Fundamental Study on Coking Inhibition for Regenerative Cooled LNG Rocket Engines

Liquefied Natural Gas (LNG) is lower cost, higher density and easier handling than Liquefied hydrogen (LH2), therefore, is expected as the most promising candidate for the next generation rocket propellant. For LNG propellant, a full expander or an expander cycle rocket engine with regenerative cooling system is expected because its molecular weight is middle value between LH2 and Kerosene. Temperature of turbopump driven LNG gas should be higher to improve the specific impulse or combustion pressure for these rocket engine. In this case, coking of LNG in heat exchanger or regenerative cooling system becomes a significant problem. In the present study, two coking inhibition methods, n-C6H14 coating and graphite coating, are presented and their effects are evaluated. Contrary to our expectation, the former method is accelerated the LNG pyrolysis, resulting of coking promotion. On the other hand graphite coating can successfully inhibit coking up to 973 K.