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

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.