On Wednesday, June 7, 2013, we had the pleasure of touring NASA Glenn’s Research Combustion Lab. The tour was led by Dr. Paxson of the Controls and Dynamics branch who Kyle used to work with. There we learned about the applications of a jet pulse propulsion engine. It is hoped that the s technology can be applied to greatly increase the efficiency of turbomachinery translating to millions of dollars in fuel savings for commercial airlines.
Pulsed propulsion is characterized by a non-steady state combustion and only require on moving part, a small reed valve. As an overview of the combustion process, fuel is injected and mixed with air, the reed valve opens, the fuel air mixture is blown into the chamber which is attached to a long tube, the mixture is ignited by a spark plug which causes a rapid hot expansion forcing the gasses out the tube causing thrust. This cycle is continuously perpetuated as the rapid acceleration of gasses out of the tube causes a drop in pressure reopening the valve, drawing in more fuel, whilst sucking back hot gasses that ignite the mixture restarting the process. This process is repeated thousands of times a second producing near continuous thrust.
On its own this propulsion system is not as efficient as a turbojet engine. However when a tube is placed some distance past the exhaust exit thrust is significantly increased. This entrains the exhaust gasses forcing all of them through the cylinder significantly increasing thrust. Dr. Paxson’s idea is to use this system to drive a turbine that compresses the air sent to the inlet of the system increasing the robustness of the system. This style of system can be used to increase efficiencies by 6%.
We were privileged enough to see not one but two live demonstrations of this system. The first went flawlessly as the small engine blared to life taking us all aback as it roared to life behind a wall of concrete at least a foot thick. The engine forced back the plate meant to measure thrust and within seconds the engine was glowing red hot. A second demonstration was attempted but despite several attempts at ignition there was no roar, it was eventually concluded that the reed valve failed. We still enjoyed the tour though.