Impact of acoustic forcing on soot evolution and temperature in ethylene-air flames

The transient coupling of soot formation flame chemistry and fluid transport in ethylene-air coflow flames at 20 and 40 Hz acoustic forcing frequencies were studied. Forcing at different frequencies and amplitudes resulted to very distinct transient soot temperature and flow conditions. The steady ethylene-air flame was excited with 20 and 40 Hz corresponding to 0.23 and 0.46 Strouhal numbers. For both frequencies forcing amplitudes of 20% 50% and 60% were numerically considered and validated against measurements at 50%. A reduction in maximum soot volume fraction for the increased forcing frequency was experimentally and numerically observed. The decrease in maximum soot volume fraction is attributed by a residence time analysis presenting shorter maximum fluid parcel residence times for the 40 Hz than for the 20 Hz case. At 40 Hz the transient evolution of maximum soot production and forced fuel velocity was almost synchronized while at 20 Hz a time lag of 32.5 ms was noted corresponding to 65% of a full period.