Description: Aerospace vehicles operating at high altitudes have the potential to be less expensive and more versatile alternatives to space based systems for earth/space science, communications, and surveillance. However, the operational flexibility of these vehicles is limited by the performance of the propulsion system. In gas turbine systems low temperatures and pressures at the combustor inlet are of concern for combustion stability and efficiency at high altitudes. The overall objective of the proposed work is to assess the feasibility of developing a high performance airbreathing combustor for hydrogen-fueled very high altitude aircraft by promoting stable combustion using thermally stable catalytic reactor technology. Our combustor concept baselines the use of strontium-substituted hexaaluminate catalyst supports, which are resilient to temperatures greater than 1500 K. In Phase I an active catalyst that provides high reactivity with hydrogen at representative conditions will be identified through laboratory testing. An empirical model of catalyst reactivity will be developed and integrated with a reactor model to produce a conceptual design of a full scale combustor for a defined very high altitude gas turbine system. The catalytic rector that will be developed through this effort represents a new, enabling technology that will dramatically increase the flexibility of aerospace vehicles.

Benefits: The proposed thermally stable catalytic combustor technology is a key to providing combustion stability in hydrogen-based gas turbine based propulsion systems operating at very high altitudes. Such propulsion systems are critical to a multitude of missions employing unmanned aerial vehicles. These systems are of significant interest to the Department of Defense (DoD) and the Defense Advanced Research Projects Agency (DARPA). In addition, this technology may have potential to provide emissions reduction in stationary gas turbine systems used for power generation. This is of interest to the U. S. Department of Energy.

NASA has shown recent interest in the use of hydrogen fuel as a means of substantially reducing the carbon emissions from commercial aircraft. A potential problem with a hydrogen-based system is that nitrogen oxides emissions may be difficult to control. The thermally stable catalytic combustor technology that will be developed through this effort may provide an approach to control the NOx emissions from a hydrogen-based aircraft platform. In addition, this technology provides a capability to extend the operating range of hydrogen-based gas turbine based propulsion systems to very high altitudes that may enable new aircraft platforms for earth and atmospheric science initiatives at NASA. Additionally, this catalyst technology could find use in other systems of interest to NASA that operate at high altitudes, such as supersonic/hypersonic vehicles or balloon-based systems, and may require additional thrust, power, or a high heat source.