Exhaust CO emissions of a laminar premixed propane-air flame interacting with cold gas jets

This study investigates a laminar premixed flame interacting with cold gas jets, at different cooling jet mass flow fractions ((m) over dot(jet)*) and diluent types, namely air and N-2. A novel burner and wall configuration is used to experimentally induce flame-cooling-air interaction (FCAl). Flame chemiluminescence imaging, exhaust temperature (T-exh) and exhaust CO emissions ([CO](exh)) measurements are conducted to characterise the flame shape and [CO](exh) response to the cooling jets. Flame imaging reveals that the cooling jets greatly affect the flame shape. Measurements of [CO](exh) demonstrate a direct correlation with T-exh, as decreasing T-exh is observed to occur with decreasing [CO](exh). Additionally, the air diluent case shows consistently lower [CO](exh) values, relative to the N-2 diluent case. Using a novel modelling approach, the cooling jets are simulated using one-dimensional (1D) fully resolved simulations (FRS). The effect of jet dilution, jet cooling and exhaust gas cooling are independently and jointly investigated in these simulations. The FRS results support the experimentally observed behaviour, and show that exhaust gas cooling and exhaust gas oxygenation produce decreased CO concentrations. Using a chemical reactor network (CRN), the jet mixing process is modelled by a perfectly stirred reactor (PSR), while the exhaust gas cooling process is modelled by a plug flow reactor (PFR). The CRN modelling shows that the jet mass flow rates dictated by (m) over dot(jet)*, the dilution time (t(dil)) assumed for cooling jet mixing, and the exhaust gas cooling residence time (t(cool)), play an important role in determining the [CO](exh). An equilibrium analysis illustrates that the relationship between [CO](exh), T-exh and exhaust O-2, is due to the thermodynamically favoured equilibrium states. Timescale analyses demonstrate that appropriate modelling of jet mixing, and accounting for the rate of exhaust gas cooling, are important for estimations of [CO](exh). (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.