Consideration of fuel and oxidizer combinations for mass and volume limited hybrid rocket motors

This research considers different storable oxidizer and fuel combinations for hybrid propulsion, looking for the most adequate candidates for mass and volume limited systems. High specific impulse I sp is the main indication for minimum mass, whereas high density specific impulse ρI sp is a good measure for smaller volume. Other aspects such as safety, handling, toxicity, burn rate, hypergolicity, and the oxidizer to fuel O/F ratio, may affect the final choice of propellant ingredient combination. For mass‐limited systems hydrogen peroxide H 2 O 2 or nitrogen tetroxide N 2 O 4 (the latter is toxic and hard to handle) oxidizers give the best results with most solid fuels (mainly hydroxyl‐terminated polybutadiene HTPB). For volume‐limited systems the same combinations may apply; however, in that case polyester fuel may be an adequate choice as well because of its high density. Nitrous oxide N 2 O is the most inadequate oxidizer for volume‐limited systems, yielding ρI sp lower by about 40 % compared to other oxidizers. Reducing the structure and insulation mass may result from decreasing the high‐pressure, high‐temperature section (the combustion chamber) and can be achieved from high O/F combinations employing N 2 O or H 2 O 2 oxidizers. N 2 O gives relatively safe system, H 2 O 2 enables hypergolic combinations, HNO 3 is good for long‐term storage, whereas paraffin wax and expandable graphite additive yield high fuel regression rate and thrust. Overall, H 2 O 2 oxidizer seems optimal for many operational aspects, but it should be chemically stabilized to minimize decomposition.