Multi-objective optimization of exhaust-heat- management strategy for diesel engines based on RSM-NSGA III and VIKOR hybrid algorithm

An efficient exhaust-heat- management strategy is vital for ensuring high-performance operation of post-treatment systems and achieving ultra-low emissions in diesel engines. This study proposes a hybrid multi-objective optimization method that integrates response surface methodology (RSM), non-dominated sorting genetic algorithm (NSGA)-III, and VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) to enhance the exhaust-heat- management strategy for diesel engines operating at low loads. The study focuses on a diesel engine with diesel oxidation catalyst (DOC) + catalysed diesel particulate filter (CDPF) + selective catalytic reduction (SCR) + ammonia slip catalyst (ASC) post-treatment system. A Box-Behnken experimental design and RSM are used, employing intake airflow, main injection timing, post-injection timing, and post-injection quantity as factors, the optimization objectives include optimization of the DOC inlet temperature, brake-specific fuel consumption (BSFC), brake-specific urea consumption (BSUC), raw nitrogen oxides (NOx) emissions, particulate matter (PM) emissions, and tailpipe carbon dioxide (CO2) emissions. A mathematical model is developed via RSM and subsequently optimized using NSGA-III to obtain the Pareto frontier. The entropy-weight method determines the objective weights, and VIKOR method identifies the optimal exhaust-heat-management strategy, which is experimentally validated. The results indicate a positive correlation between the DOC inlet temperature and the BSFC, PM, and CO2. Although the comprehensive economics is increased by 14.14 % after optimization, the hybrid optimization method significantly increases the inlet temperatures of DOC, CDPF, SCR, and ASC to 574.35, 603.15, 571.35, and 566.95 K, respectively. After optimization, the NOx conversion efficiency of SCR increase from 76.61 % to 98.67 %, and the NOx emission at the tail end decreases from 138.0 to 8.3 ppm. These results offer valuable insights for optimizing exhaust-heat- management strategies in low-load diesel engine applications.