Purdue University's new fuels aren't rocket science… well actually, they are. Purdue University is looking to break the aerospace industry out of decades of using largely the same fuels, typically either kerosene-liquid oxygen, or the more prevalent liquid-oxygen, liquid-hydrogen mix. Amid resurgence in interest in looking at new and exotic propulsion technologies, the team isn't looking to reinvent the rocket; they just want to make it better.
The team has devised a new gel fuel which has about same viscous character as orange marmalade. However, this fuel isn't meant for spreading on toast, rather it improves the safety, performance and range of rockets. The team hopes to see it used in both military and space exploration applications.
The key problem with rocket fuels is that liquid fuels, used in rockets like the Shuttle boosters, can leak. Solid fuels, like Ammonium Perchlorate Composite Propellant (APCP), on the other hand don't leak, but they also have much lower specific impulse, are harder to throttle, and require special high pressure combustion chambers.
However, according to team leader Stephen Heister, professor of aeronautics and astronautics at Purdue University, gel fuels can provide the best of both worlds. He states, "You can turn the engine on and off, you can coast, go fast or slow. You have much greater control, which means more range for missiles. The gelled propellants also tend to have a little more energy than the solid propellants."
The new gel fuels his team has devised could be put to use booster rockets for unmanned missions, or even in the boosters for NASA's new Ares manned space program, the Shuttle successor (assuming the specific impulse could be boosted high enough). Professor Heister's interdisciplinary team which is developing the fuels consists of many of the faculty at Purdue University, but also includes members from Iowa State University and University of Massachusetts.
The work is not without obstacles. Paul Sojka, a professor of mechanical engineering and an associate director of the project, is working to capture videos of the high speed jets of gel that form when the rocket is firing. He describes, "These jets are wiggling, there are pulsations, and those pulsations, we believe, lead to the formation of specific spray patterns and droplet formation. The fluid mechanics of gels are quite challenging. The viscous properties of the gel change depending on how fast it's flowing, which is not true of common liquids such as water or gasoline."
Adds Carlos Corvalan, an associate professor of food science, who is working on the product and brings gel expertise from the food industry, "Gels are more complex than ordinary solids and fluids. Fluids are characterized by viscosity, and solids are characterized by elasticity. Because gels share properties of both solids and fluids, they possess viscoelastic properties, or a combination of both."
The new fuel is hypergolic, meaning that it needs no ignition source, but burns when exposed to an oxidizer. The final system will require a small separate tank of oxidizer to burn the fuel.
Having created a promising gel fuel, characterizing how it flows out of the engines is the critical final step. A finished engine will likely spray thousands of pounds of gel per second into the engine combustion chamber. With this kind of a demanding scenario, a precise understanding of the behavior is absolutely critical. The team understands this and is working hard to set up a plethora of real world tests coupled with computer simulations to analyze many aspects of the gel behavior. If they can successfully obtain the big picture, deployment in military and NASA rockets will be almost a sure shot for them.
The project is one of a couple programs funded by a $6.4M USD U.S. Army Multidisciplinary University Research Initiative (MURI) grant.