Introduction
A hybrid rocket is basically the combination of solid and liquid rocket engines. In this fuel is in solid phase and oxidizer is either in liquid or gaseous phase. It has many advantages over solid and liquid rocket engines, which has been explained in Sutton and Biblarz [1], Altman and Holzman [2] and also available in the review paper by Pastrone
In a hybrid rocket, regression rate is the key parameter and the measurement of regression rate itself is a matter of concern, which needs major attention. It is due to non- linear burning of fuel with burn time. Various methods have been used by the researchers to determine the regression rate of hybrid rocket fuel such as ultrasonic technique X-ray radio graphic technique [7,9,13–15], and weight loss method [16–27]. In an ultrasonic technique, an array of transducers will be needed to get the complete regression rate, which would increase the overall cost and complexity of the set up. The X-ray radiographic technique uses sophisticated equipment and requires skilled man- power for its operation. These increases the overall cost of the system. The weight loss method [16–27] is the most widely used method to determine the regression rate. The drawback of this method is that to get a complete trend line of regression rate vs Gox, a series of experiments need to be carried out. An alternate method has been conceived by researchers [28–31,12] to obtain the regression rate of a hybrid fuel, which could be simpler and accurate. Here, the combustion chamber pressure is used to obtain the regression rate of the fuel. It has advantage over the weight loss method such that in a single experiment, it can give the complete trend line of regression rate vs oxidizer massflux(Gox). In this method, the relations for the chocked flow through the nozzle are used to obtain the regression rate using