Studies of Low and Intermediate Temperature Oxidation of Propane up to 100 Atm in a Supercritical-Pressure Jet-Stirred Reactor

Abstract

The low and intermediate temperature oxidation of propane has been investigated by using a novel supercritical pressure jet stirred reactor (SP-JSR) with and without 20% CO2 additions at fuel lean and rich conditions at 10 and 100 atm and 500–1000 K. The mole fractions of C3H8, O2, CO, CO2, CH2O, C2H4, CH3CHO, and C3H6 were quantified by using a micro-gas chromatograph (µ-GC). The experiment showed that different from that of 10 atm, at 100 atm only a weak negative temperature coefficient (NTC) behavior was observed because of the significant shift of the intermediate temperature HO2 chemistry to lower temperature. In addition, at 100 atm, existing models in literatures could successfully capture the onset temperatures of the low and intermediate chemistry, while under-predict the fuel oxidation quantitatively and fail to capture the NTC behavior between 650 and 780 K at both fuel lean and rich conditions. Similar discrepancy was observed in studies of n-butane and dimethyl ether (DME) oxidations in literatures, implying that there existed large uncertainties in hierarchy model development of fuels with low temperature chemistries at extremely high pressures. Reaction pathways and sensitivity analyses showed that RO2 competing reactions through (P1) RO2 = QOOH, (P2) RO2 = C3H6 + HO2, (P3) RO2 + CH2O/HO2 = RO2H + HCO / O2 dominated the low and intermediate temperature chemistries, followed by HO2 / H2O2 chemistry at 100 atm, which differed from the dominant pathway through QOOH consumption reactions at lower pressures. Especially, P3 is a new pathway of RO2 consumption at high pressures, which was not observed in importance at low pressures. Special attention should be paid to the accurate computations of n-C3H7O2 / i-C3H7O2 + CH2O and n-C3H7O2 / i-C3H7O2 + in the P3 pathway and n-C3H7O2 / i-C3H7O2 decomposition reactions in the P2 pathway at high pressures.