Literature survey for a first choice of a fuel-oxidiser couple for hybrid propulsion based on kinetic justifications

International audienceHybrid rocket propulsion presents an increasing demand because of safety and cost reasons. Numerous works cover the main related areas (regression rate, oxidiser injection, grain design and additives in solid reducer). Nevertheless, the use of detailed kinetic studies, either experimentally or numerically, remains scarce. In particular, the auto-ignition and pyrolysis delays, the nature of chemical species impacting the diffusion flame and the rate of heat release are some of the important parameters. They are rarely considered when choosing a reducer-oxidiser couple. Understanding these chemical parameters could help choosing, or later improving, the solid reducers which present low regression speeds (limiting step of hybrid engine due to low combustible gas flow rate). Since detailed chemistry is still a foreign field for hybrid rocket studies, a wide review is first presented to determine how existing chemical works can be of interest for this propulsion technique. Mechanical and thermal characteristics are also considered in addition to combustion ones. Analytical estimation of the requirements to be met by the reducer-oxidiser couple is proposed (combustion heat release and associated heat fluxes, endothermic pyrolysis effect, chemical induction delays). Moreover, the choice of a reducer depends on the operating conditions under which it is used. For this reason, some equilibrium calculations are also provided to investigate the pressure and temperature effects. Among sixteen solid reducers, only three are finally selected in a first step (high density polyethylene -HDPE-, polymethylmethacrylate -PMMA-, hydroxyl terminated polybutadiene -HTPB-). A similar work for oxidisers is conducted among thirteen compounds and three of them are selected (hydrogen peroxide -H2O2-, nitrous oxide -N2O-, pure oxygen -O2-)