Co-optimization of injection parameters and injector layouts for a methanol/diesel direct dual-fuel stratification (DDFS) engine

Direct dual fuel stratification (DDFS) is a promising combustion mode to achieve satisfactory engine performance with the effective control of ignition and combustion processes. In this study, a DDFS engine fueled with methanol and diesel was investigated at low loads based on a four-stroke light-duty naturally aspirated engine. Both injection parameters and injector layouts of the two fuels were co-optimized by the fast nondominated sorting genetic algorithm (NSGA-II). The results show that the fractions, injection timings, spray half-included angles, and injector positions of the two fuels all showed significant influences on engine performance. Finally, the high methanol fraction, advanced diesel injection timing, methanol injection timing near the top dead center, and large spray half-included angle of methanol were adopted in the optimal case to achieve both low EISFC and NOx simultaneously. Meanwhile, a centrally-mounted methanol injector was beneficial to shorten combustion duration, and the diesel injector can be arranged in a semicircle area with a radius of approximately 1.14 cm to provide the sufficiently high temperature for the complete combustion of methanol.