Browse Topic: Alternative fuels

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2025 International Conference on Solid Mechanics and Materials2026-99-1600To be published on 07/24/2026
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Tobolski, Sue
Modeling and Simulation Analysis of Liquid Hydrogen and Power Systems Based on Amesim2026-99-1608To be published on 07/24/2026
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
Experimental Investigation on Unburned Methanol and Formaldehyde Emissions from a Direct-Injection Diesel / Methanol Dual-Fuel Engine2026-99-1646To be published on 07/24/2026
For large-bore marine methanol / diesel dual-fuel engines, this study investigates the formation characteristics of unregulated emissions through experimental methods and explores the mechanisms by which engine load and injection timing influence the emissions of unburned methanol and formaldehyde. The study was carried out on a supercharged intercooled inline six-cylinder engine, and Fourier Transform Infrared Spectroscopy (FTIR) was used to monitor the exhaust composition in real time. The study shows that methanol released in the exhaust is due to the incomplete combustion of the methanol fuel. In the combustion process of methanol fuel, formaldehyde mainly arises from two pathways, the first of which is the partial oxidation of methanol inside the cylinder; secondly, the unburned methanol in the exhaust gas oxidizes in the exhaust pipe to generate formaldehyde. As the load increased from 25% to 100%, the unburned methanol emissions decreased by 29%, and formaldehyde emissions decreased by 71%. This is mainly attributed to the enhanced oxidation reaction and reduced wall crevice effect due to the increased combustion temperature. Methanol injection timing optimization was effective in controlling unregulated emissions, with methanol emissions lower at -7° CA ATDC and formaldehyde emissions reaching larger values under this condition. Delaying the diesel injection to -16°CA ATDC led to a 38% increase in unburned methanol emissions, caused by fuel spray interactions and longer stagnation, whereas formaldehyde emissions showed minimal change.
Jiang, Yuqi, Li, Hongmei, Zhang, Wenzheng, Li, Xiao, Zheng, Liang, Meng, Yangqian, Gu, Xianan, Hua, Hanqing
EUROCAE/SAE WG80/AE-7AFC Hydrogen Fuel Cells Aircraft Fuel Cell Safety GuidelinesAIR6464 (Current)7/17/2026
This document defines the technical guidelines for the safe integration of Proton Exchange Membrane (PEM) Fuel Cell Systems (FCS), fuel (considered to be liquid and compressed hydrogen storage types only), fuel storage, fuel distribution and appropriate electrical systems into the aircraft. Editorial Note: Today PEM systems and fuel storage represent the most mature FCS technology and currently forms the basis for this standard. Other types of fuel cell systems and fuels (including reforming technologies and electrolyzers), may be covered by a further update to this document.
AE-7F Hydrogen and Fuel Cells
Temperature Control Technology for Solid-state Hydrogen Proton Exchange Membrane Fuel Cell2026-99-05287/10/2026
The global trend towards green and low-carbon development is that hydrogen fuel cells, as a new type of green power device, have the characteristics of zero emissions and no pollution. Its basic principle is that hydrogen fuel directly converts chemical energy into electrical energy through electrochemical reactions, achieving energy conversion between fuel cells and internal combustion engines, thereby providing sustained and stable power. The PEMFC has attracted significant attention due to advantages such as fast start-up times and long lifespans. However, excessive temperature during the reaction process of solid-state hydrogen proton fuel cells can lead to a decrease in efficiency. This article studies the temperature control device of solid-state hydrogen fuel cells and finds that active temperature control technology can achieve precise temperature regulation, but it consumes more energy; the passive temperature control scheme can reduce energy consumption, but the response speed to low-temperature start-up is limited; The application of intelligent algorithm fuzzy PID significantly improves the temperature control accuracy under dynamic loads and effectively enhances the hydrogen release rate.
Ma, Yueyue, Liu, Jingyi, Shi, Jian, Lu, Zhaona, Bao, Xueqin
Study on Diesel-Methanol Non-Premixed Combustion Characteristics of a Marine Dual-Fuel Engine at Different Methanol Substitution Rate2026-99-05177/10/2026
Methanol use in marine engines has the potential to reduce nitrogen oxide emissions, particulates, and greenhouse gas emissions. A turbocharged four-stroke marine diesel powerplant was converted to run as a double-DI (direct injection) diesel-methanol hybrid engine. Experimental studies using a non-premixed combustion scheme showed that higher methanol substitution ratios (MSR) led to increased peak heat release rates. The combustion process displayed distinctive two-phase behaviors. Increasing MSR caused retarded ignition timing, shortened combustion duration, and improved thermal efficiency. Combustion stability was significantly improved at higher MSR. Emissions results showed NOX and HC were increased in proportion to MSR, whilst particulate emissions and CO concentrations were inversely reduced. Methanol enrichment was found to enhance NOX and HC formation processes but also accelerate soot particulate decomposition and CO oxidation mechanisms.
Li, Xiao, Jiang, Yuqi, Yan, Ping, Zheng, Liang, Li, Hongmei, Zhang, Wenzheng, Chen, Chao, Man, Zhongguo
Experimental Study of Warm-Up And Startability Operations in a Spark Ignition Engine Fueled with Ethanol Gasoline Blends2026-01-07387/1/2026
The mitigation of Greenhouse Gas (GHG) emissions poses a major challenge for the transportation sector, driving the need for renewable fuels. Bioethanol represents a promising fuel for Spark-Ignition (SI) engines, combining a reduced life-cycle CO₂ impact with advantageous combustion properties. However, despite its proven performance under steady-state conditions, the widespread of fuels with high ethanol content is still constrained by significant difficulties during engine cold-start operation. This study aims to experimentally assess the effect of ethanol concentration on cold-start performance and warm-up transient behavior of a Naturally Aspirated (NA), Port Fuel Injected (PFI) SI engine. Warm-up tests were conducted at an operating condition of 2000 rpm engine speed and 20 Nm torque using three fuels with increasing ethanol content: commercial gasoline (E5), E30 and E60. In addition, dedicated startability tests were carried out for E60 and neat ethanol (E100) at different initial engine wall temperatures to evaluate fuel sensitivity to thermal conditions during engine start. The experimental results indicate that increasing ethanol concentration has a negligible effect on the overall duration of the warm-up process, while leading to a modest reduction in both engine wall and exhaust gas temperatures. At the same time, E100 displays severe startability limitations at low initial wall temperatures, requiring repeated cranking attempts before stable operation can be achieved. The same startability issues have been observed for E60 but with limited intensity. Two minimum engine wall temperature ranges were identified for reliable cold-start operation at 20-25 °C for E60 and 25-30°C for E100. Overall, these findings experimentally confirm the dominant influence of engine thermal conditions on the reliable startability of ethanol-fueled spark-ignition engines.
Falbo, Luigi, Falbo, Biagio, Perrone, Diego, Castiglione, Teresa
Biofuel Effect on Regeneration Capability and Soot Reactivity in SCRoF Systems2026-01-07507/1/2026
Biodiesel blends (B7, B20, B100) were evaluated in a Stage V-compliant SCR on Filter (SCRoF) system for heavy-duty applications to quantify soot reactivity and filter regeneration capability. Compared to conventional diesel (B7), B20 showed slightly faster regeneration performance under real-driving conditions, while B100 resulted in reduced particulate formation and higher soot reactivity, with more intense exothermic events requiring careful management. These differences are attributed to the distinct physical-chemical properties of the fuels (oxygen content, lower heating value) and their interaction with Diesel Oxidation Catalyst (DOC)/SCRoF. All tests were conducted on an engine dynamometer with a Cursor 9 FPT (Fiat Powertrain). Findings are discussed in the context of EU Stage V limits and practical control strategies for heavy-duty applications.
Costa, Simone
Impact of High Compression Ratios on Ethanol Homogeneous Charge Compression Ignition2026-01-50386/10/2026
Ethanol requires elevated intake temperatures to initiate autoignition in Homogeneous Charge Compression Ignition (HCCI) as a high-octane single-stage fuel. To leverage the high thermal efficiency, low engine-out NOx, and near-zero soot inherent to HCCI with ethanol, a custom piston design was developed to enable high compression ratios (CR) up to 22.5:1. This study investigates HCCI combustion with ethanol at three CRs of 17.5, 20.0, and 22.5 through equivalence ratio and boost sweeps performed to assess the reduction in the intake temperature requirement at high CRs and the emissions and efficiency trade-offs. Results indicate a clear benefit with reduced intake temperature requirements with increasing CR. However, a combustion efficiency penalty was observed at high CRs. Three-dimensional Computational Fluid Dynamics (CFD) simulations were performed using Large Eddy Simulation (LES) coupled with a detailed chemistry model to investigate the underlying mechanisms of the combustion efficiency penalty. CFD results reveal that the combustion efficiency penalty at high CR is primarily due to increased crevice mass trapping unburned or partially oxidized species and a rapid expansion effect inhibiting complete carbon monoxide (CO) oxidation.
Vedpathak, Kunal, Kumar, Mohit, Motwani, Rahul, Datar, Aditya, Gainey, Brian, Lawler, Benjamin
Impact of Compression Ratio and Stroke on Hydrogen Requirement for Emission-Optimized Operation of an Ammonia-Fuelled Spark-Ignition Engine2026-37-00306/9/2026
Ammonia (NH3) fuelled engines have emerged as a promising route toward net-zero emission targets due to NH3’s carbon-free nature, ease of storage, and established handling infrastructure. However, the low laminar burning speed and narrow flammability limits of NH3 pose a significant combustion challenge, which can be addressed through hydrogen (H2) co-fuelling. For practical implementation, on-board H2 production via thermal catalytic cracking of NH3 is an attractive solution, as it eliminates the need for external H2 storage and associated handling and capital costs. Previous studies by the present authors identified a lean operating strategy that achieves an equimolar ratio of NOx and unburned NH3 (α NH3NOx ≈ 1), enabling complete conversion to nitrogen and water vapour when coupled with a Selective Catalytic Reduction (SCR) system. This strategy was further validated using cracked NH3 derived H2 in place of bottled H2 through an on-board cracker, thereby representing a practical system configuration. However, the required H2 fraction, and consequently the size and power demand of the onboard cracking system, is strongly influenced by engine architecture and operating conditions. The present study investigates the effect of compression ratio (CR) and stroke length, on H2 fraction requirements to achieve an optimum α of unity in an externally boosted SI engine. Results demonstrate that the high CR = 17.5, long stroke configuration reduces H2 enrichment by 50–60% compared to a low CR = 12.5, short-stroke engine architecture, allowing smaller onboard H2 generation systems. At high-speed, high-load conditions, it achieves over 45% thermal efficiency with stable NH3 combustion and no H2 supplementation, maintaining an α ≈ 1. Across the full operating map, NOx emissions comply with IMO Tier III and EPA Tier 4 norms, demonstrating near-zero-emission operation.
Yadav, Neeraj Kumar, Ambalakatte, Ajith, Geng, Sikai, Gopakumar Suja, Gagan, Birch, Alexander, Cairns, Alasdair, Harrington, Anthony, Hall, Jonathan
Methane Emission Mitigation in Large-Bore Dual-Fuel Engines via Negative Valve Overlap Diesel Injection: Thermochemical Pathways and Reactivity Control2026-37-00456/9/2026
Low-load natural gas–diesel reactivity controlled compression ignition (RCCI) in medium-speed marine engines is constrained by an insufficient charge thermal state. This limitation leads to partial fuel oxidation, producing high methane emissions. This work evaluates the use of negative valve overlap (NVO) combined with NVO diesel injection as an in-cylinder reactivity enhancement strategy. The simulation study was performed using the University of Vaasa’s advanced thermo-kinetic multi-zone model (UVATZ), extended for reactive simulations during NVO. The extended framework was validated against test-bench data from a prototype Wärtsilä 6L20 dual-fuel engine operating in RCCI mode. The baseline low-load operating point for reforming simulations was defined by reducing the intake manifold temperature to replicate conditions close to partial misfire with 52% combustion efficiency. The parametric sweeps of NVO injection timing and ratio showed that the strategy can be used for in-cycle fast thermal management, effectively restoring complete combustion on an individual cycle basis. In simulated conditions, the best performance was obtained with an NVO injection ratio of 0.3, with the injection scheduled before top dead center. In contrast, increasing the NVO fraction beyond ~0.3 provided no benefit and led to complete misfire due to excessive reduction of main-event high-reactivity fuel. The simulations revealed a coupled thermal–chemical control mechanism. Early NVO injections stabilize combustion through recompression heat release and an increased next-cycle intake valve closing temperature. Sufficiently late injections stabilize combustion by carrying unreacted diesel into the subsequent cycle. Injections near NVO TDC primarily undergo fuel conversion to CO, H2O, and unsaturated light/mid-range hydrocarbons with negligible thermal boost, yielding an overall reactivity deficit.
Soleimani, Amir, Nurmi, Mikael, Hunicz, Jacek, Kim, Jeyoung, Hyvonen, Jari, Mikulski, Maciej
Development of a Diesel Combustion System for Next-Generation Heavy-Duty Engines Using a Synergistic Analysis-and-Testing Approach2026-37-00046/9/2026
Regulators and policymakers have introduced increasingly stringent limits on tailpipe CO₂ and pollutant emissions to accelerate the decarbonization of heavy-duty vehicle applications. The development of innovative propulsion technologies — such as advanced combustion systems, low-friction reciprocating components, and improved aftertreatment solutions — combined with hybridization and the adoption of alternative fuels (e.g., biogas, HVO, green hydrogen), is a key pathway for meeting future emission and GHG targets. In this study, advanced combustion systems were developed for a 13-liter diesel engine for heavy-duty truck applications, with the objective of meeting forthcoming Euro VII regulations while maximizing thermal efficiency. The combustion system architecture—including open-bowl geometry with high aspect ratio, injector nozzle with wider spray opening angle, and reduced swirl ratio—was optimized using a Machine Learning–algorithm trained on high-fidelity 3D CFD combustion data. The method enabled the identification of two optimized combustion-system “recipes”, one of which was evaluated through engine tests, which refined nozzle specifications and injection strategies, using a structured Design of Experiments (DoE) approach. Results were benchmarked against a MY24 baseline combustion system, assessing efficiency, NOx–soot trade-offs, and combustion behaviors. Based on 3D-CFD results, the advanced combustion concept achieved an improvement in Brake Thermal Efficiency (BTE) of up to +0.8% points and delivered substantial NOx reductions of up to 45%, while maintaining smoke emissions at or below baseline levels. The experimental results indicate that the advanced combustion system developments designed for next-generation heavy-duty engines can further increase BTE by up to ~1% relative to the baseline combustion system, without deteriorating the soot–NOx trade-off.
Belgiorno, Giacomo, Centini, Maria Pia, Pezza, Vincenzo, Cozza, Ivan F., Pesce, Francesco C., Vassallo, Alberto, Colombo, Giovanni, Gallo, Alessandro, Mirzaeian, Mohsen, Borg, Jonathan
Comparison of Detailed Chemistry and Flamelet-Based Models for Hydrogen Combustion in a Heavy-Duty PFI Engine2026-37-00146/9/2026
Addressing climate change requires substantial reductions in CO2 emissions from the transportation sector, where alternative fuels for internal combustion engines play a crucial role. Hydrogen stands out as a compelling energy carrier capable of enabling low-carbon combustion while leveraging existing engine technologies. Its adoption can support a transition toward fuel-flexible powertrains and deliver rapid decreases in exhaust carbon emissions. This approach is particularly relevant for hard-to-abate segments, where full electrification remains challenging. Building on this perspective, this numerical study investigates the modelling behaviour of a heavy-duty port fuel injection (PFI) internal combustion engine fuelled with hydrogen. Initially, the mixture was assumed to be fully premixed to avoid uncertainties related to injection and mixing processes and to significantly reduce computational cost; this assumption was subsequently validated through selected injection simulations. A methodology was then developed to ensure robust model responses by analysing convergence over three consecutive cycles and by appropriately defining the initial and boundary conditions, as well as mesh resolution. Three representative experimental operating points were investigated: full load, maximum power, and cruise conditions. Two combustion modelling approaches were then compared. ECFM, a flamelet-based model, demonstrated its ability to match experimental data through a calibration process that accounts for turbulence-chemistry interactions via the adjustment of model parameters. In contrast, SAGE is a detailed chemistry solver that employs a kinetic reaction mechanism to directly compute reaction rates, without requiring calibration. The comparison highlighted certain limitations of SAGE arising from its underlying approach, whereas ECFM showed more stable and reliable behaviour, albeit with the need for case-specific calibration.
Scopelliti, Alex, Misul, Daniela Anna, Baratta, Mirko, Gallo, Alessandro, Rapetto, Nicola, Vargiu, Luca
Experimental Investigation on Cold Start and Warm-Up Phases for an Ethanol Fueled SI Engine2026-37-00316/9/2026
The reduction of Greenhouse Gas (GHG) emissions represents a key challenge for the transportation sector, requiring the adoption of renewable fuels capable of ensuring both environmental benefits and compatibility with existing internal combustion engine technologies. In this context, bioethanol emerges as a viable solution for Spark Ignition (SI) engines, offering a low life-cycle CO₂ footprint and favorable combustion characteristics. Nevertheless, despite its well-known advantages under steady-state operation, the widespread use of high-ethanol-content fuels is still limited by critical issues during engine cold start. The aim of this work is to experimentally investigate the influence of ethanol content on cold-start behavior and idle warm-up transient operation of a Naturally Aspirated (NA), Port Fuel Injected (PFI) SI engine. The experimental campaign was carried out under idle conditions using four fuels with increasing ethanol content, namely commercial gasoline (E5), E30, E60, and neat ethanol (E100). Cold-start and full warm-up tests were performed starting from ambient temperature, while additional dedicated experiments were conducted on E100 to evaluate startability under different initial engine wall temperatures. The results show that increasing ethanol content has a limited impact on the overall warm-up duration, while slightly reducing engine wall and exhaust gas temperatures. Conversely, E100 exhibits pronounced startability issues at low initial wall temperatures, requiring multiple cranking attempts to achieve stable idle operation. A minimum wall temperature threshold in the range of 25-30 °C was identified as necessary to ensure reliable cold start with E100. The outcomes of this study provide experimental evidence of the key role played by engine thermal conditions in enabling stable operation of ethanol fueled SI engines during cold start.
Falbo, Luigi, Falbo, Biagio, Perrone, Diego, Castiglione, Teresa
Nitrogen-Based Emissions from Ammonia Combustion in a Heavy-Duty Spark Ignition Engine2026-37-00326/9/2026
Ammonia (NH3) is a carbon-free fuel with strong potential for spark-ignition (SI) engine applications. However, the engine can produce complex nitrogen-based emissions not adequately captured by conventional engine models. This study consolidated the results of experimental and numerical studies on the use of neat NH3 combustion in a heavy-duty compression-ignition engine converted to spark-ignition operation, first for a sweep of equivalence ratios (ϕ) from 0.7 to 1.0, and another from varying the energy substitution ratio of methane (CH4)– NH3 blends from neat CH4 to neat NH3 at constant ϕ = 0.8. Two 0-D two-zone SI engine models with detailed chemistry (called “original” and “extended”) predicted engine thermodynamics and emissions. While the original model reproduced in-cylinder pressure and combustion phasing, it failed to capture the effect of fuel composition or operating condition on NO trends, both under- and over-predicting them for neat NH3 and CH4-rich operations. An extension of the model incorporating a burned-zone batch reactor and two more reactors simulating the post-combustion oxidation of the mixture exiting crevices and the DeNOx processes during exhaust blowdown were implemented to address these limitations. Analysis of NO formation pathways highlighted the differences between modeling approaches. The equilibrium assumptions in the original model restricted NO formation primarily to thermal (Zeldovich) mechanisms. In contrast, the kinetics-driven model showed that non-thermal pathways dominate NO formation for all NH3-containing cases, which shows the limitations of conventional SI models developed for hydrocarbons when applied to nitrogen-containing fuels. Post-combustion homogeneous reactors for crevice-based oxidation and exhaust blowdown revealed significant NO and N2O formation after the end of combustion at moderate temperatures (850–1200 K), suggesting that N2O formation was dominated by secondary thermal processes. Therefore, the inclusion of post-combustion chemistry and more consistent models are essential for accurate emission prediction in NH3-fueled SI engines.
Trujillo Grisales, Juan, Saenz Prado, Stefany, Alvarez, Luis F., Akkerman, Vyacheslav, Dumitrescu, Cosmin E.
Development and Experimental Validation of a 1D Model for Performance and Emissions Analysis of Oxygenated Fuel Blends in a CI Engine2026-37-00286/9/2026
Emissions reduction remains a major concern for internal combustion engines in view of increasingly stringent environmental regulations. To address these challenges while maintaining acceptable engine performance, a wide range of alternative fuels and fuel blends have been investigated to ensure the continued viability of CI engines. This study reports the effects of blending the oxygenated fuel diethylene glycol diethyl ether (DGDE) with hydrotreated vegetable oil biodiesel (HVO) on engine performance and emissions. The investigation is conducted on a 2.3-liter, four-cylinder, common-rail diesel engine, equipped with a variable geometry turbocharger and a high-pressure exhaust gas recirculation system. The objectives of this study are achieved by developing a one-dimensional predictive engine model using the commercial GT-SUITE software. The engine model is developed and experimentally validated, at various operating conditions and HVO–DGDE fuel blends, to predict their effects on combustion characteristics and emissions formation. The validation is performed against measurements collected at the engine test bed. The results indicate that increasing the blending ratio of oxygenated fuel leads to improvements in indicated mean effective pressure and a more favorable Soot–NOx emissions trade-off compared with neat HVO operation. The findings highlight the potential of oxygenated fuel blends to enhance CI engine performance while reducing emissions. This study demonstrates the effectiveness of combining experimental and numerical approaches to evaluate biodiesel–oxygenated fuel blends and provides insights for future research aimed at minimizing CI engine emissions.
Arain, M Wajahat Rasool, Foglia, Antonio, Frasci, Emmanuele, Vitek, Oldrich, Pianese, Cesare, Arsie, Ivan
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
Alcohol-Based Energy Carriers in Transportation: Status, Standards, and Outlook2026-37-00426/9/2026
The global transport sector accounts for approximately 30 % of total final energy consumption and 15.9 % of worldwide greenhouse gas (GHG) emissions, with road transport alone accounting for the largest share at 11.8 %. Decarbonizing this sector requires energy sources that combine scalable generation from renewable sources with compatibility with various modes of transportation and existing infrastructure. Methanol and ethanol emerge as promising alternative energy carriers that can leverage existing logistics infrastructure while reducing dependence on fossil fuels. Global methanol production reached 112 million metric tons, and global ethanol production totaled approximately 93.5 million metric tons in 2024, compared to more than 2 billion metric tons of gasoline and diesel produced annually. The review assesses production pathways and cost trajectories for both alcohols, evaluates fuel requirements across multiple transport modes, including passenger vehicles, light- and heavy-duty vehicles, maritime shipping, aviation, and rail, and provides regulatory frameworks governing fuel standards in six major markets, the European Union, the USA, Brazil, China, Japan, and India. From a technical perspective, the internal combustion engine is examined in greater detail as the energy conversion system, synthesizing current combustion research on engine performance, emissions characteristics, and cold-start behavior. Current standards predominantly accommodate ethanol blending for spark-ignition (SI) engines in passenger vehicle applications, with permitted concentration limits ranging from 3 % in Japan to nearly pure ethanol in Brazil. Methanol applications remain more limited in road applications. In the maritime sector, recent ISO 8217:2024 specifications and International Maritime Organization (IMO) interim guidelines have established frameworks for the use of methanol and ethanol as marine fuels. Aviation remains the most restrictive sector, with alcohol fuels explicitly prohibited in certified aviation fuels due to material compatibility and safety concerns. To unlock the decarbonization potential of methanol and ethanol in the transport sector, coordinated policy support and continued technological innovation will be essential. As production scales and regulatory frameworks mature, both alcohol fuels may play an increasingly central role in the transition toward sustainable mobility.
Fitz, Patrick, Fellner, Felix, Rößlhuemer, Raphael, Härtl, Martin, Jaensch, Malte
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
Comparative Toxicological Assessment of Exhaust Emissions from Modern Low-Emission Passenger Vehicles2026-37-00056/9/2026
As vehicle technologies evolve toward electrification and advanced aftertreatment, understanding the biological implications of their exhaust emissions remains essential. This study presents a harmonized comparative toxicological assessment of five Euro 6 vehicles representing gasoline, hybrid, plug-in hybrid, compressed natural gas (CNG), and diesel technologies. Vehicles were tested under realistic driving conditions on a chassis dynamometer. Diluted exhaust was delivered directly to human lung epithelial cells (A549) using a controlled air–liquid interface (ALI) exposure system. Solid and total particle number emissions were measured, and deposited particle mass was estimated from size-resolved distributions and deposition efficiency. Vehicles equipped with particulate filtration showed lower solid particle emissions overall, while differences between gasoline particulate filter-equipped vehicles indicated that hybridization can further influence emission levels. Diesel operation during active diesel particulate filter (DPF) regeneration produced more than two orders of magnitude higher particle number emissions compared to normal operation. When expressed as deposited mass, vehicle ranking differed from number-based emissions, highlighting that emission metrics do not directly translate into delivered biological dose. Exposure to whole exhaust consistently induced stronger cytotoxic and inflammatory responses than to gaseous phase alone. Membrane integrity disruption and IL-1β release showed clear particle-associated amplification, with the strongest effects observed during diesel DPF regeneration. These findings demonstrate persistent technology-dependent differences in particle emissions and acute biological responses among modern low-emission vehicles.
Tsakonas, Georgios, Stamatiou, Rodopi, Lazou, Antigone, Samaras, Zissis, Elihn, Karine
Evaluation of Flamelet-Based Combustion Models for Hydrogen-Ammonia Spark-Ignition Engines2026-37-00276/9/2026
Besides the electrification of the transport sector, the growing interest in alternative fuels for internal combustion engines represents a promising pathway to effectively decarbonize transportation over the coming decades. Predictive combustion models implemented within CFD frameworks are a critical tool to guide the design of next-generation internal combustion engines fuelled with alternative fuels. Accurate prediction of the combustion heat release process is influenced by multiple interacting parameters, requiring combustion models that can reliably adapt to variations in fuel chemical properties and operating conditions. In this study, two well-established combustion models considered to model combustion development in Spark-Ignition engine, namely the Extended Coherent Flame Model (ECFM) and the G-equation model, are compared to assess their capability to adapt to changes in fuel chemical composition. Both models, based on the flamelet formulation are deliberately tested beyond their nominal validity range in order to highlight their limitations when applied to a broader range of operating conditions in the case of ammonia-hydrogen blends as fuel. The numerical predictions are validated against an extensive experimental dataset obtained from a commercial light duty engine converted to single-cylinder configuration over a wide range of equivalence ratios. Both models require careful calibration of the turbulence–chemistry interaction to account for the large variability in mixture conditions (% vol. hydrogen in the blend, equivalence ratio) investigated. Furthermore, the calibration strategy is analysed in relation to the turbulent combustion regime classification. Under perfectly premixed operating conditions, as the combustion analysis is unaffected by in-cylinder stratification, the interpretation enables a direct assessment of the turbulence–chemistry interaction modelling.
Sola, Riccardo, Baratta, Mirko, Misul, Daniela, Rousselle, Christine, BREQUIGNY, Pierre, Colin, Olivier
Investigation of the Combustion of Stearic Acid-Coated Pure Aluminum Powder as Additives in Biodiesel and Diesel Blends04-19-02-00106/8/2026
In the present study, research was conducted to increase the combustion efficiency in a diesel engine by adding 100 and 200 ppm aluminum powder to diesel and biodiesel (produced from 10% spent coffee ground oil and 90% waste cooking oil) blends. Aluminum powder is a flammable metal. Due to this feature, it has been used as an additive to liquid fuels in many studies in the literature. In general, it has been reported that thermal efficiency increases with the addition of aluminum particles. However, the high explosion sensitivity of aluminum can affect its stable combustion. In addition, Al is a metal that can be easily oxidized. Therefore, coating aluminum is considered a good solution. Stearic acid has been suggested in the literature as a suitable material for coating aluminum. In this study, stearic acid, a saturated fatty acid, was used to coat aluminum particles. Stearic acid is a good surfactant, hydrophobic substance, and plasticizer. It is also a more environmentally friendly substance compared to its counterparts. In this study, aluminum particles were coated with stearic acid to increase the combustion efficiency of Al particles. To make the coating, stearic acid was dissolved in ethanol and mixed with Al particles. Then, the stearic acid coating was achieved by self-assembly using the evaporation technique. As a result of experiments conducted by adding aluminum and stearic acid-coated aluminum to diesel and biodiesel blends, the thermal efficiencies of DAl200, DAl100, and DSA@Al100 fuels were 2.99%, 3.21%, and 4.59% higher than that of standard diesel fuel, respectively. Likewise, the thermal efficiencies of B10D90Al200, B10D90Al100, and B10D90SA@Al100 fuels were 2.73%, 2.99%, and 3.62% higher than that of standard diesel fuel, respectively.
Kül, Volkan Sabri, Akansu, Selahaddin Orhan, Sarıtaş, Mehmet
Bosch shows off its first U.S. electrolyzer26TOFHP06_086/1/2026
Two of the biggest hurdles to adoption of hydrogen fuel cells are still the availability of hydrogen and its affordability. Now Bosch has taken what is a small step toward addressing availability at its Farmington Hills, Michigan, engineering center, where the company just unveiled its new electrolyzer, which uses electrical current to split water into oxygen and hydrogen to power fuel cells.
Clonts, Chris
Weight Estimation of Novel Aircraft Configurations in Early Design Phase2026-26-07736/1/2026
Initial weight estimation from Top Level Aircraft Requirements (TLAR) is a critical first step in aircraft design, yet existing empirical methods are inadequate for novel configurations such as those using Liquid Hydrogen (LH2) or Sustainable Aviation Fuels (SAF). This paper presents a hybrid methodology for top-level weight estimation of such unconventional aircraft. The approach is based on modifying a conventional baseline aircraft, integrating a new statistical model with component-specific weight estimations. A multivariate regression model to estimate the empty weight fraction (We/W0) was developed from a dataset of 44 conventional aircraft, yielding an R-squared value of 0.833. This statistical model was integrated with physics-based models for novel components, including cryogenic fuel tanks and fuel systems. The methodology accounts for iterative changes to fuselage structure and parasitic drag. Four configurations were analyzed: fuel types being Jet A1, SAF, LH2 with aft-fuselage tanks, and LH2 with under-wing podded tanks. The results demonstrate that while LH2 configurations introduce weight penalties for tanks and systems, these are significantly offset by a reduction in fuel weight, resulting in a final Maximum Takeoff Weight (MTOW) comparable to or lower than the conventional baseline. The modular nature of this methodology makes it a viable tool for exploring the design space in early-stage conceptual design.
Goyal, Tushar
EDITORIAL: Diversification key for sustainable fleets26TOFHP06_046/1/2026
We hear it often at industry events, in keynote speeches and during expert panel discussions: There is no silver bullet. Peter Voorhoeve, president of Volvo Trucks North America, says as much in this issue's Q&A (page 44). “Electric is one solution, but biodiesel is another solution, and hydrogen is, too. So we have these different fuel solutions to get to better sustainability.”
Gehm, Ryan
IN FUEL CONTROL26TOFHP06_026/1/2026
How to ensure off-highway combustion systems operate with sufficient control to meet tightening emissions standards and evolving fuel landscapes without sacrificing reliability. Off-highway equipment is being asked to do more with less. Less margin for emissions, less tolerance for downtime and less room for inefficiency, while operating under some of the most demanding duty cycles in the transport sector. Tier 4 and Tier 5 emissions standards have reshaped engine calibration strategies. Renewable diesel and biodiesel blends are entering worksites and farms at scale. At the same time, construction, mining and agricultural machines are expected to run for 20-25 years, often at sustained high load and far from service infrastructure. In this environment, combustion systems are far from being phased out.
Anderson, Todd
Experimental Investigation of Diesel, Aqueous Ammonia, and Compressed Natural Gas Mixtures on Performance and Emissions in a Compression Ignition Engine04-19-03-00115/30/2026
Abstract This study investigates and evaluates systematically the combustion, performance, and emissions characteristics of heavy-duty diesel engines fueled by diesel–ammonia–compressed natural gas triple blends. While dual-fuel systems are well-documented, the interactive effects of ammonia and CNG within a single compression ignition (CI) engine remain largely unexplored. Experiments were conducted on a 300 Nm, 660 rpm diesel engine by testing pure diesel, diesel–ammonia blends (10–20 wt.% aqueous ammonia), and triple-fuel mixtures containing 10% of the total energy from compressed natural gas. Pure diesel was first tested to provide baseline data, and subsequently blends were tested for a comparative study. The primary contribution of this work is the identification of a synergistic effect of the fuel triple blends on engine performance and emissions. Results indicate that all fuel blends improve thermal efficiency and reduce fuel consumption compared to conventional diesel. The blend containing 20% aqueous ammonia, 80% diesel, and 10% of the total fuel energy supplied by compressed natural gas achieved the highest thermal efficiency of 39.7% (7% higher than diesel) and the lowest brake specific fuel consumption of 211.22 g/kWh. Furthermore, emissions analysis revealed that carbon dioxide and nitrogen oxide emissions were significantly reduced with this triple blend. The blend decreased carbon dioxide by 26.6% and nitrogen oxide emissions by 32.1%, while hydrocarbon emissions were also lowered by up to 29.2%. Carbon monoxide emissions increased slightly for the triple blends, reaching a maximum value of 3.9028 g/kWh for the A20D80CNG10 mixture, compared to diesel operation. The slight increase in carbon monoxide emissions for triple blends highlights a trade-off in emission behavior. These findings address the combined utilization of diesel–ammonia–compressed natural gas triple-fuel mixtures in heavy-duty engines, demonstrating that strategic blending can simultaneously improve efficiency while mitigating environmental impact. Graphical Abstract
Sinkala, Happy, Sarıtaş, Mehmet, Kül, Volkan Sabri, Akansu, Selahaddin Orhan, Ünalan, Sebahattin
Potential of an In-Cylinder Pressure–Based Combustion Control for Compression Ignition Aviation Engines Operated with Sustainable Aviation Fuels2026-01-50285/29/2026
The aviation industry represents a significant greenhouse gas emitter and aims to reduce net CO2 emissions to zero by 2050. The deployment of sustainable aviation fuel (SAF), alongside measures such as increasing engine efficiency and enhancing ground handling processes, represents a key driver to reach this ambitious goal. SAF exhibits significantly different physical and chemical properties compared to conventional kerosene. The corresponding fuel specification (ASTM D7566 [1]) currently only defines fuel parameters relevant for the use in jet engines. To assess the suitability of SAF for the use in compression ignition (CI) aviation engines, a collaborative project was conducted at TU Wien—Institute of Powertrain and Automotive Technology, together with Austro Engine. ASTM D7566-certified fuels like Hydrotreated Vegetable Oil (HVO), Fischer–Tropsch–Kerosene (FTK), and Alcohol-to-Jet (AtJ) have been investigated on the engine test bench at TU Wien. The core contribution of this study is the experimental evaluation of a real-time capable in-cylinder pressure–based combustion control strategy that enables fuel-flexible and optimized CI engine operation across a wide range of SAF while accounting for mechanical constraints such as peak cylinder pressure and pressure rise rate. To evaluate the potential of such a control system, optimized engine operation was compared to operation with conventional ECU (Engine Control Unit) mapping. Furthermore, the influence of such a real-time combustion process optimization on critical emissions like NOx or soot has been evaluated. Through the implementation of an in-cylinder pressure–based combustion control, a considerable fuel-saving potential could be demonstrated across the entire fuel range. As combustion phasing is optimized toward early crank angle positions, a slight increase in NOx, with a corresponding decrease in soot is observed. Additionally, the use of automotive, piezoresistive pressure sensors was examined regarding a potential serial application. It has been shown that piezoresistive sensors (standard serial parts—calibrated for automotive application) are well-suited for determination of combustion phasing, while in-cylinder peak pressure and its position can only be determined with insufficient accuracy.
Kleissner, Florian, Hofmann, Peter
Risk Assessment of Bunkering Process for LNG River Powered Ship2026-99-17225/22/2026
At present, with the rapid development of LNG powered ships, China’s LNG powered ships have formed a certain scale, but the speed of infrastructure construction such as bunkering stations restricts the development of LNG powered ships. In this process, “tank truck-to-ship bunkering”(TTS) has become one of the most widely used bunkering methods in China because of its flexible, fast and convenient characteristics, but there are many hidden dangers in the bunkering process. According to the characteristics of TTS, fault tree method is used to identify the risk of bunkering process, and the leakage of pipeline system is listed as the basic risk factor. The leakage probability of different aperture is analyzed by industry statistics. Three different leakage scenarios are selected and the consequences are simulated by PHAST software. The study shows that the failure of the valve and flange can easily lead to the leakage of LNG in the TTS process, and the leakage of the medium aperture and the full aperture will form the liquid pool, so some measures should be taken for the protection.
Dong, Yuanchao
Effect of Burning Biomass Fuel Cyclohexanol on Diesel Engine Performance2026-99-17085/22/2026
Against the backdrop of growing global demands for energy sustainability and stricter emission regulations for diesel engines, this study investigates the performance implications of incorporating cyclohexanol—a renewable oxygenated fuel—into diesel fuel blends. Using a marine medium-speed diesel engine as the experimental platform, the research systematically evaluates engine performance and emission characteristics across a range of cyclohexanol-diesel blend ratios under low, medium, and high load conditions. Experimental findings reveal multifaceted effects of cyclohexanol blending on engine operation. Combustion of the blended fuels enhances the engine’s dynamic performance, particularly under medium and high loads, where the maximum in-cylinder burst pressure exhibits a noticeable increase. This improvement is attributed to cyclohexanol’s oxygen-carrying capacity, which promotes more vigorous and sustained combustion reactions. In terms of emissions, increasing the proportion of cyclohexanol in the fuel blend leads to significant reductions in soot and carbon monoxide (CO) emissions, reflecting the cleaner-burning properties of the oxygenated component. However, this is accompanied by an uptick in nitrogen oxide (NOx) emissions, likely due to the elevated combustion temperatures generated by the more efficient fuel oxidation process. From an economic perspective, cyclohexanol blending at consistent load levels induces a postponement in the crank angle at which peak heat release occurs during combustion. This temporal shift prolongs the effective combustion duration, enabling more complete fuel utilization within the cylinder. Consequently, fuel consumption rates decrease, and overall engine efficiency improves, highlighting the potential of cyclohexanol blends to enhance operational economy in marine propulsion systems. In summary, this study underscores the complex trade-offs associated with cyclohexanol-diesel blends: while they offer tangible benefits in power output, fuel efficiency, and reduced particulate emissions, managing the increase in NOx emissions remains a critical challenge. The results provide a foundational framework for advancing biofuel applications in marine engines, emphasizing the need for integrated emission control strategies to optimize the balance between performance and environmental sustainability.
Chen, Ke, Yang, Chenxi, Wang, Yibin, Fan, Jinyu, Liu, Yuchen, Ye, Zixiao, Huang, Jialiang
Model-based Optimization of Fuel Cell Powered Vertical Take-Off and Landing (eVTOL) AircraftF-0082-2026-02265/5/2026
Electric Vertical Take-Off and Landing (eVTOL) aircraft are poised to transform urban and regional mobility by offering zero-emission, congestion-free transportation. As regulatory frameworks evolve and advanced air mobility (AAM) gains traction, manufacturers are exploring propulsion strategies that improve range, power delivery, and overall system efficiency. A key challenge in eVTOL development is balancing range with payload capacity. While larger battery packs can extend range, they also increase system weight, reduce payload, and prolong charging times, limiting operational flexibility and turnaround time. Hydrogen fuel cells, supported by liquid hydrogen (LH₂) present a promising alternative for eVTOL propulsion. This study proposes a methodology for optimizing fuel cell propulsion systems tailored to eVTOL applications. A multi-physics modeling framework for eVTOL flight dynamics and propulsion system was developed, representing the target eVTOL configuration. For a defined flight path including vertical takeoff, hover, cruise, and landing, a Genetic Algorithm (GA) based optimization was conducted on propulsion system. The algorithm down-selected battery size, fuel cell stack specifications, and hydrogen tank capacity to meet mission requirements while minimizing propulsion system weight. The modeling framework was also used to evaluate trade-offs between payload and performance as functions of component sizing, battery chemistry and energy distribution strategy.
Garcia, Bruno, Paul, Sumit, Zeigler, Sophia, Franke, Michael, Joshi, Satyum, Araujo, Joao
Bosch shows off its first U.S. electrolyzer in support of hydrogen research26AUTD05_095/1/2026
Two of the biggest hurdles to the adoption of hydrogen fuel cells are still the availability of hydrogen and its affordability. Bosch recently took a small step toward addressing availability at its Farmington Hills, Michigan, engineering center, where the company unveiled a new electrolyzer that uses electrical current to split water into oxygen and hydrogen to power fuel cells.
Clonts, Chris
Effect of Injector Tip Temperature on Methanol Spray Dynamics during Cold-Start Conditions2026-01-03404/7/2026
Methanol is one of the most readily produced e-fuels and remains in liquid form at ambient conditions, making storage and transportation relatively simple. In the marine sector, methanol has already been actively adopted as a pathway toward carbon neutrality. For automotive sectors, methanol offers significant potential for carbon emission reduction owing to its higher octane number and lower carbon content compared with gasoline. However, its high latent heat of vaporization and low vapor pressure suppress evaporation at low ambient temperatures, leading to increased emissions during cold-start operation. To address this issue, previous studies have explored heating the injector tip or fuel rail to enhance evaporation and atomization. The present study focuses on visualizing and quantifying the improvement in methanol evaporation characteristics under cold-start conditions by applying controlled heating to the injector tip. Experiments were conducted in a constant-volume chamber where the ambient temperature was carefully regulated, while a laterally mounted injector tip was subjected to different heating levels. Extinction images were acquired to determine spatial and temporal liquid volume fraction and to visualize spray morphology and penetration behavior for both methanol and gasoline surrogate fuel E00. Moreover, three-dimensional tomography reconstructed from extinction images taken at multiple viewing angles provided an in-depth assessment of methanol spray structure, droplet distribution, and evaporation behavior with varying injector tip temperatures under simulated cold-start conditions. These findings highlight the crucial role of injector thermal management in improving methanol-fueled engine performance during low-temperature operation.
Lee, Seungwon, Kim, Hyunsoo, Bae, Sumin, Hwang, Joonsik, Bae, Choongsik
Combustion Enhancement via Discharge Current Modulation under Turbulence Conditions2026-01-03364/7/2026
Utilizing low carbon fuel in lean burn combustion presents a compelling strategy for improving thermal efficiency and reducing NOx emissions. Methane, the main content of natural gas, still receives challenge of a rapid and complete combustion process because of its low flame speed. The long combustion duration deteriorates the performance of a spark ignition engine, in terms of poor combustion instability and misfire. Although ignition timing can be utilized to adjust the combustion phasing, the ignition process faces challenges due to reduced background pressure and temperature at advanced spark timings. In this paper, a rapid compression machine equipped with a specially designed flow chamber is utilized to enhance the turbulence flow, and a custom-built ignition module is utilized to provide boosted discharge current to enhance the ignition stability under flow conditions. An effective spark energy required to enhance the combustion process is investigated under both stoichiometric and lean conditions. Further increase of discharge current amplitude beyond this boundary yields minimal impact on the flame propagation process. This study will offer important insights for developing an on-demand ignition energy profiling strategy to reduce sparkplug electrode erosion.
Jin, Long, Cong, Binghao, Yu, Xiao, Kong, Xiangxin, Reader, Graham, Zheng, Ming
Experimental Study on Macroscopic Characteristics of Ammonia Spray under Flash Boiling and Non-Flash Boiling Conditions with Large-Diameter Single-Hole Nozzles2026-01-03394/7/2026
Ammonia is regarded as a potential alternative fuel, and its spray characteristics are crucial for efficient combustion in engines. For large-bore engines suitable for heavy-duty vehicles or ships, the adoption of large-diameter nozzles is expected to ensure an appropriate fuel flow rate while improving fuel-air mixing efficiency, thereby enhancing in-cylinder combustion performance. This paper conducted an experimental study on the characteristics of liquid ammonia sprays under wide thermodynamic conditions, a wide range of injection pressures, and a wide range of nozzle diameters. The study found that at room temperature, as the ambient pressure increases from 0.1 MPa to 4 MPa, the development of spray penetration slows down. However, at 0.05 MPa, the radial expansion of the near-field spray is greater, and the penetration is slightly behind that at 0.1 MPa. The liquid penetration increases with the increase in ambient temperature. This was because the increase in temperature reduced the ambient gas density, thereby decreasing the aerodynamic resistance. Under the high-temperature and high-pressure ambient conditions of 4 MPa and 800 K, the liquid penetration is greatly limited when a 0.2 mm nozzle is used due to insufficient spray momentum and high spray vaporization rate, with the maximum penetration only about 40 mm. In contrast, the penetration of the 0.7 mm nozzle could develop to more than 85 mm. Under the ambient conditions of 4 MPa and 800 K, a "stagnation" of penetration was observed for the 0.7 mm nozzle with injection pressure of 60 MPa, where the penetration does not increase continuously. This was the result of the synergy between spray velocity gradient, aerodynamic shear force, and high-temperature evaporation. This paper conducts the first experimental study on liquid ammonia sprays using large-diameter nozzles up to 0.7 mm, providing an experimental basis for the injection optimization of large-bore liquid ammonia direct-injection engines.
Liu, Yi, Zhong, Jie, Hu, Yuchen, Zhu, Wuzhe, Yunliang, Qi, Qingchu, Chen, Wang, Zhi
Combustion Characterization of Hydroprocessed Esters and Fatty Acids (HEFA) as an Alternative Fuel for Use in IC Engines2026-01-03174/7/2026
In the endeavors to reduce reliance on fossil fuels and reduce greenhouse gas emissions, synthetic fuels from less carbon intensive feedstocks have emerged as a promising alternative to conventional fuels. These synthetic fuels have gained traction in the aviation industry as sustainable aviation fuels (SAFs). One such fuel is a synthetic paraffinic kerosene derived from hydroprocessed esters and fatty acids (HEFA). Preliminary research has also suggested that this fuel may also be favorable for use in IC engines. This investigation will explore the combustion characteristics of HEFA in an IC engine in more detail. The thermophysical properties of HEFA were investigated and found comparable to or improving upon those of ULSD. Spray atomization analysis revealed more than 25% smaller SMD compared to ULSD, and lower span factor indicating a more uniform spray which can promote faster formation of a homogenous mixture. A tribological analysis using a pin-on-disk tribometer revealed comparable lubricity compared to ULSD, without requiring any additives. A CVCC was used to investigate the autoignition characteristics of the fuels. HEFA was found to have a DCN of 58 compared to ULSD at 48. Resultingly, the ignition delay for HEFA was notably shorter compared to the baseline of ULSD. Fired engine testing was conducted using a single-cylinder CRDI experimental engine. Emissions were measured using a FTIR and Microsoot sensor. Combustion characteristics such as ignition delay, LTHR, pressure rise rate, peak pressure, ringing intensity, CA50, and combustion duration were compared to ULSD at matched operating modes. HEFA was observed to have a shorter ignition delay and smaller premixed combustion event, releasing more of its energy in mixing controlled combustion. This caused CA50 and overall combustion duration to be extended compared to ULSD. The combustion behavior of HEFA contributed to significant reductions in NOx and Soot emissions compared to ULSD. Cycle variability was reduced by half for HEFA, indicating smoother engine operation and combustion stability. These results showcase the versatility of this SAF to be used in IC engines with conventional combustion strategies.
Soloiu, Valentin, Willis, James, Norton, Coleman, Davis, Zachary, Peralta Lopez, Guillermo, Rahman, Mosfequr
The Effects of Ethanol on Combustion in a Super-Lean-Burn Engine2026-01-03034/7/2026
To mitigate global warming, many countries are working toward carbon neutrality. Reducing CO₂ emissions from vehicles requires electrification technologies in hybrid and plug-in hybrid electric vehicles (HEVs, PHEVs) and improving thermal efficiency of internal combustion engines (ICEs). Lean-burn combustion is one approach to improving ICE thermal efficiency. Biofuels and synthetic fuels can also reduce CO₂ emissions in existing vehicles. Ethanol, a bio-derived fuel, is widely used in varying contents worldwide, and its further utilization is anticipated. This study examines the effects of ethanol blending on emissions, thermal efficiency, knocking, and combustion speed in a super-lean-burn engine. Gasoline surrogates with varying ethanol contents were tested at an excess air ratio (λ) of 2.5. Higher ethanol content reduced nitrogen oxides (NOx) emissions due to lower adiabatic flame temperature. Total hydrocarbon (THC) emissions measured by a Flame Ionization Detector (FID) showed a decreasing trend; however, after correction for low sensitivity to ethanol and aldehydes, no significant differences were observed. Thermal efficiency increased with ethanol content, due to reduced cooling losses. Knocking was mitigated by the higher Research Octane Number (RON) from ethanol blending; however, the extent was smaller than in the production engine operating at λ = 1. This mechanism was examined through ignition delay calculations. At λ = 2.5 and in-cylinder pressures above 9 MPa, the 50–90% combustion duration was prolonged, attributable to suppressed ethyl radical formation under lean conditions and a greater influence of the reaction in which methyl radicals consume hydrogen atoms to produce methane under high-pressure conditions.
Sugata, Kenji, Matsubara, Naoyoshi, Yamada, Ryota, Kitano, Koji
The Influence of Split Injection Ratio on Efficiency and NO x Emissions in a Pilot Diesel-Ignited Hydrogen Direct Injection Engine2026-01-03294/7/2026
This study investigates the impact of the hydrogen split injection ratio on the combustion of pilot diesel-ignited hydrogen direct-injection engines, which is expected to affect hydrogen-air mixture conditions and thus flame propagation and diffusion flame developments. Experiments were conducted on a 1-litre single-cylinder diesel engine equipped with an additional hydrogen injector operating at 35 MPa. Hydrogen accounting for 95% of total input energy was injected at 150 and 60 °CA bTDC for the first and second pulses, which were selected as high-efficiency injection timings from previous equal-split injection tests. The 5% diesel energy was injected near TDC to control CA50 at 10 °CA aTDC. While varying the split ratio between the two hydrogen injections, in-cylinder pressure/aHRR profiles, engine efficiency/power output and engine-out emissions of NOx and CO2 were evaluated. Results showed that the hydrogen split ratio does not significantly affect IMEP/efficiency, which consistently achieved a 17.2% increase over the diesel baseline. While CO2 emissions remained at a very low level due to high substitution of hydrogen energy, they showed no dependency on the split ratio. By contrast, NOx emissions were highly sensitive to the hydrogen injection split ratio. Increasing the first hydrogen injection fraction to 30% reduced NOx, attributed to decreased locally rich mixtures formed by late second hydrogen injection and increased lean mixture homogeneity from early first hydrogen injection, leading to a slower burning effect. However, further increasing the first injection fraction led to higher NOₓ emissions due to increased hydrogen compression, which raised TDC and combustion pressure.
Zhao, Yifan, Chan, Qing Nian, Kook, Sanghoon
Effect of Passive Pre-Chamber Geometry on Performance and Emissions of a Single-Cylinder Natural Gas Large Bore Engine2026-01-03334/7/2026
The maritime industry is one of the most energy-intensive sectors, characterized by high fuel consumption and significant environmental impact. As global trade relies on shipping, the challenge of reducing pollutants and greenhouse gas emissions becomes ever more pressing. Natural gas (NG) is considered as a transitional fuel, capable of lowering CO₂ emissions by 20–30% compared to conventional marine fuels. However, to fully harness this potential, significant advances in combustion technology are necessary, particularly with ultra-lean combustion strategies. One of the most promising pathways is pre-chamber combustion, a solution that can simultaneously improve the efficiency and sustainability of NG marine engines. In this scenario, the passive pre-chamber geometry plays a key role, as it directly influences ignition behavior, combustion stability, and exhaust emissions. This work presents an experimental study conducted on a single-cylinder marine engine prototype, retrofitted from a diesel baseline, and equipped alternatively with four passive pre-chambers featuring different geometrical configurations. The tests were conducted at an engine speed of 1500 rpm and different loads to evaluate the influence of pre-chamber geometry on engine performance and exhaust emissions. Key parameters such as combustion phasing, efficiency, and pollutant formation were analyzed and compared between the four setups. Results showed that pre-chamber design affects the interaction between the turbulent jets and the main chamber mixture, leading to significant variations in both combustion efficiency and emission trends. These findings provide new insights into the role of passive pre-chamber geometry in optimizing large-bore NG marine engines, offering a valuable contribution to the development of cleaner and more efficient propulsion systems for the maritime sector.
Marchitto, Luca, Tornatore, Cinzia, Pennino, Vincenzo, Mariani PhD, Antonio, Beatrice, Carlo, Accurso, Francesco, Gorietti, Valentina, Pesce, Francesco, Giardino, Angelo, Vitti, Luciano
Effects of the Spark Location and Timing in a Heavy-Duty Hydrogen-Fueled Engine2026-01-03314/7/2026
The use of hydrogen in internal combustion engines offers a promising route to lower-carbon propulsion in heavy-duty transportation. However, its distinct combustion characteristics as high flame speed, wide flammability limits, and susceptibility to abnormal combustion, necessitate careful engine and ignition system design. This study numerically investigates the combined effects of spark plug (SP) location and ignition timing on the performance of a heavy-duty diesel engine converted to spark-ignition and operated with hydrogen as fuel at reduced compression ratio. The numerical study aims to guide engine design. Three-dimensional computational fluid dynamics simulations with detailed hydrogen chemistry were conducted to evaluate flame development, and relevant combustion metrics under different loads. Model validation against engine combustion data and hydrogen injection from a low-pressure, high-mass-flow direct injector are also presented. The results demonstrate that SP placement is pivotal to control for combustion stability and efficiency due to the complex in-cylinder mixing and stratification associated with direct hydrogen injection. For each load, optimal ignition timings were identified. Highlights demonstrate the feasibility of installing the SP close to the jet-forming cap (injector tip) to exploit local enrichment and enhance flame propagation.
Menaca, Rafael, Shakeel, Mohammad Raghib, Panithasan, Mebin, Liu, Xinlei, Qahtani, Yasser, AlRamadan, Abdullah, Cenker, Emre, Silva, Mickael, Pei, Yuanjiang, Turner, James, Im, Hong
Experimental Study of Hydrogen Combustion in Argon-Oxygen Mixture Using an Optical Engine2026-01-03284/7/2026
The Argon Power Cycle (APC) is an emerging high-efficiency combustion technology for internal combustion engines. In APC, the conventional air-based working fluid is replaced with an inert argon gas. This substitution inherently increases engine efficiency through thermodynamic properties of argon, in particular a high adiabatic factor ?? ~1.67. A hydrogen-fueled APC engine offers the potential for highly efficient zero emission combustion by also eliminating nitrogen oxide (NOx) formation. In the present paper, hydrogen combustion is studied in an optical heavy-duty research engine, with the objective of providing the first visualization of H2 combustion in an argon–oxygen mixture. A comparative analysis of high-speed optical imaging and in-cylinder pressure measurements is conducted for two different modes: 1) conventional air operation and 2) argon-oxygen mixture operation. The high-speed images reveal a distinctly different combustion process between the two operating modes. The main results of the study are as follows: 1) The cylinder peak temperature during compression, estimated from cylinder pressure, increases from approximately 800K (air) to 1200K (argon-oxygen). 2) Abrupt hydrogen pre-ignition was observed for the argon-oxygen mixture, leading to strong pressure oscillations. In contrast, for hydrogen-air combustion, the mixture was ignited by the spark without pre-ignition. 3) The initial heat release was significantly higher in the argon-oxygen mixture yielding a pressure rise in a few crank angle degrees (CAD) in contrast to 5-10 CAD for the air mixtures. 4) Extremely lean hydrogen combustion was observed for the argon-oxygen case.
Kapp, Joakim, Cheng, Qiang, Kaario, Ossi, Vuorinen, Ville
Assessing Energy Use, Cost, and Emissions of Small Regional Rail Vehicles: Methodology and Case Study on a German Track2026-01-04194/7/2026
This work evaluates a standardized 30-ton, 16 m railbus platform optimized for unelectrified regional service, focusing on propulsion system design and trade-offs between range, cost, and emissions. A MATLAB/Simulink drive-cycle model was developed to simulate energy consumption and component performance under realistic operating conditions. The Erfurt–Rennsteig route in Germany (130 km round trip, gradients up to 6 %) was selected as a representative case study. The model incorporates detailed sub-models for traction motors, lithium-ion batteries (LFP and LTO), fuel storage, fuel cells, and ICE gensets across multiple fuel options (diesel, gasoline, methane, ethanol, methanol, HVO, FAME, and hydrogen). Battery lifetime is estimated using a combined cycle- and calendar-aging model using the rainflow algorithm to extract charge cycles, while cost models include capital, fuel, maintenance, track fees, and staffing. Results show that battery-electric configurations achieve 1 kWh/km energy use, while hybrid systems range from 2–4 kWh/km depending on fuel and secondary power unit. Control strategies that enable deeper cycling of the traction battery reduce fuel consumption by 7–18 %, with further savings possible from larger battery or genset capacities. Well-to-wheel greenhouse gas emissions vary widely: from near-zero for renewable fuels and clean electricity mixes to over 1,000 gCO2/kWh for fossil-based options. Lifecycle cost analysis indicates that while fuel may represent up to 25 % of total costs, track and station fees dominate operational expenses. Autonomous operation could eliminate oboard staffing costs, amounting to 25–35 %.
Ahrling, Christoffer, Tuner, Martin, Gainey, Brian, Torkiharchegani, Amir, Scharmach, Marcel, Hertel, Benedikt, Alaküla, Mats
BEV Incremental CO 2 Emissions in a Ranked Order Electric Grid2026-01-04244/7/2026
Battery Electric Vehicles (BEV) have been sold as ‘Zero Emissions Vehicles’ (ZEV) by governments to reduce transportation CO2. While they are not ZEV because they run on grid electricity, they could be ‘effectively ZEV’ if the incremental CO2 is ‘very small’. At the national level, this is estimated using following metrics: (1) Internal Combustion Engine Vehicle (ICEV) fuel consumption, from the total US gasoline consumption divided by the total fleet miles driven, 25 mpg or 350 g CO2/mi, (2) Strong Hybrid Electric Vehicles (HEV) about one third less, 240 g CO2/mi. (3) BEV energy consumption, using data from systematic on-road testing of a wide range of vehicles, estimated at 40 kWh/100 mi for a US sales mix. (4) Electricity marginal CO2: in a ranked order grid, zero-CO2 sources are prioritized and supplemented by fossil sources. IEA hourly data show that the US 48 contiguous states are self-contained, with zero-CO2 sources providing a third of total demand. The response to hourly demand changes comes largely from natural gas and coal power stations, with EPA data showing a combined marginal CO2 of 600 g CO2/kWh. On replacing an ICEV by a BEV, the reduction in gasoline use, - 350 g CO2/mi, is offset to two thirds by higher electricity consumption, 40 x 600 / 100 = + 240 g CO2/mi. BEV marginal CO2 is therefore similar to HEV, and not ‘much smaller’ than ICEV. This is because HEV engines and fossil power stations have similar efficiency and similar fuel CO2 intensity.
Phlips, Patrick
Physics-Based Simulation for Sustainable Fuels Part 2.2: Inter-Ring Pressure Measurements and 2D/3D Ring Dynamics Analysis across Multiple Engine Platforms – Heavy Duty and Large Bore2026-01-02804/7/2026
The growing demand for sustainable mobility and transportation is accelerating the adoption of alternative fuels, particularly hydrogen, in internal combustion engines. The first part of this publication series highlights the significance of 2D simulation as a crucial and computationally efficient tool for the precise development of hydrogen Power Cylinder Units. This approach demonstrates predictive capability proofed through engine tests, achieving a reduction in lube oil consumption by 5 g/h during high-load operations, alongside a 28% decrease in blow-by and an 11% reduction in hydrogen flow to the crankcase. To provide deeper insights into the complexities identified in Part 1, this study employs inter-ring pressure measurements across various engine types and configurations, including light vehicles, heavy-duty trucks, and large-bore applications, covering a broad range of engine displacements from 2 to almost 100 liters. Part 2.1 focuses on understanding the cyclic variations and mechanisms that lead to oil emissions during low-load operations at a light vehicle, while this investigation in Part 2.2 focuses on upper compression ring instabilities, cyclic variation in a heavy-duty engine and as well as the factors contributing to irregular combustion phenomena at a large bore engine. Complementing predictive 2D simulations and inter-ring pressure measurements, targeted 3D analyses are performed for capturing three-dimensional effects such as bore distortion and ring conformability. These analyses yield valuable insights into oil transport mechanisms that can contribute to irregular combustion. Part 3 of this publication series will concentrate on 3D oil transport simulations and optimization, including predictions of absolute lube oil consumption ranges of the hydrogen engine discussed in Part 1, while building on the valuable insights gained from the in-depth investigation of Part 2.
Köser, Philipp, Moreira, Rui
The Impact of Mid-Level Ethanol Blends on Reliability, Performance and Emissions in Gasoline Engine2026-01-03024/7/2026
To reduce CO₂ emissions from automobiles, it is essential to improve system efficiency through the electrification of vehicles with internal combustion engines (ICEs), such as hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs), as well as through enhancements in ICE thermal efficiency. Additionally, biofuels and synthetic fuels are gaining attention as promising options to reduce CO₂ emissions from existing vehicles. Among these alternative fuels, ethanol, a bio-derived fuel, is already used at varying concentrations in many countries, and its further adoption is expected. Expanding the fleet of flex-fuel vehicles (FFVs) capable of running on high ethanol blends is one approach; however, increasing ethanol content in conventional gasoline, which is more widely used, is considered to have a greater impact on CO₂ reduction. A key issue is how existing vehicles adapt to increased ethanol concentrations such as E20, E30, and E40. This study focuses on turbocharged engines typically found in heavier passenger vehicles, which are less likely to be electrified, to assess the effects of varying ethanol concentrations on performance, efficiency, emissions, and reliability. The evaluation showed that increasing ethanol concentration from E0 to E40 in a fixed Blend stock for Oxygenate Blending (BOB) resulted in comparable or slightly improved torque and thermal efficiency, with emissions remaining similar and abnormal combustion tendencies suppressed. No reliability issues were observed in endurance testing. Furthermore, advancing ignition timing to take advantage of ethanol’s knock resistance within the constraints of mass-produced engines revealed that medium ethanol concentrations are sufficient to realize these benefits. Therefore, to improve output and thermal efficiency across a wider range of vehicles using the same ethanol volume, medium concentrations may be more advantageous than higher concentrations.
Matsubara, Naoyoshi, Sugata, Kenji, Koyama, Takashi, Ochi, Yuta, Aoki, Mizuki, Hashima, Takashi, Kodama, Kohei, Tomoda, Keiju, Kojima, Masakiyo
Combustion and Emission Characteristics of Biodiesel and Renewable Diesel in a 4-Stroke Locomotive Engine2026-01-03154/7/2026
Rail transportation in North America consumes over 4 billion gallons of diesel fuel [1]. This is raising energy security and supply chain resilience concerns. Adopting renewable or alternative fuels is a practical approach to reduce petroleum dependence and improve supply security. The objective of this paper is to investigate the combustion and emission characteristics of biodiesel and renewable diesel as drop-in fuels without engine modification. In this study, a single-cylinder, four-stroke locomotive engine was employed to investigate the combustion and emissions characteristics of four fuels: conventional diesel No. 2, plant-based biodiesel, animal-based biodiesel, and renewable diesel. The experimental campaign was carried out under both part-load and full-load operating conditions, with injection duration adjusted to achieve the targeted engine load and speed. Results indicate that both biodiesel fuels and renewable diesel deliver comparable peak in-cylinder pressure and brake thermal. efficiency relative to No. 2 diesel, demonstrating their possible use as drop-in fuels. Reductions in smoke emissions were observed for both biodiesels and renewable diesel fuels. However, plant-based and animal-based biodiesels both showed increases in NOx emissions under part-load conditions. At full load, elevated exhaust gas recirculation (EGR) ratios suppressed NOx formation across fuels, limiting assessment of biodiesel-specific NOx effects. Among the fuels tested, renewable diesel provided an additional advantage: reduced CO₂ emissions compared to both biodiesels. This study suggests that renewable diesel is a promising option for rail applications, combining operational performance comparable to petroleum diesel with reduced smoke and CO₂ emissions. Biodiesel, while effective at reducing smoke, may require further strategies to control NOx emissions.
Ewphun, Pop-Paul, Biruduganti, Munidhar, El-Hannouny, Essam, Longman, Douglas, Fu, Xiao, Subramanya, Raghavendra
Optimization Strategies of Gliding Arc Plasma-Based Ammonia Cracker towards Onboard Applications2026-01-02924/7/2026
Ammonia has emerged as a viable hydrogen energy carrier owing to its superior hydrogen density and mature industrial utilization. However, ammonia faces critical challenges including inadequate ignition characteristics and sluggish combustion kinetics, necessitating supplementary high-reactivity fuels for optimizing combustion. Onboard ammonia decomposition technology resolves this problem through on-demand hydrogen real-time production. Among existing ammonia decomposition methods, gliding arc plasma (GAP) demonstrates exceptional promise for onboard hydrogen production given its high processing flow rate，decent hydrogen conversion rate, and transient response capability. Prevailing research predominantly relies on experimental approaches, with insufficient understanding of the effects of specific electrical field parameters and inlet pressure on system performance. This study established a quasi-one-dimensional numerical model for GAP-assisted ammonia decomposition. A comprehensive analysis was conducted to examine the influence of key electric field parameters, such as reduced electric field strength (REFS) and electron density (De), on ammonia conversion rate and energy efficiency. Furthermore, the study explored the synergistic effects of inlet pressure and electric field parameters on system performance under constant mass flow rate conditions. The results indicate that increasing REFS and De significantly substantially elevates ammonia conversion rate, but energy efficiency decreases as these parameters increase. Keeping a constant NH3 inlet mass flow rate, the gas velocity decreases when the inlet pressure increases and then extends the residence time. Consequently, the ammonia conversion rate significantly improves while the energy efficiency slightly decreases. By increasing inlet pressure and simultaneously reducing REFS or De, system energy efficiency can be effectively enhanced without altering ammonia conversion rates. This study demonstrates the synergistic regulation mechanism of electric field parameters and inlet pressure on hydrogen production performance, providing optimization strategies for GAP reactor design.
Dong, Guangyu, Li, Xian, Zhou, Yanxiong, Xu, Jie, Li, Liguang
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
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
Reactivity Controlled Compression Ignition (RCCI) Combustion Engine Characteristics Fuelled with Diesel/Compressed Natural Gas (CNG) and Diesel/Methanol Fuel Pairs2026-01-03194/7/2026
Ultra-low oxides of nitrogen (NOx) and particulate matter (PM) from reactivity-controlled compression ignition (RCCI) combustion have motivated researchers to explore more about low temperature combustion (LTC) engines. In this study, a comparative analysis of combustion, performance, and emission characteristics of RCCI combustion fuelled with diesel/compressed natural gas (CNG) and methanol/diesel fuel pairs has been carried out with respect to baseline compression ignition (CI) combustion. All experiments were performed in a constant speed engine at four different engine loads. For RCCI combustion experiments, a constant premixed ratio (rp= 0.50) and 15% exhaust gas recirculation (EGR) were used. The results exhibited a significant reduction in NOx emissions and relatively smoother RCCI combustion compared to baseline CI combustion. RCCI mode combustion resulted in relatively superior engine performance compared to baseline CI combustion, especially at higher engine loads. A comparison between the RCCI combustion fuelled with gaseous fuel (CNG) as a low reactivity fuel (LRF) and a liquid fuel (methanol) showed a slightly lower brake thermal efficiency (BTE) of CNG/diesel fuelled RCCI combustion compared to methanol/diesel fuelled RCCI combustion at low loads. As the load increased, the trend of BTE was reversed. The combustion characteristics of CNG/diesel fuelled RCCI combustion were found to be more stable compared to methanol/diesel fuelled RCCI combustion. The NOx emissions were lowest in methanol/diesel fuelled RCCI irrespective of engine load. At low load, methanol/diesel fuelled RCCI suffered from higher hydrocarbon (HC) and carbon monoxide (CO) emissions, while CNG/diesel fuelled RCCI maintained relatively lower HC and CO emissions.
Saikia, Bhargav, Kant, Akshay, Gupta, Abhishek, Singh, Akhilendra Pratap
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