Browse Topic: Lean burn engines

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Nitrogen-Based Emissions from Ammonia Combustion in a Heavy-Duty Spark Ignition Engine2026-37-00326/9/2026
Ammonia (NH3) is a carbon-free fuel with strong potential for spark-ignition (SI) engine applications. However, the engine can produce complex nitrogen-based emissions not adequately captured by conventional engine models. This study consolidated the results of experimental and numerical studies on the use of neat NH3 combustion in a heavy-duty compression-ignition engine converted to spark-ignition operation, first for a sweep of equivalence ratios (ϕ) from 0.7 to 1.0, and another from varying the energy substitution ratio of methane (CH4)– NH3 blends from neat CH4 to neat NH3 at constant ϕ = 0.8. Two 0-D two-zone SI engine models with detailed chemistry (called “original” and “extended”) predicted engine thermodynamics and emissions. While the original model reproduced in-cylinder pressure and combustion phasing, it failed to capture the effect of fuel composition or operating condition on NO trends, both under- and over-predicting them for neat NH3 and CH4-rich operations. An extension of the model incorporating a burned-zone batch reactor and two more reactors simulating the post-combustion oxidation of the mixture exiting crevices and the DeNOx processes during exhaust blowdown were implemented to address these limitations. Analysis of NO formation pathways highlighted the differences between modeling approaches. The equilibrium assumptions in the original model restricted NO formation primarily to thermal (Zeldovich) mechanisms. In contrast, the kinetics-driven model showed that non-thermal pathways dominate NO formation for all NH3-containing cases, which shows the limitations of conventional SI models developed for hydrocarbons when applied to nitrogen-containing fuels. Post-combustion homogeneous reactors for crevice-based oxidation and exhaust blowdown revealed significant NO and N2O formation after the end of combustion at moderate temperatures (850–1200 K), suggesting that N2O formation was dominated by secondary thermal processes. Therefore, the inclusion of post-combustion chemistry and more consistent models are essential for accurate emission prediction in NH3-fueled SI engines.
Trujillo Grisales, Juan, Saenz Prado, Stefany, Alvarez, Luis F., Akkerman, Vyacheslav, Dumitrescu, Cosmin E.
Predictive Modelling of NO x and Unburned Hydrogen Emissions in a Direct-Injection Hydrogen Spark-Ignition Engine2026-37-00076/9/2026
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
Effects of Gasoline Composition and Operating Parameters on the Response of End-Gas Autoignition to Nitric Oxide in a Lean-Burn DI-SI Engine2026-01-03134/7/2026
Lean operation of spark-ignition engines can lead to engine thermal efficiency gains and lower NOx emissions due to reduced combustion temperatures. Yet, lean operation could still face challenges in end-gas autoignition and knock generation due to higher intake pressures and trapped NO in the residual gas. This study evaluates the impact of NO on end-gas autoignition for two gasoline fuels with similar octane rating but different composition: high cycloalkane fuel (HCA) and high olefin fuel (HO). Experiments were performed at stoichiometric and lean (λ = 2) conditions and at two engine speeds of 1400 rpm and 2000 rpm. Accompanying chemical kinetics simulations in CHEMKIN revealed that the mechanisms controlling the effect of NO on autoignition are similar λ = 2 and λ = 1, with NO + HO2 = NO2 + OH being the main pathway for enhancing reactivity by promoting low-temperature heat release (LTHR). The compositionally different fuels reacted differently to NO seeding and engine speed, and differences were augmented at λ = 2 compared to λ = 1 as the end-gas autoignition shifted to the low temperature regime. HO, which has inherent low temperature chemistry, was strongly impacted by engine speed at low NO seeding levels, with no noticeable peak of LTHR detected at 2000 rpm. On the other hand, LTHR of HCA was marginally affected by shortened residence time at higher engine speed as NO + HO2 reaction was not greatly affected by shorter time scales, since HO2 production was sustained even at 2000 rpm to support OH generation from NO + HO2. Contrary to HO, HCA exhibited greater sensitivity to NO seeding, as the increased OH production at higher NO concentrations offset the OH-quenching effect of cyclopentane, which accounts for 28.6% of HCA’s composition. Consequently, a sensitivity analysis revealed that fuels with weak inherent low-temperature chemistry, like HCA, are likely to be more sensitive to variations in NO concentration and charge temperature, whereas fuels with strong low temperature chemistry are more sensitive to variations in end-gas λ and intake pressure.
Kim, Namho, Abboud, Rami, Sjöberg, Magnus, Lopez Pintor, Dario, Saggese, Chiara, Matsubara, Naoyoshi, Kitano, Koji, Yamada, Ryota, Sugata, Kenji
CuSCR Catalysts Under H 2 -ICE Exhaust Gas Conditions2026-01-03614/7/2026
In the near to mid-term, hydrogen internal combustion engines (H2-ICE) can be a bridge technology for reducing carbon emissions. A few challenges anticipated under lean-burn H2-ICE operation are the significant drop in turbo-out temperatures, combined with higher water content, and the possible presence of unburned hydrogen in the exhaust, which could have a potential impact on performance and durability of the downstream exhaust aftertreatment system, particularly oxidation and SCR catalysts, as these conditions can suppress low-temperature oxidation activity, perturb Cu-site speciation and redox cycling in SCR catalysts, and exacerbate hydrothermal aging under sustained wet operation. This study examines the impact of excess water and residual hydrogen on Cu-SCR durability, active site chemistry, and stability for the case with and without an upstream oxidation catalyst, through aging tests at 450 °C and 550 °C. Changes in Cu redox cycles were assessed through site quantification using multiple titration techniques to determine the influence of excess H2O and H2 on catalyst performance and aging.
Kim, Mi-Young, Daya, Rohil, Kamasamudram, Krishna
A Pathway to Exceed 50% Indicated Thermal Efficiency for Gasoline Engines with Active Pre-Chamber2026-01-03004/7/2026
Research on high efficiency and low emission control strategies are crucial for addressing energy security and pollution challenges for combustion engines of vehicles. This paper investigates the effects of increasing the compression ratio and excess air coefficient (λ) in naturally aspirated engines via active pre-chamber technology, and further enhancing λ through the synergy of active pre-chamber with intake boosting and Miller cycle technology, on combustion efficiency and pollutant emissions. Experiments were conducted on a high-compression-ratio (up to 16.6) single-cylinder gasoline engine. Under natural aspiration, the effective compression ratio was raised via valve timing, while λ was increased using integrated passive and active pre-chamber systems. Under boosted conditions, intake flow was controlled via a flow meter, and λ was controlled via an active pre-chamber to analyze the λ distribution and thermal efficiency at high-efficiency operating points. Results indicate that under natural aspiration, increasing the effective compression ratio to 15.8 and λ to 1.4 improved the indicated thermal efficiency (ITE) to 40.3%. Further deployment of an active pre-chamber enabling ultra-lean combustion (λ=2.0) achieved an ITE of 43.3% while reducing NOx emissions to 53×10-6. Under boosted intake pressure with Miller cycle, elevating intake pressure to 282kPa and achieving ultra-lean combustion (λ=2.0–2.2) resulted in ITE over 50%, with NOx emissions consistently below 50×10-6 (ppm - parts per million).
Deng, Jun, Li, Xiaoliang, Miao, Xinke, Xu, Bingxin, Zhang, JianQi, Li, Liguang
Effect of Passive Pre-Chamber Geometry on Performance and Emissions of a Single-Cylinder Natural Gas Large Bore Engine2026-01-03334/7/2026
The maritime industry is one of the most energy-intensive sectors, characterized by high fuel consumption and significant environmental impact. As global trade relies on shipping, the challenge of reducing pollutants and greenhouse gas emissions becomes ever more pressing. Natural gas (NG) is considered as a transitional fuel, capable of lowering CO₂ emissions by 20–30% compared to conventional marine fuels. However, to fully harness this potential, significant advances in combustion technology are necessary, particularly with ultra-lean combustion strategies. One of the most promising pathways is pre-chamber combustion, a solution that can simultaneously improve the efficiency and sustainability of NG marine engines. In this scenario, the passive pre-chamber geometry plays a key role, as it directly influences ignition behavior, combustion stability, and exhaust emissions. This work presents an experimental study conducted on a single-cylinder marine engine prototype, retrofitted from a diesel baseline, and equipped alternatively with four passive pre-chambers featuring different geometrical configurations. The tests were conducted at an engine speed of 1500 rpm and different loads to evaluate the influence of pre-chamber geometry on engine performance and exhaust emissions. Key parameters such as combustion phasing, efficiency, and pollutant formation were analyzed and compared between the four setups. Results showed that pre-chamber design affects the interaction between the turbulent jets and the main chamber mixture, leading to significant variations in both combustion efficiency and emission trends. These findings provide new insights into the role of passive pre-chamber geometry in optimizing large-bore NG marine engines, offering a valuable contribution to the development of cleaner and more efficient propulsion systems for the maritime sector.
Marchitto, Luca, Tornatore, Cinzia, Pennino, Vincenzo, Mariani PhD, Antonio, Beatrice, Carlo, Accurso, Francesco, Gorietti, Valentina, Pesce, Francesco, Giardino, Angelo, Vitti, Luciano
The Effects of Ethanol on Combustion in a Super-Lean-Burn Engine2026-01-03034/7/2026
To mitigate global warming, many countries are working toward carbon neutrality. Reducing CO₂ emissions from vehicles requires electrification technologies in hybrid and plug-in hybrid electric vehicles (HEVs, PHEVs) and improving thermal efficiency of internal combustion engines (ICEs). Lean-burn combustion is one approach to improving ICE thermal efficiency. Biofuels and synthetic fuels can also reduce CO₂ emissions in existing vehicles. Ethanol, a bio-derived fuel, is widely used in varying contents worldwide, and its further utilization is anticipated. This study examines the effects of ethanol blending on emissions, thermal efficiency, knocking, and combustion speed in a super-lean-burn engine. Gasoline surrogates with varying ethanol contents were tested at an excess air ratio (λ) of 2.5. Higher ethanol content reduced nitrogen oxides (NOx) emissions due to lower adiabatic flame temperature. Total hydrocarbon (THC) emissions measured by a Flame Ionization Detector (FID) showed a decreasing trend; however, after correction for low sensitivity to ethanol and aldehydes, no significant differences were observed. Thermal efficiency increased with ethanol content, due to reduced cooling losses. Knocking was mitigated by the higher Research Octane Number (RON) from ethanol blending; however, the extent was smaller than in the production engine operating at λ = 1. This mechanism was examined through ignition delay calculations. At λ = 2.5 and in-cylinder pressures above 9 MPa, the 50–90% combustion duration was prolonged, attributable to suppressed ethyl radical formation under lean conditions and a greater influence of the reaction in which methyl radicals consume hydrogen atoms to produce methane under high-pressure conditions.
Sugata, Kenji, Matsubara, Naoyoshi, Yamada, Ryota, Kitano, Koji
Development and Preliminary Combustion Experiments of a Prototype Engine with Sleeve Valves Based on the Focusing Compression Principle2026-01-02954/7/2026
Our laboratory has proposed the focusing compression principle which employs pulsed super-multi jets of gas colliding around the chamber center. This principle aims to achieve high thermal efficiency by reducing both exhaust and cooling losses. Exhaust loss is minimized due to relatively-silent high compression. Cooling loss is reduced due to thermal insulation caused by fuel-air mixture being confined to the chamber center and the compressible flow effect. In previous studies, we conducted fundamental gasoline combustion experiments on a proof-of-concept opposed-piston engine which incorporated this principle. This engine featured eight intake nozzles in an octagonal configuration and utilized non-sinusoidal and strongly asymmetric piston movements. The results indicated the possibility of high thermal efficiency based on less knocking under high compression, and the potential for stable combustion under lean-burn conditions. As a next step towards practical application with durability, we have developed a new opposed-piston engine with a small displacement of 123 cc which maintains intake ports of octagonal configuration, featuring a unique valve system. This unique valve system is characterized by setting a cylindrical-shaped sleeve-valve in between the inner and outer- cylinders. On operation, these sleeve-valves move along the central axis of cylinders, opening or closing all eight ports on the cylinder walls simultaneously. In this paper, we first show details of the present new engine developed and its preliminary experiments including non-combustion motoring experiments, and also combustion experiments using gasoline. The engine was successfully motored up to 750 rpm with no gas leakage around the sleeve-valve at compression process. Combustion experiments were initially tested from slightly-lean conditions.
Nishizawa, Tomohiko, Naitoh, Ken, Baba, Shotaro, Ukegawa, Hiraku, Yamada, Sota, Ozono, Yuka, Abiko, Mirei, Suzuki, Yosuke, Hara, Namito, Ito, Yoshikuni, Matsubara, Kosaku, Uenoyama, Kazuyuki
Combustion Enhancement via Discharge Current Modulation under Turbulence Conditions2026-01-03364/7/2026
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
The Impact of Various Renewable Hydrocarbons on Performance and Emissions in a Super Lean Burn Engine2026-01-03064/7/2026
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
Investigation of CDI and TCI Ignition Characteristics for Lean Hydrogen-Air Mixtures in a Constant Volume Combustion Chamber2026-01-03274/7/2026
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
Effect of Pre-Chamber Geometry on Methanol Cold-Start Combustion in an SI Engine2026-01-03074/7/2026
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
TOC99-08-01-0TOC2/11/2026
TOC
Tobolski, Sue
Increasing the Efficiency of Hydrogen Direct Injection Internal Combustion Engines through the Use of Miller Cycles and Water Injection03-19-01-00011/31/2026
Hydrogen-fueled reciprocating engines typically feature reasonable efficiencies and low engine-out emissions but low power density, compromising their utility and economics. Previous hydrogen engine research has found efficiency and anti-knock benefits when using either Miller cycles or water injection. This article therefore studies, for the first time, a directly injected (DI), spark-ignited, heavy-duty, turbocharged and hydrogen-fueled engine operated with both Miller cycles and water injection. Miller cycles, with either early or late intake valve closure, and water injection combine to achieve high engine efficiencies approaching 50%, which is significantly higher than the same engine with standard valve timing. The increased susceptibility of hydrogen autoignition in these Miller cycles is overcome by water injection, which simultaneously increases the charge density, counteracting both lean-burn hydrogen’s and Miller cycles’ commonly observed power loss. This demonstrates that the combination of DI, Miller cycles, and water injection is a pathway toward highly efficient, low-emission, hydrogen-fueled engines with power densities that are comparable to conventional engines.
Mortimer, Joel, Poursadegh, Farzad, Brear, Michael, Yang, Yi
Optimizing Hydrogen Engine Performance a Comparative Study of Lean & Stoichiometric Calibration Approach2026-26-02611/16/2026
Hydrogen combustion in internal combustion engines offers numerous advantages, such as zero CO2 emissions and high flame speed, which make it a promising alternative fuel for green vehicle solutions. In order to maximize the engine performance with hydrogen, however, meticulous calibration of the air-fuel mixture must be performed, particularly when lean and stoichiometric combustion conditions are considered. Lean burning, i.e., excess air, offers better thermal efficiency and lower NOx emissions but can cause lower engine power and combustion instability. Stoichiometric combustion, however, ensures complete combustion of the fuel-air mixture, but at the cost of higher combustion temperatures and consequently, high NOx emissions. Calibration strategies for hydrogen engines are presented in this paper by comparing the lean and stoichiometric strategies and their implications on engine power output, efficiency, and emissions. Test data from several hydrogen engine configurations demonstrate that lean burn with EGR addition can be employed to minimize NOx emissions at the expense of tight engine stability and power control. On the other hand, stoichiometric operation yields more power but with the requirement for complex emission control systems. The compromises between these calibration strategies are presented in the paper and recommendations are provided on optimizing the performance of hydrogen engines for different operating conditions.
Jadhav, Ajinkya, Bandyopadhyay, Debjyoti, Sutar, Prasanna S, Sonawane, Shailesh Balkrishna, Rairikar, Sandeep D, Thipse, Sukrut S
A Review of the Application and Research Progress of Turbulent Jet Ignition Technology03-18-08-004712/3/2025
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
Investigation of Active Pre-Chamber Ignition on an Optically Accessible Ultra-Lean DI Hydrogen Engine2025-01-052411/25/2025
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
Experimental Investigations on Lean Burn Spark-Ignition Engine Using Alcohol-Gasoline Blends2025-28-021311/6/2025
Alcohol fuels are regarded as a feasible approach to address rising energy demands and reduce the dependency on fossil fuels, with ethanol and methanol emerging as a promising renewable fuel for spark-ignition engines. In this research work, tests were performed on a spark ignition engine altered from a diesel engine that employs ethanol/methanol-gasoline blend as fuel operating under lean conditions. The experiments were conducted at 10.5:1 compression ratio and 1500 rpm under full throttle condition with three fuel blends namely M10 (10% of methanol+ 90% gasoline), E10 (10% of ethanol+ 90% gasoline), E5M5 (5% of each ethanol and methanol+ 90% gasoline). Investigational results reveals that alcohol-gasoline blends displayed low COV of IMEP. Furthermore, the alcohol-gasoline mixtures enhanced the peak in-cylinder pressure owing to improved flame speed and flammability limits. Adopting lean-burn operation and high compression ratio can efficiently improve combustion attributes in an alcohol-gasoline fuel operated spark ignition engine.
Devunuri, Suresh, Porpatham, Dr. E
Development of Supercharged Direct-Injection Two Stroke Engine with Intake and Exhaust Valve for Series Hybrid (2nd Report)- To Realize Lean Burn -2025-32-002311/3/2025
The two-stroke engine, known for its small displacement and high performance, is space-efficient when installed in a vehicle. As such, incorporating two-stroke engines into HEVs is an effective way to reduce vehicle weight and optimize engine space. However, one downside is that the amount of unfired elements in the exhaust gas increases due to the air/fuel mixture being expelled into the exhaust system during the scavenging process. Moreover, combustion can become unstable due to the large volume of residual burned gases in the cylinder. To address these issues, we propose a two-stroke engine equipped with intake and exhaust valves that directly inject fuel into the cylinder. In our first report, we presented an engine design and method that enable high scavenging efficiency and stable combustion in a two-stroke engine [1]. In this second report, we share the results of our research aimed at improving fuel efficiency and achieving low emissions, all while maintaining the high performance typical of a two-stroke engine. To enhance fuel efficiency, the amount of burned gas was optimized by adjusting the timing and lifting the intake and exhaust valves. Lean combustion was achieved by leveraging the high temperature in the cylinder, utilizing its excellent ignitability. Additionally, it has been reported that THC emissions—a common issue in two-stroke engines—are reduced by preventing unburned gas from being expelled into the exhaust pipe through the adoption of in-cylinder direct injection.
Sakurai, Yota, Hisano, Atsushi, Saitou, Masahito, Ichi, Satoaki
Investigation of Transient High Current Ignition for Lean Mixture in Spark Assisted Compression Ignition2025-01-039010/7/2025
Lean burn combustion is an effective strategy to reduce the in-cylinder temperature. Hence reduce NOx emissions and increase the thermal efficiency of the system. One essential aspect of successful combustion is the flame kernel initiation and development. However, as the fuel-air mixture becomes leaner, challenges arise in achieving a stable flame kernel initiation and a moderate speed of flame propagation. This empirical research aims to investigate the impact of the transient high current ignition strategy on flame kernel development, flame propagation and auto-ignition timing of lean Dimethyl Ether (DME). In this work, a rapid compression machine is employed at engine-relevant conditions, a pressure of ~15 bar and temperature of ~650K. Spark-assistance is applied at the end of compression to enable a spark-assisted compression ignition combustion mode. The spark event is initiated by a transient high current ignition system, which includes a traditional transistorized coil ignition and an in-parallel high-voltage capacitor for boosting the transient current, enabling high discharge energy (up to 11.3J). The combustion process is qualitatively assessed with high-precision pressure data acquisition along with high-speed images and quantitatively processed through image processing. Test results indicate that as spark energy increases, faster flame propagation is observed resulting in a shorter time requirement for reaching the auto-ignition in lean DME along with a shorter combustion duration.
Asma, Sabrina, Yu, Xiao, Jin, Long, Tjong, Jimi, Zheng, Ming
Experimental Investigation of the Comparison between Helium and Hydrogen Jets Exiting a DI Outward-Opening Injector via Schlieren Technique2025-24-00689/7/2025
This paper deals with the hydrogen-to-helium jets comparison within the framework of the assessment of helium as a potential hydrogen surrogate. The comparison is centred on the assessment of the combined action of pressure ratio with gas properties on the dynamics of the jet exiting an outward-opening injector. The shots are performed at injection pressures and backpressures ranging from 21 to 36 bar and from 1.2 to 5 bar, respectively. The Schlieren technique is deployed to capture the jets images. The study demonstrates that at certain pressure ratios helium is an appealing solution bridging the lab safety with fidelity to hydrogen-like jet behaviour. Decreasing pressure ratio minimizes the hydrogen-to-helium difference in axial penetration and area, enabling helium to yield a hydrogen-like development. The findings underscore the impact of the pressure ratio on how the gas properties, such as density and diffusivity, dictate the evolution of the axial propagation and area, respectively.
Coratella, Carlo, Tinchon, Alexis, Hespel, Camille, Dober, Gavin, Foucher, Fabrice
Effects of Varying the Air-Fuel Equivalence Ratio at Different EGR-Rates on a Medium-Speed LNG-Diesel Dual-Fuel Engine2025-24-00419/7/2025
The dual-fuel combustion process, which is offered as a retrofit solution for conventional diesel engines by various manufacturers, represents an option for reducing emissions from internal combustion engines and is already available today. Current dual-fuel engines run on liquefied natural gas (LNG), which is usually of fossil origin. Due to the existing infrastructure and the possibility of producing LNG by means of electrolysis and methanation, LNG can already be produced in a 100% climate-neutral way and thus make a contribution to climate neutrality in the shipping industry. The adoption of exhaust gas recirculation (EGR) systems in the maritime sector became more significant in 2020 following the enforcement of the sulphur emission cap. By lowering the sulphur content in the fuel, technologies in the exhaust tract are also conceivable without the use of expensive scrubber systems. Dual-fuel LNG/diesel engines are typically operated in lean-burn mode to reduce the risk of knocking and to comply with the nitrogen oxide limits in accordance with IMO TIER III. However, one disadvantage of the lean-burn combustion process is climate-damaging methane (CH4) slip due to incomplete combustion. To address this issue, an EGR system can be employed to mitigate nitrous oxides (NOx) emissions and prevent engine knocking at richer air-fuel mixtures, as an alternative to increasing the air-fuel equivalence ratio lambda. In the context of this paper, experimental investigations are conducted on a single cylinder medium speed dual-fuel engine, where EGR rates of up to 35% are examined across various lambda values. The adjustment of lambda is achieved by varying the charge air pressure using an externally driven compressor station for charge air supply. The results of the presented investigations provide insights into the emission reduction potential of a targeted variation in EGR rates and lambda, thus making an important contribution to more environmentally friendly ship propulsion systems.
Seipel, Pascal, Glauner, Manuel, Dinwoodie, Jules, Buchholz, Bert
Smart Ignition Coil for H2 ICE Application with Combustion Diagnostic System for Misfire Detection2025-24-00589/7/2025
The transition to decarbonized transportation necessitates significant modifications to internal combustion engines for alternative carbon-neutral fuels, particularly hydrogen. The integration of alternative systems is crucial for improving engine control, facilitating real-time engine health monitoring and facilitate early problem detection. This study investigates the potentialities of an ignition system specifically designed for H2 applications, with the integration of a smart coil diagnostic system with the aim to enhance engine performance and control capabilities. Experiments were conducted on a single-cylinder research engine across varying spark advanced, throttle positions, and engine speeds, comparing the novel ignition system with integrated diagnostics against traditional spark plug. Results demonstrate improvements in combustion stability and control when innovative spark plug was employed. Compared to a conventional spark plug, the Hy2Fire® system consistently delivered superior performance, achieving a peak indicated mean effective pressure (IMEP) of 4.85 bar (vs 4.68 bar) and maintaining a coefficient of variance of IMEP (CoVIMEP) below 2% across a broad range of conditions. The system demonstrated earlier combustion phasing (AI50 reduced by over 1 CAD) and improved combustion stability, especially under lean-burn (λ = 2.0) scenarios. Analyzing diagnostic signals from the smart coil's secondary spark current offers a promising avenue for evaluating combustion quality and its relationship to in-cylinder pressure, thus representing significant advancements. A dual-method approach, employing artificial intelligence algorithms for signal processing, enabled precise identification of maximum in-cylinder pressure with an error below 10%, and detection of anomalies such as misfire events. This analysis facilitated the precise identification of in-cylinder maximum pressure, a crucial parameter for engine performance evaluation, and the detection of critical anomalies such as misfire, which can severely impact engine longevity and efficiency. The system's behavior under the varying operating conditions tested has been thoroughly analyzed, highlighting its robustness and adaptability.
Ricci, Federico, Papi, Stefano, Avana, Massimiliano, Dal Re, Massimo, Grimaldi, Carlo
Experimental Analysis of Enhanced Scavenging Efficiency in Hydrogen-Powered Internal Combustion Engines for Heavy-Duty Applications2025-24-00569/7/2025
The purpose of this work is to highlight the benefits of improved scavenging efficiency for premixed, lean-burn, spark-ignited heavy-duty engines fueled by hydrogen. Scavenging efficiency measures the effectiveness of replacing exhaust gases with fresh air (or an air-fuel mixture) within the cylinder of an internal combustion engine. Enhanced scavenging efficiency reduces residual gas content and increases the proportion of fresh air, resulting in a cooler local mixture temperature. Additionally, it improves heat dissipation within the combustion chamber, cooling potential hotspots and allowing for earlier injections with fewer restrictions due to combustion anomalies, particularly pre-ignitions. To increase scavenging efficiency in a 4-stroke internal combustion engine, valve timing adjustments were made by introducing a valve lift profile with greater overlap of the exhaust valve closing and the inlet valve opening sequences. Additionally, a high-efficiency turbocharger was used to reduce backpressure and thereby increase the pressure gradient across the engine and promote scavenging. A test campaign was conducted on a 12.9-liter inline 6-cylinder heavy-duty engine to determine the impact of increased scavenging efficiency. The benefits were quantified using indicators such as intake and exhaust manifold pressures and maximum power output. In addition to an engine map and a full-load performance study, start-of-injection trade-offs were made at various engine speeds, loads, and different lambda targets. The test results confirmed the anticipated improvements. The increased valve overlap, and the high-efficiency turbocharger led to enhanced volumetric efficiency and a greater negative pressure differential between the intake and exhaust manifolds. These enhancements were particularly beneficial in the high-load area, where high boost pressure is essential to achieve the desired lambda value. At lower loads, where the engine typically operates in throttled conditions with a positive pressure gradient, no deterioration was observed. In summary, implementing the scavenging concept enabled the engine to operate more stable and achieve on average approximately 15 % higher performance without experiencing pre-ignition. Additionally, the lower local mixture temperature reduced thermal stress on the combustion chamber hardware, which helps mitigate wear and potential engine damage.
Schuette, Christoph, Borg, Jonathan, Giordana, Sergio, Rapetto, Nicola
Enhancing Ammonia Combustion in Heavy-Duty SI Engines: A 3D-CFD Study on Pre-Chamber Ignition, Methane Addition, and Spark Timing Optimization2025-24-00069/7/2025
Ammonia is a promising fuel for achieving zero-carbon emissions in internal combustion engines. However, its low flame speed and heat of combustion pose significant challenges for efficient combustion. The pre-chamber (PC) spark-ignition (SI) system offers a viable solution by generating multiple ignition points in the main chamber (MC), enhancing combustion efficiency and enabling at the same time lean-burn operation. This study investigates the combustion characteristics and emissions of an active PC spark-ignition heavy-duty engine fueled with ammonia and ammonia-methane mixtures through numerical 3D-CFD simulations performed using the CONVERGE software. These simulations provide an accurate representation of the complex chemical and physical phenomena occurring within the combustion chamber. The study starts from a fully methane-fueled case, validated against experimental data, and subsequently explores different ammonia-methane mixtures. Then, a detailed spark timing (ST) analysis is conducted, varying the ST from 14° to 50° BTDC, to determine the optimal ignition timing for each fuel blend in terms of both performance and emissions. The findings contribute to the ongoing efforts to improve the efficiency and environmental sustainability of heavy-duty spark-ignition engines, aligning with increasingly stringent emissions regulations. The results indicate that optimal performance is achieved with the PC entirely fueled by methane and the MC operating with a 80% NH3 – 20% CH4 mixture, with a ST of 38° BTDC.
Palomba, Marco, Salahi, Mohammad Mahdi, Cameretti, Maria Cristina, Mahmoudzadeh Andwari, Amin
High Lambda Boosting for Hydrogen Internal Combustion Engine02-18-03-00238/29/2025
The commercial vehicle industry continues to move in the direction of lower emissions while reducing its carbon footprint. This study focuses on hydrogen internal combustion engines (H2-ICE) since it offers a zero-carbon solution to the industry while showing very low NOx emissions when coupled to a conventionally sized aftertreatment SCR system. This work highlights modeling efforts for analyzing key boosting configurations to operate a hydrogen engine at high lambda (relative air–fuel ratio) for lowering NOx, maintain the aftertreatment system reasonable in size, and improving brake thermal efficiency (BTE). GT-Power was used to model H2-ICE engines from 13L to 19L in displacement with different boosting architectures. Key configurations include a variable geometry turbine (VGT) turbocharger coupled with a supercharger (SC), a VGT with higher engine displacement, and a VGT coupled in series with a fixed geometry turbine (FGT) turbocharger. An exhaustive study comparing these boosting architectures together for steady-state and transient regime performance is the novelty for this study, which is a gap in the existing literatures. Base diesel power curves from both 13L and 15L engines were studied, having maximum brake mean effective pressures (BMEP) from 18 to 21 to 23 bar with λ ≥ 2.2. The VGT+SC was studied with multiple variants including splitting the charge air cooler (CAC) into two parts to provide cooling both pre and post SC, a SC clutch, and a SC bypass. The results show that the VGT (upstream) + SC variant utilizes the SC at low engine speed and high torque, along with all transient regimes from low to high load. The VGT+SC architecture, besides its complexity with clutch and bypass, successfully supports high λ operation (≥2.4), achieving a peak BTE of 43%, and significantly reduces NOx emissions without the need for EGR or large aftertreatment systems. This variant shows the fastest transient response relative to all other configurations in time-to-torque and acceleration cycles while rivaling the highest BTE. VGT+SC can also meet 5500 ft altitude performance with λ ≥ 2.2, leading to low NOx with the same SCR size equivalent to diesel engines and without EGR. Transient response and high BTE are essential to showing that this zero-carbon H2-ICE solution is viable for the commercial vehicle market.
Gurjar, Shubham, McCarthy, Jr., James E., Manickavasagan, Thirumoolan, Chaudhari, Amol S., Nimeshkumar, Parmar, Bachu, Pruthvi, Bitsis, Christopher
Development of After-Treatment Systems and Control Strategy for a Hybrid-Dedicated Homogeneous Lean Burn Engine2025-01-02176/16/2025
The development of lean-burn gasoline engines has continued due to their significant improvements in thermal efficiency. However, challenges associated with NOx emissions have hindered their mainstream adoption. As a result, the development of an effective NOx after-treatment system has become a key focus in lean-burn engine research. Additionally, HC emissions pose another challenge, as they tend to increase under lean combustion conditions while their conversion efficiency simultaneously declines. This study presents a novel after-treatment system incorporating a lean NOx trap(LNT) and a passive SCR(pSCR) system. This configuration enables efficient NOx reduction at a competitive cost while maintaining operational simplicity. Moreover, conventional catalyst technologies, including three-way catalysts (TWCs) and fuel-cut NOx traps (FCNTs), were optimized to maximize conversion performance under lean operating conditions. To further enhance system performance, various control strategies were explored, including advanced temperature management of after-treatment systems, the regeneration strategy of LNT, and optimized catalyst purge strategies during the cold-start phase. The proposed after-treatment system and control strategies were validated through vehicle testing on a chassis dynamometer. The results demonstrated that a hybrid vehicle equipped with a lean-burn gasoline engine and new after-treatment system can achieve a 10% improvement in fuel efficiency while remaining compliant with future emission regulations, underscoring its viability for real-world applications.
Oh, Heechang, Lee, Jonghyeok, Sim, Kiseon, Lim, SeungSoo, Park, Jongil, Park, Minkyu, Kang, Hyunjin, Han, Donghee, Lee, Kwiyeon, Song, Jinwoo
Parametric Analysis of Injector Operational Parameters, Charge Dilution, and Intake Valve Opening on In-Cylinder Motion and Flame Development in an Automotive, Lean-Burn, Gasoline Engine with High-Tumble2025-01-01986/16/2025
The effect of injection pressure, start of injection (SOI) timing, charge dilution, and valve timing on charge motion and early flame development was investigated for a pre-production automotive gasoline engine. Experiments were performed in a single-cycle optical engine designed to represent the high-tumble (Tumble ratio = 1.8), lean-burn engine. Time-resolved particle image velocimetry (PIV) was used to characterize velocity flow fields throughout the swept volume during the intake and compression strokes. Diffuse back illuminated imaging allowed for visualization and quantification of the injected liquid fuel spray and its interactions with the tumble vortex. Hydroxyl (OH*) chemiluminescence imaging was performed to image spark channel elongation and early flame kernel development. It was observed that an optimal injection timing of 320° before top dead center (bTDC) resulted in attenuation of the tumble motion and an associated reduction in compression flows that shifted the tumble vortex toward the intake valves. These effects were amplified with higher injection pressures or advanced injection timings but muted for lower injection pressures or retarded injection timings. This differs from previous observations with a moderate tumble head (tumble ratio = 1.5), where the optimal injection timing resulted in augmentation of the tumble motion due to the momentum of the injected fuel spray, increasing the compression flows. Chemiluminescence imaging and visualization of the spark behavior of the high-tumble engine revealed that the optimal injection timing produced a highly stretched spark channel that consistently deflected toward the exhaust valves, with the flame kernel rapidly expanding in the recirculation zone at the time of spark, leading to a faster overall flame development in the combustion chamber. Variations of the parameters that increased flow velocities (lower injection pressures and retarded injection timings) resulted in less consistent spark positioning and flame kernel development, as well as a higher chance of observing restrikes of the spark. This is suspected to be why the optimal injection timing for the high-tumble head resulted in the attenuation of the tumble motion and reduced flow velocities compared to the moderate tumble head. These results suggest that it is crucial to balance the interactions between the tumble motion and the fuel spray with the with how the flow affects the quality of the spark channel and early kernel development at the time of spark. The interplay between the bulk flow motion and electrode-generated wake turbulence will be discussed, with experimental data compared to companion large eddy simulation results.
MacDonald, James, Ekoto, Isaac, Han, Donghee, Lee, Jonghyeok
Development of Combustion System for a Hybrid-Dedicated Homogeneous Lean Burn Engine2025-01-02166/16/2025
This study explores strategies to extend the lean combustion limit, improve thermal efficiency, and reduce engine-out emissions in a hybrid-dedicated homogeneous lean-burn engine. Under lean combustion conditions, slow laminar flame speed hinders flame kernel growth, leading to combustion instability and limiting lean limit of air excess ratio. To address this challenge, the combustion system is developed to generate high-intensity in-cylinder flow promoting plasma channel expansion at the spark plug gap and enabling the formation of larger initial flame kernel. A newly designed intake port and piston bowl geometry were introduced to enhance tumble flow, significantly raising convective flow speed at the spark plug gap. This accelerated the initial combustion process and effectively expanded the lean combustion limit. A high-energy multiple ignition was also implemented to prevent spark channel blow-off or short circuit caused by increased electrical resistance, further improving combustion stability under lean operation. Additionally, new spray pattern was developed to enhance mixture homogeneity and robustness, thereby reducing HC and NOx emissions. An electric supercharger was integrated to precisely manage air dilution and to provide a sufficient boost for powering a D-segment SUV when combined with hybrid electric motors. The synergy of these technologies enabled stable combustion at air excess ratio exceeding λ=2.0, achieving the maximum peak thermal efficiency of 45% and NOx emissions below 0.3 g/kWh at 2000 rpm and 8.5 bar. This study highlights the impact of each technology on combustion characteristics and underscores the potential of lean-burn engines as a viable solution for meeting stringent future emission regulations with significant carbon reduction.
Oh, Heechang, Lee, Jonghyeok, Sim, Kiseon, Park, Jongil, Kim, Taekyun, Kang, Hyunjin, Hong, Seungwoo, Han, Donghee, Kim, Dokyun
An Experimental and Numerical Study of Ultra-Lean Combustion Characteristics of Methanol Direct Injection using Various Coil Spark Ignition Strategies2025-01-02006/16/2025
Methanol is significantly emerging as a promising alternative fuel in the pursuit of carbon neutrality. This study aims to analyze the combustion characteristics of methanol in a spark-ignition (SI) engine operating under high compression ratios and ultra-lean conditions through both experimental and simulation approaches. The objective is to derive optimized combustion efficiency by employing various ignition strategies based on discharge energy. To this end, experiments were conducted using a Rapid Compression Expansion Machine (RCEM) to replicate realistic engine environments. The effects of discharge energy and spark duration across different spark coil configurations were investigated through both experimental methods and computational fluid dynamics (CFD) simulations. The experimental results showed that the use of multiple spark coils achieved an energy release rate of approximately 239 mJ/s, more than twice that of the single-coil configuration. Simulation results were in good agreement with the experimental findings. In the single-coil setup, combustion indicators such as in-cylinder pressure were significantly influenced by variations in spark duration. In contrast, the multi-coil configuration demonstrated higher peak values in several combustion characteristics, but once a certain threshold of discharge energy was exceeded, the improvements in performance became marginal. This suggests that simply increasing the spark duration is not always an effective strategy for optimizing the spark channel in methanol SI engines. Furthermore, the multi-coil ignition strategy significantly reduced the ignition delay, contributing to improved combustion stability under lean-burn conditions. As a result, the multi-coil strategy achieved an indicated thermal efficiency (ITE) approximately 10% higher than that of the single-coil approach, with the maximum efficiency observed at 30.4% in the 10-coil strategy.
Choi, Jeongyeon, Lim, Ocktaeck
Thermal Efficiency Improvement and Emission Reduction of Methanol Spark Ignition Engine Using Lean-Burn Strategy2025-01-02246/16/2025
Methanol is a promising fuel for achieving carbon neutrality in the transportation sector, particularly for internal combustion engine vehicles. With its high-Octane number, methanol enables higher thermal efficiency compared to gasoline engines. Additionally, its wide flammability range allows stable engine operation under lean burn conditions at low to mid-load levels. These characteristics make methanol well-suited for lean-burn strategies, which reduce pumping losses and enhance thermal efficiency. However, there remains a lack of studies on the influence of injection timing under different lean conditions, particularly in a wall-guided spark ignition engine. Wall-guided systems use the chamber wall or piston surface to redirect and stratify the fuel-air mixture near the spark plug at the time of ignition. The combustion performance of lean-burn engines in highly sensitive to variations in injection and excess air ratio. In this study, experiments were conducted on a single-cylinder engine to examine the combustion and emission characteristics under varying excess air ratios and the injection timings. At an SOI of -180 CAD aTDC, a thermal efficiency of 47.5% was achieved when the excess air ratio was increased. This corresponds to a 5.62% improvement in efficiency compared to the condition with excess air ratio (λ) 1.2 condition, representing the largest increase among all tested conditions. Due to high thermal efficiency, high vaporization heat of methanol, and low combustion temperature of lean conditions, nitrogen oxides emission decreased from 10.24 g/kWh to 2.23 g/kWh. However, corrected hydrocarbon emission increased from 3.07 g/kWh to 6.98 g/kWh under SOI -120 CAD aTDC condition, leading to the decline in combustion efficiency.
Lee, Seungwon, Kim, Hyunsoo, Hwang, Joonsik, Bae, Choongsik
Simultaneous Direct-Photography of Flame Propagation Inside Pre-Chamber and Main-Chamber in Gasoline Engine with Passive Pre-Chamber2024-32-00954/18/2025
Pre-chamber combustion is well known for the effective way to improve thermal efficiency in internal combustion engine. An active pre-chamber can accomplish super lean burn while a passive pre-chamber can easily improve combustion with low-cost. Therefore, various studies have been carried out. However, since its combustion characteristics are very complicated, the sequence of events for torch ignition and flame propagation in main-chamber from ignition and flame propagation inside pre-chamber have not been well clarified. Especially, investigation on the process from torch ejection to ignition of mixture in main-chamber has been carried out using combustion vessels and rapid compression machines, but this phenomenon has not been clarified. In this study, three types of optically accessible passive pre-chamber with different orifice patterns (normal six orifices, asymmetric five orifices and tangential five orifices) were designed and installed to a single-cylinder gasoline spark ignition engine. Also, an optical-scope was designed uniquely and installed to main-chamber. The flame propagation inside pre- and main-chambers was taken simultaneously by using two high speed cameras. In addition, the temperature distribution around the torch ejection in main-chamber was taken by high speed IR (Infrared) camera. As a result, cyclic variation in flame propagation direction inside pre-chamber and variation in timing of torch ejection in main-chamber were observed. In the cycles when torch ejected to the intake side first, the flame propagation was shifted to the same side inside pre-chamber. This variation of flame propagation direction changed by the orifice pattern of pre-chamber, the flame propagation direction of pre-chamber with tangential orifices were the most stable inside both pre-chamber and main-chamber. Visualizing the temperature distribution during torch ejection showed that the mixture in main-chamber was ignited locally around the torch.
Hokimoto, Satoshi, Moriyoshi, Yasuo, Kuboyama, Tatsuya, Egashira, Shuichi, Nagai, Yoshitaka
Improvement of Lean Burn Characteristics with Ozone Addition in a Diesel Micro-pilot Natural Gas Engine2024-32-01044/18/2025
Ozone (O3) was introduced into the intake air in a natural gas fueled engine ignited by micro-pilot of diesel fuel, to utilize the reactive O-radicals decomposed from the O3 for the promotion of the combustion and for improvements in the thermal efficiency and exhaust emissions. Experiments were carried out in a single cylinder engine to elucidate the effects of the ozone addition under the lean burn conditions. A supercharger was employed to increase the intake air amount and vary the equivalence ratio of natural gas. The experimental results showed that the O3 addition has a limited effect on the ignition of the diesel fuel injected near top dead center, while the heat release during the flame propagation in the natural gas/air mixture was increased at the lower equivalence ratio of natural gas. Further the ignition of natural gas was promoted, resulting in the increase of the combustion efficiency and the degree of constant volume heat release. The cooling loss and the NOx emissions decreased due to the leaner burn achieved by the supercharging. Overall, the indicated thermal efficiency and the exhaust emissions can be improved by the supercharging combined with the O3 addition.
Kobashi, Yoshimitsu, Miyata, Shoki, Kawahara, Nobuyuki, Inagaki, Ryuya
Studying the Lean Burn Operation in Two-Wheelers to Increase Fuel Efficiency and Investigate the Use of Lean NOx Trap Catalyst (LNT) for Lean Burn System2024-32-00584/18/2025
This study offers an overview of the impact of lean burn technology in two-wheeler vehicles, specifically concentrating on enhancing the fuel economy and addressing the challenges associated with its adoption. Lean burn systems, characterized by a fuel-air mixture with a higher air content than stoichiometric ratio. The study focuses on technology which meets stringent emission standards while enabling the optimization of fuel efficiency. The lean burn system employs strategies to optimize air-fuel ratio using electronic fuel injection, ignition timing control, and advanced engine control algorithms like - updated torque modulation control algorithm for drivability, lambda control algorithm for rich and lean switch and NOx modelling algorithm for LNT catalyst efficiency tracking. The challenges related to lean burn systems, includes issues related to combustion stability, nitrogen oxide (NOx) emissions, and their impact on drivability, is summarized in the study. Mitigation strategies, ranging from after-treatment systems to catalyst technologies, are discussed as means to address these challenges while preserving the benefits of lean burn operation. Furthermore, this study sheds light on the Lean NOx Trap (LNT) catalyst which is a critical component in modern emission control systems, particularly in the context of lean burn engines. Designed to reduce nitrogen oxides (NOx) emissions, the Lean NOx Trap catalyst operates efficiently in oxygen-rich environments, such as those found in lean burn systems. It captures and stores NOx during fuel-lean conditions and subsequently releases and converts them to harmless nitrogen and oxygen when the engine switches to a fuel-rich state. In conclusion, this study synthesizes the current knowledge on lean burn technology in two-wheelers, offering valuable insights for researchers, engineers, and industry stakeholders. By addressing technological advancements, challenges, and future directions, it aims to contribute to the ongoing efforts to enhance the efficiency and sustainability of two-wheeled transportation systems.
Somasundaram, Karthikeyan, Sivaji, Purushothaman, John Derin, C, Vishal, Karwa, Manoj Kumar, S, Maynal, Rajesh
Effect of Ignition Position on Lean Limit of Main Chamber Combustion in Pre-Chamber Ignition2024-32-00224/18/2025
An engine was built in this study that enabled the conditions in a pre-chamber and in the main combustion chamber to be visualized simultaneously for the purpose of elucidating the mechanism of pre-chamber combustion. An investigation was made of how the state of pre-chamber combustion, including the location of initial flame generation and its subsequent propagation, influenced pre-chamber jet combustion. The state of pre-chamber combustion was intentionally varied by changing the position of pre-chamber ignition. As a result, it was found that changing the position of pre-chamber ignition varied the location where the pre-chamber flame occurred, how the flame propagated and the timing and strength of the flame jet that was ejected into the main chamber. The results revealed that these differences in the state of pre-chamber combustion markedly changed the rate of combustion fluctuation, combustion period, lean-burn limit and other combustion characteristics depending on the ignition position. This indicates that the state of pre-chamber flame formation must be clarified and optimally controlled in order to optimize engine combustion by applying pre-chamber jet combustion.
Onuma, Takeru, Yamada, Hiroto, Ugajin, Taisei, Shinozaki, Kaito, Tahara, Ryota, Iijima, Akira
Investigation on the Applicability of Passive Type Pre-Chamber with One Port Fuel Injection System to Small Gasoline Engines2024-32-00334/18/2025
Pre-chamber combustion has been applied as a method of low fuel consumption in spark ignition engines, and in recent years the application of pre-chambers to gasoline engines has also been actively studied. In many gasoline engines, stoichiometric combustion is common. We decided that a passive type pre-chamber with only one port fuel injection is sufficient for stoichiometric combustion. The pre-chamber system relatively has two merits of lower cost and ease of installing than other prechamber systems. Therefore, we focused on investigating the effects of improving combustion speed and knock resistance in use of the passive type pre-chamber and the applicability of the pre-chamber system in various operating points. As the concrete approach, we evaluated the heat balance and the knock resistance with and without a pre-chamber in engine bench test. As a result, the knock resistance and the fuel consumption were improved. In addition, as a result of considering lean burn in the passive type pre-chamber in order to further improve fuel consumption in the future, the fuel consumption in use of the passive type pre-chamber was also improved compared to that in case of no pre-chamber. Furthermore, as a result of evaluating the combustion characteristics of the pre-chamber due to differences in operating points depending on the combination of engine revolution and engine load, it was found that while sufficient rapid combustion was obtained even at high engine revolution, combustion became unstable at extremely low load. Moreover, under high load, pre-ignition could occur in the pre-chamber over time. We analyzed these mechanisms and discussed countermeasures.
Nakao, Yoshinori, Sakurai, Yota, Hisano, Atsushi, Saitou, Masahito, Suzuki, Tomoharu
Effects of Injection Timing and Pressure on Combustion Performance and Emissions in Hydrogen Direct Injection Engine2025-01-84214/1/2025
As the demand for cleaner and more efficient propulsion systems increases, hydrogen internal combustion engines have emerged as a promising solution due to their high thermal efficiency and zero-carbon emissions potential. Achieving ultra-lean combustion conditions (lambda > 2.8) in hydrogen engines significantly improves thermal efficiency while maintaining combustion stability and reducing knock intensity. However, hydrogen injection timing and pressure are crucial factors influencing the combustion and emission characteristics of hydrogen engines. This study investigates the effects of hydrogen injection timing and pressure on the combustion performance and emission characteristics of a direct injection hydrogen engine under different load conditions. Experimental tests were conducted on a multi-cylinder engine equipped with a hydrogen direct injection system, focusing on part-load operation to explore the interplay between injection parameters and engine performance. Results show that retarding the start of injection (SOI) monotonically increased NOx emissions, while effective thermal efficiency peaked before declining. At a BMEP of 0.6 MPa, retarding the SOI from 240 deg CA BTDC to 180 deg CA BTDC improved thermal efficiency by approximately 1 percentage point. Additionally, increasing hydrogen injection pressure improved thermal efficiency. However, excessively high pressures reduced mixture homogeneity due to shorter injection durations, longer combustion periods, and increased knock propensity, leading to higher NOx emissions. The engine achieved high thermal efficiency at a hydrogen injection pressure of 5 MPa across the range of load conditions tested.
Du, Jiakun, Wu, Guangquan, Chen, Hong, Sun, Fanjia, Xie, Fangxi, Li, Yuhuai, Sun, Yao, Qi, Hongzhong, Li, Yong
Performance and Emissions Analysis of a Hydrogen-Powered Heavy-Duty High Compression Ratio SI Engine Across Various Loads and Speed at Ultra-Lean Condition2025-01-84284/1/2025
With the global shift towards sustainable and low-emission transportation, hydrogen-fueled engines stand out as a promising alternative to traditional fossil fuels, offering significant potential to reduce greenhouse gas emissions. This study provides a comprehensive evaluation of the performance and emissions characteristics of a hydrogen-powered heavy-duty compression ignition engine, which has been modified to operate as a Spark Ignition (SI) engine with a high compression ratio of 17:1. The evaluation was conducted across various speeds, loads, and spark timings under ultra-lean combustion conditions. The analysis utilized a modified 6-cylinder, 13-liter Volvo D13 diesel engine, configured to operate in single-cylinder mode with the addition of a spark plug for SI operation. The study examined key performance metrics, including brake thermal efficiency (BTE), power output, and specific fuel consumption, under the selected operating conditions. Emissions profiles for nitrogen oxides (NOx), carbon dioxide (CO2), and unburned hydrogen (uH₂) were also assessed to understand the environmental impact. The results demonstrated that hydrogen operation can significantly improve thermal efficiency while maintaining adequate power output across various operating conditions. Optimal performance and reduced NOx emissions were observed within specific lambda ranges, underscoring the potential of fine-tuning the air-fuel mixture to enhance both efficiency and emissions. Notably, NOx emissions were found to be negligible under most operating conditions. This study offers critical insights into the viability of hydrogen as a sustainable fuel for heavy-duty engines, paving the way for greener and more efficient transportation solutions. The findings highlight the importance of precise control over engine parameters to maximize the benefits of hydrogen combustion, thereby driving further advancements in hydrogen engine technology.
Dyuisenakhmetov, Aibolat, Panithasan, Mebin Samuel, Cenker, Emre, AlRamadan, Abdullah, Im, Hong, Turner, James
A Comparison of Stoichiometric and Lean Burn Ammonia-Hydrogen Co-Fuelling in a Modern Spark Ignition Engine2025-01-84324/1/2025
Ammonia (NH3) is emerging as a promising fuel for longer range decarbonised heavy transport, predominantly due to relative favourable characteristics as an effective hydrogen carrier. This is despite generally unfavourable combustion and toxicity attributes, restricting ammonia’s end use to applications where robust health and safety protocols can always be assured. In the currently reported work, a spark ignited thermodynamic single cylinder research engine was equipped with separate gaseous ammonia and hydrogen port injection fuelling, with the aim of understanding the impact of varied co-fuelling upon combustion, fuel economy and engine-out emissions (and the arising implications upon future emissions after-treatment). Under stoichiometric conditions, the engine could be operated in a stable manner on pure NH3 at low-to-medium speeds and medium-to-high engine loads, with up to ~20% hydrogen (by energy) required at the lowest engine loads. Engine-out NH3 emissions remained relatively high across the stoichiometric operating map (ranging between 7000-8000ppm), with engine out NOx remaining comparatively low (between 1000-2000ppm). An alternative lean burn operating strategy was then investigated, with the intent of balancing ammonia slip versus NOx to a degree facilitating minimised tailpipe emissions by future use of Selective Catalytic Reduction (SCR) emissions after-treatment technology, where the NH3 slip can be directly utilised as NOx reductant (i.e. eliminating the need for a urea storage and injection system found in conventional SCR systems). Ideally such SCR systems operate with a fixed “alpha ratio” equal to ~1 (where this ratio is the ratio of engine-out NH3 to NOx on a ppm basis, with a value of unity indicating the ideal amount of reductant to simultaneously consume NH3 slip and decompose NOx). This was achieved by conducting a series of parametric sweeps, varying the air-to-fuel ratio and hydrogen content in the fuel mix to evaluate the ideal combinations of hydrogen substitution ratio and relative air-to-fuel ratio (λ) to achieve an alpha ratio of 1. It was concluded that operating the engine with ~20% hydrogen and slightly lean (λ~1.2) would result in an ideal alpha ratio of ~1 across most of the operating map, with little variation in alpha ratio or lambda noted with changing engine load. The results indicate, apparently for the first time, the high promise of a lean burn spark ignition ammonia/hydrogen co-fuelling strategy for balancing engine-out NOx and NH3 emissions via SCR after-treatment. The supplementary hydrogen along with the lean operation was noted to also result in small improvements in indicated thermal efficiency of 1-2% compared to baseline stoichiometric operation with minimum hydrogen.
Ambalakatte, Ajith, Geng, Sikai, Murugan, Reese, Varaei, Amirata, Cairns, Alasdair, Harrington, Anthony, Hall, Jonathan, Bassett, Michael
Effect of Hydrogen Addition on Abnormal Combustion of Pre-Chamber Natural Gas Engine at High Load2025-01-84264/1/2025
In cogeneration system, the pre-chamber natural gas engine adopts combustion technologies such as ultra-high supercharged lean burn and Miller cycle to increase the theoretical efficiency by increasing the specific heat ratio and the mechanical efficiency by improving the specific power. In recent years, the use of hydrogen fuel has been attracting attention in order to achieve carbon neutrality, and it is required to operate existing high-efficiency natural gas engines by appropriately mixing hydrogen. For this purpose, it is important to have natural gas and hydrogen co-combustion technology that allows combustion at any mixture ratio without major modifications. The authors mixed hydrogen into the fuel of an ultra-high supercharged lean burn pre-chamber natural gas engine (Bore size: 200mm) that has already achieved high efficiency and performed combustion experiments at BMEP (Brake mean effective pressure) of 2 MPa or more. The engine load and hydrogen mixture ratio were used as operating parameters to search for the optimal air excess ratio and ignition timing. Abnormal combustion such as pre-ignition and thud occurs in the high load and high hydrogen mixture regions, but the occurrence regions may or may not overlap, and it was found that this limits the operable limit on the high load and high hydrogen mixture sides. We reported on the operating range in which each type of abnormal combustion occurs, the relationship between the frequency of occurrence and operating conditions, the fact that the pattern of abnormal combustion occurrence is not continuous, the relationship and continuity with the cycles before and after, and the fact that pre-ignition is less likely to occur when the pre-chamber excess air ratio is large. Furthermore, we investigated a method of separating the main chamber pressure oscillation caused by the ejection jet from pre-chamber combustion, known as ringing, from the pressure oscillation caused by knocking. We have set a threshold for the maximum amplitude of high-frequency components and separating knocking from ringing by the frequency of occurrence.
Morikawa, Koji, Kimura, Shin, Sakai, Shunya, Moriyoshi, Yasuo
Next Gen Automotive Heat Shield with Improved Thermo-Oxidative Properties2025-01-81524/1/2025
Alpha Engineered Composites’ thin profile textile composite heat shields provide thermal protection through several thermodynamic mechanisms including: radiation reflection; heat spreading; and finally heat transfer resistance. Typical under the hood automotive applications require heat shield average operational temperature up to 225°C, but newer internal combustion engines are being designed for higher operational temperatures to: increase efficiency through higher compression cycle ratios and lean burning; boost power through turbocharging; increase energy density; and support advanced emissions controls like EGR that can increase average operational temperature up to 300°C. Unfortunately, thermo-oxidative degradation mechanisms negatively impact the polymer structural adhesive within a heat shield textile composite and degrade thermal protection mechanisms. High average operational temperature degradation of traditional versus next generation textile composite heat shields is comparatively studied via radiant panel assessment, combined with both adhesion and thermogravimetric analysis focused on the structural adhesive integrity in the aggregate thin profile textile composite. Property changes, due to thermomechanical degradation, resulting in textile composite loss of integrity including layer delamination, physical polymer microcracking, and buckling of expected geometry and the subsequent negative impact on thermal protection clearly dictates the need to transition to a next generation of structural adhesive polymer chemistry. This transition is also necessary to ensure that under the hood engine compartment integrity is maintained as internal combustion engine technology takes operational advantage of higher operating temperature to reap greater efficiency, power/energy density, and environmental benefits.
Vazquez, Mark
Development of a 6.7L Direct Injection, Lean Burn H2 Spark Ignition Engine for Medium- and Heavy-Duty Commercial Vehicles2025-01-83934/1/2025
This work is part of a production-intent program at Cummins to develop a 6.7L direct injection (DI), lean burn H2 spark ignition (SI) engine for medium- and heavy-duty commercial vehicles that are intended to be compliant with global VII criteria pollutants emissions standards. The engine features a low-pressure DI fuel injection system, a tumble-based combustion system with a pent-roof combustion chamber, two-stage boosting system without EGR, and dual overhead cams (DOHC) with cam phasers. The paper focuses primarily on the performance system architecture development encompassing combustion system, air-handling system, and valve strategy. Comprehensive 3D-CFD guided design analysis has been conducted to define the tumble ports, injection spray pattern, and injection strategy to optimize charge homogeneity and turbulence kinetic energy (TKE). In addition, the boosting system architecture and the valve strategy have been thoroughly evaluated through 1-D system-level engine cycle analysis. Steady-state test results showed that the engine produces >40% BTE over a wide range of engine speed and load while achieving the targeted torque and power. The use of a well-matched, two-stage boosting system produces λ >2.0 across the full engine operating map, thereby leading to low engine-out NOx emissions when combined with the tailor-designed combustion system. Moreover, the engine system demonstrated robust performance over WHTC test cycle.
Liu, Lei, Zhang, Yu, Qin, Xiao, Hui, He, Min, Xu, Leggott, Paul
Designing Next-Generation Piston Geometry for LPG Powered Spark Ignition Engines: An Integrated CFD and Experimental Approach2025-28-01232/7/2025
The efficiency of combustion has a major impact on the performance and emission characteristics of a spark-ignited LPG (Liquified Petroleum Gas) engine. The shape of the combustion chamber determines the homogeneous charge intake velocity, which is crucial for the turbulent motion that encourages flame propagation and quickens combustion. It need the right amount of compression ratio, charge squish velocity and turbulent kinetic energy to sustain combustion and propel laminar flames. There are a number of names for the motion of the charge within the cylinder: swirl, squish, tumble and turbulence. All of these terms affect how air and fuel are mixed and burned. Piston shape affects in-cylinder motion, which in turn reduces fuel consumption and improves combustion characteristics. The shape of the piston quench zone has a substantial impact on the charge velocity inside the combustion chamber. The impact on charge motion was analyzed using computer modeling using STAR-CD on pentroof central bowl quenched pistons with different quench areas (10, 20, 30, and 40%). The results were validated by conducting experiments on pistons that had a compression ratio of 10:1 and a greater quench area than is currently utilized in the industry. Results showed that performance, combustion characteristics, and emissions could all be enhanced in a lean-burn SI engine running on LPG with a 30% increase in piston quench area.
Sagaya Raj, Gnana, R L, Krupakaran, Pasupuleti, Thejasree, Natarajan, Manikandan
Experimental Investigation of Hydrogen or Methane Injection in Active Pre-Chamber on a Lean Combustion Gasoline Engine2025-01-71061/31/2025
With the global promotion of carbon neutrality policies, internal combustion engine (ICE) of traditional fossil fuel is gradually transitioning to carbon neutral fuel ICE, and hybrid dedicated engines are gradually replacing traditional internal combustion engines in the passenger car market. Ultra-lean combustion supported by active pre-chamber is one of the key technologies for achieving high thermal efficient over 45% BTE. However, there are still issues like cold start and PN emissions caused by impingement of liquid fuel injection in pre-chamber, and there is still room for improvement in thermal efficiency by less energy of pilot ignition fuel. Gaseous fuel such as hydrogen or methane have no wetting issues, and can be more easily controlled in terms of the injection amount in pre-chamber, thereby using a less amount of gaseous fuel as the pilot ignition fuel could be a solution. Due to the above situation, this article conducted experiments on a lean burn gasoline engine by injecting hydrogen or methane instead of gasoline into the pre-chamber to ignite the gasoline in the main chamber, and investigate its performance, combustion and emissions. The results show that, there is a best value for both the equivalent calorific value substitution ratio of hydrogen or methane injection in pre-chamber and global lambda, which results in lowest fuel consumption. Due to the fact that hydrogen has a higher activity and none carbon molecule while methane has a lower activity and property of easily generating soot precursors through C1 radicals, the performance of hydrogen and methane injection in the pre-chamber is significantly different: Compared to gasoline injection in pre-chamber, hydrogen injection in pre-chamber can reduce ISFC and significantly decrease PN. Methane injection in pre-chamber increases ISFC and PN, the more retarded the SOI is, the higher the PN results. Hydrogen injection in pre-chamber can breaking through the limitation of ignition angle being too forward of traditional pre-chamber in cold start. This article provides data and solutions for the transition from fossil fuels to carbon neutral fuel step by step.
Liu, Yaodong, Liu, Mingli, He, Zhentao, Li, Xian, Zhao, Chuan, Qian, Dingchao, Qu, Hanshi, Li, Jincheng
The Influence of Excess Air Ratio on NOx Emissions of Turbocharged Direct Injection Hydrogen Internal Combustion Engines2025-01-70941/31/2025
Direct injection in the cylinder of a hydrogen internal combustion engine results in increasing NOx emissions in high-temperature oxygen rich environments. To explore the effect of excess air ratio λ on the NOx emissions of a direct injection hydrogen fueled internal combustion engine (HICE), a CFD simulation model was built based on a turbocharged direct injection hydrogen internal combustion engine using Converge software, and investigates the impact of lean burn on the NOx emissions. The simulation results show that increasing the excess air ratio λ can lower the in-cylinder mean temperature and effectively reduce the generation of NOx. The maximum temperature difference between λ=2.1 and λ=2.7 is 400K when engine speed is 4500 r/min. As the engine speed increases, under the same condition of λ, different loads at different speeds result in differences in the reaction temperature inside the cylinder, with higher temperatures at high speeds, so both the cylinder temperature and NOx emissions increase. The maximum cylinder pressure and mean cylinder temperature also increase when engine speed increase.
Peng, Tianyu, Luo, Qinghe, Tang, Hongyang
Enhanced High-Temperature Performance of NH 3 -SCR Catalysts for Lean-Burn Engines2025-01-70431/31/2025
NOx after-treatment has greatly limited the development of lean-burn technology for gasoline engines. NH3-Selective Catalytic Reduction (SCR) technology has been successfully applied to NOx conversion in diesel engines. For gasoline engines, SCR catalyst is required to maintain high activity over a higher temperature window. In this study, we utilized a turbocharged and intercooled 2.0 L petrol engine to investigate the NOx conversion of two zeolite-based SCR catalysts, Cu-SSZ-13 and Fe/Cu-SSZ-13, at exhaust flows ranging from 80 to 300 kg/h and exhaust temperatures between 550 to 600°C. The catalysts were characterized using SEM, ICP, XRD, H2-TPR, NH3-TPD, and other methods. The selected Fe/Cu-SSZ-13 catalyst showed higher NOx conversion (>80%) in the temperature range of 550~600oC and 80~300 kg/h exhaust gas flow. NOx output could be controlled below 10ppm. The characterization results showed that although the specific surface area and acidic sites decreased after the aging treatment for Fe/Cu-SSZ-13, they still retained active sites, showing higher activity and stability.
Pan, Shiyi, Wang, Ruwen, Zhang, Nan, Xu, Zhiqin, Hu, Jiangtao, Liao, Xiuke, Duan, Pingping, Chen, Ruilian
Jet-Induced Compression Ignition (JICI)—Application of Spark-Assisted Compression Ignition (SACI) in a Combustion System with Active Pre-Chamber03-18-01-00091/17/2025
The application of short burn durations at lean engine operation has the potential to increase the efficiency of spark-ignition engines. To achieve short burn durations, spark-assisted compression ignition (SACI) as well as active pre-chamber (PC) combustion systems are suitable technologies. Since a combination of these two combustion concepts has the potential to achieve shorter burn durations than the application of only one of these concepts, the concept of jet-induced compression ignition (JICI) was investigated in this study. With the JICI, the fuel is ignited in the PC, and the combustion products igniting the charge in the main combustion chamber (MC) triggered the autoignition of the MC charge. A conventional gasoline fuel (RON 95 E10) and a Porsche synthetic fuel (POSYN) were investigated to assess the fuel influence on the JICI. Variations of the relative air/fuel ratio in the exhaust gas (λex) were performed to evaluate both the occurrence of the JICI and the dilution capability. To assess the sensitivity of the JICI, variations of the engine speed and the engine load were performed. When using RON 95 E10, a shift from a conventional PC combustion to the JICI was observed between λex = 2.3 and λex = 2.5. The variations of the engine speed and the engine load revealed an increased JICI intensity when the engine speed decreased and when the engine load increased. When using POSYN, no JICI was observed. The occurrence of the JICI was correlated to the knock resistances of the fuels, i.e., the lower knock resistance of RON 95 E10 yielded the JICI, whereas the higher one of POSYN did not. At λex = 2.8, applying POSYN resulted in an increase of the burn duration of 5.5°CA, which was a relative increase of 41%, compared to the use of RON 95 E10 due to the absence of the JICI in case of POSYN. However, the application of POSYN resulted in the highest net indicated efficiency (ηi,net). In particular, the application of RON 95 E10 yielded a maximum of ηi,net = 41.5% at λex = 2.6, whereas using POSYN resulted in a maximum of ηi,net = 42.6% at λex = 2.2 due to the higher knock resistance of POSYN.
Burkardt, Patrick, Günther, Marco, Villforth, Jonas, Pischinger, Stefan
Optimization of a Virtual H2 Engine Using a 1D Simulation Tool Targeting High Engine Performance along with Near-Zero Emission Levels2024-24-00159/18/2024
Hydrogen engines are currently considered as a viable solution to preserve the internal combustion engine (ICE) as a power unit for vehicle propulsion. In particular, lean-burn gasoline Spark-Ignition (SI) engines have been a major subject of investigation, due to their reduced emission levels and high thermodynamic efficiency. Lean charge is suitable for passenger car applications, where the demand of mid/low power output does not require an excessive amount of air to be delivered by the turbocharging unit, but can difficulty be tailored in the field of high-performance engine, where the air mass delivered would require oversized turbocharging systems or more complex charging solutions. For this reason, the range of feeding conditions near the stochiometric is explored in the field of high-performance engines (20 BMEP), leading to the consequent issue of abatement of pollutant emissions. In this work, a 1D model is applied to the modeling of a four cylinder engine fueled with direct injection (DI) of hydrogen. The lambda condition has been chosen as the best compromise between performance and emission levels, tailoring the same power output of an equivalent SI gasoline engine. The main limitation experienced is the coupling with the turbocharging unit, which must guarantee the necessary boost pressure and air mass flow at all operating conditions. Low engine revolution speeds at full load have been experienced to be the most critical operating points. This work proposes an optimization of the engine layout, exploring the adoption of electrically assisted turbochargers as well as of a two-stage compression units, to reach the desired engine power output. A demanding driving cycle (the RTS-95) has been tested for all the engine configurations, where the low end revolution speed at full load is frequently reached. The different engine configurations are investigated in terms of performance, of energy required by the electrified units (which is around 600 Wh) as well as in terms of performance of the after-treatment system. Compared to a non-electrified configuration, the analysis shows that, where the lack of boost pressure is balanced by a reduction of the lambda, the usage of an electrified boosting system allows the achievement of both engine performance and reduction of pollutant emissions of around 11 mgNOx/km.
Marinoni, Andrea, Montenegro, Gianluca, Cerri, Tarcisio, Della Torre, Augusto, Onorati, Angelo
Dual Injection Concept and Lean Burn Characteristics with Methanol on a SI-Engine2024-24-00309/18/2024
The research for sustainable alternative fuels for combustion engines was driven by the urgency to meet future emission regulation norms and mitigate climate change and dependency on fossil fuels. In this context, methanol emerges as a promising candidate due to its potential for greenhouse gas-neutral production methods and its advantageous characteristics for employment in SI engines. Adverse effects, such as elevated emissions due to incomplete combustion along with liner impingement and oil dilution as a consequence of the high injected fuel mass and the large enthalpy of vaporization, can be improved by a dual injection concept. The tests were conducted on a single-cylinder research engine derived from a common passenger vehicle engine. The exhaust gas composition was measured with an FTIR-analyzer employing a methanol-specific evaluation method, standard exhaust gas analyzers, and a solid particle counter system with 10 and 23 μm cut-off sizes. The ratio of DI mass to total mass injected in one cycle (xDI) was varied at low-, mid-, and high-load operation points at 2000 rpm and stoichiometric conditions. Further investigations for lean-burn concepts with a variation of xDI were carried out and evaluated based on variables such as engine performance, efficiency, and emissions. The measurements show a strong charge cooling effect for DI, thereby reducing NOx, although this effect saturates at a mid-load. By splitting the injected fuel mass, an xDI of 30 % shows the highest reduction in NOx at high-load and a reduction of unburned fuel in the exhaust gas of up to 62 %. Particle measurements indicate the interaction of methanol with the liner for both PFI and DI, leading to increased particle emissions. For high-load and dual injection with xDI = 30 % and 50 %, these emissions are found on a level one magnitude lower than compared to DI operation. Lean burn operation with dual injection shows the extension of the lean burn limit at certain points. However, the potential efficiency increase is diminished by undesirable combustion characteristics with prolonged burn durations.
Fitz, Patrick, Fellner, Felix, Rößlhuemer, Raphael, Härtl, Martin, Jaensch, Malte
TOC99-06-03-0TOC6/21/2024
TOC
Tobolski, Sue
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