Dimethyl ether energy ratio effects in a dimethyl ether-diesel dual fuel premixed charge compression ignition engine

The combination of port DME induction and in-cylinder diesel direct-injection compression ignition combustion was studied in a two-cylinder engine. The port DME energy ratio was proved to be one of main variables affecting the combustion. Thus, the main goals of this paper were to investigate the effects of DME energy ratio on combustion and emission characteristics of the diesel engine at this dual-fuel PCCI combustion mode. In order to evaluate the characteristics of this combustion mode, the conventional direct-injection compression ignition engine performance was provided to make a detailed comparison. Furthermore, special concern was focused on the complex combustion process analysis. DME port induction and diesel in-cylinder direct-injection combustion process was composed of the homogeneous charge compression ignition combustion and conventional diffusive combustion. Although DME energy ratio had little impact on the start timing of cool flame, the negative temperature coefficient region shortened and the start timing of HCCI high-temperature reaction advanced as DME energy ratio increased. It could also be discovered that, as DME energy ratio increased, the maximum heat release rate of DME HCCI increased as well as the peak values of cylinder pressure and mass-averaged temperature; however, the maximum heat release rate of diesel combustion decreased. Results also showed the brake thermal efficiency slightly increased with a rise of DME energy ratio. In the case of emission, smoke emissions decreased, NOx emissions decreased first but this decreasing trend was inhibited later, while HC and CO emissions increased with a rise of DME energy ratio. (C) 2013 Elsevier Ltd. All rights reserved.