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 su-percritical 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, O 2 , CO, CO2, CH2O, C2H4, CH3CHO, and C 3 H 6 were quantified by using a micro-gas chromatograph ( & mu;-GC). The experiment showed that different from that of 10 atm, at 100 atm only a weak negative temperature coefficient (NTC) behav-ior 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 tem-peratures 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 discrep-ancy 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 / O 2 domi-nated 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-C 3 H7O2 / i-C3 H7O2 + CH2O and n-C3H7O2 / i-C3H7O2 + in the P3 pathway and n-C3H7O2 / i-C3H7O2 decomposition reactions in the P2 pathway at high pressures.& COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The low and intermediate temperature oxidation of propane was studied in a supercritical pressure jet stirred reactor (SP-JSR) under different conditions. The experiment found a weak negative temperature coefficient (NTC) behavior at 100 atm due to the shift of intermediate temperature HO2 chemistry to lower temperature. Existing literature models could capture the onset temperatures of low and intermediate chemistry, but failed to predict the fuel oxidation quantitatively and capture the NTC behavior. This highlights the uncertainties in developing hierarchy models for fuels with low temperature chemistries at extremely high pressures.