Effects of Injection Parameters on the Combustion and Emission Characteristics of Diesel-Piloted Direct-Injection Natural Gas Engine during Idle Conditions

The purpose of this paper is to investigate the effects of injection parameters on combustion and emission characteristics of a six-cylinder diesel-piloted direct-injection natural gas engine at idle conditions. The tests were conducted at three injection pressures (15, 18, and 24 MPa), two different injection intervals (0.7 and 1.0 ms), and start of natural gas injection in the range of 4-13 degrees before top dead center (BTDC). The experimental results revealed that in terms of cylinder pressure and heat release rate, the maximum cylinder pressure and the maximum heat release rate were substantially higher at the injection pressure of 24 MPa and increased gradually with advanced injection timing, while only slightly influenced by injection interval. In terms of combustion parameters, the ignition delay was reduced by adoption of higher injection pressure and the rapid combustion duration was extended more evidently with the advance of injection timing. In terms of emissions, application of relatively lower injection pressure of 15 and 18 MPa had benefits in reduction of CO, HC, and NOx emissions; CO emissions were higher with advanced injection timing and could be improved with shorter injection interval at the injection pressure of 15 and 18 MPa, while NOx emissions exhibited the same trend for all injection pressures. (C) 2014 American Society of Civil Engineers.