Effects of spark timing and methanol addition on combustion characteristics and emissions of dual-fuel engine fuelled with natural gas and methanol under lean-burn condition

This paper aimed to study the effects of spark timing and methanol addition on the combustion characteristics and emissions of a natural gas/methanol dual-fuel engine. The engine speed is maintained at 1600 rpm and the brake mean effective pressure (BMEP) is maintained at 0.387 MPa with an excess air/fuel ratio of 1.3. The methanol energy substitution ratio (MSR) is set to 0%, 7.5%, and 14.5%. The spark timings are varied from 18 °CA to 38 °CA before the top dead centre, in intervals of 4 °CA. The results demonstrate that for a specific spark timing, the methanol addition increases the peak cylinder pressure, the maximum of the heat release rate, and the peak cylinder mean temperature. Concurrently, it decreases the flame development period (CA_0-10) and the flame propagation period (CA_10-90) with an increase in the MSR. An improvement in the brake thermal efficiency (BTE), a reduction in the total hydrocarbon (THC) emission, and an increase in the nitrogen oxide (NO_X) emission are achieved using methanol enrichment. In addition, the effect of these trends is more pronounced with an increase in MSR. In contrast, for a specific MSR, a spark timing advance increases the peak cylinder pressure and temperature, while decreasing the exhaust temperature under an identical BMEP. Moreover, the spark timing at the maximum BTE retards as MSR increases.