Hybrid Rockets as Post-Boost Stages and Kick Motors

Hybrid rockets are attractive as post-boost stages and kick motors due to their inherent safety and low cost, but it is not clear from previous research which oxidizer is most suitable for maximizing ΔV within a fixed envelope size, or what impact O/F shift and nozzle erosion will have on ΔV. A standard hybrid rocket design is proposed and used to clarify the impact of component masses on ΔV within three 1 m3 envelopes of varying height-to-base ratios. Theoretical maximum ΔV are evaluated first, assuming constant O/F and no nozzle erosion. Of the four common liquid oxidizers: H2O2 85 wt%, N2O, N2O4, and LOX, H2O2 85 wt% is shown to result in the highest ΔV, and N2O is shown to result in the highest density ΔV, which is the ΔV normalized for motor density. When O/F shift is considered, the ΔV decreases by 9% for the N2O motor and 12% for the H2O2 85 wt% motor. When nozzle erosion is also considered, the ΔV decreases by another 7% for the H2O2 85 wt% motor and 4% for the N2O motor. Even with O/F shift and nozzle erosion, the H2O2 85 wt% motor can accelerate itself (916 kg) upwards of 4000 m/s, and the N2O motor (456 kg) 3550 m/s.

Investigation of Liquid Droplet Flow Behavior in a Vertical Nozzle Chamber

This study aims to better understand the aluminum oxide agglomerates break-up mechanism, consequently determining the best solution for the solid rocket motor (SRM) nozzle erosion problem. Two-phase air-water flow experimental investigation was conducted as a substitute for liquid aluminum agglomerates and exhaust combustion gases. The results show that increasing the exhaust air velocity enhances the droplet's break-up tendency in terms of reducing the average diameter and increasing droplets number per the testing channel volume. Numerical models were constructed and validated using the experimental results. The percentage error in the droplets' average diameter and number is between 6–15% and 8-18%. Furthermore, the effect of reducing the liquid surface tension was studied. The results showed that it facilitates water bodies' separation from the interface surface, as a result of the reduced bounding forces between surface's molecules, which enhances the break-up process (0.5-17% increase in the droplets' average diameter and 4-100% increase in its number) and reduce the droplets impact on the nozzle walls, hence reduce the SRM nozzle erosion problem.