Effect of Diesel Injection Timing on Peak Pressure Rise Rate and Combustion Stability in RCCI Engine

In the present study, experiments of reactivity control compression ignition (RCCI) combustion mode is performed on a single cylinder automotive diesel engine with development ECU (electronic control unit). For achieving RCCI combustion mode, low reactivity fuel (i.e., gasoline/methanol) is injected into the intake manifold, and high reactivity fuel (i.e., diesel) is directly injected into the engine cylinder. Mass of fuel injection per cycle and their injection events are controlled using ECU. This study presents the experimental investigation on the effect of high reactivity fuel injection timings on peak pressure rise rate (PPRR) and combustion stability in RCCI engine. The combustion parameters, i.e., PPRR, indicated mean effective pressure (IMEP) and total heat release (THR) are calculated from the in-cylinder pressure measurement data. In-cylinder pressure is measured using a piezoelectric pressure transducer installed on the engine cylinder head. A crank angle encoder of 0.1 CAD resolution is used for determining the crank position for cylinder pressure data logging. In-cylinder pressure traces for 1000 consecutive engine cycles are recorded for the investigation of cyclic variations in IMEP, and THR. Statistical technique and wavelet transform are used for combustion stability analysis. Wavelet transform has a potential to analyze the non-stationary signal in frequency as well as time domain simultaneously. Diesel injection timing plays a significant role to achieve stable RCCI operation and allows to operate an engine within the limit of acceptable PPRR limit up to a specific engine load-speed condition. Results indicate that the advanced diesel injection timing leads to higher PPRR. The IMEP time series data was also analyzed by fitting different probability density functions. Generalized extreme value (GEV) distribution is found to cover the entire range of distribution shapes observed in IMEP ensemble at different RCCI operating conditions.