Comparative study of pilot-main injection timings and diesel/ethanol binary blends on combustion, emission and microstructure of particles emitted from diesel engines

In this study, anhydrous ethanol was directly mixed with diesel fuel and applied to an old diesel engine to improve nitrogen oxides (NOx)-smoke trade-off relationship. Multiple injection strategies (MISs) including various main-pilot injection combinations were selected as the main variables. The results demonstrated that the diesel fuel could be mixed with up to 15% ethanol by volume without phase separation at room temperature. The influence of MISs on the cylinder pressure and heat release rate (HRR) was greater than that of the diesel/ethanol blends. Adding ethanol to diesel fuel had nearly no effect on the peak cylinder pressure, but delayed the start of combustion, greatly increased the peak value of HRR and ignition delay, and reduced the combustion duration. The coefficient of variation of the indicated mean effective pressure (COVimep) and maximum pressure raise rate of all test fuels under all test additions were less than 3% and 3 bar/degrees CA, far below their limits, indicating that this diesel engine without any modifications can run well with these diesel/ethanol binary blends. The most interesting result was that the addition of ethanol to diesel fuel could simultaneously reduce NOx and smoke emissions as well as particle diameter.