| Many practical engine problems such as knock in spark ignition engines and cold start in heavy duty diesel engines are related to an important preignition process---autoignition. Strong evidence has shown that preignition chemistry of hydrocarbons at low and intermediate temperatures plays a critical role in autoignition. A negative temperature coefficient (NTC) of reaction rate is observed for most fuels in this region, where the overall reactivity decreases as reaction temperature increases. Understanding the mechanism of NTC could help us to elucidate the chemistry controlling ignition. The NTC behavior is generally believed to result from a shift in dominance from alkylperoxies to conjugate alkenes in the NTC region. One special fuel, neopentane, does not have a conjugate alkene, but its cool flame behavior implies that it has NTC behavior as well. Obviously, the accepted mechanism of NTC behavior does not apply to this fuel. Therefore, elucidating the oxidation mechanism of neopentane could contribute to our basic understanding of preignition chemistry associated with autoignition and to refining the existing mechanisms and, hence, this fuel is examined in this research program.;This study investigates the preignition chemistry of neopentane and butanes. The research includes both experimental and modeling efforts. In the experimental work, the detailed stable oxidation products of neopentane oxidation are obtained in a pressurized flow reactor over the temperature range of 610 ∼ 810 K at the elevated pressure of 8 atmosphere, using a combination of on-line Fourier Transform Infrared Spectrometry and non-dispersive infrared analysis. The NTC behavior of neopentane oxidation has been confirmed and the temperature range of NTC has been determined. The detailed speciation profiles from neopentane oxidation are obtained and analyzed. The data from the experiments are examined and analyzed in light of the presently accepted neopentane oxidation mechanism.;In the modeling work, the data collected from neopentane oxidation are applied to test and refine a detailed chemical kinetic neopentane oxidation mechanism developed at Lawrence Livermore National Laboratory. Also, the results of the detailed neopentane modeling work are compared with the results from propane. In another separate but related effort, a previously developed reduced chemical kinetic model describing the autoignition of primary reference fuels in our research engine is extended to the butanes. Finally, suggestions to improve the current hydrocarbon oxidation mechanism and reduced models are made based on this study. |
