HIGH-TEMPERATURE IGNITION OF PROPANE WITH MTBE AS AN ADDITIVE - SHOCK-TUBE EXPERIMENTS AND MODELING

Ignition of propane has been studied in a shock tube and by computatio nal modeling to determine the effect of methyl tert-butyl ether (MTBE) as a fuel additive. MTBE and isobutene were added in amounts up to 25 % of the fuel to propane-oxygen-argon mixtures in shock tube experimen ts covering a range of temperatures between 1450 and 1800 K. Ignition delays were measured from chemiluminescence at 432 nm due to excited C H radicals. The temperature dependence of the ignition rates was analy zed to yield Arrhenius parameters of E(a) ca. 40 kcal/mol and A ca. 10 (9) s-1 for the overall propane reaction and E(a) ca. 34 kcal/mol and A ca. 10(8.3) s-1 for the overall propane/MTBE reaction. Reactions inv olving MTBE and its decomposition products were combined with an estab lished propane mechanism in a numerical model to describe the kinetic interaction of this additive with a typical hydrocarbon fuel. The expe riments and the kinetic model both show that MTBE and isobutene retard propane ignition with nearly equal efficiency. The kinetic model demo nstrates that isobutene kinetics are responsible for inhibition by bot h MTBE and isobutene, and the specific elementary reactions that produ ce this behavior are identified. (C) 1994 John Wiley & Sons, Inc.