Browse Topic: Gas engines

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Experimental and Kinetic Modeling Study of Aged Natural Gas Three-Way Catalyst Performance2026-01-03734/7/2026
The applicability of three-way catalyst (TWC) models for system-level aftertreatment simulations under transient operating conditions of natural gas engines depend on accurate integration of reaction kinetics as a function of the air-fuel equivalence ratio lambda(λ). A comprehensive global kinetic model has been developed for an aged commercial three-way catalyst (TWC), incorporating key reaction pathways including oxidation of CO, CH₄, C₂H₆, and H₂; reforming of CH₄ and C₂H₆; the water-gas shift reaction; and NO reduction via CO and H₂. The model also accounts for oxygen storage capacity (OSC) and its dynamic interaction with CO and H₂. To calibrate kinetic parameters, systematic bench-scale flow reactor experiments were conducted under lean, stoichiometric, and rich conditions. Performance metrics focused on CH₄ and C₂H₆ oxidation and reforming across varying O₂ and CO concentrations, and NO reduction with CO and H₂ under different oxygen levels. Experimental results revealed that CO suppresses the reforming of CH₄ and C₂H₆. NO conversion was observed between 150°C and 600°C, with H₂-driven reduction producing NH₃, N₂, and N₂O depending on lambda (λ). Under rich conditions, complete NO conversion occurred from 150°C, while lean conditions showed reduced NO conversion at elevated temperatures due to H₂ oxidation. NO reduction with CO initiated at 250°C, achieving full conversion under rich conditions. The model accurately captures the influence of λ on NO reduction with both H₂ and CO, predicts NH₃ formation under rich conditions, and simulates H₂ generation via the water-gas shift reaction above 400°C. It successfully reproduces λ sweep data (λ = 0.95–1.02) and demonstrates CO inhibition effects on H₂ oxidation and NO reduction. This global model is validated with dithering reactor data and qualitatively captures key trends in data which aids in catalyst sizing, calibration robustness and the system level modeling of end of useful life parts. Further validation of the current developed model with lean-rich cycle tests confirms the model’s ability to predict NOx slip at the onset of rich cycles impacting the ability to accurately predict NOx emissions during engine braking events in system level models.
Raj, Richa, Kim, Mi-Young, Aigbiremolen, Grace, Srinivasan, Anand
Impact of Hydrogen on Methane and Pollutant Emissions over Three-Way Catalysts with Natural Gas–Hydrogen Blends2026-01-03574/7/2026
Blending natural gas (NG) with hydrogen (H₂) can improve combustion and engine performance while potentially facilitating the catalytic conversion of methane and other pollutants, resulting in cleaner tailpipe emissions. This study evaluates the impact of H2 on the conversion of methane, CO, and NOx emissions on a commercial three-way catalyst (TWC) in a flow reactor using synthetic gas mixtures that simulate stoichiometric engine exhausts with NG or NG+H₂ combustion. The work examines whether, and how, the additional amount of H₂ in the exhaust stream affects the conversion efficiency of methane and other pollutants. Experiments were conducted with both degreened and aged catalysts under controlled conditions, systematically varying temperature, the air-to-fuel equivalence ratio (λ), and λ modulation. Test conditions covered λ values from 0.996 to 1.000 to represent nominally stoichiometric engine operation with different λ modulation amplitudes, as well as a range of temperatures to inform control strategies for effective CH₄, CO, and NOₓ reduction. Overall, the results show that hydrogen addition significantly improves the conversion efficiency of CH₄ and NOₓ, particularly at temperatures below 500 °C. More significantly, this study highlights that exhaust gas composition, operating temperature, λ management, and the oxygen storage capacity of the TWC all play major roles in affecting the tailpipe emissions from NG and NG+H₂ combustion.
Prikhodko, Vitaly, Wang, Min, Park, Yeonshil, Chen, Hai-Ying, Pihl, Josh
Experimental Evaluation of After-Treatment Solutions for Heavy-Duty Natural Gas Vehicles to Meet Future CNVII Regulations2026-01-03764/7/2026
The heavy-duty truck market in China has seen a significant increase in the adoption of natural gas-powered engines over the past two years. Simultaneously, the anticipated release of the China VII emissions regulation proposal by the end of 2025 is expected to impose stricter emissions limits on all heavy-duty engines, including new particulate number (PN10) thresholds analogous to those in the Euro 7 regulation. While tailpipe oxides of nitrogen (NOx) and methane (CH4) emissions from natural gas engines can be mitigated through tighter lambda control and adjustments to catalyst volume and precious metal (PGM) loading, addressing NOx and particulate number (PN) emissions necessitate more advanced after-treatment solutions. Although natural gas combustion is virtually soot-free, the entrainment of lubricating oil into the combustion chamber, especially during cold-start conditions, poses a challenge, leading to potential exceedance of the proposed future China VII limits. Additionally, PN emissions from natural gas vehicles are highly dependent on duty-cycles and the state of the actual engine, with applications involving frequent stop/go operation experiencing increased piston ring wear, and thus, higher oil consumption, and elevated PN emissions. This study aimed to evaluate the performance of different after-treatment solutions for natural gas engines in meeting future China VII emissions standards, with a particular focus on the efficacy of particle filters for controlling PN10 emissions. Three different after-treatment configurations, comprising close-coupled and underfloor three-way catalysts, as well as bare and coated filters, were tested on a 15L China VI commercial natural gas engine in a controlled laboratory environment. Emissions and PN10 data were collected over regulatory cold and hot World Harmonized Transient Cycle (WHTC) test cycles, and analyzed for light-off behavior, conversion efficiencies, system pressure drop, and filtration effectiveness for particles as small as 10nm. The relative advantages and challenges of each configuration are discussed. The results indicate that natural gas engines will likely require the integration of particle filter devices to comply with future China VII PN10 limits. The results also show that NOx compliance is challenging and fine-tuning of the lambda calibration is essential for CNVII.
Gao, Jiahui, Besch, Marc, Ding, Ning, He, Suhao, Zhao, Yuxin, Yixiao, Li, Shen, Ye
Experimental Characterisation of Combustion, Performance, and Emissions in a Hydrogen Fueled Opposed Piston Engine2026-01-03354/7/2026
Recent studies have demonstrated that the current Internal Combustion Engine (ICE) can be adapted to operate with hydrogen for the decarbonisation of transport and gensets. This is mostly done by conversion of conventional 4-stroke compression ignition diesel engines or spark ignition gas engines for heavy-duty vehicles or 4-stroke spark ignition gasoline engines for light-duty applications. This study aims to assess the adoption of pure hydrogen direct injection technology on a novel two-stroke opposed-piston engine designed by Carnot Engine Ltd. The engine provides a flexible platform that can operate in both compression ignition and spark ignition modes, allowing it to adopt multiple fuels. For the first time, a single cylinder prototype version of this new engine was operated and tested with hydrogen at Brunel University of London. During the engine experiment, a spark ignition timing sweep was carried out at low and mid-loads up to 10 bar IMEP to identify the Minimum ignition advance for Best Torque (MBT). Then, a complete mapping of the fuel injection strategies and lambda matrix was performed to optimise engine efficiency and combustion stability at low loads. The outcome of this study demonstrates an impressive indicated thermal efficiency of 58.7% at a load of 5 bar indicated mean effective pressure (IMEP) when the engine was operated with an ultra-lean mixture of lambda 3.2. Additionally, the engine-out NOx emissions decreased from the maximum 1863 ppm at lambda 1.38 to less than 20 ppm at lambda 3.2. Furthermore, the steady-state engine-out emissions show near-zero carbon emissions at all operating conditions.
Mohamed, Mohamed, Roeinfard, Nima, Wang, Xinyan, Zhao, Hua, Watts-Farmer, Archie, Rahman, Nadiur, Lempp, Francis
Total Cost of Ownership Reduction Using Passive Pre-Chamber Ignition in Natural Gas Engines2026-01-03094/7/2026
Spark plug durability is a factor affecting the total cost of ownership (TCO) of spark-ignited natural gas engines, with some heavy-duty platforms requiring plug replacement after only 750 hours of operation. The high ignition energy demand under lean or diluted conditions accelerates electrode wear, shortening plug life and increasing maintenance frequency. This work evaluates passive pre-chamber (PC) ignition operating at lowered spark energies as a strategy to reduce spark energy requirements and extend plug durability, thereby lowering TCO. Experiments were conducted on a medium-duty Cummins 6.7L ISB engine at 1600 RPM and 50% load under varying exhaust gas recirculation (EGR) dilution levels (0–40%). Two passive pre-chambers with 1.1 mm and 1.6 mm nozzle diameters were compared with conventional spark ignition (SI). SI was operated with a fixed coil dwell of 4 ms (~90 mJ), while the PC configuration was tested across 2–4 ms dwell times (~30–90 mJ). Cylinder pressure analysis revealed that PC ignition sustained stable combustion at significantly lower spark energies than SI, with improved combustion stability at ~30 mJ compared with SI at ~90 mJ. The PC system also extended the dilution tolerance beyond that achievable with SI, while delivering up to ~2% higher indicated thermal efficiency and reducing the COV by nearly 90% at 30% EGR. A TCO analysis was conducted to assess the economic benefit of adopting a passive PC system operating at reduced spark energies compared to SI. It was found that adopting a passive PC system could reduce TCO by approximately $11,000 per engine over a five-year operational period, primarily due to fuel savings, extended spark plug life, and reduced maintenance frequency. These projections were weighed against the additional hardware cost of the pre-chamber, yielding a rapid estimated return on investment of ~300 operating hours. Therefore, this work motivates continued research and development of passive PC technology and its commercial adoption in natural gas engines used in transportation applications.
Dhotre, Akash, Voris, Alex, Okey, Nathan, Kane, Seamus, Rajasegar, Rajavasanth, Northrop, William
Influence of Lubrication Oil on Hydrogen Fuel-Share Combustion in a Conventional Medium-Speed Marine Diesel Engine2026-01-50142/23/2026
Carbon-free fuels present a potential solution for achieving climate-neutral operation of marine engines. However, their availability is minimal at the moment, though a steady increase can be expected in the coming years. During this transition phase, engine concepts that offer conventional diesel operation and a partial blending of alternative fuels to substitute diesel become interesting. This can be achieved, for example, by blending hydrogen in the intake air of a diesel engine, known as hydrogen fuel-share. Due to the high reactivity of hydrogen, its use in engines is limited by abnormal combustion phenomena (e.g., pre-ignition, knocking combustion), which current research on pure gas engines has shown to be strongly promoted by lube oil reactivity. Building on these fundamental investigations, this paper examines the influence of lubricating oil on the combustion characteristics of a H2 fuel-share medium-speed diesel engine and quantifies the potential to increase the hydrogen share using a less reactive engine oil. For this purpose, single-cylinder engine tests were conducted and supported by 0D/1D simulations with GT-Power and Cantera. The engine was configured as a conventional medium-speed marine diesel, equipped with a hydrogen port fuel injection (PFI) system on the cylinder head. A thermally stable ester-based gas engine oil was used for reducing reactivity compared to a state-of-the-art mineral diesel engine oil. The results show reduced auto-ignition tendency during compression and a mitigation of backfire. An increase in average effective CO2 reduction of up to 17 percentage points is demonstrated, resulting in a total CO2 reduction of 39% on a standard load profile for main propulsion engines. These findings highlight that the choice of lubricating oil can play a key role in increasing the hydrogen share in H2 fuel-share diesel engines, thereby supporting the transition toward climate-neutral propulsion concepts.
Achenbach, Tobias, Meinert, Robert, Mahler, Kay, Kunkel, Christian, Rösler, Sebastian, Prager, Maximilian, Jaensch, Malte
Development of an Oxy-Hydrogen Engine for Power Generation Application Using Simulation and Experiment2026-26-02601/16/2026
Hydrogen is a zero-carbon fuel suitable for the de-carbonization of power generation and the industrial sector. Green hydrogen produced via the electrolysis of water is the most sustainable fuel to achieve a net-zero carbon economy. Oxy-hydrogen (hydrogen and oxygen) generated onsite from the electrolyzer can be fed to engine with the intake air to enhance power and combustion efficiency with near-zero exhaust emissions. In this study, a 15 kVA two-cylinder natural gas spark-ignition generator set was used. The engine was retrofitted to operate on an oxy-hydrogen-air mixture. A maximum of 43% of rated engine load was achieved during the preliminary experiments. GT-Power software was used to calibrate the 1D model using experiment data and generate the burn profile of oxy-hydrogen-air mixture. The calibrated and validated 1D model was used for further predictive simulations. The power limiting factors were identified via simulations for flow and power improvement. The simulations revealed that boosting the intake air through supercharging is necessary to achieve the power targets and lean engine operation (for lower NOx emissions). A suitable supercharger was selected based on the maximum airflow requirement and was modeled for further analysis. The maximum operating limits of air-fuel ratio and oxygen volume percentage in air for predictive simulations were fixed at 80 and 40%, respectively. The airflow management and power achievement becomes critical at high-altitude conditions due to lower ambient pressure and density. The results revealed that the selected supercharger is suitable for high-altitude conditions as well. However, NOx emissions increased drastically at high-altitude conditions due to higher oxygen concentration, in-cylinder temperature, and heat flux. Selective catalytic reduction (SCR) is necessary for oxy-hydrogen engines at high-altitude conditions. This study would be helpful in the development of oxy-hydrogen engines, aiding in the transition towards a zero-carbon economy.
Marwaha, Akshey, Tule, Shubham, Mishrikotkar, Prasad, Aghav, Yogesh
Development of High BMEP Natural Gas Engine with Knock Mitigation2026-26-01211/16/2026
The stringent emission norms over the past few years have driven the need to use low-carbon fuels and after treatment technology. Natural gas is a suitable alternative to diesel heavy-duty engines for power generation and transportation sectors. Stoichiometric combustion offers the advantages of complete combustion and low carbon dioxide emissions. Turbocharging and cooled exhaust gas recirculation (EGR) technology enhances the power density along with reduced exhaust emissions. However, there are several constraints in the operation of natural gas spark ignition engine such as exhaust gas temperature limit of 780 °C, sufficient before turbine pressure for EGR drivability, boost pressure, peak cylinder pressure limit and knocking. These limits coulld restrict the engine BMEP (brake mean effective pressure). In the present study, tests were conducted on a V12, 24 liters, heavy duty natural gas fuelled spark ignition engine (600 HP) with different EGR and turbocharger configurations to achieve 16 bar BMEP without abnormal combustion. Considering the maximum exhaust temperature limit of 780 °C of exhaust system, minimal engine hardware changes were done to ensure less complexity, cost-effective engine development with robust design. The turbine trim was decreased from 89% to 84% to avoid excessive high before turbine backpressure, backflow of residual gases into cylinder and knock possibility. EGR system optimization with mixer enhanced EGR mixing and distribution in all cylinders that improved BSFC by 3%. During knock calibration, the offset to base ignition timing was used for individual cylinders to mitigate knock. Endurance trial of 100 hours was carried out to validate the reliability of engine design and calibration, and no issues were detected. The developed engine is the highest BMEP V12 engine in its segment in India using stoichiometric combustion with cooled EGR and three-way catalyst. The engine is certified with latest Indian CPCB IV+ emissions norms.
Khaladkar, Omkar, Marwaha, Akshey
For CNG and FFV Fuel Application Exhaust Valve Redesign and Robustness Improvement to Combat Abnormal Valve Guide and Seat Wear2026-26-01251/16/2026
Today, passenger car makers around the world are striving to meet the increasing demand for fuel economy, high performance, and silent engines. Corporate Average Fuel Economy (CAFE) regulations implemented in India to improve the fuel efficiency of a manufacturer's fleet of vehicles. CAFE goal is to reduce fuel consumption and, by extension, the emissions that contribute to climate change. CNG (Compressed Natural Gas) engines offer several advantages that help manufacturers meet and exceed these standards. The demand for CNG vehicles has surged exponentially in recent years, CNG engine better Fuel efficiency and advantage in CAFÉ norms make good case for OEM & Customer to use more CNG vehicle. CNG is dry fuel compared to gasoline. These dry fuels lack lubricating properties, unlike conventional fuels like petrol, diesel and biofuels, which are wet and liquid. Consequently, the operations and failures associated with these fuels differ. The materials and designs of engine parts, such as fuel lines, ECU, exhaust valves, and cylinder heads, vary depending on the fuel used. In CNG engine most challenging issue is leakage at Valve seat and Valve face interface causing unstable combustion and power drop. This study discusses the countermeasures adopted to address the high valve face, Valve guide and valve seat wear in cylinder heads and engine valves. The investigation focuses on material, design, and manufacturing process improvements specially for Exhaust valve, supported by part-level and vehicle-level validation and testing for CNG exhaust valves and cylinder heads.
Poonia, Sanjay, Kumar, Chandan, Sharma, Shailender, Khan, Prasenjit, Bhat, Anoop, P, Prasath, Neb, Ashish
Optimization of Negative Crankcase Pressure Mechanism to Minimize Oil Pumping into Combustion Chamber and Ensure Particulate Number Compliance in Euro VI Emission for Natural Aspirated Gas Engine2026-26-02231/16/2026
Emissions regulations, such as Euro VI, drives the Automotive industry to innovate continuously in Engine development. One significant challenge is the engine oil pumping from the crankcase into the combustion chamber, where it participates in combustion, which contributes to increased Particulate Numbers and fails to meet Euro VI emission compliance. This issue is most noticeable during engine idling and motoring conditions. During this time, a higher negative pressure difference develops between the intake manifold, which is acting above the combustion chamber and the engine crankcase. This pressure difference drives oil-laden blow-by aerosols past piston rings during the intake stroke and through the valve stem seals, allowing oil into the combustion chamber. The impact of the pressure difference between the intake manifold and crankcase was studied by varying the crankcase pressure through crankcase ventilation system. The results confirm that oil entry into the combustion chamber, contributing to combustion, occurs primarily through the piston rings, contributing to increase in Particulate Number (PN). To address this issue, it becomes necessary to introduce a mechanism that optimizes negative crankcase pressure across varying engine operating conditions. By reducing the pressure difference between the intake manifold and crankcase, this mechanism prevents oil entering the combustion chamber, thereby minimizing Particulate Number emissions and ensuring Euro VI compliance. This study focuses on the development and implementation of a negative crankcase pressure control system via the crankcase ventilation system. Through targeted optimization, it provides an effective way to control oil pumping into the combustion chamber, thereby enhancing emission control and advancing the development of cleaner Naturally Aspirated Gas engines.
R, Mahesh Bharathi, Bondfale, Shubham, Jeyaprakasan, Dharoon Gautham
Combustion Chamber Geometry Comparison in Natural Gas Engines under Conventional and Dethrottled Operation2025-36-021712/18/2025
Growing interest in cleaner energy has spurred progress in engine technology, focusing on greater efficiency and lower emissions. Methane-based fuels, like compressed natural gas (CNG), have become an alternative for spark-ignition engines, especially in Brazil. Among performance strategies, dethrottled operation stands out by reducing intake restrictions and minimizing pumping losses, a major inefficiency in conventional spark ignition engines. This improves thermal efficiency and reduces both fuel consumption and emissions. This study experimentally examines the performance and combustion of a CNG-powered Hyundai HR 2.5 16V engine, converted from diesel to spark ignition with natural gas, comparing factory (omega) and custom (reentrant) piston geometries under both conventional and dethrottled modes. The research evaluates how piston design affects combustion stability, efficiency, and emissions across different load strategies. Tests were conducted at 7, 8, and 9 bar loads, as well as full load, with engine speed at 1800 rpm. In conventional mode, load was controlled by the throttle at stoichiometric conditions (λ = 1); in dethrottled mode, the throttle was fully open, and load was controlled by mixture enleanment (λ > 1). The reentrant piston was designed to intensify turbulence at ignition, supporting faster flame propagation and combustion stability for methane fuels, especially under lean conditions. Results showed that the custom piston consistently delivered lower COVimep, shorter combustion durations, and higher thermal efficiency compared to the factory geometry. Dethrottled operation significantly reduced specific fuel consumption at low loads and improved indicated efficiency, despite increased THC. These effects were mitigated in part by improved combustion quality from the custom piston. Overall, the combination of dethrottling and optimized piston design offers a promising approach to improving the performance of natural gas engines operating under partial-load conditions.
Silva, Cristian Douglas Rosa da, Garlet, Roberto Antonio, Dapper, Jackson Mayer, Fagundez, Jean Lucca Souza, Lanzanova, Thompson Diórdinis Metzka, Martins, Mario Eduardo Santos
Multi-Objective Optimization of Oxyfuel Gas Engine Using Stochastic Engine Model and Detailed Chemistry2025-01-052911/25/2025
The energy transition initiatives in Germany’s renown coal mining region Lusatia have driven research into Power-to-X-to-Power technologies, where synthetic fuel is produced from renewably sourced hydrogen and captured CO2, and converted to electricity and heat through oxyfuel combustion. This work investigates the multi-objective optimization of oxyfuel gas engine using a stochastic engine model and detailed chemistry. Exhaust gas recirculation (EGR) rate, initial cylinder temperature and pressure, spark timing, piston bowl radius and depth are selected as design parameters to minimize the exhaust temperature at exhaust valve opening and indicated specific fuel consumption (ISFC) corresponding to oxyfuel operation with different dry and wet EGR rates. The optimization problem is solved for a dry EGR and four wet EGR cases with various CO2/H2O fractions, aiming to achieve comparable performance as in conventional natural gas / air operation, and energy-efficient carbon capture. The case with the lowest humidity (T10deg) had the lowest temperature of 1537 K, while the one with the highest vapor fraction (T70deg) attained the minimum 260 g/kWh ISFC. The superiority of the T10deg case is offset by much higher cooling demand (3.06 kW) for CO2 separation than that for T70deg case (0.81 kW). The constraint for combustion efficiency (>65%) limited the solution space towards high ISFC values, while the constraint for low indicated mean effective pressure (IMEP) (>7 bar) and the constraint for high IMEP (<8 bar) limited the solution space in between the two distinct clusters of feasible designs, and towards high exhaust temperature, respectively. The optimized designs from all the cases could outperform the reference case in terms of IMEP, nevertheless they fell below 31% indicated efficiency, which is associated with stoichiometric combustion.
Asgarzade, Rufat, Franken, Tim, Mauss, Fabian
Performance Analysis of a Hydrogen-blended Naturally Aspirated Gas Engine with a Dedicated Exhaust Gas Recirculation System2025-32-004611/3/2025
With the publication of the Renewable Energy Directive (RED) III in 2022, the European Union increased its renewable energy consumption target to 42.5% by 2030. Consequently, gaseous fuels derived from renewable electricity, particularly green hydrogen, are expected to play a pivotal role in the decarbonization of the energy sector. One promising application of green hydrogen is its integration into combined heat and power (CHP) plants, where it can replace natural gas to reduce CO2 emissions. Pure hydrogen as fuel or blended with natural gas has demonstrated potential for lowering both pollutant emissions and fuel consumption while maintaining or even enhancing engine performance. But it is expected, that the amount of available green hydrogen will be limited in the beginning. So new engine systems with hydrogen and natural gas for CHP plants are required, that offer more CO2-benefit and NOx reductioon than from fuel substitution only. In the LeanStoicH2 project, a novel approach was developed to optimize the operation of a four-cylinder stationary gas engine for hydrogen utilization. The project introduced a customized exhaust gas recirculation (EGR) system in which the exhaust gas from a hydrogen-fueled cylinder is fully recirculated into the intake mixture of three other cylinders operating stoichiometrically with natural gas. This configuration leverages the benefits of both lean and stoichiometric combustion strategies. After passing a lower temperature condenser, the dry recirculated exhaust gas, which is CO2- and H2O-free, dilutes the intake mixture of the three cylinders, mimicking lean operation and thus increasing engine efficiency due to the higher isentropic coefficient (κ). Simultaneously, this approach reduces combustion temperatures, thereby lowering knock tendency and engine wear. Furthermore, the stoichiometric operation of the EGR-receiving and emission relevant cylinders allows for the effective use of a three-way catalyst, significantly reducing pollutant emissions. Experimental results confirm that this innovative combustion strategy enhances indicated efficiency from 41.5% to 43.5% compared to series operation, and maintains low NOx tail pipe emissions. These findings highlight the potential of advanced hydrogen combustion strategies to improve the sustainability and performance of gas engine CHP plants, supporting the transition toward a greener energy landscape.
Salim, Naqib, Beltaifa, Youssef, Kettner, Maurice
Development of a Combined Injection and Ignition Unit for a Gas Engine with Direct Hydrogen Injection Integrated into the Standard Spark Plug Access Hole2025-32-005911/3/2025
To achieve the desired fuel switch from natural gas to hydrogen in internal combustion engines for combined heat and power units, it is necessary to make some adjustments to the fuel supply system. External gas mixers increase the probability of backfiring when natural gas is replaced by hydrogen. In addition, the low density of hydrogen results in a loss of power. Therefore, direct gas injection is preferred when using hydrogen. A drawback of direct injection is the requirement of higher injection pressures to achieve the desired fuel mass and mixture homogeneity as well as the additional access to the combustion chamber for the direct gas injector in the cylinder head. This paper proposes an alternative approach that does not necessitate the implementation of a high-pressure direct injection system nor additional access to the combustion chamber via the cylinder head. A combined injection and ignition unit, called HydroFit, was developed which uses a sleeve inside the spark plug bore to supply hydrogen to the combustion chamber. The hydrogen is injected into the combustion chamber via capillaries integrated into the sleeve with a moderate pressure below 1.5 MPa. Hydrogen quantity is controlled by PFI solenoid valves which are protected from combustion chamber pressure by check valves. The spark plug is mounted inside the sleeve. The HydroFit prototype was tested on a naturally aspirated single cylinder gas engine at an engine speed of 1500 rpm. A parameter variation was conducted to analyse the influence of the combustion phasing as well as the start and the end of the injection on performance and NOx emissions. The results were compared to operation with port fuel injection. The results confirm that the general concept of the HydroFit unit is functional, achieving 75% of the targeted hydrogen mass flow. However, hydrogen slip caused by the low hydrogen mass flow, combined with the high volume inside the sleeve, results in decreased engine power. Compared to port fuel injection, the NOx emissions are slightly higher, presumably due to poorer mixture homogenisation.
Rischette, Nic, Holzberger, Sascha, Helms, Sven, Kettner, Maurice
Development of the Hydrogen Fueled Internal Combustion Engine for Off-Road Applications2025-32-006611/3/2025
This paper focuses on the potential application of hydrogen fueled internal combustion engine (HICE) in the off-road market, examining HICE based on a diesel engine. In the transition to HICE, priority was given to compatibility with existing systems, minimizing changes from the base engine. By adopting a PFI (Port Fuel Injection) method for fuel injection, low-pressure hydrogen supply was achieved. To address the issue of backfire associated with PFI, optimization of injection pressure using a variable pressure control valve, along with adjustments to valve timing and injection timing, was implemented to suppress backflow of residual gases into the intake system and minimize hydrogen retention. Regarding pre-ignition, in addition to suppressing hotspots, the relationship between the homogenization of the air-fuel mixture and NOx emissions was examined, revealing a correlation. This engine was mounted on a generator, and efforts were made to improve the important characteristic of responsiveness in generators. As a result, it was confirmed that the responsiveness is comparable to that of existing gas engine generators.
Shiraishi, Kentaro, Kishi, Shinji, Kato, Daichi, Mitamura, Kenta, Murakami, Kei, Mikuni, Yusuke
Experimental Study on Hydrogen-Methane Co-Combustion in Small Gas Engines2025-32-005511/3/2025
Hydrogen fuel has garnered significant attention as a key method for adapting internal combustion engines to a carbon-neutral society. Hydrogen is a carbon-free fuel that does not produce CO2 emissions during combustion. However, its wide flammability range and extremely low ignition energy present technical challenges when applied to internal combustion engines, such as the frequent occurrence of abnormal combustion phenomena like pre-ignition and knocking. Furthermore, the low energy density of hydrogen makes it difficult to achieve high power output. Additionally, hydrogen’s high adiabatic flame temperature and short quenching distance result in increased NOx emissions and cooling loss, which are further obstacles to its use. To address these issues, this study focuses on methane blending as a remedial approach. Experiments were conducted using a naturally aspirated engine with a premixed intake method to investigate the effects of methane-hydrogen blending. The following key findings were obtained: 1 The heat release rate can be controlled by adjusting the blending ratio. 2 Pre-ignition and knocking can be suppressed. 3 Power output can be improved. 4 NOx emissions can be reduced. 5 Thermal efficiency can be enhanced by optimizing the blending ratio based on engine load conditions. The insights gained through this study demonstrate the potential of internal combustion engines in achieving a low-carbon and decarbonized society.
Tanaka, Kenta, Tani, Toshihiro, Sako, Takahiro
Toward Sustainable Heavy-Duty Transport: Evaluating Charge Dilution and Advanced Corona Ignition System Effects on SI Natural Gas Engine Efficiency and Combustion Characteristics2025-24-00249/7/2025
Reducing greenhouse gas (GHG) emissions in the transportation sector is a significant challenge. A multi-technology approach is the most practical and sustainable solution for minimizing the environmental impact of road transport. Alternative gaseous fuels derivable from bio sources have the potential to significantly cut equivalent carbon dioxide (CO2eq) emissions from a Well-to-Wheel (WtW) perspective, and the development of technologies that allow to improve the efficiency of natural gas-powered Heavy Duty (HD) Spark Ignition (SI) engines is of strategic importance. In such applications, charge dilution strategies might have the potential to increase engine efficiency at a relatively low implementation cost. Diluting the in-cylinder charge can reduce fuel consumption by decreasing wall and pumping losses, and increasing the Heat Capacity Ratio (γ). The coupling with innovative technologies aimed at enhancing ignition energy, influencing combustion development, could be a promising scientific path for achieving more significant results. This work presents an experimental study conducted on a modern natural gas HD SI Single Cylinder Engine (SCE) to analyze the efficiency and emission benefits achievable through charge dilution. Additionally, a characterization of the prototypal 2nd generation Advanced Corona Ignition System (ACIS gen2) was conducted for a preliminary assessment of its potential in gaseous fuel context, and to investigate the effects of its higher ignition energy on combustion features under both diluted and non-diluted charge conditions. The steady-state tests have been carried out across the low/medium load and speed range of the engine map, replicating the most common operating conditions for on-road use cases. The results highlight that charge dilution positively impacts the thermodynamic efficiency of gas HD SI engines within specific limits, lowering the Indicated Specific Fuel Consumption (ISFC) by up to 10%. The ACIS gen2 reduced the combustion duration, particularly impacting the early stages, producing an additional improvement in the ISFC of 1% to 2% in stoichiometric conditions; and suggested further potential that could be obtained by optimizing the entire system. Both technologies show that their use could be beneficial in hydrogen applications.
Di Domenico, Davide, Napolitano, Pierpaolo, Papi, Stefano, Ricci, Federico, Golini, Stefano, Rapetto, Nicola, Giordana, Sergio, Beatrice, Carlo
Combustion System Optimization of Commercial Vehicle Hydrogen Engines via 3DCFD Simulations and Single Cylinder Engine Measurements: Injector Cap, Injection Strategy and Intake Duct Design2025-24-00089/7/2025
The development of hydrogen fueled engines has dramatically accelerated in recent years. They have gained much in operating reliability and the specific power outputs is at least comparable to those of current natural gas engines. This has been made possible by combining specific development tools derived from the development of compression-ignition and spark-ignition engines. These include jet visualization techniques (Schlieren, PIV, and LIF), video endoscopy on engine, and 3-D fluid dynamics simulations. In hydrogen engines for commercial vehicles, efforts have so far been made to keep engine components as unchanged as possible from similar diesel or gasoline versions. Similarly, some manufacturers have favored the port fueled injection (PFI) solution because it is easier to implement than the in-cylinder (DI) injection one. The present work concerns the evaluation of the further improvement potential made possible by using direct injection (DI) technology, and intervening on both the geometry of the intake ducts and the design of the injector-mounted cap. The analysis of these interventions makes use of single-cylinder engine measurements and 3D CFD calculation of the fuel mixing process during the compression phase. Moreover, the flexibility of the direct injection system, that allows changing the injection timing with further improvement on the engine efficiency, was also considered. Despite the maturity already achieved by the hydrogen engine for commercial vehicle applications, the measurements and the simulations outlined in the present work throws new light in the further (high) development potential of this technology.
Gaballo, Maria Rosaria, Iacobazzi, Marino, Burtsche, Thomas, Cornetti, Giovanni
Cylinder Balancing Algorithms: Enabling the Transition to Future Fuels in Large-Bore Spark-Ignited Engines2025-24-00179/7/2025
Large-bore spark-ignited engines equipped with individual cylinder injection systems require advanced balancing strategies to achieve optimal combustion performance and mitigate risks associated with abnormal combustion phenomena. The integration of highly reactive fuels, such as hydrogen, introduces additional challenges for high-power-density, low-speed engines. This study investigates closed-loop cylinder balancing strategies utilizing real-time cylinder pressure feedback to optimize engine operation. Key performance metrics were evaluated on a 20-cylinder medium speed stationary gas engine (8.5 MW electrical power) under eight different control strategies. The results indicate that the tested balancing methods reduce average knock intensity and variation of combustion peak pressure across all cylinders compared with original manufacturer control strategy. Furthermore, the study demonstrates that a well-balanced engine offers significant advantages, including enhanced power output, a 0.5% improvement in thermal efficiency, and a 20% reduction in NOx emissions. These findings highlight the critical role of cylinder pressure-based balancing algorithms in improving the performance, efficiency, and environmental sustainability of engines operating on natural gas and hydrogen blends. This research provides a unique experimental campaign with valuable insights into the development of next-generation combustion control systems in large-scale industrial and power generation applications.
Martelli, André, Penaranda, Alexander, Martinez, Santiago, Zabeu, Clayton, Salvador, Roberto
Influence of Gas Pressure Levels on Injection Timing, Combustion Anomalies, and Emissions of a Hydrogen Gas Engine2025-24-00539/7/2025
A former diesel heavy-duty engine was retrofitted to hydrogen operation to simultaneously facilitate the shift from fossil to renewable fuels and maximize the quantity of reusable engine parts. Simply changing the fuel in this case does not make a properly working engine; the burning process needs to be realized in a premixed flame regime, rather than a diffusional flame regime. Therefore, an additional ignition source is necessary. A well-known characteristic of hydrogen is the low need for ignition energy and the wide range of ignitable air/ fuel ratios. Both must be considered to reach a diesel engine equivalent performance. Port fuel injection (PFI) and direct injection (DI) are commonly used in spark-ignited internal combustion engines. Some disadvantages, such as weak volumetric efficiency and combustion abnormal phenomena like backfire, are connected to PFI. To further improve the volumetric efficiency, high boost pressures are needed. To maximize volumetric efficiency with DI, injection timing after intake valve closure is mandatory. With a high-pressure level for hydrogen injection, a new field of application possibilities is generated regarding the degree of freedom in the injection timing. Furthermore, combustion anomalies can be prevented or their effects mitigated. The influence of pressure on the mixture formation mechanisms and time scales regarding engine load and speed variation was investigated. Simultaneously, the exhaust gas was analyzed concerning the common emissions, nitrogen oxide (NOx), and hydrogen slip (H₂ slip). Investigations were carried out on a single-cylinder research engine in two experimental setups. A low-pressure direct injection setup with pressure levels up to 30 bar and a high-pressure direct injection setup with up to 200 bar pressure. While varying the hydrogen injection pressure, two novel injectors were in use. The single-cylinder research engine’s displacement is representative of heavy-duty applications such as trucks, buses, and excavators. In a series application in a four-cylinder diesel engine setup, the following data is representative of the employed engine type: IMEP of 24.5 bar @ 1400 U/min NOx 9.1 g/kWh | ind. Eff 46.5%
Rößlhuemer, Raphael, Fellner, Felix, Fitz, Patrick, Prager, Maximilian, Jaensch, Malte
Investigation of the Combustion Process of a Thermally Conditioned Active Prechamber in Monovalent Operation with Ammonia2025-24-00289/7/2025
The debate over synthetic fuels is intense especially in sectors with a high energy demand like maritime [1, 2]. Hydrogen production from renewable sources is growing, but immediate measures for decarbonization are needed [3, 4]. In this context, the project MethMag was funded, and a gas engine for methane combustion with an innovative cooling concept and a purged prechamber (PC) spark plug was virtually developed [5, 6]. Validation with data from the test bench demonstrates that the simulations accurately represent the operating conditions [7, 8]. This combustion process is adapted for ammonia, which is being considered as a climate-friendly fuel of the future, particularly in maritime transportation [4, 9]. This fuel faces significant combustion challenges and is therefore mostly considered in complex, bivalent systems [10]. In particular, the prechamber is examined regarding the ignitability of ammonia. The overarching objective is to eliminate the necessity for a secondary fuel system, thereby reducing system complexity and associated costs. The transition to ammonia highlights the need for further adjustments. The geometry of the PC cap significantly affects turbulence and mixture formation in the prechamber [11]. While swirl caps generate high turbulence, the mixture formation is inadequate. Tumble caps, on the other hand, provide advantages in mixture formation by achieving an earlier increase in turbulence, even though the maximum turbulence is lower. For ammonia combustion, PC wall conditioning is not essential, given the inherently low combustion temperatures. However, conditioning can improve cold-start behavior by accelerating PC combustion and offering greater flexibility in ignition timing [12]. Direct injection into the prechamber enhances fuel mixing and reduces sensitivity to ignition timing adjustments. This leads to higher efficiency and better combustion characteristics, particularly at lean air-fuel ratios [13, 14]. Operating with a lean ammonia-air mixture is challenging but offers benefits for non-selective catalytic reduction (non-SCR) of nitrogen oxides. Simulations show that operation with λ = 1.2 and λ = 1.4 is feasible, although efficiency decreases at leaner mixtures [15].
Rothe, Paul, Bikas, Georgios, Mauss, Fabian
Experimental and Numerical Study on the Performance and Exhaust Emissions of a Single-Cylinder Natural Gas Large Bore Engine Equipped with Passive Pre-Chamber2025-24-00229/7/2025
The maritime industry is among the most energy-intensive sectors, and achieving fleet decarbonization is crucial to significantly reduce greenhouse gas emissions. As a transitional fuel, natural gas (NG) presents a viable short-to-midterm solution. Compared to conventional marine fuels, NG has the potential to lower carbon dioxide emissions by approximately 20–30%. However, to fully leverage this potential on carbon footprint reduction, substantial advancements in combustion technologies are required. One promising approach to enhance the efficiency of SI NG engines is the implementation of Passive Pre-Chamber (PPC) technology. This strategy enables leaner combustion, improving thermal efficiency, mitigating the occurrence of knocking, and reducing NOx emissions. This study presents both experimental and numerical investigations to analyze the impact of charge dilution and ignition timing on the performance and emissions of a single-cylinder prototype NG PPC SI engine for marine application, retrofitted from baseline diesel architecture. Numerical simulations combining 1D and 3D CFD approaches were used to guide the combustion system and engine component design, optimizing valve timing, compression ratio, and fuel injection parameters to mitigate knock and improve thermal efficiency. Based on numerical simulations, excess air effects on thermodynamic efficiency and flame speed were evaluated. The experimental tests were conducted at 1500 rpm constant engine speed under different load conditions. Variation of the air-to-fuel ratio and spark advance were performed to characterize their effects on engine operation. The results were utilized to validate a 1D model, which demonstrated a high level of accuracy in reproducing the combustion evolution. PPC technology enabled high charge dilution (λ≈1.7). The coefficient of variation of IMEP remained below 1.5% throughout a wide range of λ values and combustion phasing conditions, indicating stable combustion. The engine exhibited indicated efficiencies of over 45%, marginally exceeding the predictions obtained from numerical simulations. This research underscores the potential of PPC technology in enhancing the efficiency and sustainability of NG-fueled marine engines, offering valuable insights to optimize combustion strategies for future low-emission propulsion systems.
Marchitto, Luca, Pesce, Francesco, Accurso, Francesco, Tornatore, Cinzia, Gorietti, Valentina, Buzzi, Luca, Grosso, Alessandro, Luci, Matteo, Napolitano, Pierpaolo, Pennino, Vincenzo, Beatrice, CARLO, Di Domenico, Davide, Giardino, Angelo
Variable Valve Actuation and Multiple Injections to Enhance the Gas Exchange of a Passive Pre-Chamber Igniter2025-01-03157/2/2025
Pre-chambers, in general, represent an established technology for combustion acceleration by increasing the available ignition energy. Realizing rapid fuel conversion facilitates mixture dilution extension with satisfying combustion stability. More importantly, knock-induced spark retarding can be circumvented, thus reducing emissions and increasing efficiency at high engine loads. Adapted valve actuation and split injections were investigated for this study to enhance the gas exchange of a passive pre-chamber igniter in a single-cylinder engine. The findings support the development of passive pre-chamber ignition systems operable over the whole engine map for passenger vehicles. There are two configurations of pre-chamber igniters: passive pre-chambers and scavenged pre-chambers. This study focuses on the passive design, incorporating an additional small volume around the spark plug into the cylinder head. Hot jets exit this volume after the ignition onset through several orifices. These jets ignite the mixture in the main chamber, surpassing the ignition energy delivered by a spark plug. However, the major challenge for such igniters is the replacement of the residual gases during engine gas exchange. The combustion products of the previous working cycle need to be replaced by a fresh air-fuel mixture to facilitate the subsequent ignition. Controlling the pre-chamber gas exchange is decisive for series applications. The geometrical design of the pre-chamber influences its gas exchange. However, additional measures that are adaptable during engine operation must be identified to ensure stable engine operation. For this study, the adaptation of the intake valve actuation was investigated, and the cyclic variation was successfully reduced. Splitting the fuel injection into two separate events further enhanced combustion stability. Comprehensive measurements of the exhaust gas composition underlined the effectiveness of the introduced parameters to enhance passive pre-chamber ignition. Furthermore, analysis of the pressure traces in the main and pre-chamber provides insight into pre-chamber gas exchange and combustion initiation.
Fellner, Felix, Härtl, Martin, Jaensch, Malte
Design of a New Overhead Two-Stroke Engine Braking Device and Braking Performance Evaluation2025-01-50487/1/2025
The braking safety of heavy-duty vehicles is widely concerned. This paper proposed a new purely mechanical transmitted OHC two-stroke braking device. The rigid–flexible coupled dynamics model of the device and the engine working process simulation model were used for joint simulation. The effects of CR lift, environmental conditions, compression ratio, and braking type on the engine braking performance were comprehensively evaluated. The result shows: good consistency of valve operation is obtained by using pure mechanical transmission. During the braking process, the in-cylinder pressure acts directly on the valves and significantly affects the maximum valve lift of the CR phase, therefore excessive in-cylinder pressure will reduce the reliability of the braking device. When the CR lift increases from 1.9 to 2.8 mm, the braking power per liter increases at low altitude, but first increases and then decreases at high altitude. The decrease in engine speed and compression ratio as well as the increase in altitude lead to the decrease in braking power per liter. A benchmark of braking performance was taken from a high-compression-ratio (17) engine with a four-stroke decompression brake. For the high-compression-ratio (17) engine with two-stroke brake, the maximum in-cylinder pressure was reduced from 6.30 to 3.84 MPa, and the braking power per liter was increased by 24.5%–32.3% at low altitude and 93.2%–110.2% at high altitude. For the low-compression-ratio (11.6) engine with two-stroke brake, the maximum in-cylinder pressure is reduced to 2.83 MPa, and the braking power per liter changes less at low-altitude conditions and increases by 54.8%–67.1% at high-altitude conditions. The two-stroke braking device will greatly improve the braking safety and device components’ reliability on heavy-duty trucks, broaden the operating speed range, and promote the popularization and application of low-compression-ratio engines such as natural gas engines and methanol engines.
Cui, Jingchen, Wang, Bing, Tian, Hua, Tian, Jiangping, Long, Wuqiang
Experimental Evaluation of Direct and Port Fuel Injection Strategies on a Heavy-Duty Liquefied Petroleum Gas Engine03-18-03-00225/9/2025
Liquefied petroleum gas (LPG) is a popular alternative fuel in the transportation sector as a result of its favorable physical and chemical properties, availability, and relatively lower emissions compared to conventional fuels. However, much of its use is currently in light-duty applications, usually in manifold or port-injected configurations primarily due to their simplicity and ease of conversion. However, there are shortfalls in heavy-duty applications where decarbonization efforts are direly needed. The key reasons for this shortfall in alternative fuel adoption in the heavy-duty sector are the deficit in engine performance when compared to conventional heavy-duty diesel engines and the lack of specialized hardware to bridge this performance gap, for example, direct injectors optimized for LPG fuel operation on large-bore engines. To address this, this study evaluated the performance, emissions, and combustion characteristics of a heavy-duty single-cylinder research engine, the Cummins ISX15L, in direct injection (DI) mode with an injector designed for liquid LPG and in a baseline port fuel injection (PFI) mode using an off-the-shelf injector currently in use on commercially available LPG engines. The engine had a compression ratio of 9.3 and a fuel delivery system designed to supply LPG at 1.6 MPa and 17.2 MPa in PFI and DI modes, respectively. The influence of both injection strategies at different start of injection (SOI) timings, equivalence ratios, combustion phasings, and engine load conditions were then investigated. The DI strategy was responsible for the highest brake thermal efficiency (BTE) recorded on the engine, 36.9%, 7% higher than the BTE in PFI mode at the same lean engine condition. The DI configuration achieved a 39% reduction in bsNOx but increased bsCO emissions by 22% compared to PFI at stoichiometric conditions. The PFI strategy demonstrated an insensitivity to the SOI timing unlike the DI strategy, which was highly unstable at retarded SOI timings.
Fosudo, Toluwalase, Windom, Bret, Olsen, Daniel
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
Study on the Optimal Pre-Chamber Geometry for Active Pre-Chamber Gas Engines2024-32-00234/18/2025
In a pre-chamber engine, fuel in the main-chamber is ignited and combusted by the combustion gas injected from the pre-chamber. Therefore, further fuel dilution is possible and thermal efficiency can be also improved. However, adding a pre-chamber to an engine increases the number of design parameters which have a significant impact on the main combustion and the exhaust gas. Then, in this study, the optimum geometry of the pre-chamber in an active pre-chamber gas engine was investigated. The considered parameters were the volume of pre-chamber, the diameter of a nozzle hole, and the number of nozzle holes. 18 types of pre-chambers with different geometries were prepared. Using these pre-chambers, engine experiments under steady conditions were conducted while changing the conditions such as engine speeds, mean indicated pressure and air excess ratio. Based on the experimental data, neural network models were constructed that predict thermal efficiency, NOx and CO emissions from the pre-chamber geometries and the engine operation conditions. Employing these models as objective function, the optimal geometry of the pre-chamber is obtained as Pareto solutions. The availability of this method to determine the optimal geometry of pre-chamber was proved since the general trade-off relationship between thermal efficiency and NOx was shown.
Yasuda, Kotaro, Yamasaki, Yudai, Sako, Takahiro, Takashima, Yoshitane, Suzuki, Kenta
Experimental Investigations of a Hydrogen Fueled Natural Gas Engine and Ion Current Measurement for Combustion Diagnostics in Pure Hydrogen Operationwith Water Injection2024-32-00654/18/2025
In the ongoing effort to decarbonize energy supply, a notable shift involves the conversion or retrofitting of combined heat and power plants to operate on hydrogen as an alternative to natural gas. In this transformative landscape, extensive research is underway to develop and explore innovative combustion processes for hydrogen-fueled engines, aiming to comprehend and optimize combustion processes concerning both engine performance and emissions. Among the various methods available for monitoring the combustion process and engine control, ion current sensing presents itself as a viable option. A unique feature of this research lies in utilizing the engine's spark plug itself as an electrical sensor, measuring the ion current generated during the flame development and combustion processes. Given the limited research on ion current sensing for hydrogen combustion processes, a series of experiments were conducted and presented in this work. These experiments involved sweeps of water-to-fuel ratio (WFR) on a naturally aspirated gas engine consisting of four cylinders, of which only one cylinder is being operated with pure hydrogen as fuel. The primary findings highlight the feasibility of measuring ion current even within hydrogen-air combustion under extremely lean mixtures (λ > 3). Furthermore, it is firstly presented that the levels of WFR significantly affect measured ion current signals. Using the measured data from the conducted sweeps, characteristics of the ion current signals are correlated with combustion parameters. It is foremost proven, that the first rise of the ion current signal correlates well with the calculated combustion start CA05. In essence, this research not only contributes to the evolving landscape of hydrogen-based energy solutions but also sheds light on the potential of ion current sensing as a reliable tool for monitoring and optimizing combustion processes in these engines, thereby enabling broader goals of sustainable and efficient energy systems.
Salim, Naqib, Beltaifa, Youssef, Kettner, Maurice, Loose, Oliver, Weißgerber, Tycho
Enhancing Low Temperature Lean Combustion of CH4-H2 Blends through a Prechamber Equipped Engine2024-32-00444/18/2025
The use of hydrogen as a sustainable fuel in the short term is hampered by the impossibility of large scale use due low availability. In order to promote decarbonization, complementary solution for a smooth transition is to dilute it in a mixture with methane, in a current Port Fuel Injection (PFI) internal combustion engine (ICE). This can be done as a retrofit after limited structural modifications, such as the introduction of a passive prechamber. Such a solution allows a reduction of the carbon footprint of traditional ICEs through more efficient combustion (both the prechamber technology and the hydrogen fuel properties promote an increase in combustion speed) and a reduced carbon content in the fuel. The present research activity has been carried out through numerical investigation based on three-dimensional CFD analyses to simulate the behavior of a natural gas engine fueled with CH4-H2 blends. The combustion mechanism for the fuel blend was validated against measurements of the flame front propagation carried out on an optical engine. The focus of the work is to evaluate the effect of both the hydrogen share and the charge dilution. The introduction of a passive prechamber was necessary to stabilize the mixture ignition and increase the combustion speed. In particular, simulations were carried out for increasing hydrogen content, from 0% to 30% in volume, and increasing excess air from stoichiometric (λ=1.0) to ultra-lean (λ=1.8), in order to achieve a Low Temperature Combustion (LTC). For each operating condition investigated, the ignition advance was optimized in order to maximize the gross indicated mean pressure (GMEP). The results show that, at λ = 1.4, 20% H2 is sufficient to obtain a slightly higher GMEP than using pure CH4, while at the same time guaranteeing a 40% reduction of raw NOx emissions. When further increasing the value of λ up to 1.8, slow combustion is obtained even with 30% share of H2. In this case, hot EGR is needed to increase the reactivity of the mixture and allow achieving a complete combustion.
Balduzzi, Francesco, Ferrara, Giovanni, Di Iorio, Silvana, Sementa, Paolo
Evaluating the Potential of a Turbo-Compound System for a Heavy-Duty Natural Gas Engine: A Modelling Study2025-01-83554/1/2025
Combining a low-carbon content fuel, such as natural gas, with a high-efficiency engine can reduce greenhouse gas emissions significantly in hard-to-electrify long-haul trucking applications. Turbo-compounding, where an additional power turbine is installed in the exhaust stream after the turbocharger turbine, can extract useful amounts of energy from diesel engine exhaust at high loads. This work assesses the net benefits of combining turbo-compounding with a high-efficiency, natural gas fuelled heavy-duty engine. The effects on brake specific fuel consumption (BSFC), greenhouse gas emissions, and engine-out emissions of nitrogen oxides (NOx) and methane (CH4) are considered. The experimentally validated 1D model for a 13L diesel pilot- direct injection of natural gas, heavy-duty engine in GT-SUITETM is used to develop a series turbo-compound model. The effects of turbine sizes and flow capacities in fixed-geometry turbocharging and power turbines are evaluated on the engine’s performance, considering the trade-off between power output in the power turbine and turbo-compound losses because of increased back pressure. A parametric analysis is conducted in the 1D model to select the best combination of turbine sizes and the gear ratio between the power turbine’s shaft and engine’s crankshaft to optimize the rotational speed of the power turbine. The results show that the turbocharging turbine’s size has the most significant effect on BSFC. The model results indicate that the most promising combination of turbines may reduce BSFC by 1% to 4% at high loads within the range of 1000 rpm to 1400 rpm, with even larger reductions of 5% to 6% at the peak power conditions around 1600 rpm. At lower loads (below 40%), the BSFC increased from 1% at mid-load to 6% or more at low loads. The net benefits of the turbo-compound system are evaluated in a developed class-8 truck model in GT-SUITETM over standard long-haul and regional delivery transient drive cycles with different cargo loads. The truck transient simulation results show that fuel consumption was reduced by 2% to 4% in 35% to 100% cargo loads in drive cycles with more cruising time but did not change substantially in lower cargo loads. More benefits in higher cargo loads are attributed to the shifted engine operating points to the higher loads where the turbo-compound system significantly improves engine system efficiency. The truck simulation results also showed that the turbo-compound system did not change the cumulative engine-out NOx and CH4 emissions over the studied drive cycles.
Balazadeh, Navid, Munshi, Sandeep, Shahbakhti, Mahdi, McTaggart-Cowan, Gordon
Operating the Tour Split-Cycle Engine on Hydrogen/Methane Fuel Blends to Achieve High Efficiency and Reduction of Both GHG and NOx Emissions2025-01-84224/1/2025
Decarbonized or low carbon fuels, such as hydrogen/methane blends, can be used in internal combustion engines to support ambitious greenhouse gas (GHG) emission reduction goals worldwide, including achieving carbon neutrality by 2045. However, as the volumetric concentration of H2 in these fuel blends surpasses 30%, the in-cylinder flame propagation and combustion rates increase significantly, causing an unacceptable increase in nitrogen oxides (NOx) emissions, which is known to have substantial negative effects on human health and the environment. This rise in engine-out NOx emissions is a major concern, limiting the use of H2 fuels as a means to reduce GHG emissions from both mobile and stationary power generation engines. In this study, an experimental investigation of the combustion performance and emissions characteristics of a 4th generation Tour split-cycle engine was undertaken while operating on 100% methane and various hydrogen/methane fuel blends (30%, 40%, and 50% by volume of hydrogen). Taking advantage of the Tour engine’s superior operating flexibility and its inherent capability to manipulate combustion phasing, the results demonstrate that the Tour split-cycle engine operating on hydrogen/methane fuel blends is capable of high brake thermal efficiency and reduced GHG emissions, while at the same time exhibiting reduced engine-out NOx emissions.
Bhanage, Pratik, Cho, Kukwon, Anderson, Bradley, Kemmet, Ryan, Tour, Gilad, Atkinson, Chris, Tour, Hugo, Tour, Oded
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
Development of the Tour Split-Cycle Internal Combustion Engine2025-01-83944/1/2025
The Tour engine is a novel split-cycle internal combustion engine (ICE) that divides the four-stroke Otto cycle of a conventional ICE between two separate cylinders, an intake and compression cylinder and a second expansion and exhaust cylinder, interconnected by an innovative charge transfer mechanism. The engine working fluid, air and fuel, is inducted into the engine and compressed by a dedicated compression cylinder, transferred with minimal pressure loss via an input port to a specifically designed combined spool shuttle transfer mechanism and combustion chamber. It is then ignited and then transferred from the combustion chamber via an exit port to a separate expansion cylinder where it is expanded and exhausted from the engine. The primary advantage of the Tour engine is that it provides the engineering freedom to independently design, control and optimize the compression, combustion, and expansion processes within a slider-crank piston engine. By decoupling the compression ratio from the expansion ratio and by allowing better combustion phasing, the Tour engine can be optimized to operate on any gaseous or liquid fuel with improved power output, exhaust emissions, and fuel efficiency. Tour Engine Inc. has undertaken the development of this engine technology since 2005, with support from private funding and major grants, from early functional prototypes to the current advanced clean sheet design 5-kW engine, specifically developed for both high efficiency and ultra-low nitrogen oxides (NOx) emissions. The current evolution of the Tour engine, a 5-kW natural gas-fueled spark-ignited engine, has been extensively tested for over 1000 hours of operation without any major failures. This paper describes an overview of the Tour engine architecture as well as the 5-kW prototype engine’s performance, efficiency, and exhaust emissions characteristics. This alternative fuel engine has demonstrated ultra-low engine-out NOx emissions with state-of-the-art brake thermal efficiency (BTE) for an engine in this power range.
Tour, Oded, Cho, Kukwon, Hofman, Yehoram, Anderson, Bradley, Kemmet, Ryan, Morris, Daniel, Wahl, Michael, Bhanage, Pratik, Sivan, Ehud, Tour, Gilad, Atkinson, Chris, Tour, Hugo
Exploring the Effects of Varying Pre-Chamber Geometry in a Heavy-Duty Natural Gas Optical Engine under Dilution Conditions2025-01-84074/1/2025
Pre-chamber combustion is an advanced ignition strategy that has been shown to enhance spark ignition (SI) combustion stability in natural gas (NG) engines by providing distributed ignition sites from turbulent jets and enhancing main-chamber turbulence. Pre-chamber combustion has been proven especially advantageous compared to SI in ultra-lean and dilute operating conditions. This work involves experimental investigation of the effects of varying passive pre-chamber nozzle configuration on pre-chamber and main chamber combustion under simulated exhaust gas recirculation (EGR) dilution (0 and 20%) conditions in a heavy-duty, single-cylinder, optically accessible NG engine at stoichiometric fuel-air ratio. Pre-chamber nozzle configurations include four pre-chambers with constant nozzle area to pre-chamber volume ratio (A/V) with different nozzle sizes and orientations and one configuration with larger nozzles. The optical engine is operated in a skip-fire sequence consisting of 18 motored cycles followed by two consecutive fired cycles to elucidate the effect of combustion residuals (internal EGR) on combustion evolution. Pressure-based diagnostics are used to monitor pre-chamber and subsequent main chamber combustion, and optical diagnostics include high-speed OH* chemiluminescence to visualize the development of pre-chamber jets and the resulting ignition of the main chamber charge. Heat release analysis of the in-cylinder pressure data indicates that a faster pre-chamber pressure rise does not always translate into faster main-chamber combustion. The pre-chamber with the smallest nozzle diameter produced the highest pre-chamber pressure rise and fastest combustion under non-diluted conditions. However, dilution delays the main chamber ignition for smaller nozzles despite a comparable rise in pre-chamber pressure compared to configurations with larger nozzles. This effect is more pronounced for cycles with in-cylinder combustion residuals in addition to external dilution. Additionally, it was observed that pre-chambers with swirling nozzles have a faster pressure rise in the pre-chamber and main chamber under dilute conditions. Optical diagnostics suggest that the main reason for the delay between the pre-chamber pressure rise and main-chamber combustion lies in jet quenching and delayed re-ignition, which can even lead to misfire if jets emitted from small nozzles combined with dilution fail to re-ignite.
Dhotre, Akash, Nyrenstedt, Gustav, Rajasegar, Rajavasanth, Varma, Arun, Singh, Satbir, Northrop, William, Srna, Ales
Probabilistic Analysis Approach to Evaluate Gear Tooth Strength in the Hypocycloid Engine03-18-02-00153/8/2025
This study introduces a probabilistic analysis approach to evaluate the gear tooth strength for the hypocycloid engines, which are particularly significant in internal combustion (IC) engine applications due to their unique design and critical requirements for both efficiency and durability. The research utilizes the stress–strength interference (SSI) theory within a “design for reliability” framework to develop a robust methodology for designing the internal gear mechanism required for the hypocycloid gear mechanism (HGM) engine, in accordance with American Gear Manufacturers Association (AGMA) standard gear rating practices. This approach incorporates probabilistic factors to address variations in HGM component parameters, gear material properties, and engine operational conditions. To validate the design and ensure accuracy, a finite element method (FEM)-based verification is employed, to identify potential failure points and enhance the overall reliability of the HGM engine. The probabilistic analysis results strongly agreed with the FEM results across a range of different HGM engine design versions. A quantitative assessment of the investigated gear pairs showed that the highest reliability is associated with the lowest variation for bending stress number and the largest face width of the gear pair. This comprehensive method ensures that the hypocycloid gear engine meets the high-performance standards required for its effective operation.
ElBahloul, Mostafa A., Aziz, ELsayed S., Chassapis, Constantin
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
Prediction of Combustion Characteristic Parameters of High Efficiency and Low Emission Hydrogen-Enriched Compressed Natural Gas Engine Under Closed-Loop Control2025-01-71031/31/2025
Closed-loop combustion control is highly beneficial for improving the efficiency and reducing the emissions of spark ignition internal combustion engines. In this paper, the key parameter (CA50) of closed-loop combustion control and its effect on the combustion and emissions were explored experimentally in a six-cylinder hydrogen enriched compressed natural gas (HCNG) engine. Moreover, the particle swarm optimization (PSO) back propagation neural network (BPNN) algorithm improved by various hybrid strategies was employed for CA50 prediction. The experimental results reveal that CA50 has a significant impact on the combustion characteristics and emissions of the HCNG engine. Meanwhile, statistical analysis illustrates that CA50 follows a normal distribution and has no self-correlation. Considering the one-to-one correspondence between CA50 and the spark timing, it is suitable to select CA50 as the feedback parameter. The simulation results indicate that the CA50 prediction model established by the PSO-BPNN method has high prediction performance and excellent generalization ability, with an average mean absolute error (MAE) of 0.25°CA and correlation coefficient (R) of more than 0.997. To further enhance the model’s performance, the PSO-BPNN models optimized by various hybrid strategies were compared, concluding that the hybrid strategies can significantly improve the convergence speed without sacrificing prediction accuracy. Among them, the NaPSO-BPNN method has the fastest convergence speed, and its CPU running time is 73.02% less than that of the PSO-BPNN model.
Duan, Hao, Yan, Yu, Ren, Xianfeng, Yin, Xiaojun, Wang, Jinhua, Zeng, Ke
Large-Bore HFO Engine Gas Conversion for Power Plants – Part A: Numerical Assessment2024-36-016012/20/2024
In the global scenario marked by the increasing environmental awareness and the necessity on reducing pollutant emission to achieve the decarbonization goals, action plans are being proposed by policy makers to reduce the impact of the climate change, mainly affecting the sectors that most contribute to CO2 emissions such as transportation and power generation. In this sense, by virtue of the National Energy Plan 2050, the Brazilian market will undergo the decommissioning of thermal power plants fueled by diesel and heavy fuel oil (HFO) by 2030, compromising about 6.7 GW of power capacity according to the Brazilian Electricity Regulatory Agency (ANEEL) database. An alternative to the scrapping of these engine power plants is their conversion to operate with fuels with a lower carbon footprint, such as the natural gas. This work, therefore, aims to numerically assess the conversion feasibility of a HFO large bore four-stroke turbocharged engine to operate with natural gas by means of a one-dimensional engine modeling. First, the 1D non-converted engine model operating with HFO is validated with experimental data. Then, the conversion of the HFO engine to natural gas is carried out by adding a wastegate for the air-fuel ratio control, changing the compression ratio and the fuel injection, and introducing the pre-chamber ignition system. At this stage, the performance of the engine operating with most of its stock components is evaluated, including the presence of knock, fuel slip, and components that may not be suitable for NG operation and must be adapted, redesigned, or replaced. After that, modifications on the valve timings are proposed to reduce the methane slip and allows a proper scavenging. In conclusion, this study numerically assessed converting an HFO engine to natural gas, identifying new component specifications and presenting alternatives to maintain engine performance post-conversion.
Gonçalves, Vinícius Fernandez, Zabeu, Clayton Barcelos, Antolini, Jácson, Salvador, Roberto, Almeida, Rogério, Valiati, Allan Soares, Filho, Guenther Carlos Krieger
Phase Detection Relevance in Engine Torque Determined by Instantaneous Engine Speed2024-01-427011/5/2024
Accurate flywheel torque estimation in combustion engines can be used for monitoring engine performance, creating the potential for lowering emissions and fuel costs. Recently a method was proposed to determine the mean flywheel torque from instantaneous engine speed using the n-th order Fourier series, where n is the number of cylinders firing per crank revolution. However, instantaneous engine speed is affected by two separate torque contributions. The torque resulting from reciprocating masses in the engine, i.e., reciprocating torque, and the torque produced by combustion pressure, i.e., gas torque. Gas torque and reciprocating torque signals have the same frequency but are in opposite phases. Since the resultant torque at the flywheel is the sum of gas and reciprocating torques, there is a need to remove reciprocating torque from the total torque at the flywheel. This requires knowing whether gas or reciprocating torque has a larger amplitude. Here, a method is proposed to determine whether gas or reciprocating torque has a larger amplitude via the phase of engine speed; this method is a step towards a practically implementable virtual torque sensor. This methodology of torque estimation is evaluated through on-road testing on a truck powered by a Cummins ISX12G compressed natural gas engine at engine speeds of 1000-2100 RPM and at different transmission gear ratios and throttle conditions. The proposed algorithm demonstrated a mean absolute percentage error of 13.2%.
Ely, Nathan, Iddum, Vivek, Ghantasala, Muralidhar, Meyer, Richard T.
Development of a NG Engine Predictive Simulation Model and Investigation of Engine Performances under Hydrogen-Blended Operation2024-24-00299/18/2024
Hydrogen-powered mobility is believed to be crucial in the future, as hydrogen constitutes a promising solution to make up for the non-programmable character of the renewable energy sources. In this context, the hydrogen-fueled internal combustion engine represents one of the suitable technical solution for the future sustainable mobility. In a short-term perspective, the development of the green hydrogen production capability and distribution infrastructure do not allow a substantial penetration of pure hydrogen IC engines. For this reason, natural gas – hydrogen blends can represent a first significant step towards decarbonization, also determining a trigger effect on the hydrogen market development. The present paper is focused on the analysis of the combustion and performance characteristics of a production PFI natural gas engine, run on blends with 15% in volume of hydrogen (HCNG). More specifically, a fuel-flexible, predictive 1D simulation model has been developed within the Gasdyn code and validated against experimental data, under natural-gas operation. The model features the application of a predictive combustion model, which intrinsically accounts for the fuel burning characteristics through the specification of its laminar burning speed. The model has then been applied to the HCNG fueling case, with no changes in the combustion model settings, and showed rather good accuracy, thus demonstrating its fuel flexibility. The model was then used as a digital twin of the real engine, and the engine calibration was optimized in order to fully exploit the potential benefits of the hydrogen blending, with no or minor modification of the engine design with respect to a production spark ignition engine.
Baratta, Mirko, Di Mascio, Valerio, Misul, Daniela, Marinoni, Andrea, Cerri, Tarcisio, Onorati, Angelo
Enhancing Homogeneity and Combustion Efficiency in Gas Engines: A Novel Approach through Swirl-Inducing Air Intake Pipe Modifications2024-24-00399/18/2024
The lack of a homogeneous air-fuel mixture in internal combustion engines is a major cause of pollutant emissions, such as carbon monoxide (CO) and hydrocarbons (HC). This paper focuses on the design, simulation, and testing of a modified air intake pipe for a gas engine, incorporating deflectors to induce a swirl effect in the air-fuel mixture. To determine the optimal configuration for the deflectors and the diameter of the air intake pipe, several Computational Fluid Dynamics (CFD) simulations were conducted. The best results were then tested on a real gas engine. The primary objective of this study is to offer a solution for increasing the homogeneity level of the air-fuel mixture in gas engines, without requiring significant changes to engine components. In this case, achieving this goal involves only relatively small modifications to the air intake pipe. The results indicate that the swirl effect effectively enhances the homogeneity of the air-fuel mixture by generating higher turbulence along the air intake path. Critical to the success of the modification is the maintenance of the original pressure drop along the pipe. To compensate for the restriction caused by the deflector in the cross-sectional area of the air intake pipe, it is necessary to increase the diameter of the pipe. The most challenging aspect was achieving a reduction in CO and HC emissions due to the deflectors, rather than solely relying on the increased diameter of the air intake pipe. Importantly, the goal was to maintain engine power without a corresponding increase in fuel consumption. Contrary to the common belief that any device disrupting the free flow through the air intake pipe causes pressure losses, our findings suggest that the right configuration of pipe diameter, along with the appropriate number and positioning of deflectors, can yield better results than maintaining an unrestricted airflow. In summary, our work presents a device intended for implementation in the air intake pipe of gas engines, inducing a swirl in the air-fuel mixture without creating pressure losses compared to the original engine condition. This modification successfully reduces CO and HC levels, serving as an indicator of improved combustion resulting from a more homogeneous air-fuel mixture.
Gutierrez, Marcos, Taco, Diana
Hexagon Agility and Brudeli aim to electrify CNG powertrains24TOFHP08_078/1/2024
Hexagon Agility announced a collaboration with Norwegian EV transmission supplier Brudeli Green Mobility at the 2024 ACT Expo in Las Vegas. The partnership's goal is the integration of Hexagon Agility's CNG/RNG (compressed/renewable natural gas) systems with Brudeli's plug-in PowerHybrid system. This technology will reportedly offer fleets the capability to maintain diesel ICE duty cycles while providing fuel cost savings and help OEMs achieve global decarbonization goals. “The Brudeli PowerHybrid enables fleet owners to retain the power, performance and fuel cost savings offered by natural gas engines, while simultaneously harnessing the efficiencies of electric,” said Eric Bippus, EVP sales & systems development, Hexagon Agility. “We believe hybrids could play a role in commercial trucking in the future, and we are excited to take an active role bringing that to the market.”
Wolfe, Matt
Measurements in the Recirculation Path of a Fuel Cell System2024-01-30097/2/2024
The study demonstrates the possibility and in particular the method to derive the efficiency of the entire fuel cell power system by measuring specific data of the recirculation path of the anode circuit of a fuel cell system. The results demonstrate the capabilities of the existing test rig and enable investigations on the suitability of auxiliary components. This study focuses on the hydrogen recirculation path equipped with multiple sensors and a needle valve to enable the required operating conditions of the fuel cell. Running a startup load profile without reaching the equilibrium state at all steps, the dynamic of the system and the requirements to the sensor parameters, such as sampling rate and precision, was seen. Additionally, it became obvious that the recirculation pump used is oversized, but a load point shift compensated this artifact. In detail, the stoichiometry and the efficiency of the entire system was evaluated. It was seen that the hydrogen concentration is approximately constant over the whole range of power of the fuel cell. Furthermore, all the results corresponded to the expectations so that it can be assumed that the test bench is working correctly. Further investigations will follow.
Allmendinger, Frank, Martin, Benedikt, Schmidtmann, Marlen
Development of a Hybrid-Electric Medium-HD Demonstrator Vehicle with a Pent-Roof SI Natural Gas Engine2024-37-00266/12/2024
In response to global climate change, there is a widespread push to reduce carbon emissions in the transportation sector. For the difficult to decarbonize heavy-duty (HD) vehicle sector, hybridization and lower carbon-intensity fuels can offer a low-cost, near-term solution for CO2 reduction. The use of natural gas can provide such an alternative for HD vehicles while the increasing availability of renewable natural gas affords the opportunity for much deeper reductions in net-CO2 emissions. With this in consideration, the US National Renewable Energy Laboratory launched the Natural Gas Vehicle Research and Development Project to stimulate advancements in technology and availability of natural gas vehicles. As part of this program, Southwest Research Institute developed a hybrid-electric medium-HD vehicle (class 6) to demonstrate a substantial CO2 reduction over the baseline diesel vehicle and ultra-low NOx emissions. The development included the conversion of a 5.2 L diesel engine to spark-ignited natural gas with an aluminum, pent-roof cylinder head to provide a diesel-like torque curve and engine NOx emissions below 0.02 g/hp-hr (0.027 g/kWh). In parallel, a vehicle modeling study was performed to determine an optimum hybrid architecture for an Isuzu F-Series truck to provide the largest impact on fleet emissions. Variations of motor/generator location, battery voltage, and storage capacity were evaluated. Finally, the demonstration truck was built with the prototype engine and P2 plug-in hybrid system to provide performance and emissions validation of the overall concept. The vehicle was tested over several HD drive cycles, including the Greenhouse Gas Emissions Model (GEM) certification cycles, and provided satisfactory performance. The GEM cycle results demonstrated a greater than 25% reduction in CO2 for the multi-purpose and urban subcategories. For the regional subcategory testing with a high percentage of highway speeds operation, the vehicle demonstrated a 13% reduction in CO2 due primarily to the lower carbon intensity fuel.
Wallace, Julian, Mitchell, Robert, Rao, Sandesh, Jones, Kevin, Kramer, Dustin, Wang, Yanyu, Chambon, Paul, Sjovall, Scott, Williams, D. Ryan
Guided Port Injection of Hydrogen as an Approach for Reducing Cylinder-to-Cylinder Deviations in Spark-Ignited H2 Engines – A Numerical Investigation2024-37-00086/12/2024
The reduction of anthropogenic greenhouse gas emissions and ever stricter regulations on pollutant emissions in the transport sector require research and development of new, climate-friendly propulsion concepts. The use of renewable hydrogen as a fuel for internal combustion engines promises to provide a good solution especially for commercial vehicles. For optimum efficiency of the combustion process, hydrogen-specific engine components are required, which need to be tested on the test bench and analysed in simulation studies. This paper deals with the simulation-based investigation and optimisation of fuel injection in a 6-cylinder PFI commercial vehicle engine, which has been modified for hydrogen operation starting from a natural gas engine concept. The focus of the study is on a CNG-derived manifold design which has been adapted with regard to the injector interface and is already equipped with so-called gas injection guiding tubes for targeted fuel injection in front of the intake runners of the individual cylinders. Significant deviations between the averaged cylinder pressure profiles of the individual cylinders observed on the test bench point to an issue with the equal distribution of the fuel supply to the individual cylinders. A subsequent 3D CFD simulation of the internal manifold flow showed geometry-induced turbulence of the fresh air flow in the area of the hydrogen supply outlet of several cylinders, which can lead to variations in cylinder-specific fuel quantities. In order to minimise the influence of the air flow in the manifold on the fuel injection, a dedicated injection guide concept for the gas injection tubes in the intake manifold has been designed with the aim of moving the position of hydrogen injection closer to the intake valves. In this study, this concept is analyzed based on first results obtained from a detailed 3D CFD simulation, especially in terms of the uniformity of hydrogen distribution between the cylinders, mixture formation and the effect on combustion.
Jung, Philipp Emanuel, Guenthner, Michael, Walter, Nicolas
Effect of Dithering on Post-Catalyst Exhaust Gas Composition and on Short Time Regeneration of Deactivated PdO/Al 2 O 3 Catalysts under Real Engine Conditions2024-37-00026/12/2024
Fossil fuels such as natural gas used in engines still play an important role worldwide which however is also exacerbating climate change as a result of carbon dioxide emissions. Although natural gas engines show an overall low pollutant emissions level, methane slip due to incomplete combustion occurs, causing methane emissions with a more than 20 times higher global warming potential than CO2. Additionally, further tightening of emissions legislation is to be expected bringing methane emissions even more into focus making exhaust gas aftertreatment issues remain relevant. For lean gas applications, (Pd)-based catalysts turned out to convert CH4 most efficiently usually being supported by metal oxides such as aluminium oxide (Al2O3). Water (H2O) contained in the exhaust gas causes strong inhibition on Pd catalysts. In real exhaust gases, not only water vapour but also pollutants and sulphur-containing compounds such as hydrogen sulphide (H2S) or sulphur oxides (SOx) are poisoning the catalytic converter. Rich pulses decomposing sulphur species adsorbed on Pd-Pt methane oxidation catalysts, enable efficient regeneration of heavily poisoned catalysts. A strategy similar to operation with rich pulses, but with a different motivation, is the use of high-frequency oscillations between lean and rich exhaust gas, so-called dithering, to improve pollutant conversion. A combination of a stoichiometric pulse while simultaneously dithering shows better results in recovery as well as emissions during regeneration than a pure rich pulse.
Tomin, Sebastian, Wagner, Uwe, Koch, Thomas
Application of MAN Loop Scavenging in a 125 cc Two-Stroke Racing EngineSAE-PP-003955/8/2024
The use of MAN-type loop scavenging port arrangements in a 125 cc two-stroke racing engi-ne is being investigated. These make it possible to provide larger cross-sections for the trans-fer ports, but at the expense of the exhaust port cross-section. The investigation is carried out using 1D calculations with GT-Suite. It is shown that significantly higher maximum outputs are possible in this way. However, this requires large exhaust widths, as otherwise the exhaust port is too small and the advantage of the larger transfer cross-section is overcompensated. Mixed forms between the original MAN loop scavenging and Schnürle loop scavenging can represent a good compromise. One open point is the quality of the scavenging. A study found in the literature on the use of MAN loop scavenging on a small engine shows significantly worse results than is known from large engines. There is still a need for further investigation here.
Eilts, Peter
Effect of Timing Strategy on Mixture Formation, Performance and Emission of Inlet Injection Hydrogen Engine2024-01-26144/9/2024
In order to scrutinize the timing variables impacting the combustion performance and emissions of the Port Fuel Injection hydrogen engine (PFI-H2ICE), a model of a four-cylinder hydrogen engine is meticulously built utilizing the 1D software GT-POWER. The effect of excess air coefficients and timing strategies (including the intake valve opening timing (IVO), the start of injection timing (SOI), and ignition timing) is analyzed in this study. The main conclusions are as follows: The hydrogen engine remold from the Isuzu JE4N28 nature gas engine manifests a lean combustion threshold ranging between 2.0 and 2.5. Notably, advancing intake valve opening timing by 20°CA has proven beneficial to the brake thermal efficiency (BTE) of the hydrogen engine while reducing the NOx emissions by a substantial margin, and advancing intake valve opening timing bears the virtue of strengthen the positive influence of the start of injection timing upon the engine's combustion performance. The longer the formation duration of the air-fuel mixture from the start of hydrogen injection timing to the ignition timing enables the better the combustion performance of the engine and the lower the NOx emissions. The outside-cylinder mixing time shows a stronger impact on the brake thermal efficiency, whereas the inside-cylinder mixing time has a greater impact on NOx emissions. The influence level of ignition timing, start of injection timing, and intake valve opening timing upon the combustion performance and emissions of the hydrogen engine decreases successively.
Hu, Zhiyuan, Yin, Li, Zhang, Yunhua, Lou, Diming, Tan, Piqiang, Liu, Dengcheng
Methane Conversion in Stoichiometric Natural Gas Engine Exhaust2024-01-26324/9/2024
Stoichiometric natural gas (CNG) engines are an attractive solution for heavy-duty vehicles considering their inherent advantage in emitting lower CO2 emissions compared to their Diesel counterparts. Additionally, their aftertreatment system can be simpler and less costly as NOx reduction is handled simultaneously with CO/HC oxidation by a Three-Way Catalyst (TWC). The conversion of methane over a TWC shows a complex behavior, significantly different than non-methane hydrocarbons in stoichiometric gasoline engines. Its performance is maximized in a narrow A/F window and is strongly affected by the lean/rich cycling frequency. Experimental and simulation results indicate that lean-mode efficiency is governed by the palladium’s oxidation state while rich conversion is governed by the gradual formation of carbonaceous compounds which temporarily deactivate the active materials. Lean/rich cycling around stoichiometry enables a higher CH4 oxidation as the oxygen storage seems to balance the individual effects of Pd oxidation and rich deactivation. In this work, the catalytic reaction mechanisms involved in CH4, CO and NOx conversion were studied by means of a multi-scale experimental campaign and mathematical modeling. Initially, a detailed kinetic study was performed on the synthetic-gas bench to understand the underlying phenomena and formulate the appropriate reaction mechanisms. The model was then evaluated under transient reactor experiments while final validation was performed against driving cycle measurements on the engine bench.
Karamitros, Dimitrios, Ibraimova, Adjer, Konstantinidis, Konstantinos, Koltsakis, Grigorios, Choi, Sungmu, Cho, Jiho
Effects of Spark Plug Operating Conditions on Electrode Erosion and Surface Deformation2024-01-21004/9/2024
An experimental study of the spark ignition process for SI engines was conducted to study spark plug erosion and the effect of breakdown voltage/energy on electrode surface deformation. The experiments were conducted outside of an engine, in both a pressurized constant volume optical chamber and in a high-pressure vessel heated within a furnace with gas temperatures as high as 730°C. J-gap spark plugs designed for natural gas engines were studied at elevated temperature and under a range of pressures to investigate electrode wear characteristics. Both iridium-alloy and platinum-alloy cathode (center electrode) and anode (ground strap) spark plugs were investigated. In addition, single spark events were performed on polished platinum cathode surfaces to allow the visualization of craters from individual spark events in order to quantify how their size and shape were affected by energy deposition and breakdown characteristics. The spark plug electrodes were investigated using optical profilometry, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis. The furnace erosion tests were run with up to 30 million spark events for a given spark plug. The breakdown voltage was found to generally increase, as expected, with increasing electrode wear as the number of spark events increased. The rate of increase of the breakdown voltage was greatest during the early portion of a trial, presumably as the relatively sharp edges of the center electrode experienced wear. Consistent with prior studies, platinum-based spark plugs were found to erode significantly more than iridium-based plugs under identical scenarios.
Tambasco, Corey, Hall, Matthew, Matthews, Ron
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