New experimental results on transpiration cooling for hydrogen/oxygen rocket combustion chambers

While previous experimental activities of DLR focused on low pressure applications of combustion chamber segments cooled with either water or gaseous hydrogen wich have been performed at the DLR test facilities P6.1 and M3, this paper presents the most recent experimental results obtained at the high pressure GH₂/LO₂ test facility P8. For this purpose, DLR model combustor B, a 10 MPa regeneratively cooled experimental combustion chamber having modular design was applied to implement transpiration cooled segments at different downstream positions of the combustion chamber. These recent DLR experiments have been performed for combustion chamber pressures ranging between 3.5 and 10 MPa and a constant oxidizer/fuel mixture ratio of 6.5. Screening tests at lower pressures showed nickel alloys to be favorable for transpiration cooling purposes. Hence, for the high pressure tests reported here only the material porosity was changed with a variation of the typical pore size between 1 μm and 5 μm. The mass flow rate of the coolant, ambient gaseous hydrogen, has been varied in a wide range to increase the existing data base for modeling and verification purposes as well as to gain experience and to check the limits of operability of this cooling technique especially at the low end of coolant mass flow rates. After a brief description of the governing equations and some available models as well as a short presentation of the experimental setup and the operating conditions, the paper focuses on the experimental results and their comparison with the models derived for transpiration cooling applications. Based on the results of this comparison a modification of the model of Kays and Crawford is suggested.