Modeling of Jet Autoignition in a Microrocket Combustion Chamber

Abstract

Under contract of the European Space Agency, a 1 N bipropellant thruster system operating exclusively with green propellants was developed. One of the main properties to be investigated is the autoignition capability and conditions in a miniaturized combustion chamber. Hydrogen peroxide (87 wt%) and kerosene comprise the propellant combination of choice for this study. For the prediction of autoignition conditions, an analytic nonadiabatic autoignition model of the ignition conditions for a choked and nonchoked flow reactor has been developed. The model uses a single step forward chemical reaction and includes a residence time distribution of the propellants. A particular focus of the investigation is the probability of autoignition as a function of the pressure–temperature conditions and the combustion chamber geometry. For the validation of the autoignition model, a comprehensive test campaign was conducted. The autoignition conditions predicted by the model agree very well with the ones observed in the experiments. Additionally, the model identifies physical parameters that contribute to a previously empirical parameter. In conclusion, with the autoignition model, it is straightforward to design a propulsion system for a given inlet temperature, minimum desired ignition pressure, and blowdown ratio.