A family of skeletal mechanisms for methane oxidation at high pressure

The use of methane as a fuel in a wide range of rocket engine applications represents one promising route due to its benefits at a system level. Although several detailed kinetic mechanisms for methane oxidation exist, only a small subset proved to adequately reproduce the fundamental reaction pathways that appear under oxy- fuel conditions and high-pressure levels, typical of liquid rocket engines’ thrust chambers. Nonetheless, the search for computationally cheap schemes, eventually specialized for specific applications, represents an unavoidable theme in the space propulsion field. This is accompanied by the need for simplified mechanisms that may deal with off-stoichiometric mixtures, that deserve special attention in closed-cycle, staged combustion, liquid-fueled rocket engines. In this work, the generation of a set of skeletal mechanisms for methane oxidation at high pressures is carried out starting from the C1 − C4 version of the detailed kinetic mechanism by Zhukov. The mechanism reduction process is accomplished via an improved algorithm proposed by Malpica Galassi et al., that builds on the computational singular perturbation (CSP) framework by introducing an additional layer of automation based on the tangential stretching rate (TSR) and the species’ participation index to TSR. Based on this, the intrinsic target species set is dynamic and automatically identified through the process, leading the algorithm to include a minimal number of species/reactions that ensure global observables replication without any a-priori knowledge of the chemical pathways. Various reduction strategies are carried out, targeting different applications and operating conditions of interest in space propulsion. The objective is to provide a set of compact mechanisms that may cover a wide range of O/F ratios and chemically reacting flow conditions that characterize aerospace applications. In this regard, the entire set of CSP-based skeletal mechanisms is tested against the corresponding validation targets, including ignition delay time, laminar flame speed, counterflow diffusion flame extinction, and perfectly stirred reactor (PSR) calculations showing appreciable predictive accuracy compared with the detailed parent kinetic scheme.