Spectral and total radiation properties of turbulent non-luminous jet flames

In combustion systems, flame radiation is commonly the most significant mode of heat transfer and thus the ability to accurately model radiative heat transfer is of great interest. Experimental data, including radiative heat flux (qr), total radiative heat loss ( QR) and spectral radiation intensities (I λ), are essential for the validation of radiation models. Instantaneous spectral radiation intensity data also provide fundamental information about the fluctuating scalars in turbulent flames. Motivated by this, instantaneous Iλ of six turbulent non-luminous jet flames, as well as q r and QR of three of these flames, were investigated experimentally and numerically. The burner and the operating conditions were selected to take advantage of high quality scalar measurements available in the literature. A radiometer was used in the measurements of qr and QR; and the discrete transfer method and a narrow band gas radiation model were adapted for the computations. A fast infrared array spectrometer (FIAS) was used to measure Iλ. By using stochastic time and space series (TASS) simulations, the instantaneous Iλ were also computed accounting for the effects of scalar fluctuations on radiation, called turbulence-radiation interactions. In the TASS based calculations, radial variations of the integral length and time scales of scalar fluctuations were obtained by using a tomography-like procedure. This procedure requires measurements and calculations of Iλ, for diametric and chord-like paths at various radial positions from the flame edge to the axis. The calculated spectral and total radiation properties were in good agreement with the experimental data. The key contributions of this study include the development of the tomography-like TASS simulation and the use of standard flames for which high quality scalar property data are available. The TASS simulation allows the first estimates of scalar length and time scale distributions in turbulent flames. The use of several standard flames for radiation studies not only leads to a more complete set of radiation data but also a more reliable evaluation of the radiation models without the uncertainties of the scalar predictions. Future studies should consider buoyant fires as well as soot-containing luminous flames.