Lars Eigenmann

Effect of temperature and concentration fluctuations on radiative heat transfer in turbulent flames

Radiative heat transfer in turbulent flames is significantly affected by fluctuations of temperature and concentration. In an effort to better understand this complex nonlinear phenomenon, an extensive experimental investigation of a model combustor supported by a numerical analysis is presented. The combustor is fired by propane. The flame is of the diffusion type, highly turbulent, and nonluminous. The experimental techniques include detailed examination of the temperature probability density distribution by CARS N2 thermometry, as well as time and spectrally resolved IR spectroscopy. It was found from the CARS measurements that the temperature probability density distribution is relatively broad in the reaction zone of the model combustor, whereas in the mixing zone it is of Gaussian shape with a relatively small variance. To gain insight into the turbulence/radiation interaction, the radiation spectra recorded at the wall of the combustor are compared to the spectra predicted by a radiation model. The radiation model takes into account the turbulent fluctuations of temperature and species concentrations and contains different methods for representing the scalar fluctuations. If both temperature and concentration fluctuations are considered in the radiation model, good agreement between predicted and experimentally recorded radiation spectra is obtained. The radiation model revealed that as a consequence of the strong temperature fluctuations turbulence/radiation interaction is significant in the reaction zone. The effect is particularly pronounced for the 2.7 μm CO2/H2O radiation band and the H2O radiation bands at lower wavelength. In the mixing zone, radiation is only slightly affected by the scalar fluctuations caused by the weak temperature fluctuations. The present work demonstrates that turbulence/radiation interaction has a significant impact on the heat transfer to the combustor walls in the vicinity of the reaction zone and that advanced radiation models are capable of predicting this effect correctly.

Local measurements in a three-dimensional jet-stabilized model combustor

Measurements of velocity, temperature and species concentration in a three dimensional jet-stabilized combustor are presented. The modular design of the combustor permits the use of either gaseous or liquid fuels. For the investigations presented here, fuel oil has been chosen which is atomized by an air-blast atomizer. Access to the reacting flow field for probes as well as for non intrusive optical measurement techniques is provided by several windows along the combustor axis.Velocity measurements in the mixing zone and even in the primary zone of the combustor are performed by means of a two-component Laser Doppler Velocimeter (LDA). Platinum rhodium/platinum thermocouples (PtRh/Pt) specially designed for reduced internal heat losses are used for the investigation of the temperature field. A cranked, water cooled probe is employed in order to detect local species concentrations.The experimental results reveal detailed information about the characteristics of the reacting flow field. The interaction of fuel atomization and flame stabilization in the primary zone is illustrated by a direct comparison with experimental data of the gaseous fuel case investigated earlier [ 1 ]. The results gained here serve as an excellent database to verify numerical models for the description of liquid spray combustion.Copyright