Comprehensive optimisation of the economy and emissions of diesel engines: A full factorial design approach combining the Kriging method, NSGA III, and TOPSIS

• Full-factorial design and Kriging-NSGA-III-TOPSIS used for engine optimization. • Proposed CE metric evaluates diesel engines' overall economic performance. • Optimized results outperform original engine when β < 1.5. This study proposes a multi-objective optimisation method using a full factorial design and Kriging- non-dominated sorting genetic algorithm (NSGA) III- technique for order preference by similarity to ideal solution (TOPSIS) to reduce fuel and urea consumption and emissions. Experiments were carried out with main injection timing, injection pressure, and exhaust gas recirculation rate as factors. A Kriging model was established, and multi-objective optimisation was performed via NSGA III to obtain Pareto fronts. Results indicated that the Kriging-NSGA-III-TOPSIS method effectively reduced nitrogen oxides, particulate matter, and and reduce overall costs. The optimal solution was determined using TOPSIS, achieving a comprehensive score of 0.8225. A new metric, comprehensive economics (CE), combining brake-specific fuel and urea consumption, was introduced to assess diesel engine performance. The CE of the engine was decreased from 212.63 g/kWh to 211.71 g/kWh. BTE, in-cylinder pressure, maximum pressure rise rate, BSCU and original NOx increased by 0.95%, 3.94%, 5.74%, 17.47% and 25.15% respectively. BSFC, tailpipe NOx, and original PM decreased by 0.96%, 93.47% and 15.24% respectively. When β < 1.5, the CE performance optimised diesel engine surpassed that of the original engine. This study provides a theoretical basis for optimising the economic performance and emissions of diesel engines.