Doped methane flames

NO doped Methane Flames. Most of the NO passes through the flame unreacted, and the NO primarily acts as an inert diluent. Diluting the flames with 1.5% NO causes the adiabatic flame temperatures to drop by about 100 K and the calculated flame speeds to decrease by about 10%. The NO fraction decreases by less than 10% through the flame front for these flames which were doped far above the equilibrium NO concentrations (420-3700 ppm depending on stoichiometry). In the experiments there was no post flame decay in the NO concencentrations ( 5%), while the calculations do show some decay (<2%/mm) which depends upon stoichiometry. The calculated post flame conversion rate of NO to Nj decreases as the super-equilibrium radicals (e.g. 0 and OH) decay. 

NHa Doped Methane Flames. While the addition of NO to a methane-air flame acts primarily as a diluent, the addition of NH3 richens the mixture leading to competition for the available oxygen. This richening effect also reduces the equilibrium NO concentration of these near stoichiometric flames (O.8<0< .2). 

Combined NO and NH Doped Methane Flames. Adding both NO and NH3 to methane-air flames provides the opportunity to enhance the reducing effect of the NHi + NO reactions. Typically the flames are doped with NO concentrations far in excess of the equilibrium concentrations consequently we see NO concentrations which are appreciably reduced by the NH3 addition. 

Ammonia-doped methane flames, 96-98 Ammonia flame... 

Rahinov, I., Goldman, A., and Cheskis, S., Absorption spectroscopy diagnostics of amidogen in ammonia-doped methane/air flames. Combust. Flame, 145, 105, 2006. 

Pure ammonia flames are studied experimentally and theoretically to isolate the amine chemistry. Ammonia and NO doped methane-air flames are also studied as models for flames with fuel-bound nitrogen and flames diluted with NO from EGR. We conclude from these studies ... 

NO alone doped into methane flames is only reduced by the slow three-reaction Zeldovitch mechanism. No appreciable reduction due to the ammonia reaction mechanism is found. 

In this paper we first summarize the ability of the NH kinetic mechanism of Dasch and Blint ( ) to describe the major properties of ammonia-oxygen-diluent flames. This mechanism is constructed solely from literature rate constants and is specifically valid only for flames leaner than 0=1.2 Having validated the ammonia mechanism, we then investigate the yield of NO from methane-air flames which have been doped with NH3 and NO. The NH3 doped... 

Having validated the mechanism on ammonia-oxygen flames, the yield of NO from nitrogen doped CH4-air flames was examined. Both NH3 and NO doping were investigated. Only post-flame NO concentrations were measured. These are compared with calculations of the full kinetics and with adiabatic equilibrium calculations. The calculated profiles indicate the complexity of the NO dynamics in these flames. The temperature and major species profiles in the undoped flames had been studied in earlier work( ). Three near stoichiometric methane-air flames having initial equivalence ratios(0) of 0.8, 1.0 and 1.2 are diluted with less than 5 volume percents of NH3 or NO. In this section NO concentration is expressed both as a mole fraction and as a fraction of the total nitrogen concentration ... 

Figure 6. Temperature and NO fraction spatial profiles for 0 = 0.8 methane-air flame doped with S% (vol) NH3 and 1.5% NO.

Contrary to pure ammonia combustion where the primary source of N2 comes from reactions of NH2 with NO, ammonia doped into methane-air flames is combusted to N2 via the N + NO reaction. 

Pd-doped catalysts have been produced by USS [82]. The fingerprint of Pd adopting the octahedral coordination of Fe in LaFeo,95Pdo,o503 has been observed in the XANES spectra of the material prepared by spray synthesis (27m /g) similarly to the preparation by the amorphous citrate method (14m /g) [17,82]. In contrast, the flame-made material of the same composition (22m /g) exposed metallic Pd particles on LaFeOs similarly to preparation by solution combustion. The different nature of the Pd species obtained by changing the synthesis method dramatically influences their catalytic performance, since PdO nanoparticles exposed at the surface of the mixed oxide exhibit catalytic activity, whereas Pd—O species in the bulk of the mixed oxide are inactive, at least in the case of methane oxidation [27]. In contrast to LaFeOs, LaMnOs did not allow Pd to adopt the octahedral coordination irrespective of synthesis method. Therefore, the coordination of Pd strongly depends on both the composition of the perovskite-type oxide and the synthesis method. 

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