Effect of CO2/N2 Dilution on Characteristics of Liquid Fuel Combustion in Flameless Combustion Mode

Abstract

ABSTRACT This paper presents the effect of CO2 and N2 dilution in the oxidizer stream on combustion and emission characteristics in a flameless combustor operating with kerosene and biodiesel as a fuel. The thermal input is varied from 30 kW (7.5 MW/m3) – 53 kW (13.3 MW/m3) and inlet air temperature are varied from 300 K to 800 K. CO2/N2 are added to dilute the oxidizer stream in a proportion of 15% of total air volume to reduce the O2 concentration in the air stream. Reacting and non-reacting flow simulations show that the flow field improves significantly as both the flow velocity and temperature distributions become uniform. Distribution of the reactant dilution ratio becomes more uniform and a maximum value of Rdil = 4.89 is achieved for 30 kW conditions. The reduced O2 concentration in the oxidizer results in enhanced dilution of fresh air-fuel mixture thereby enables uniform temperature and flow field. For the air preheating case, CO2 dilution does not affect the velocity and thermal fields significantly. The measured CO emissions are marginally increased due to CO2 dilution; however, NOx emissions are significantly reduced. N2 dilution results in increased levels of NOx, contrary to the perception of the inert role of N2 addition even though the combustor operating temperatures are lower than 1800 K. The measurements of acoustic pressure emissions show a sharp decrease during flameless combustion mode.