Micro-GA optimization analysis of the effect of diesel injection strategy on natural gas-diesel dual-fuel combustion

Abstract

In this work, a comprehensive evaluation was conducted to study the effect of diesel injection strategy on natural gas-diesel dual-fuel combustion using micro genetic algorithm (micro-GA) optimization. Firstly, the effects of different injection strategies with the same combustion chamber were studied under multiple operating conditions. The results showed that for a double injection strategy, over 45% thermal efficiencies can be obtained within the constraints of peak pressure, peak pressure rise rate, and NOx emission for all the conditions. For a single injection strategy, the thermal efficiencies achieved at the low and medium loads are above 45%, while that of the high load can only reach to 35.5%. Higher combustion loss and heat transfer are responsible for the decreased thermal efficiency for the single injection. Secondly, the effects of different combustion chamber designs with the same injection strategy were further investigated. It showed that under a fixed operating condition, the percent energy substitution and exhaust gas recirculation fraction for efficient and clean combustion are not varied with the combustion chamber design, while the injection timing and pressure, and injection split ratio should be carefully selected. Although the ignition and combustion processes are different, the bulk combustion characteristics and engine performance are similar. The difference in thermal efficiency between the different combustion chamber configurations is attributed to the difference of heat transfer. With the double injection strategy, the engine could use a simpler combustion chamber design that lowers the heat transfer for further improvement of the thermal efficiency.