Droplet Vaporization/Combustion Stability-Based Design of Pre-Combustion Chambers for Hybrid Propellant Rocket Motors

Hybrid Propellant Rocket Motors (HPRMs) have been advancing rapidly in recent years. These improvements are finally increasing their competitiveness in the global launch-vehicle market. However, some topics, such as the pre-combustion chamber design, still require more in-depth studies. Few studies have examined this subject. This work proposes a low-computational-cost algorithm that calculates the minimum pre-combustion chamber length, with a vaporization and feed-system coupled instability model. This type of analysis is a key tool for minimizing a vehicle’s size, weight, losses, and costs. Additionally, coupling with internal ballistics codes can be implemented. Furthermore, the results were compared with real HPRMs to verify the algorithm’s reliability. The shortened pre-chamber architecture trimmed the inert mass and reduced the feed-system pressure requirement, boosting overall propulsive energy efficiency by ≈8% relative to conventional L*-based designs. These gains can lower stored-gas enthalpy and reduce life-cycle CO and CO2-equivalent emissions, strengthening the case for lighter and more sustainable access-to-space technologies.