The in-situ and localized observation of heat release in turbulent flames is important for the validation of computational modeling of turbulent flows with combustion. In the present work we obtain localized information on heat release rate (HRR) by the commonly accepted technique of the simultaneous and single-shot planar imaging of OH and CH 2 O concentrations by laser-induced fluorescence (LIF). Additionally, we combine this with the simultaneous line-of-sight and temporally resolved chemiluminescence detection of OH * , spatially integrated within the flame volume, interrogated by the laser sheets used for the HRR imaging technique. The combined diagnostic methods are demonstrated for a swirl-stabilized, premixed turbulent methane/air flame of 30-kW thermal power, and they show the existence of correlations between both HRR-sensitive diagnostic techniques.

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Computed Tomography of Chemiluminescence (CTC) was used to reconstruct the instantaneous three-dimensional (3D) chemiluminescence field of a high-power industrial flame, which was made optically accessible, for the first time. The reconstruction used 24 projections that were measured simultaneously, in one plane and equiangularly spaced within a total fan angle of 172.5°. The 3D results were examined by plotting both vertical and horizontal slices, revealing highly wrinkled structures with good clarity. The results presented are one of a series of experimental demonstrations of CTC applications to turbulent gaseous flames. The work reveals the potential to use any kind of luminescence measurement, such as emission from heated particles in coal-fired flames, for analysis of the flame shape directly in 3D.

A detailed comparison has been conducted between chemiluminescence (CL) species profiles of OH * , CH * , and C 2 * , obtained experimentally and from detailed flame kinetics modeling, respectively, of atmospheric pressure non-premixed flames formed in the forward stagnation region of a fuel flow ejected from a porous cylinder and an air counterflow. Both pure methane and mixtures of methane with hydrogen (between 10 and 30 % by volume) were used as fuels. By varying the air-flow velocities methane flames were operated at strain rates between 100 and 350 s −1 , while for methane/hydrogen flames the strain rate was fixed at 200 s −1 . Spatial profiles perpendicular to the flame front were extracted from spectrograms recorded with a spectrometer/CCD camera system and evaluating each spectral band individually. Flame kinetics modeling was accomplished with an in-house chemical mechanism including C 1 -C 4 chemistry, as well as elementary steps for the formation, removal, and electronic quenching of all measured active species. In the CH 4 /air flames, experiments and model results agree with respect to trends in profile peak intensity and position. For the CH 4 /H 2 /air flames, with increasing H 2 content in the fuel the experimental CL peak intensities decrease slightly and their peak positions shift towards the fuel side, while for the model the drop in mole fraction is much stronger and the peak positions move closer B. Prabasena · M. Röder · T. Dreier ( ) · to the fuel side. For both fuel compositions the modeled profiles peak closer to the fuel side than in the experiments. The discrepancies can only partly be attributed to the limited attainable spatial resolution but may also necessitate revised reaction mechanisms for predicting CL species in this type of flame.

A method for laser-induced fluorescence (LIF) imaging of formaldehyde (CH2O) that discriminates against the interfering signal from polycyclic aromatic hydrocarbons (PAHs) is presented. This technique uses an interference filter with 11 transmission bands that closely match the most prominent fluorescence features of CH2O upon excitation at 355 nm. The signal increases by a factor of 12 with the multi-band filter compared to a single-band filter. Slight angle-tuning of the filter shifts the transmission maxima to the minima in between the CH2O-LIF features. The pixel-by-pixel difference between the images collected at the two filter angles thus provides CH2O images free of PAH interference, providing the capability for selective single-pulse CH2O-LIF imaging in engine combustion even under fuel-rich conditions.