The response of a Helmholtz pulse combustor to changes in the stream-wise position of a stagnation plate

The response of a premixed, methane-fired (10-kW), self-aspirating Helmholt z pulse combustor to changes in the stream-wise position of a stagnation pl ate is investigated. Experimental measurements of operating frequency peak pressure amplitude and exhaust emissions of NO, NO2 and CO are presented an d discussed. The trends of operating frequency and peak pressure amplitude were all consistent with the Rayleigh criterion. The most stable operation occurred with the effective heat release point in the cycle preceding the a coustic resonance peak. The trend of NOx emissions versus the stream-wise p osition of the stagnation plate was found to be dependent on the tailpipe l ength. NOx emissions were typically below 10 ppm (dry, 3% O-2). With consta nt air/fuel ratio, an interesting switch from predominately NO emission to NO2 emission was observed as the stream-wise position of the stagnation pla te was altered. This was attributed to increased mixing with progressively cooler residuals.