Study on combustion and emission of a dimethyl ether-diesel dual-fuel premixed charge compression ignition combustion engine with LPG (liquefied petroleum gas) as ignition inhibitor

A scheme of the DME-diesel dual-fuel PCCI (premixed charge compression ignition) combustion is an attractive option of relatively high thermal efficiency, low emission and operating costs as well as availability of wide DME (dimethyl ether) resource. However, one of the main problems in the DME-diesel dual-fuel PCCI operation is that an early start of combustion easily leads to detonation due to high cetane number and better auto-ignition property of DME, and above-mentioned phenomenon is especially pronounced with a large DME energy ratio or at higher loads. Thus, LPG (liquefied petroleum gas), as a kind of ignition inhibitor, is added into DME for changing the property of port premixed fuel, and the effects of LPG quantity on the combustion and exhaust performance of a DME-diesel dual-fuel PCCI engine is investigated in this paper. Experimental results show that the appearing positions of the maximum cylinder pressure and mass-averaged temperature shift towards later crank angles and their peak values decline slightly when LPG mass fraction in DME/LPG mixture (f_L) increases. The start of combustion postpones, and the combustion duration shortens with a rise of f_L. Simultaneously, brake thermal efficiency and NO_x emission reduce slightly; whereas the number concentration of particles firstly increases but then decreases with a rise of f_L.