Regression characteristics of the cylindrical multiport grain in hybrid rockets

The purpose of this experimental research is to investigate combustion characteristics of the cylindrical multiport grain of a hybrid rocket motor and to highlight port number effects on the regression rate. The physical model of concern includes an oxidizer supply system, a multiport fuel grain, and a combustor with pre- and postchamber. Several design parameters, such as the port number, fuel type (polyethylene and polymethylmethacrylate), and end-burning effects, are experimentally analyzed using small- and large-scale grain, where grain diameters of 50 and 96 mm are used, respectively. For the oxidizer mass flux ranging from 10 to 300 kg/m² · s, the increase of port number positively shifts the oxidizer-to-fuel ratio to near its optimum value and the increase of regression rate is damped beyond three ports, regardless of grain size. It is observed that the radiation effect on the regression rate of polyethylene is much more dominant than that of polymethylmethacrylate, and that the end-burning effect can lead to a mismeasurement of the regression rate in large-scale grain. Emphasis was placed on merging effects among fuel gain ports having four and five ports to analyze how port geometrical configuration may influence the chamber pressure and thrust drop.