Diesel micro-pilot ignited methanol dual-fuel compression ignition engines represent a promising pathway to achieve high methanol substitution rate and low-emission combustion. In this study, a one-dimensional simulation model was established using GT-Power, and a hybrid multi-objective optimization method integrating response surface methodology, non-dominated sorting genetic algorithm-II (NSGA-II), and technique for order preference by similarity to an ideal solution (TOPSIS) was proposed. The optimization objectives were to maximize indicated thermal efficiency and minimize NOx specific emissions. Methanol injection timing, methanol injection duration, methanol substitution rate, and compression ratio were selected as decision variables. First, the effects of these parameters on combustion and emission characteristics were systematically analyzed. Subsequently, the Box-Behnken design and response surface methodology were employed to establish the mapping relationship between input parameters and responses. Finally, the Pareto optimal solution set was obtained using NSGA-II algorithm, and the optimal solution was further determined via TOPSIS method. The results indicate that methanol injection timing and compression ratio are the dominant factors influencing combustion performance and indicated thermal efficiency. Compared with the baseline case, the optimized parameters are as follows: methanol injection timing of - 23.5 degrees CA, injection duration of 30 degrees CA, methanol substitution rate of 97.5 %, and compression ratio of 22. Under these conditions, NOx specific emissions remained nearly unchanged, decreasing slightly from 9.047 to 9.041 g/kW & sdot;h, while the indicated thermal efficiency increased from 48.314 % to 49.283 %. Therefore, optimizing the pursuit of optimal indicated thermal efficiency while maintaining NOx specific emissions without deterioration. This study provides a theoretical basis for parameter matching and coordinated optimization of diesel micro-pilot ignited methanol dual-fuel engines.

Understanding the intricate interplay between soot dynamics and chemical reactions within catalytic diesel particulate filters (CDPF) is crucial for enhancing both filtration efficiency and regeneration performance. In this paper, we establish a unified pore-scale multiphysics model based on the Eulerian-Lagrangian framework to comprehensively resolve the transport, deposition, and oxidation of soot. Distinguishing itself from conventional empirical correlations and stochastic-based approximations, the system models soot deposition through fundamental physical principles, integrating elastic deformation and surface adhesion mechanics at the particle-wall interface. Simultaneously, it incorporates a robust oxidation model that accounts for the competitive kinetics of both O2 and NO2 pathways, enabling comprehensive coverage of all CDPF operating regimes. Validated against three classical benchmark cases, the model demonstrates superior accuracy in capturing interfacial mass transfer and particle-wall interactions. Simulation under a typical CDPF low-temperature operating condition emphasizes the pivotal role of NO2 and a catalyst in promoting regeneration and reveals complex synergistic and competitive effects between distinct reaction pathways. Notably, the reaction rate of direct O2 pathway is accelerated by a factor of 87 in the presence of the catalyst. For ultra-fine soot particles ( 50 nm), the Brownian motion and thermophoretic forces directly dictate the deposition efficiency. Their strong thermal sensitivity also underscores the necessity for an integrated soot transport-deposition-oxidation framework. To support further research, the model implementation can be accessed at https://github.com/zhangyujing2001/CDPF_Multiphysics_Model.git [Y. Zhang, Y. Zhang, L. Fang, D. Lou, P. Tan, and Z. Hu (2026). "Data for 'A unified pore-scale multiphysics model for the integrated soot transport-deposition-oxidation in catalytic diesel particulate filters,'" GitHub. https://github.com/zhangyujing2001/CDPF_Multiphysics_Model].

This study investigated the use of Cu/SSZ-13 (3 wt% Cu, Si/Al = 18) for SCR (Selective Catalytic Reduction) system of hydrogen internal combustion engines (H-2-ICEs). Standard and fast SCR activities were evaluated under severe hydrothermal aging and transient steam perturbation, and multi-scale characterizations elucidated deactivation mechanisms. Cut-off tests with 10% and 30% H2O quantified water sensitivity of fresh and aged catalysts, showing that transient perturbation at 30% H2O selectively weakened low-temperature NH3 adsorption and high-temperature tolerance, thereby suppressing standard SCR across low- and high-temperature regimes. With NO2 co-feed, fast SCR exhibited enhanced low-temperature activity via nitrate-assisted pathways, whereas at high temperature aged samples exhibited performance gains, suggesting that high humidity altered the competition between SCR and oxidation side reactions. H-2 showed a dual effect, with low temperature promotion and higher temperature inhibition. Cumulative aging at 10% H2O converted ZCu(OH) to Z(2)Cu with concomitant Bronsted acid loss; 30% H2O further generated dispersed CuOx/CuAl2O4 and extra-framework Al, causing coupled declines in redox capacity and acidity. At the coated-core level, a water sensitivity index showed reversible, moderate inhibition for fresh cores but pronounced susceptibility after aging, including high-humidity promotion at elevated temperatures. System level engine bench integration identified an optimal ammonia to NOx ratio (NSR) of similar to 1.1, achieving near zero NOx over the WHSC cycle. Overall, severe humidity accelerated the transformation of active Cu species and acid sites, while cross scale evaluation linked microscopic deactivation to macroscopic performance, providing a mechanistic basis for designing durable SCR catalysts under humid H-2 ICE exhaust conditions.

Ultra-lean hydrogen direct-injection spark-ignition engines offer high-efficiency, low-carbon potential for heavy-duty applications, but their combustion is highly sensitive to injection-governed mixture stratification in the vicinity of the spark plug. In this study, a validated three-dimensional numerical model was employed to investigate how injection phasing, split ratio, and inter-injection interval affect ignition-neighborhood mixture distribution, early flame development, combustion phasing, and indicated thermal efficiency. For single injection, retarding SOI produced a distinctly non-monotonic response. A moderate SOI retard reorganized the near-spark mixture field into a more favorable state, strengthening local enrichment while maintaining workable stratification, which accelerated flame-kernel establishment, advanced CA50 from about 12.5°CA ATDC to 6.5–7.3°CA ATDC, shortened CA10–ST from about 10–11°CA to 5–6°CA, reduced combustion duration from about 38°CA to 30–32°CA, and increased indicated thermal efficiency from about 43–44% to about 45%. Further SOI retard, however, drove the near-spark mixture toward excessively lean and highly heterogeneous conditions, so that the accompanying increase in turbulent kinetic energy could no longer compensate for the deterioration in ignitability and combustion development. For split injection, the main advantage lay in decoupling bulk-charge preparation from ignition-region conditioning. Within the mass-split-ratio group, an equal mass split provided the most favorable response by achieving a better balance between background mixture formation and near-spark enrichment, while a moderately retarded injection window further promoted early flame development and combustion phasing. In contrast, excessively long inter-injection intervals preserved stratification into the end of compression but prolonged late-stage combustion, resulting in a non-monotonic efficiency response. Overall, the results indicate that, under ultra-lean conditions, precise control of the local mixture state near the spark plug is more critical than turbulence enhancement alone for improving combustion and efficiency.

With increasingly stringent emission regulations for heavy-duty engines and the growing demand for decarbonization in the transportation sector, the development of efficient low-carbon alternative fuels has become a key technological pathway. Methanol, as a renewable oxygenated liquid fuel, has attracted extensive attention in internal combustion engines due to its favorable storage and transport properties and low-carbon potential. However, its low cetane number, high latent heat of vaporization, and low energy density limit its performance in single-fuel applications. Therefore, establishing methanol dual-fuel combustion systems is regarded as an effective approach to improve combustion efficiency and emission performance. This paper systematically reviews the research progress of methanol dual-fuel engines. First, the physicochemical properties of methanol and their effects on spray, ignition, and combustion processes are analyzed. Subsequently, the combustion characteristics and compatibility mechanisms of three typical dual-fuel systems, including methanol-gasoline, methanol-diesel, and methanol-hydrogen, are discussed in detail. On this basis, the regulatory effects of injection strategies, combustion chamber optimization, and advanced combustion modes on combustion processes and emission characteristics are further summarized. The results indicate that dual-fuel synergistic mechanisms can effectively improve the ignition characteristics of methanol, enhance thermal efficiency, and significantly reduce nitrogen oxide and particulate matter emissions. Finally, a systematic technical framework for efficient and clean combustion is proposed, providing theoretical support and development directions for the engineering application of methanol in heavy-duty engines.

As emission regulations continue to tighten limits on particle number (PN), Catalytic Diesel Particulate Filters (CDPF) play a crucial role in achieving particulate capture and catalytic oxidation. However, the coupled effects of catalyst coating morphology on pore-scale flow behavior, particulate deposition, and pressure drop remain insufficiently understood. Based on the DPF channel structure reconstructed from high-resolution 3D X-ray microscopy (XRM), representative 2D cross-sections were selected to establish pore-scale numerical models. Using the LBM and cellular automata, this study investigated the effects of uniform and non-uniform catalytic coating distributions, as well as different coating loadings, on the local velocity field, pressure drop, and particle collection efficiency. The results indicate that non-uniform coating tends to generate localized high-velocity regions and low-velocity dead zones within narrowed flow passages, thereby altering particle transport paths and promoting earlier particle deposition in the upstream region of the DPF. As the coating thickness increases, the pressure drop rises nonlinearly, and particle accumulation is enhanced in locally constricted regions. The particulate capture efficiencies of the uniform and non-uniform coating strategies are very close (99.11% and 98.92%, respectively). Under the three coating cycles coating condition considered here, the pressure drop of the non-uniform coating case is approximately 50% of that of the corresponding uniform coating case, suggesting that spatial regulation of catalyst distribution may help alleviate the pressure-drop penalty while maintaining a comparable capture level. Overall, the pore-scale analysis of flow fields and particle deposition in CDPF may provide useful insight into catalyst coating design and structural optimization under increasingly stringent PN constraints.

The oxidation regeneration performance of the catalyzed diesel particulate filter (CDPF), a standard configuration for current diesel engines, depends on high-performance soot catalysts. This work systematically studied the Pt-Pd synergistic effect and Ce doping regulation mechanism of CDPF soot catalyst, using physicochemical characterization, catalytic activity evaluation, and density functional theory (DFT) calculation methods. The results show that Ce doping refines particle size, enhances catalyst particle distribution, and increases specific surface area (SBET), and these improvements increase with Ce content; however, a reverse trend is observed with the Ce doping amount reaching 20 wt%. The incorporated Ce primarily exists as Ce3+ and Ce4+ species, which enhance the oxygen transfer rate on the catalyst surface, improving its soot oxidation performance, thus lowering the ignition temperature and activation energy. A best catalyst performance occurs at the 10 wt% Ce doping level, with the ignition temperature T10 and the activation energy reducing to 260.95 degrees C and 168.77 J/mol, respectively. The DFT results indicate that the catalyst performance improvement with Ce doping is due to the formation of CeOx and Pt-Pd interfaces, providing high-activity sites for the adsorption and activation of O2 and NO, and enhancing electron transfer to adsorbed molecules. The synergistic effect of the crystal lattice oxygen mechanism and the MvK lattice oxygen mechanism enhance reactive oxygen species and their generation pathways, which is beneficial for the soot oxidation

As a key component affecting the service life of Stirling engine, the piston seal ring work for long periods in harsh environments, such as high temperatures, high speeds, and reciprocating motion. This study focused on the polytetrafluoroethylene (PTFE) composite seal rings filled with nano-zirconia (nano-ZrO2). The synergistic effects of polyimide (PI) and carbon fiber (CF) with nano-ZrO2 on the tribological properties of PTFE sealing materials were analyzed. Meanwhile, the sealing performance of the piston ring is investigated under the cold-start conditions, and the 200- hour dynamic sealing tests are completed. The results show that the PTFE composites with PI are not suitable for high temperature and high-speed reciprocating seals. CF can significantly improve the sealing performance of piston rings. The synergy between Nano-ZrO2 and CF promotes a denser friction transfer film, which greatly enhances the wear resistance of the sealing material. The results obtained from material testing and component bench testing collectively indicate that the fabricated PTFE composite materials possess considerable potential for practical application in Stirling engine cylinders.

This study examines how the equivalence ratio (phi) governs the combustion behavior and knock propensity of a hydrogen-fueled engine under ultra-lean to lean conditions. Engine experiments were conducted at various phi values (0.26-0.45) to measure in-cylinder pressure and combustion metrics. The results show that increasing phi markedly advances combustion phasing and accelerates flame development. At phi = 0.45, the KI in certain cylinders exceeded 0.5, and the average KI rose from 0.2 to 0.3 as phi increased - highlighting a clear rise in knock risk with richer mixtures. Meanwhile, combustion stability improved significantly: the cycle-to-cycle coefficient of variation of IMEP decreased from >3.5% at phi = 0.26 to similar to 1.5% once phi > 0.30, indicating enhanced stability. Using principal component analysis (PCA), the complex influences of phi were distilled into dominant features: phi emerged as the dominant factor affecting combustion rate, phasing, stability, and knock tendency. The PCA revealed how higher phi shifts the combustion regime toward faster, more efficient burning but with increased knock tendency. These findings provide a valuable data basis for optimizing hydrogen engine operation - emphasizing that equivalence ratio tuning is critical to balancing efficiency gains against knock mitigation in lean-burn hydrogen engines.

Active pre-chamber (APC) ignition enables ultra-lean combustion, yet practical operability depends on the implemented dilution strategy and control. Because direct same-hardware comparisons between different dilution routes remain limited in the open literature, this study contrasts two implementable dilution strategies-fuel-based dilution (reducing main-chamber fueling at approximately fixed intake pressure) and intake-pressure-based dilution (varying the absolute intake-manifold pressure at a fixed main injection command)- in an optically accessible single-cylinder APC SI engine at 2000 r/min under CA50-controlled conditions. Synchronized pre-/main-chamber pressure and natural-luminosity imaging are used to map the operability envelope and the trade-offs in IMEP, stability, indicated efficiency, and measured NO/HC from lambda = 1.2 to 2.2. For lambda <= 1.8, fuel-based dilution is associated with faster apparent heat-release development and lower measured NO. Near the ultra-lean limit (lambda >= 2.0), the intake-pressure-based route tends to retain higher Delta Pmax (pressure-based proxy) and more persistent detectable luminosity, accompanied by a higher indicated thermal efficiency in the present optical low-load configuration and a suppressed HC rise. A pressure-derived pre-chamber index is further partitioned into three stages (JetE,-JetE3) as processing-defined descriptors. Because the two strategies require different actuation adjustments to meet CA50 and do not strictly match thermodynamic state at the same lambda, the results are interpreted as strategy-level, route-associated responses within the present test window. The tested intake-pressure route should be regarded as a sub-atmospheric, de-throttling-like intake-pressure variation rather than genuinely boosted operation; within this scope, the results provide lambda-dependent strategy windows for extending APC lean operability.

The wall-flow DPF (Diesel Particulate Filter) is currently the most effective technical solution for diesel particulate reduction, with its porous medium playing a crucial role in particulate matter capture and regeneration processes. This study constructs a DPF porous medium model based on the Quartet Structure Generation Set (QSGS) and optimizes its flow domain. The optimized model demonstrates better flowability. Enhancing the velocity at the inlet can markedly improve the heat transfer efficiency. The Lattice Boltzmann method is employed to methodically examine the heat transfer properties of the DPF porous medium at the micro-nano level. The results indicate that the optimized porous medium model exhibits higher temperature uniformity in the temperature field distribution, especially in the middle region in the horizontal direction, and improves the heat transfer efficiency of the porous medium. When the dimensionless inlet velocity increases from 1 × 10− 5 to 1 × 10− 3, the dimensionless temperature in each region increases significantly. The thickness of the wall greatly influences the temperature in the central area of the front half. The thicker the wall, the lower the dimensionless temperature in the same region, and the poorer the heat transfer performance of the porous medium. The presence of porosity does not markedly influence the spread of temperature across various horizontal areas. The temperature distribution under different porosities fluctuates irregularly with changes along the y-axis. When the porosity decreases from 0.8 to 0.6, the temperature in each region along the y-axis increases significantly. The objective of this research is to uncover the heat transfer properties of the DPF porous medium on a micro-nano level, laying a theoretical groundwork for optimizing DPF structure.

Ethanol and gasoline have long been used as blending fuels, yet their combined application in active pre-chamber (PC) jet ignition systems remains scarcely studied. This work integrates CFD simulations with optical singlecylinder engine (OSCE) experiments to evaluate anhydrous ethanol and gasoline as PC jet-ignition fuels in a port fuel injection spark-ignition engine (2000 rpm, PLFI = 20 MPa, tID = 0.3-0.8 ms). Results show that ethanol yields a lower global excess-air ratio (2PC) but a narrower spatial 2 distribution at ignition, indicating more homogeneous in-chamber mixing. Consequently, ethanol promotes earlier jet phasing and shorter main-chamber burn duration, while maintaining comparable jet intensity. Ethanol operation further produces lower combustion temperatures and NO emissions, albeit with higher HC, and its particulate behavior transitions from elevated particle number (PN) at short tID (<= 0.4 ms) to substantially lower PN than gasoline when tID >= 0.5 ms. Soot remains negligible in the pre-chamber and primarily originates from gasoline combustion in the main chamber. Overall, the study demonstrates ethanol's potential as a low-carbon jet-ignition fuel that supports efficient, lowtemperature combustion and cleaner emissions in spark-ignition engines.

Hydrogen internal combustion engines (HICEs) provide a promising zero-carbon pathway, yet studies on combustion chamber design for port fuel injection (PFI) HICEs remain limited. This work investigates three chamber geometries (shallow bowl, deep bowl, and 0)-type) to evaluate their effects on in-cylinder flow, mixture distribution, combustion, and knock characteristics using a multi-indicator assessment. Results show that during late compression, the shallow bowl chamber forms a compact flow structure without central stagnation, achieving the highest tumble ratio and turbulence kinetic energy (TKE), at least 8.81% higher than others. It also exhibits the lowest mixture non-uniformity, reduced by at least 11.4%, indicating superior mixing quality. Under identical excess air ratio, the 0)-type chamber shows faster flame propagation and more concentrated heat release, while the shallow bowl demonstrates lower knock tendency. Overall, the shallow bowl chamber achieves the best balance between mixture formation, combustion, and knock suppression.

Electrically heated catalyst (EHC) has the potential to alleviate uncontrolled emissions during vehicle startup phase by actively heating exhaust to activate catalyst reactions. This study evaluated the pollutant control performance of a low-power EHC coupled with DOC/DPF/SCR aftertreatment system under Cold/Hot World Harmonized Transient Cycle (WHTC) conditions. The study adopted a conservative heating strategy obtained from a model gas test bench. The results indicate that activating EHC in cold environments can directly reduce 21.40% of CO, 51.69% of THC, and 17.85% of NOx, in compliance with Euro VII emission regulations. In the performance testing of vehicles under actual road conditions, the intervention of EHC achieved a NOx conversion efficiency of over 85% for the vehicle under all operating conditions. The energy efficiency analysis of EHC shows that the energy transfer efficiency and energy level conversion efficiency are affected by the flow rate and environmental temperature gradient. From the perspective of policy promotion costs, adopting a new configuration of aftertreatment system is more competitive than some current policies.

Injection pulse width (IPW) is a critical parameter governing the mixture formation and combustion characteristics of port fuel injection (PFI) hydrogen internal combustion engines (HICEs). Based on a heavy-duty sixcylinder PFI HICE, this study investigates the effects of five IPW conditions (56 degrees CA to 68 degrees CA) on mixture distribution via 3D simulation. By introducing the hydrogen mass spatial mixing deficiency (HSMD) and spatial angular distribution, the regulatory mechanism of IPW on the temporal and spatial distribution of the air-fuel mixture in the intake port and cylinder is quantitatively revealed. The results show that with the reduction of IPW, the peak in-cylinder pressure and peak heat release rate decrease by 24.69% and 33.93%, respectively, accompanied by an extended combustion duration. The late combustion phase is the most significantly affected by the IPW. Under long IPW conditions (>= 62 degrees CA), the maximum pressure oscillation amplitude of partial monitoring points exceeds 0.1 MPa, indicating a prominent knock tendency. In the intake port, hydrogen mainly flows through the single-side manifold. A shorter IPW advances the peak HSMD with a higher peak value, and simultaneously restricts the circumferential diffusion of hydrogen. The maximum in-cylinder turbulent kinetic energy increases by 7.5% with the reduction of IPW, while the mean HSMD rises and the phase of the peak value advances. The hydrogen-rich region before ignition gradually shrinks with the shortening of IPW.

The Diesel Particulate Filter (DPF) is an essential device for meeting stringent vehicle emission regulations. Ash bridges-sintered ash structures spanning DPF channel walls-represent a critical failure mode that degrades DPF performance by increasing pressure drop, fuel consumption, and particle emissions. While prior studies have characterized ash bridge morphology, but quantitative assessment of their impact under real engine conditions remains limited. This study experimentally evaluates the influence of ash bridges derived from Zn-, Ca-, Mg-, and composite-based lubricant additives on DPF pressure drop, specific fuel consumption (SFC), and filtration efficiency using an engine test bench. Ash-based DPFs were prepared via accelerated loading on a burner bench, verified in our previous work, and tested under three protocols: (1) steady-state cycles (no prior soot, to assess intrinsic resistance), (2) soot accumulation, (3) active regeneration. Results show that even without soot, ash bridges introduce significant basic pressure drop: Mg-bridged > Ca-bridged > composite-bridged > Zn-bridged > fresh DPF, governed by blockage rate and bridge position. During soot loading, Mg- and composite-based DPFs reached > 40 kPa pressure drop within 0.5-0.7 h, with SFC surging to 260-280 g/kWh, due to reduced effective volume and localized soot compaction. Regeneration responses varied: Ca-bridges maintained high resistance (flat pressure profile), Mg and composite bridges induced severe congestion effects leading to thermal run-away and sharp pressure peaks (>40 kPa), and Zn-bridges delayed pressure drop decline due to obstructed convective heat transfer shifting regeneration to a conduction-dominated process. Filtration efficiency degradation was related to load and speed: under high load or high speed, Mg-based DPFs exhibited PN efficiency < 97% due to increased wall velocity and particle blow-off/escape; Zn-based DPFs showed consistently lower efficiency due to wall breakage. Ca-based DPFs maintained high efficiency across conditions. The results provide quantitative benchmarks for optimizing lubricant formulations.

The diesel particulate filter is an effective technology to reduce diesel particulate emissions, and its performance is closely related to catalyst loading. Based on the platform test system of heavy diesel engine, the influence of catalyst amount on the pressure drop, gas state and particulate emission reduction performance of diesel CDPF regeneration was studied. The results show that the exhaust back pressure of catalyst increases linearly with the increase in catalyst loading. When catalyst loading increases from 0 g/ft(3) to 5, 10 and 20 g/ft(3) (1 ft(3) =0.0283 m(3)), the average exhaust back pressure increases from 2.94 kPa to 3.44, 3.96 and 4.51 kPa, respectively. The larger the amount of catalyst, the better the emission reduction effect of the catalytic converter on CO and total hydrocarbon (THC). When catalyst loading increases from 0 g/ft(3) to 5, 10 and 20 g/ft(3) , CO emission decreases from 78.94 & times;10(-6) to 71.39 & times;10(-6), 68.12 & times;10(-6 )and 63.30 & times;10(-6), and THC emission concentration decreases from 57.34 & times;10(-6) to 48.31 & times;10(-6), 46.93 & times;10(-6) and 44.51 & times;10(-6), respectively. The amount of catalyst has a significant effect on NO oxidation, but not on NOx emission concentration. Catalyzed diesel particulate filter (CDPF) can achieve a reduction rate of more than 95% for particulate matter and particulate number. Increasing catalyst loading improves the particulate emission reduction effect of CDPF, with a more significant improvement in the reduction effect of nucleation particles. The results of this study have important reference value for the design of high-performance CDPF.

Ultra-lean hydrogen direct-injection engines require coordinated control of mixture preparation and early flame development to achieve high efficiency and robust combustion. This study numerically investigates the coupled effects of injection timing, mass split, overall injection phasing, and inter-injection interval in a heavy-duty hydrogen spark-ignition engine operating at 950 rpm under the investigated ultra-lean condition. Five single-injection cases and ten split-injection cases were compared using near-spark excess-air-ratio and turbulent-kinetic-energy statistics, three-dimensional G = 0 flame-front evolution, combustion phasing, and indicated thermal efficiency. For single injection, moderate retard of the start of injection produced the most favorable near-spark mixture condition, shortened the CA10–ST early combustion-establishment duration from approximately 10–11°CA to 5–6°CA, advanced CA50 from about 12.5°CA ATDC to 6.5–7.3°CA ATDC, and increased indicated thermal efficiency from approximately 43–44% to about 45%. Further retard increased local turbulence but produced a leaner and more spatially dispersed ignition-neighborhood mixture, resulting in slower combustion development. For split injection, the first pulse primarily established the background mixture and flow field, whereas the second pulse adjusted local enrichment closer to spark timing. An equal mass split provided the most favorable response within the mass-split group, while moderately retarding the overall injection window further accelerated early flame growth and combustion phasing. Excessively long inter-injection intervals preserved stronger stratification but prolonged the late CA90–CA50 combustion stage. Across all cases, higher efficiency was consistently associated with a shorter CA10–ST interval, earlier CA50, and a favorable near-spark mixture state rather than with increased turbulence intensity alone. These results demonstrate that coordinated control of injection scheduling provides an effective route for optimizing ultra-lean hydrogen combustion and indicated efficiency.

Hydrogen fueled (H2) engines, owing to their zero carbon emission characteristics, have attracted increasing attention as a promising pathway toward carbon neutrality. To investigate the operability boundaries and combustion stability of a turbocharged direct injection (DI) H2 engine near the lean and rich operability limits in terms of lambda, bench tests were conducted on a 2.261 L turbocharged DI H2 engine. The lean and rich stability limits for stable operation under different operating conditions were identified, and the combustion and emission characteristics near the lambda boundaries were systematically analyzed. In addition, correlation analysis was employed to quantify the relationships among key operating parameters under various conditions. The results showed that, at 1400 rpm and 50 N m, excessively low lambda induced a secondary maximum cylinder pressure peak (Pmax) and was accompanied by increased cycle-to-cycle fluctuations. Within the tested speed and load range, the lean operability boundary expanded to lambda = 4.9 with increasing engine speed. Correlation analysis further confirmed that engine speed and lambda were the dominant factors governing variations in Pmax and combustion phasing, providing a basis for stable combustion boundary management of DI hydrogen engines.