Experimental study on stratified and homogeneous combustion of a methanol direct-injection spark-ignition engine

In a methanol direct-injection spark-ignition (DISI) engine retrofitted from a 4-cylinder diesel engine, the fuel needs to be injected into the cylinder near the end of compression stroke to realize the stratified combustion at partial loads for improving fuel economy. However, at high loads, the fuel needs to be injected into cylinder during intake stroke to realize the homogeneous combustion for achieving high power output. The results show that the methanol DISI engine can operate within the excessive air ratio of 2.23 and its maximum brake thermal efficiency reaches 35.3%. The methanol DISI engine exhibits higher power output than that of the original diesel engine. The cyclic variations of imep maintains low under a wide range of operating conditions, which shows a stable combustion. NOx and soot emissions can be decreased simultaneously.