Abstract
This study focuses on the ability of chemical mechanisms to describe the recently discovered phenomena of pre-spark heat release (PSHR) due to low-temperature chemistry. Experiments were conducted at fixed air and fuel flow rates for a range of intake temperature that spanned the threshold for PSHR. It was found that when PSHR occurred, the knock-limited combustion phasing was insensitive to intake temperature. A three-zone model using full chemistry was used to investigate the phenomenon with both a detailed and skeletal chemical kinetic mechanism. Both mechanisms predicted the presence of PSHR. The skeletal mechanism was found to more faithfully reproduce the experimentally observed phasing of the PSHR with intake temperature at the two speeds investigated. The model results showed that end gas heat released was observed even for conditions for which the PSHR was not observed, i.e., the low temperature heat release in the end gas was obscured by the deflagration heat release. The chemical change to the unburned zone would affect both the mixture flame sped and autoignition characteristics. The model results were used to explore regions where PSHR would be found.
