Combustion characteristics of initial port diameter variation of solid fuel in hybrid rocket motor

The Combustion characteristic with respect to initial port diameter variation in hybrid rocket motor is investigated using single port cylindrical grain. Experimental studies are performed with GOX and GN₂O as oxidizers, and HDPE as fuel. Four initial port diameters of 10 mm, 15 mm, 20 mm and 25 mm were tested to see the effect of initial diameter on the burning rate where the regression rate behaved differently depending on the type of oxidizer. With GOX as oxidizer, the regression rates for the four port diameters are laid closely to each other so that they can be represented by a single empirical correlation i.e., as if the effect of initial port diameter can be negligible on the burning rate. At the contrary with GN₂O, the regression rates are hardly represented by a single empirical correlation, and a large scatter of O/F ratio is observed with different initial diameters implying that the effect of initial port diameter can be important on the burning rate. While the behavior of regression rate on the variation of initial port diameter appeared differently depending on the type of oxidizer, the burning rate of fuel at a given oxidizer mass flow rate is decreased with increasing initial port diameter due to the decrease of heat flux from the flame to the solid fuel surface for both the oxidizer. A simple relation between thrust at the nozzle throat and initial geometry characteristic which is composed of oxidizer mass flow rate, initial port diameter and fuel grain length is proposed for the design method of hybrid rocket motor.