Inhibition effect of doping methyl tert-butyl ether compounds to n-heptane on homogenous charge compression ignition combustion

This article reports an experimental study on the combustion characteristics and emissions of homogenous charge compression ignition (HCCI) combustion using n-heptane doped with methyl tert-butyl ether (MTBE). The experiments were conducted on a single cylinder HCCI engine using neat n-heptane and 10%, 20%, 30%, 40% and 50% (by volume) MTBE/n-heptane blends at constant engine speed. The experimental results reveal that the ignition timing of the low temperature reaction (LTR) gets retarded, the peak values of heat release during the LTR decrease and the negative temperature coefficient (NTC) duration gets prolonged with the increase of MTBE in the blends. Consequently, the ignition timing of the high temperature reaction (HTR) gets delayed and both the attainable maximum indicated mean effective pressure (IMEP) and the lowest stable IMEP increase. Parametric studies on CO and HC emissions reveal that the maximum combustion temperature, pressure rise rate, IMEP, ignition timing of the HTR, combustion duration and fuel components have important impacts on HC emission, while the main parameters that show an important influence on CO emissions are the maximum combustion temperature, pressure rise rate, IMEP and combustion duration. Moreover, in order to suppress the CO and HC emissions to a low level, the maximum combustion temperature should be higher than 1500 K, the maximum pressure rise rate larger than 0.5 MPa/°CA, the IMEP above 0.3 MPa and the combustion duration shorter than 9 °CA.