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Methods used for the study of the kinetics of exhaust hydrocarbon reactions are reviewed, compared and contrasted. The isothermal plug flow reactor which allows the determination of time resolved concentration histories of reactants, intermediate products, and final products is suggested as, perhaps, the most desirable and versatile system for the study of moderate temperature hydrocarbon oxidation reactions. The isothermal plug flow reactor allows the gas phase reactions to be studied with kinetically well-defined, repeatable, homogeneous reaction conditions that are essentially free of heterogeneous interference. Due to the detailed data obtainable and the controlled reaction conditions, kinetic mechanisms can be studied and evaluated. Investigations that used this technique are reviewed and examples cited to demonstrate the unique capabilities of the plug flow reactor.

The reaction of ethylene in engine exhaust gases has been studied using a turbulent plug flow reactor. The effects of ethylene, oxygen, and nitric oxide concentrations and of temperature on the reaction were investigated. Nitric oxide was found to be consumed in the reaction and partially converted to nitrogen dioxide. For temperatures up to 649 °C, little formation of carbon dioxide was measured for a reaction time of 140 ms. Increasing the oxygen concentration above 4% gave no increase in the oxidation rate. The Kinetics of the reaction were such that it was not possible to describe the reaction with a simple Arrhemus rate expression. The only other hydrocarbon found was a trace of acetylene at a reaction temperature of 649 °C.