SIMULATION OF NON-AUTOIGNITED AND AUTOIGNITED LAMINAR NON-PREMIXED JET FLAMES OF SYNGAS IN HEATED COFLOW AIR

The characteristics of non-autoignited and autoignited flames of syngas (CO/H-2 mixture) fuels with heated coflow air have been investigated numerically. The simulations accounting for the differential diffusion have been performed by adopting several kinetic mechanisms to test the models' ability in predicting the flame behaviors observed previously. The results agreed well with the observed nozzle-attached flame characteristics in case of non-autoignited flames. For autoignited lifted flames in high temperature regime, a unique autoignition behavior can be predicted having HO2 and H2O2 radicals in a broad region between the nozzle and stabilized lifted flame edge. Species' profiles as a function of temperature showed a similarity with a homogeneous autoignition case. The autoignited liftoff height was correlated well in terms of the jet velocity multiplied by the square of ignition delay time, in agreement with previous experimental data. The simulation results tested with various kinetic mechanisms, however, could not predict the non-monotonic liftoff height behavior with jet velocity for autoignited flames observed experimentally at relatively low temperature. The initial temperature in the simulation should be higher at about 80 K as compared to experimental conditions to have comparable liftoff heights. The result suggested a necessity to improve kinetic mechanisms at atmospheric pressure conditions.