CO/UNBURNED HYDROCARBON EMISSIONS OF STRONGLY-PULSED TURBULENT DIFFUSION FLAMES

Abstract

The CO and unburned hydrocarbon (UHC) emissions of pulsed turbulent diffusion flames were examined by injecting unheated ethylene into a combustor with an air coflow at atmospheric pressure. In all cases the flames were fully modulated (fuel flow fully shut off between injection intervals). Video imaging was performed and time-averaged emissions were measured on the combustor centerline. For short injection times ( ≤ 46 ms), compact, puff-like structures were generated. Longer injection times produced elongated flame structures with flame lengths closer to that of steady flames. The highest emission indices of CO and UHC were found for compact, isolated puffs. The emissions for all flames approached the steady-flame levels for a duty cycle (jet-on fraction) of approximately 0.4. This suggests that there are combinations of injection time and duty cycle for fully modulated, turbulent diffusion flames that produce emissions comparable to the steady flame but with a significantly shorter flame length.

Keywords:

• turbulent diffusion flames
• HCs
• CO

This work was supported by NASA, Microgravity Research Division, under Cooperative Agreement NCC3-673. The authors acknowledge the assistance of Mr. J.E. Usowicz and Dr. R. Sangras with the setup of the experiments reported here, and also helpful discussions with Mr. D.P. Stocker and Dr. U.G. Hegde.