By chance, I’ve come across two different innovative hybrid rocket motor designs in the past day:
/– The following article describes a hybrid solid-fuel/liquid oxidizer engine in which the fuel is laid out with a 3D printing technique that allows for channels to be distributed to allow for more controlled, efficient burning: A Rocket Engine that Prints Its Own Fuel : Hybrid rocket engines are rare, but a clever technique could make them more common – Technology Review.
/– A reader sent me a paper about a hybrid motor design presented at the AIAA Joint Propulsion Conference last July: Development of Staged Combustion Aft-Injected Hybrid (SCAIH) Propulsion at Cesaroni Technology Inc by B. Pilon and J. Louwers, Cesaroni Technology Inc, Gormley, Ontario, L0H 1G0, Canada. (Abstract, pdf)
As shown in the diagram below, in the conventional hybrid on the left, the oxidizer enter at the top and flows through the core opening of the fuel. In the SCAIH design, the oxidizer enters at the aft end of the fuel, which consists of “fuel-rich solid propellant gas generator (GG) grain” instead of an inert fuel.
> Combustion of this solid GG propellant produces a warm fuel-rich gases (? 1700oF), which is then injected/mixed with additional liquid oxidizer in a separate post combustion chamber. The injector process is similar in nature to liquid propulsion systems. Combustion then occurs between the warm fuel gas and the supplementary oxidizer (?6000oF) and expelled out a nozzle in a conventional manner.
The Cesaroni team has built and tested a prototype SCAIH and the results are described in the paper.
I’m sure the AIAA wouldn’t like me to post the paper so I’ll just give the conclusion:
> A sub-scale staged combustion aft-injected hybrid motor was developed and successfully demonstrated through out five tests. The unique gas generator propellant was developed and incorporated into this sub-scale motor. An effective start-up sequence was clearly shown and refined, which included the validation of spontaneous ignition between the fuel-rich warm gas and liquid oxygen flow. Stable combustion was observed in all test cases, although a detailed analysis with high frequency pressure transducers and data acquisition equipment is still required.. The sub-scale motor did deliver a sea-level Isp of 257 seconds (Ispvac = 282s) at an operating pressure of 700 psi, which was a significant improvement over typical solid propellant motor. An existing nozzle was used to reduce cost and development time, however significant nozzle erosion occurred which introduce additional complications with the injection parameters. Improving the nozzle is required before refinement of the injector can be done to increase efficiencies.
Update: I’m told the authors own the copyright and say it’s OK with them to post the paper so here it is: AIAA-2010-6786.pdf (2.9MB)