| The influence of droplet slip velocity fluctuations on NO formation in a single droplet flame burning behind a premixed flame front is numerically investigated. For the modeling of hydro-carbon oxidation and NO formation detailed chemical mechanisms are used. The main objective of this study is to identify the mechanisms governing the NO formation in droplet flames exposed to turbulent flow conditions. The numerical investigation revealed a significant impact of droplet slip velocity fluctuations on droplet flame characteristics. Depending on excitation frequency, slip velocity mean value and amplitude, strong changes in the mean value of the NO formation rate are observed. The interaction of gas phase velocity fluctuations with droplet burning is of sequential character. Flow field perturbations translate into droplet slip velocity fluctuations due to momentum coupling. This coupling effect acts as a high pass filter with a cut off frequency determined by the droplet Reynolds number and diameter. The burning rate and NO formation of the droplet flame are affected by these droplet slip velocity fluctuations. The droplet flame acts as a low pass filter. The droplet flame response in the pass band was found to be non linear. Finally, the droplet flame time scale was found to correlate with a heat release time scale, suggesting that heat release is the process which is governing the ability of droplet flames to respond to slip velocity fluctuations. |
