Experimental investigation on performance and combustion characteristics of spark-ignition dual-fuel engine fueled with methanol/natural gas

This study aims to evaluate the performance, emissions, and combustion characteristics of a methanol/natural gas dual-fuel spark-ignition engine by conducting several experiments. A heavy-duty natural gas engine is modified by adding a methanol port-injection system to accelerate the burning rate, increase the thermal efficiency, and reduce the hydrocarbon emission. The effects of the methanol energy substitution ratio (MSR) on the brake thermal efficiency, heat release rate, peak cylinder temperature, flame development period, flame propagation period, and emissions are investigated under light, medium, and heavy loads (brake mean effective pressures of 0.387, 0.775, and 1.163 MPa, respectively) at an engine speed of 1600 rpm and a relative air/fuel ratio of 1.3. The results show that the peak cylinder pressure, peak cylinder temperature, and heat release rate increase with an increase in the MSR. A larger MSR leads to a shorter flame development period and flame propagation period as well as earlier combustion phasing. In addition, the brake thermal efficiency increases and the equivalent brake specific fuel consumption decreases significantly with methanol enrichment under the three engine load conditions. For exhaust emissions, the brake specific total hydrocarbon emission decreases while the brake specific nitrogen oxide emission increases slightly with an increase in the MSR. For cycle-by-cycle variation, the coefficient of variation in the indicated mean effective pressure increases slightly with an increase in the MSR. In addition, the peak ringing/knocking intensity is found to be 2.05 MW/m² that is much less than the critical knocking point (5 MW/m²). Therefore, there was no knocking throughout the entire experiment.