Matching characteristics between fuel injection and intake control parameters significantly affect overall performances in diesel engine at variable altitudes. Prior to optimizing the control parameters of diesel engines operating at high altitudes areas, there is a necessity to identify the influence law of fuel injection and intake parameters on engine performance. This study focused on the effects of main injection timing (MIT), fuel injection pressure (FIP), EGR rate, and variable nozzle turbocharger (VNT) opening on the combustion, performances and NO_x and smoke emissions in a turbocharged diesel engine at different altitudes (2000, 1,000, and 0 m). Strategies for optimization of engine performance and the coupling relationship between these parameters were analyzed. The results showed that as the altitude increased from 0 m to 2000 m, the engine torque dropped by 2.9%, the BSFC increased by 2.6%, the NO_x emissions reduced by 11.8%, and the opacity smoke increased by 26.2%. The effects of MIT, FIP, EGR rate and VNT opening on engine performances were more significant at high altitudes. As the MIT was advanced at 2000 m altitude, the engine torque increased by 5.6%, the BSFC reduced by 5.9%, the opacity smoke decreased by 55%, while the NO_x emissions increased by 54%%. Advance the injection timing properly can overcome the altitude effect on engine power. With the FIP increased from 105 to 130 MPa at 2000 m, the engine torque reduced by 1.7%, the BSFC increased by 1.6%, the opacity smoke dropped by 44.5%, and the NOx emissions increased by 17.5%. When the EGR rate increases by 5%, the NO_x emission reduces by 16.4%,17.9 and 21.9 respectively at 0, 1,000 and 2000 m altitude. The EGR rate should be properly reduced to obtain the recovery of engine power at plateau. As the VNT vane opening decreased from 40% to 20%, the NO_x emission increase by 9.4% and 9.9% at 0 m and 1,000 m respectively, and it reduces by 3.9% at 2000 m, while the opacity smoke reduces by 38.9% at different altitudes. The optimization of VNT vane opening requires a balance between combustion performance and pumping losses. The multi-objective collaborative optimization technique should be applied to optimize these parameters to help improve engine efficiency and emissions at high altitudes.

Diesel/methanol dual-fuel engines are crucial for the decarbonization and sustainable development of transportation and industrial sectors in the carbon-neutral era. However, challenges such as low combustion efficiency, operational instability, and high emissions persist, particularly under low-load conditions. This study provides a comprehensive investigation into the combined effects of injection strategy, methanol substitution ratio (MSR), and exhaust gas recirculation (EGR) on the emission characteristics and fuel economy of a methanol–diesel dual-fuel engine under a 25% load. Multiobjective optimization was performed using response surface methodology (RSM) and the Nondominated Sorting Genetic Algorithm-III (NSGA-III). The results indicate that the interaction between the MSR and EGR has a considerable impact on both engine performance and exhaust emissions. Increasing MSR from 5 to 20% reduced nitrogen oxides (NO _x ) by 11.2–11.7% and particle number (PN) by 12.8–16.1% but increased hydrocarbon (HC) by up to 231.8% and carbon monoxide (CO) by up to 231.7%, while a higher EGR rate (0–30%) effectively reduced NO _x by 29.8–33.4% at the expense of 151.5–171.5% higher PN emissions, and slightly decreased HC by 2.6–2.8%, lowered equivalent brake-specific fuel consumption (ESFC) by 1.0–1.4%, and improved brake thermal efficiency (BTE) by 1.9–2.7%. Furthermore, advancing main injection timing (MIT) by 8° CA ATDC (from 5° CA ATDC to −3° CA ATDC) and increasing fuel injection pressure (FIP) from 80 to 100 MPa contributed to 27.2 to 27.9% lower NO _x emissions and 1.6 to 3.5% higher BTE, although their impacts on PN, CO, and HC emissions were more complex. The RSM model constructed in this study exhibited high predictive accuracy, with the coefficient of determination (R ²) exceeding 96% and the error between predicted and experimental values of BTE, NO _x , and PN being only 1.102, 1.046, and 5.465%, respectively. The implementation of the optimized parameters (average: MSR = 5.23%, EGR = 4.06%, MIT = −1.98° CA ATDC, FIP = 90.49 MPa) resulted in simultaneously minimized emissions and a BTE of over 33% (1.47% higher than that in the pure diesel mode). NO _x and PN emissions were maintained below 250 ppm and 2.5 × 10⁷ #/cm³, respectively, with an average reduction of 5.11 ppm in NO _x and 0.14 × 10⁷ #/cm³ in PN compared to the original engine operating in pure diesel mode. This study underscores the effectiveness of AI-driven optimization in advancing the performance and emission characteristics of diesel/methanol non-road dual-fuel engines.

Methanol/diesel RCCI combustion has emerged as a promising high-efficiency, ultralow-emission strategy for the sustainable development of diesel engines under carbon neutrality targets. This study experimentally investigates the coupled effects of excess air coefficient (λ) and altitude (0–2000 m) on combustion characteristics and emissions in a methanol–diesel RCCI (MD-RCCI) engine under low and medium operating conditions. Results show that decreasing λ can enhance the combustion of relatively lean mixtures, significantly reducing total hydrocarbon (THC) emissions. At 1400 rpm-25% load, reducing λ from 3.5 to 2.0 lowered THC emissions by 46.0%, 42.5%, and 34.1% at 0, 1000, and 2000 m, respectively. At 1800 rpm-50% load, decreasing λ from 2.25 to 1.5 further reduced THC emissions by 64.2%, 68.6%, and 68.7% across the same altitudes. As λ decreases, the peak in-cylinder pressure declines, while the peak cylinder temperature and exhaust gas temperature (EGT) gradually rise. The peak heat release rate (HRR) increases at low load but decreases at medium load. However, an excessively low λ leads to markedly retarded combustion phasing and elevated NOx, soot, and particulate number (PN) emissions. With increasing altitude at fixed λ, ignition delay lengthens and both peak pressure and HRR decrease, whereas peak temperature and EGT increase. THC emissions declined by 21.0% (low load) and 16.4% (medium load) from 0 to 2000 m, while NOx emissions slightly rise due to higher combustion temperatures. In contrast, soot and PN emissions increase owing to deteriorated air–fuel mixing and incomplete combustion under oxygen-deficient high-altitude conditions. The influence of λ and altitude on CO emissions shows load-dependent responses. At low load, CO emissions first increase and then decrease with decreasing λ (peaking near λ = 2.5) and rise with altitude (up to +46.7% at λ = 2.75). At medium load, CO emissions consistently decrease with both richer mixtures and higher altitude (average reduction of 6.0%). These findings provide quantitative insights for optimizing the MD-RCCI engine calibration across varying altitude environments and support its practical deployment in real-world applications.