Response of Soot Temperature to Unsteady Inlet Airflow Under Modulated Condition and Naturally-Occurring Combustion Dynamics

Abstract

The response of soot temperature to unsteady inlet airflow is characterized using pyrometry. The unsteady inlet airflow is achieved by either modulating inlet air or naturally-occurring unstable flame, running on a jet fuel at fuel-rich conditions. The inlet air is modulated by a siren device running at frequencies between 150 and 250 Hz and up to 60% of modulation level (u’/um) is achieved. Also, the combustor can be run naturally unstable at the same inlet operating condition by changing the combustor length. For the pyrometry, the emission from whole flame at 660 nm, 730 nm and 800 nm is recorded and the three-color pyrometry is used to measure soot temperature. The effect of non-isothermal distribution of soot in flame on the measured temperature is also considered. The level of overall temperature fluctuation under inlet flow modulation (Trms/Tmean) is about an order of magnitude lower than that of flame emission fluctuation (Irms/Imean). Under naturally occurring instability the measured soot temperature is in phase with the pressure measured in the combustor, indicating that the measured soot temperature can be used as a quantity related to combustion dynamics for fuel-rich sooty flames.