Methane has many possible advantages as a fuel for reusable rocket engines and is therefore extensively discussed. However, the characteristics of methane as a coolant in a regenerative cooling system are widely unknown. Especially the heat transfer deterioration that occurs in the vicinity of the critical point is a major concern and a severe drawback. To investigate this phenomenon and to establish a broad data basis for the validation of numerical simulations, tests were performed with a subscale combustion chamber. The combustion chamber contains different cooling channel geometries (rectangular cooling channels with the aspect ratios [height-to-width ratio]: 1.7, 3.5, 9.2, and 30) and was cooled with cryogenic methane. Results close to the critical point show a distinct maximum in hot gas wall temperature, which is a clear evidence of heat transfer deterioration. The test results indicate a strong dependency on the occurrence of this effect toward cooling channels with a low aspect ratio.

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Hydrogen and Methane are two fluids that are either used or in discussion as propellants for upper and lower stage rocket engines. The conception of a regenerative cooling system is a crucial part in the design of a rocket engine and so is the detailed knowledge of the coolants behavior and the heat transfer capabilities. Hydrogen is a very efficient and well known cooling fluid whereas the properties of methane as a cooling fluid are intensively investigated nowadays. Experiments were performed with a subscale combustion chamber that is divided into four sectors around the circumference each containing rectangular cooling channels with different aspect ratios. Cryogenic hydrogen and liquid methane were used as cooling fluids. These experiments provide a broad data basis that is used for the validation of CFD simulations. The simulations are capable of predicting wall temperatures for high pressure conditions. Thermal stratification effects that are known to limit cooling properties in high aspect ratio cooling channels arise for both fluids, but the effects are much stronger for hydrogen compared to methane. However in the vicinity to the critical point, when it comes to heat transfer deterioration, the simulations show large deviations to the experimental values.