Engineers Test Actively Cooled CMC Panels for Rocket and Scramjet Engines

  • Published
  • By Materials and Manufacturing Directorate
  • AFRL/ML
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  AFRL engineers, under an Integrated High-Payoff Rocket Propulsion Technology (IHPRPT) contract with Teledyne Scientific Company (Thousand Oaks, California), completed environmental testing on actively cooled ceramic matrix composite (CMC) panels. The panels tested extremely well in both rocket rigs and scramjet rigs, proving that CMC materials have the durability necessary for withstanding these extreme environments. CMCs boast two important attributes over current state-of-the-art engine materials--namely, they are lighter weight and have higher operating temperatures. Consequently, utilizing CMC components will lead not only to increased payloads
and reduced operations cost, but to improved engine efficiencies and higher-velocity flight as well. The end result will ensure the availability of high-performance rocket engines and scramjets for future Air Force launch and hypersonic systems.

AFRL initiated this IHPRPT contract with Teledyne to develop CMCs as lightweight alternatives to the nickel-based alloys from which rocket engine and scramjet components are presently fabricated. The effort has achieved many innovations in CMC fabrication and has steadily advanced the technology readiness level of these materials for rocket and scramjet propulsion applications.

In one test, engineers evaluated actively cooled carbon-fiber-reinforced silicon carbide (C/SiC) and silicon-carbide-fiber-reinforced C/SiC panels in Cell 22, a rocket rig used for assessing advanced rocket engine materials in an oxygen/hydrogen combustion environment. Researchers arranged the test panels (which measured 3" x 10") in the rig so that the high-temperature combustion gases (which reach 5800°F) impinged directly upon them. Thus, they subjected the panels to aerothermal conditions and heat flux equivalent to what would be experienced at the upper end of a typical boost engine nozzle (as with the space shuttle main engines). The test panels survived multiple firings of various durations, with a cumulative exposure of 40 minutes and individual cycles lasting up to 8 minutes. This oxygen/ hydrogen rocket combustion exposure is the longest ever achieved for such actively cooled materials and equates to 5-10 launch cycles for a boost rocket engine (depending on flight profile).

The second test series took place in AFRL's scramjet rig. Engineers installed an actively cooled C/SiC panel in the combustor wall of the rig and subjected it to 20 engine runs lasting approximately 1 minute each. Researchers observed that the test panel looked pristine after the testing.

Now that the durability of the materials and robustness of the cooled structures have been demonstrated in subscale, flat-panel configurations--and fabrication processes have been demonstrated for other shapes, such as bell nozzles--the next step towards advancing the technology will be to increase the size and complexity of test articles to better represent actual components.