Cooling Potential of Methane in Rocket Nozzle Cooling Channels : A Conjugate Heat Transfer Analysis

Abstract: The use of hydrocarbons as fuel in rocket propulsion has been of great interest to the aerospace industry in recent years. Specifically, natural gas with a high content of methane has taken the interest of several actors, among them Sweden-based GKN Aerospace who in collaboration with KTH Royal Institute of Technology have started the MERiT project. In this project, the potential of methane as a fuel is explored through conjugate heat transfer analysis of a cooling channel geometry on a test rig. The goal is partly to find what the cooling potential of the methane is, and partly to determine the risks of thermal cracking occurring in the cooling channel. This report aims to provide a CFD analysis of the behavior of a test rig developed in earlier stages of the project. The analysis is to be used to provide design points that real experiments can be based upon. Studied behaviors include limitations regarding overheating, choke in the cooling channel and efficiency of the rig. In addition to this, the fluid temperature is studied in order to provide an estimate of which design points provide the highest potential risk of thermal cracking. In experiments, this potential risk is to be evaluated and explored in order to judge the viability of methane as a fuel. From this thesis a database of design points has been built regarding two potential channel geometries with different alloy materials. The post process and gathering of data are designed in such a way that specific behaviors can be monitored depending on a specific input. Inputs include mass flow, heat flux, inlet temperature and outlet pressure of the test rig. These were parametrized such that 243 specific design points could be examined for each channel geometry. Concluding this thesis, it was found that 131 of the cases examined for the first channel geometry were within the realm of being useful, and that a few cases fall within the realm of being at risk for coking. The risk for choke in the cooling channel is apparent at high mass flows and low pressures. The efficiency is heavily tied to heat flux and inlet temperature but shifts to be more dependent on Reynold’s number when cases with unintended behavior are filtered out.