High Heat Flux Surface Coke Deposition and Removal Assessment

Abstract

Abstract : The internal surfaces of liquid hydrocarbon-fueled rocket engine thrust chambers, throats, and nozzles are exposed to high pressure combustion products at temperatures beyond 6000 F. Regenerative cooling is widely used in these engines to prevent overheating of the copper alloy liners. As a result, high heat flux fuel-wetted surfaces reach temperatures where fuel carbon deposits (coke) form. Coke has a much lower thermal conductivity than copper - thicknesses of only a few millionths of an inch can cause liner temperatures to increase to dangerous levels. Moreover, reusing launch vehicles and main engines increases the likelihood that unsafe levels of coke will be deposited over the course of multiple missions. Therefore, there is a need for a method to survey coke layer thicknesses and locations in the cooling channels so that engine operating margins, service intervals, and lifetimes can be determined. Unfortunately, the cooling channel geometry combined with thin coke layers makes this a difficult and challenging problem. Reaction Systems, Inc. has developed a low temperature oxidation method that can rapidly remove the coke layers in the cooling channels and at the same time map their location. We demonstrated this technique in a recent SBIR Phase II effort, which included depositing coke on copper surfaces at heat fluxes in excess of 20 Btu/in2-s under pressure, temperature, and flow conditions that match those experienced in liquid hydrocarbon-fueled rocket engines. Surface analysis was used to characterize the carbon concentration on the surface of the copper substrate after the coking cycle and also measure the thickness of the carbon deposit. These analyses were used to also demonstrate that the carbon was completely removed from the substrate using our low temperature oxidation process.