Experimental assessment of lean-burn characteristics for a modified diesel engine operated in methanol direct injection spark ignition (DISI) mode at full throttle condition

Abstract

In this study,the lean-burn characteristics of a high-compression direct injection spark ignition (DISI) methanol engine were investigated. The tests were conducted on a modified diesel engine in methanol DISI mode at three excess air ratios (1.2, 1.3, and 1.4) and injection timings from −60° to −300° crank angle (CA) after top dead center (ATDC). The engine was run at 1500 rpm, 100% throttle opening, and spark timing at maximum brake torque condition. The results demonstrated that the test engine under lean-burn condition can obtain the higher indicated thermal efficiency (ITE), but the lower indicated mean effective pressure (IMEP). The THC, CO, CO2 and NOX emissions are all reduced with the increased λ. Injection timing had a large influence on the combustion and emissions and these influences became largely in the case of retarded injection conditions. There existed an optimum injection timing of −240 °CA ATDC where the IMEP and ITE got their highest values along with the lowest coefficient of variation in indicated mean effective pressure (COVIMEP). Meanwhile, the THC and CO emissions are lowest, but the CO2 and NOX emissions highest. The methanol engine can obtain the maximum toque of 27.6 N·m, which is 25.3% more than the original diesel engine at the same speed. Meanwhile, there was no knocking throughout the entire experiment, and the maximum pressure rise rate and COVIMEP were found to be 0.4 MPa and 4.1%, and those are much less than the critical points of 1.0 MPa and 5%, respectively.