Rich flame

Total sulfur in air, most of which is sulfur dioxide, can be measured by burning the sample in a hydrogen-rich flame and measuring the blue chemiluminescent emission from sulfur atom combination to excited S2 (313). Concentrations of about 0.01 ppm can be detected. 

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. 

Reaction 2 has been invoked because C3H3 + is apparently formed in a primary ionization step since the ion appears early in the flame front, its concentration maximizes in rich flames (this is true of no other positive ion observed), and it is present in the flame front in large concentrations (9). However, not all the experimental evidence is consistent with this mechanism for producing C3H3+ it might also be produced through an ion molecule reaction, which will be considered below. 

For the analysis of the chemical structure of flames, laser methods will typically provide temperature measurement and concentration profiles of some readily detectable radicals. The following two examples compare selected LIF and CRDS results. Figure 2.1 presents the temperature profile in a fuel-rich (C/O = 0.6) propene-oxygen-argon flame at 50 mbar [42]. For the LIF measurements, 1% NO was added. OH-LIF thermometry would also be possible, but regarding the rather low OH concentrations in fuel-rich flames, especially at low temperatures, this approach does not capture the temperature rise in the flame front [43]. The sensitivity of the CRDS technique, however, is superior, and the OH mole fraction is sufficient to follow the entire temperature profile. Both measurements are in excellent agreement. For all flames studied here, the temperature profile has been measured by LIF and/or CRDS. 

Intermediate species concentrations in fuel-rich flames (C/O = 0.5) of the two isomeric esters methyl acetate (left) and ethyl formate (right) burnt under identical conditions mole fraction, h height species named on the left side of each graph correspond to left y-axes, species on the right to right y-axes. 

Ofiwald, P. et al.. Isomer-specific fuel destruction pathways in rich flames of methyl acetate and ethyl formate and consequences for the combustion chemistry of esters, /. Phys. Chem. A, 111, 4093,2007. 

Kohse-Hoinghaus, K. et al., Combination of laser- and mass-spectroscopic techniques for the investigation of fuel-rich flames, Z. Phys. Chem., 219, 583, 2005. 

Lamprecht, A., Atakan, B., and Kohse-Hoinghaus, K., Fuel-rich flame chemistry in low-pressure cyclopentene flames, Proc. Combust. Inst., 28,1817, 2000. 

Experimentally, two modes of extinction, based on the separation between the twin flames are observed. Specifically, the extinction of lean counterflow flames of n-decane/02/N2 mixtures occurs with a finite separation distance, while that of rich flames exhibits a merging of two luminous flamelets. The two distinct extinction modes can be clearly seen in Figure 6.3.2. As discussed earlier, the reactivity of a positively stretched flame with Le smaller (greater) than unity increases (decreases) with the increasing stretch rate. Therefore, the experimental observation is in agreement with the... 

Or, more generally, to one-step reactions with a relatively weak dependency on T. This may occur in combusting flows where the adiabatic temperature rise is small for example, in a rich flame near extinction. 

It solely operates on the principle of photon emission. If P- or S-containing hydrocarbons are ignited in a hydrogen-rich flame, it gives rise to chemiluminescent species spontaneously which may subsequently be detected by a suitably photomultiplier device. Hence, FPD is regarded as a specific detector for P- or S-containing compounds. 

The term prompt NO derives from the fact that the nitrogen in air can form small quantities of CN compounds in the flame zone. In contrast, thermal NO forms in the high-temperature post-flame zone. These CN compounds subsequently react to form NO. The stable compound HCN has been found in the flame zone and is a product in very fuel-rich flames. Chemical models of hydrocarbon reaction processes reveal that, early in the reaction, O atom concentrations can reach superequilibrium proportions and, indeed, if temperatures are high enough, these high concentrations could lead to early formation of NO by the same mechanisms that describe thermal NO formation. 

The catalytic reduction of the radicals, particularly the O atom, by sulfur compounds will generally reduce the rates of reactions converting atmospheric nitrogen to NO by the thermal mechanism. However, experiments do not permit explicit conclusions [21], For example, Wendt and Ekmann [46] showed that high concentrations of S02 and H2S have an inhibiting effect on thermal NO in premixed methene-air flames, while deSoete [47] showed the opposite effect. To resolve this conflict, Wendt el al. [48] studied the influence of fuel-sulfur on fuel-NO in rich flames, whereupon they found both enhancement and inhibition. 

Within the frame of the present first series of experiments it was almost always oxygen which was injected into supercritical water-methane mixtures. There were several reasons for this first choice. One of these was the desire, to study rich flames and their possible products first. Often the water to methane mole fraction ratio was 0.7 to 0.3. But mixtures down to a methane mole fraction of 0.1 were also used. It was possible, however, to inject oxygen and methane simultaneously into the supercritical water and produce a flame. Not possible was the production of true premixed flames. After a retraction of the thin inner nozzle capillary of the burner (see Fig. 1 b) the two gases could be mixed just below the reaction cell, but the flame reaction proceeded from the nozzle tip in the cell back towards this mixing point immediately. 

Hansen, N. Klippenstein,S. J. Miller,]. A. Wang, J. Cool, T. A. Law, M. E. Westmoreland, P. R. Kasper, T. Kohse-Hoinghaus, K. Identification of CjH,j Isomers in Fuel-Rich Flames by Photoionization Mass Spectrometry and Electronic Structure Calculations. Phys. Chem. A 2006,110, 4376-4388. 

Catalyst monoliths may laos be employed as catalytic combustion chambers preceding aircraft and stationary gas turbines. As shown diagramatically in Fig. 16, a catalytic combustor comprises a preheat region, a catalyst monolith unit and a thermal region. In the preheat region, a small fuel-rich flame burner is employed to preheat the fuel-air mixture before the hot gases reach the monolith unit. Additional fuel is then injected into the hot gas stream prior to entry to the monolith where... 

In an oxygen-rich flame, and at temperatures above 1200 C, CuCl is unstable and will react to form CuO and CuOH. CuOH emits in the 525-555 nanometer region (green ) and substantial emission may overpower any blue effect that is also present. Copper oxide, CuO, emits a series of bands in the red region, and this reddish emission is often seen at the top of blue flames, where sufficient oxygen from the atmosphere is present to convert CuCl to CuO [111. 

The exact synthetic chemistry which produces PAH in a fuel-rich flame is not well known, even today. It is clear, however, that PAH can be produced from almost any fuel burned under oxygen deficient conditions. Since soot is also formed under these conditions, PAH are almost always found associated with soot. As an example of the PAH assemblage produced by combustion systems. Figure 1 shows gas chromatographic mass spectrometry (GCMS) data for PAH produced by the combustion of kerosene ( ). The structures of the major compounds are also given in Figure 1. We draw the reader s attention to a number of features of this PAH mix-... 

Flame temperature varies from one part of the flame fo another, as indicated in Section 2.2.2. Figures 2.5 and 2.6 show this effect for a stoichiometric and a fuel-rich flame, respectively. 

Comparative figure (with Fig. 2.5) showing a fuel-rich flame temperature distribution. Temperatures in °C. 

Under reducing conditions hydrogen atoms are the main chain carriers. Data from fuel-rich flames indicate that SO2 is efficient in catalyzing H-atom recombination. The H-atom removal presumably involves the following reaction sequence ... 

Droplets entering the flame evaporate then the remaining solid vaporizes and decomposes into atoms. Many elements form oxides and hydroxides in the outer cone. Molecules do not have the same spectra as atoms, so the atomic signal is lowered. Molecules also emit broad radiation that must be subtracted from the sharp atomic signals. If the flame is relatively rich in fuel (a rich flame), excess carbon tends to reduce metal oxides and hydroxides and thereby increases sensitivity. A lean flame, with excess oxidant, is hotter. Different elements require either rich or lean flames for best analysis. The height in the flame at which maximum atomic absorption or emission is observed depends on the element being measured and the flow rates of sample, fuel, and oxidizer.6... 

Chemical interference is caused by any component of the sample that decreases the extent of atomization of analyte. For example, SO and PO hinder the atomization of Ca2+, perhaps by forming nonvolatile salts. Releasing agents are chemicals that are added to a sample to decrease chemical interference. EDTA and 8-hydroxyquinoline protect Ca2+ from the interfering effects of SO and PO. La3+ also can be used as a releasing agent, apparently because it preferentially reacts with PO and frees the Ca2+. A fuel-rich flame reduces certain oxidized analyte species that would otherwise hinder atomization. Higher flame temperatures eliminate many kinds of chemical interference. 

Sulfur Dioxide. Both flame photometric and pulsed fluorescence methods have been applied to the continuous measurement of S02 from aircraft. In the flame photometric detector (FPD), sulfur compounds are reduced in a hydrogen-rich flame to the S2 dimer. The emission resulting from the transition of the thermally excited dimer to its ground state at 394 nm is measured by using a narrow band-pass filter and a photomultiplier tube. 

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