Determination of the NOx emission reduction potential of an aerodynamically valved pulse combustor

The control of fuel and oxidizer injection by means of an aerodynamic valve is an established technique to overcome the mechanical and lifetime limitations of a conventional flapper valve in pulse combustors. In particular, the aerodynamic type of valve enables significantly higher frequency operation to be achieved, values well in excess of 100 Hz being readily attainable. The combustion phase of the operating cycle is confined to a time of the order of 1 msec which, in turn indicated that NO_x formation is determined kinetically rather that being established by thermodynamic equilibrium. This paper presents an analytical and experimental investigation of a novel type of pulse combustor developed by clean energy combustion systems, Inc. The work reported here is part of an ongoing effort to characterize this type of pulse combustor and focused on determining NO_x emission performance for differing geometries, operating conditions and fuel/oxidizer ratios. The kinetics of NO_x formation are first reviewed and the measurement techniques employed are presented. This latter include both acoustic and optical methods to obtain time domain performance in addition to average values in the combustor exhaust. Results are presented for differing geometries and operating frequencies and the kinetic nature of NO reactions are experimentally confirmed. Exhaust levels of less than 10 ppm are reported and are compared with the performance of steady state combustors operating under similar conditions.