Researchers from Hokkaido University analyzed static firing tests of a hybrid rocket motor using liquid nitrous oxide as the oxidizer and high-density polyethylene as the fuel
A hybrid-propellant rocket is a rocket with a rocket motor that uses rocket propellants in two different phases: one solid and the other either gas or liquid. Some examples of hybrid rockets include ‘SpaceShipTwo’ a hybrid rocket-powered spaceplane manufactured by Virgin Galactic Ltd. Use of hybrid rocket offers several advantages over liquid bi-propellant and solid rocket counterparts such as logistical cost savings and reduced risks during operations. Several hybrid rockets have relied on self-pressurizing ability of nitrous oxide (N2O) such as the SpaceShipTwo and SpaceShipOne. The combination of N2O and high-density polyethylene (HDPE) as propellant offers storability, nontoxicity, and stable burning with minimal combustion oscillations in hybrid rocket apogee kick motors. However, the performance of hybrid rockets that rely on this propellant combination is less assessed.
Now, a team of researchers from Hokkaido University focused on developing experimental methodology to obtain results from the analysis of tests conducted under the propellant combination of N2O/HDPE for the histories of nozzle erosion, characteristic exhaust velocity efficiency, and fuel consumption. The team suggested optimizations to ballistic reconstruction techniques that are established non-intrusive data collection and analysis methods, to cost-effectively collect data on hybrid rockets using this propellant combination. The team also focused on efficiently conducting basic combustion analysis to develop a hybrid rocket apogee kick motor with the help of N2O as the oxidizer and HDPE as the fuel.
The team introduced time-resolved fuel mass consumption into the equations that regulate the characteristic exhaust velocity and thrust. This improvement helped the team to collect and assess time histories of combustion efficiency, fuel regression rate, and nozzle throat erosion at the same time. Six firing tests were conducted to correlate the combustion efficiency transients and fuel regression rate. The team also obtained a larger erosion onset factor threshold compared to when oxygen is used as the oxidizer. In future research, the team plans to boost the development of hybrid rocket projects using N2O/HDPE with the help of data reduction methodology. The research was published in the journal MDPI Aerospace on April 17, 2019.
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