The development of weapons that can travel at hypersonic speeds is becoming a high priority to the US Air Force. A key technology needed for the continued development of these propulsion systems is the ability to cool the combustor by flowing fuel through channels machined in the walls. Currently, the cooling capacity of kerosene-based fuels is relatively low even with endothermic cracking reactions, and this limits the Mach number that can be achieved. Moreover, increasing the fuel cooling capacity by raising the fuel flow is not practical because the additional fuel would over-fuel the combustor or have to be dumped overboard. Likewise, allowing the fuel to reach higher temperatures is not feasible because coke formation could lead to heat exchanger failure. Therefore, there is a strong need to develop new endothermic fuels and custom heat exchanger/reactors that can deliver substantially higher heat sink capacities.
Under a very successful Phase I project with the US Air Force, Reaction Systems has identified a fuel and catalyst combination that can undergo a chemical reaction that produces much higher endotherms than currently available with kerosene-based fuels.
Reaction Systems has just been notified of a Phase II award to continue development of the fuel/catalyst system and design a custom heat exchanger/reactor for use in a hypersonic engine.
Reaction Systems has a novel solution to the heat transfer issue that may open the door to practical hypersonic aircraft propulsion.
According to Jeff Engel, COO of Reaction system, in hypersonic flight the combustor temperature gets so high that materials can’t survive in that environment; you have to continually cool the combustor sections. They are developing a fuel system to absorb that heat load from the combustor specifically, so that the final speed of the vehicle is faster.
At hypersonic speeds, conventional heat transfer processes would burn off the airframe in a fraction of a second. That’s why Reaction Systems’ endothermic fuel system works: heat isn’t rejected to ambient; instead, the fuel is the working fluid, but not in the conventional sense.
Reaction Systems’ heat absorbing fuel is a key enabling technology, but transferring the heat to the working fluid, while providing a maximum surface area for catalysis inside the heat exchanger, is essentially impossible to achieve with conventional heat exchanger fabrication technologies.
Additive manufacturing from Faustson Tool Corporation is enabling the heat exchange technology. Fauston has built successful parts for NASA and several major aerospace OEMs, including parts for the F-35 program, and has extensive experience in 5-axis machining and multi-axis EDM.
Fauston recently added metal additive capability in the form of a M2 cusing Multilaser machine from Concept Laser, a GE Additive company. With a 250 x 250 x 280mm build envelope, dual lasers, 20-80micron layer thickness and, critically, the ability to process aerospace “hot-section” superalloys, the Faustson-Concept Laser relationship was the right process in the right place at the right time.
Faustsons’s M2 cusing Multilaser can build with a variety of high-performance alloys, including cobalt-chromium grades, Ti6Al4V, pure titanium and the material for Reaction Systems’ heat exchanger, Inconel 718.
Other Hypersonic projects at Reaction Systems
Aircraft and missiles capable of rapid global strike and reconnaissance must fly at hypersonic speeds to achieve their performance goals. Future air-breathing hypersonic aircraft and missiles are expected to be powered by supersonic combustion ramjet (scramjet) engines. Unfortunately, scramjet engines only operate well at high speed and must be boosted there by a separate system. In the near term, this capability will probably be realized first in scramjet-powered missiles boosted to high speed with solid rocket motors. Ignition of the scramjet combustor at the end of the boost phase can be difficult to achieve due to the relatively low air pressures, temperatures, and residence times in the combustor as well as cold fuel and engine hardware. In a Phase I project Reaction Systems investigated an innovative new approach utilizing thermally stable catalysts or high temperature catalysts to decompose N2O, resulting in a very hot N2/O2 mixture that can be used to promote fuel ignition. Our approach incorporates the use of wall-mounted catalysts for increased heat flux. The use of a catalyst can significantly decrease ignition time delay and can also be combined with the liquid fuel injection system to achieve good fuel atomization, penetration, and mixing into the engine air flow.