Effects of DME-Isobutane Blended Fuels on Combustion and Emissions Reduction in a Passenger Car Diesel Engine

Abstract

This paper investigates the effect of isobutane blended dimethyl ether (DME) fuels on the spray behaviors, combustion, and emission reduction characteristics in a diesel engine. To investigate the influence of DME-isobutane blends, measurements of the spray characteristics from the spray visualization, combustion characteristics, and emissions reduction characteristics were conducted under various injection timings and isobutane blending ratios. In this experiment, isobutane fuel was blended into DME to make up for the lower heating value (LHV) of DME. The isobutane blending ratio of DME-isobutane blends was changed from 10 to 30% using the isobutane mass fraction. To investigate the effect of the isobutane blending ratio on the combustion and emission characteristics of a diesel engine, five types of fuels were applied: diesel, DME, DME90LP10, DME80LP20, and DME70LP30 (where numerical values indicate the weight fraction percentage). In this paper, the results of the visualization tests show that the DME and DME-isobutane blended fuels have slightly shorter results than that of conventional diesel fuel beyond 1.7 ms of elapsed time. The spray cone angles show similar trends, although with a slight decrease as the ratio of isobutane in the DME-isobutane blends was increased. The combustion pressure of the DME-isobutane blends decreased as the isobutane blending ratio was increased in the test range, showing higher pressure than that of conventional diesel fuel. The ignition delay increased when the injection timing was retarded; it also increased with increased amounts of isobutane in the DME-isobutane mixture. The results of cumulative heat release and heat release rate show that the increase in isobutane blending ratio resulted in retarded heat release. As the isobutane blended ratio was increased, the brake-specific nitrogen oxides (NOx) of DME-isobutane blends were increased compared to DME fuel. The soot emissions of the DME and DME-isobutane blends were nearly zero compared to those of conventional diesel. The CO emissions of the DME-isobutane blending fuels increased compared to that of DME fuel with the isobutane blending ratio. The DME and DME-isobutane fuels showed lower HC emissions, with the exception of the late injection timing of the DME70LP30 fuel.