Browse Topic: Ignition systems

Items (2,093)

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

NO _x Formation Characteristics of Lean Hydrogen Combustion: From 0D Analysis to Comprehensive 3D-CFD Engine Investigations

2026-01-0732

7/1/2026

The transition toward climate-neutral transportation requires powertrain concepts that combine high efficiency with low pollutant emissions. In this context, hydrogen-fueled internal combustion engines represent a promising solution when hydrogen is produced from renewable energy sources. Owing to its specific molecular properties, hydrogen offers new possibilities for influencing and optimizing the combustion process and reducing the emission formation. This paper presents a numerical approach for characterizing the NOx formation in a single-cylinder research engine equipped with port fuel injection and a passive pre-chamber ignition system. The single-cylinder is operated over a wide range of engine loads and speeds, covering air-to-fuel ratios from λ=1.5 to 2.5 and achieving up to 23 bar indicated mean effective pressure. The study focuses on the influence of engine load and mixture composition on NOx emissions. A dedicated look-up table approach in combination with several reaction parameters based on the extended Zeldovich mechanism are evaluated through comparison with experimental data. Furthermore, multiple sampling positions within the CFD mesh are examined. The simulations reproduce measured trends across variations in load and air-to-fuel ratio with good accuracy. At high load and λ=1.5, NOx emissions of up to 6000 ppm are produced, decreasing exponentially with increasing excess air. Finally, potential NOx reduction strategies for the single-cylinder are examined. While influencing the mixture homogenization shows limited effectiveness, temperature-based actions prove to be more effective. Among the investigated approaches, a Miller intake valve strategy yields the largest benefit, achieving approximately 10% NOx reduction by lowering end-of-compression temperatures and increasing residual gas dilution under otherwise identical operating conditions.

Gal, Thomas, Vacca, Antonino, Chiodi, Marco, Schmelcher, Robin, Kulzer, Andre Casal

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

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

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

Optimal Strategies for SI H2 Combustion System and Pre-Ignition Investigation through Advanced Optical Techniques

2026-01-0324

4/7/2026

The rapidly transforming mobility sector is confronted with a dual challenge: achieving market expansion while significantly reducing emissions. Even if vehicle electrification tends to be favored in developed nations, it is widely acknowledged that no single solution is universally optimal. Within this context, hydrogen emerges as a compelling energy vector. It can be used both in fuel cells and internal combustion engines. This latter benefits from a well-known architecture and existing production infrastructures constituting a viable short-term and cost-effective solution especially for light or heavy-duty and off-road applications. In this context, investigation on the hydrogen spark-ignited internal combustion engine was performed, focusing especially on critical abnormal combustions. Indeed, during early development phase, abnormal combustion management was a challenge requiring the identification of the root cause of these issues. This work, based on the use of a versatile single-cylinder engine, is dedicated to the optimization of hydrogen combustion through adaptations of injection strategy to minimize the NOx production and improve the combustion efficiency. A dedicated attention was paid to study the effects of different parameters of the hydrogen injection system, such as the location of the injector, the targeting and the injection pressure. Subsequently, a specific cylinder head has been designed to allow endoscopic optical access into the combustion chamber for a visualization of the combustion related phenomena using a high-speed UV intensified camera. The work was especially focused on abnormal combustion analysis such as pre-ignition and allows to analyze the behavior of different spark plugs. Different injection configurations were tested and their effects on combustion were evaluated using both adiabatic heat release rate analysis and in-cylinder movies obtained through the optical setup described above. It provides valuable data about mixture preparation, flame propagation and cycle to cycle fluctuations. Conventional heat release rate analysis gives macro level data of the combustion stroke whereas the endoscopic images provide 2D flame fields that enhance the understanding of the combustion characteristics. This work finally leads to a better understanding of abnormal combustion occurrences and guides towards the choice of relevant injection and ignition strategies, especially at full load.

Londos, Benoit, Bardi, Michele, Serrano, David, Laget, Olivier, Gautrot, Xavier, Bramoullé, Clément, Cordier, Matthieu

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

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 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

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

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

Investigation of CDI and TCI Ignition Characteristics for Lean Hydrogen-Air Mixtures in a Constant Volume Combustion Chamber

2026-01-0327

4/7/2026

The discharge characteristics of ignition systems critically influence flame kernel formation and ignition stability under lean-burn conditions. This study experimentally compares a transistor coil ignition (TCI) and a capacitor discharge ignition (CDI) system in a constant-volume combustion chamber using hydrogen–air mixtures. The electrical behavior of both systems was first characterized through synchronized measurements of voltage, current, and high-speed imaging under various operating conditions with a resistive spark plug. The CDI system exhibited high-current (≈750 mA), short-duration (≈250 μs) discharges with strong instantaneous power but limited total spark-gap energy (≈5 mJ), while the TCI system produced lower-current, longer-duration (≈3 ms) discharges with higher cumulative energy (≈30 mJ). Flow-field tests revealed that the TCI discharge duration and energy release were strongly influenced by airflow, whereas CDI discharge behavior remained largely unchanged at flow velocities around 20 m/s. Ignition experiments with lean H₂–air mixtures (λ = 2.5–4.0) demonstrated that both systems can reliably ignite the mixture under quiescent and moderate-flow conditions, but the CDI system failed to sustain ignition near the lean limit. The results highlight the distinct energy-transfer mechanisms of the two ignition concepts and provide guidance for optimizing ignition design in future hydrogen internal combustion engines.

Cong, Binghao, Jin, Long, Yu, Xiao, Zhou, Qing, Tjong, Jimi, Zheng, Ming

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

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

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

A Comparative Study of Evaluation Indicators of Spark Plug Electrode Erosion Resistance Using High Energy Ignition

2026-01-0291

4/7/2026

Lean combustion is one of the effective methods to improve the efficiency of engine. High energy ignition can significantly enhance the stability of lean combustion, attracting widespread attention in engine applications, particularly in GDI engines. However, higher ignition energy accelerates the erosion rate of spark plug electrodes, thereby shortening their lifespan. This study used an erosion testing system for spark plug center electrode materials based on a self-made high energy ignition device and proposed corresponding evaluation indicators. Using this system, the erosion resistance of eight different electrode materials was assessed through three indicators. The results indicate that the testing system enables rapid detection on the erosion resistance of spark plug electrode materials. Connecting the center electrode to the cathode can accelerate electrode material erosion and shorten the testing cycle. Compared to the other two indicators, the electrode volume presented more stable measurement accuracy, making it a more reliable approach for evaluating the erosion resistance of spark plug electrodes. Under the test conditions, iridium-based alloys possess superior erosion resistance with lower erosion than platinum-based alloy.

Zhang, Jianqi, Sun, Nan, Miao, Xinke, Li, Yang, Zhou, Chuan, Deng, Jun, Li, Liguang

Effect of Pre-Chamber Geometry on Methanol Cold-Start Combustion in an SI Engine

2026-01-0307

4/7/2026

Vehicle pollutant emissions are a major challenge in the development of internal combustion engines. To meet increasingly strict regulations, the automotive sector is exploring alternative fuels and lean-burn strategies. Methanol is gaining importance as a carbon-neutral fuel due to advances in green production technologies. Methanol, despite its potential for renewable production, faces severe limitations due to its inherent poor cold-start performance with conventional ignition systems. In this context, the present study aims to investigate the influence of pre-chamber ignition on cold-start combustion by using high-speed optical diagnostics to visualize flame propagation while simultaneously measuring in-cylinder pressure and engine performance. A major result concerns the significant cyclic variability of conventional spark ignition (SI) under cold-start conditions, which exhibits significant cyclic variability. Instead, passive pre-chamber ignition significantly enhances cold-start combustion stability, lowering CoV IMEP to below 3% at λ = 1.0 and sustaining stability under 5% even in ultra-lean conditions (λ = 1.6), where conventional SI operation fails. Flame visualization quantitatively confirms that this stability stems from distributed, multi-point ignition, which accelerates initial flame propagation by 3-4x compared to SI. These findings demonstrate that pre-chamber ignition can effectively overcome the traditional "cold-start" problem for methanol, enabling stable combustion from the first cycles. This provides an invaluable dataset for CFD model validation, as it captures a highly stable combustion process largely independent of the adverse thermal boundary conditions typical of cold start, thereby simplifying the modeling challenge.

Sementa, Paolo, Altieri, Nunzio, Tornatore, Cinzia

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

The Impact of Various Renewable Hydrocarbons on Performance and Emissions in a Super Lean Burn Engine

2026-01-0306

4/7/2026

Compared to regular fuels, biofuels can play a key role as low-carbon transitional energy sources for ICE vehicles as the fleet moves towards increasing electrification. Blending of ethanol plays a key role in enhancing the anti-knock properties of the fuel and also allows renewable hydrocarbons (such as bio-naphtha) to be incorporated into the blend whilst maintaining an acceptable overall fuel quality. Super lean burn ICE technology with λ between 2 and 3 can lead to enhanced fuel economy and reduced NOx emissions. The Toyota prototype engine used to generate data for this project injects most of the fuel in PFI mode to generate a homogeneous super-lean charge in the cylinder, but just before spark ignition the DI injector sprays a small amount of fuel towards the spark plug to create a richer charge near the spark plug to promote flame kernel development. Various fuel formulations with high biofuel content were tested in both conventional and super lean burn engines. Certain fuel compositions were formulated with faster burning components such as ethyl benzene. The super lean burn engine showed a clear link between faster combustion and minimization of unburned fuel losses, thereby resulting in a further efficiency benefit. The effect of fuel composition on particulate emissions was more complex: although the conventional engine emitted higher particulate numbers (PN) when operating on fuels with a higher content of heavier aromatics (as might be predicted from standard particulate index approaches), the super lean burn engine suggests that additional factors are at play which are discussed in the paper.

Aradi, Allen, Krueger-Venus, Jens, Jain, Sandeep Kumar, Cracknell, Roger, Kolbeck, Andreas, Shibuya, Masahiko, Yamada, Ryota, Matsubara, Naoyoshi, Kitano, Koji

Total Cost of Ownership Reduction Using Passive Pre-Chamber Ignition in Natural Gas Engines

2026-01-0309

4/7/2026

Spark plug durability is a factor affecting the total cost of ownership (TCO) of spark-ignited natural gas engines, with some heavy-duty platforms requiring plug replacement after only 750 hours of operation. The high ignition energy demand under lean or diluted conditions accelerates electrode wear, shortening plug life and increasing maintenance frequency. This work evaluates passive pre-chamber (PC) ignition operating at lowered spark energies as a strategy to reduce spark energy requirements and extend plug durability, thereby lowering TCO. Experiments were conducted on a medium-duty Cummins 6.7L ISB engine at 1600 RPM and 50% load under varying exhaust gas recirculation (EGR) dilution levels (0–40%). Two passive pre-chambers with 1.1 mm and 1.6 mm nozzle diameters were compared with conventional spark ignition (SI). SI was operated with a fixed coil dwell of 4 ms (~90 mJ), while the PC configuration was tested across 2–4 ms dwell times (~30–90 mJ). Cylinder pressure analysis revealed that PC ignition sustained stable combustion at significantly lower spark energies than SI, with improved combustion stability at ~30 mJ compared with SI at ~90 mJ. The PC system also extended the dilution tolerance beyond that achievable with SI, while delivering up to ~2% higher indicated thermal efficiency and reducing the COV by nearly 90% at 30% EGR. A TCO analysis was conducted to assess the economic benefit of adopting a passive PC system operating at reduced spark energies compared to SI. It was found that adopting a passive PC system could reduce TCO by approximately $11,000 per engine over a five-year operational period, primarily due to fuel savings, extended spark plug life, and reduced maintenance frequency. These projections were weighed against the additional hardware cost of the pre-chamber, yielding a rapid estimated return on investment of ~300 operating hours. Therefore, this work motivates continued research and development of passive PC technology and its commercial adoption in natural gas engines used in transportation applications.

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

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

Flame Velocity and Combustion Behaviour of Ammonia–Hydrogen Blends: A Combined Experimental and Numerical Study

2026-01-0320

4/7/2026

Ammonia is emerging as a promising energy vector for decarbonising the maritime sector. However, its low flame speed can lead to incomplete combustion, reduced engine efficiency, and increased emissions of unburned ammonia (NH3). Blending hydrogen with ammonia helps to address these issues, but the fundamental combustion characteristics of such mixtures remain insufficiently understood. This study examines the combustion dynamics of an NH3–H2 blend containing 30% hydrogen at 3 bar initial pressure. Experiments were performed in a 1.2 L optically accessible constant-volume combustion chamber fitted with a wall-mounted surface spark plug. High-speed shadowgraph imaging with 6,000 fps captured the flame evolution throughout the combustion process. The pressure and temperature values were monitored using piezoresistive pressure transducers and K-type thermocouples. Combustion times and flame extensions were extracted via post-processing of flame images using custom MATLAB algorithms. The combustion process was examined from the initial start to a diameter of 60mm. Complementary CFD simulations were carried out in CONVERGE using the C3MechV3.5 chemical mechanism. To match the experimental conditions, the numerical studies were conducted at an ambient pressure of 0.3 MPa and an equivalence ratio of 1.0. The model predicted flame propagation times accurately, achieving an average relative error of 2.95% and an R2 value of 0.991. A third-order polynomial correlation was derived to predict instantaneous flame diameter as a function of time, enabling interpolation for intermediate combustion stages for both simulation and experimental results. Error analysis indicated that the model achieved its best performance for medium-sized flames (30–45 mm) but exhibited larger discrepancies at the smallest and largest diameters. Nevertheless, within the 20–60 mm range, deviations remained between −9.5% and +3.4%.

Bodur, Tuna Murat, Bowling, William, La Rocca, Antonino, Cairns, Alasdair

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

Ignition System Measurements Procedure

J973_202603 (Current)

3/11/2026

This SAE Recommended Practice specifies the design and/or evaluation with the specific equipment, conditions, and methods for distributorless battery ignition systems intended for use in various internal combustion engines including automotive, marine, motorcycle, and utility engine applications. The test procedures listed in this document are limited to measurements performed on a test bench only and do not include measurements made directly on engines or vehicles. This standard is not intended to supply information for battery ignition systems used in aircraft applications of any type.

Ignition Standards Committee

Optimization of Combustion Stability and Fuel Economy for Dedicated Hybrid Engines with High Exhaust Gas Recirculation Rate

03-19-02-0008

2/26/2026

In recent years, the rapid growth of hybrid vehicles has driven the development of dedicated hybrid engines (DHEs) as a key powertrain technology for achieving high thermal efficiency and low emissions. Driven by stringent emissions regulations and demand for improved fuel economy, enhancing thermal efficiency in gasoline engines remains a critical industry challenge. Exhaust gas recirculation (EGR) technology dilutes oxygen in the intake charge, suppresses knock, and optimizes combustion phasing. However, excessive EGR rates compromise combustion stability by inducing elevated cyclic variability and potential misfire, posing challenges in maintaining stable combustion and improving fuel efficiency at high EGR levels. Thus, combustion stability and fuel efficiency optimization in Geely’s DHEs under high EGR conditions was investigated in this article. In this study, a high tumble combustion system was designed to enhance charge motion and promote stable flame propagation. Furthermore, exhaust gases were drawn from the upstream side of the three-way catalyst to realize high EGR rate. Additionally, high-energy ignition system was applied to ensure stable combustion under high EGR dilution conditions. Compared with the 1.5T engine with a similar technical route, the optimized DHE achieved a 5.4% increase in EGR rate and a 7.2 g/kWh reduction in brake specific fuel consumption (BSFC). These results demonstrate the feasibility of high EGR operation in gasoline engines through synergistic combustion system design and ignition enhancement, offering a scalable solution for meeting future fuel efficiency and emissions targets.

Li, Qiang, Deng, Xiaorong, Ren, Siming, Zhang, Peiyi, Zhu, Yunfeng, Li, Hongzhou, Yan, Pingtao, Gu, Xiangsheng

Comprehensive Engine Testing Methodologies for Hydrogen Internal Combustion Engine Validation with Combustion & Performance Evaluation Techniques

2026-26-0256

1/16/2026

Validation of hydrogen-fuelled internal combustion engine (H2 ICE) is critical to assess its feasibility as sustainable transportation with zero carbon emissions. This experimental analysis conducted on Ashok Leyland’s 6cylinder 2V engine to evaluate the engine performance & durability with hydrogen fuel. Combustion behaviour of hydrogen ICE needs to be closely monitored during continuous operation of validation testing, due to its unique properties compared to other conventional fuels. During engine run, a pre-ignition source can cause knock event leading to instant failure of critical parts like piston assembly, spark plug, liner, valves & cylinder head. Also, hotspots inside IMF leads to backfire affecting the air intake & fuel injection assembly. This study emphasizes the significance of precise instrumentation of thermocouples across engine on cylinder head, intake manifold & exhaust manifold, to detect performance detoriation and combustion abnormalities causing knocking & backfire. Crankcase ventilation system design plays a critical role in evacuating the blowby gas from engine block. This paper explains methodology to measure the moisture condensation from blowby gas, as it leads to oil emulsification. Experimental data shows variation in inlet manifold air temperature directly impacts engine power as H2 ICE operates at higher stoichiometric ratio. Increase in air intake temperature from turbo compressor out is a result of barometric temperature and pressure variation. This measurement is critical to understand the engine performance variation in real-time operating condition. Hence validation of H2 ICE necessitates a specialized instrumentation during testing to monitor the performance parameters and hardware detoriation. This research provides critical insights into the procedural adaptations required for H2 ICE testing and validation by integrating frugal instrumentation with experimental analysis. This study offers a robust framework for assessing engine performance, reducing operational risks, and ensuring test results reliability. These findings contribute to the design & development of hydrogen-fuelled engines, facilitating their adoption as a sustainable alternative for transportation while addressing durability, emissions, and regulatory compliance challenges.

Vasudevan, Sindhuja, J, Narayana Reddy, Bolar, Yogesh Ganesh, Pandey, Sunil, N, Harish, N R, Varatharaj, Karthikeyan, K, Kumar D, Kishore

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

Misfires Detection in Bi-Fuel Engines – A Brief Note

2026-26-0120

1/16/2026

With the expansion of compressed natural gas (CNG) filling station in India, bi-fuel vehicles are gaining popularity in recent times. Bi-fuel engine runs on more than one fuel, say in both CNG and petrol. Hence, the engine must be optimized in both the fuel modes for performance and emissions. However, due to the inherent differences in combustion characteristics: ignition dynamics and fuel properties, they pose a significant challenge in case of detection of misfires. Misfires are caused because of faulty injection systems and ignition systems and incorrect fuel mixture. Accurate detection is essential as misfires deteriorate the catalysts performance and may impacts emission. Misfires (or engine roughness) is calculated from engine crankshaft speed signal. In this study, the effectiveness of crankshaft-based misfires detection method, comparison of misfire signals magnitude in bi-fuel modes and practices developed for accurate detection of misfires is presented.

Thiyagarajan, Abhinav, N, Gobalakrishnan, R, Hema

Technologies and Strategies for High Brake Thermal Efficiency Gasoline Engine to Meet the Future CO ₂ Emission Targets in India

2026-26-0072

1/16/2026

The Indian automobile industry is experiencing a significant shift, propelled by environmental necessities and national climate obligations set at the CoP26 summit, aiming for a 45% decrease in CO₂ emissions by 2030 and reaching carbon neutrality by 2070 [1]. Transportation continues to be a significant source of air pollution; consequently, India is enhancing its regulatory frameworks with BS VI Stage 2 regulations, CAFE Phase III norms set for 2027, and CAFE Phase IV by 2032 [2]. Furthermore, the transition from MIDC to WLTP driving cycle is meant to increase the accuracy of the efficiency and emissions assessments [2]. To comply to these upcoming regulations, the automotive industry is moving toward producing high efficiency engines in India. A naturally aspirated (NA) 1.5L, 4-cylinder inline gasoline engine was selected from Indian market for this study. Maximum Brake Thermal Efficiency (BTE) of this engine is around 37%. Assessment of new technologies were performed by implementing them stepwise to see the impact on BTE. A well calibrated 1D GT-SUITE model was considered from FEV database to perform the simulation-based approach to increase the BTE by improving the stroke/bore (s/B) ratio, increasing the compression ratio, implementing Atkinson cycle with variable valve timing (VVT) / variable valve lift (VVL) optimization, and charge motion refinement for optimal in-cylinder combustion. Low temperature cooled EGR (TEGR < 70°C) and pre-catalyst pick-up distributed EGR strategies were simulated to improve the combustion stability and pumping loss for BTE improvement. Friction losses were further minimized by implementing the polished surfaces, electrification of auxiliary components, and other advanced surface treatments. Advanced technologies including Dual Port Fuel Injection (Dual PFI) system, high energy ignition system with thermal swing coatings, and system designed to operate with highly diluted mixture are required to achieve maximum BTE. These technologies would also be explored in this study. This paper also covers the rivals' restrictions put on engine geometry and number of cylinders concerning possible max. BTE level with which the engine can achieve. With the completed study, the efficiency step walk document indicated BTE improvement from each technology step to achieve a target max. BTE for the engine.

Garg, Shivam, Fischer, Marcus, Emran, Ashraf, Jagodzinski, Bartosch, Franzke, Bjoern

Numerical Analysis of the Performance of an Engine with a Pre-Chamber Equipped with an Air Injector Operating in TJI Mode

2025-36-0187

12/18/2025

The sustainability of the transportation sector demands the continuous development of new technologies in internal combustion engines, aiming at reducing pollutant and greenhouse gas emissions while increasing fuel conversion efficiency. Pre-chamber (PC) ignition systems have recently emerged as an important technological pathway to explore. These systems generate turbulent combustion gas jets capable of accelerating flame propagation in the main chamber. The use of this mechanism enables a more homogeneous and efficient combustion, as well as allowing an increase in the compression ratio, resulting in improvements in engine performance and a reduction in pollutant emissions. One of the strategies to further enhance the benefits of pre-chambers is the introduction of air injectors. The objective of this modification is to promote the cleaning of residual gases that remain in the pre-chamber after combustion, mitigating adverse effects such as mixture dilution and ignition instabilities, in addition to favoring more complete combustion. In this context, the present study presents a numerical analysis of the performance and emissions of a single-cylinder research engine operating in turbulent jet ignition (TJI) mode with a pre-chamber equipped with air injectors. Simulations were performed using CONVERGE CFD software to evaluate the baseline pre-chamber configuration and three variations with conical air injectors featuring orifices of 2 mm, 1 mm, and 0.5 mm connected to the pre-chamber. The results showed that the 1 mm orifice configuration exhibited the best performance compared to the baseline configuration and other variations, delivering higher combustion efficiency and indicating superior residual gas cleaning.

Rocha, Hiago Tenório Teixeira Santana, Oliveira, Wender Pereira de, Filho, Fernando Antonio Rodrigues, Baeta, José Guilherme Coelho, Guzzo, Márcio Expedito, Assis, Marcelo Suman Silva, Moreira, Thiago Augusto Araujo

Turbulent Jet Ignition Engine: Calibration of Flame Multipliers for Combustion Model

2025-36-0239

12/18/2025

With the implementation of increasingly stringent regulations for pollutant emissions, such as Proconve L8 [1], which requires a 37% reduction in NOx and non-methane organic gases (NMOG) emissions for light passenger vehicles compared to previous regulations, the automotive engineering community is constantly evolving to develop prediction models that are capable of predicting the performance of Internal Combustion Engines (ICE). With this, the society search solutions to increase fuel conversion efficiency and reduce fuel emissions. In a special case, related to the study of the turbulent jet ignition (TJI) engine, there was a need to develop a refined numerical model that allows for the accurate design of the ignition pre-chamber geometry. In view of this, a one-dimensional modeling was carried out in the GT-SUITE ® software, in its modeling environment for Internal Combustion Engines (ICE), GT-POWER ®, with the objective of determining its ideal volume, parameters such as internal volume, number, diameter and length of holes, the distance between the spark plug and the pre-chamber orifices, and the operating mode were evaluated, which directly influence the projection of the flame front and the overall indicated efficiency.

Silva, Arthur Medeiros, Souza, Ediwaldo Júnio de, Rocha, Hiago Tenório Teixeira Santana, Filho, Fernando Antônio Rodrigues, Guzzo, Márcio Expedito, Oliveira, Wender Pereira de, Baeta, José Guilherme Coelho

Optimization of Biogas Combustion in SI Engines Applied to the Pre-Chamber Ignition System

2025-36-0209

12/18/2025

The diversification of the energy matrix, combined with the use of renewable and less polluting fuels in internal combustion engines, has encouraged numerous research efforts both nationally and internationally. In this context, the utilization of waste for biofuel production stands out as a promising alternative, offering a clean and economically viable energy source. Biogas is one of the most sustainable options and has been widely used in the industry. However, it presents low lower heating values (LHV) and difficulties in burning stoichiometric mixtures, which compromise engine performance, resulting in higher specific fuel consumption and lower power output compared to fossil fuels. To address this challenge, this study aimed to improve biogas combustion in internal combustion engines by investigating the application of a new pre-chamber ignition system in the combustion process and engine performance parameters. For this, experimental tests were conducted with two biofuel concentrations for evaluation: (100% CNG) and (85% CNG + 15% CO2), enriching the stoichiometric mixture and applying calibration methodologies in a single-cylinder engine adapted to operate with biogas, assessing engine performance parameters and gas emissions. The application of pre-chamber ignition showed significant improvements in energy efficiency, resulting in approximately a 12% torque gain in stoichiometric mixtures, contributing to more efficient combustion and a reduction in hydrocarbon emissions. The use of mixtures in the range of 1.0 to 1.2 led to emission reductions between 60% and 35% compared to the engine without the pre-chamber, demonstrating the pre-chamber’s ability to promote more complete combustion even in leaner mixtures. The data obtained provide valuable insights for the development and application of new technologies in biogas-powered internal combustion engines, contributing to advancements in this research area.

Siqueira, Caio Henrique Moreira, Ázara, Luiz Eduardo Martins, Ribeiro, José Vitor Puttini, Soares, Gabriel Faria, Silva, Fábio Moreira, Alvarez, Carlos Eduardo Castilla

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

Performance Analysis of Methanol- Ethanol Blend Fuel in a Spark-Ignition Flex-Fuel Engine

2025-36-0148

12/18/2025

Flex-fueled vehicles (FFV) dominate the Brazilian market, accounting for over 75% of the national fleet. Ethanol fuel is widely used, primarily in the form of hydrated ethyl alcohol fuel (HEAF). Given the similar physicochemical properties of ethanol and methanol, fuel adulteration is a growing concern, often involving the addition of anhydrous ethanol, methanol, or even water to hydrated ethanol. These adulterants are visually imperceptible and can only be detected through analyses conducted by regulatory agencies using specialized instruments. However, they can significantly affect vehicle performance and accelerate engine component deterioration. The experiment was performed with a small displacement 3-cylinder port fuel injection flex-fuel engine on an engine test bench (dynamometer) and compared when fueled with ethanol and methanol. Data acquisition included combustion pressure, spark plug temperature, torque, air-fuel ratio, fuel flow, spark maps, and the overall effects of methanol adulteration on combustion. The results indicate that engines designed and calibrated to operate with hydrated ethanol exhibit different combustion behaviors when methanol is present in the fuel mixture. Methanol increases combustion pressure and temperature inside the chamber, creating a highly corrosive environment due to both the elevated temperature and the chemical properties of methanol. Fuel consumption increased when methanol was used in the engine calibrated for ethanol. The findings highlight the potential risks associated with fuel adulteration, emphasizing its impact on engine durability, vehicle fuel economy, and maintenance costs.

Mascarenhas, Giovana Rebellato, Gomes, Ederson, Cruz, Diego, Duque, Edson Luciano

A Review of the Application and Research Progress of Turbulent Jet Ignition Technology

03-18-08-0047

12/3/2025

For the sustainable development of human society, energy saving, emission reduction, and carbon reduction are urgent challenges to be addressed in the energy industry. As a power device for energy conversion in the transportation sector, the internal combustion engine also needs to enhance its thermal efficiency while cutting pollutant emissions. To meet the current stringent requirements, lean combustion has been widely studied as an effective strategy. However, the ignition difficulty resulting from lean burn needs to be addressed. As a high-energy ignition system, the prechamber turbulent jet ignition can accelerate in-cylinder combustion, thereby enhancing engine efficiency and reducing emissions. Thus, it is considered a promising technology. This review reveals efforts to apply prechamber ignition systems to optimize combustion in the engine characterized by low-carbon fuels and low-emission features. First, this article briefly introduces the evolution of the prechamber turbulent jet ignition technology. Second, the ignition mechanism, the influence of fuel in the prechamber and structure of prechamber on the combustion performance of the spark ignition engine are emphatically introduced. The structural parameters like nozzle diameter, nozzle orientation, nozzle number, and prechamber volume have a significant effect on the in-cylinder combustion. This review summarizes the research achievements regarding the structural parameters. Finally, this study demonstrates the performance improvement of engines equipped with turbulent jet ignition technology.

Bai, Xiujuan, Zheng, Dayuan

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

Visualization of Ammonia Engine by Pre-Chamber Igniter

2025-01-0530

11/25/2025

Ammonia is considered more and more as a promising carbon-free fuel for internal combustion engines to contribute to the decarbonization of several sectors where replacing conventional engines with batteries or fuel cells remains unsuitable. However, ammonia properties can induce some challenges for efficient and stable combustion. This study investigates the use of an active pre-chamber ignition system fueled with hydrogen and compares it to conventional spark ignition, with a focus on lean limit operation and early flame development. Experiments were conducted on a single cylinder optical engine with a compression ratio of 9.5, equipped with a quartz window in the piston for natural flame luminosity imaging using a high-speed camera. The engine was fueled with a mixture of 95% ammonia and 5% hydrogen by volume. Ammonia was injected and mixed with air in the intake port while hydrogen was directly injected into the prechamber. As a function of the intake pressure (1.0, 0.9, 0.8, and 0.7 bar), the lean operating limit was determined as 0.7, 0.8, 0.85, 0.9 for both active pre-chamber and spark ignition strategies. In fact, with hydrogen prechamber ignition, significant faster combustion was achieved which reduced by 30% the overall combustion duration. The visualization of natural emission of flame revealed a more distributed and faster flame propagation with the active prechamber, indicating a higher ignition performance and faster combustion under lean ammonia-hydrogen conditions, highlighting its potential for extending operating limits and improving combustion robustness.

Rousselle, Christine Mounaim, Brequigny, Pierre, Gelé, Raphaël, Moreau, Bruno

Ammonia Combustion with Active Pre-Chamber Spark Plug - a CO ₂ -Free Combustion Process

2025-01-0527

11/25/2025

As a zero-carbon fuel, ammonia has the potential to completely defossilize combustion engines. Due to the inert nitrogen present in the molecule, ammonia is difficult to ignite or burn. Even if the ammonia can be successfully ignited, combustion will be very slow and there is a risk of flame quenching, i.e. the flame going out before the ammonia-air mixture has been almost completely converted. Both the difficult flammability and the slow combustion result in high ammonia slip, which should be avoided at all costs. The engine efficiency is also greatly reduced. Safe ignition and burn-through can be achieved by drastically increasing the ignition energy and/or using a reaction accelerator such as hydrogen. The planned paper will use detailed 1D and 3D CFD calculations to show how high the potential of ammonia combustion in an internal combustion engine is when an active pre-chamber is used as the ignition system. As a result of the flame jets penetrating into the main combustion chamber filled with ammonia, this allows a so-called space ignition and a very high ignition energy to be achieved. The latter is particularly high if the fuel used in the pre-chamber is hydrogen, for example. As hydrogen can be obtained directly from the ammonia via an on-board cracker in the vehicle, this would be a single-fuel combustion process. The paper will focus on the potential how fast and save the combustion can be, what combustion efficiencies can be obtained and what amount of hydrogen is needed from the onboard cracker (operated with Waste heat from the exhaust system) to build a very stable and highly efficient ammonia-based passenger car combustion system.

Sens, Marc, von Roemer, Lorenz, Rieß, Michael, Fandakov, Alexander, Casal Kulzer, Andre

Investigation of Active Pre-Chamber Ignition on an Optically Accessible Ultra-Lean DI Hydrogen Engine

2025-01-0524

11/25/2025

Hydrogen is a promising alternative to conventional fuels for decarbonizing the commercial vehicle sector due to its carbon-free nature. This study investigates the ignition and flame propagation characteristics of hydrogen in a 2-liter single-cylinder optical research engine representative of the commercial vehicle sector. The main objective was to enable high power density operation while minimizing NOx emissions. For that, ultra-lean combustion was employed to lower in-cylinder temperatures, addressing the challenge of NOx formation. To counteract delayed and unstable combustion under lean conditions, an active pre-chamber ignition system was implemented. It uses a gas-purged pre-chamber with separate hydrogen injection and spark plug ignition. Turbulent hot gas jets from the pre-chamber ignite the fresh mixture in the main combustion chamber, enabling faster and more stable ignition compared to conventional spark plugs. Additionally, the low volumetric energy density of hydrogen, which limits performance in port fuel injection due to air displacement, was addressed through direct hydrogen injection into the combustion chamber to increase the mixture heating value. High-speed imaging techniques, including Schlieren and OH chemiluminescence, were used alongside thermodynamic analysis to study combustion dynamics. Results demonstrate that the active pre-chamber ignition system achieved stable combustion at ultra-lean conditions (λ up to 4) without knocking phenomena. Essentially, NOx-free operation was possible for λ > 2.5. Pre-chamber conditions were found to influence performance trade-offs: richer mixtures enhanced stability and combustion speed, while leaner mixtures minimized NOx emissions. Comparative measurements with a standard spark plug showed that pre-chamber ignition leads to more stable and faster ignition, unlocking additional performance and efficiency potential. These findings demonstrate the viability of hydrogen as a carbon-neutral zero-emission fuel for commercial vehicle engines.

Borken, Philipp, Bill, Daniel, Link, Lukas, Dinkelacker, Friedrich, Hansen, Hauke

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

High-Tension Ignition Cable

J2031_202511 (Current)

11/6/2025

The specifications contained in this SAE Standard pertain to high-tension ignition cable used in road vehicle engine ignition systems.

Ignition Standards Committee

Firing TDC Identification Through Wasted Spark Duration Measurements During Cranking of Small Engines

2025-32-0085

11/3/2025

Implementing control techniques through “virtual sensors” is extremely attractive for small size engines, given that cost effectiveness is essential. This work presents a routine for identifying the firing TDC through measurement of spark duration. Previous capability of correctly identifying cycle phasing through this route was confirmed during normal operation of a power unit that featured a wasted spark ignition system. Starting with the hypothesis that this could be implemented during engine cranking, the procedure was adapted for identifying the firing TDC as quickly as possible; it was also developed with the specific task of requiring less time for synchronization, compared to the previous version. The new method was verified on a small size 50 cc single cylinder engine that featured a recoil starter mechanism. Correct identification was confirmed, with the possibility of generating the reference signal as early as the 2nd cycle that featured normal operation of the ignition system; to put things into perspective, a minimum of 5-6 such cycles were recorded during multiple cranking events. Compared to the rpm based evaluation, more consistent identification could be achieved, mostly due to the fact that the spark duration measurements were influenced less by the varying engine speed during cranking.

Irimescu, Adrian, Merola, Simona

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

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