Experimental evaluation of performance of heavy-duty SI pure methanol engine with EGR

Because methanol can be synthesized from captured CO2 and green H2, it is a promising alternative fuel for reducing carbon emissions from heavy-duty vehicles. Experiments were conducted on a multi-cylinder port fuel injection spark-ignition (SI) heavy-duty pure methanol engine modified from a natural gas engine. The main objective was to evaluate the performance of a heavy-duty SI pure methanol engine and its improvement over the original natural gas engine. The effects of the exhaust gas recirculation (EGR) rate and spark timing on the brake thermal efficiency (BTE), as well as the NOx, CO and HC emissions, were investigated under a wide range of operating conditions. The experimental results indicated that the pure methanol engine had a BTE of > 40% BTE in a brake mean effective pressure (BMEP) range of 1.27-2.17 MPa at speeds ranging from 1000 to 1700 rpm and that the peak BTE was ~ 41.4%, which was higher than that of the original natural gas engine by an absolute 3%. The EGR tolerance of methanol engine was high and the coefficient of variation of the indicated mean effective pressure (COVIMEP) could be maintained below 2%, even at 31% EGR. With an increase in the EGR rate, the CO emissions first decreased and then increased. The partial oxidation of unburned methanol contributed to higher CO emissions when the EGR rate reached a critical value. Advancing the spark timing increased the HC emissions at a low EGR because of the lower post-oxidation temperature; however, it reduced the HC emissions at a high EGR rate because of the more stable combustion. At a BMEP above 0.87 MPa, the NOx, HC and CO emissions ranged from 0.055 to 1.185 g/kWh, from 2.4 to 13.05 g/kWh, and from 6.36 to 10.88 g/kWh, respectively. The pure methanol engine had lower NOx and CO emissions but higher HC emissions than the original natural gas engine.