An Experimental Study On Actively Controlled Dump Combustors

A closed-loop liquid-fueld active control technique was applied in a dump combustor to enhance its combustion performance. Practical issues involving liquid fuel scaling effects and affordable control methods were studied experimentally. The results shed new light on the requirement of critical fuel flux effects of fuel droplet size on control and novel controller concepts that would help the future development work. The critical fuel flux was found to be dependent on the fuel droplet size and initial magnitude of the instabilities. When the fuel droplet size Do was reduced in the controlled injection the control efficiency for heat flux actuation increased significantly. The analysis yielded an exponential dependency on the droplet size. For a moderate droplet Reynolds number considered in this study the amplitude of controlled heat release for a given fuel amount was inversely proportional to the droplet size by a factor of Do( -1.4). Also two novel controller concepts which incorporated practical designs were tested and were shown to work effectively compared to the baseline case. One of the concepts was based on injecting fuel pulses at sub-harmonic frequencies of the instability thus addressing the limited actuator frequency response. The other concept utilized both open-loop and closed-loop control schemes to obtain enhanced performance including extension of the stable combustion zone. These results open up the possibility of applying the active combustion control technology to advanced propulsion devices.