On surface temperature measurements with thermographic phosphors: A review

Sidewall quenching of atmospheric laminar premixed flames studied by laser-based diagnostics

To study devolatilization, ignition, and volatile combustion processes of single coal particles at a fundamental level, a flat flame burner was designed to provide oxygen-enriched exhaust gas environments at elevated temperatures and varying gas compositions. In one set of experiments coal particles were carried by a central jet using a gas mixture of the same composition as the flat flame. By this means a homogenous and connected flame was generated. At the instant when single coal particles transited this stationary flame, start of particle heat-up was well defined. This allows studying start of ignition more accurately compared to the other set of experiments where an inert carrier gas jet was used for transportation of coal particles. Heat-up and ignition were retarded temporally due to precedent mixing between inert gas and ambient flue gases. Coal particles with a high percentage of volatiles (36 wt%) and a particle distribution ranging from 90 to 125 µm were used. Coherent anti-Stokes Raman spectroscopy (CARS) measurements were performed to characterize ambient gas phase temperatures. By high-speed laser-induced fluorescence, imaging of OH-radicals ignition and volatile combustion was visualized for individual coal particles. Reaction zones surrounding each coal particle and the corresponding distances to coal particles were identified. This distance depended strongly on oxygen concentration of the ambient flue gas atmosphere. In addition to an improved phenomenological understanding the data may serve for model validation.

Investigation of ignition and volatile combustion of single coal particles within oxygen-enriched atmospheres using high-speed OH-PLIF

Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman spectroscopy (CARS) is developed utilizing a two-beam phase-matching approach for one-dimensional (1D) measurements demonstrated in an impinging jet burner to probe time-resolved head on quenching (HOQ) of a methane/air premixed flame at Φ  = 1.0 and Reynolds number = 5000. Single-laser-shot 1D temperature profiles are obtained over a distance of at least 4 mm by fitting the pure-rotational N 2 CARS spectra to a spectral library calculated from a time-domain CARS code. An imaging resolution of ∼61 μm is obtained in the 1D-CARS measurements. The acquisition of single-shot 1D CARS measurements, as opposed to traditional point-wise CARS techniques, enables new spatially correlated conditional statistics to be determined, such as the position, magnitude, and fluctuations of the instantaneous temperature gradient. The temperature gradient increases as the flame approaches the metal surface, and decreases during quenching. The standard deviation of the temperature gradient follows the same trend as the temperature gradient, increasing as the flame front approaches the surface, and decreasing after quenching.

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Development of two-beam femtosecond/picosecond one-dimensional rotational coherent anti-Stokes Raman spectroscopy: Time-resolved probing of flame wall interactions

This work presents first-of-its-kind high-speed planar laser-induced fluorescence measurements of the hydroxyl radical in the boundary layer of single coal particles. Experiments were performed in a laminar flow reactor providing an oxygen-enriched exhaust gas environment at elevated temperatures. Single coal particles in a sieve fraction of 90–125 µm and a significant amount of volatiles (36 wt%) were injected along the burner’s centerline. Coherent anti-Stokes Raman spectroscopy measurements were taken to characterize the gas-phase temperature. Time-resolved imaging of the OH distribution at 10 kHz allowed identifying reaction and post-flame zones and gave access to the temporal evolution of burning coal particles. During volatile combustion, a symmetric diffusion flame was observed around the particle starting from a distance of ~150 µm from the particle surface. For subsequent char combustion, this distance decreased and the highest OH signals appeared close to the particle surface.

Characterization of single coal particle combustion within oxygen-enriched environments using high-speed OH-PLIF

An impinging jet burner was developed to investigate flame-wall interactions (FWI) using laser based diagnostics. CO concentrations were measured with two-photon laser-induced fluorescence (LIF) in combination with coherent anti-Stokes Raman spectroscopy (CARS) gas phase temperature measurements. Besides being the principal factor in chemical kinetics, temperature data is required to correct the CO LIF data for various factors like density variation, quenching and variation in the Boltzmann population. Phosphor thermometry was used to determine surface temperatures of the wall and to estimate the heat flux. In an parameter study Reynolds numbers and fuel equivalence ratio were varied.

Simultaneous Measurements of Temperature and CO Concentration in Stagnation Stabilized Flames

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Simultaneous Measurements of Temperature and CO Concentration in Stagnation Stabilized Flames