Burners flat flame

An Erlenmeycr or other form of Combustion Furnace.— The usual length is 80-90 cm. (31-35 in.), and it is provided with 30 to 35 burners. Flat flame burners are undesirable. 

FIGURE 4.19 Cooling effect in flat flame burner apparatus. 

As the important effect of temperature on NO formation is discussed in the following sections, it is useful to remember that flame structure can play a most significant role in determining the overall NOx emitted. For premixed systems like those obtained on Bunsen and flat flame burners and almost obtained in carbureted spark-ignition engines, the temperature, and hence the mixture ratio, is the prime parameter in determining the quantities of NOx formed. Ideally, as in equilibrium systems, the NO formation should peak at the stoichiometric value and decline on both the fuel-rich and fuel-lean sides, just as the temperature does. Actually, because of kinetic (nonequilibrium) effects, the peak is found somewhat on the lean (oxygen-rich) side of stoichiometric. 

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. 

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). 

Instrumental methods have become more sophisticated to face these challenges. In particular, Westmoreland and Cool have developed a flame-sampling mass spectrometer that has provided several revelations in terms of relevant molecular intermediates in combustion. " Their setup couples a laminar flat-flame burner to a mass spectrometer. This burner can be moved along the axis of the molecular beam to obtain spatial and temporal profiles of common flame intermediates. By using a highly tunable synchrotron radiation source, isomeric information on selected mass peaks can be obtained. This experiment represents a huge step forward in the utility of MS in combustion studies lack of isomer characterization had previously prevented a full accounting of the reaction species and pathways. 

The NTC phenomenon actually varies with pressure and combustion environment it is much different in a jet engine than in a diesel engine, which in turn is much different than in an internal combustion engine, which in turn is much different from a flat-flame burner. For the purposes of this review, we have focused on a simplified case. 

Fig. 1.1 Illustration of a premixed flat-flame burner and an opposed-flow diffusion flame.

Fig. 16.8 Illustration of a premixed flat-flame burner. Fuel and oxidizer are first premixed, and then flow through a porous burner face. A steady, one-dimensional flat flame is stabilized by heat transfer to the cooled burner face. The solutions shown here are for a methane-air flame, in which the air contains water vapor at 100% relative humidity. By plotting the temperature and selected species profiles, one can observe some of the complexities of flame structure.

At the relatively low inlet velocity of U =30 cm/s, the flame is stabilized by heat transfer to the inlet manifold. This is essentially the situation in the typical flat-flame burner that is found in many combustion laboratories (e.g., Fig. 16.8). The laminar burning velocity (flame speed) of a freely propagating atmospheric-pressure, stoichiometric, methane-air flame is approximately 38 cm/s. Therefore, since inlet velocity is less than the flame speed, the flame tends to work its way back upstream toward the burner. As it does, however, a... 

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. 

Using the frozen excitation model to analyze the data shown in Fig. 3, and calibrating the system via Rayleigh scattering (8J, a total OH number density of 4 x 1C>16 cm 3 was calculated for an assumed flame temperature of 2000 K in the methane-air torch. Nt was not compared directly with the results of absorption studies future flat flame burner studies will involve direct comparison of absorption and fluorescence. 

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). 

Validation of the Global Rates Expressions. In order to validate the global rate expressions employed in the model, temperature and concentration profiles determined by probing the flames on a flat flame burner were studied. Attention was concentrated on Flames B and C. The experimental profiles were smoothed, and the stable species net reaction rates were determined using the laminar flat-flame equation described in detail by Fristrom and Westenberg (3) and summarized in Reference (8). 

The reactor 07) consists of 5 by 28 cm flat flame burner downfired into a chimney of similar dimensions, fitted with Vycor windows for optical access. Access ports for droplet injection and sample probing are provided. As illustrated in Figure 3, fuel droplets are normally injected ballistically across the face of the burner. 

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