Combustion Characteristics of a Marine Dual-Fuel Engine at Different Methanol Substitution Rate

2026-99-0517

7/10/2026

Methanol use in marine engines has the potential to reduce nitrogen oxide emissions, particulates, and greenhouse gas emissions. A turbocharged four-stroke marine diesel powerplant was converted to run as a double-DI (direct injection) diesel-methanol hybrid engine. Experimental studies using a non-premixed combustion scheme showed that higher methanol substitution ratios (MSR) led to increased peak heat release rates. The combustion process displayed distinctive two-phase behaviors. Increasing MSR caused retarded ignition timing, shortened combustion duration, and improved thermal efficiency. Combustion stability was significantly improved at higher MSR. Emissions results showed NOX and HC were increased in proportion to MSR, whilst particulate emissions and CO concentrations were inversely reduced. Methanol enrichment was found to enhance NOX and HC formation processes but also accelerate soot particulate decomposition and CO oxidation mechanisms.

Li, Xiao, Jiang, Yuqi, Yan, Ping, Zheng, Liang, Li, Hongmei, Zhang, Wenzheng, Chen, Chao, Man, Zhongguo

A Holistic CFD Methodology for Full- and Multi-Cycle Simulation of Hydrogen Direct-Injection Internal Combustion Engines

2026-37-0016

6/9/2026

Hydrogen is emerging as a viable energy carrier for the decarbonization of internal combustion engines (ICEs), representing a necessary step toward the long-term sustainability of this technology. In particular, hydrogen direct injection (DI) operation is receiving increased attention due to its inherent advantages over port fuel injection (PFI), such as reduced risks of abnormal combustion, higher specific power, and improved thermal efficiency. However, the mixture preparation process in DI operation generally leads to a stratified charge, especially under intermediate-to-late injection strategies, which in turn strongly affects ignition, combustion performance, and engine-out emissions. Therefore, investigating mixture formation, its key influencing parameters, and the resulting effects on the combustion process is essential for the proper design and optimization of hydrogen-fuelled DI ICEs. In this context, computational fluid dynamics (CFD) emerges as a powerful tool to address this research gap. Nevertheless, the numerical simulation of hydrogen DI ICEs presents several challenges, mainly related to the high pressure ratios across the injector nozzle, which generate under-expanded hydrogen jets with complex shock structures, as well as to the combustion behaviour of lean air–hydrogen mixtures characterized by thermo-diffusive instabilities. Consequently, the development of a high-fidelity and computationally efficient CFD methodology is a key requirement. In this work, a retrofitted single-cylinder engine (SCE) equipped with a hollow-cone injector is simulated over the entire engine cycle, considering operation under a moderately late DI strategy. First, the proposed 3D-CFD methodology is validated against the engine experimental data to assess its predictivity. The same operating condition is then investigated through multi-cycle simulations to evaluate numerical stability and analyse convergence behaviour. The results show that the air–hydrogen mixture is highly stratified at ignition timing, yet the methodology accurately captures the in-cylinder pressure and heat release rate evolution, also across multiple engine cycles.

Capecci, Marcolucio, Lucchini, Tommaso, Sforza, Lorenzo, Pezza, Vincenzo, Tosi, Sergio

Effects of Engine Geometries on the Combustion Characteristics of a Heavy-Duty Hydrogen Spark-Ignition Engine

2026-37-0046

6/9/2026

For heavy-duty applications, hydrogen (H2) internal combustion engines offer a practical solution for future transportation. However, the influence of cylinder head flow characteristics and piston geometry on lean H2 combustion remains insufficiently understood. This study presents a comprehensive computational investigation of three engine configurations characterized by distinct in-cylinder flow dynamics: mild swirl and tumble (Engine a), strong tumble (Engine b), and strong swirl (Engine c). High-fidelity three-dimensional computational fluid dynamics simulations were performed for both port-fuel injection (PFI) and direct injection (DI) strategies. The impact of piston geometry was evaluated by comparing the baseline piston with a flat piston, while the spark timing was optimized to achieve favorable combustion phasing. Combustion and NOx formation were modeled using a G-equation-based combustion framework incorporating diffusive-thermal instability effects and a validated in-house H2 chemical mechanism. Turbulence-flame interactions were further characterized using Borghi-Peters diagrams. Under PFI operation, the strong-tumble configuration (Engine b) generated the highest turbulent kinetic energy (TKE), resulting in faster flame propagation, more advanced combustion phasing, and improved thermal efficiency. The flat piston further enhanced efficiency by reducing mixture confinement within piston-induced recirculation zones. Under DI operation, H2 injection significantly increased turbulence intensity, and a flat piston promoted higher TKE near spark timing in Engines b and c by reducing mixture-wall interaction, leading to faster combustion compared with the baseline piston. In contrast, the original piston produced higher TKE within the piston bowl in Engine a due to stronger recirculation. Additionally, the strong-tumble configuration achieved the most homogeneous mixture distribution under DI conditions. These results demonstrate that in-cylinder flow structure, piston geometry, and DI injection strongly affect turbulence generation, mixture formation, and combustion performance. The strong-tumble configuration shows the greatest potential for achieving high thermal efficiency with controlled emissions in lean H2 spark ignition engines.

Liu, Xinlei, Menaca, Rafael, Cenker, Emre, Silva, Mickael, Qahtani, Yasser A., Pei, Yuanjiang, Turner, James W.G., Im, Hong G.

Predictive Modelling of NO _x and Unburned Hydrogen Emissions in a Direct-Injection Hydrogen Spark-Ignition Engine

2026-37-0007

6/9/2026

Hydrogen is emerging as a compelling energy carrier for future transportation due to its potential to enable fully decarbonised operation and near-zero tailpipe pollutant emissions. Realising this potential in reciprocating internal combustion engines requires a detailed understanding of the complex interactions governing hydrogen combustion and emissions formation. In this context, physics-based reduced-order emission predictive modelling offers a powerful means to accelerate the development and optimisation of hydrogen-fuelled engines by enabling rapid evaluation of operating strategies without the need for extensive experimental campaigns. This study investigates the simulation of nitrogen oxides (NOx) and unburned hydrogen (uH2) emissions from a 0.5L spark-ignition direct injection single-cylinder research engine within a 1D-0D simulation approach. For NOx prediction, a simplified kinetic mechanism is coupled with both a 0D two-zone combustion model and a thermal multi-zone in-cylinder representation, enabling assessment of the need to account for temperature stratification for accurate prediction. For uH₂ emissions, phenomenological sub-models describing flame wall quenching and top-land crevice mechanisms are implemented and calibrated to capture the dominant sources of hydrogen escape during combustion. The models are validated against an experimental dataset spanning a wide range of engine conditions, including variations in engine load, relative air–fuel ratio from stoichiometric to ultra-lean combustion, dilution via exhaust gas recirculation, and spark timing. The comparison highlights the models' ability to reproduce observed physical trends across different engine operating conditions for both NOx and uH2. Regarding NOx emissions, the accounting of temperature stratification with the multi-zone model enables more accurate predictions of trends and absolute values. The uH2 model provides fundamental insights into hydrogen engine flame propagation by highlighting the need for flame propagation in the top-land crevice at richer λ to reproduce observed trends. Overall, the study provides insights into both hydrogen-specific emission mechanisms and key modelling requirements for accurate pollutant simulation in hydrogen engines.

Malfi, Enrica, De Felice, Massimiliano, Esposito, Stefania, Ribnishki, Aleksandar, King, Aidan, Akehurst, Sam, Jones, Peter, Goyal, Harsh

Effect of EGR Rate on Cyclohexanol-Diesel Dual-fuel Engines

2026-99-1709

5/22/2026

To reduce high NOx emissions from diesel-cyclohexanol blends, this study employed a marine medium-speed diesel engine as the experimental platform. An in-cylinder combustion model was developed and meshed using AVL - FIRE software, with model validity validated against experimental data. Tests were conducted at four load conditions (25%, 50%, 75%, and 100% load) with a 30% cyclohexanol blend (C30) and four EGR rates (0%, 7.5%, 10%, and 12.5%) to analyze combustion characteristics, emissions, and fuel economy. The results showed that the introduction of EGR had a striking inhibitory effect on NOx emissions. At 100% load with 12.5% EGR rate, NOx emissions were substantially reduced compared to baseline operation without EGR. However, EGR implementation led to delayed ignition timing, reduced in-cylinder pressure, and worsened fuel economy. Therefore, an appropriately calibrated EGR strategy can effectively reduce NOx emissions, though it requires optimization to mitigate adverse effects on combustion performance and efficiency.

Liu, Yuchen, Yang, Chenxi, Fan, Jinyu, Chen, Ke, Ye, Zixiao, Huang, Jialiang

Experimental Study of Knock Resistance Offered by Direct Water Injections in a Single-Cylinder Spark Ignition Engine

03-19-02-0011

4/11/2026

Stochastic end-gas autoignition in spark ignition (SI) engines, commonly called “knock,” limits attainable engine efficiencies. Multiple pathways to extend SI engine operation into knock-limited regions have been studied, including direct water injection (DWI). This study employs single-cylinder engine experiments with a centrally mounted water injector to investigate the knock resistance offered by compression stroke water injections, which, through incomplete mixing, can thermally stratify the cylinder. In SI, thermally stratifying injections are expected to forcibly widen the cylinder temperature distribution by preferentially cooling the cylinder periphery. The end-gas is in the cylinder periphery. A cooler end-gas would result in longer ignition delays, thus providing knock resistance. The difference between intake temperature required to match knock-limited CA50 and a baseline intake temperature at the load of 8 bar IMEPg (gross indicated mean effective pressure) was used to quantify the “effective charge cooling” for the injection timings studied. A higher positive value for the effective charge cooling implies higher knock resistance. Effective charge cooling values for early compression stroke injection timings (−180° to −120° aTDC) were observed in the range of ~35−45 K. Later compression stroke and intake stroke injection timings displayed effective charge cooling values in the range of ~5−35 K and ~0−20 K. A compression stroke injection timing sweep was performed at a load of 6 bar IMEPg while holding the spark timing, intake temperature, and water mass constant to study the effect of injection timing on the combustion process. Although CA50 advanced while delaying the injection timing (−180° to −80° aTDC), post-CA50 burn durations stayed nearly constant, a behavior consistent with the presence of thermal stratification. Thus, it was concluded that injection timings that heterogeneously cool the cylinder provide higher knock resistance compared to bulk cooling.

Datar, Aditya, Vedpathak, Kunal, Gainey, Brian, Lawler , Benjamin

Investigation of In-Cylinder Cycle-to-Cycle Variation Using PIV, LIF and RANS Simulation

2026-01-0299

4/7/2026

Cycle-to-cycle variation (CCV) of combustion is an issue that inevitably arises in internal combustion engines. There is a need to clarify and improve the situation, as well as predict it using computational fluid dynamics (CFD). This study involved carrying out experimental analyses of the factors that cause combustion cycle fluctuations, as well as predicting the CCV of gas flow using RANS. To elucidate the CCV in gas flow and combustion within gasoline engine, simultaneous TR-PIV, PLIF and direct-photography of flame propagation were performed using an optical single-cylinder engine, CCV prediction model for gas flow using RANS was verified. The results revealed the following: The variation in the equivalence ratio per cycle has little effect on initial combustion but does influence IMEP. Evaluating the laminar flame speed, SL and turbulent flame speed, ST as factors determining initial combustion revealed almost no correlation with SL, while moderate correlations were observed between ST and CA10. The position of the tumble vortex center at ignition timing was found to be critical; the vortex center position most favorable for advancing combustion timing was located to diagonally below the spark plug. The angular velocity at the center of the tumble vortex in the ensemble averaged flow significantly affected the turbulence kinetic energy (TKE) at the ignition timing, initial flame propagation speed, and CA10 phase. A model predicting cycle fluctuations during non-combustion was developed and verified against experiments. The CCV predicted using the spatial-based model reproduced the experimental CCV trends.

Hokimoto, Satoshi, Moriyoshi, Yasuo, Kuboyama, Tatsuya

Investigation of Flame Speed Effects towards Knock Suppression in a Boosted Spark-Ignited Engine Using 1-D Modeling

2026-01-0311

4/7/2026

To combine high efficiencies and low pollutant emissions, engine manufacturers have developed downsized spark-ignited (SI) engines in light- and medium-duty applications utilizing charge boosting and high compression ratio. While these techniques have proven effective, abnormal combustion such as auto-ignition and knock present a challenge and an important limitation towards high efficiencies. In this work, simulations have been utilized for knock onset predictions as well to provide relevant insights and trends of engine and fuel parameters including flame speed on auto-ignition. A one-dimensional (1-D) GT-Power model was utilized in this study with a semi-predictive flame propagation model and kinetic mechanism solver to isolate the flame propagation rate on auto-ignition and knock. This work presents a comprehensive study of the laminar flame speed (LFS) effect on combustion at knocking conditions in a high compression ratio long stroke engine (LSE) fueled by propane. Knock onset and index from GT-Power as well as cylinder pressure were compared, as well as pressure-temperature trajectories and Borghi-Peters diagrams, while changing LFS via a multiplier at fixed ignition timing, fixed combustion phasing and knock-limited spark advance (KLSA). Moreover, cycle-to-cycle variability (CCV) was modeled through GT-Power. Results exhibited consistent trends at each condition, showing a significant importance of combustion phasing on knock onset and index. High flame speed displayed a reduction in knock index at fixed combustion phasing and KLSA conditions as well as a decrease in CCV, even eliminating knock onset at extreme LFS values, thus highlighting the benefits of faster flame speed in SI combustion with respect to engine efficiency and knock avoidance.

Douvry-Rabjeau, Julien, DelVescovo, Dan

A Comparative Study of Combustion Stability Improvement via Prolonged Discharge Duration under Engine Idling Conditions

2026-01-0308

4/7/2026

Proper control over combustion and emission characteristics under engine idling conditions remains to be challenging, especially when engine block temperature is low. A specially designed common-coil pack was demonstrated to improve engine idling stability in previous SAE congress. In this paper, the progress on further development of the ignition system was reported with improved system stability and enhanced ignition performances. The impact of the prolonged discharge duration on the combustion stability was investigated on a turbocharged 4-cylinder production engine, with special attention to cylinder-by-cylinder variation under cold and hot engine block temperatures. It is observed that a prolonged discharge duration can reduce both cycle-to-cycle and cylinder-to-cylinder variations significantly. Especially under cold engine block temperature conditions, prolonged discharge duration together with advanced spark timing can increase engine load and reduce carbon monoxide emissions effectively. Then, the total energy consumption of the ignition system under various operation conditions were calculated and compared with the engine power gained by the ignition system.

Yu, Xiao, Jin, Long, Leblanc, Simon, Ting, David, Zheng, Ming

Relative Knocking Intensity to Discuss Similarities and Differences between Low- and High-Speed Knocking Phenomena

2026-01-0312

4/7/2026

Knock intensity, the maximum half-amplitude of pressure oscillation, reaches 1 MPa once in thousands of cycles under a certain boosted high-load condition at the engine speed of 5000 min-1, which is named high-speed super knock. In the present study, a mass-production turbo-charged direct-injection gasoline engine is operated for the indicated mean effective pressure of 1.7 MPa at the engine speed of 1500 to 5000 min-1. Unburned-zone autoignition timing is estimated using Livengood-Wu integral coupled with a small set of ignition delay time equations, which matches that detected from the differential value of net heat release rate, with a difference below 2 degrees in the whole range of engine speed. As unburned-zone autoignition timing advances, ignition delay time in an unburned zone at the autoignition timing shortens. Whenever autoignition occurs at 15 degrees after TDC, the ignition delay time is the period of about 10 degrees, regardless of engine speed. Knock intensity divided by the intensity of pressure oscillation induced by the main combustion, is named relative knock intensity. True heavy knock with an extremely-large relative knock intensity occurs occasionally at the low engine speed of 1500 to 2000 min-1, of which the occurrence rate decreases with the increase in engine speed. The high-speed super knock also has an extremely-large relative knock intensity, which might be a rare occurrence of the true heavy knock. A propagation flame front is visualized at autoignition timing using 20 ion probes mounted on the combustion chamber roof. When the high-speed super knock occurs, a relatively-large volume of unburned zone is located directly below the exhaust valves. However, no remarkable autoigniton heat release is observed.

Zeng, Changzhi, Kuboyama, Tatsuya, Yatsufusa, Tomoaki, Okuyama, Shota, Kuwahara, Kazunari

Experimental Study on the Effect of Ignition Strategy on Combustion and Emissions in a Direct Injection Hydrogen Engine

2026-01-0330

4/7/2026

Hydrogen-fueled internal combustion engines (H₂ICEs) are a promising pathway toward carbon-neutral transportation, but their efficiency and emissions performance are highly sensitive to ignition control strategies. This study systematically investigates the combined effects of spark timing (−10 to −26 °CA BTDC) and spark energy (25–40 mJ) on combustion characteristics in a direct injection H₂ICE operating at a constant speed of 1400 r/min under low, medium, and high load conditions. Results show that spark timing advance produces load-dependent effects: at low load, it increases the peak heat release rate while delaying peak pressure and shortening combustion duration; at medium and high loads, it advances both peaks toward TDC with an optimal spark timing shifting closer to −14 °CA. Ignition delay was only slightly reduced at low load but significantly shortened by about 3 °CA at high load. NOx emissions increased nearly linearly with spark advance, while slight retardation effectively halved NOx at low load without compromising torque. Increasing spark energy reduced ignition delay by up to 23% and shortened combustion duration by 2–4 °CA at low load, resulting in a torque increase from 48 to 60 N·m; however, the benefits diminished with increasing load. Additionally, higher spark energy led to a moderate NOₓ rise, particularly under medium load. These findings offer valuable insights into the optimization of ignition strategies for H₂ICEs, providing a foundation for improving combustion efficiency while minimizing emissions in zero-carbon hydrogen-powered engine systems.

Zhao, Keqin, Lou, Diming, Zhang, Yunhua, Fang, Liang, Tan, Piqiang, Hu, Zhiyuan

Emission and Combustion Characteristics of a Hydrogen Direct-Injection Spark Ignition Engine Using EGR

2026-01-0325

4/7/2026

This study experimentally investigates the combined effects of exhaust gas recirculation (EGR) and injection timing on the combustion and emission characteristics of a hydrogen direct injection engine. A single-cylinder 395 cc research engine was used, with injection timing varied from 60° to 180° BTDC and EGR rates from 0% to 30%. In-cylinder pressure, apparent heat release rate (AHRR), NOx, and unburned hydrogen concentrations were measured to analyze the influence of mixture formation and dilution on engine performance. Under non-EGR conditions, retarding the injection timing promoted mixture stratification, resulting in faster flame propagation and shorter combustion duration. However, localized high-temperature regions increased NOx formation, while incomplete combustion in lean or rich zones elevated unburned hydrogen emissions. When EGR was introduced, both ignition delay and combustion duration increased due to reduced oxygen concentration and thermal dilution. Nevertheless, the net indicated mean effective pressure (nIMEP) and indicated thermal efficiency (ITE) decreased by less than 1.6% and 1%, respectively, demonstrating that hydrogen’s fast combustion characteristics compensated for the reactivity loss. As the EGR rate increased, the formation of NOx and the emission of unburned hydrogen showed noticeable changes. At 30% EGR, NOx emissions decreased by up to 76% compared to the non-EGR baseline while maintaining stable combustion. However, excessive EGR resulted in increased unburned hydrogen emissions. These findings confirm that, with a properly optimized EGR rate, EGR is a more effective strategy than injection timing control for NOx reduction, achieving significant reduction with minimal efficiency penalty, and providing design insights for practical hydrogen-fueled engines.

Yang, Heetae, Ki, Youngmin, Kim, Jungho Justin, Kim, Jinsu, Bae, Choongsik, Hwang, Joonsik

Fuel Effects on EGR Tolerance of Synthetic Gasoline Fuels in a DISI Engine

2026-01-0305

4/7/2026

Drop-in synthetic gasoline fuels are an attractive alternative to traditional fossil fuels for transportation due to their high energy density, compatibility with the existing fleet and potential to decrease carbon intensity. Despite of meeting gasoline standards, the composition of these fuels can vary depending on the feedstock used for production and the production process, which has been shown to affect engine performance and emissions. This study investigated the effects of synthetic fuel composition on combustion in a direct-injection spark-ignition engine. Spark timing sweeps from the stability limit to the knock limit were performed with three different bio-fuels, methanol-to-gasoline, ethanol-to-gasoline and hydrotreated-biomass gasoline, at different exhaust gas recirculation (EGR) rates, and results were compared against a research-grade E10 (10%vol ethanol) regular gasoline representative of petroleum gasoline available in the US. Octane index analyses showed that knock resistance differences between fuels cannot be explained by their octane rating when EGR is added. Results demonstrated that adding EGR at medium loads is a very effective approach to increase efficiency despite of increasing burn duration because higher EGR rates led to lower pumping loses and lower heat transfer, while keeping combustion efficiency constant. The impact of EGR on combustion has shown to be very sensitive to fuel composition, and the knock resistance of fuels with strong low-temperature chemistry increased more with EGR addition that that of fuels with mild low-temperature chemistry. Similarly, the early flame propagation of fuels with strong low-temperature chemistry is more affected by EGR, limiting retardability and EGR tolerance. Results from this study indicated that, despite being considered drop-in, composition variability of synthetic fuels can be leveraged to improve engine performance.

MacDonald, James, Narayanan, Abhinandhan, Lopez Pintor, Dario, Matsubara, Naoyoshi, Kitano, Koji, Yamada, Ryota, Sugata, Kenji

Development of an ‘Online’ Combustion System Calibration Method using a Non-Dominated Sorting Genetic Algorithm

2026-01-0285

4/7/2026

Calibration is a major resource bottleneck and source of risk in powertrain technology development. A promising alternative to the typical design-of-experiments (DoE) approach is the use of a ‘Non-Dominated Sorting Genetic Algorithm’ (NSGA) calibration method, where an iterative process is used to directly identify the Pareto Fronts between performance metrics, for example, net mean effective pressure (NMEP) and NOx emission. The goal of the present work was to develop and demonstrate a fully ‘online’ combustion system calibration method based on an NSGA, where the algorithm operates directly on experimental data rather than empirical models as is typical in the literature. This was completed by first designing an optimal NSGA for combustion system calibration and then demonstrating its use for an experimental combustion system calibration on a single cylinder gasoline engine at one operating condition. Results from the design process here indicate that ‘online’ NSGAs have a strong potential to outperform traditional DoEs in the development of Pareto-optimal engine calibrations; however, NSGA performance is highly sensitive to the specific parameters used in the algorithm logic. The highest sensitivity was to the mutation logic within the genetic reproduction process, and second was the number of genes (calibrations) included in the overall process. Inclusion of both the Primary and Secondary non-dominated Pareto fronts in the set of Pareto-optimal calibrations was found to be critical to the success of the NSGA. When demonstrated for an experimental combustion system calibration the NSGA operated effectively and as expected, continually providing ‘upward’ pressure to generate calibrations that maximize NMEP but also ensure the breadth of the Pareto front (NOx) is scanned with high fidelity. In comparison to a traditional DoE approach, the NSGA was nearly twice as accurate in identifying calibrations along the Pareto front for the same number of total experiments. The Pareto-optimal calibrations developed by the NSGA are reasonable for these operating conditions and in excellent agreement with the literature. The present work strongly motivates and supports further development of NSGA methods for use in more complex systems and situations including for electrified and hybrid powertrains.

Mansfield, Andrew

Effects of the Spark Location and Timing in a Heavy-Duty Hydrogen-Fueled Engine

2026-01-0331

4/7/2026

The use of hydrogen in internal combustion engines offers a promising route to lower-carbon propulsion in heavy-duty transportation. However, its distinct combustion characteristics as high flame speed, wide flammability limits, and susceptibility to abnormal combustion, necessitate careful engine and ignition system design. This study numerically investigates the combined effects of spark plug (SP) location and ignition timing on the performance of a heavy-duty diesel engine converted to spark-ignition and operated with hydrogen as fuel at reduced compression ratio. The numerical study aims to guide engine design. Three-dimensional computational fluid dynamics simulations with detailed hydrogen chemistry were conducted to evaluate flame development, and relevant combustion metrics under different loads. Model validation against engine combustion data and hydrogen injection from a low-pressure, high-mass-flow direct injector are also presented. The results demonstrate that SP placement is pivotal to control for combustion stability and efficiency due to the complex in-cylinder mixing and stratification associated with direct hydrogen injection. For each load, optimal ignition timings were identified. Highlights demonstrate the feasibility of installing the SP close to the jet-forming cap (injector tip) to exploit local enrichment and enhance flame propagation.

Menaca, Rafael, Shakeel, Mohammad Raghib, Panithasan, Mebin, Liu, Xinlei, Qahtani, Yasser, AlRamadan, Abdullah, Cenker, Emre, Silva, Mickael, Pei, Yuanjiang, Turner, James, Im, Hong

Combustion Enhancement via Discharge Current Modulation under Turbulence Conditions

2026-01-0336

4/7/2026

Utilizing low carbon fuel in lean burn combustion presents a compelling strategy for improving thermal efficiency and reducing NOx emissions. Methane, the main content of natural gas, still receives challenge of a rapid and complete combustion process because of its low flame speed. The long combustion duration deteriorates the performance of a spark ignition engine, in terms of poor combustion instability and misfire. Although ignition timing can be utilized to adjust the combustion phasing, the ignition process faces challenges due to reduced background pressure and temperature at advanced spark timings. In this paper, a rapid compression machine equipped with a specially designed flow chamber is utilized to enhance the turbulence flow, and a custom-built ignition module is utilized to provide boosted discharge current to enhance the ignition stability under flow conditions. An effective spark energy required to enhance the combustion process is investigated under both stoichiometric and lean conditions. Further increase of discharge current amplitude beyond this boundary yields minimal impact on the flame propagation process. This study will offer important insights for developing an on-demand ignition energy profiling strategy to reduce sparkplug electrode erosion.

Jin, Long, Cong, Binghao, Yu, Xiao, Kong, Xiangxin, Reader, Graham, Zheng, Ming

Experimental Characterisation of Combustion, Performance, and Emissions in a Hydrogen Fueled Opposed Piston Engine

2026-01-0335

4/7/2026

Recent studies have demonstrated that the current Internal Combustion Engine (ICE) can be adapted to operate with hydrogen for the decarbonisation of transport and gensets. This is mostly done by conversion of conventional 4-stroke compression ignition diesel engines or spark ignition gas engines for heavy-duty vehicles or 4-stroke spark ignition gasoline engines for light-duty applications. This study aims to assess the adoption of pure hydrogen direct injection technology on a novel two-stroke opposed-piston engine designed by Carnot Engine Ltd. The engine provides a flexible platform that can operate in both compression ignition and spark ignition modes, allowing it to adopt multiple fuels. For the first time, a single cylinder prototype version of this new engine was operated and tested with hydrogen at Brunel University of London. During the engine experiment, a spark ignition timing sweep was carried out at low and mid-loads up to 10 bar IMEP to identify the Minimum ignition advance for Best Torque (MBT). Then, a complete mapping of the fuel injection strategies and lambda matrix was performed to optimise engine efficiency and combustion stability at low loads. The outcome of this study demonstrates an impressive indicated thermal efficiency of 58.7% at a load of 5 bar indicated mean effective pressure (IMEP) when the engine was operated with an ultra-lean mixture of lambda 3.2. Additionally, the engine-out NOx emissions decreased from the maximum 1863 ppm at lambda 1.38 to less than 20 ppm at lambda 3.2. Furthermore, the steady-state engine-out emissions show near-zero carbon emissions at all operating conditions.

Mohamed, Mohamed, Roeinfard, Nima, Wang, Xinyan, Zhao, Hua, Watts-Farmer, Archie, Rahman, Nadiur, Lempp, Francis

Effect of Ignition Timing on Combustion Characteristics in Ammonia-Hydrogen Blended Fuel Engine with Passive Pre-Chamber

2026-01-0323

4/7/2026

Against the backdrop of energy structure transformation and upgraded environmental protection requirements, ammonia has been gaining significant traction for its potential application as a zero-carbon fuel. However, it faces challenges such as difficult ignition, slow combustion rate, and low heating value. Thus, researching efficient combustion strategies suitable for ammonia as a fuel holds great significance. In this study, a two-cylinder diesel engine was modified into an ammonia-hydrogen blended fuel engine. Experimental study coupled with numerical simulations were carried out to investigate the effects of varying ignition timing on the combustion characteristics employed a passive pre-chamber ammonia-hydrogen fuel engine. The results show that the peak in-cylinder pressure exhibits a "first increase then decrease" trend as the ignition timing is retarded, reaching a maximum value of 7.42 MPa at the ignition timing of -27.5°CA ATDC. When the ignition timing is retarded beyond -15°CA ATDC, a double-peak phenomenon appears in the in-cylinder pressure curve. The peak heat release rate (HRR) gradually increases with the retardation of ignition timing, but excessively retarded ignition diminishes the proportion of constant-volume combustion in the combustion process. The combustion rate is the fastest when the ignition timing is -20°CA ATDC under the operating conditions of an engine speed of 1800 r·min-1, a hydrogen energy fraction (HEF) of 11.6%, and a λ of 1.0, with the shortest combustion duration (CA10~CA90) of 22.5°CA, which leads to the highest indicated thermal efficiency of 42.5%.

Deng, Jun, Luo, Mingyu, Shang, Quanbo, Tang, Yongjian, Qin, Jie, Li, Liguang

Characterisation of Particle Number and Size from a DI SI Engine Operating on Hydrogen versus Gasoline: Operating Sensitivities and Filtration Effects

2026-01-0378

4/7/2026

Hydrogen Internal Combustion Engines (H₂ICEs) offer the potential for near-zero carbon emissions. However, while nitrogen oxide (NOₓ) emissions have been extensively studied, particulate emissions, specifically particle number (PN), which are widely attributed to in the literature to lubricant oil pyrolysis and exacerbated by hydrogen’s short quenching distance, remain less well understood. This study investigates exhaust-gas particle emission characteristics from a spark-ignition, single-cylinder research engine based on MAHLE Powertrain’s downsizing engine combustion system. The work was carried out at Brunel University of London and compares gasoline and hydrogen direct-injection strategies (central versus side injection) across a wide range of operating conditions, including variations in engine speed, load, air–fuel ratio (λ), rail pressure, and spark timing. While previous studies have investigated hydrogen particle formation mechanisms under isolated operating conditions, the combined influence of combustion strategy, mechanical engine condition, and exhaust filtration has not been systematically explored within a single experimental framework. This study characterises PN emissions and particle size distributions (PSDs) from a direct-injection spark-ignition research engine operating on hydrogen and gasoline under steady-state conditions. The effects of injection strategy (central versus side), air–fuel ratio (λ), rail pressure, and spark timing are examined, alongside a controlled comparison between a freshly overhauled engine and a mechanically worn configuration to assess sensitivity to oil-control condition. Particle measurements were performed using a fast-response differential mobility spectrometer equipped with a catalytic stripper to isolate solid particles, with results interpreted using SPN₁₀-equivalent metrics for comparative analysis. In addition, a series-production gasoline particulate filter (GPF) was evaluated under hydrogen operation to assess its ability to attenuate the ultrafine particles characteristic of H₂ICE exhaust. The results show that hydrogen combustion produces substantially lower engine-out PN than gasoline under comparable operating points, with particle size distributions strongly biased toward sub-23 nm diameters. PN emissions under hydrogen operation exhibit sensitivity to injection targeting, mixture strength, rail pressure, and engine mechanical condition, consistent with literature linking lubricant oil ingress and near-wall combustion behaviour to hydrogen PN formation. The GPF demonstrated measurable PN reduction under hydrogen operation in the single-cylinder, steady-state configuration examined Overall, this work provides an internally consistent dataset linking hydrogen combustion behaviour, engine mechanical condition, and injection strategy to PN emissions and filtration response under steady-state conditions. The findings are intended to inform calibration development, hardware design, and future certification-grade studies, rather than to demonstrate regulatory compliance.

Harrington, Anthony, Zaman, Zayne, Nickolaus, Chris, Zhao, Hua, Wang, Xinyan, Hall, Jonathan

Performance Optimization of 2 Cylinder Flex Fuel Engine for Small Commercial Vehicle – A STEP TOWARDS SUSTAINABILITY

2026-26-0119

1/16/2026

Increasing ethanol blending in gasoline is significant from both financial (reducing dependency on crude oil) and sustainability (overall CO2 reduction) points of view. Flex Fuel is an ethanol-gasoline blend containing ethanol ranging from 20% to 85%. Flex Fuel emerges as an exceptionally advantageous solution, adeptly addressing the shortcomings associated with both gasoline and ethanol. Performance optimization of Flex Fuel is a major challenge as fuel properties like knocking tendency, calorific value, vapour pressure, latent heat, and stoichiometric air-fuel ratio change with varying ethanol content. This paper elaborates on the experimental results of trials conducted for optimizing engine performance with Flex Fuel for a 2-cylinder engine used in a small commercial vehicle. To derive maximum benefit from the higher octane rating of E85, the compression ratio is increased, while ignition timing is optimized to avoid knocking with E20 fuel. For intermediate blends, ignition timing is suitably interpolated. Fuel injection pressure is increased to address the higher fuel flow requirement, and a fuel heater is added to address cold starts with E85 fuel. Ethanol content detection is done through software, and by suitable interpolation, fuelling and ignition timing are optimized for the entire range of Flex Fuel in a single calibration file. Engine performance with E20 & E93 fuel is optimized considering all mechanical and thermal limits of the engine through various iterations. The experimental results are analysed using the first principle method.

Kulkarni, Deepak, Malekar, Hemant A, Upadhyay, Rajdip, Katkar, Santosh, Undre, Shrikant

Effect of E20 Fuel on Vehicle Performance Parameters of 694CC Gasoline Engine for Commercial Vehicle Application

2026-26-0565

1/16/2026

In alignment with its carbon reduction commitments, India is transitioning towards higher ethanol-blended fuels, with E20 set for nationwide implementation by 2025. Ethanol is a renewable, domestically produced biofuel produced through fermentation of biomass such as sugarcane, corn. It possesses a higher octane rating and oxygen content compared to conventional gasoline, making it a favorable additive for improving engine performance and reducing emissions. This study investigates the impact of E20 fuel on performance parameters of a 694 cc MPFI , water-cooled, twin-cylinder gasoline engine. For deriving maximum benefits of increased Octane rating of E20, compression ratio was increased to 12.5:1. Experimental analysis was conducted to assess the changes in combustion behavior, brake specific fuel consumption (BSFC), torque output, engine out emissions and thermal efficiency when operating on E20 compared to baseline gasoline (E10). Base results indicate that E20 promotes more efficient combustion, owing to its higher laminar flame speed and elevated oxygen content, leading to a 3–4% improvement in low-end torque across real-world operating speed ranges. Conversely, on-road evaluations reveal a 3–4% fuel economy penalty with E20 relative to E10. Recovering E10-comparable fuel efficiency with E20 necessitates comprehensive engine calibration optimization, supported by targeted hardware modifications. Additionally, the high octane rating of ethanol reduces knock propensity, enabling the adoption of more aggressive ignition timing and higher compression ratios without compromising engine durability. Thermal benefits are also taken into consideration, with a reduction in peak mid-catalyst temperatures by approximately 30–40°C, this enables stoichiometric operation throughout operating range without any enrichment. These improvements suggest that engines calibrated specifically for E20 can be benefited through fuel’s inherent properties to achieve higher thermal efficiency and lower tailpipe emissions. In conclusion, the incorporation of E20 fuel in internal combustion engines shows notable advancements in engine performance and efficiency.

Kulkarni, Deepak, Malekar, Hemant A, Thonge, Ravindra, Kanchan, Shubham

Development of High BMEP Natural Gas Engine with Knock Mitigation

2026-26-0121

1/16/2026

The stringent emission norms over the past few years have driven the need to use low-carbon fuels and after treatment technology. Natural gas is a suitable alternative to diesel heavy-duty engines for power generation and transportation sectors. Stoichiometric combustion offers the advantages of complete combustion and low carbon dioxide emissions. Turbocharging and cooled exhaust gas recirculation (EGR) technology enhances the power density along with reduced exhaust emissions. However, there are several constraints in the operation of natural gas spark ignition engine such as exhaust gas temperature limit of 780 °C, sufficient before turbine pressure for EGR drivability, boost pressure, peak cylinder pressure limit and knocking. These limits coulld restrict the engine BMEP (brake mean effective pressure). In the present study, tests were conducted on a V12, 24 liters, heavy duty natural gas fuelled spark ignition engine (600 HP) with different EGR and turbocharger configurations to achieve 16 bar BMEP without abnormal combustion. Considering the maximum exhaust temperature limit of 780 °C of exhaust system, minimal engine hardware changes were done to ensure less complexity, cost-effective engine development with robust design. The turbine trim was decreased from 89% to 84% to avoid excessive high before turbine backpressure, backflow of residual gases into cylinder and knock possibility. EGR system optimization with mixer enhanced EGR mixing and distribution in all cylinders that improved BSFC by 3%. During knock calibration, the offset to base ignition timing was used for individual cylinders to mitigate knock. Endurance trial of 100 hours was carried out to validate the reliability of engine design and calibration, and no issues were detected. The developed engine is the highest BMEP V12 engine in its segment in India using stoichiometric combustion with cooled EGR and three-way catalyst. The engine is certified with latest Indian CPCB IV+ emissions norms.

Khaladkar, Omkar, Marwaha, Akshey

Artificial Neural Network-Based Performance and Emission Prediction for Hydrogen-Combustion Multicylinder Engines

2025-36-0237

12/18/2025

In response to the pressing need to reduce greenhouse gas emissions from the transportation sector, hydrogen-fueled internal combustion engines (H2ICEs) have emerged as a promising alternative to conventional fossil-fueled powertrains. However, optimizing H2ICEs presents challenges in balancing performance with emissions, particularly in nitrogen oxide (NOx) formation This study proposes a data-driven methodology using an artificial neural network (ANN) to predict key emission and performance metrics: NOx emissions, brake mean effective pressure (BMEP), brake specific fuel consumption (BSFC), brake power, and brake thermal efficiency, based solely on engine operational parameters. Experimental data were collected from a three-cylinder Ford EcoBoost engine under varying conditions of intake pressure, spark timing, air-fuel ratio, engine speed, and valve timing. Feature selection was performed using the Spearman correlation coefficient, identifying engine speed, start of injection angle (SOI), air-fuel ratio (λ), and intake pressure as the most important input variables. Bayesian optimization was employed to tune the ANN’s hyperparameters, resulting in a network architecture with a single hidden layer consisting of 10 neurons using the tanh activation function, optimized with the Adam optimizer at a learning rate of 0.01. The final ANN model exhibited satisfactory predictive performance, achieving correlation coefficients greater than 0.97 for most outputs and exceeding 0.95 across all predicted variables. These results demonstrate that the proposed ANN effectively captures the nonlinear behavior of hydrogen-fueled engines and offers a valuable tool for reducing the experimental burden in engine calibration and development, thereby supporting the advancement of hydrogen-powered mobility solutions.

Pasa, Bruno Roberto, Silveira, Juliano Pereira, Fagundez, Jean Lucca Souza, Lanzanova, Thompson Diórdinis Metzka, Martins, Mario Eduardo Santos, Salau, Nina Paula Gonçalves

Multi-Objective Optimization of Oxyfuel Gas Engine Using Stochastic Engine Model and Detailed Chemistry

2025-01-0529

11/25/2025

The energy transition initiatives in Germany’s renown coal mining region Lusatia have driven research into Power-to-X-to-Power technologies, where synthetic fuel is produced from renewably sourced hydrogen and captured CO2, and converted to electricity and heat through oxyfuel combustion. This work investigates the multi-objective optimization of oxyfuel gas engine using a stochastic engine model and detailed chemistry. Exhaust gas recirculation (EGR) rate, initial cylinder temperature and pressure, spark timing, piston bowl radius and depth are selected as design parameters to minimize the exhaust temperature at exhaust valve opening and indicated specific fuel consumption (ISFC) corresponding to oxyfuel operation with different dry and wet EGR rates. The optimization problem is solved for a dry EGR and four wet EGR cases with various CO2/H2O fractions, aiming to achieve comparable performance as in conventional natural gas / air operation, and energy-efficient carbon capture. The case with the lowest humidity (T10deg) had the lowest temperature of 1537 K, while the one with the highest vapor fraction (T70deg) attained the minimum 260 g/kWh ISFC. The superiority of the T10deg case is offset by much higher cooling demand (3.06 kW) for CO2 separation than that for T70deg case (0.81 kW). The constraint for combustion efficiency (>65%) limited the solution space towards high ISFC values, while the constraint for low indicated mean effective pressure (IMEP) (>7 bar) and the constraint for high IMEP (<8 bar) limited the solution space in between the two distinct clusters of feasible designs, and towards high exhaust temperature, respectively. The optimized designs from all the cases could outperform the reference case in terms of IMEP, nevertheless they fell below 31% indicated efficiency, which is associated with stoichiometric combustion.

Asgarzade, Rufat, Franken, Tim, Mauss, Fabian

Optimization of Injection Parameters for a Free-Piston Engine Equipped with Flat-Head Combustion Chamber

2025-01-5075

11/11/2025

The free-piston engine represents a paradigm shift in internal combustion engine technology, with its unique structure promising efficiency gains. However, injection parameters are one of the core elements of free-piston engine performance. This study employs computational fluid dynamics analysis to optimize the spray cone angle and start of injection timing for a two-stroke dual-piston opposed free-piston engine equipped with a flat-head combustion chamber. A three-dimensional transient model incorporating dynamic adaptive mesh refinement was constructed by using CONVERGE 3.0 software. The results indicate that a spray cone angle of 25° achieves optimal fuel distribution, yielding a peak indicated thermal efficiency of 42.14% and an indicated mean effective pressure of 9.08 bar. Crucially, advancing the ignition timing to 215°CA improves mixture homogeneity but simultaneously increases peak cylinder temperatures and NOx. Conversely, delayed start of injection timings reduces NO emissions by 58.6% at the expense of 8.2% indicated mean effective pressure. Comprehensive optimization shows that the combination of θ = 25° and SOI = 215°CA achieves 19.94 kW indicated power and 99% fuel evaporation, balancing performance and emissions. This study establishes a fundamental framework for optimizing injection parameters in combustion systems of free-piston engines, providing valuable reference for developing highly efficient, low-emission power systems in practical applications.

Xu, Zhaoping, Yang, Shenao, Liu, Liang

Computational Investigation on a Boosted Uniflow Scavenged Direct-Injection Combustion Engine (BUSDICE) with Alcohol Fuels

2025-32-0027

11/3/2025

Alcohol fuels, produced from renewable energy sources, are considered a crucial solution for achieving life-cycle carbon neutrality in internal combustion engines. The Boosted Uniflow Scavenged Direct-Injection Combustion Engine (BUSDICE) exhibits significant potential for high thermal efficiency with an aggressive downsizing design. In this study, a computational investigation was carried out to assess the spray mixing and combustion characteristics of BUSDICE fuelled with methanol and ethanol, compared with gasoline, under a high-load condition. The injection duration of methanol and ethanol is significantly longer than that of iso-octane, leading to incomplete evaporation. The mixture exhibits an “outer-rich, central-lean” stratification pattern due to the short mixing time and swirl flow transportation for all three fuels. However, the prolonged injection of methanol induces stronger turbulence, which can enhance the local mixing. The spatial mixture stratification, particularly near the spark-local area, has a strong influence on the initial kernel development and flame propagation. Consequently, methanol exhibits a shorter ignition delay than ethanol under the same spark timing, leading to faster flame propagation attributed to a richer equivalence ratio around the spark plug. Nevertheless, the ignition and combustion performance of ethanol can be improved by advancing the spark timing. The spark timing study reveals that alcohol fuels can operate under high load without knocking, whereas iso-octane requires retarded ignition timing to prevent knocking. As a result, methanol and ethanol provide a better IMEP and ITE than iso-octane under high-load conditions. From an emissions perspective, due to their low carbon-to-hydrogen (C/H) ratio and high oxygen content, unburnt hydrocarbon emissions decrease significantly when using alcohol fuels, especially methanol, for which these emissions are almost zero. However, the soot of ethanol shows a slight increase than iso-octane, due to the highly stratified mixture and incomplete combustion. Additionally, the NOx of ethanol and methanol increases due to the higher combustion temperatures than iso-octane. Overall, the results highlight the strong potential of alcohol-fuelled BUSDICE engines as compact and sustainable solutions for small-displacement powertrains, offering high thermal efficiency and substantially reduced pollutant emissions.

Feng, Yizhuo, Lu, Enshen, Dong, Shuo, Keshtkar, Hossein, Wang, Xinyan, Zhao, Hua

Effect of Plasma-Assisted Ignition on Combustion and Emission Characteristics of Two Stroke Engines with Different Fuels

2025-32-0030

11/3/2025

This study explores the effect of plasma-assisted ignition (PAI) on combustion stability and emissions in two-stroke spark-ignition engines. Two engine platforms were evaluated: a conventional single-cylinder two-stroke engine and a thermodynamically advanced opposed-piston two-stroke (OP2S) engine. The OP2S engine configuration offers reduced heat loss and higher power density due to its uniflow scavenging and favorable geometry, but suffers from high residual gas fraction, which increases ignition difficulty and combustion instability. To address this, nanosecond-pulsed PAI was applied in various spatial arrangements and discharge voltages, using both gasoline and a low-reactivity gasoline/DMC blend fuel. Spark ignition timing was held constant at the minimum advance for best torque across all tests. Combustion stability was assessed via indicated mean effective pressure (IMEP) and its coefficient of variation, while CO and HC emissions were measured as environmental indicators. Results show that PAI significantly enhanced ignition stability, reducing COVIMEP by up to 84% and HC emissions by up to 24%, depending on fuel and engine type. The OP2S engine showed greater responsiveness to ignition configuration and plasma positioning due to its uniflow scavenging method. These findings confirm that PAI is a promising strategy for improving ignition robustness and emission performance in both conventional and advanced two-stroke engine architectures.

Liu, Jinru, Yamazaki, Yoshiaki, Otaki, Yusuke, Kato, Hayato, Kobayashi, Daichi, Umegaki, Tetsuo, Asai, Tomohiko, Iijima, Akira

Experimental Study of hCNG on Single Cylinder 395cc Spark Ignition Engine for Performance and Exhaust Emission

2025-32-0050

11/3/2025

There is growing demand for energy utilization due to stricter environmental emission norms to reduce greenhouse gases and other threats posed due to the emissions are major motivation factors for researchers to adopt on strategic plans to decrease the usage of energy and reduce the carbon contents of fuels, the usage of hydrogen or blend of hydrogen with CNG as a fuel in internal combustion engines is the best option. As hydrogen has lower volumetric energy density and higher combustion temperature, pure hydrogen-fueled engines produce lower power output and much higher NOx emissions than gasoline-fueled engine at stoichiometric air-fuel ratio. Blending of hydrogen with CNG provides a blended gas termed as hydrogen-enriched natural gas (hCNG). hCNG stands for hydrogen enriched compressed natural gas and it combines the advantages of both hydrogen and methane. The addition of Hydrogen to CNG has potential to even lower the CNG emissions and is the first step towards promotion of a Hydrogen economy. hCNG allows customers early hydrogen deployment with nearly commercial technology. Spark ignition Engines can be calibrated for lower NOx and greenhouse gas emissions. Spark ignition engine is compatible to run on hCNG with minimum modifications. In the present study 395cc water cooled spark ignition engine with port fuel injection system was used to explore CNG and hCNG fuel with 18% Hydrogen in CNG for comparing engine performance and effective way to reduce emissions. A series of experiments were carried out on engine test dynamometer also on vehicle chassis dynamometer on 3-wheeler vehicles with different ignition timing, operating lambda. Hydrogen with CNG as a fuel in SI engines has shown significant positive impact on efficiency with lean lambda limits. With 18% Hydrogen in CNG make it possible to run the engine leaner, resulting in lower emission for CO2, CO, HC however with higher NOx emissions. To reduce NOx emission on engine, novel water injection technology added on engine to reduce NOx emission by 43%. Experimental study on vehicle infers emission reduction on Indian driving cycle, also reduction in CO2 emission has shown improvement in fuel consumption of vehicle on driving cycle with lean lambda, retarded ignition timing with 18% percentage of Hydrogen blended with CNG. Spark ignition engine with 18% Hydrogen in CNG fuel on three-wheel vehicle met Bharat Stage 6 emission norms. Emission result infers 41% margin in CO, 15% margin in NOx, 45% margin in HC+NOx and 9% improvement in CO2 emission which resulted in 10% improvement in fuel economy with hCNG when compare with CNG fuel. Finally, it has been said that hCNG fuels is next alternate fuel with the use of hydrogen in future vehicle fuel.

Syed, Kaleemuddin, Chaudhari, Sandip, Khairnar, Girish, Sajjan lng, Suresh

Development of Anti-SideSlip Control for Motorcycles Using IMU

2025-32-0037

11/3/2025

In motorcycle racing and other competitions, there is a technique to intentionally slide the rear wheel to make turns more quickly. While this technique is effective for high-speed riding, it is difficult to execute and carries risks such as falling. Therefore, an anti-sideslip control system that suppresses unintended or excessive sideslip is needed to ensure safe, natural, and smooth turning. In anti-sideslip control, the slip angle is usually used as a control parameter. However, for motorcycles, it is necessary to know the absolute direction of the vehicle's movement. To determine this, GPS or optical sensors are required, but using such sensors for driving is costly and may not provide accurate measurements due to contamination or other environmental factors, making it impractical. Therefore, an anti-sideslip control system was developed by calculating another parameter that indicates the characteristics of the slip angle, without measuring the slip angle itself, thus eliminating the need for impractical sensors. To detect sideslip, lean angles calculated using two different methods are used. The first lean angle calculates the true value even when side slip occurs, while the second lean angle shows a higher value than the true value when side slip occurs. The difference between these is defined as the slide amount, which can be detected as a parameter representing side slip. When a sideslip is detected, the drive force reduction control suppresses the sideslip to bring the slide amount closer to the target slide amount. To suppress sideslip, drive force reduction through ignition retardation is used. As an experiment, the slide amount obtained by the current method was compared with the values from a GPS device capable of calculating the slip angle. It was confirmed that the differential value of the slip angle obtained from the GPS and the slide amount had a very similar waveform. Furthermore, a test was conducted to verify whether the anti-sideslip control effectively suppressed sideslip during actual driving, and it was confirmed that applying this control allowed for more stable cornering. The effectiveness and validity of the anti-sideslip control were confirmed through the above experiment.

Nakano, Kyosuke, Kawai, Kazunori, Takeuchi, Michinori

Study on Combustion Detection of a Spark-Ignition Engine with Fuel Variation Using Various Sensors

2025-32-0052

11/3/2025

The use of alternative fuels, such as biofuels and synthetic fuels in small mobility engines has become more common these days. Although these fuels contribute to the carbon neutrality, it is known that they do not have a certain fuel composition, which significantly affects the combustion characteristics of an engine, such as knocking and combustion duration. Therefore, to get the most out of these sustainable fuels, it is necessary to develop engine systems that are highly robust to variations in fuel composition. To achieve this goal, a method to sense fuel characteristics onboard using sensors already widespread in use or can be installed inexpensively is required. Although in-cylinder piezoelectric pressure sensors are useful for research in the laboratory, it is not suitable for the use in commercial engines because of its high cost. Therefore, the use of other sensors should be considered. The purpose of this study is to experimentally analyze what information related to combustion and fuel can be obtained from multiple cost-effective sensors mounted on an engine. For that goal, a linear multiple regression model and Neural Network (NN) model was developed to estimate fuel’s Lower Heating Value (LHV) and combustion duration. Experiments were conducted on a 4-cylinder spark ignition (SI) engine, and combustion characteristics of multiple fuels were investigated while varying engine operating conditions. In addition to gasoline, CH4 gas was introduced into cylinders to simulate the change in fuel composition. Sensors used in this study include intake and exhaust pressure sensors, thermocouples, and in-cylinder ion current sensor. Selection of input variables (sensors) for the regression models were done based on the results of the experiment, and linear multiple regression model and NN model were developed. The prediction errors (RMSE) for LHV were 0.54 MJ/kg with linear regression model and 0.95 MJ/kg with NN model. For CA10-90, prediction errors were 6.15 deg with linear regression model and 14.48 deg for NN model. Since the accuracy of the models were not high enough, hyperparameter tuning was done using Bayesian optimization, and prediction accuracies were improved. However, further work, such as building physical model,increasing sample size, or adding extra sensors, must be done to use these models for engine control.

Hayashi, Kohei, Kim, Jihoon, Yamasaki, Yudai

Analysis of Flame Propagation Characteristics in a Hydrogen Engine using an Optically Accessible Engine

2025-32-0061

11/3/2025

This study focused on the effects of hydrogen on the flame propagation characteristics and combustion characteristics of a small spark-ignition engine. The combustion flame in the cylinder was observed using a side-valve engine that allowed optical access. The fundamental characteristics of hydrogen combustion were investigated based on combustion images photographed in the cylinder with a high-speed camera and measured cylinder pressure waveforms. Experiments were conducted under various ignition timings and equivalence ratios and comparisons were made with the characteristics of an existing hydrocarbon liquid fuel. The hydrogen flame was successfully photographed, although it has been regarded as being difficult to visualize, thus enabling calculation of the flame propagation speed. As a result, it was found that the flame propagation speed of hydrogen was much faster than that of the existing hydrocarbon fuel. On the other hand, it was difficult to photograph the hydrogen flame directly in the lean region. In future studies, it will be necessary to reduce the shooting speed or to conduct investigations based on spectroscopic measurements. Regarding hydrogen combustion, it was found that the combustible range of hydrogen was broad even when the experimental conditions were substantially varied. It was also found that the combustible period was much shorter than that of the existing hydrocarbon fuel. Misfiring and after-firing were observed in hydrogen combustion where the ignition timing was close to top dead center as well as under a lean condition. This confirmed that there are issues concerning hydrogen combustion stability under such conditions.

Arai, Yuto, Ueno, Takamori, Suda, Ryosuke, Sato, Ryoichi, Nakao, Yoshinori, Ninomiya, Yoshinari, Matsushita, Koichiro, Kamio, Tomohiko, Iijima, Akira

A Study of Knocking Characteristics in a Hydrogen SI Engine under High Compression Ratio

2025-32-0063

11/3/2025

This study investigated the knocking characteristics of a hydrogen spark ignition engine for the purpose of increasing efficiency and expanding the operating range. In recent years, research focused on carbon neutrality has been vigorously conducted, and hydrogen has attracted attention as a next-generation fuel for internal combustion engines (ICEs). The combustion characteristics of hydrogen are vastly from those of existing gasoline. It is essential to have a sufficient understanding of the combustion characteristics of hydrogen in order to develop next-generation ICEs designed to operate on hydrogen fuel. There are especially many aspects of the knocking mechanisms of hydrogen that are unclear. Consequently, those characteristics and mechanisms must be clarified for the purpose of expanding the operating range of hydrogen engines and enhancing their efficiency. In this study, experiments were conducted using a single-cylinder hydrogen engine that was operated at a high compression ratio of 17:1. High-intensity knocking was observed while operating the engine under various ignition timings and equivalence ratios. The knocking intensity and knocking mode characteristics were examined based on the observed knocking data.

Ishihara, Hiromasa, Kishibata, Shunsuke, Miyake, Shota, Iida, Tomoya, Kuwabara, Kenta, Yoshihara, Shintaro, Miyamoto, Sekai, Iijima, Akira

Knock Sensors for Two Wheelers Applications

2025-32-0079

11/3/2025

This paper describes the design and characteristics of the knock sensor. The sensor is already used as a commodity product for automotive applications and used by all automotive OEMs for spark ignited combustion engines. With the arrival of the electronic fuel injection on the two wheelers, further optimization of the combustion can be obtained. Although there are many publications on the engine knock strategy, little is known publicly about the sensor itself. The knock sensor is an accelerometer based on a piezoelectric component; it provides an analog signal of the engine vibration. The Electronic Control Unit will filter the signal according to a specific strategy and defines the presence and intensity of the engine knock. The ECU will act accordingly on the ignition timing. The inner structure as well as the mechanical and electrical interface are described in this article.

van Est, Jeroen, Prieu, Corentin

Computational Fluid-Dynamics Analysis of the Effect of Ethanol-Air Mixture Supply in a Heavy-Duty Engine

2025-24-0029

9/7/2025

As part of the Bio-FiRE-for-EVer research project aiming to propose a solution for off-grid charging stations based on the adoption of a reciprocating engine, this study investigated the combustion development and pollutant emissions of an 8.7 l six-cylinder heavy-duty PFI internal combustion engine fueled by ethanol. The reference experimental case features critical issues in the formation of the air-fuel, mainly due to the slow evaporation rate of the alcohol fuel inside the intake manifold via a single point injection, providing a non-uniform and averagely rich (λ=0.89) reactant mixture inside the cylinders. For this purpose, an in-depth analysis of the in-cylinder phenomena is performed by using a CFD solver for the reacting flow. A geometry of the cylinder system complete with intake and exhaust ducts is created for calculations with the three-dimensional Ansys FORTE code. The inclusion of the inlet duct in the computational domain allows the experiencing of several setups of the mixture. Indeed, due to the uncertainties on the complete vaporization of ethanol, experimental data allowed a preliminary validation of the CFD based predictions by considering the presence of liquid fuel fraction (30%) in the inlet duct. After the model calibration, firstly, a more favorable air-fuel ratio condition of λ=1 is examined and then, two alternative solutions are proposed to optimize the engine performance via a multipoint injection upstream of the intake valves but still considering a rich mixture. Based on the results it is demonstrated that the presence of liquid represents a more realistic condition achieving outputs closer to the experimental measurements. The adjustment of air-fuel ratio to a stoichiometric value by only enhancing the amount of air leads to significant improvements in terms of mechanical outputs and CO emissions. Besides, an optimized injection setup can overcome the maldistribution of fuel among cylinders, its incomplete oxidation and reduce the percentage of fuel that remains liquid forming a film on the duct’s wall.

De Robbio, Roberta, Cameretti, Maria Cristina, Palomba, Marco, Tuccillo, Raffaele

Overview of Current Developments of Pre-Chamber Spark Plugs for Passenger Car Applications

2025-24-0152

9/7/2025

The internal combustion engine (ICE) is projected to remain the dominant technology in the transport sector over the short to medium term, and there exists significant potential for further improvements in fuel economy and emission reductions. One promising approach to enhancing the efficiency of spark ignition engines is the implementation of passive pre-chamber spark plugs. The primary advantages of pre-chamber-initiated combustion include the mitigation of knocking, an increase in in-cylinder turbulence, and a combustion process that is both faster and more stable compared to that achieved with conventional J-gap spark plugs. Additionally, the higher ignition energy provided by pre-chamber spark plugs enables operation under higher intake pressures, maintains similar exhaust gas recirculation rates, and supports leaner combustion conditions. These benefits are predominantly attributed to volumetric ignition via hot, reactive jets. However, the pre-chamber spark plug also presents several challenges. Its drawbacks include suboptimal cold-start behavior, difficulties in catalyst heating when accompanied by aggressive spark retard, and inferior low-load performance resulting from reduced charge motion, elevated residual gas concentrations within the pre-chamber, and increased wall heat transfer at low loads. Furthermore, the challenge of adequately heating the catalytic converter persists due to delayed ignition timing. In this study, various passive pre-chamber configurations were systematically investigated and evaluated based on key performance metrics. Engine operation was categorized into three specific regimes: catalyst heating on a cold engine (operated at 1200 rpm with an IMEP of 3 bar), the optimal efficiency point corresponding to a minimum brake specific fuel consumption (operated at 2000 rpm with an IMEP of 14 bar), and a high-speed load sweep conducted at 4000 rpm. The experimental campaign was executed in two phases, allowing for iterative design modifications informed by the findings of the initial phase. Ultimately, the optimized pre-chamber design successfully achieved a minimal specific exhaust heat flux (SEHF), maintained the desired combustion stability, and extended the high-load operating envelope up to an IMEP of 18.5 bar.

Korkmaz, Metin, Juressen, Sven Eric, Rößmann, Dominik, Kapus, Paul E., Pino, Sandro

Numerical Analysis of the Combustion Process in a Pre-Chamber Marine Engine Fueled with Ammonia-Hydrogen Mixtures

2025-24-0021

9/7/2025

Ammonia and hydrogen, as carbon-neutral fuels, possess the potential to play a crucial role in the decarbonization of the mobility sector. This research examines the optimization of the combustion process in a marine spark-ignition engine through the use of a passive pre-chamber. The study has been carried out using computational fluid dynamics (CFD) models. Considering a hydrogen content in the fuel blend of 15% by volume, at a fixed equivalence ratio equal to 0.8, two different nozzle diameters have been tested, and the optimal spark timings have been identified. Then, the effect of different hydrogen amounts in the fuel mixture on the engine’s performance and emissions has been assessed. An optimal spark timing of 712 CAD has been found for both 3 mm and 5 mm nozzles at the specified operating point. The 5 mm nozzle provides slightly higher IMEPH and gross efficiency, with minimal impact on emissions. Reducing hydrogen in the fuel blend from 15% to 10% lowers IMEPH from 31 to 12 bar and gross efficiency from 46.9% to 18.8%. At 5% hydrogen, combustion cannot start. This decrease in the hydrogen amount raises unburned ammonia, NO2, and N2O emissions, while NO emissions are significantly reduced. Decreasing hydrogen content reduces turbulent kinetic energy in the combustion chamber.

D'Antuono, Gabriele, Lanni, Davide, Galloni, Enzo, Fontana, Gustavo

In-Cycle Predictability and Control of Knock in a PFI HD SI Engine Fueled with Methanol

2025-24-0019

9/7/2025

Knock is an anomalous combustion occurrence limiting the efficiency of the spark-ignited engine, hence increasing fuel consumption and emissions. The global aim to cut the emissions from green-house-gases therefore makes knocking combustion a very appropriate research topic of today. This paper explores the possibility to do in-cycle spark timing control of knock, based upon cycle-to-cycle adaptation of the temperature of a hypothesized hot spot. The potential for post-spark timing control is also examined. Experiments were carried out on a single cylinder port fuel injected spark ignited engine fueled with methanol. Knock was quantified by the Maximum Amplitude of Pressure Oscillations metric and predicted by the Livengood-Wu integral. Normalized distributions, together with different σ confidences, of the in-cylinder state such as gas temperature, in-cylinder pressure and Livengood-Wu integral were computed both pre- and post-spark timing. Type I and Type II errors of the computed metrics revealed that knocking cycles cannot be distinguished from normal cycles, and that hot spots are likely not the root cause of auto-ignition in the current engine. Hence, in-cycle control of knock based upon a hypothesized hot spot temperature would be fruitless. A proven method to mitigate knock in-cycle is the use of water injection. Nevertheless, the post-spark timing analysis showed that this control post-spark timing may be counterproductive. The knocking and normal cycle combustions have a large overlap before the knocking occurs. Therefore, in-cycle regulation through water injection can penalize normal cycles, to a degree that the indicated thermal efficiency would drop more than just retarding the spark timing to 1% knocking (regular knock controller). Lubricant oil, instead of hot spots or fuel-rich spots, was demonstrated to be the most plausible cause of knock in the current engine-fuel configuration.

Ainouz, Filip, Lius, Andreas, Cronhjort, Andreas, Stenlaas, Ola

Parametric Analysis of Performance and Efficiency of Free-Piston Linear Generators with 1D and CFD Simulations

2025-24-0105

9/7/2025

High efficiency, fuel flexibility, and seamless integration with electrified systems are fundamental prerequisites for the next generation of internal combustion engines. In this context, the free-piston linear generator (FPLG) evolves the traditional internal combustion engine concept (ICE) by replacing the crankshaft mechanism with a linear generator, directly converting piston motion into electricity. The FPLG offers several advantages, including higher efficiency in converting mechanical energy to electricity, the ability to operate with a variable compression ratio, and reduced heat losses during the expansion stroke. Among the various tested architectures, the two-stroke, opposed-piston FPLG appears to be the most promising. However, detailed numerical and experimental investigations are necessary to fully understand how performance and efficiency are influenced by the intricate interplay of processes governing electricity generation. In particular, the significant differences between conventional crankshaft-based engines and FPLG kinematics have a profound impact on gas exchange and combustion processes. This study presents a numerical analysis of the key parameters affecting the performance and efficiency of spark-ignition opposed-piston FPLGs. Simulations were conducted using a modified 1D code, which accounts for the effects of electrical load and gas spring pressure on piston motion. Given the unconventional geometry featuring uni-flow scavenging and a side-mounted spark plug, preliminary CFD simulations were performed to develop realistic intake and exhaust system schematics and to establish an appropriate heat release rate profile. Methane was chosen as the fuel for two main reasons: it can be produced from biogenic sources and is applicable to both mobility and power generation. Additionally, its high octane number makes it particularly suitable for FPLG operation at high compression ratios. A single-cylinder unit (~250 cm3) was simulated as an initial step toward developing a small-scale prototype. Simulations examined the effects of gas spring pressure, charging pressure, electrical load, and spark timing. The results indicate that efficiency is maximized by applying the highest possible load under given operating conditions and introducing backpressure on the exhaust side to improve trapping efficiency.

Morandi, Nicola, Lucchini, Tommaso, Gianetti, Giovanni, Baratta, Mirko, Misul, Daniela, Santonocito, Fabrizio

ML-based Identification of Lactones for Blend Studies and Combustion Performance in a Spark-Ignition CFR Engine

2025-24-0071

9/7/2025

The identification of sustainable fuels that exhibit optimal physico-chemical properties, can be synthesized from widely available feed-stocks, enable cost-effective large-scale production, and integrate seamlessly with existing infrastructure is essential for reducing global carbon emissions. Given their high energy density, efficient handling, and versatility across applications, renewable liquid fuels remain a critical component of even the most ambitious energy transition scenarios. Lactones, cyclic esters derived from the esterification of hydroxycarboxylic acids, feature a ring structure incorporating both a carbonyl group (C=O) and an ether oxygen (O). Variations in ring size and carbon chain length significantly influence their physicochemical properties, which in turn affect their performance in internal combustion engines. According to predictive models based on artificial neural networks, valerolactone, hexalactone, and heptalactone isomers show promise as fuels in spark-ignition engines due to their high octane (RON and MON) values. In this work, a novel blending study of three lactones was performed to understand miscibility with iso-octane and certification gasoline and blending limitations. A blending limitation for one of the lactones was discovered and a single blend fraction of 30% lactone balanced with certification gas was tested in a spark ignition engine for the three lactones. An equivalence ratio sweep was performed for each fueling blend tested and no reduction in IMEPn and net fuel conversion efficiency was observed by displacing certification gasoline with renewable fuel.

Sirna, Amanda, Loprete, Jason, Ristow Hadlich, Rodrigo, Assanis, Dimitris, Patel, Rutvi, Mack, J. Hunter

A Study on Sensitive Spots in Hydrogen Engines

2025-24-0059

9/7/2025

Premature self-ignitions in hydrogen internal combustion engines have been associated with the presence of hot spots. However, local increases in charge reactivity may be triggered not only by elevated temperatures but also by composition inhomogeneities. Such non-uniformities, in addition to imperfect mixing (e.g., in the case of direct hydrogen injection), may result from external contamination by more reactive components, such as lubricant oil. The present study aims to shed light on the mechanism through which lubricant oil contamination leads to the formation of sensitive spots, by analysing the behaviour of an isolated droplet suspended in a hydrogen/air environment. The “HyLube” chemical kinetic mechanism was employed to reproduce the chemical behaviour of lubricant oil, as it was specifically developed for this purpose. A one-dimensional numerical model was used to simulate the heating, vaporization, and combustion of the droplet. Zero-dimensional simulations were also performed using the open-source code Cantera (vers. 3.0.1) to better asses the effects of contamination. The impact of key operating conditions – such as ambient temperature, pressure, and composition, as well as droplet temperature and size – was investigated. The temporal evolution of selected variables, including the calculated instantaneous local charge reactivity, was analysed to characterise the fundamental mechanisms through which lubricant oil alters the charge reactivity and promotes early flame development within the combustion chamber of hydrogen-fuelled engines. The results contribute to a better understanding of how pre-ignition may occur due to lubricant oil contamination.

Distaso, Elia, Baloch, Daniyal Altaf, Amirante, Riccardo, Tamburrano, Paolo

Numerical Investigation of Lean Neat Ammonia Combustion in a Heavy-Duty Diesel Engine Converted to Spark Ignition

2025-24-0032

9/7/2025

Ammonia (NH3) use as fuel poses technical challenges such as increased nitrogen-based and unburned NH3 emissions. This study used a 0D model coupled with detailed NH3 kinetics to evaluate the effect of equivalence ratio (ϕ) from 0.7 to 1.0 in a heavy-duty compression ignition engine converted to spark ignition operation. The goal was to evaluate how ϕ affected NOx and N2O formation and/or destruction at constant fuel energy per cycle, engine speed, and CA50. Simulated NOx emissions (i.e., NO + NO2) followed a trend similar to the one typically observed for hydrocarbon fuels in a SI engine, but that was different from the experiment. In addition, it underpredicted NOx emissions for ϕ = 0.7 by 79% and overpredicted NOx emissions for ϕ = 1 by 576%. The simulation showed that thermal NO production was more than 80% from the total NO production, but the effect of ϕ on this percentage was negligible. Then, predicted N2O emissions had an opposite trend and were three orders of magnitude lower than the experiment. Under the assumption that post-combustion phenomena can explain these differences, an additional reactor simulating of the chemistry inside the unburned mixture exiting crevices post combustion at ϕ = 0.9 predicted N2O production similar to experimental data and an additional 20 ppm of NO. A third reactor simulating the exhaust blowdown predicted substantial DeNOx reactions (up to 3000 ppm decrease in NOx), and a large N2O production above experimental values. Therefore, the significant DeNOx and N2O formation reactions could explain the differences between the 0-D engine simulation and experiments even when accounting for the real mixture inhomogeneities, which emphasizes the importance of capturing both in-cylinder and post-EVO conditions when modeling NOx and N2O emissions in an IC engine.

Saenz Prado, Stefany, Alvarez, Luis F., Trujillo Grisales, Juan M., Akkerman, Vyacheslav, Dumitrescu, Cosmin E.

Combustion Characteristics and Efficiency of a Turbocharged Hydrogen-Fueled Internal Combustion Engine Under Ultra-Lean, High-Load Conditions

2025-24-0048

9/7/2025

The transportation industry seeks sustainable alternatives to fossil fuels, and hydrogen internal combustion engines (H₂ICE) have emerged as a practical solution. They offer near carbon-free operation while integrating with existing engine technology and infrastructure. Thanks to hydrogen’s specific properties, lean combustion can be achieved, significantly reducing NOx emissions. However, operating a commercial engine under ultra-lean conditions at high load presents challenges, particularly in maintaining volumetric efficiency and power density. This study analyzes the combustion behavior, NOx emissions, and loss mechanisms in a four-cylinder, direct-injection, hydrogen-fueled engine, equipped with a variable geometry turbine (VGT). The engine was tested at three BMEP levels (8, 10, and 12 bar) under ultra-lean conditions, with lambda varied between 2.2 and 3.6. Unlike conventional approaches, fuel mass was held constant at each load, and lambda was adjusted by varying intake air mass to isolate the effects of air-based dilution on combustion. This strategy was enabled by using the VGT, which provided high intake pressures necessary for sustaining ultra-lean operation at high loads. Three test scenarios were designed to decouple the influence of lambda, intake pressure, and spark timing on combustion behavior. A validated 0D/1D model developed in GT-SUITE was used alongside experimental data for detailed combustion insight. The results showed stable combustion across all tested lean conditions, with indicated thermal efficiency (ITE) peaking near 44% around λ = 3. NOx emissions were reduced to near-zero levels above λ = 3.4. Energy balance analysis revealed that increasing lambda reduced wall and exhaust heat losses, while unburned fuel and pumping losses increased under very lean conditions. The results also emphasized the critical role of intake pressure in influencing peak in-cylinder pressure and combustion phasing, particularly at fixed spark timing.

Azizianamiri, Sobhan, Tauzia, Xavier, Maiboom, Alain, Perrot, Nicolas

Development of a Compact Hydrogen Engine for Commercial Applications

2025-24-0060

9/7/2025

As the individual and commercial vehicle industries seek sustainable alternatives to conventional internal combustion engines (ICEs), hydrogen-fueled rotary engines are emerging as a promising solution for several applications. This paper presents an innovative approach for the development of a hydrogen rotary engine that is integrated within a hybrid system. By exploiting the unique characteristics of rotary engines, such as compact size and high power-to-weight ratio, the electric machine, the battery and the rotary engine can be accommodated in the installation space of a conventional ICE with comparable power, despite the reduced power density of hydrogen as a fuel in ICEs. As a first step, the hydrogen engine is naturally aspirated and equipped with direct injection. To develop a suitable calibration for the engine’s application, the influence of calibration parameters such as ignition and injection are investigated. The study examines the influence of these on operating behavior, fuel efficiency and emissions. This is supported by comprehensive measurement systems including cylinder pressure indication and emission analysis, which allows deep insights into the combustion process. First results show, that the ignition timing has only a minor influence on efficiency, but the formation of nitrogen oxides (NOx) varies by a factor of more than five as a result of an adjustment. Instead, the efficiency is primarily dependent on the mixture formation, which is significantly influenced by the injection pressure and timing. This research highlights the potential of hydrogen rotary engines as a viable route to near-zero emission mobility. Further research and testing are underway to fully realize the benefits of this powertrain configuration in the transition to a more sustainable transport ecosystem.

Endres, Jonas, Beidl, Christian, Hofmann, Silas

Comparison between Spark-Ignition and Passive Pre-Chamber Combustion in a Methanol Fuelled Heavy-Duty Engine at Different Speeds, Loads, and EGR Dilutions

2025-24-0030

9/7/2025

Decarbonizing the transport sector requires solutions that reduce CO₂ emissions while improving the efficiency of existing engine platforms. This study explores a retrofit strategy in which a heavy-duty diesel engine is converted to Otto-cycle operation and equipped with a passive pre-chamber combustion (PPCC) system. Methanol was used as the fuel due to its high octane number, low carbon intensity, and favourable combustion properties. The performance of the PPCC system is experimentally compared to conventional spark ignition (SI) across varying engine speeds, loads, and exhaust gas recirculation (EGR) levels. A dual-dilution strategy, combining lean operation (λ = 1.6) with EGR, was applied to extend dilution tolerance and assess the feasibility of operating near stoichiometry. All tests were conducted under steady-state conditions with fixed spark timing. Results show that PPCC consistently delivers faster combustion than SI across all conditions, with greater stability and reduced sensitivity to operating variations. Increasing engine speed shortened combustion duration, while EGR extended it. At higher loads, PPCC performance improved due to increased pressure differential between the pre-chamber and main chamber. Unlike SI, which became unstable beyond an EGR-diluted λ = 1.15, PPCC maintained stable operation up to stoichiometry at 36% EGR. This enabled potential compatibility with a three-way catalyst (TWC), with less than a 1% efficiency penalty and no degradation in combustion stability. However, SI outperformed PPCC in terms of overall efficiency, largely due to higher combustion completeness. The lower combustion efficiency of PPCC, linked to increased crevice volume and surface losses, also led to significantly higher total hydrocarbon (THC) emissions. These findings highlight the trade-offs between ignition stability and efficiency demonstrating that with proper calibration, PPCC can support high-dilution operation and conventional aftertreatment in retrofitted heavy-duty engines running on low-carbon fuels such as methanol.

Fong Cisneros, Eric J., Hlaing, Ponnya, Cenker, Emre, AlRamadan, Abdullah, Turner, James WG

Investigation of the Combustion Process of a Thermally Conditioned Active Prechamber in Monovalent Operation with Ammonia

2025-24-0028

9/7/2025

The debate over synthetic fuels is intense especially in sectors with a high energy demand like maritime [1, 2]. Hydrogen production from renewable sources is growing, but immediate measures for decarbonization are needed [3, 4]. In this context, the project MethMag was funded, and a gas engine for methane combustion with an innovative cooling concept and a purged prechamber (PC) spark plug was virtually developed [5, 6]. Validation with data from the test bench demonstrates that the simulations accurately represent the operating conditions [7, 8]. This combustion process is adapted for ammonia, which is being considered as a climate-friendly fuel of the future, particularly in maritime transportation [4, 9]. This fuel faces significant combustion challenges and is therefore mostly considered in complex, bivalent systems [10]. In particular, the prechamber is examined regarding the ignitability of ammonia. The overarching objective is to eliminate the necessity for a secondary fuel system, thereby reducing system complexity and associated costs. The transition to ammonia highlights the need for further adjustments. The geometry of the PC cap significantly affects turbulence and mixture formation in the prechamber [11]. While swirl caps generate high turbulence, the mixture formation is inadequate. Tumble caps, on the other hand, provide advantages in mixture formation by achieving an earlier increase in turbulence, even though the maximum turbulence is lower. For ammonia combustion, PC wall conditioning is not essential, given the inherently low combustion temperatures. However, conditioning can improve cold-start behavior by accelerating PC combustion and offering greater flexibility in ignition timing [12]. Direct injection into the prechamber enhances fuel mixing and reduces sensitivity to ignition timing adjustments. This leads to higher efficiency and better combustion characteristics, particularly at lean air-fuel ratios [13, 14]. Operating with a lean ammonia-air mixture is challenging but offers benefits for non-selective catalytic reduction (non-SCR) of nitrogen oxides. Simulations show that operation with λ = 1.2 and λ = 1.4 is feasible, although efficiency decreases at leaner mixtures [15].

Rothe, Paul, Bikas, Georgios, Mauss, Fabian

Experimental and Numerical Study on the Performance and Exhaust Emissions of a Single-Cylinder Natural Gas Large Bore Engine Equipped with Passive Pre-Chamber

2025-24-0022

9/7/2025

The maritime industry is among the most energy-intensive sectors, and achieving fleet decarbonization is crucial to significantly reduce greenhouse gas emissions. As a transitional fuel, natural gas (NG) presents a viable short-to-midterm solution. Compared to conventional marine fuels, NG has the potential to lower carbon dioxide emissions by approximately 20–30%. However, to fully leverage this potential on carbon footprint reduction, substantial advancements in combustion technologies are required. One promising approach to enhance the efficiency of SI NG engines is the implementation of Passive Pre-Chamber (PPC) technology. This strategy enables leaner combustion, improving thermal efficiency, mitigating the occurrence of knocking, and reducing NOx emissions. This study presents both experimental and numerical investigations to analyze the impact of charge dilution and ignition timing on the performance and emissions of a single-cylinder prototype NG PPC SI engine for marine application, retrofitted from baseline diesel architecture. Numerical simulations combining 1D and 3D CFD approaches were used to guide the combustion system and engine component design, optimizing valve timing, compression ratio, and fuel injection parameters to mitigate knock and improve thermal efficiency. Based on numerical simulations, excess air effects on thermodynamic efficiency and flame speed were evaluated. The experimental tests were conducted at 1500 rpm constant engine speed under different load conditions. Variation of the air-to-fuel ratio and spark advance were performed to characterize their effects on engine operation. The results were utilized to validate a 1D model, which demonstrated a high level of accuracy in reproducing the combustion evolution. PPC technology enabled high charge dilution (λ≈1.7). The coefficient of variation of IMEP remained below 1.5% throughout a wide range of λ values and combustion phasing conditions, indicating stable combustion. The engine exhibited indicated efficiencies of over 45%, marginally exceeding the predictions obtained from numerical simulations. This research underscores the potential of PPC technology in enhancing the efficiency and sustainability of NG-fueled marine engines, offering valuable insights to optimize combustion strategies for future low-emission propulsion systems.

Marchitto, Luca, Pesce, Francesco, Accurso, Francesco, Tornatore, Cinzia, Gorietti, Valentina, Buzzi, Luca, Grosso, Alessandro, Luci, Matteo, Napolitano, Pierpaolo, Pennino, Vincenzo, Beatrice, CARLO, Di Domenico, Davide, Giardino, Angelo

Enhancing Ammonia Combustion in Heavy-Duty SI Engines: A 3D-CFD Study on Pre-Chamber Ignition, Methane Addition, and Spark Timing Optimization

2025-24-0006

9/7/2025

Ammonia is a promising fuel for achieving zero-carbon emissions in internal combustion engines. However, its low flame speed and heat of combustion pose significant challenges for efficient combustion. The pre-chamber (PC) spark-ignition (SI) system offers a viable solution by generating multiple ignition points in the main chamber (MC), enhancing combustion efficiency and enabling at the same time lean-burn operation. This study investigates the combustion characteristics and emissions of an active PC spark-ignition heavy-duty engine fueled with ammonia and ammonia-methane mixtures through numerical 3D-CFD simulations performed using the CONVERGE software. These simulations provide an accurate representation of the complex chemical and physical phenomena occurring within the combustion chamber. The study starts from a fully methane-fueled case, validated against experimental data, and subsequently explores different ammonia-methane mixtures. Then, a detailed spark timing (ST) analysis is conducted, varying the ST from 14° to 50° BTDC, to determine the optimal ignition timing for each fuel blend in terms of both performance and emissions. The findings contribute to the ongoing efforts to improve the efficiency and environmental sustainability of heavy-duty spark-ignition engines, aligning with increasingly stringent emissions regulations. The results indicate that optimal performance is achieved with the PC entirely fueled by methane and the MC operating with a 80% NH3 – 20% CH4 mixture, with a ST of 38° BTDC.

Palomba, Marco, Salahi, Mohammad Mahdi, Cameretti, Maria Cristina, Mahmoudzadeh Andwari, Amin

Numerical Analysis of Direct-Injection and Combustion Inside a H2 Engine

2025-01-0301

7/2/2025

The direct injection of hydrogen (H2) inside internal combustion engines (ICEs) is gaining large research interest over the port-fuel injection strategy, because of several advantages as higher volumetric efficiencies, increased power output and reduced risks of abnormal combustion. However, the required high pressure ratios across the injector nozzle produce moderate-to-high under-expanded jets, characterized by complex flow structures. This poses a challenge for the numerical modelling of the mixture preparation by means of 3D computational fluid dynamics (CFD) approaches. In this work, a validated 3D-CFD methodology has been employed to simulate the closed-valve cycle of a direct injection H2 engine equipped with a centrally mounted hollow-cone injector and a non-axisymmetric piston bowl. First, injection and mixture preparation have been studied considering an early injection at the beginning of the compression stroke, and a delayed injection in the second half of the compression stroke. The results show how the higher in-cylinder pressure encountered by the delayed injection produces a jet characterized by a lower degree of under-expansion and a slower penetration. Moreover, the distribution of the in-cylinder mixture close to the ignition timing highlights that the stratification is greater for the late injection strategy. In both cases, the piston geometry also plays a crucial role in the mixture preparation because of non-conventional flow recirculation generated during the jet-piston interaction. Afterwards, combustion simulations have been carried out to further understand the effect of the injection timing on the premixed flame propagation. The results point out a reduced combustion duration for the delayed injection case. This can be explained by a twofold effect: a locally enriched mixture near the ignition point, speeding up the early flame kernel development, and a higher turbulence intensity around the ignition timing, which accelerates the overall flame speed.

Capecci, Marcolucio, Sforza, Lorenzo, Lucchini, Tommaso, D'Errico, Gianluca, Pezza, Vincenzo, Tosi, Sergio

Comparison of Spark and Turbulent Jet Ignition in a Fully Ammonia-Fueled Engine

2025-01-0201

6/16/2025

Ammonia (NH3) is an emerging carbon-free fuel with the potential to decarbonize the energy sector. However, its widespread adoption is hindered by challenges like low flame speed, high ignition energy, elevated emissions of nitrogen oxides (NOx), and unburned NH3. These limitations necessitate innovative combustion strategies for efficient and stable engine operation. This study investigates the potential of turbulent jet ignition (TJI) to overcome these challenges through the implementation of a pre-chamber, a small auxiliary chamber equipped with a spark plug to create hot, reactive jets that propagate into the main chamber, promoting rapid combustion from distributed ignition sites. In this work, TJI operation is compared to conventional spark ignition (SI) in a diesel engine platform retrofitted for 100% ammonia operation. Experiments were conducted at 1200 and 1800 RPM across varying loads (25%, 50%, 75%, and 100%) with equivalence ratio and spark timing sweeps. Combustion performance, stability, and emissions (NH3, NOx, and N2O) for both ignition systems were compared. Results demonstrate that TJI significantly improves combustion stability, with the coefficient of variation in indicated mean effective pressure reduced by over 50% compared to SI at part loads. Additionally, TJI allowed operation with retarded spark timing. Emissions analysis revealed comparable NOx levels but reduced unburned NH3 and N2O emissions in TJI mode. These findings highlight the ability of turbulent jet ignition to address the inherent challenges of ammonia combustion, providing a pathway for its integration into practical engines. Future work will focus on optimizing pre-chamber design to further improve combustion efficiency and explore emissions control strategies for broader applications.

Dhotre, Akash, Voris, Alex, Okey, Nathan, Kane, Seamus, Northrop, William

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