Effect of injection strategies for noise reduction during low temperature combustion-conventional diesel combustion mode transition in a heavy duty diesel engine

Low temperature combustion (LTC) in diesel engines was implemented to reduce nitrogen oxides (NOx) and particulate matter (PM) simultaneously. However, like other advanced combustion regimes LTC is still limited to low load operating range. Thus, mode transition to conventional diesel combustion (CDC) must be well achieved in order to cover the entire operation range. Not only power output from the engine, but also combustion noise level must be stabilized during mode transition, for driver comfort. In this study, a series of injection strategies was conducted in a heavy duty diesel engine to investigate their effect on power output and combustion noise level during mode transition. Results showed that for a smooth mode transition, a gradual nonlinear shift in injection timing and duration is beneficial. It was also found that for some cycles, injection duration should be dropped to a level below the starting and ending level to fine-tune the power output. The finally achieved injection strategy showed an improvement in stability, represented by the coefficient of variation (COV) of indicated mean effective pressure (IMEP). It was also found that the maximum pressure rise rate (MPRR) was suppressed, denoting that combustion noise was successfully reduced.