Abstract
Compared to natural gas spark-ignition (SI) combustion, dual-fuel (DF) mode could achieve higher indicated thermal efficiency (ITE). The major disadvantages of natural gas DF combustion are rough combustion at high load, high CO and total hydrocarbon (THC) emissions, and low natural gas substitution rate. In the present work, a comparison of using polyoxymethylene dimethyl ethers (PODEn) and diesel as pilot fuels for natural gas DF combustion is presented. The experiments were conducted at two conditions: 1000rpm 4bar indicated mean effective pressure (IMEP), and 1000rpm 12bar IMEP. Compressed natural gas (CNG) was injected into the intake manifold and pilot fuel was injected directly into the cylinder. The experiments covered both conventional and low temperature DF combustion. Experiments were conducted with 0% exhaust gas recirculation (EGR) and 60% CNG substitution ratio at 4bar IMEP. At 12bar IMEP, 90% substitution ratio and 30% EGR rate were chosen. The impact of the start of pilot fuel injection (SOI) on natural gas DF combustion was studied. In comparison with the conventional combustion, low temperature combustion reduced NOx emissions and improved ITE. Compared to diesel, PODEn achieved lower THC, CO, NOx, soot emissions and higher efficiency, indicating it is a promising pilot fuel for natural gas DF combustion.
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