Laminar burning velocities of C2H4/N2O flames: Experimental study and its chemical kinetics mechanism

Abstract

Abstract Nitrous oxide fuel blend propellants have great potential to be used in rocket engine, and investigations on the fundamental combustion characteristics of such propellants are therefore necessary to control flashback and develop their chemical kinetics mechanism. Laminar burning velocities (LBVs) of C2H4/N2O flames are measured by using spherical expansion flames in this paper at 0.5–2.0\xa0atm and 280\u202fK. The present method for upper and lower limits of effective flame radius is reasonable for the experimental stretched flame speeds can be fitted very well with the flame stretch rates. The LBVs of C2H4/N2O flames are smaller than those of C2H4/N2/O2 flames (same N/O ratio as N2O) at conditions near stoichiometric ratio, while they are larger than those at other conditions especially at fuel-rich side. The LBVs of C2H4/N2O flames are not sensitive to the pressure in the measured range. Two kinds of sub-mechanisms are applied for detailed chemical kinetics mechanisms of C2H4/N2O reactions, which are USC Mech II-2 for hydrocarbon reactions as well as GRI 3.0 mechanism and San Diego mechanism for nitrogen oxide reactions respectively. Eight key elementary reactions are chosen based on the sensitivity analysis, and the effects of their available rate constants from literatures on the LBVs are tested. Modified mechanisms for C2H4/N2O reactions are therefore proposed by replacing the rate constants of these key elementary reactions, which predicts well for LBVs of hydrocarbon/N2O flames. Sensitivity analyses are performed for C2H4/N2O flames at different equivalence ratios, it is found that the N2O decomposition is a dominant reaction in conditions near stoichiometric ratio, while it is the codominant and nondominant reaction in fuel-lean and fuel-rich conditions respectively. Furthermore, the reaction pathways of oxidizers consumption in C2H4/N2O flames and C2H4/N2/O2 flames are analyzed, and the observations on the LBVs of these two flames in the experiment can be well explained through the reaction pathways and their relative changes under fuel-lean, stoichiometric and fuel-rich conditions.