Pre and post combustion hydrocarbon oxidation studies related to engine knock and emissions

Higher engine efficiencies and lower exhaust emissions are the two major goals of the automotive research community. In this thesis, pre combustion oxidation related to engine knock and efficiency and post combustion oxidation related to hydrocarbon emissions have been studied.;In order to improve our understanding of olefin autoignition chemistry, experiments were conducted with 1-butene and 1-pentene in a high pressure flow reactor. As the widely accepted reaction mechanisms failed to explain the reactivity and product distribution, hydrogen abstraction and oxygen addition reactions similar to alkane chemistry were proposed and supported by kinetic analysis. This constitutes a significant improvement to the olefin autoignition chemistry.;Since nitric oxide (NO) is present in the end gases of engines, its effect on hydrocarbon oxidation and autoignition was examined in an engine and a pressurized flow reactor. The engine results with primary reference fuel blends showed that NO can enhance reactivity in the negative temperature coefficient region and cause autoignition. This was the first reported result showing the effect of NO on engine autoignition (Prabhu, et al., 1993). A chemical basis for this interaction was also proposed.;Hydrocarbon emissions from spark ignited engines are formed when a fraction of the fuel escapes combustion and is exhausted along with the burned gases. Post combustion oxidation of this fuel, in the cylinder and exhaust port, plays an important role in determining exhaust hydrocarbon emission levels. Experiments were conducted with seven gaseous fuels and their blends to identify the factors controlling post combustion oxidation. Subsequently, detailed time resolved exhaust port sampling experiments were conducted to examine the sample composition and importance of oxidation at various stages of the exhaust process. The time resolved data showed that the post combustion oxidation levels are high in the gases exiting the cylinder in the blowdown process and decrease significantly in the exhaust stroke.;The oxidation chemistries of two primary reference fuel blends with octane numbers of 87 and 92 were examined in a motored engine at low and intermediate temperatures (...