Hybrid Rocket Nozzle Erosion with Microaluminum-Added Fuel

Because of its relatively low cost and wide availability, carbon graphite is one of the most widely used ablative nozzle materials in hybrid rocket propulsion. The erosion characteristics of the nozzle material have paramount importance because it directly influences the I_sp performance. This is especially the case for upper-stage or in-space rocket motors operating with very long burn times. In this study, the effect of aluminum-added fuel on the graphite nozzle erosion is studied. In the experimental studies, a high regression rate paraffin-based fuel is loaded with micrometer-size aluminum powder for nozzle erosion reduction. In our approach, aluminum is added at high concentrations as a fuel ring in front of the main paraffin-based fuel which contains no aluminum. Based on the motor tests conducted with gaseous oxygen as an oxidizer, it is shown that aluminum addition decreased the nozzle erosion rate up to 45% and increased the nozzle erosion onset time by 1 to 3s. The new method of introducing an energetic powder in a fuel ring positioned at the fore end of the motor offers an easy and scalable way of reducing the nozzle erosion and improving the I_sp performance of the rocket motor.