Flame burner measurements

Procedure (ii). Make certain that the instrument is fitted with the correct burner for an acetylene-nitrous oxide flame, then set the instrument up with the calcium hollow cathode lamp, select the resonance line of wavelength 422.7 nm, and adjust the gas controls as specified in the instrument manual to give a fuel-rich flame. Take measurements with the blank, and the standard solutions, and with the test solution, all of which contain the ionisation buffer the need, mentioned under procedure (i), for adequate treatment with de-ionised water after each measurement applies with equal force in this case. Plot the calibration graph and ascertain the concentration of the unknown solution. 

For flame emission measurements, burners of the Meker type with a circular orifice covered by a grille are used whereas in atomic absorption spectrometry, a slit burner is preferred. In both cases, the flame consists of two principal zones or cones (Figure 8.21(b)). The inner cone or primary... 

Prompt NO mechanisms In dealing with the presentation of prompt NO mechanisms, much can be learned by considering the historical development of the concept of prompt NO. With the development of the Zeldovich mechanism, many investigators followed the concept that in premixed flame systems, NO would form only in the post-flame or burned gas zone. Thus, it was thought possible to experimentally determine thermal NO formation rates and, from these rates, to find the rate constant of Eq. (8.49) by measurement of the NO concentration profiles in the post-flame zone. Such measurements can be performed readily on flat flame burners. Of course, in order to make these determinations, it is necessary to know the O atom concentrations. Since hydrocarbon-air flames were always considered, the nitrogen concentration was always in large excess. As discussed in the preceding subsection, the O atom concentration was taken as the equilibrium concentration at the flame temperature and all other reactions were assumed very fast compared to the Zeldovich mechanism. 

Figure 15.4 A comparison of turbulent flame speeds measured in the TC apparatus with theoretical predictions and measurements by earlier investigators using other types of burners 1 — TC results, 2 — Abdel-Gayed et al. [3], 3 — Chang and Shepherd [1], 4 — Bedat and Cheng [2], 5 — Anand and Pope [15], and 6 — Yakhot [16]... 

The experimental setup for diode-laser sensing of combustion gases using extractive sampling techniques is shown in Fig. 24.8. The measurements were performed in the post-flame region of laminar methane-air flames at atmospheric conditions. A premixed, water-cooled, ducted flat-flame burner with a 6-centimeter diameter served as the combustion test-bed. Methane and air flows were metered with calibrated rotameters, premixed, and injected into the burner. The stoichiometry was varied between equivalence ratios of = 0.67 to... 

Multiplexed diode-laser sensors were applied for measurement and control of gas temperature and species concentrations in a large-scale (50-kilowatt) forced-vortex combustor at NAWC to prove the viability of the techniques and the robustness of the equipment for realistic combustion and process-control applications [11]. The scheme employed was similar to that for measurements and control in the forced combustor and for fast extractive sampling of exhaust gases above a flat-flame burner at Stanford University (described previously). 

The measurements were made across the top of a flat flame burner, and as can be seen, trapping is significant for mole fractions larger than about 0.15 PPM. 

Figure 10. Temperature measurements in flat Ht-air diffusion flame. The exit of the flat flame burner is shown schematically (O), radiation-corrected thermocouple measurements (A) Ht CARS temperatures (A), Ot CARS temperatures.

Among other new methods, tunable laser absorption spectroscopy using infrared diode lasers offers prospects for improved accuracy and specificity in concentration measurements, when a line-of-sight technique is appropriate. The present paper discusses diode laser techniques as applied to a flat flame burner and to a room temperature absorption cell. The cell experiments are used to determine the absorption band strength which is needed to properly interpret high temperature experiments. Preliminary results are reported for CO concentration measurements in a flame, the fundamental band strength of CO at STP, collision halfwidths of CO under flame conditions, and the temperature dependence of CO and NO collision halfwidths in combustion gases. 

Two flat flame burners have been employed, a 4 cm 10 cm burner with a ceramic-lined chimney for NO measurements (4) and a 2.6 cm x 8.6 cm open-faced burner with a nitrogen shroud flow for CO measurements. Both burners operate at atmospheric pressure with laminar, premixed methane-air mixtures. These burners work satisfactorily over a broad range of fuel-air equivalence ratios, but both have cold boundary regions which cause non-uniform conditions along the optical axis that can be important in the data analysis (4). 

Experiments are currently in progress to measure CO and NO concentrations in a flat flame burner by diode laser spectroscopy. Comparative measurements are also being made using microprobe sampling with subsequent analysis by non-dispersive infrared and chemiluminescent techniques. Some preliminary laser absorption results for CO are reported here initial results for NO have been published separately (4). Also reported are initial data for collision halfwidths in combustion gases. 

Robben and co-workers have exploited these facts to measure mean and rms temperature fluctuations in a turbulent flat flame (2) and above a catalytic surface (8). By measuring the postflame temperature on a flat flame burner, as a function of reactant flow rate, a precise measurement of laminar flame speed was reported by Muller-Dethlefs and Weinberg (9). 

Aspirate solutions into a fuel-lean air—acetylene flame and measure iron absorbance at 248.33 nm. For procedures involving chelation—extraction, treat standard solutions in the same manner as samples. Aspirate organic solutions into a flame previously optimized on the organic solvent. Flush burner with extracting solution after aspiration of each standard and sample solution. Carry out determinations on beer and plant sample extracts within... 

These experimental measurements on flat flame burners revealed that when the NO concentration profiles are extrapolated to the flame-front position, the NO concentration goes not to zero, but to some finite value. Such results were most frequently observed with fuel-rich flames. Fenimore [9] argued that reactions other than the Zeldovich mechanism were playing a role in the flame and that some NO was being formed in the flame region. He called this NO, prompt NO. He noted that prompt NO was not found in nonhydrocarbon CO-air and H2-air flames, which were analyzed experimentally in the same manner as the hydrocarbon flames. The reaction scheme he suggested to explain the NO found in the flame zone involved a hydrocarbon species and atmospheric nitrogen. The... 

An important application of the heated flat-flame burner is the photolytic perturbation of the post cool-flame gases downstream from the stabilized cool-flame of n-heptane [83]. The chemical perturbation was initiated by an incident laser beam which dissociated H2O2 to OH radicals. The relaxation of the excess OH, measured by laser induced fluorescence, was shown to be tied to the principal reaction modes in alkane oxidation, namely propagation, termination and net branching. Global rate parameters were quantified from the decay curves. 

The numerical model for n-butane oxidation, by Pitz et al. [228], was used also by Carlier et al. [21] to simulate experimental studies of the two-stage combustion of n-butane at 0.18 MPa on a flat-flame burner and, following this validation, to simulate the ignition delays of n-butane in a rapid compression machine. The numerical studies of the burner experiments were extended by Corre et al. [233]. For simulations of the behaviour on a flat-flame burner the chemical model was computed in an isothermal mode, the experimental one-dimensional temperature profile being introduced as an input parameter. Among the important aims of the tests by Corre et al. [233] was the rationalization of the predicted extent of n-butane consumption throughout the development of the first (cool-flame) and second stages of combustion, with that observed experimentally. The experimental study by Minetti et al. [22, 116] included the detection and measurement of RO2 and HO2 radicals by esr, the one-dimensional spatial profiles of which were simulated by Corre et al. [233],... 

The technique of flame atomic absorption spectrophotometry accomplishes this by aspirating the sample solution into a burner chamber, where it is mixed with a fuel gas and an oxidant gas. The mixture is then burned in a specially designed burner head (Fig. 2). The light beam is directed lengthway down the burner, and the absorption of the analyte atoms in the flame is measured. The most commonly used gas mixtures are air with acetylene and nitrous oxide with acetylene. Experimental conditions are well-defined in the literature, and cookbook conditions are available from most instrument manufacturers. In addition, many instruments are computer-controlled, and typical conditions are available directly on the operating screen. 

The flask is clamped over a bunsen burner with a small flame. The measuring apparatus consists of the measuring tube (M), the levelling tube (N) and a connecting tube (Z) of special construction ... 

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