Combustion Technologies Relating to Hybrid Rockets

Abstract

This paper summarizes researches about combustion technologies related to hybrid rockets, focusing on the enhancement of regression rates of solid fuels and the development of techniques for measuring fuel gasification rate. Methods for enhancing the regression rate were divided into two groups: improving the physical or chemical properties of a solid fuel, and improving the combustion flow field in a combustion chamber. In the former group, the use of liquefying fuels like paraffin-wax has become the mainstream of recent hybrid rocket development activities because these fuels have been shown to provide regression rates that are two to three times higher than values encountered with conventional solid fuels. Measuring the history of the fuel gasification rate in a hybrid rocket is not easy, and it has been an important subject in this field. Measurement techniques fall into two categories: the direct measurement of fuel thickness or fuel weight, and reconstruction techniques that estimate fuel flow rate through easily measurable histories such as liquid oxidizer flow rate, chamber pressure, thrust, etc. Recently, a new method to estimate the nozzle throat area history during firing was developed by improving on a reconstruction technique.