HYdrocarbon Propellants Enabling Reproduction of Flows in Rocket Engines
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.

The Technology
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.
(Left) NASA's HYPERFIRE performing flow testing with integrated Schlieren flowfield imaging. (Right) Examples of NASA HYPERFIRE test articles, including a Schlieren test article (top) and centerbody diffuser test article (bottom).
  • Vastly reduces testing cost and timeline: NASAs HYPERFIRE enables the end-to-end (i.e., design, fabrication, and testing) rocket aerodynamics testing process to be performed in roughly one month (~90% schedule reduction relative to hot-fire testing), and at low-cost (~98% reduced cost relative to using hot-fire testing).
  • Portable & self-contained: The HYPERFIRE is portable, self-contained, and includes integrated control and data acquisition. It can be moved via forklift and shipped to a testing location. It plugs into a wall power outlet and requires no external components.
  • Improves testing accuracy: Heated ethane generated and flowed through test articles by NASAs HYPERFIRE is more effective than traditional simulants (e.g., nitrogen, steam) used in cold-flow testing thus, results using the system are more representative of the aerodynamics of the test article than conventional cold-flow testing. Error rates for the 14 tests run to date using the HYPERFIRE have been on the order of ~2% cumulatively for steady state operation, and ~5% for transient development of the plume structure.

  • Rocket engine testing & development
  • Fundamental nozzle research
  • Simulation of combustion products (e.g., automotive testing)
Technology Details

SSC-00598 SSC-00561
"Physical Simulation of Rocket Exhaust Aerodynamics Using Heated Ethane: Conceptual Foundations," Daniel R. Jones, June 2019, https://ntrs.nasa.gov/citations/20190030272

"Physical Simulation of Rocket Exhaust Aerodynamics Using Heated Ethane: Prototypical Experiments," Daniel R. Jones, October 2020, https://ntrs.nasa.gov/citations/20205009122
Stay up to date, follow NASA's Technology Transfer Program on:
facebook twitter linkedin youtube
Facebook Logo Twitter Logo Linkedin Logo Youtube Logo