Multi-objective optimization of the performance and emission characteristics for a dual-fuel engine with hydrogen addition

In this work, multi-objective optimization of a dual-fuel engine with hydrogen addition was performed with a hybrid approach of RSM-NSGA II-TOPSIS. The optimization objective variables include NOx, CH4 emissions and indicated specific fuel consumption (ISFC); decision variables include H2 addition ratio, diesel injection timing (DIT), spray angle (SA) and swirl ratio (SR). Firstly, a computational fluid dynamics (CFD) model of a dual-fuel engine cylinder was established, and a chemical reaction mechanism containing 53 species and 325 reactions was developed by the CHEMKIN program. Then, a regression model of the objective variables was obtained by the response surface method and multi-objective optimization was performed by NSGA II genetic algorithm. Finally, the optimal solution was selected from the Pareto front by the TOPSIS decision method. The distribution of the Pareto front showed that a higher hydrogen addition ratio, DIT at 10-20 degrees CA BTDC, SA at 90-110 degrees and SR at 0.6-0.8 or 1.2 provided a better trade-off between the three objectives. The optimal solution can reduce NOx, CH4 emissions and ISFC by 8.21%, 61.64% and 4.59%, respectively, compared to the original solution. Optimization of. decision variables effectively mitigate the trade-off between NOx, CH4 emissions and ISFC for a dual-fuel engine with hydrogen addition at low loads.