Prediction and Measurement of the Soot Build-Up in Film-Cooled Rocket Engines

ABSTRACT: The need for improved performance of liquid rocket engines requires efficient wall cooling technologies to mitigate high heat fluxes from hot combustion gases to the engine wall in the thrust chamber. High heat fluxes to the chamber liners can be overcome by fuel film cooling (FFC) of the inside chamber using the liquid propellant. Moreover, the thermal cracking of the fuel creates coke deposition which acts as a thermal barrier coating. However, FFC is not well understood due to complex interactions between the vaporization of the multi-component liquid film and the hot combustion gases. Therefore, in order to better understand pyrolysis of RP fuels under FFC conditions, an experimental and modeling study will be performed to investigate various coke deposition mechanisms in a controlled environment relevant to FFC rocket engine conditions. An in-situ measurement technique based on thin film IR absorption for coke deposition thickness will be developed. The experimental data obtained in the proposed work will be used to develop detailed and reduced chemical kinetics models for coke deposition. The computationallyaffordable global and quasi-global reduced kinetics models for RP fuel oxidation and coke deposition will be implemented in CFD to simulate rocket engine FFC.; BENEFIT: The ultimate result of this research will be a comprehensive chemical kinetic mechanism that can be used to generate reduced kinetics models that can be implemented in CFD for predicting coke deposition of jet fuels, especially RP fuels. CSE has developed a detailed five-component surrogate kinetics mechanism for aviation grade fuels through previous SBIR programs funded by the U. S. Air Force. This well-validated comprehensive kinetic mechanism will be incorporated into the chemical kinetic modeling software, rkmGen, developed by CSE in an earlier SBIR supported by the Air Force (Contract# FA8650-11-C-2188). This product will facilitate the ability of the U. S. Military and engine OEMs to easily obtain high fidelity model predictions for the coking properties of RP-2, JP-8, and Jet-A fuels at conditions relevant to various engine applications. In addition, the detailed surrogate kinetic mechanism will be used to derive reduced kinetic models using rkmGen software for the CFD simulations of practical applications. CSE anticipates that the revenue from this work will be generated from providing both engineering services to the OEMs and USAF and through the licensing of the tool. The product developed in this work will be a useful tool for rocket and missle applications for the US Air Force and engine OEMs. Discussions with engine design teams indicate that the capabilities of this project will greatly enhance current design tools in use by equipment manufacturers. The use of this tool will significantly reduce development costs by eliminating some design iterations and hardware testing, which are both expensive and time-consuming. This tool will be applicable to any system in a rocket engine that utilizes coke deposition for liner protection.