Experimental Study on the Stratified and Homogeneous Charge of a Direct-Injection Spark Ignition Methanol Engine

Abstract

Based on the gasoline direct-injection spark ignition (DISI) engine technologies and methanol fuel characteristics, a complex-guided multi-hole spray coupled with induction swirl and chamber-wall-guided stratified-charge combustion system for a DISI methanol engine was developed. It was retrofitted from a four-cylinder diesel engine with a compression ratio of 14. It was developed to run on methanol in stratified-charge and homogeneous-charge combustion modes; under part-load operating conditions, stratified-charge combustion is adopted to improve fuel economy while, under high- and full-load conditions, the homogeneous-charge combustion mode is adopted for the purpose of a higher power output. Under both combustion modes, the key parameters of the combustion system were matched and optimized respectively. The operating map for both combustion modes was obtained. Then, the engine power performance, emissions, and combustion characteristics were studied. The power output of the developed methanol engine is higher than that of the original diesel engine. By using the stratified combustion mode under low-load conditions, the engine fuel economy (the brake thermal efficiency) is improved; the stratified-charge combustion of methanol performed relatively well with acceptable values of the coefficient of the cyclic variation in the indicated mean effective pressure. The smoke and nitrogen oxide emissions from the DISI methanol engine are both reduced simultaneously and significantly.