A Novel Thermal Method for Rapid Coke Measurement in Liquid Rocket Engines

ABSTRACT: The surfaces of rocket engines are exposed to high pressure combustion products at temperatures up to 6000°F. Regenerative cooling can cause coke to form on the heat exchanger surfaces and the intention to reuse engines creates the potential for excessive coke accumulation, reduced cooling efficiency, and eventual engine failure. Therefore, there is a need to develop a method to characterize coke layer thickness so that engine lifetimes can be predicted. In the Phase I project, Reaction Systems identified an approach than can rapidly and accurately map very thin layers of coke deposited in the cooling channels. We detected coke thicknesses of less than a millionth of an inch in a multichannel plate test article and identified where the coke was located. The overall objective for Phase II is to advance the technology and transition it to a full scale application. In Phase II, we will construct a 1/2 scale cooling channel replica, deposit coke, and demonstrate that our method can detect coke deposits one millionth of an inch thick in these cooling channels. We will also show that our method is effective on coke produced at the very high heat fluxes that occur in rocket engine cooling channels. BENEFIT: The technology will be useful for government and commercial applications. The DoD and AFRL have recently been studying reusable launch vehicles for the eventual replacement of the Evolved Expendable Launch Vehicle (EELV) system, currently scheduled to be phased-out in 2030. Developing a reusable, fast turn-around launch capability vehicle would allow the DoD to amortize the cost of these launch vehicles over a large number of launches. The ability to reuse a vehicle even ten times could reduce the on-going launch services costs of the government by 90% of current costs. Since the engines are a major part of the cost of a rocket, increasing the reusability of these components by mapping coke deposition could substantially improve the number of missions each engine can provide. There is also a great deal of commercial interest in reusable launch vehicles. Current manufacturers and users of RP/LOx rocket engines would be the primary customers for our technology. This list is fairly small but is increasing in size with the commercialization of space tourism and space launch services. SpaceX, for example, currently has over a $2B order backlog for their Falcon 9 and Falcon Heavy series of expendable launch vehicles and soon expect to break the mythical $1000 per pound of payload cost to LEO. SpaceX is also actively looking at ways to return both their first and second stages back to the launch site for refurbishment and reuse. SpaceX has experienced an approximately 100% growth in orders per year for the past few years, and expects this trend to continue or accelerate in the future as their launch costs decrease.