Effects of premixed ratio on combustion characteristics of a homogeneous charge compression ignition-direct injection engine fueled with dimethyl ether

A two-cylinder, direct injection diesel engine was modified for a homogeneous charge compression ignition-direct injection (HCCI-DI) engine fueled with dimethyl ether. Effects of premixed ratio on HCCI-DI combustion characteristics were experimentally investigated. The results show that in HCCI-DI combustion, as premixed ratio Rp increases, the peak pressure increases and its phase advances gradually; the first peak of pressure rise rate increases and the second peak decreases, and their phase advances gradually. With the increase of Rp, the cool flame peak increases gradually, the peaks of premixed combustion and diffusion combustion decrease gradually. The in-cylinder pressure is decomposed using discrete wavelet transform, the details D1, D2, D3, D4, D5, and D6 are obtained. The relative energy value of pressure at D6, D5, and D4 decreases gradually. The same results are obtained at 0.32MPa brake mean effective pressure (BMEP), 0.24MPa BMEP, and 0.16MPa BMEP. The combustion state plays an important role in determining wavelet relative energy distribution of in-cylinder pressure over details. With increases of Rp, the energy value of in-cylinder pressure at D6 increases gradually, but the energy value at D5 and D4 decreases. It transforms from at D4 and at D5, to at D6 with the increase of Rp. (C) 2014 AIP Publishing LLC.