Influence of micro-aluminum addition to paraffin-based fuels on graphite nozzle erosion rate

One of the most used ablative cooling material for the hybrid rocket motors is the carbon graphite and the erosion of this material during the operation of these motors causes the loss of chamber pressure and Isp. Especially, long burning upper stage rocket motors suffer more from the nozzle erosion. One of the ways to combat the nozzle erosion is to change the fuel composition in order to reduce the oxidizing species at the nozzle and create a protective liquid fuel film on the surface of the nozzle. To study this method, we have decided to use a paraffin-based fuel because of its high regression rate and aluminum powder addition for nozzle erosion reduction. Aluminum is added as a fuel ring at the front of the paraffin-based fuel which makes this method to be scalable for bigger hybrid rocket motors. In our experimental tests with gaseous oxygen as an oxidizer, aluminum addition decreased the nozzle erosion rate nearly %45 and increased the nozzle erosion onset by 5 seconds. Both of these combined improve the hybrid rocket motor considerably. This new and innovative method to add an energetic material such as aluminum to the hybrid rocket fuel as a fuel ring offers very low-cost, easy to implement and highly effective way of reducing the nozzle erosion and by doing that improving the performance of the motor to a great extent.