Experimental study on cycle-to-cycle variations in natural gas/methanol bi-fueled engine under excess air/fuel ratio at 1.6

Abstract

In this study, the cycle-to-cycle variations in natural gas/methanol bi-fueled engines under excess air/fuel ratio at 1.6 was analyzed. In order to examine the impact of the methanol substitution ratio (MSR) on cyclic variability, four values of MSRs (MSR = 0%, 3.6%, 7.5%, and 11.5%) were selected under low load conditions. The results showed that the variations in the multicycle in-cylinder pressure traces decreased with the increase in MSR. In addition, the variations in peak in-cylinder pressure (Pmax), peak of pressure rise rate (dp/dϕ)max, 50% mass fraction burned (CA50), peak of averaged gas temperature (Tmax), and indicated mean effective pressure (IMEP) in 100 consecutive cycles decreased with the increase in MSR. Meanwhile, the higher was the MSR, the narrower was the range of frequency distribution of Pmax, (dp/dϕ)max, CA50, Tmax, and IMEP covered. In addition, the coefficient of variation in IMEP (COVIMEP) decreased with the increase in MSR for a specific spark timing. For instance, as MSR increased from 0% to 11.5%, the value of COVIMEP decreased from 2.25% to 1.28% when the spark timing was set to 46°CA BTDC. This is because methanol addition to natural gas leads to faster combustion with less cyclic variability.