Combustion and emission characteristics of a diesel engine with DME as port premixing fuel under different injection timing

This work dealt with the combustion and exhaust performance of a DME premixed charge compression ignition diesel engine. With the port premixing DME, the heat-release process was made up of the premixed charge homogeneous charge compression ignition combustion and diffusion combustion. The incylinder fuel injection timing and port premixing DME quantity played the important roles in combustion and emission control. They had little impact on the peak position of heat-release rate (HRR) during LTR phase. However, they had great effects on the peak values and the crank-angle positions corresponding to the HRR peaks during HTR and diffusion combustion phase. The peak value of HRR increased and the crank-angle corresponding to the HRR peak advanced with an incremental DME quantity or an early injection during HTR phase. However, the peak value of HRR dropped with an incremental DME quantity or a late injection during the diffusion combustion phase. p(max) and T-max increased with an incremental DME quantity or an early injection. At the fixed direct-injection timing, BSFC decreased slightly with a rise of DME quantity due to CA50 closer to TDC. At a fixed DME quantity, BSFC was lowest when diesel was injected into cylinder at 7 degrees CA BTDC. Moreover, as more DME was aspirated from port, NOx emissions decreased firstly but this decreasing trend ceased later. Smoke reduced, but CO and HC increased with a rise of DME quantity. Meanwhile, like the conventional DICI operation, NOx increased, but smoke, CO and HC declined with an early direct-injection. (C) 2013 Elsevier Ltd. All rights reserved.