Studies on a liquid fuel based two stage flameless combustor

This paper presents the experimental and numerical results for a two stage combustor capable of achieving flameless combustion mode with 20 kW thermal input and heat release density up to 5 MW/m(3). The fuel and oxidizer are supplied at ambient conditions. The concept of high swirl flows has been adopted to achieve high internal recirculation rates, residence time and increased dilution of the fresh reactants in the primary combustion zone, resulting in flameless combustion mode. Air is injected through four tangential injection ports located near the bottom of the combustor and liquid fuel is injected through a centrally mounted pressure swirl injector. Preliminary computational analysis of the flow features shows that decrease in the exit port diameter of the primary chamber increases the recirculation rate of combustion products and helps in achieving the flameless combustion mode. Based on preliminary computational studies, a 30 mm primary chamber exit port diameter is chosen for experimental studies. Detailed experimental investigations show that flameless combustion mode was achieved with evenly distributed combustion reaction zone and uniform temperature distribution in the combustor. The CO and NOx emissions are reduced from 350 to 11 ppm and 45 to 12 ppm respectively at an equivalence ratio of 0.92, as operation of the combustor changes from conventional to flameless combustion mode. Measurement of CO and NOx emissions show that these emissions are reduced by an order of magnitude when operated in flameless combustion mode. The acoustic emission levels are reduced by 6-8 dB as combustion mode shifts from conventional mode to flameless combustion mode. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.