Reduced kinetics mechanisms for ram accelerator combustion
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abstract
Two skeletal kinetics mechanisms for reactive CH4/O2and H2/O2ram accelerator flowfields are presented. Both models were derived from a 190-reaction, 38-species kinetics mechanism (RAMEC or RAM accelerator MEChanism) that successfully reproduces the high-pressure (>50 atm), low-dilution (<70%), fuel-rich chemistry of ram accelerator mixtures. The reduction procedure for the CH4/O2mechanism utilized a detailed-reduction technique with ignition delay time and heat release as the selection criteria. The methane-based mechanism (REDRAM or REDuced RAM accelerator mechanism) contains 34 reactions and 22 species and predicts ignition times to better than 5% and postcombustion temperatures to within 10 K of the full mechanism for a representative range of ram accelerator mixtures and conditions. This CH4/O2mechanism is an improvement over existing reduced methane-oxidation mechanisms that are based on lower-pressure, higher-temperature chemistry. An 18-step, 9-species mechanism is presented for hydrogen-based ram accelerator combustion that is based on the H2/O2submechanism of the RAMEC/Gas Research Institute GRI-Mech 1.2 methane-oxidation mechanism. The H2/O2kinetics model includes HO2and H2O2chemistry near the second and third explosion limits, necessary for ignition at ram accelerator pressures but lacking in certain finite rate chemistry models currently in use.
