Comparison study of SPEA2+, SPEA2, and NSGA-II in diesel engine emissions and fuel economy problem

Recently, the technology that can control NOx and Soot values of diesel engines by changing the electronically controllable parameters has been developed. However, there is a trade-off relationship between fuel economy and NOx values. Therefore, the diesel engines that can change their characteristics with along to the driving environment should be emerged in the future. For designing these kinds of engines, the Pareto solutions that can express the trade-off between fuel economy and NOx values are needed. In that case, the derived non dominated solutions should have the diversity not only in the objective space but also in the design variable space. SPEA2+ is one of multi objective genetic algorithms and is developed based on SPEA2. The derived non dominated solutions by SPEA2+ have the diversity in both objective space and design variable space. In this study, the diesel engines that have high fuel economy and small amounts of NOx and Soot are designed by SEPA2+. The results are compared with those of SPEA2 and NSGA-II. From the discussions, it is found that the solutions of SPEA2+ have the diversity not only in the objective space but also in the design variable space. These characteristics are very suitable for designing diesel engines whose parameters are changing against the driving environment.