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Show a highly luminous flame. For the measurements shown in Figure 8. the data was collected in the plane of the N G injectors. The results confirm that indeed high concentrations of acetylene are being produced enhancing soot formation. Laser extinction probe for local soot volume fraction measurements The laser beam extinction technique has been widely applied to measure soot volume fraction [13. 14]. Through a joint collaboration with Rouen University (CORIA laboratory), this technique was adapted to measure local soot volume fraction in industrial-scale turbulent diffusion oxy-flames. The experimental set-up is shown in Figure 9. A multi-mode optical fiber transmitting the He-Ne laser beam is located inside a water-cooled probe that is radially traversed in the furnace. The laser beam intensity / is modulated by a chopper and is measured by photodiode after being filtered by an interference filter at two locations: first before entering the optical fiber I0. and second, after crossing the flame la and exiting the furnace opposite side. The two intensities I0 and la are measured at several radial positions for the emitting probe and during a time period of about 10 s and using a sampling frequency equal to 10 kHz. The integral over the radial position x of the time averaged extinction coefficient Kx can be computed from the following equation: J_ (i (xtX\ I UoMj The local time averaged extinction coefficient is computed by taking the derivative according to x of the previous equation. Then, by assuming validity of the Rayieigh approximation (TTD/A. « 1 . where D is the soot mean diameter and A the laser beam wavelength), the extinction coefficient becomes equal to the absorption coefficient aj[15]. From the local soot absorption coefficient, one can deduce the local soot volume fraction jv knowing the soot refraction index (m-n-iK). 36/r fv n/c ax ~ ' 5 5 2 ^^~ A (n~ -K +2)' +4n~K^ Figure 10 shows soot volume fraction results obtained using 1 MW ALGLASS pipe-in-pipe gas burner staged with two oxygen lances at 8 0 % of the total stoichiometric oxygen flow rate and furnace wall temperature at 1300°C. The soot volume fraction profiles are symmetric, with a maximum concentration reaching 0.14 p p m on the flame axis, at 1.03 m downstream from the burner. NON-INTRUSIVE FLAME DIAGNOSTICS Non-intrusive diagnostics are employed for two main purposes: combustion control and flame characterization. Section 4.1 presents a technique for flame monitoring that can be used for purposes of burner control. Sections 4.2 and 4.3 describe simple and efficient imaging techniques for investigating flame structure and mixing properties. Section 4.4 presents optical temperature diagnostics currently in development for time-resolved measurements. The objective is to obtain temperature histograms in order to characterize the turbulence-temperature interaction and its impact on N Ox formation. UV-VIS Flame Emission Monitoring The observation of light emission from a flame provides basic qualitative information for evaluating general flame characteristics such as stability, overall geometry, luminosity and in some cases assessing whether the combustion is fuel-rich or fuel-lean. T o obtain a more detailed and quantitative analysis of the flame, emission characteristics utilizing conventional spectroscopy and imaging techniques are routinely used. The ultra-violet (UV), visible, and infrared (IR) spectral regions can provide useful information for characterizing the flame. The UV-visible region is associated with intermediate combustion radicals that emit at known characteristic wavelengths, whereas the infrared region is generally associated with stable combustion species, e.g.. C O . C O ; and H :0. The U V spectral range of interest for our 5 |
