The effects of hydrodynamic stretch on the flame propagation enhancement of ethylene by addition of ozone

The effect of O-3 on C2H4/synthetic-air flame propagation at sub-atmospheric pressure was investigated through detailed experiments and simulations. A Hencken burner provided an ideal platform to interrogate flame speed enhancement, producing a steady, laminar, nearly one-dimensional, minimally curved, weakly stretched, and nearly adiabatic flame that could be accurately compared with simulations. The experimental results showed enhancement of up to 7.5% in flame speed for 11 000ppm of O-3 at stoichiometric conditions. Significantly, the axial stretch rate was also found to affect enhancement. Comparison of the flames for a given burner exit velocity resulted in the enhancement increasing almost 9% over the range of axial stretch rates that was investigated. Two-dimensional simulations agreed well with the experiments in terms of flame speed, as well as the trends of enhancement. Rate of production analysis showed that the primary pathway for O-3 consumption was through reaction with H, leading to early heat release and increased production of OH. Higher flame stretch rates resulted in increased flux through the H + O-3 reaction to provide increased enhancement, due to the thinning of the flame that accompanies higher stretch, and thus results in decreased distance for the H to diffuse before reacting with O-3.