Experimental investigation of spray and combustion characteristics of dimethyl ether in a common-rail diesel engine

Various characteristics of dimethyl ether (DME) as an alternative fuel for compression ignition engines were experimentally investigated including its spray characteristics, combustion performance, and emission reduction in a common-rail diesel engine. The spray behavior of DME was analyzed in terms of injection rate, spray development, and spray tip penetration, which were measured by an injection rate meter and a high-pressure spray chamber equipped with a spray visualization system. In addition, the engine performance and indicated mean effective pressure (IMEP), as well as exhaust emissions, including oxides of nitrogen (NOx), soot, hydrocarbons, and carbon monoxide were measured at various injection and operating cycle parameters. The combustion characteristics of DME fuel were compared with those of conventional diesel fuel in a diesel engine. Experimental results show that DME has an injection delay 0.03 ms shorter and a maximum injection rate 21% higher than those of diesel fuel at a constant injection pressure of 50 MPa and an injection mass of 8 mg/cycle. At a fixed energizing duration and injection pressure, a greater mass of DME was injected than that of diesel fuel. The DME-operated engine produced almost negligible soot emissions but also considerably higher NOx emissions than the engine operated with diesel fuel at a fixed IMEP.