Optimization of a diesel/natural gas dual fuel engine under different diesel substitution ratios

Abstract

Dual fuel engines are attracting more and more attentions due to their low emissions and high efficiency compared with traditional single fuel engines. However, complex parameters coupling remains challengeable issues in dual fuel engine optimization. Here, the objective of this study is to optimize the diesel fuel ratio and the combustion parameters of a diesel/natural gas dual fuel engine by coupling the genetic algorithm with a 3D CFD engine combustion simulation. A total number of 9 parameters were optimized simultaneously. The results indicate that the optimized diesel injection timing is gradually postponed with the increase of the pilot diesel quantity. The indicated specific energy consumption (ISEC) can be achieved when the fuel ratio is in the range of 0.2 to 0.3 and injection timing is in the range of −30 to −15 °CA ATDC. The open bowl geometry is chosen in all the Pareto front solutions, which indicates the advantages of this chamber type for the dual fuel combustion mode. The compression ratios, exhaust gas recirculation (EGR) rates are gradually concentrated to several optimal values, while the swirl ratios are widely distributed in the range from 0.5 to 1.2. Furthermore, the temporal and spatial distribution of the cylinder temperature, NOx and CH4 emissions analysis showed that the higher diesel fuel ratio will generate a widely distributed high temperature region, which is beneficial for the methane oxidation. In addition, lower EGR rate and higher diesel injection quantity are beneficial to methane oxidation. This work illustrates a new optimization method for dual fuel engine complex parameters.