Abstract
This study investigated the effects of high exhaust gas recirculation (EGR) rates on dimethyl ether (DME) fuel combustion performance, exhaust emissions and particle emission characteristics in a small direct injection diesel engine under various injection timings. To examine the effect of EGR and injection timings, the experiment was performed under high EGR rates (0%, 30%, 50%) and injection timings were varied from 40° before top dead center (BTDC) to top dead center (TDC) of the crank angle to examine the effects of early injection of DME fuel. The combustion pressures and heat release rates for different EGR rates followed similar trends. As the injection timing was advanced, the indicated mean effective pressure (IMEP) differed little in response to EGR rate in the range from TDC to 25° BTDC, and more for crank angles beyond 25° BTDC. DME combustion exhibited very little soot emission, but soot emission increased slightly with EGR rate. The use of high EGR during combustion produced very low NOx concentrations but increased HC and CO emissions for advanced injection timings from 25° BTDC to 40° BTDC. The use of EGR increased both the emissions of total particle number and particle volume over the whole range of the injection timings; for all cases, total particle volume decreased as injection timing was advanced.
Highlights
Dimethyl ether (DME, CH3OCH3) is one of the most promising alternative fuels for diesel engines.It can be synthesized from natural gas, coal, or crude oil, as well as from non-fossil fuel feed-stocks
dimethyl ether (DME) fuel is advantageous in compression ignition (CI) engines, with an oxygenated molecular structure composed of an oxygen atom between two methyl radicals (CH3)
García et al [4] showed that the homogeneous charge compression ignition (HCCI) combustion mode produces very low nitric oxides (NOx) and soot emissions, and noted some problems associated with HC emissions, fuel consumption, and difficulty controlling the start of ignition
Summary
Dimethyl ether (DME, CH3OCH3) is one of the most promising alternative fuels for diesel engines. It can be synthesized from natural gas, coal, or crude oil, as well as from non-fossil fuel feed-stocks (biomass and waste products). Due to the absence of direct carbon-carbon (C-C) bonding, DME can drastically reduce or suppress the formation and development of soot during combustion in a compression ignition engine. Due to these benefits in diesel engines, DME is the most promising alternative fuel for diesel engines [1,2]. The use of cooled EGR in an engine running in HCCI combustion mode resulted in ultra-low
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