Compound combustion and pollutant emissions characteristics of a common-rail engine with ethanol homogeneous charge and polyoxymethylene dimethyl ethers injection

Abstract

Polyoxymethylene dimethyl ethers (PODE)-ethanol compound combustion was conducted on a 4-cylinder turbocharged intercooling common-rail diesel engine, in which the ethanol homogeneous charge was ignited by the direct injection of PODE in the cylinder. The ethanol fuel was injected into the intake manifold of the engine at a certain energy fraction (0, 20, 30, 40 or 50%) of the fuel. This research is aimed to investigate the effects of premixed ethanol ratio on the compound combustion and exhaust pollutant emissions characteristics of the engine with a diesel oxidation catalyst (DOC). The results show that at low load, with the increment of ethanol ratio, the combustion phase of the compound combustion is postponed, the maximum combustion pressure decreases, the combustion duration increases firstly and then decreases, while the amount of premixed combustion and its peak heat release rate increase. At high load, premixed ethanol is prone to spontaneous combustion before PODE ignition. Both the maximum combustion pressure and the premixed heat release rate increase sharply. CA50 gets close to the top dead center (TDC), the combustion duration extends, and the ringing intensity increases with the increment of ethanol ratio, while the brake thermal efficiency is remarkably improved. Compound combustion simultaneously decreases the NOX and soot emissions, and changes the trade-off relation of NOX and soot at low load. But at high load, due to premixed ethanol spontaneous combustion, soot emission increases with the increment of ethanol ratio. The NO2, HC, CO, formaldehyde and acetaldehyde emissions of compound combustion are much higher compared to those of pure PODE combustion, and they all increase with the increment of ethanol ratio. Whereas, DOC can efficiently purify these increased emissions, even at low load, the catalytic efficiency of DOC is higher than 81.9%. After DOC, compound combustion does not cause excessive pollutant emissions.