Towards a comprehensive understanding of mode transition between biodiesel-biobutanol dual-fuel ICCI low temperature combustion and conventional CI combustion – Part Ⅰ: Characteristics from medium to high load

Abstract

This research work studied the mode switching between ICCI low temperature combustion and conventional CI combustion in a single-cylinder diesel engine. The combustion characteristics during the mode switching process with various control parameters, such as injection timing, numbers, duration, exhaust gas recirculation (EGR) rates, were detailed analyzed at medium and high engine loads. Experimental results show that the smoothness mode switching between ICCI combustion and CI combustion can be achieved within one cycle after switching another combustion mode at medium and high engine loads, and less fluctuation of IMEP is observed. At medium load, there is a wide range of butanol energy ratio (EButanol) to achieve smooth mode transition with stable combustion. However, at high engine load, higher EButanol and earlier biodiesel second direct injection timing are inadequate for the mode transition because of the higher combustion noise. EGR strategy is used to improve the smoothness of CA50 and exhibit NOx emissions. It is not needed the cycle-by-cycle injection modulation to achieve the smoothness of CA50 and the same level of NOx emissions when the EGR rate is 34.2% under ICCI combustion and 37.6% under CI combustion, respectively, with insignificant changes of IMEP and acceptable maximum pressure rise rate.