Deposit Formation and Heat Transfer for Bioethanol-Fueled Rocket Engine Combustion Chamber Liners

Abstract

The sulfur attack and coking of bioethanol fuel in rocket engine combustion chamber cooling channels were evaluated based on the results of field tests conducted under engine operating conditions for a copper alloy and a nickel alloy. The field test was conducted in the open air because this apparatus is about 6 m long and for the safety of operators. After the experiments, test specimens were subject to electron probe microanalyzer and x-ray diffractometer analyses, as well as roughness and Brinell hardness measurements. It became clear that increased surface roughness due to sulfur attack was only observed in the case of high sulfur content, whereas no significant evidence of sulfur attack was observed in other cases of normal bioethanol. Increased surface roughness due to coking was observed in most cases for the nickel alloy, and it was particularly noticeable in the case of long duration. The current evaluation of the heat transfer coefficient revealed a tendency for it to change at bioethanol temperatures higher than 500 K, depending on the constant pressure specific heat, which should be considered in the design of combustion chamber cooling channels for bioethanol-fueled rocket engines. From engine system calculations taking into account the effect of coking, it was found that coking and not material cycle fatigue was the driving factor in determining the number of times of reusability in cases in which the nickel alloy was used at the cooling chamber outer cylinder.