Expander and coolant-bleed cycles of methane-fueled rocket engines

Abstract

This paper describes the characteristics of methane-fueled rocket engines and compares these characteristics with those of hydrogen-fueled engines in terms of both expander and coolant-bleed cycles. Methane vaporizes in a cooling jacket under low-pressure operating conditions, whereas it liquefies in the turbine in the coolant-bleed cycle. The thermodynamic property of methane limits the operating range of methane-fueled engines. When the coolant-bleed cycle is used, the specific impulse degradation of methane-fueled engines becomes larger compared to that of hydrogen-fueled engines. This is due to methane having a lower specific heat and temperature after regenerative cooling. Even though the heat absorbing ability of methane is much lower than that of hydrogen, methane-fueled engines can operate with higher chamber pressures using the expander cycle. This is due to the larger density and the higher temperature after the regenerative cooling of liquid methane. Throttling of the methane-fueled engines does not have a great impact on the pump exit pressure in the expander cycle, whereas it increases the bleed ratio and degrades the specific impulse in the coolant bleed cycle of methane-fueled engines.