Numerical study of the performance and NOx emission of a diesel-methanol dual-fuel engine using multi-objective Pareto optimization

The effect of methanol addition on the performance and NOx emission of a diesel engine was investigated using one-dimensional engine cycle simulation. The methanol component was injected into the intake manifold of a diesel engine at a certain energy fraction (0, 5, 10, or 15%) of the fuel. The in-cylinder pressure and temperature decreased as the methanol content increased due to the lower cetane number and lower heating value of methanol. The resulting decrease in the combustion efficiency lowered the NOx emission and brake thermal efficiency of the engine, and consequently deteriorated the brake specific fuel consumption (BSFC). The BSFC decreased but the NOx emission increased with advanced injection timing under dual-fuel operating conditions. Response surface plots of the BSFC and NOx emission as a function of the injection timing and exhaust gas recirculation (EGR) rate were obtained using a design of experiment method. The optimal Pareto fronts that improved both the BSFC and NOx emission were found. The EGR rate had a greater influence on the optimal Pareto front than the injection timing, which suggested that design parameters such as the injection timing and EGR rate could be used to control the performance and emission under various duel-fuel conditions.