INVESTIGATIONS ON EMISSION CHARACTERISTICS OF LIQUID FUELS IN A SWIRL COMBUSTOR

Flameless combustion is an effective method to suppress CO and NOX emissions from combustion systems with improved combustion efficiency. Flameless combustion is achieved through simultaneous preheating and dilution of fresh reactants with internal recirculation of hot combustion products leading to a distributed reaction zone and uniform temperature distribution throughout the volume of the combustor. In the present study, a high-intensity swirl-based combustor operating with liquid fuel in a flameless combustion mode is developed for industrial applications and designed to run at atmospheric pressure conditions. Detailed investigations on the emission characteristics for various operating conditions in flameless combustion mode have been reported. The experiments have been carried out for a range of heat release rates varying from 5 to 10 MW/m(3). Swirl flow pattern is achieved through tangential air injection to enhance the internal recirculation of hot combustion products into fresh reactants. Preliminary numerical studies aimed at understanding flow pattern in four different combustor configurations show that recirculation rate increases with an increase in the divergence angle of the combustor. This helps achieve flameless combustion mode. Recirculation rate increases with a decrease in the outlet diameter from 80 mm to 25 mm. Based on the degree of the combustion completeness, extended frustum of the cone-based configuration (60.) has been proposed to obtain low emission combustion mode with liquid fuels. Temperature distribution and emissions are measured and compared for different thermal inputs (heat release intensities) and air-preheat temperatures. Measurements of acoustic, CO, and NOX emissions show that these emissions are reduced by an order of magnitude when the combustor is operated in flameless combustion mode as compared to conventional combustion mode.