Combustion development in a gasoline-fueled spark ignition-controlled auto-ignition engine operated at different spark timings and intake air temperatures

WOS: 000507202700001Spark ignition-controlled auto-ignition is a combustion strategy to overcome the challenges in a homogeneous charge compression ignition or controlled auto-ignition combustion which has a limited operation region and does not have any direct control of the combustion timing. However, the spark ignition-controlled auto-ignition combustion can result in a large cyclic variability due to two main distinctive combustion phases developing initially by flame propagation and following controlled auto-ignition combustion throughout an engine cycle. Characterization of combustion development is, therefore, required to maintain a stable engine operation under spark ignition-controlled auto-ignition combustion. In this research, experimental studies were carried out to investigate spark ignition-controlled auto-ignition combustion development at different spark advances and intake air temperatures. Combustion analyses were performed employing pressure-based heat release and mass fraction burn curve to determine the main combustion parameters along with transition points (corresponding to crank angles) to controlled auto-ignition and mass fraction burnt by flame propagation. The results reveal that transition point has a strong correlation with crank angle position where 10% of fuel mass consumed combustion phasing rather than mass fraction burnt by flame propagation at the same intake air temperature. The cycles with a higher mass fraction burnt by flame propagation can result from early flame development at the advanced spark timings (at -30 and -40 degrees CA) while the slow flame development at a spark timing of -20 degrees CA due to late transition point corresponding to crank angle occurred. Besides, it is also found that flame propagation phase more contributes to the cyclic variation in the whole combustion process