Research could hasten the dawn of hybrid rocket engines

Hybrid rocket fuel research being done by a University of Alabama in Huntsville (UAH) mechanical engineering doctoral student could hasten the day when a simpler, safer, more economical rocket engine propels space missions.

At UAH’s Johnson Propulsion Center, Matthew Hitt has experimented with varying solid fuel grain sizes to see how they burn at different combustion chamber pressures and oxidizer flow rates in an effort to improve the performance of hybrid engines.

“This is another step in making hybrids – which are a safer alternative to either solid or liquid engines – more practical for actual application,” he says.

Advised by Dr. Robert Frederick, director of UAH’s Propulsion Research Center, Hitt attended the 2015 Combustion Summer School at Princeton University and has submitted a paper on his work to the American Institute of Aeronautics and Astronautics 2015 Propulsion and Energy Forum, set for July 27-29 in Orlando, Fla.

Improving the efficiency has to do with improving the fuel regression rate – a scientific way of saying you get the solid fuel to burn faster so it recedes back from the flame front at a faster rate.

“By increasing the fuel regression rate – which can lead to simpler designs – you are leaving less unburned fuel, so you are not carrying all this dead weight,” Hitt says.

Not having to carry fuel that won’t end up getting burned could reduce the weight of the rocket, allow for use of a smaller engine for the same flight result, or allow for a larger payload due to the weight savings.

Perfecting hybrid engines has been intriguing to rocket scientists globally because of the tantalizing benefits a hybrid engine offers over both conventional solid rocket engines and over liquid fuel/liquid oxidizer engines.

Rather than having a valuable human or satellite payload sitting atop two premixed solid propellants that could explode if accidentally ignited, in a hybrid engine one propellant is a solid and the other is a liquid.

“You’re not sitting on a bomb,” says Hitt. Having half the combustion equation as a solid beats a liquid/liquid combination in weight and cost savings, because half of the valves and associated equipment needed to pressurize and control liquids are eliminated. And unlike a solid fuel engine, a hybrid can be throttled and shut down.

Read more: UAH student’s research could hasten the dawn of hybrid rocket engines