Effect of Penetrative Combustion on Regression Rate of 3D Printed Hybrid Rocket Fuel

3D printing manufacturing is used to manufacture hybrid rocket fuel grains featuring a special grid-like structure in order to control combustion performance. An innovative penetrative combustion mechanism, capable of affecting regression rate, was noticed during the combustion of low-packing density grains. The 3D printing manufacture was implemented using acrylonitrile-butadiene-styrene (ABS) material to clarify this mechanism and the corresponding combustion performance. Grid-like structure fuels with different packing densities were prepared to assess the effects of penetrative combustion on fuel combustion performance. The thermal decomposition of ABS was analyzed by infra-red spectroscopic analysis (FTIR) and thermogravimetric analysis-differential thermal scanning (TG-DSC). The internal structure of the ABS grains was observed by high-resolution 3D micro-computed tomography (μCT). All fuel grains were burned in a hybrid 2D radial burner, allowing visualization of the combustion process and evaluation of the ballistic parameters. The experimental results suggest that the combustion process of the ABS porous grains includes two regimes, both featuring an increased regression rate. In the normal layer-by-layer burning regime, at Gox=45 kg/(m2·s), the regression rates of 100% and 90% ABS increased by 29.6% and 38.1%, respectively, compared with solid ABS which was manufactured by a computerized numerical control (CNC) lathe. In the fracture-led volumetric burning regime, data acquisition is more difficult, but the regression rate is again observed to increase as the packing density decreases.