Effects of multi-orifice configurations of the quench plate on mixing characteristics of the quench zone in an RQL-TVC model

Abstract

CO2 concentration measurements and Particle Image Velocimetry (PIV) measurements were performed to investigate the effect of multi-orifice plate geometry on mixing characteristics of a rich-burn quick-quench lean-burn trapped vortex combustor (RQL-TVC). The mixing characteristics in the quench zone were discussed in terms of the mixing degree and the mixing uniformity. And the penetration and the residence time of discrete jet flows conducted by multi-orifice plates were analyzed. The diameter (D) and the quantity (n) of orifices in the multi-orifice plate which composed two rows of orifices was varied, but the blockage ratio (BR) remains constant as approximately 81.5%. The distance of the orifice rows (h) equals D corresponding to the orifice in each plate respectively. The location of the first row is not changed, consequently the position of the second row and the orifice relative position ratio of S/D (S presents the spacing between adjacent orifice mid-points) were varied with D. Through measuring the CO2 concentration, the mixing degree and the mixing uniformity in the quench zone are determined. The penetration and residence time of discrete jet flow conducted by multi-orifice quench plates were quantified by PIV measurements. Results show that the quench plate with the smaller number and the larger diameter of orifices has the most momentum and mass corresponding to the longer penetration and residence time, so that this multi-orifice quench plate has the highest unmixedness rate. On the contrary, that with the shortest penetration is not benefit for occurring the full mixing in the quench zone. Therefore, there is an optimization of multi-orifice configuration existing for the design of multi-orifice quench plates which affect the mixing characteristics of the quench zone in RQL-TVC. The mixing progress in the quench zone depends greatly on discrete jet flows, of which the penetration depth falls into the range from 28mm to 48mm. The multi-orifice plate, designated as M6D8.0 with 6 orifices and 8.0mm-diameter, offers the intermediate length of penetration depth (approximately 35mm). The residence time of discrete jet flows derived from PIV results is between 0.6ms and 1.2ms. Most of that is less than 1ms and meets the requirement of the critical time scale of complete quick-mixing.