Combustion Characteristics and NOx Emissions of a Dimethyl-Ether-Fueled Premixed Charge Compression Ignition Engine

This work investigated premixed charge combustion ignition (PCCI) and partial premixed charge compression ignition (PPCCI) combustions for dimethyl ether (DME) fuel to obtain a dramatic reduction in NOx emissions. Negligible NOx emissions were attainable with advanced injection timing under low engine load conditions using PCCI combustion. At higher engine load conditions, a dual injection strategy consisting of an initial injection at 100 degrees BTDC and a second injection later than top dead center (TDC) offered extremely low NOx, emissions while maintaining moderate engine output. The second injection timing, which was later than 10 degrees after top dead center (ATDC), showed a reduction in NOx, emissions by over 90% compared to the single-injection case, in which the lowest NOx emission levels could be achieved. The indicated mean effective pressure (IMEP) of PPCCI combustion was less sensitive to the timing of the second injection than compared to that of conventional combustion using single injection near TDC. PCCI combustion with the first injection effectively ignited the fuel for the second injection. This explains the lower sensitivity of IMEP to the timing of the second injection with PPCCI combustion.