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.

Addressing the critical role of spray characteristics in mixture formation and combustion characteristics, this study investigates methanol-blended, ethanol-blended, and five pure alcohol fuels (methanol, ethanol, isopropanol, *n*-butanol, isobutanol). Spray dynamics were captured via high-speed photography and Schlieren imaging in a constant-volume chamber. Computational simulations isolated the effects of fuel properties (density, viscosity, surface tension) and ambient conditions (pressure, temperature) on spray morphology. A Random Forest (RF) model leveraging out-of-bag (OOB) error estimation quantified parameter importance and predicted spray characteristics (penetration, cone angle, area). After hyperparameter tuning, the optimized RF model achieved high-fidelity predictions (e.g., spray area: R2 = 0.98, RMSE = 118). Key findings reveal ambient pressure as the dominant factor influencing spray characteristics, followed by ambient temperature, while fuel properties exhibit operating-condition-dependent effects. This integrated experimental-computational-ML framework enables rapid spray parameter optimization and facilitates inverse design of alcohol-fuel nozzles and combustion chambers, advancing cleaner and more efficient combustion technologies.

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.

Owing to its superior combustion performance, abundant reserves and clean combustion products, hydrogen has been regarded as a promising alternative fuel for internal combustion engines (ICEs). The direct injection hydrogen internal combustion engines can offer larger power without the risk of backfires, compared to port fuel injection. To avoid the NOx emission and improve the power output, lean boosting is adopted to reduce the pressure-increase rate and combustion temperature. As well as the low exhaust temperature of hydrogen engine, which pose significant challenges for the turbocharger system. Against this background, an experimental study was carried out on an 8.2 L DI hydrogen engine. Three types of turbochargers were compared: wastegate turbocharger (WG), variable geometry turbocharger (VGT), and two-stage turbocharger (TS). All tests were performed under operating conditions constrained by pre-ignition and super-knock, aiming to maximize thermal efficiency. The brake thermal efficiency (BTE) varied from 31.1% to 34.4% across the tested engine speeds. The TS turbocharger yielded the maximum BTE of 34.4% at 1300 rpm. This work further investigated the effects of different turbochargers on the energy and exergy distributions of the engine. Energy analysis results reveal that the two-stage turbocharge exhibits the lowest exhaust energy loss, the variable geometry turbocharger demonstrates the lowest coolant energy loss, and the wastegate turbocharger achieves the lowest intercooler loss. Exergy analysis results indicated that the TS system achieved the maximum total available exergy efficiency of 67.9% at 1600 rpm, accompanied by the minimum exergy destruction.

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.

To investigate the influences of direct injection strategies on the combustion and emission performances of hydrogen/gasoline dual-fuel engines, a turbocharged direct-injection gasoline engine was modified into a dualfuel engine for hydrogen and gasoline, which was equipped with HDI) Experiments were conducted under stoichiometric and lean-burn conditions to investigate the influence of hydrogen direct injection timing, hydrogen ESR, and 2 on in-cylinder pressure, HRR, combustion phase, cycle variation, BTE, and exhaust emissions. The results show that hydrogen addition most significantly shortens the early flame development, thereby accelerating flame propagation, advancing combustion phase, enhancing Pmax and BTE, reducing HC and CO emissions due to more complete combustion, while increasing NOX emissions caused by elevated in-cylinder temperature. EOI remarkably affects mixture formation and combustion performance, and - 180 degrees CA ATDC is verified as the optimal injection timing, which provides sufficient mixing time and favorable combustion phasing. Under lean-burn conditions, the coupling control of ESR and 2 achieves a balanced trade-off between efficiency and emissions. Excessively lean mixture or overly retarded injection timing would prolong combustion duration, increase cycle variation and incomplete combustion products.

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".

Spark assisted compression ignition is a crucial combustion mode for sustainable engine development due to its efficiency and low emissions. However, its widespread adoption is limited by cycle-to-cycle variation. The impacts of mixture reactivity and thermodynamic state on the development of each combustion stage and their mechanism are examined. The findings demonstrate that dilution level variation significantly influences combustion, with parameter adjustments distinctly affecting the correlation between overall combustion and its stages. Specifically, varying EGR and cooling water temperature strengthens the correlation between cycle-to-cycle variation and auto-ignition duration, while modifying negative valve overlap, compression ratio, and intake temperature enhances the correlation between cycle-to-cycle variation. It was found that auto-ignition and CA50 are significantly correlated. Auto-ignition advances with CA50 within 15 °CA ATDC under negative valve overlap, intake temperature, and compression ratio, and delays with increasing flame propagation stage (≤16 °CA). When lambda is changed, the CA50 limit for identifiable auto-ignition is 16 °CA ATDC; with cooling water temperature = 55 °C, it falls to 12 °CA ATDC. Furthermore, IMEP falls when end-gas auto-ignition cycle variation surpasses 15%. The impacts of mixture reactivity and thermodynamic state on end-gas auto-ignition cycle variation were quantitatively assessed using a Kriging model. In the conditions under investigation, end-gas auto-ignition cycle variation is highly sensitive to EGR, followed by negative valve overlap and intake temperature. The best combination (negative valve overlap =20 °CA, EGR = 7%, lambda =1.1, intake temperature = 40 °C, cooling water temperature = 85 °C, compression ratio = 15.4) lowering end-gas auto-ignition cycle variation to a minimum of 7.01%.

Knock severely restricts the development of downsized and turbocharged gasoline engines, and fuel formulation optimization is a cost-effective knock suppression strategy. This study combines experimental tests, CFD simulations and reactive force field molecular dynamics (ReaxFF-MD) simulations to investigate the knock suppression mechanism of methanol blending in RON92 gasoline for a 2.0 L turbocharged spark-ignition engine, with methanol mass blending ratios (MR) controlled at 0%, 5%, 10% and 15%. Experimental results show that methanol blending significantly smooths in-cylinder pressure traces and reduces knock intensity (KI) without obvious impact on combustion speed, and the in-cylinder thermal environment and flame propagation characteristics show negligible differences under different MR, indicating fuel intrinsic properties dominate knock suppression. ReaxFF-MD simulations at 1800-2400 K reveal methanol has little effect on gasoline's thermal pyrolysis and initial fragmentation, but effectively inhibits the formation of key intermediates (CH2O and CO) associated with low-temperature oxidation and chain reactions. This work verifies the excellent knock suppression performance of low-proportion methanol blending, and clarifies its atomic-scale mechanism from intermediate evolution and product formation, providing a theoretical basis for high-performance anti-knock fuel design and engine knock control.

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.

To enhance fuel-air mixing in compression ignition engines, the Lateral swirl combustion system (LSCS) was proposed and demonstrated excellent performance in diesel engines. However, no studies have yet applied LSCS to the increasingly popular diesel/ammonia dual-fuel engines. This study investigates the role of LSCS in diesel/ ammonia Reactivity Controlled Compression Ignition (RCCI) combustion and its potential to enhance zerocarbon fuel utilization. By introducing an LSCS chamber with a rim structure and developing a 3D computational model based on nitrogen tracking method, we examined the impact of Start of injection (SOI) and Swirl Ratio (SR) on in-cylinder combustion and emission characteristics. Results show that the LSCS rim structure enhances wall jet and improves air utilization. Across all SOI conditions, LSCS achieved higher Indicated mean thermal efficiency (ITE) than non-convex combustion system (NCCS), with a maximum improvement of 1.9%. The greenhouse gas (GHG) emissions were slightly reduced, while emission of unburned ammonia was reduced by approximately 13%. At SR = 1.25, the interaction between wall jet and swirl motion created optimal local equivalence ratio distribution, resulting in maximum ITE, an increase of 1.34% compared to the original LSCS case, as well as the minimum GHG and ammonia emissions. Therefore, LSCS demonstrates potential to further enhance diesel/ammonia RCCI engine performance while reducing GHG and unburned ammonia emissions.

Ammonia is a promising carbon-free fuel owing to its high hydrogen density and mature storage and transportation infrastructure. In ammonia–hydrogen internal combustion engine–proton exchange membrane fuel cell (AHICE–PEMFC) powertrains, liquid ammonia serves as both the fuel and hydrogen carrier, enabling coordinated energy conversion between the engine and fuel cell for improved energy efficiency. However, NOx emissions from ammonia combustion remain a key barrier to practical application. Intake humidification offers a potential in-cylinder mitigation strategy, yet systematic comparisons of different humidification pathways and their optimal operating ranges remain limited. This study investigates the emissions–efficiency characteristics of an ammonia–hydrogen engine under two intake humidification strategies: fresh-air water injection and fuel cell cathode exhaust gas blending. A multi-physics simulation model is developed to analyze the evolution of in-cylinder temperature fields and high-temperature reaction zones under varying intake humidity. The feasibility of cathode exhaust-based humidification is evaluated, and a marginal emission reduction rate-based method is proposed to compare the optimal operating regions of the two strategies. Results show that increased intake humidity weakens the temperature-sensitive NOx formation environment through a unified mechanism involving increased mixture specific heat, reduced peak temperature, delayed high-temperature reaction zones, and modified radical availability. For ammonia–hydrogen combustion, this NOx mitigation should be interpreted as the combined outcome of thermal NO formation, fuel-bound nitrogen oxidation, and possible de-NOx reactions rather than as the suppression of thermal NO alone. For fresh-air water injection, the intermediate humidity level of approximately 21.8 gH2Okg−1dryair represents a favorable emission–efficiency compromise, where a 1% efficiency penalty corresponds to an 8.80% NOx reduction. The cathode exhaust blending strategy shows only an 8.18% lower marginal NOx reduction efficiency while reducing water demand by 50.37%. By utilizing internally generated water vapor and residual oxygen, PEMFC cathode exhaust blending links engine-side NOx control with PEMFC water management and air-supply integration, providing quantitative guidance for coordinated air and humidity management as well as emission–efficiency improvement in AHICE–PEMFC powertrains.

The diesel/ammonia combustion mode can significantly cut down carbon emissions, while the growth in fuel NOx due to the introduction of ammonia poses a potential emission problem. To explore the generation and reduction mechanisms for different sources of NO (oxidant-source NO and fuel N*O), an ammonia/n-heptane chemical kinetic mechanism was constructed. With the N element tracking method, the different sources NO emission characteristics of a diesel/ammonia reactivity-controlled compression-ignition (RCCI) engine were probed through varying diesel start of injection (SOI), injection pressure, nozzle hole number, and spray angle. The results indicated that in a diesel/ammonia RCCI engine, the production of fuel-source N*O occurred earlier than that of oxidant-source NO. During the NO reduction process, thermal DeNOx mainly occurred at the center of the combustion chamber and near the edge oxidant-source NO, and fuel-source NO emissions initially increased and then decreased. The area of unburned ammonia distribution is most enriched near the cylinder wall. As the SOI increased, at higher injection pressures, fuel-source NO was generally higher, while at medium injection pressures, oxidant-source NO emissions were higher. The trends of oxidant-source NO and fuel-source N*O with an increasing nozzle hole number were opposite, while the change in total NO emissions was not significant. When the spray angle was reduced to 122 degrees, the total NO emissions decreased by 49% compared to the original 162 degrees. This suggests that adjusting the spray angle can significantly lower NO emissions without reducing engine efficiency.

The combustion state of methanol/polyoxymethylene dimethyl ether (PODE) spark ignition dual fuel engine at high premix ratios requires further optimization. The combustion behavior of spark ignition dual fuel engines is governed by the coordinated control of spark ignition and PODE autoignition, and the influence of in-cylinder PODE distribution on combustion and emissions remains unexplored. Changing the configuration of direct-injection injector can create different fuel distributions within the cylinder, and the research on the synergistic relationship between in-cylinder fuel distributions and spark plug ignition in dual fuel engines is still a blank field. To change the injection area of PODE in the cylinder and explore the influence of in-cylinder PODE distribution on combustion and emissions, the original 5-hole injectors were modified to create a 2-hole injector with spray near spark plug and a 2-hole injector with spray far away from spark plug. Research findings indicate that compared to original 5-hole injector, the 2-hole injector with spray close to spark plug enhances PODE distribution near the spark plug, resulting in more stable combustion. However, the 2-hole injector with spray far away from spark plug reduces PODE distribution in the vicinity of spark plug, resulting in a cyclic variation of more than 10% at all test points. The overall fuel injection rate of the 2-hole injector is slow, which leads to delayed combustion phase and needs to be improved by advancing PODE injection timing. Compared with the original 5-hole injector, the 2-hole injector requires early injection timing to optimize the combustion state, and the advance degree of injection timing decreases with the increase of premix ratio. Additionally, the uneven distribution of PODE generated by the 2-hole injector leads to an increase in incomplete combustion and a slight decrease in thermal efficiency. The coordinated optimization of the arrangement of direct-injection injector and spark plug needs to be considered.

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.

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.