July 20, 2007
The primary experiment underway at the Research Combustion Lab Tour was the development of a jet pulse propulsion engine for applications in aeronautics and potentially commercial airlines. This brainchild of Daniel Paxson could potentially save about 6% on the amount of fuel consumed by commercial turbojet engines which translates into many millions of dollars.
Pulse propulsion is a type of non-steady state combustion engine that only contains one moving part, a relatively small, thin petal valve. Fuel is injected into a device that mixes it with air (essentially a carburetor), the petal valve opens, and the fuel/air mixture is blown into a chamber with a long tube attached to it. Initially, combustion begins when a sparkplug ignites the mixture and the hot gasses expand rapidly, shooting out of the tube and generating thrust.
This rapid acceleration of the gases opens the petal valve and sucks in more fuel/air mixture, but it also pulls some of the combusting exhaust gasses back through the tube and into the combustion chamber. These hot exhaust gasses ignite the new mixture and a second pulse occurs. These pulses occur several thousand times each second. The thrust generated in this fashion is good but not as efficient as turbine engines currently being used. However, when a cylinder is placed some distance past the opening in the tube where the exhaust gasses exit, the thrust is significantly increased.
The exiting vapors for vortices that pull in more air from the open area between the detonation tube and the cylinder. The exhaust gasses and the now entrained air are all forced through the entrainment cylinder which significantly increases the thrust of the system. Tests are only run for 15 seconds because of the extreme high temperatures generated by the engine and the room is very well insulated since the noise generated is enough to permanently destroy a person’s ear drums.
Current developments and future work include using this system to drive a turbine that compresses the air sent to the inlet of the system and making the whole apparatus more robust. Also, different valves may be researched since the petal valves are prone to breaking and newer systems or materials may extend the operational life of the engine significantly.