The effect of the addition of nitrogen oxides on the oxidation of propane: An experimental and modeling study

摘要

The oxidation of propane (C3H8), with the addition of different oxides of nitrogen (NO, NO2, and N2O) in concentrations of 0 - 2000 ppm, has been investigated for stoichiometric mixtures, at compressed temperatures of (T-C) = 690 - 1420 K, and at compressed pressures of (p(C)) = 2.0 - 3.0 MPa using both a rapid compression machine and a high-pressure shock tube. These new ignition delay time (IDT) measurements, together with C-3/NOx data available in the literature, provide a direct validation of NUIGMech1.3 which includes an updated C-3/NOx sub-mechanism. The experimental results show that the mixtures with NO2 and NO/NO2 added have longer IDTs, inhibiting reactivity at T-C 800 K, compared to the base C3H8/"air' mixtures indicating the complex chemical interactions involved. Both the inhibiting and prompting effects depend on the concentrations of NO and NO2 added and on the temperature regime. The addition of 1000 ppm NO2 significantly reduces the negative temperature coefficient (NTC) behavior of C3H8 in the temperature range 715-800 K compared to the addition of 200 ppm. Model predictions with 1000 ppm NO added, assuming no conversion of NO to NO2, are significantly slower than for both the 0 and 1000 ppm NO2 addition cases at T-C < 800 K. Although NO and NO2 addition have different impacts on C3H8 oxidation at low-, intermediate, and high-temperatures, the addition of 1000 ppm N2O did not show any chemical effect at the conditions studied. NUIGMech1.3, with the updated C-3/NOx sub-mechanism, reproduces the sensitisation effect of NOx on C3H8 with generally good agreement. Sensitivity and flux analyses have been performed to highlight the key reactions controlling ignition. The analyses show that competition between the reactions ?+NO2 harr;R?+NO and ? +NO2 (+M) harr; RNO2 (+M) governs NOx sensitization on propane ignition. The inhibiting effect of NO and NO2 addition to propane stems from the nC(3)H(7)+ NO2 harr; nC(3)H(7)O + NO and nC(3)H(7)O(2) + NO harr; nC(3)H(7)? + NO2 reactions, which compete for nC(3)H(7)O(2) radicals, reducing the rate of isomerization of nC(3)H(7)O(2) into C(3)H(6)OOH1-3 (R?(2) ? QOOH). (C) 2022 The Author(s). Published by Elsevier Inc. on behalf of The Combustion Institute.