Experimental Investigation of Combustion Characteristics in a Heavy Duty Natural Gas Engine under Light Load with Methanol Addition 2017-01-2268

Engines fuelled with Liquefied natural gas (LNG) have been widely used in the heavy-duty vehicles. However, they suffer from poor combustion performance and flame instability under fuel-lean condition. In this work, experiments were performed on a turbo-charged, spark-ignition engine fuelled with natural gas (NG) and methanol. The combustion characteristics such as in-cylinder pressure, heat release rate (HRR), burned mass fraction (BMF), ringing/knock intensity (RI), ignition delay, centroid of HRR, and coefficient of variation (COV) of indicated mean effective pressure (IMEP) were analyzed under light load (brake mean effective pressure=0.3876 MPa) with different methanol substitution rates (MSR=0%, 16%, 34%, 46%). The experimental results showed that combustion phase advanced with the increase in MSR due to faster burning velocity of methanol. Knock only occurred at MSR=46%, 2000 rpm. When the MSR rose 0% to 46%, the centroid of HRR shifted from 7.23° ATDC to 5.52° ATDC, the maximum in-cylinder pressure (P_max) increased from 46.1 bar to 53.5 bar and the crank angle (CA) corresponding to P_max moved from 9.5° ATDC to 6.5° ATDC at 1200 rpm. Similar with combustion phenomenon at 1200 rpm, the combustion phase advanced at 2000 rpm as well. Moreover, shorter ignition delay, higher in-cylinder pressure and larger rate of pressure rise were observed compared with pure NG mode. However, the interdependence between pressure parameters and their corresponding CA became weaker at MSR=46%. Meanwhile, the COV of IMEP and ignition delay measured in 100 cycles increased slightly.