The Advent engine test at NASA’s Stennis Test Facility has revealed problems with the Oxygen injection system. Careful review of the test data and detail viewing of the post-run hardware provided good guidance for design of the next engine.
The engine test has been very productive for both Advent Launch Services and NASA’s Stennis test facility. Dealing with flow dynamics can be quite a challenge with the relatively high-density cryogenic oxygen. Cryogenic liquid Oxygen tends to accelerate to flow velocity relatively slowly and then the closure of a valve … or the filling of a volume with a somewhat limited outlet capability can result in relatively high pressure “spikes”. Once the problems of that sort were solved, the engine test itself progressed as planned. The cold flow tests with liquid nitrogen went well, revealing the challenge of cooling down the system sufficiently to avoid vapor bubbles in the delivered fluid.
The first engine run was automatically terminated at about 3 seconds because the thrust didn’t rise quite as quickly as expected. The second test was terminated because the spark igniter didn’t generate the required spark. Detail investigation revealed that the spark plug was shorted by metal that had been vaporized and deposited on the spark plug during the first run. The vaporized metal was obviously caused by improper injection of the oxygen. The exact cause of the improper injection is apparently the result of two factors that were not considered in the design … dynamic boiling of the oxygen and the relatively low thermal inertia of the injection port. These factors will be a major influence in the new engine design.
The new Methane/Oxygen test system at Stennis is very impressive. The data system is able to provide the information very quickly, supporting successive tests with a single propellant loading. The automatic safety features and the ample visual recordings are second to none. The experienced personnel know what to look for and are a true blessing to work with. The Advent team is looking forward to future work with them.