New Insights into the Combustion Reaction Kinetics of Ethylene/Nitrous Oxide Green Propellant at Intermediate Temperatures.

Nitrous oxide (N2O) and ethylene (C2H4) blending fuel is one of the most representative nitrous oxide fuel blend propellants. To address deficiencies in the study of the C2H4/N2O model at intermediate temperatures, this work investigates the C2H4 + N2O potential energy surface using quantum chemistry at the CCSD(T)/aug-cc-pVQZ//B3LYP/6-311++G(d,p) level. Rate constants over 333-2000 K and 0.1-100 atm are calculated based on RRKM/ME theory. According to our calculation results, the addition reaction C2H4 + N2O → CH2CH2N2O is identified as the dominant chain-initiation step under the present investigated conditions, which decomposes via two primary pathways. The CH2CH2N2O → CH2O + CH2NN pathway competes strongly with the CH2CH2N2O → CH3CHO + N2 channel due to their close energy barriers. Well-skipping reactions of C2H4 + N2O → CH3CHO + N2 and C2H4 + N2O → CH2O + CH2NN, as well as a newly computed pathway CH2NN → CH2 + N2, are also important under combustion-relevant conditions. These obtained reaction pathways and their related rate constants are incorporated into four different models, i.e., GRI 3.0 model, Konnov 2009 model, Glarborg 2018 model, and Zhang 2023 model. The updated reactions significantly improve all their predictions of ignition delay times at intermediate temperatures. The impact of the theoretical calculation results on the mechanism of N2O/C2H4 oxidation is analyzed. At intermediate temperatures, chain-initiation reactions between N2O and C2H4 successfully bypass the unimolecular decomposition of N2O that requires high activation energy. Therefore, C2H4 tends to react directly with N2O, and aldehyde-related reactions are responsible for chain propagation and OH formation. In contrast, at high temperatures, the decomposition of N2O is activated, and the reactions between C2H4 and reactive radicals become another important pathway for fuel consumption. Consequently, the contribution of the direct reaction between C2H4 and N2O is weakened.