Dilution of Cryogenic Liquid Rocket Propellants during Pressurized Transfer

Abstract

In the testing of rocket engines and engine components, such as thrust chambers and gas generators, the rocket engineer is regularly faced with the job of transferring cryogenic liquid propellants, using pressure feed from a storage tank, through a flow system and into the combustion device to be tested. At Rocketdyne, liquid oxygen is quite commonly used as a propellant. In the testing of engine components inert pressurants are usually used, for example, helium or nitrogen. However, because of the cost and logistics, nitrogen is preferred. When gaseous nitrogen is used as the pressurant, we have repeatedly run into testing conditions which have resulted in condensation of nitrogen and subsequent mixing in the tanked liquid oxygen. This dilution of the liquid oxygen effects a loss of performance and imposes mechanical difficulty in maintaining a regulated propellant tank pressure.