Against the backdrop of an increasingly severe energy crisis, developing electrochemical optimization approaches for biomass-fueled engines holds substantial importance. This study constructs a multi-fuel combined supply system based on gasoline port injection (GPI), bio-ethanol direct injection (BEDI), and negative pressure oxy-hydrogen intake, and explores the coupled influence mechanisms of bio-ethanol direct injection ratio (BEDIr), direct injection pressure (DIP), and oxy-hydrogen flow rate on the performance of a spark ignition (SI) engine. Experimental findings indicate that the introduction of oxy-hydrogen significantly improves combustion characteristics. Compared to the baseline condition without oxy-hydrogen and with 0% BEDIr, at an oxyhydrogen flow rate of 16 L/min, the peak cylinder pressure (Pmax) was increased by 7.4%, and the coefficient of variation of indicated mean effective pressure (COVIMEP) decreases by 37.4%. Oxy-hydrogen improves the engine's tolerance to high BEDIr conditions, and moderately increasing DIP can synergistically enhance the brake mean effective pressure (BMEP) under high BEDIr and significantly shorten flame-development and rapidcombustion intervals. In terms of emissions, increased BEDIr reduces CO and HC emissions, an effect strengthened further by oxy-hydrogen addition. For the increase in NOx emissions by oxy-hydrogen, high BEDIr (60-80%) effectively suppresses combustion temperature through its high latent heat of vaporization, forming a favorable complementary relationship in emissions.

Oxyhydrogen, a hydrogen-based fuel, is commonly used to enhance the performance of ethanol-gasoline engines. We experimentally investigated the combustion characteristics and emissions of a multi-fuel combined supply system using oxyhydrogen negative pressure induction, bioethanol direct injection (BEDI), and gasoline port fuel injection. At 1500 rpm and excess air ratio 1, integrated oxyhydrogen technology improves combustion efficiency and significantly reduces CO and HC emissions; however, NOx emissions increase. With increasing BEDI pressure, the indicated mean effective pressure (IMEP) and maximum in-cylinder pressure increase initially and then decrease. CO and HC emissions show a similar trend, decreasing initially and then increasing, while NO is reduced by an average of 14.09%. Advancing BEDI timing benefits the cyclic coefficient of variation of IMEP. When the BEDI timing is within 250-300 degrees CA BTDC, HC, CO, and particulate emissions reach their lowest levels, with particulates decreasing by up to 70.11%.

Turbulent Jet Ignition (TJI) engines show promising potential for enhancing engine efficiency. However, they differ significantly from conventional spark ignition engines in terms of in-cylinder combustion modes, rendering traditional detonation evaluation methods inadequate for accurately assessing TJI engine detonation states. This study introduces two new metrics: Before θPmax (the crank angle corresponding to peak cylinder pressure) Detonation Energy (BPDE) and After θPmax Detonation Energy (APDE) to characterize the knock behavior of TJI engines. Through analyzing the knock characteristics of the TJI engine under different compression ratio (CR), the author found that when the CR increased from 13 to 17 and the ignition angle was set to 12°CA bTDC, the engine's AMAPO increased by 0.55 MPa, and TDE increased by 0.8 MPa·°CA. However, when the CR reached 19, although TDE increased by 0.192 MPa·°CA, AMAPO decreased by 0.145 MPa. Two newly introduced metrics explain this phenomenon: when the CR increased from 17 to 19, ABPDE rose by 62.3% while AAPDE decreased by 15.5%. Knock energy primarily shifted to ABPDE, causing AAPDE to decline and resulting in the decrease of AMAPO. Additionally, no super-knock phenomena were observed at a CR of 19 and 70% load. The knock frequency distribution of TJI engines at different CRs was analyzed using Fast Fourier Transform (FFT). Statistical probability distribution (PD) and cumulative distribution (CD) were employed to estimate changes in Maximum Amplitude Pressure Oscillation (MAPO) across varying CRs. The knock characteristics of TJI engines were further detailed.

Based on a three-dimensional simulation platform, this study investigated the effects of N2, CO2, and O2 as dilution gases on the combustion and emission performance of methanol engines under constant total fuel quantity, dilution ratio of 10%/20%, and blending ratio of 0%/10%/20% conditions. In terms of combustion performance, diluting the syngas can shorten the ignition delay period and combustion duration, advance the combustion center, increase the peak cylinder pressure and temperature, and the effect is most significant when CO2 is diluted (for example, in the 20% dilution ratio CO2 condition, the 20% blending ratio is 3.5 °CA shorter than 0%); the ignition delay period and combustion duration become longer, the cylinder pressure decreases under CO2 conditions, and slightly increases under N2 and O2 conditions. In terms of emission performance, NOX emissions are CO2 < N2 < O2 (at a 10% dilution ratio and 10% blending ratio, CO2 relative to O2 reduces NOX by 98.5%); under O2 conditions, syngas blending reduces CO emissions, while under N2 and CO2 conditions, it increases, and under CO2 with a 20% dilution ratio, CO sharply increases; syngas blending reduces the emissions of HC, CH3OH, and CH2O, and under O2 dilution, the CO emissions are the lowest, and they increase as the dilution ratio increases. In summary, N2 dilution is beneficial for the coordinated optimization of combustion and NOX emissions.

Amid the escalating global energy crunch, the sustainable clean energy is a core development direction for power systems. This study employs a combined experimental and numerical analysis approach to systematically investigate the effects of fuel supply strategies on combustion performance for an engine utilizing a ternary-fuel combined supply system consisting of "oxyhydrogen negative pressure inhalation + bio-isopropanol direct injection + and gasoline port injection" (ONPI + BIDI + GPI). The numerical analysis indicates that increasing the oxyhydrogen blend ratio enhances the peak concentrations of key radicals (OH, HO2, HCO) and intermediate products (H2O2, CO), optimizes the OH distribution in the cylinder, and raises the temperature in the cylinder. This explains the experimental observation that ONPI significantly improves engine combustion performance. Bench test results indicate that when the bio-isopropanol direct injection timing (BIDIT) is set in the intake stroke, HRR, Pmax, and combustion process parameters of the engine are significantly better than when set during the compression stroke. The engine's HRR, Pmax, IMEP, combustion process parameters, and CoVIMEP all improved with an appropriate increase in bio-isopropanol direct injection pressure (BIDIP), but excessively high BIDIP actually deteriorated the in-cylinder combustion environment. Notably, the coupled optimization of ONPI and BIDIT can enhance the power performance and combustion process of engines. Finally, this paper proposes "ONPIv = 16 L/min +250 degrees C A BTDC <= BIDIT <= 300 degrees C A BTDC + BIDIP = 9 MPa" as a feasible fuel supply strategy for improving the combustion performance of the system under the test conditions.

Spark-assisted compression ignition (SACI) enables high-efficiency and clean combustion. However, existing studies focus mainly on knock suppression, with insufficient research on the multi-parameter coupling effects on two-stage combustion phasing, especially for methanol-gasoline blends. To achieve precise combustion control, higher thermal efficiency, and lower emissions, this study investigates the effects of excess air ratio (excess air ratio) and valve strategy on SACI combustion and performance under various methanol blending ratios. Results show methanol blending ratio and excess air ratio effects on SACI are negative valve overlap (NVO) dependent. When the NVO = 20-40 degrees CA, the end-gas auto-ignition advances and then retards as the methanol blending ratio increases, accompanied by a decrease in end-gas auto-ignition cycle variation (COVCI) and a shorter flame propagation stage (AIT-SP). When the NVO reaches 60 degrees CA and the methanol blending ratio is >= 40%, the end-gas auto-ignition steadily advances, while the COVCI dramatically increases and the AIT-SP extends. Increasing excess air ratio to 1.3 still promotes end-gas auto-ignition and maintains a high end-gas auto-ignition combustion ratio at NVO = 20-60 degrees CA. However, at NVO between 80 and 100 degrees CA, only excess air ratio at 1.1 helps auto-ignition. Increasing excess air ratio further raises COVCI. Also, adjusting both NVO and excess air ratio optimizes equivalent specific fuel consumption (ESFC) and cuts NOx emissions. Adding methanol further reduces emissions. To optimize ESFC and discover the best control strategy for various methanol blending ratios, a neural network model was developed and validated, and the adaptive particle swarm optimization method was used for parameter optimization. The results reveal that all of the optimized parameters enhance ESFC when compared to the original.

Combining biobutanol and oxyhydrogen in an SI engine can reduce fossil-fuel use and improve power, but oxyhydrogen increases NOx. Without sacrificing combustion stability, this work investigates lean-burn coupled with exhaust gas recirculation for a gasoline port injection + biobutanol direct injection + oxyhydrogen in-cylinder negative pressure indraft engine, across five oxyhydrogen flow levels, four exhaust gas recirculation ratios, and three excess air ratios. Results show that with lean-burn + exhaust gas recirculation, oxyhydrogen more effectively lowers the coefficient of variation of indicated mean effective pressure and increases indicated mean effective pressure, peak cylinder pressure, and peak heat release rate. With 16 L/min oxyhydrogen, the negative effects of 6-12% exhaust gas recirculation on CA 0-10 and CA 10-90 are mitigated for all excess air ratios, and the crank angle corresponding to peak pressure remains optimal under lean conditions when 6% <= exhaust gas recirculation <= 12%. Oxyhydrogen reduces CO and HC after exhaust gas recirculation, while lean-burn dominates CO reduction. Exhaust gas recirculation suppresses NO more than lean-burn. At 1.1 <= excess air ratios <= 1.2, the optimal exhaust gas recirculation is 12%, ensuring favorable in-cylinder conditions. Overall, lean-burn + exhaust gas recirculation effectively controls NO and maximizes thermal efficiency and renewable-fuel substitution. The optimal strategy is "oxyhydrogen = 16 L/min, exhaust gas recirculation = 12%, 1.1 <= excess air ratios <= 1.2".

The complementary utilization of oxyhydrogen and bio-isopropanol in carbon-neutral fuel engines can effectively enhance power output and combustion stability. However, oxyhydrogen blended combustion results in an increase in NOx emissions. To address this issue, this study explores the synergistic mechanisms of lean-burn coupled with exhaust gas recirculation (EGR) in an engine featuring oxyhydrogen negative pressure inhalation (ONPI), bio-isopropanol direct injection (BIDI), and gasoline port injection (GPI). Standard gasoline engines typically face stability limits around λ = 1.1, whereas this ternary fuel strategy achieves stable combustion at λ = 1.2. The experimental findings show that the core operational metrics were effectively enhanced by the composite dilution effect of EGR and mild lean-burn. An OFR of 16 L/min advances the combustion phasing (CA 0–10, CA 10–90) and restores core power outputs (IMEP, Pmax) at λ = 1.1 to the same level as λ = 1 at a specific EGR rate. Meanwhile, operating at λ = 1.1 can successfully lower CO emissions by about 90.4% on average compared to λ = 1. EGR is an effective method for lowering NO emissions. At an EGR rate of 18%, NO emissions are reduced far below the baseline engine level even at OFR = 16 L/min, representing an average reduction of about 84.86% compared to the operation without EGR. However, an excessively high EGR rate can lead to a sharp increase in both the cyclic variations (CoVIMEP) and engine-out HC emissions. Therefore, the EGR rate must be carefully optimized. Conversely, a small amount of EGR helps to reduce HC emissions and CoVIMEP. In conclusion, “OFR = 16 L/min, λ = 1.1, and EGR rate = 12%” represents the most favorable operational regime for the BIDI + ONPI + GPI architecture. The combination of EGR and lean-burn is a very efficient and clean combustion method.

At present, although bio-ethanol has become a widely used renewable energy source, it is still unable to fully replace fossil fuels in power systems. The key issue lies in the fact that its high latent heat of vaporization significantly deteriorates the combustion environment within the cylinder; however, the blended combustion of hydrogen-based fuels holds promise for resolving this critical issue. This paper presents simulation and experimental studies conducted on a gasoline port injection + bio-ethanol direct injection + HHO negative pressure inhalation (GPI+BEDI+HNPI) engine. The study investigates the optimizing effects of different fuel supply strategy coupling schemes (BEDIr, BEDIT, HNPIv) on the engine’s combustion and emission characteristics. The results indicate that earlier BEDIT and HNPI coupling can effectively mitigate the negative effects of a larger BEDIr on engine power performance, the combustion process, and combustion stability, while also improving the engine’s tolerance to a larger BEDIr. While HNPI can effectively cut HC and CO emissions, it results in a rise in NOx emissions. Increasing the BEDIr helps mitigate this issue. Overall, the fuel supply strategy “HNPIv = 16 L/min + BEDIr = 60% + 300°CA BTDC ≤ BEDIT ≤ 350°CA BTDC” enables the engine to achieve relatively ideal emission levels while maintaining combustion characteristics.

Hydrogen direct injection engines offer a promising pathway toward clean transportation by enabling flexible fuel-air control and supporting lean-burn operation. However, the coupling effects of injection pressure and injector design on spray morphology, in-cylinder mixture formation, and combustion behavior remain insufficiently understood. This study presents a systematic investigation into these interactions through a three-tiered methodology combining constant volume combustion chamber experiments, computational fluid dynamics simulations, and engine validation. Three types of injectors-including a needle-type single-hole, outward-opening, and outward-opening with a flow guide structure-were tested. The results demonstrate that spray structure and penetration were highly dependent on injector configuration. The needle-type single-hole injector exhibited strong axial penetration, while the outward-opening with a flow guide structure injector promoted broader lateral dispersion. Computational fluid dynamics simulations revealed that injection pressures of 40 and 50 bar optimized turbulent kinetic energy and mixture stratification near ignition timing. Engine tests confirmed that 50 bar achieved the highest in-cylinder pressure and combustion efficiency (Indicated mean effective pressure = 6.49 bar, Coefficient of variation = 0.65 %). All conditions maintained low nitrogen oxides emissions (<30 ppm). The experimental and numerical results show consistent trends, reinforcing that injection pressure must be carefully matched with injector geometry to ensure efficient and stable combustion. These findings provide valuable guidance for the calibration of hydrogen direct injection engines and highlight key considerations for developing low-emission hydrogen powertrains.

Ammonia-hydrogen mixed fuel offers the potential for zero carbon emissions for internal combustion engines. Pre-chamber turbulent jet ignition (TJI) technology can significantly improve combustion performance. However, in the confined space of an engine, jet-wall impingement is inevitable. This study investigates the jet-wall interaction effect in an ammonia-hydrogen pre-chamber TJI system using a visualized constant volume combustion chamber. The results indicate that a higher hydrogen volume ratio (V-H) in the main chamber markedly shortens both ignition delay and combustion duration. When V-H rises from 0 to 0.1, the ignition delay and combustion duration of the wall-impinging jet are reduced by 91.7 % and 32.0 %, respectively. A transition to direct ignition behavior occurs at Phi(pre,& planckh;) >= 1.5, significantly accelerating combustion. Additionally, a strong coupling effect between pre-chamber orifice diameter (D-pre) and hydrogen equivalence ratio (Phi(pre,& planckh;)) is observed, where larger D-pre (>= 3.5 mm) and higher Phi(pre,& planckh;) (>= 1.7) shorten ignition delay by enhancing jet penetration and reactivity. The shortest combustion duration occurs at D-pre = 3.0-3.5 mm and Phi(pre,& planckh;) = 1.6-1.8, optimizing hot jet penetration and turbulence generation.

To achieve carbon peaking and carbon neutrality goals, it is urgent to improve the thermal efficiency of engines and application of carbon-neutral fuels. The renewability and low emissions of isopropanol-n-butanol-ethanol (I-B-E) blends were receiving increasing attention, and spark-assisted compression ignition (SACI) was a high-efficiency combustion mode suitable for future engines. Therefore, this article designed 11 different I-B-E blends and investigated their differences in combustion and emissions performance under SACI combustion mode. It was found that regardless of the load, there was little difference in the auto-ignition timing of various I-B-E blends. Increasing the content of isopropanol and ethanol in I-B-E resulted in a decrease in the ratio of auto-ignition, COVIMEP, COVPmax and COVPRRmax. Regardless of the I-B-E composition, there was no significant relationship between COVCA5-CI and COVCACI-90. At light load, increasing the energy ratio of ethanol in I-B-E blends increased ITE by 2.11 % compared to n-butanol. After the load increased, regardless of the load, adjusting the composition of the I-B-E blends appropriately can achieve highest ITE and lowest ESFC. Increasing the energy ratio of ethanol and isopropanol in I-B-E blends was beneficial for reducing BSNOx and BSHC emissions. The BSCO emissions were not significantly related to the I-B-E components.

This study experimentally and numerically evaluates the impact of ammonia-water direct injection (DI) nozzle configurations on knock suppression in gasoline spark-ignition (SI) engines under high-load conditions. The original six-hole injector was modified into two single-hole variants: DI-1 (nozzle holes oriented toward the piston) and DI-2 (holes directed toward the cylinder head). Experiments analyzed 12 end-of-injection (EOI) timings (-330 degrees CA to 0 degrees CA ATDC) and varying direct injection ratios (DIr) to assess knock suppression, combustion stability, and temperature distribution. Numerical simulations using CONVERGE software validated experimental results and provided insights into in-cylinder spray dynamics and flame propagation. Findings revealed that DI-1 significantly outperformed DI-2, achieving a broader effective knock suppression range (KI reduction up to 42 %) at minimal pulse widths (DIr = 3.5 %) due to enhanced cooling of the end-gas mixture via piston-directed spray alignment with tumble flow. Early-phase injection near bottom dead center (BDC, -180 degrees CA ATDC) optimized cooling efficiency by maximizing spray dispersion during compression, whereas delayed injection post-BDC diminished suppression due to altered spray-wall interactions. The original six-hole injector, despite requiring higher DIr (9.5 %), demonstrated robust cooling performance but faced challenges in precise low-flow control. Combustion analysis highlighted that ammonia-water injection reduced peak cylinder pressure (by 8-12 %) and delayed combustion phasing (CA50 by 4-6 degrees CA), necessitating a balance between DIr and ignition timing to avoid excessive retardation. Temperature field simulations confirmed DI-1's superior peripheral cooling, reducing high-temperature regions (>730 K) by 18 % compared to DI-2. This work underscores the viability of ammonia-water as a knock inhibitor and proposes nozzle orientation optimization as a critical pathway for minimizing inhibitor consumption while maintaining thermal efficiency. The results provide actionable insights for designing high-performance DI systems in downsized, high-efficiency SI engines.

Methanol is the most promising carbon-neutral alternative fuel for the future. This paper studies the impact of DMG (dissociated methanol gas) double injection parameters in a methanol port injection engine to enhance the improvement of DMG on methanol dilution combustion performance. Additionally, it seeks to understand the optimization results of DMG direct double injection parameters for combustion performance at different DMG blending ratios. Optimizing DMG double injection parameters can effectively shorten CA10-IG (crank angle corresponding of 0 %-10 % heat release) and CA90-CA10 (crank angle corresponding of 10 %-90 % heat release), and reduce HC (hydrocarbons) and CO (carbon monoxide) emissions, BSFC (brake specific fuel consumption) and COVIMEP (coefficient of variation of indicated mean effective pressure), while slightly rising NOx (nitrogen oxides) emissions. As DMG blending ratio rises, optimization results of first and second injection timings remain constant, while second injection ratio decreases, reaching 40 %, 20 %, and 20 % at blending ratios of 10 %, 15 %, and 20 %. Moreover, DMG double injection extends the dilution combustion limit compared to single injection. At blending ratios of 10 %, 15 %, and 20 %, double injection reduces BSFC by 2.8 %, 1.4 %, and 1.2 % at the dilution combustion limit compared to single injection.

Understanding hydrogen jet formation in hydrogen-fueled direct injection engines is essential for optimizing incylinder mixture preparation and achieving high-efficiency, low-emission combustion. This study introduces a dual-scale analytical framework that links near-field shock dynamics with far-field spray evolution, providing a more comprehensive perspective compared to previous studies that primarily focused on either experimental observations or numerical simulations alone. Constant volume combustion vessel experiments were combined with high-fidelity numerical simulations to systematically evaluate the effects of nozzle pressure ratio, nozzle hole diameter, and ambient temperature on hydrogen jet development. The results demonstrate that the nozzle pressure ratio is the dominant factor governing jet momentum, morphology, and entrainment, while nozzle hole diameter controls shear layer growth and dispersion scale, and ambient temperature plays a secondary role by promoting instabilities and lateral expansion. The proposed framework effectively captures the coupling between compressible shock-vortex interactions in the near field and large-scale dispersion in the far field. These findings provide new insights into hydrogen mixture formation and offer theoretical guidance for developing more efficient and controllable injection strategies in hydrogen direct injection engines.

The co-combustion of ammonia and gasoline is one of the effective measures to improve energy efficiency and reduce carbon emissions in spark-ignition engines. However, it requires high-energy ignition to enhance combustion performance. Passive pre-chamber can improve the combustion characteristics of ammonia–gasoline mixtures with minimal modifications to the engine. Nevertheless, current research on this topic remains incomplete, particularly lacking comprehensive performance assessments of passive pre-chamber turbulent jet ignition (TJI) combined with ammonia addition in four-cylinder gasoline engines. This study focuses on the effects of the ammonia energy ratio (ER) and excess air ratio (λ) on the combustion characteristics, engine performance, and emission characteristics of ammonia–gasoline dual-fuel under the TJI mode. The results indicate that TJI combined with spark timing adjustment can ensure an optimal combustion phase and achieve stable combustion within a λ range of 1.0–1.5 and an ammonia ER of 0–47

To attain carbon neutrality goals, enhancing the thermal efficiency of engines and application of carbon-neutral fuels is essential. The renewability and low emissions of alcohols are receiving increasing attention, and spark induced compression ignition (SICI) is a high-efficient combustion mode. However, issues such as knocking limit the application of SICI engines. The diluted composition and dilution level are key factors affecting the SICI combustion and knocking. This paper designs 16 dilution strategies to explore the effects of different strategies on the performance and knocking of SICI. It was observed that the combination of fresh air and internal EGR (iEGR) significantly improved the average maximum amplitude of pressure oscillations (MAPO) and in-cylinder pressure. Regardless of the dilution level (& empty;dilution), the combination of external EGR (e-EGR) and i-EGR significantly reduced the average MAPO and maximum pressure. After optimizing ignition timing, the degree of auto-ignition decreased with the increase of isopropanol content in IBE. BSCO emissions were lowest when fueled with n-butanol. The combination of e-EGR and i-EGR significantly reduced the BSNOx emissions of all IBE blends. When & empty;dilut ion = 22.15 %, the combination of e-EGR and i-EGR resulted in a reduction of BSNOx emissions for n-butanol, IBE361, and IBE631 by 3.87 %, 53.71 %, and 46.52 %, respectively.

The pre-chamber engine wall's structure has a significant effect on the ignition and combustion performance pre-chamber turbulent jets. This study identified an abnormal combustion phenomenon in the case of secondary jets, which was characterized by the pre-chamber pressure rise rate exceeding 30 times the normal rate owing pre-chamber jet impingement on the wall. To investigate this phenomenon, we examined the causes of ignition events resulting from the interaction between pre-chamber jets and the wall by using a visualized constant volume combustion chamber experimental platform and by conducting CFD simulations. The results indicated that for a certain range of the wall-nozzle distance, pre-chamber jet impingement on the wall is advantageous for reducing the ignition delay and increasing the combustion speed. Under lean burn conditions, pre-chamber jets impinging on the wall led to both direct and delayed wall-impinging ignition owing to the wall structure. Pre chamber jet impingement on concave or flat wall surfaces generated more intense impinging turbulence than that on convex wall surfaces, resulting in the improvement of both ignition and flame propagation speeds. Thus, the wall surface at the impingement point of pre-chamber jets should not be convex as this would reduce the jet ignition performance and increase the probability of secondary jet occurrence, leading to irreversible damage the pre-chamber structure.

It is crucial to improve the thermal efficiency of engines and the application of alcohols to achieve carbon neutrality goals. However, challenges such as knock limit the use of high compression ratio engines. The dilution strategy has been proven to be an effective means of suppressing knock. In addition, to further overcome the limitation of knocking on the thermal efficiency of high compression ratio alcohol engines, the core relationship between auto-ignition and knock should be clarified. This article explores the effects of different dilution strategies and ratios (Rd) on the auto-ignition process of IBE. Meanwhile, the relationship between key parameters of auto-ignition and knock, as well as their correlation with combustion, performance, and emissions was innovatively explored. It was found that cycles with earlier auto-ignition timing occur before knock cycles, indicating that auto-ignition is a necessary condition for knock. MAPO had a negative correlation with auto-ignition timing and positive correlation with CI ratio and CI stage. Among them, the CI stage had a greater impact on MAPO than others. Regardless of Rd, CA50 and CA10-90 were highly correlated with MAPO and CI stage but cannot directly determine the auto-ignition timing and CI ratio. The MAPO and CI stages were the main causes of ITE transformation. There was no significant correlation between BSCO and BSHC emissions and MAPO, auto-ignition timing, CI ratio, and CI stage. In addition, reducing MAPO and prolonging the CI stage are effective measures to maintain low BSNOx.

Abnormal combustion phenomena pose significant challenges for the application of hydrogen direct injection engines. This study investigates the suppression of these issues in pure hydrogen direct injection engines through the use of variable valve timing and split injection strategies. The research addresses a critical gap in the current literature, as these strategies have not been widely explored in hydrogen direct injections, despite their successful application in gasoline engines. Results demonstrated that significant reductions in pre-ignition at early-mid compression-stroke events by up to 38 % were observed with specific valve timing adjustments, alongside decreased in knock intensity by 34.5 % and knock probability by 38.6 % with optimal intake valve closing timing set at 227 degrees crank angle before top dead center. Furthermore, configurations utilizing split end of injection timing at 30 degrees crank angle before top dead center and split injection ratio of 0.6 achieved a substantial 64 % reduction in specific pre-ignition events and split injection ratio of 0.7 resulted in a 63.0 % and 63.7 % decrease in knock intensity and knock probability, respectively, compared to initial valve timing and single injection. However, it was found that higher split injection ratio values, while effective in reducing abnormal combustion, led to diminishing returns in brake thermal efficiency. Achieving optimal performance required a careful balance between suppressing pre-ignition at early-mid compression-stroke events and knock phenomena while maintaining or improving brake thermal efficiency. The findings offer critical insights for advancing hydrogen direct injection engine technology, promoting decarbonization in transportation, and supporting global carbon neutrality goals. Future research should focus on optimizing variable valve timing and split injection strategies for various operational conditions and explore their integration with other advanced technologies, such as turbocharging and exhaust gas recirculation, to further enhance hydrogen combustion stability.