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

Abstract

Spark 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 °CA) while the slow flame development at a spark timing of −20 °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.