Browse Topic: Combustion chambers

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Effects of Equivalence Ratio on Hydrogen Combustion Flow and NOX Emission Characteristics in a Jet-Trapped Vortex Combustor2026-99-08067/30/2026
The jet-trapped vortex combustor presented in this study was designed based on the trapped vortex combustor with good flame stability by introducing a jet flame-stabilization method. Leveraging the superior air-fuel mixing efficiency and enhanced heat and mass transfer of the jet stabilization method, this configuration addresses the inherent limitations of heat and mass transfer between the mainstream flow and the cavity in a conventional trapped vortex combustor. To investigate the influence of different hydrogen-air equivalence ratios on the flow dynamics, combustion performance, and emission within the jet-trapped vortex combustor, numerical simulations were conducted in this study. The results show that under different equivalence ratios, a vortex pair structure can be formed in the mixing zone between the hydrogen jet and the air jet. Complete combustion can be achieved at all equivalence ratios except for Φ = 1.56. When Φ is below 0.86, the axial distance required to achieve complete combustion progressively decreases as the equivalence ratio is reduced. The temperature distribution in the combustor is more uniform with minimal variation, and the concentration of NO emissions decreases progressively. Among these cases, the combustion efficiency, temperature distribution, and NO emission characteristic of the combustor are relatively better at Φ = 0.34.
Yan, Pinghua, Hou, Xinglong, Ren, Guanlong, Sun, Haijun, Luo, Kun, Yang, Shucheng
3D Computational Fluid Dynamics Analysis of the Performance and Emissions of an Off-Highway Port Fuel Injection Hydrogen Engine03-19-04-00187/27/2026
To fulfil the global aspiration of achieving net-zero emissions, hydrogen as a fuel seems to be one of the promising candidates. High energy density per unit mass and zero carbonaceous emissions are the two salient advantages that hydrogen offers. In the present study, a set of detailed chemistry-based 3D CFD combustion simulation has been carried on a 3-cylinder turbocharged, water-cooled port fuel injection SI Hydrogen engine to understand its optimum air–fuel ratio, compression ratio, spark timing and combustion chamber geometry. The simulations have been conducted at the full load of the rated power and maximum torque engine rpms. During simulation, the λ zone for study is restricted between 2.1 and 2.7. Two different bowl geometries (spherical and cylindrical), with two compression ratio options (12 and 14) are explored in the simulations. While the spherical bowl seems to accommodate flame front better than the cylindrical bowl, the compression ratio of 12 is a safer choice to control the maximum rate of pressure rise (dp/dθ). At full load and rated speed, the indicated thermal efficiency drops by 7.7% as the λ swings from 2.1 to 2.7, whereas the indicated specific NOx and dp/dθ drop by 99% and 81%, respectively. Similarly, at full load and maximum torque RPM, the indicated thermal efficiency drops by 6.4% with λ swing from 2.1 to 2.7, whereas the indicated specific NOx and dp/dθ drop by 99% and 91%, respectively. Beyond λ = 2.4 NOx reaches almost to zero, however, at a compromise of the thermal efficiency. The dp/dθ remains well within the acceptable limit under this scenario. To account this trade-off between the performance and emission parameters, optimum λ zone has been found out to be between 2.3 and 2.5.
Satre, Santosh Dadasaheb, Mukherjee, Nalini Kanta, Kumar, Sanjeev, Nene, Devendra
Modeling and Simulation Analysis of Liquid Hydrogen and Power Systems Based on Amesim2026-99-16087/24/2026
Hydrogen-powered aircraft primarily utilize the conversion of liquid hydrogen into gaseous hydrogen to replace aviation kerosene, where hydrogen is directly combusted to provide propulsion. This study applied Amesim software to establish a complicated model simulating the liquid hydrogen to gaseous hydrogen conversion and ignition combustion processes. The simulation contains converting liquid hydrogen into gaseous hydrogen through a heat exchanger and simulating the mixture of gaseous hydrogen and air in the engine combustion chamber, and then igniting the mixture. The pressure, temperature, and flow rate of gaseous hydrogen and air during the ignition and combustion process in the engine combustion chamber, as well as the outlet temperature of the combustion chamber, are simulated and analyzed. The results demonstrate that during the simulation process, the internal pressure of the liquid hydrogen storage tank, the outlet pressure and flow rate of the liquid hydrogen pump, and the pressure and flow rate of gaseous hydrogen meet the requirements of the ignition combustion test. In addition, varying gaseous hydrogen flow rates had significant impacts on the temperature of the combustion chamber during combustion.
Gao, Pengfei, Wang, Lijian
Numerical Analysis of Directly Injected Hydrogen into a High-Pressure Chamber2026-01-07457/1/2026
Hydrogen Internal Combustion Engines have emerged as an option for decarbonizing heavy-duty transportation. However, injecting high-pressure hydrogen gas into pressurized combustion chambers induces complex compressible flow phenomena, including choked flow and under-expanded supersonic jet structures, which challenge conventional modeling approaches for optimizing engine performance and emissions. This study conducts a numerical investigation of transient hydrogen injection into a high-pressure argon environment, benchmarking a 2D axisymmetric Computational Fluid Dynamics (CFD) model against high-fidelity experimental optical measurements. Utilizing Ansys Fluent with a density-based solver, coupled with the k-ω SST turbulence model and species transport equations, simulations were performed at injection pressures of 6 MPa and 10 MPa into a 1 MPa ambient chamber. The simulation successfully captured fundamental compressible physics, including Mach disk formation and significant expansion cooling near the nozzle exit. Validation results revealed a strong dependency on the nozzle pressure ratio (nPR). At 6 MPa (nPR=6), the model achieved good agreement with experimental data, predicting tip penetration depth within 10% . However, at 10 MPa (nPR=10), while axial penetration depth predictions remained within the 10% error margin, they were consistently underestimated, and radial dispersion was significantly under-predicted. These discrepancies at high energy levels highlight the challenges of predicting turbulent entrainment within the current modeling framework. The results suggests that the observed deviations are likely to be caused by combined limitations related to the RANS turbulence model, the potential shortcomings of the 2D axisymmetric assumption in resolving highly transient mixing phenomena, the meshing strategy used, the constant assumption made about the coefficient of discharge, and the crucial role of the Turbulent Schmidt number (SCt).
Castilla Batun, Uriel Isaac, Alzahrani, Fahad
Numerical Simulation of Spark-Ignited Flame Kernels towards Prospective Application to Hydrogen SI Engines2026-37-00156/9/2026
The ongoing energy transition demands the decarbonization of the transport sector, for which the use of premixed hydrogen in spark-ignition (SI) engines appears very promising. However, modeling the combustion of the lean hydrogen/air mixtures required for safe, efficient, and low-NOx engine operation involves multiple open issues. Correct prediction of flame kernel initiation and growth is a difficulty that hydrogen shares with hydrocarbon fuels, while properly accounting for the instabilities that characterize lean hydrogen flames is an additional demanding task. In this work, a 1D kernel expansion model of general validity recently proposed by the authors is implemented into OpenFOAM, an open-source 3D CFD software package, to enable numerical simulation of expanding spark-ignited flame kernels. Firstly, the OpenFOAM framework is presented focusing on XiFluid, its flame propagation model based on a regress variable whose evolution depends on the laminar flame speed. Then, the authors’ kernel expansion model, based on the transient thermo-diffusive theory, is briefly recalled to highlight its capabilities and outputs. The coupling between OpenFOAM and authors’ model is split into two stages, namely ignition and expansion. During the ignition stage, an artificial profile of the regress variable is temporarily imposed to ensure a stable numerical solution, following which the kernel expansion is simulated by feeding into XiFluid an equivalent flame speed extracted from the 1D model. The coupling is currently formulated for laminar kernels, simulations of which are conducted firstly for conventional fuels (methane and propane) and then for hydrogen. The results are validated against outcomes of experimental tests performed in a constant-volume combustion chamber operated by engine manufacturer Wärtsilä. The validation is satisfactory for all fuels, although minor disagreements appear in case of intense flame stretch. These will be addressed in future developments, which will also extend this approach to unstable turbulent hydrogen flames in SI engines.
Dotteschini, Enrico, Pretto, Marco, Giannattasio, Pietro, Gadalla, Mahmoud
A Predictive Methodology for 3D-CFD Simulation of Piston Thermal Field in Sustainable High-Performance Engines2026-37-00026/9/2026
In recent years, especially in high-performance spark-ignition engines, the thermal stress of pistons has gradually increased due to the implementation of various technologies, aimed at meeting emission reduction and specific power increase requirements. If the heat is not properly dissipated, cracking and plastic deformation of the material as well as formation of hot spots triggering pre-ignition in the combustion chamber mixture can occur. This last aspect is even more true considering innovative fuels such as hydrogen. To overcome these problems, one or more jets of oil are directed towards the piston under-crown region, impacting at high speed. This technique ensures immediate cooling and allows the engine performance to be increased without compromising the useful life. In order to optimize the oil jet effectiveness, 3D-CFD can be proficiently adopted. In this regard, the aim of this work is to define a robust numerical methodology able to simulate oil jet impingement and piston thermal field. In particular, a 3D-CFD Volume-of-Fluid (VoF) simulation is used to numerically assess the oil jet impact and provide a map of heat transfer coefficients, which, in turn, is adopted in a 3D-CHT model to estimate the piston thermal field. The proposed methodology is validated against experimental data on a high-performance engine piston. In particular, a pair of oil jets is investigated and the resulting heat transfer coefficient map is exploited to obtain the thermal field of the piston, which is finally compared to the available experimental temperature measurements. The results show that the predicted temperatures agree with the experimental data within an error lower than 2.5%.
Duni, Andrea, Berni, Fabio, Breda, Sebastiano, Fontanesi, Stefano, Gilioli, Filippo
Investigating the Potential of Two Individually Controlled Injectors per Rotor for a Direct Injection Hydrogen Wankel Engine2026-37-00086/9/2026
Hydrogen-fueled rotary engines offer a promising zero-emission solution for compact commercial powertrains. This study reports experimental results from the further development of a naturally aspirated, direct-injection hydrogen rotary engine by HTM. Initial applications, such as an airport baggage tractor, demonstrated technical feasibility but revealed pre-ignition that limited maximum torque. To address this, mixture formation was investigated using an experimental setup with two independently controlled injectors feeding a single rotor injection channel. The effects on operating behavior, efficiency, and NOx emissions were evaluated. The dual-injector configuration significantly shortens injection duration and improves spatial distribution of hydrogen within the combustion chamber. Enhanced mixture control suppresses pre-ignition and enables higher mean effective pressure. Systematic variation of injection timing under representative steady-state conditions also shows potential for NOx reduction through differentiated injector operation. In-cylinder pressure analysis and exhaust gas measurements provide detailed insight into combustion characteristics and abnormal events. The dual-injector setup increases torque capability and operational robustness without additional mechanical complexity, supporting the use of hydrogen rotary engines in compact hybrid systems and stationary power applications.
Endres, Jonas, Beidl, Christian, Herold, Tim, Lavall, Philipp, Schmidt, Marvin, Hofmann, Silas, Kahl, Jonas
Performance and Combustion Characteristics of Coryton SUSTAIN Classic Super 80 Carbon-Neutral Fuel versus EN 228 in a 1980s Fiat 500 Engine2026-37-00336/9/2026
The energy transition requires a rapid reduction in the use of fossil fuels, whose combustion generates substantial greenhouse-gas emissions. In Europe, transport alone accounts for roughly a quarter of total greenhouse-gas emissions, with road transport being the predominant component. In this context, the use of biofuels has emerged as a potential solution for limiting further increases in CO₂ emissions. However, most studies available in the literature evaluate the performance of these fuels on modern engines, while their effects on historic carburetted engines remain largely unexplored. This is particularly significant given the large fleet of historic vehicles across Europe, supported by a long-standing tradition of vehicle preservation, associations, and classic car collectors. The main historic-vehicle federations advise caution and the use of low-ethanol formulations so as not to damage elastomers, fuel tanks, and carburettor float bowls. For this reason, a few suppliers have developed fuels specifically for classic vehicles. Among this minority, in 2023 Coryton Advanced Fuels introduced the SUSTAIN Classic line, including the Super 80 variant. In the present study, the performance, fuel consumption, and emissions of an air-cooled, four-stroke Fiat 500 engine fueled with commercial RON 95 gasoline and Coryton SUSTAIN Classic Super 80 were analyzed. A first test comprised a complete sweep from 1000 to 5000 RPM and a second test evaluated four different main jets at maximum torque speed and maximum power speed. To evaluate the performance, the engine was installed on a test bench equipped with a torque meter. Static pressure and temperature sensors were employed to characterize the engine operating conditions, while a dynamic pressure sensor installed in the combustion chamber was used to analyze the combustion characteristics. Exhaust emissions were also measured using a gas analyzer, allowing for a detailed and accurate comparison of the effects associated with the use of the two fuels.
Tarchiani, Marco, Fossati, Federico, Raspanti, Sandro, Baroni, Alberto, Ferrara, Giovanni, Romani, Luca
On Natural Gas Combustion Split into Diesel Like Architecture of a Compression Ignition Engine Retrofitted for Spark Ignition Operation2026-37-00296/9/2026
In commercial areas that no longer favor diesel engines, such as Europe, it might be interesting to convert an existing compression ignition engine to the spark ignition operation and to use natural gas (NG) because of its advantages: availability of still abundant supplies worldwide and environmental benefits compared to conventional liquid fossil fuels. This paper first presents experimental results on NG combustion inside such a converted engine with diesel-like architecture dedicated to light-duty vehicles and passenger cars. Particularly, our study carried out at the engine test bed revealed that in certain operating points (low speed and load, stoichiometric mixture and rather high spark advance), the combustion is split into two distinct events (first, a fast combustion inside the cylinder and piston bowl and then, a slower combustion occurring outside the bowl-in combustion chamber, in other words, in the squish region), which is not specific to the standard spark ignition engine. This is clearly illustrated by a rate of heat release profile with two peaks. The explanations for such combustion event are also supported by a 3D CFD study showing the in-cylinder NG distribution. The combination of experimental and numerical investigations contributes to the understanding of NG combustion in the diesel like architecture of the converted CI engine when subjected to deliberately extreme conditions, namely non-optimal spark advance setting exceeding the maximum brake torque spark advance.
Clenci, Adrian F., Popa, Robert, Berquez, Julien, Iorga-Siman, Victor, Magheru, Catalin, Punov, Plamen, Niculescu, Rodica
Rapid Fuel Distribution Prediction in RCCI Marine Engines Using CFD-Informed, Active Learning Framework2026-37-00176/9/2026
Accurate prediction of in-cylinder fuel distribution (FD) is fundamental to reduced-order combustion modeling and emissions prediction yet remains computationally prohibitive with high-fidelity CFD alone. This work develops a CFD-informed machine-learning surrogate for spatial FD in a large-bore diesel engine, based on a Wärtsilä W20 injector and representative engine conditions. A fully coupled injector–spray–engine CFD framework under engine-like RCCI inert conditions determines the needle-lift profile and resolves the combined effects of injector geometry, needle dynamics, and operating conditions on in-cylinder flow, capturing physical phenomena not reproducible by isolated free-spray simulations. A high-fidelity database is generated using Latin Hypercube Sampling, from which FD is extracted at 15 CAD before top dead center within an annular multi-zone (MZ) representation consistent with reduced-order combustion models. A multi-output Random Forest (RF) surrogate, augmented with uncertainty-driven active learning, is trained to predict the complete spatial FD vector. Prediction errors are higher near the combustion chamber core than in liner-adjacent zones, reflecting stronger nonlinear coupling and localized data sparsity. To address this, four additional CFD samples are selected from regions of maximum predictive uncertainty and incorporated into the training dataset. This targeted enrichment markedly improves surrogate performance, reducing mean absolute error (MAE) under worst-case input conditions. Although localized error amplification persists in a few zones, these regions are systematically identified and can be mitigated through further adaptive sampling using candidates proposed by the updated surrogate. Convergence of the active-learning framework is assessed using mean MAE, worst-zone MAE, global L1 error, and ensemble-based predictive uncertainty, ensuring robust and consistent accuracy across the design space. The framework integrates CFD-resolved physics, machine-learning surrogates, uncertainty quantification, and adaptive sampling, providing a scalable and physically consistent approach for efficient FD prediction in advanced engines.
Moradi, Jamshid, Salahi, Mahdi, Heidarabadi, Shadab, Andwari, Amin, Konno, Juho, Wik, Christer, Mikulski, Maciej
CFD Modelling of an Asymmetric Hydrogen Injector Cap for Direct Injection Applications: Design Impact on Jets Structure and Momentum Flux2026-37-00116/9/2026
The adoption of hydrogen as a carbon-neutral sustainable fuel for internal combustion is regarded as a promising solution to reduce greenhouse gases and pollutant emissions. In this framework, the injection system plays a crucial role, being responsible for delivering a large amount of fuel to the combustion chamber. Currently, low-pressure direct injection is considered one of the best solutions to ensure the appropriate fuel delivery. The use of caps has proven particularly effective, as they enable a potentially unlimited range of geometries while minimizing modifications to the injector hardware. Experimental campaigns and computational fluid dynamics (CFD) simulations can be used together as complementary tools to speed up the development process and explore multiple combinations of parameters, thereby optimizing the overall design of both the engine and the caps. In the present paper, a single-hole GDI-derived hydrogen prototype injector equipped with a two-hole asymmetric cap and fed with hydrogen is analyzed through both experiments and CFD simulations under two different operating conditions in terms of rail pressure. Cap pressure, overall fuel instantaneous mass flow rate and hole-specific jet momentum have been measured during the experimental campaign. The resulting data were used as boundary conditions and as targets for the validation of steady-state CFD computations, where the same equipment has been simulated. In particular, the momentum flux produced by the two jets emerging from the forming cap was used to validate the numerical methodology against experimental outcomes. Moreover, the exact dimensions of cap holes have been taken by means of optical microscope and applied to the simulation to compare the real geometry against the nominal one. Therefore, the impact of the effective cap geometry is explored, evidencing a noticeable dependence specifically of the cap backpressure and therefore of the injection system performance on the details of the cap design.
Pavan, Nicolo, Breda, Sebastiano, Duni, Andrea, Martino, Manuel, Fontanesi, Stefano, Postrioti, Lucio
TOC99-08-02-0TOC4/13/2026
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Tobolski, Sue
Relative Knocking Intensity to Discuss Similarities and Differences between Low- and High-Speed Knocking Phenomena2026-01-03124/7/2026
Knock intensity, the maximum half-amplitude of pressure oscillation, reaches 1 MPa once in thousands of cycles under a certain boosted high-load condition at the engine speed of 5000 min-1, which is named high-speed super knock. In the present study, a mass-production turbo-charged direct-injection gasoline engine is operated for the indicated mean effective pressure of 1.7 MPa at the engine speed of 1500 to 5000 min-1. Unburned-zone autoignition timing is estimated using Livengood-Wu integral coupled with a small set of ignition delay time equations, which matches that detected from the differential value of net heat release rate, with a difference below 2 degrees in the whole range of engine speed. As unburned-zone autoignition timing advances, ignition delay time in an unburned zone at the autoignition timing shortens. Whenever autoignition occurs at 15 degrees after TDC, the ignition delay time is the period of about 10 degrees, regardless of engine speed. Knock intensity divided by the intensity of pressure oscillation induced by the main combustion, is named relative knock intensity. True heavy knock with an extremely-large relative knock intensity occurs occasionally at the low engine speed of 1500 to 2000 min-1, of which the occurrence rate decreases with the increase in engine speed. The high-speed super knock also has an extremely-large relative knock intensity, which might be a rare occurrence of the true heavy knock. A propagation flame front is visualized at autoignition timing using 20 ion probes mounted on the combustion chamber roof. When the high-speed super knock occurs, a relatively-large volume of unburned zone is located directly below the exhaust valves. However, no remarkable autoigniton heat release is observed.
Zeng, Changzhi, Kuboyama, Tatsuya, Yatsufusa, Tomoaki, Okuyama, Shota, Kuwahara, Kazunari
Persistent Elevated Soot Emissions Induced by Clustered Stochastic Preignition Events2026-01-03144/7/2026
Stochastic Preignition (SPI) is an abnormal combustion phenomenon that can occur in spark-ignition engines particularly under high-load operation. SPI is characterized by uncontrolled initiation of combustion prior to spark discharge, an abnormal combustion process that can lead to severe knock events and significant engine damage. SPI has been associated with fuel properties, lubricant composition, and engine design and operation. In this work, a single-cylinder test engine with a dry-sump oil system was utilized to study the SPI response of E10 and E25 fuels with a range of Reid Vapor Pressure (RVP). An automated test procedure was employed, consisting of ten square-waved load profile segments, with each segment composed of 5 min of low-load operation followed by 25 min of sustained high-load operation. These tests were replicated across multiple days of testing including a lubricant triple flush between tests, and an online Fuel in Oil diagnostic measurement. Exhaust particulate emissions were continuously measured by an AVL microsoot sensor (MSS). Elevated particulate matter emissions were observed to occur concurrently with SPI events as blooms of soot. Particularly after clustered events (i.e., multiple SPI cycles occurring within 10 consecutive engine cycles), high soot emissions were observed to persist over several days of sequential operation despite daily lubricant changes, a complete warm-up procedure, and sustained low-load operation between test segments. This result implies that the particulate emissions trends may be dominated by deposit-based effects, where higher load operation is needed to alter deposition and formation processes. The observed soot blooms were also found to correspond to a reduction in the engine fueling and the fuel engine oil dilution rate despite the engine exhaust remaining at stoichiometric exhaust operation. These observations suggest that post-SPI events, pathways for lubricant migration and consumption into the combustion chamber may occur until these pathways are closed from deposit formation or ring dynamics during extended operation. These observed sooting propensity persisted with all fuels tests, but a linear correlation was observed between the summation of soot and particulate matter index (PMI) value for each fuel as well as SPI events, proving that PMI is a crucial fuel property for reducing SPI.1
Splitter, Derek, Jatana, Gurneesh, DelVescovo, Dan, Douvry-Rabjeau, Julien, Fioroni, Gina, Chapman, Elana, Salyers, John
Physics-Based Simulation for Sustainable Fuels Part 1: Simulation-Driven Hydrogen Engine Power Cylinder Unit Optimization and Experimental Confirmation2026-01-02784/7/2026
The demand for sustainable mobility and transportation is accelerating the adoption of alternative fuels, particularly hydrogen, in internal combustion engines. However, these engines present specific risks, such as flammable crankcase gas accumulation from blow-by and irregular combustion resulting from oil transport into the combustion chamber. Addressing these challenges requires advanced simulation tools to optimize power-cylinder-unit performance, specifically piston ring and gas dynamics. This study demonstrates the success of physics-based 2D simulation for hydrogen PCU design optimization, focusing on blow-by reduction and control of gas-flow-driven oil transport. Unlike commercial codes with adjustment and fitting parameters, the 2D simulation code – developed by Massachusetts Institute of Technology and successfully applied by MAHLE over decades – is fundamentally physics-based, enabling direct predictive capability without empirical calibration. Leveraging the validated “Healthy PCU System” design methodology 2D ring and gas dynamics models guided component optimization across the entire operating map. Comprehensive engine testing on a hydrogen-fueled platform confirmed simulation predictions, achieving a 28% reduction in blow-by and elimination of reverse-flow-driven oil transport. The optimized PCU design demonstrated significant improvements in lube oil consumption, with reductions of 5 g/h during high-load operations directly addressing hydrogen engine safety and performance requirements. While 2D simulation delivers excellent trend accuracy and captures average system behavior, it cannot resolve three-dimensional effects - such as ring and bore distortion conformability or ring gap positioning and ring rotation phenomena – which are responsible for local oil emissions or irregular combustion. Complementary 3D simulation analysis, combined with detailed inter-ring pressure measurements, provides essential insights into these localized phenomena and real engine behavior, as demonstrated in Part 2 of this publication series. As a further step, 3D oil transport simulation and lube oil consumption range prediction will be conducted as Part 3 of this publication series. This publication series establishes 2D simulation as the essential, computationally efficient tool for precise and efficient PCU development, while confirming that 3D analysis and experimental inter-ring pressure measurements are necessary to fully understand complex ring-liner interactions across multiple engine platforms.
Köser, Philipp, Moreira, Rui, Deuß, Thomas, Morgado, Leonardo
Ultra-Low NOx Technologies for Heavy-Duty Applications with Reduced Total Cost of Ownership2026-01-02944/7/2026
The utilization of gasoline engines in heavy-duty vehicles for the purpose of continental transportation is in direct competition with conventional diesel engines. It’s imperative that the operating performance of the gasoline engine is equivalent to the diesel engine, and that the gasoline engine shows efficiency benefit to both cost segments, the product manufacturing costs and total cost of ownership (TCO). The 11.6-liter gasoline engine developed has been designed and applicated in such a way that it operates at a stoichiometric combustion air ratio (λ = 1) across the entire engine map range without exception. In combination with external exhaust gas recirculation (EGR) this strategy does not result in a substantial decrease in the absolute NOx concentration in raw emissions compared to the diesel engine with 15.0-liter displacement, but it facilitates the cost-efficient utilization of the three-way catalyzer as the main exhaust aftertreatment system, thereby reducing NOx emissions to the detection limit. This reduction is necessary for adherence to the stringent future emission standards for heavy trucks that are being established by the U.S. regulatory authorities (EPA; CARB) for model years commencing in 2027. In addition to the stoichiometric operating strategy, the engine features an innovative combustion chamber geometry, including a high compression ratio, high EGR compatibility within the real engine operating range, and an optimized crankshaft drive. This already tested technology package is now being applied to heavy-duty engines, proving its scalability and effectiveness. Its application to heavy-duty engines not only promises significant production cost savings but also ensures compliance with future emission regulations. By integrating high EGR rates and high compression ratio, the engine achieves optimal combustion efficiency, thereby minimizing emissions without compromising performance. The engine efficiency is demonstrated by its brake thermal efficiency of 43.1% and an extended map range with a specific consumption of less than 200 g/kWh. In a real heavy-duty driving cycle, the average consumption is 228 g/kWh (vs. 217.5 g/kWh), resulting in a significant reduction in total operating costs on the American market using gasoline as fuel.
Medicke, Mario, Arnold, Thomas, Bohme, Jan, Krause, Matthias, Leesch, Mirko
Optimal Strategies for SI H2 Combustion System and Pre-Ignition Investigation through Advanced Optical Techniques2026-01-03244/7/2026
The rapidly transforming mobility sector is confronted with a dual challenge: achieving market expansion while significantly reducing emissions. Even if vehicle electrification tends to be favored in developed nations, it is widely acknowledged that no single solution is universally optimal. Within this context, hydrogen emerges as a compelling energy vector. It can be used both in fuel cells and internal combustion engines. This latter benefits from a well-known architecture and existing production infrastructures constituting a viable short-term and cost-effective solution especially for light or heavy-duty and off-road applications. In this context, investigation on the hydrogen spark-ignited internal combustion engine was performed, focusing especially on critical abnormal combustions. Indeed, during early development phase, abnormal combustion management was a challenge requiring the identification of the root cause of these issues. This work, based on the use of a versatile single-cylinder engine, is dedicated to the optimization of hydrogen combustion through adaptations of injection strategy to minimize the NOx production and improve the combustion efficiency. A dedicated attention was paid to study the effects of different parameters of the hydrogen injection system, such as the location of the injector, the targeting and the injection pressure. Subsequently, a specific cylinder head has been designed to allow endoscopic optical access into the combustion chamber for a visualization of the combustion related phenomena using a high-speed UV intensified camera. The work was especially focused on abnormal combustion analysis such as pre-ignition and allows to analyze the behavior of different spark plugs. Different injection configurations were tested and their effects on combustion were evaluated using both adiabatic heat release rate analysis and in-cylinder movies obtained through the optical setup described above. It provides valuable data about mixture preparation, flame propagation and cycle to cycle fluctuations. Conventional heat release rate analysis gives macro level data of the combustion stroke whereas the endoscopic images provide 2D flame fields that enhance the understanding of the combustion characteristics. This work finally leads to a better understanding of abnormal combustion occurrences and guides towards the choice of relevant injection and ignition strategies, especially at full load.
Londos, Benoit, Bardi, Michele, Serrano, David, Laget, Olivier, Gautrot, Xavier, Bramoullé, Clément, Cordier, Matthieu
Experimental 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
Accelerated Computed Tomography for Spray Characterization2026-01-03414/7/2026
Computed tomography (CT) is a valuable diagnostic technique for visualizing spray plume direction and assessing mixture quality within combustion chambers under engine-relevant conditions. High-speed extinction imaging followed by tomographic reconstruction enables temporally and spatially resolved measurements of liquid volume fraction and plume evolution in multi-plume sprays. Traditionally, tomographic reconstruction requires capturing multiple angular views by rotating the injector and averaging over numerous injections to ensure statistical convergence. This process is time-intensive, particularly due to the large volume of data acquisition and the corresponding delays in data saving, particularly when acquiring many injections per view angle. In this study, we investigate the minimum number of injections required to achieve sufficient CT image quality, thereby significantly reducing experimental time. Two injectors are evaluated: a symmetric 8-hole Spray M injector from the Engine Combustion Network (ECN), and an asymmetric 6-hole injector (THN206) designed for lateral mounting in the cylinder. For Spray M injector, methanol is injected at ambient temperature (20°C) and a backpressure of 0.5 bar. For the asymmetric THN206 injector, the methanol injection is performed at 60°C with a backpressure of 1 bar. In both cases, the injection pressure is 200 bar and 73 different viewing angle are acquired. We analyze how the number of averaged shots influences the convergence of optical thickness and the resulting CT image quality. Key metrics include optical density shot-to-shot variation, centerline profiles and plume direction angles. By comparing these parameters across both injector configurations, we identify an optimized injection count for rapid tomographic imaging. Our results demonstrate that using a two-shot strategy can reduce the total acquisition time by 86% compared to the previous 27-shot averaging approach, while maintaining 3D tomographic image quality sufficient for comparisons to computational fluid dynamic predictions of plume direction, growth, and interaction. These findings highlight the potential for broader and more accessible application of fast CT techniques in spray characterization, without the need for excessive experimental resources.
Yi, Junghwa, Wan, Kevin, Pickett, Lyle
Challenges to Ranking Diesel Fuels for NO x Emissions Using a Constant-Volume Combustion Chamber2026-01-03484/7/2026
The market is witnessing an unprecedented proliferation of low-emission fuel components. To effectively evaluate the suitability of these novel fuels for engine applications, fuel blenders and original equipment manufacturers require rapid and reliable assessment methodologies. Traditionally, such evaluations rely on comprehensive engine testing, which, while thorough, is both time-intensive and costly. In response to the growing diversity of emerging fuel options, this work aims to establish a streamlined screening approach capable of effectively replicating the outcomes of full-scale engine testing. We examined the use of a constant volume combustion chamber for the measurement of fuel effects on NOx emissions, with the goal of developing a method to rapidly screen or rank fuels in a small - volume experiment. A small amount of fuel was injected into air at 650°C and 20 bar, where it ignited and burned. The chamber was sampled post-combustion using a chemiluminescence NOx analyzer. Extensive sampling method development was required to obtain repeatable results. Seven hydrocarbon fuels and two biodiesel fuels were tested, all of which have shown difference in NOx emissions in past engine studies. When using a single injection event to deliver the same amount of fuel energy, the test method could not clearly demonstrate the difference in NOx emissions between the hydrocarbon fuels as reported in engine combustion studies. Heat release rate analysis suggested this was caused by large differences in ignition delay and premixed burn fraction for the fuels tested. To improve this, a dual-injection strategy was used. It included a small “pilot” injection followed by a main injection, timed based on each fuel’s ignition delay to coincide with the pilot heat release. This strategy helped reduce differences in heat release caused by how quickly each fuel ignites. For hydrocarbon fuels, this approach revealed the expected relationship between NOx emissions and fuel type. Two soy biodiesel samples did not show higher NOx as observed in engine studies. This suggests that the current test method may not fully reflect engine conditions where biodiesel tends to produce more NOx. Further improvements in test method and setup are recommended to better align constant volume chamber conditions with engine conditions under which biodiesel shows increased NOx emissions.
Luecke, Jon, Rahimi, Mohammad, Mohamed, Samah, Naser, Nimal, Chausalkar, Abhijeet, McCormick, Robert
Flame Velocity and Combustion Behaviour of Ammonia–Hydrogen Blends: A Combined Experimental and Numerical Study2026-01-03204/7/2026
Ammonia is emerging as a promising energy vector for decarbonising the maritime sector. However, its low flame speed can lead to incomplete combustion, reduced engine efficiency, and increased emissions of unburned ammonia (NH3). Blending hydrogen with ammonia helps to address these issues, but the fundamental combustion characteristics of such mixtures remain insufficiently understood. This study examines the combustion dynamics of an NH3–H2 blend containing 30% hydrogen at 3 bar initial pressure. Experiments were performed in a 1.2 L optically accessible constant-volume combustion chamber fitted with a wall-mounted surface spark plug. High-speed shadowgraph imaging with 6,000 fps captured the flame evolution throughout the combustion process. The pressure and temperature values were monitored using piezoresistive pressure transducers and K-type thermocouples. Combustion times and flame extensions were extracted via post-processing of flame images using custom MATLAB algorithms. The combustion process was examined from the initial start to a diameter of 60mm. Complementary CFD simulations were carried out in CONVERGE using the C3MechV3.5 chemical mechanism. To match the experimental conditions, the numerical studies were conducted at an ambient pressure of 0.3 MPa and an equivalence ratio of 1.0. The model predicted flame propagation times accurately, achieving an average relative error of 2.95% and an R2 value of 0.991. A third-order polynomial correlation was derived to predict instantaneous flame diameter as a function of time, enabling interpolation for intermediate combustion stages for both simulation and experimental results. Error analysis indicated that the model achieved its best performance for medium-sized flames (30–45 mm) but exhibited larger discrepancies at the smallest and largest diameters. Nevertheless, within the 20–60 mm range, deviations remained between −9.5% and +3.4%.
Bodur, Tuna Murat, Bowling, William, La Rocca, Antonino, Cairns, Alasdair
Investigation of CDI and TCI Ignition Characteristics for Lean Hydrogen-Air Mixtures in a Constant Volume Combustion Chamber2026-01-03274/7/2026
The discharge characteristics of ignition systems critically influence flame kernel formation and ignition stability under lean-burn conditions. This study experimentally compares a transistor coil ignition (TCI) and a capacitor discharge ignition (CDI) system in a constant-volume combustion chamber using hydrogen–air mixtures. The electrical behavior of both systems was first characterized through synchronized measurements of voltage, current, and high-speed imaging under various operating conditions with a resistive spark plug. The CDI system exhibited high-current (≈750 mA), short-duration (≈250 μs) discharges with strong instantaneous power but limited total spark-gap energy (≈5 mJ), while the TCI system produced lower-current, longer-duration (≈3 ms) discharges with higher cumulative energy (≈30 mJ). Flow-field tests revealed that the TCI discharge duration and energy release were strongly influenced by airflow, whereas CDI discharge behavior remained largely unchanged at flow velocities around 20 m/s. Ignition experiments with lean H₂–air mixtures (λ = 2.5–4.0) demonstrated that both systems can reliably ignite the mixture under quiescent and moderate-flow conditions, but the CDI system failed to sustain ignition near the lean limit. The results highlight the distinct energy-transfer mechanisms of the two ignition concepts and provide guidance for optimizing ignition design in future hydrogen internal combustion engines.
Cong, Binghao, Jin, Long, Yu, Xiao, Zhou, Qing, Tjong, Jimi, Zheng, Ming
The Membrane Engine: Concept, Model, and First Results03-19-01-00032/12/2026
This study investigates the feasibility of a novel internal combustion engine (ICE) architecture, termed the membrane engine, in which the conventional piston is replaced by a flexible elastic membrane. Although the concept appears in several patent documents proposing reduced friction, improved sealing, and lower heat losses, no empirical data has been published to support these claims. To the authors’ knowledge, this work presents the first membrane engine built and experimentally tested. The primary aim is to verify whether such an engine can operate as a functional ICE, regardless of its current efficiency or performance level. To support concept validation, a simplified mathematical model was developed to describe the membrane’s deformation and its effect on combustion chamber volume. Unlike conventional piston engines, the membrane introduces a pressure-dependent geometry, enabling a variable compression ratio. The model is not intended to predict performance but to assist in interpreting experimental results and assessing feasibility. It combines geometric and pressure-induced volume changes and was constructed conservatively to avoid overestimating deformation effects. A single-cylinder spark-ignition prototype was built by modifying an existing piston engine. Experimental tests were conducted under motored and fired conditions, with comparative measurements taken against the unmodified engine. Results confirmed that the membrane engine can sustain combustion and produce torque. Notably, the exhaust stroke exhibited a steeper pressure drop, suggesting improved scavenging, and the torque trace showed a distinct positive spike post-combustion. These findings support the hypothesis that the membrane’s dynamic behavior influences combustion and gas exchange. While some patent claims remain unverified, the study demonstrates that the membrane engine is a viable concept. The results provide a foundation for further development and refinement, including material selection and advanced modeling. Future work will focus on improving durability, expanding the operating envelope, and exploring hybrid configurations for waste heat recovery.
Allmägi, Roland, Ilves, Risto
Experimental Study of Entrainment by Hydrogen-Like Impinging Jets of Various Types in a Confined Compartment03-19-01-00062/9/2026
Recent literature has highlighted significant heat transfer losses and elevated particle formation in direct-injection hydrogen engines, particularly when compared to hydrocarbon fuels such as methane. These challenges are attributed to hydrogen’s unique physicochemical properties, notably its short flame quenching distance and high diffusivity, as well as the interaction between the hydrogen jet and lubricated cylinder surfaces, which promotes lubricant entrainment into the combustion chamber. Consequently, a fundamental understanding of these entrainment mechanisms is a prerequisite for developing engineering strategies to enhance thermal efficiency and mitigate particle formation. The reported study investigates gaseous jet–air interaction in a confined volume to elucidate the influence of injector geometry on jet propagation and air entrainment. Three distinct jet configurations were examined: the wide hollow-cone, the narrow hollow-cone, and the round jets. The jet evolution and propagation were recorded using the Schlieren optical imaging technique for various pressure ratio values. The results indicate that for the wide hollow-cone jet, impingement on the vertical wall of the confined space is decoupled from horizontal surface impingement. Furthermore, this configuration yields a higher total entrained mass compared to narrow hollow-cone and round jets, under identical injected mass and pressure ratios. A notable finding is the inverse correlation between injection pressure and entrained volume for a fixed injected mass. Consequently, this study proposes new quantitative metrics for evaluating mixture preparation in direct-injection internal combustion engines.
Ben David Holtzer, Ben Binyamin, Tartakovsky, Leonid
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
Unveiling the Dynamics of Methanol-Diesel Dual Direct Injection Compression Ignition Combustion: A Synergistic Experimental and Numerical Study2026-26-01101/16/2026
The pressing global need for de-fossilization of the transport sector, especially within the heavy-duty segment, has intensified the exploration of alternative clean fuels. In this context, methanol gained traction due to their renewable production pathways, carbon-neutrality, and are being highly promoted by the Indian government to reduce CO2 emissions. Dual direct injection compression ignition (DDICI) is an effective combustion strategy to use methanol in heavy-duty engines, which combines the advantage of high-efficiency compression ignition with the clean-burning potential of methanol. In contrast to spark-ignited premixed methanol engines, this strategy involves a diffusion combustion of the methanol flame, thereby eliminating knocking and enabling running with high compression ratios. This experimental and numerical study presents a comprehensive investigation into the DDICI strategy using methanol as primary fuel and diesel as a pilot for ignition assistance. The work benchmarks the methanol DDICI operation against baseline diesel operation, catering the required combustion chamber modifications, fuel injection strategy, system layout and capturing key metrics like thermal efficiency and emissions. The numerical study details the effect of swirl spray orientation, and positioning of the pilot injector, on the charge distribution and the ignition. The 3D-CFD models used for the simulation model are well validated against experimental results to capture in-cylinder combustion dynamics and emission trends. The experimental results demonstrate that methanol DDICI achieves a thermal efficiency improvement of up to 2.5-3.0 % at high load with NOx reduction of about 50 % at similar exhaust gas recirculation (EGR) ratio compared to the baseline diesel. Additionally, it demonstrated soot-free combustion and lower in-cylinder temperatures reducing thermal stresses. The introduction of swirl led to improved mixture formation, promoted gradual ignition and enhanced post-flame oxidation, thereby reducing CO emissions. Furthermore, the simulation results revealed that the reduced spatial separation between diesel and methanol spray plume facilitates faster ignition and smoother combustion. In this regard, the stagger angle of 12.5° with 9-hole nozzle resulted in lower maximum pressure rise rate compared to 22.5°, with similar levels of thermal efficiency and NOx emissions.
Singh, Inderpal, Dhongde, Avnish, Raut, Ankit, Güdden, Arne, Emran, Ashraf, Berry, Sushil
Evaluation of Intercooler Effectiveness with No Fan, Single Fan, and Dual Fan: A Simulation and Experimental Study2026-26-05791/16/2026
Turbochargers play a crucial role in modern engines by increasing power output and fuel efficiency through intake air compression, thereby improving volumetric efficiency by allowing more air mass into the combustion chamber. However, this process also raises the intake air temperature, which can reduce charge density, lead to detonation, and create emissions challenges—such as smoke limits in diesel engines and knock in gasoline spark-ignited (GSL) engines. To mitigate this, intercoolers are used to cool the compressed air. Due to packaging constraints, intercoolers are typically long and boxy, limiting their effectiveness, especially at low vehicle speeds where ram air flow is minimal. This study investigates the use of auxiliary fans to enhance intercooler performance. Two methodologies were adopted: 1D simulation using GT-Suite and experimental testing on a vehicle under different fan configurations—no fan, single fan, and dual fans (positioned near the intercooler inlet and outlet). Results indicated that auxiliary fans significantly enhance heat transfer at low speeds, with dual fans offering the highest improvement—up to 8–13% greater efficiency during hill climb conditions compared to no fan. At high speeds, benefits were negligible (<1%) due to sufficient natural airflow. These results support the application of intercooler fans for improved thermal management under low-speed, high-load conditions.
Patra, Somnath, Hibare, Nikhil, Ganesan, Thanigaivel, Gharte, Jignesh Rajendra
Improving Cold Start and Transient Performance of Medium BMEP CEV Stage V Engines at Low Ambient Temperature and Pressure2026-26-01421/16/2026
Meeting the stringent emissions norms of CEV stage V for medium BMEP engines, CI engines present significant challenges, particularly concerning cold startability. Low ambient temperatures and pressures intensify the cold start difficulties which are characterized by prolonged cranking, incidences of misfiring, compromised transient response and overall engine performance. This paper highlights the strategies and technologies employed to enhance cold start and transient performance of medium BMEP engines under such demanding environmental conditions. Investigations were conducted up to an altitude of 4500m and ambient temperatures as low as-20°C, utilizing only air heater at intake manifold as the sole cold start aid. This cost effective approach is integrated with an optimized combustion chamber design, along with minimal pilot injection timing and quantity to facilitate smooth ignition and stable combustion during cold start. The paper also explore the techniques to improve the engine transient response, minimize smoke and PM emissions during speed and load changes under these extreme environmental conditions, such as turbocharger response, fuel delivery control, and dynamic injection timing and rail pressure adjustments.
Saxena, Harshit, Lokare, Prasad, Santhosh, Ajith, Gandhi, Naresh, Shinde, Prashant
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
Methodology for Characterizing the Spray of an Internal Combustion Engine Fuel Injector2025-36-019412/18/2025
This study presents a methodology for characterizing the spray of an internal combustion engine (ICE) fuel injector, focusing on direct injection (DI) systems. It addresses the knowledge gap in academic research regarding injector spray patterns by conducting experimental tests and numerical simulations. Using a Bosch HDEV 1.1 pressure swirl injector and EXXSOL D60 test fluid, spray characteristics were captured with a high-speed camera under varying injection pressures and ambient/counterpressure conditions. These experimental data were used to calibrate a numerical model for simulating spray dynamics within the combustion chamber. The research examines the impact of parameters such as breakup length and breakup size constant on spray behavior, revealing that the breakup size constant significantly affects spray penetration. The study successfully developed and validated a methodology for characterizing and modeling fuel injector sprays, providing a valuable reference for optimizing future ICE fuel pattern designs and contributing to enhanced combustion performance and compliance with emission standards.
Paula Araújo, Gabriel Heleno, Assis, Marcelo Suman Silva, Malaquias, Augusto Cesar Teixeira, Carvalho Torres Filho, Marcos, Baeta, José Guilherme Coelho
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
Combustion Chamber Pressure and Temperature Analysis Based on Heat Release Rate Parameters of a Spark Ignition Engine2025-36-008212/18/2025
Internal combustion engines have been developed and widely used since the last century, and they continue to be extensively employed today. Engine development has progressed significantly, and due to the environmental impacts caused by their use, new technologies are being developed to reduce pollutant formation after the combustion process and to increase thermal efficiency. Computational modeling is a tool that has supported this development and can be categorized into three types: zero-dimensional, quasi-dimensional, and three-dimensional models. The 0D and 1D models offer a good balance between computational processing time and result uncertainty when compared to three-dimensional models. The Wiebe function is a simple analytical approach capable of describing the fuel burn rate in combustion engines. Previous studies have shown that applying this function yields results that accurately describe the apparent heat release rate in PFI engines.The present study aims to determine the pressure curve using the Wiebe function and the heat release rate theory developed by Heywood. The tests were conducted on a four-cylinder spark-ignition engine fueled with regular type C gasoline, operating under two different torque conditions. Based on the proposed model, the temperature gradient during the combustion process was obtained. Tools capable of measuring in-cylinder pressure and temperature are robust but have high operational costs; therefore, predictive models can significantly reduce expenses associated with such measurements. The results were compared with data collected from bench dynamometer tests for validation.
Souza Pereira, Felipe Augusto de, Araújo Moreira, Thiago Augusto de, Filho, Fernando Antônio Rodrigues
The Technological Concept of a Self-Adjusting Segmented Ceramic Sealing System for a Turboshaft Engine with Isochoric Combustion03-18-08-004612/8/2025
The article presents self-adjusting segmented ceramic seals designed for a novel turboshaft engine operating according to the Humphrey thermodynamic cycle. The sealing system is an integral part of the developed engine concept, which features rotating isochoric combustion chambers. The seals utilize centrifugal force as the sealing force, enabling uniform sealing regardless of thermal conditions and associated deformations. The sealing consists of segments with adjustable dimensions in both circumferential and transverse directions. The sealing elements should be made of Si3N4 ceramic, characterized by high thermal resistance (1300°C) and low thermal expansion (3.2•10−6/°C). The article presents three different variants of sealing systems, differing in terms of the technological possibilities of their manufacturing. Special treatments must be applied to ensure high machining accuracy of the sealing elements. The proposed sealing system is a critical point in the design of an engine with isochoric combustion chambers. Successful sealing is key to the implementation of the Humphreys thermodynamic cycle, which offers higher engine efficiency compared to classical turboshaft engines available on the market. The article concludes with the presentation of a model for experimental investigations, along with its thermal analysis.
Tarnawski, Piotr
Knock Phenomenon Investigation in SI Engine Fuelled with Ammonia-Hydrogen Mixture2025-01-053211/25/2025
Ammonia has emerged as a compelling carbon-free alternative fuel for applications in sectors such as power generation and heavy-duty transportation, where thermal energy conversion plays a dominant role. Its potential lies in its high hydrogen content, carbon-free combustion, and the feasibility of large-scale storage and transport. However, ammonia’s combustion behavior poses significant challenges due to its low reactivity, characterized by a low laminar burning velocity, high autoignition temperature, and narrow flammability range. These properties hinder stable and efficient operation in conventional internal combustion engines. A common strategy to mitigate these limitations involves blending ammonia with hydrogen—often generated via on-board catalytic cracking of ammonia—which improves ignition and flame speed. Despite these benefits, the presence of hydrogen increases the risk of knock, particularly in high-compression-ratio engines designed to improve thermal efficiency. This research focuses on evaluating knock phenomena associated with ammonia-hydrogen fuel blends in spark-ignition ICEs. First, a Methane Number was obtained for all ammonia-hydrogen blends to quantify the impact of hydrogen on ammonia knock reactivity under conditions close to those of the Motor Octane Number. The second part of this study explores the impact of knock for a fuel mixture consisting of 90% ammonia and 10% hydrogen by volume under varying engine parameters such as combustion chamber design and compression ratio on knock onset and severity. Experiments were conducted at engine speeds of 1000, 1500, and 2000 RPM, across intake pressures ranging from 1.0 to 1.8 bar (in 0.2 bar increments), equivalence ratios between 0.9 and 1.1, and intake temperatures of 60, 65, and 85°C. This study aims to identify the key parameters influencing knock intensity, onset, and distribution, as well as overall combustion properties.
Hurault, Florian, Brequigny, Pierre, Foucher, Fabrice, Rousselle, Christine
Ammonia Combustion with Active Pre-Chamber Spark Plug - a CO 2 -Free Combustion Process2025-01-052711/25/2025
As a zero-carbon fuel, ammonia has the potential to completely defossilize combustion engines. Due to the inert nitrogen present in the molecule, ammonia is difficult to ignite or burn. Even if the ammonia can be successfully ignited, combustion will be very slow and there is a risk of flame quenching, i.e. the flame going out before the ammonia-air mixture has been almost completely converted. Both the difficult flammability and the slow combustion result in high ammonia slip, which should be avoided at all costs. The engine efficiency is also greatly reduced. Safe ignition and burn-through can be achieved by drastically increasing the ignition energy and/or using a reaction accelerator such as hydrogen. The planned paper will use detailed 1D and 3D CFD calculations to show how high the potential of ammonia combustion in an internal combustion engine is when an active pre-chamber is used as the ignition system. As a result of the flame jets penetrating into the main combustion chamber filled with ammonia, this allows a so-called space ignition and a very high ignition energy to be achieved. The latter is particularly high if the fuel used in the pre-chamber is hydrogen, for example. As hydrogen can be obtained directly from the ammonia via an on-board cracker in the vehicle, this would be a single-fuel combustion process. The paper will focus on the potential how fast and save the combustion can be, what combustion efficiencies can be obtained and what amount of hydrogen is needed from the onboard cracker (operated with Waste heat from the exhaust system) to build a very stable and highly efficient ammonia-based passenger car combustion system.
Sens, Marc, von Roemer, Lorenz, Rieß, Michael, Fandakov, Alexander, Casal Kulzer, Andre
Investigation of Active Pre-Chamber Ignition on an Optically Accessible Ultra-Lean DI Hydrogen Engine2025-01-052411/25/2025
Hydrogen is a promising alternative to conventional fuels for decarbonizing the commercial vehicle sector due to its carbon-free nature. This study investigates the ignition and flame propagation characteristics of hydrogen in a 2-liter single-cylinder optical research engine representative of the commercial vehicle sector. The main objective was to enable high power density operation while minimizing NOx emissions. For that, ultra-lean combustion was employed to lower in-cylinder temperatures, addressing the challenge of NOx formation. To counteract delayed and unstable combustion under lean conditions, an active pre-chamber ignition system was implemented. It uses a gas-purged pre-chamber with separate hydrogen injection and spark plug ignition. Turbulent hot gas jets from the pre-chamber ignite the fresh mixture in the main combustion chamber, enabling faster and more stable ignition compared to conventional spark plugs. Additionally, the low volumetric energy density of hydrogen, which limits performance in port fuel injection due to air displacement, was addressed through direct hydrogen injection into the combustion chamber to increase the mixture heating value. High-speed imaging techniques, including Schlieren and OH chemiluminescence, were used alongside thermodynamic analysis to study combustion dynamics. Results demonstrate that the active pre-chamber ignition system achieved stable combustion at ultra-lean conditions (λ up to 4) without knocking phenomena. Essentially, NOx-free operation was possible for λ > 2.5. Pre-chamber conditions were found to influence performance trade-offs: richer mixtures enhanced stability and combustion speed, while leaner mixtures minimized NOx emissions. Comparative measurements with a standard spark plug showed that pre-chamber ignition leads to more stable and faster ignition, unlocking additional performance and efficiency potential. These findings demonstrate the viability of hydrogen as a carbon-neutral zero-emission fuel for commercial vehicle engines.
Borken, Philipp, Bill, Daniel, Link, Lukas, Dinkelacker, Friedrich, Hansen, Hauke
Sustainable Engines with Carbon-Neutral Fuels – Fast Adaptation for Efficient Multi-Fuel Operation by Tailored Charge Motion Design2025-01-053411/25/2025
As a fundamental element of measures to reduce the carbon footprint of commercial applications, carbon-neutral fuels are increasingly coming into focus for heavy installations. In addition to diesel substitute fuels, alternative energy carriers like NG, H2, MeOH and NH3 are gaining increasing attention. The energy conversion of these fuels is typically taking place on the principle of premixed combustion, which places different demands on fuel injection and mixture formation, as compared to optimized diesel-like combustion. Accordingly, the demand to layout multi-fuel capable engine designs centers to a high share on the above-mentioned design that can burn these different fuels with high efficiency and support a high degree of commonality with the in-series engine to carry over reliable operation and to maintain attractive cost figures. FEV has developed the Charge Motion Design (CMD) process, which can be applied to design the intake ports and combustion chambers for multi-fuel cylinder heads in the initial phase. This advanced methodology features the capabilities to predict the performance of different configurations for the various fuels based on condensed and simplified CFD simulations and dedicated post-processing routines. These correlations are tuned and calibrated to representative engine data for individual fuels to determine the characteristics. This paper highlights the detailed application of the CMD process for cylinder head and combustion chamber definition on the base of measurements on a state-of-the-art modular single-cylinder HD engine. Six configurations of the port designs and charge motion concepts were investigated. A comparison of the concepts was first performed with the CMD fuel correlations for H2. Three concepts with varying degrees of tumble were chosen for further detailing. The results of the case study are presented along with supporting engine measurements. In addition to previously tuned correlations, new measurements with NH3 were used to calibrate and synchronize the correlations of the CMD process. A dedicated variant of the DI H2 injection in addition to the ammonia port injection was investigated as well. The CMD fuel correlations were correlated to the testing data and later applied to all configurations to evaluate their performance and suitability. This technical study highlights the potential of CMD-driven design to enable flexible, efficient, and cost-effective multi-fuel combustion.
Koerfer, Thomas, Dhongde, Avnish, Boberic, Aleksandar, Zimmer, Pascal, Pischinger, Stefan
Optimization of Injection Parameters for a Free-Piston Engine Equipped with Flat-Head Combustion Chamber2025-01-507511/11/2025
The free-piston engine represents a paradigm shift in internal combustion engine technology, with its unique structure promising efficiency gains. However, injection parameters are one of the core elements of free-piston engine performance. This study employs computational fluid dynamics analysis to optimize the spray cone angle and start of injection timing for a two-stroke dual-piston opposed free-piston engine equipped with a flat-head combustion chamber. A three-dimensional transient model incorporating dynamic adaptive mesh refinement was constructed by using CONVERGE 3.0 software. The results indicate that a spray cone angle of 25° achieves optimal fuel distribution, yielding a peak indicated thermal efficiency of 42.14% and an indicated mean effective pressure of 9.08 bar. Crucially, advancing the ignition timing to 215°CA improves mixture homogeneity but simultaneously increases peak cylinder temperatures and NOx. Conversely, delayed start of injection timings reduces NO emissions by 58.6% at the expense of 8.2% indicated mean effective pressure. Comprehensive optimization shows that the combination of θ = 25° and SOI = 215°CA achieves 19.94 kW indicated power and 99% fuel evaporation, balancing performance and emissions. This study establishes a fundamental framework for optimizing injection parameters in combustion systems of free-piston engines, providing valuable reference for developing highly efficient, low-emission power systems in practical applications.
Xu, Zhaoping, Yang, Shenao, Liu, Liang
An Open-Source Solenoid Injector Driver Circuit for Fuel Injection Research03-18-07-004111/10/2025
Common rail, high-pressure electronic fuel injection is one of the primary technologies enabling high-efficiency and low emissions in modern diesel engines. Most fuel injectors utilize an actively controlled solenoid valve to actuate a needle that modulates the fuel supply into the combustion chamber. The electrical drive circuit for the injector requires extensive development costs, and thus, most designs are proprietary in nature, making it difficult to perform academic studies of the fuel injection processes. This research presents an injector driver circuit to control one or more solenoid injectors simultaneously for research-based injector development efforts. The electrical circuit was computationally modeled and optimized iteratively, and then, electronic hardware was developed to demonstrate control of a Bosch CRIN3 solenoid diesel injector as proof of concept. In addition, the injector performance was quantified by the fuel rate of injection (ROI) profiles obtained in a test rig utilizing the momentum flux method. Results show that the electronic control inputs do not affect the initial fuel ROI profile, which is impacted mainly by the injector geometry and associated fluid dynamics effects.
Bogdanowicz, Edward, Agrawal, Ajay, Lemmon, Andrew N., Bittle, Joshua
Effect of EGR and Ethanol additive on Performance and Emission Characteristics of Diesel Engine Fuelled with Rubber Seed Biodiesel Blends2025-28-022411/6/2025
Alcohol is being considered as an alternative to traditional fuels for compression ignition engines due to their oxygen content and biomass origin. Although alcohol generally has lower cetane numbers, which makes them more favorable for premixed combustion, they also offer potential for lowering emissions in internal combustion engines, particularly when combined with strategies such as exhaust gas recirculation (EGR). This research focuses on enhancing the performance of a single-cylinder, four- stroke diesel engine by introducing ethanol into the intake port during the intake phase. Diesel and rubber seed biodiesel were used as primary fuels and were directly injected into the combustion chamber. The findings indicated that adding ethanol to rubber seed biodiesel, along with 10% EGR, led to improved brake thermal efficiency and a reduction in NOX emissions. The ethanol injection timing and duration were optimized for effective dual-fuel operation. At full engine load, the highest brake thermal efficiency recorded with a 20% ethanol energy share was 34% for diesel, 31.16% for B20 with EGR, and 31.15% for B20 without EGR. Furthermore, NOX emissions were reduced by 25.44% and 26.08% for B10 with EGR and B20 with EGR, respectively, at peak thermal efficiency. On the downside, increasing ethanol contribution raised HC, CO₂, and smoke emissions across all loads for both B10 and B20 with EGR. Additionally, B10 and B20 with EGR experienced higher peak cylinder pressures and maximum rate of pressure rise, while ethanol uses also resulted in shorter combustion duration and increased heat release rates.
Saminathan, Sathiskumar, G, Manikandan, Bungag, Joel Quendangan, T, Karthi
Measurement of the Liquid Fuel Film on the Combustion Chamber Wall of a Gasoline Engine using a Novel Capacitive Sensor2025-32-001811/3/2025
The reduction of exhaust emissions and particulate matter from internal combustion engines remains a critical challenge, particularly under cold start and warm-up conditions, where a significant portion of total emissions is generated. In spark-ignition (SI) gasoline engines, the formation of liquid fuel films on intake ports wall, piston and cylinder wall surface significantly contributes to unburned hydrocarbon and particulate emissions. Also, the fuel film adhering to the wall can be a cause of the lubricating oil dilution. To address these issues, a novel capacitive sensor, fabricated using MEMS technology, was developed and applied to investigate the behavior of liquid fuel films formed inside the combustion chamber of a single-cylinder engine. The sensor detects changes in capacitance caused by fuel film adhesion to the sensor surface. The sensor was installed in a single-cylinder test engine along with a direct fuel injector allowing for the controlled formation of fuel films on the sensor surface. Ethanol was used as the injected fuel for film formation due to its higher permittivity compared to iso-octane, the fuel used for engine operation. This choice enhanced the sensor sensitivity to film presence. Four experimental configurations were tested, varying the sensor’s location (intake vs. exhaust side) and whether the ethanol spray directly impinged on the sensor. The engine was operated at 2000 rpm with an intake pressure of 90 kPa. The coolant temperature was varied from 20 °C to 80 °C to simulate cold start and warm-up conditions. The transition from motoring to firing operation was used to replicate transient startup behavior, and the sensor output was monitored cycle-by-cycle. Results showed that the sensor effectively captured the formation and evaporation of the fuel film. Sensor output was significantly higher at locations exposed to direct ethanol spray, particularly at lower coolant temperatures, indicating greater film accumulation. Conversely, positions shielded from the spray exhibited minimal signal variation. Additionally, sensors mounted on the exhaust side showed faster recovery to baseline values, attributed to higher wall temperatures promoting quicker evaporation. In conclusion, the developed capacitive sensor demonstrated high sensitivity and reliability in detecting in-cylinder fuel films under realistic engine conditions. Its compact design and ease of integration make it a promising diagnostic tool for studying fuel film dynamics in production engines.
Kuboyama, Tatsuya, Nakajima, Takeru, Moriyoshi, Yasuo, Takayama, Satoshi, Nakabeppu, Osamu
Development of Automatic Calibration System for PFI Engines2025-32-008411/3/2025
This report summarizes the research findings on fuel injection calibration methods, aiming to improve engine performance and reduce environmental impact. In Port Fuel Injection (PFI) engines, the injected fuel adheres to the port walls and mixes with air as it vaporizes, then flows into the combustion chamber. Traditionally, the fuel injection quantity is determined by the base map, which is calibrated for a steady state, and corrections for transient conditions. During steady-state operation, the air-fuel ratio of the mixture is uniquely determined by the amount of fuel injected, allowing for reproducible calibration. However, during transient conditions, the amount of fuel adhering to the walls and the amount vaporized do not balance, necessitating transient compensation to achieve the desired air-fuel ratio. Traditional transient compensation has been adapted for each engine model based on experience to accommodate differences in port shapes and injector placements. This approach has not always resulted in optimal calibration and often required significant time. To address this issue, a new transient compensation logic and an automated calibration system have been developed, enabling efficient and optimal calibration. The implementation of this system eliminates variations due to the skill level of the calibration engineer and reduces time requirements. Furthermore, optimal calibration contributes to improved engine performance and reduced environmental impact.
Haraguchi, Kazuki
Advanced Multi-Fidelity Simulation of Piston Oil Jet Cooling in High-Performance Engines2025-32-008111/3/2025
The development of next-generation hydrogen-fueled engines introduces critical challenges related to thermal loads within the combustion chamber, particularly in high-performance applications. To address the extreme temperatures encountered, effective piston cooling strategies, such as oil jet impingement, are essential. Accurately predicting thermal stresses to prevent component failure is therefore crucial. However, numerical simulations often come with significant computational costs. This paper presents a comprehensive multi-fidelity modeling approach to predict the thermal behavior of pistons under these demanding conditions. The model integrates a simplified 3D thermal representation of the piston, a lumped-parameter mechanical model of the piston-liner assembly, and convective boundary conditions obtained at various levels of fidelity, from high-level Computational Fluid Dynamics (CFD) simulations to literature correlations. Additionally, the study examines the influence of different approaches to defining boundary conditions on the model’s predictive capability. Calibration of the model was achieved using experimental temperature measurements obtained by sampling residual surface hardness at 8 points on the piston crown after prolonged stationary operation at maximum power in a conventional naturally aspirated high-performance gasoline engine test case. The results demonstrate a strong correlation between experimental data and numerical predictions, validating the model's accuracy. Additionally, the study investigates the influence of piston crown thickness and the positioning of the cooling oil injection point on the maximum temperatures reached during operation. Findings reveal the critical role of both geometric design and cooling strategies in optimizing thermal performance. This work provides a robust, flexible, and affordable simulation framework for evaluating piston thermal behavior, contributing to the design of reliable engines capable of withstanding extreme thermal conditions.
Sassoli, Andrea, Romani, Luca, Ferrara, Giovanni, Paolicelli, Giovanni, Balduzzi, Francesco
Investigating the Influence of Intake Runner Configuration on Scavenging and Combustion Processes in Elliptical Rotor Engines2025-32-008911/3/2025
Elliptical rotor engines (ERE), also known as X-engines, feature intake and exhaust ports located on the rotating rotor. As the rotor turns, these ports traverse the entire combustion chamber, sequentially completing the scavenging process in three distinct combustion chambers through coordination with the cylinder walls. This intake and exhaust characteristic significantly differs from the characteristic found in traditional Wankel rotor engines. This study established an optical elliptical rotor engine to obtain the in-cylinder flow field by using Particle Image Velocimetry (PIV) and constructed a CFD model based on the experimental results. Then the effects of two different intake runners on the scavenging and combustion process of ERE were investigated. The results indicated that: Due to structural limitations, the prolonged intake port opening duration results in significant gas backflow during the intake process. The curved intake runner exhibits a higher turbulent kinetic energy (TKE), while the straight intake runner achieves faster intake velocity. At engine speeds of 3000 r/min, 5000 r/min, and 9000 r/min, the straight intake runner improved volumetric efficiency by 2.6%, 4.6%, and 22.8% compared to the curved intake. At low speed, the curved intake runner demonstrates superior maximum cylinder pressure and combustion performance due to its faster flame propagation speed. However, at high engine speed, the influence of intake runner on the in-cylinder flow field diminishes. The straight intake runner’s higher volumetric efficiency compensates for its slower flame propagation speed, resulting in better cylinder pressure and combustion parameters compared to the curved intake runner.
Qin, Jing, Wang, Yingbo, Pei, Yiqiang, Yao, Dasuo, Deng, Xiwen
Effect of Plasma-Assisted Ignition on Combustion and Emission Characteristics of Two Stroke Engines with Different Fuels2025-32-003011/3/2025
This study explores the effect of plasma-assisted ignition (PAI) on combustion stability and emissions in two-stroke spark-ignition engines. Two engine platforms were evaluated: a conventional single-cylinder two-stroke engine and a thermodynamically advanced opposed-piston two-stroke (OP2S) engine. The OP2S engine configuration offers reduced heat loss and higher power density due to its uniflow scavenging and favorable geometry, but suffers from high residual gas fraction, which increases ignition difficulty and combustion instability. To address this, nanosecond-pulsed PAI was applied in various spatial arrangements and discharge voltages, using both gasoline and a low-reactivity gasoline/DMC blend fuel. Spark ignition timing was held constant at the minimum advance for best torque across all tests. Combustion stability was assessed via indicated mean effective pressure (IMEP) and its coefficient of variation, while CO and HC emissions were measured as environmental indicators. Results show that PAI significantly enhanced ignition stability, reducing COVIMEP by up to 84% and HC emissions by up to 24%, depending on fuel and engine type. The OP2S engine showed greater responsiveness to ignition configuration and plasma positioning due to its uniflow scavenging method. These findings confirm that PAI is a promising strategy for improving ignition robustness and emission performance in both conventional and advanced two-stroke engine architectures.
Liu, Jinru, Yamazaki, Yoshiaki, Otaki, Yusuke, Kato, Hayato, Kobayashi, Daichi, Umegaki, Tetsuo, Asai, Tomohiko, Iijima, Akira
Numerical Analysis of Combustion Stability and Efficiency Improvement in Ammonia Engine Utilizing Passive Turbulent Jet Ignition (PTJI)2025-32-004911/3/2025
Ammonia, a carbon-neutral fuel, is a promising candidate for next-generation engine applications. However, its low flame speed (~7cm/s) and prolonged ignition delay (~10ms at stoichiometric conditions) impose significant challenges in achieving stable and efficient combustion across varying operating conditions. At high-speeds, incomplete combustion due to limited residence time reduces efficiency, while at low-speeds, ignition instability and low combustion temperatures hinder reliable operation. To address these challenges, the Passive Turbulent Jet Ignition (PTJI) system has been proposed to enhance turbulence-driven mixing and improve ignition characteristics. This study focuses on optimizing a PTJI system for ammonia-fueled engines using a three-phase methodology. First, the 800cc 2-cylinder gasoline engine was modified for ammonia using numerical analysis, and a baseline analysis of the combustion characteristics was conducted. Next, a turbulent intensity study within the PTJI system was performed to determine an optimal configuration for stable combustion. Results show that PTJI increased turbulent intensity by up to 120% compared to conventional spark ignition, enhancing flame propagation and reducing ignition delay. Finally, PTJI effectiveness was evaluated under both high-speed and low-speed conditions. At 2000rpm, PTJI increased combustion temperature by ~150K, improving ignition stability and reducing cycle-to-cycle variations, thereby improving the convergence of the analysis. At 3000rpm, PTJI accelerated flame propagation speed by ~50%, facilitating complete fuel-air mixture combustion and enhancing thermal efficiency. In conclusion, this research demonstrates that PTJI is a viable solution for overcoming the inherent limitations of ammonia combustion. By increasing turbulence intensity and improving flame propagation, PTJI enables more stable and efficient ammonia engine operation, offering a promising approach for future carbon-neutral powertrains.
Ju, Kangmin, Kang, Hyun-Ung, Kim, Jeong Hyeon
Full-Cycle CFD Modeling of a Wankel Engine for UAV Applications Tommaso Lucchini, Federico Ramognino, Giovanni Gaetano Gianetti2025-32-001311/3/2025
Rotary engines offer a highly attractive solution for uncrewed aerial vehicles (UAVs) and portable power generation, thanks to their compact design, high power-to-weight ratio, fewer moving parts, and ability to operate on multiple fuels. Despite their promising advantages, these engines still require significant improvements to match the efficiency and lifespan of traditional reciprocating internal combustion engines. In particular, fuel consumption is impacted by heat losses due to the high surface-to-volume ratio of the combustion chamber, as well as the unfavorable interaction between the rotor and stator, which slows down flame propagation. To address these challenges, computational fluid dynamics (CFD) has become an important tool for the study and optimization of Wankel engines, providing insight into how fuel efficiency is influenced by the complex interactions between combustion chamber design, flame dynamics, flow characteristics, and turbulence distribution. This work presents a CFD methodology for simulating gas exchange and combustion in Wankel engines. The proposed approach considers the contemporary operation of the three working chambers whose mesh is deformed and dynamically connected with the intake and exhaust ports. A flamelet model predicts the premixed combustion process. The proposed methodology has been validated under operating conditions representative of UAV applications, involving constant-speed operation with variable loads to mimic different altitudes. Results from CFD simulations were compared against experimental data, including in-cylinder pressure and heat release rate, as well as 1D engine simulation data to analyze the gas exchange processes. The findings demonstrate that this CFD-based approach can be applied to design and optimization of Wankel engines, offering high accuracy at a reduced computational cost.
Lucchini, Tommaso, Gianetti, Giovanni, Ramognino, Federico, Cerri, Tarcisio, Marmorini, Luca, Buttitta, Marco
Effect of In-Cylinder Hydrogen Mixture Formation on Hydrogen Combustion2025-32-006511/3/2025
Global efforts to mitigate climate change include ambitious long-term strategies by countries to achieve net-zero greenhouse gas emissions by 2050. The automotive sector is exploring carbon-free powertrains, with hydrogen emerging as a key technology. Its zero-emission potential positions it for widespread adoption in power generation, transportation, and industry. Hydrogen engines, particularly direct injection engines offering high power and efficiency, are gaining traction due to their adaptability using existing engine components. However, in a hydrogen direct injection engine, achieving proper mixing of hydrogen and air in the cylinder is challenging, making in-cylinder mixture formation a crucial factor for ensuring stable combustion. To predict hydrogen mixture formation in the cylinder, we conducted a Schlieren visualization experiment of the hydrogen jet. Based on the results, a detailed hydrogen jet model for the direct injection injector was developed. This model was then integrated into the in-cylinder analysis, allowing an investigation into the impact of injection timing on hydrogen combustion. Furthermore, hydrogen combustion experiments were carried out using a single-cylinder hydrogen direct injection engine, and the accuracy of the in-cylinder analysis results was validated.
Hisano, Atsushi, Saitou, Masahito, Sakurai, Yota, Ichi, Satoaki
Diesel Combustion Parameter Estimation via Machine Learning – A Comparative Study2025-32-004111/3/2025
This paper presents an analysis and comparison of distinct approaches for data-driven combustion parameter estimation for Diesel engines. Thereby, characteristic quantities are modelled by a set of selected regression models and via a convolutional neural network (CNN). While the former use settings from the Engine Control Unit (ECU) as input, the latter works by processing the raw crankshaft vibration signal. The central point of this study is a broad evaluation of data-driven modelling for Diesel combustion. This includes whether using a signal recorded from individual combustion cycles achieves better representation of the target values than using operational parameters from the ECU which cannot reflect unforeseeable, stochastic phenomena within the combustion chamber. This was evaluated by assessing predictions of six combustion characteristics: the crank angle of 10, 50 and 90 percent mass fraction burned, Peak-Firing-Pressure, Combustion Duration, and Ignition Delay. In two series of experiments, it is established that individual cycle data processed via a CNN does not provide an advantage over feature-based machine learning using operation parameters. Specifically, Support Vector Regression (SVR) and Partial Least Squares (PLS) are found to produce estimates of satisfactory quality when making predictions over varied conditions within a single operating point or extrapolating to an entirely unseen operating point. The results suggest that, at least in selected, practically relevant settings, computationally efficient, classical regression models with low-dimensional inputs can compete with or even outperform neural models trained on large amounts of high-dimensional data. This is underlined by the PLS model outperforming the CNN by an average RMSE margin of 1.99°CA for CA50, and 9.93 bar for Peak-Firing-Pressure, respectively, across all experiments.
Ofner, Andreas Benjamin, Sjoblom, Jonas, Geiger, Bernhard, Haghir Chehreghani, Morteza
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
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