Experimental study and prediction model of combustion stability and combustion mode variation of burning methanol/biodiesel blends for diesel engines

Abstract

The combustion stability is an essential metric for evaluating the stable operation of an engine. To analyze the underlying reasons affecting the combustion stability, tests of modified engines fueled by methanol/biodiesel blends were carried out. The influence of the potential ignition point (PIP), activation energy (Ea) field, flame diffusion, and other combustion characteristic parameters on the combustion stability is quantitatively analyzed through the CFD simulation model. The results show that under 2400 r/min and 100% load, a 10% volume concentration of methanol increases the peak pressure. The variation of the pressure and combustion characteristic parameters increased with the increase in methanol concentration. The increase in methanol concentration increases the number of PIP, expands the distribution range of low Ea, and reduces the flame diffusion rate. The PIP, Ea field, and flame diffusion have an echelon progressive, positive correlation with the combustion mode. The increase in methanol concentration is sufficient to cause the conversion of the mixed fuel combustion mode, and the corresponding methanol volume concentration threshold is 21–22%.