HYPERFIRE

In order to maintain the low cost, simplicity, and quick turnaround of cold-flow testing while improving accuracy, NASA evaluated unconventional gases for use as simulants. During such evaluations, NASA discovered that by adjusting stagnation temperature, the isentropic exponent of ethane can be tuned to approximate those of common rocket propellants (e.g., hydrogen, hypergols, alcohols, and hydrocarbons). Furthermore, due to ethanes high auto-ignition temperature and resistance to condensation, tuned ethane enables testing of expansion ratios much larger than conventional inert-gas testing. To leverage this discovery, NASA developed a hardware-based system to treat ethane and obtain nozzle chamber conditions that match the appropriate aerodynamics for a specific test. The system, named HYPERFIRE, works in the following manner. Liquid ethane is transferred to a piston-style run tank, where it is pressurized. Then, the ethane is run through two insulated pebble beds where it is heated, vaporized, and stabilized. Finally, the treated ethane is transferred from the second pebble bed to a small thrust takeout structure, and through the test article. Control of valves and regulators is managed by an onboard computer, accessed via a LabVIEW™ interface. The system is mounted on a hurricane-resistant steel frame to enable transportation via forklift. Heated ethane reproduces the aerodynamics of combustion products at low temperatures relative to alternative testing methods. Thus, test articles can be manufactured using low-cost, low temperature rated, transparent materials (e.g., acrylic). In addition to reducing testing cost, this grants optical access to internal flowfields, enabling advanced diagnostic techniques (e.g., Schlieren imaging, particle image velocimetry) not possible with hot-fire testing and less meaningful with conventional cold-flow testing. The two main sub-scale, ground-based rocket aerodynamics testing techniques hot-fire testing and cold-flow testing pose a series of tradeoffs. Hot-fire testing is generally much more accurate, but is often burdensome, costly, and requires long lead times due to design work, infrastructure preparation, etc. Cold-flow testing is much less expensive and has a rapid turnaround time, but conventional simulants (e.g., nitrogen, steam) used in cold-flow testing yield less accurate results (i.e., results that are not sufficiently representative of test article performance). While researching methods to optimize such tradeoffs, engineers at NASAs Stennis Space Center discovered that ethane can be tuned to approximate rocket exhaust plumes generated by several common rocket propellants. This led NASA to develop the HYdrocarbon Propellants Enabling Reproduction of Flows in Rocket Engines (HYPERFIRE), a sub-scale, non-reacting flow test system. HYPERFIRE uses heated ethane to enable physical simulation of rocket engines powered by a broad range of propellants in an inexpensive, accurate, and simple fashion.