Reduced kinetic mechanism for methane/oxygen rocket engine applications: a reliable and numerically efficient methodology

Abstract

CFD simulations of turbulent reacting flows based on finite rate chemistry often employ reduced kinetic mechanisms to decrease the computational cost, especially if the combustion of hydrocarbons is involved. This work presents a chemical-kinetic methodology, consisting of the formulation, development, testing and validation of a reduced, skeletal mechanism targeted to the Liquid Rocket Engines (LRE) combustion of CH4/O2. The reduced mechanism is generated for combustion processes involving medium-high pressures and ignition of undiluted methane-oxygen, using the 0D/1D open-source software Cantera. The presented mechanism, named Medium Pressure Rocket Burn (MPRB), is achieved from a semi-detailed kinetic scheme, i.e. Lu30, derived from the detailed mechanism GRI-Mech 3.0. Identification of the main chemical reaction paths and sensitivity analysis applied in a sequence leading to a final scheme consisting of 19 species and 51 reactions. Promising results are obtained in terms of ignition delay times and comparison with experimental measurements in high-pressure shock tube tests. The validation is extended to the turbulent case using a sub-scale single-injector combustion chamber with a gaseous injection of CH4/O2 as a benchmark. First, Improved Delayed Detached Eddy Simulations (IDDES) based on a non-adiabatic flamelet database are in good agreement with the available experimental data, although the average thermal load foreseen by MPRB is about 12.6% higher than the case with Lu30 used as reference. Secondly, RANS simulations based on the Eddy Dissipation Concept (EDC) show that accurate results can be obtained with an affordable computational cost, compared to the previously investigated detailed chemistry calculations. Overall the successful validation of the presented reduced mechanism encourages its use for CH4/O2 combustion regimes within this range of applicability.