Flame fuel-lean

Aspirate solutions into an air—acetylene flame (fuel-lean for sodium measurement) and measure absorbances at 589.00 nm and 766.49 nm for sodium and potassium, respectively. Use less sensitive wavelengths of 330.24/330.30 nm and 404.41 nm for sodium and potassium, respectively, when more concentrated (by a factor of about 200) solutions are used. 

Connect the appropriate gas supplies to the burner following the instructions detailed for the instrument, and adjust the operating conditions to give a fuel-lean acetylene-air flame. 

Set up a double-beam atomic absorption spectrophotometer with a lead hollow cathode lamp and isolate the resonance line at 283.3 nm adjust the gas controls to give a fuel-lean acetylene-air flame in accordance with the operating manual supplied with the instrument. 

The sensitivity of atomic absorption can often be enhanced by aspirating solutions in organic solvents. The increased sensitivity is due to a number of factors, but can be attributed in large part to the lower viscosity and surface tension as compared to aqueous solutions. The flow rate is increased and smaller droplets are formed which are more efficiently vaporized. When organic solvents are aspirated, a fuel lean flame must be used in order to burn the solvent. 

For our estimations and the adiabatic control volume in Figure 4.10, 7b should be the adiabatic flame temperature. Consider a fuel-lean case in which no excess fuel leaves the control volume. All the fuel is burned. Then by the conservation of species,... 

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. 

Based on conventional thinking, lower temperatures should result in a decrease of thermally produced NO, . However, despite the substantially lower temperatures in the PSR, as shown in Fig. 26.4a, the NO, mole fractions do not significantly differ between the two reactors, except for very fuel-lean mixtures, near extinction of self-sustained flames. Similar behavior was recently observed when radiation from... 

Figure 26.56 is the corresponding plot for 12% inlet H2 in air. In this case, there is an extinction at about 1000 K for both reactors. The qualitative features are similar to that of the PSR discussed above for 28% H2 in air. For such fuel-lean mixtures, the flame is attached to the surface. As a result, the thermal coupling between the surface and the gas phase is strong, and reduction in surface temperature affects the entire thermal boundary layer resulting in significant reduction of NOj,. These results indicate that the bifurcation behavior, in terms of extinction, determines the role of flame-wall thermal interactions in emissions. 

Ignite the flame and ensure that it is blue with a very faint tinge of yellow above the primary cone. If it appears to be too fuel lean or fuel rich, adjust the fuel flow rate control accordingly. 

The reaction diagram of Fig. 14.1 applies to methane oxidation under both flame [423] and flow reactor [146] conditions. At high temperatures and fuel-lean to stoichiometric conditions, the conversion of methane proceeds primarily through the sequence CH4 -> CH3 -> CH2O -> HCO -> CO -> CO2. At lower temperatures or under fuel-rich conditions the reactions of CH3 with O or O2 are less competitive. Under these conditions two CH3 radicals may recombine and feed into the C2 hydrocarbon pool,... 

The theoretical and experimental results for a fuel-lean methane-air flame are given in Figures 5-7. These results include temperature and major species compositions. The experimental and theoretical results are compared by matching the abcissas of the temperature profiles. The model very accurately predicts the slope of the temperature profile but predicts a larger final flame temperature than is measured. This is a consequence of heat lost to the cooled, gold-coated burner wall that is 1.5 mm away from the positions where data were taken. 

Figure 5. Temperature, CH4, and C02 profiles for a fuel-lean ( == 0.86) atmospheric-pressure, premixed, laminar CHh- air flame. The experimental data are from laser Raman scattering and the theoretical predictions are from the computer code of Ref. 1 (---------), theory (%), temperature (N2) (O), C02 (A), CH...

One point which is often overlooked when optimizing fuel-to-oxidant ratio is that the optimum fuel flow is sometimes matrix-dependent. For example, the determination of calcium in water using an air-acetylene flame is more sensitive if a fuel-rich flame is used. If, however, the samples contain dilute sulfuric acid, a more fuel-lean flame usually gives substantially improved sensitivity. As a general rule, it is best to find optimal conditions for the particular matrix which you are analysing. 

Flame Analyses. Smoothed temperature and mole fraction versus distance plots and the associated net reaction rate versus distance plots for a fuel-lean and fuel-rich flame are shown in Figures 1 and 2, respectively. The computer-generated symbols in the figures identify the species associated with each curve they do not denote data points. Approximately 16 data points from each flame were used to generate the curves. 

Somewhat unexpected is the relatively low consumption of CO in the excess oxygen flame. The CO profile of Figure 1-a shows only about 60 percent of the CO was oxidized to CO2. Other fuel-lean flames probed also showed incomplete combustion of the CO. Equilibrium CO levels were not attained in most of the flames. 

Emissions of soot on the other hand represent a smaller fraction of the overall emission, but are probably of greater concern from the standpoint of visibility and health effects. It has been suggested that soot emissions from fuel oil flames result from processes occurring in the vicinity of individual droplets (droplet soot) before macroscale mixing of vaporized material, and from reactions in the bulk gas stream (bulk soot) remote from individual droplets. Droplet soot appears to dominate under local fuel lean conditions (1, 2), while bulk soot formation occurs in fuel rich zones. Factors which are known to affect soot formation from liquid fuel flames include local stoichiometry, droplet size, gas-droplet relative velocity and fuel properties (primarily C H ratio). 

Compared to PFD and ASD, CSD SRC has the potential for producing a low carbon (<10%) fly ash under low N0X> staged combustion conditions if flame temperature can be maintained sufficiently high during both fuel rich and fuel lean stages, thereby making the CSD SRC fly ash amenable to collection in electrostatic precipitators. 

Procedure Use an atomic absorption spectrophotometer equipped with a 4-in., single-slot burner head. Set the instrument to previously determined optimum conditions for organic solvent aspiration (3 to 5 mL/min) and at a wavelength of 283.3 nm Use an air-acetylene flame adjusted for maximum lead absorption with a fuel-lean flame. Aspirate the blanks, the Standard Solutions, and the Sample Solution, flushing with water and then with Aqueous Butyl Acetate between... 

Aspirate solutions into a fuel-lean air—acetylene flame to measure magnesium at 285.21 nm and into a fuel-rich nitrous oxide—acetylene flame to determine calcium at 422.67 nm. 

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