Abstract: The study reviews the sampling environments and chemical transformations of nitrogen oxides that may occur within probes and sample lines while sampling combustion products. Experimental data are presented for NO/sub x/ transformations in silica and 316 stainless steel tubing when sampling simulated combustion products in the presence of oxygen, carbon monoxide, and hydrogen. A temperature range of 25 to 400/sup 0/C is explored. In the absence of CO and H/sub 2/, 316 stainless steel is observed to promote the reduction of nitrogen dioxide to nitric oxide at temperatures in excess of 300/sup 0/C, and silica is found to be passive to chemical transformation. In the presence of CO, reduction of NO/sub 2/ to NO is observed in 316 stainless steel at temperatures in excess of 100/sup 0/C, and reduction of NO/sub 2/ to NO in silica is observed at 400/sup 0/C. In the presence of H/sub 2/, NO/sub 2/ is reduced to NO in 316 stainless steel at 200/sup 0/C and NO/sub x/ is removed at temperatures exceeding 200/sup 0/C. In silica, the presence of H/sub 2/ promotes the reduction of NO/sub 2/ to NO at 300/sup 0/C and the removal of NO/sub x/ above 300/sup 0/C.
Abstract: The measurement techniques for delineating fuel-air mixing and transport in gas turbine combustion, as well as examples of representative results, are provided in this overview. The summary is broken into applications for gaseous fuels and liquid fuels since many diagnostics which are specific to the phase of the fuel have been developed. Many possible methods for assessing the general mixing have been developed, but not all have been applied to practical systems either under scaled or under actual conditions. With respect to gaseous mixing processes, planar laser-induced fluorescence (PLIF) based on acetone is now starting to be successfully applied to actual systems and conditions. In spray-fired systems, the need to discriminate between phases leads to considerable complication in delineating fuel-air mixing. Methods that focus on the discrete phase have successfully provided details relative to the droplets. These include phase Doppler interferometry (PDI), which is becoming ubiquitous in application to practical devices and under practical conditions. PDI is typically being applied to quantify droplet sizes, although the volume flux, which is relevant to fuel-air mixing, in practical systems is also being reported. In addition, PLIF strategies that focus upon the behaviour of the droplets are now being developed. However, PLIF strategies that can discriminate between phases either in the fuel or with respect to the liquid fuel and combustion air are also being developed. In terms of characterizing the vector fields associated with the mixing process, laser anemometry (LA), although it is tedious to apply, has proven reliable even in the presence of droplets. Newer methods such as DPIV and FRS have seen only limited application in practical systems but appear promising. In terms of scalar fields, LIF and PLIF have also been applied successfully to these systems, and examples of the measurements of concentrations of various radical species such as OH are found throughout the literature.
Abstract: This study contributes to the topic of nitrogen oxide (NOx) formation at the level of single droplet and droplet array combustion The results show that the trade-off between ambient temperature and available oxygen determines the NOx formation of droplets burning in hot exhaust gas The degree of droplet vaporization has an effect on flame stabilization around the droplet and on NOx formation In the ignition model, the NOx production rate turns out to be very sensitive against the ignition position
Cites background from "Chemical transformations of nitroge..."
...Stainless steel tubing is found to promote chemical transformation when sampling fuel-rich combustion products [122, 371]....
...Potential sampling artifacts were minimized by a careful selection of materials for the entire sampling equipment [293, 371]....
...Three general types of chemical transformation of these nitrogen oxides prevail in probes and sample lines [136, 217, 266, 371]:...
...For instance, local concentrations of NO and NO2 are required to assess the chemical mechanisms responsible for the formation of NOx [56, 183, 371, 374]....
...Chromium, nickel, and copper, for instance, are well-known to be active catalysts, and it can be concluded that untreated stainless steel is not an adequate material for gas sampling equipment [122, 136, 145, 179, 247, 371, 387]....
Abstract: This paper presents a review of the capabilities of probe techniques for combustion diagnostic and outlines the most significant sources of error inherent to their use. The emphasis of the search is on measurements of temperature and on those of major species and ion concentrations in combusting environments, and attention is focused to elucidate the importance of probe measurements to improve understanding of turbulent combustion.
Abstract: Future aeropropulsion gas turbine combustion requirements call for operating at very high inlet temperatures, pressures, and large temperature rises. At the same time, the combustion process is to have minimum pollution effects on the environment. Aircraft gas turbine engines utilize liquid hydrocarbon fuels which are difficult to uniformly atomize and mix with combustion air. An approach for minimizing fuel related problems is to transform the liquid fuel into gaseous form prior to the completion of the combustion process. Experimentally obtained results are presented for vaporizing and partially oxidizing a liquid hydrocarbon fuel into burnable gaseous components. The presented experimental data show that 1200 to 1300 K reaction product gas, rich in hydrogen, carbon monoxide, and light-end hydrocarbons, is formed when flowing 0.3 to 0.6 fuel to air mixes through a catalyst reactor. The reaction temperatures are kept low enough that nitrogen oxides and carbon particles (soot) do not form. Results are reported for tests using different catalyst types and configurations, mass flowrates, input temperatures, and fuel to air ratios.
Abstract: The formation was followed by probing flames of ethylene, methane, or propane with N2-O2 mixtures. The known kinetic laws of the well-understood N2-O2-NO system (limited by the rate of the reaction O+N2→N+NO) described the growth of nitric oxide in the post-flame gas, after hydrocarbons were consumed, but could not describe a faster, transient formation of nitric oxide in the primary reaction zone. The transient formation did not occur in hydrogen or carbon monoxide flames, and therefore, may involve an attack of carbon or hydrocarbon radicals on nitrogen molecules (e.g., CH+N2→HCN+N). At atmospheric pressure, the transient formation gave its greatest yield in flames containing 1.3 to 1.4 times the stoichiometric amount of fuel. Its yield increased somewhat with pressure, particularly in fuel-lean flames, so that at 3 atmos pressure the nitric oxide formed quickly in the primary reaction zone was about the same in flames of 0.8 as of 1.4 mixture strength. The transient formation possessed a relatively weak temperature dependence. Extrapolating the measurements, one can suggest that the new mechanism may contribute significantly to the emission of nitrogen oxides from a gas turbine, but the major contribution occurs by the known mechanism of the N2-O2 system.
Abstract: The oxidation of CO by NO and by O 2 has been studied on a number of supported transition metal oxide catalysts. On supported chromia the oxidation of CO by NO is faster than by O 2 ; however, with mixtures of NO and O 2 the reaction is selective towards O 2 . The application of continuous mass-spectrometer monitoring to the study of surface state changes in chromia catalysts is outlined. The method was extended to determine the oxidation state of the surface in situ during reaction. In the oxidation-reduction cycle involving alternate passage of HeCO and HeO 2 mixtures at 500 °, the majority of the surface atoms undergo a change of oxidation state from Cr 6+ to Cr 2+ . The extent of this change diminishes with decreasing temperature. Mixtures of He and NO oxidize the surface of supported chromia to a lesser extent than HeO 2 . During the CONO reaction the average surface oxidation state is lower than in the presence of oxygen. A tentative explanation is offered for the selectivity for oxygen over nitric oxide in the oxidation-reduction reactions on commonly employed catalysts.
Abstract: A prototype instrument monitoring ozone or nitric oxide has been used for photochemical smog studies in the laboratory and the atmosphere. The principle of the detector is based on the chemiluminescent reaction
Abstract: Nonuniformities and rates of mixing are found to play an important role in determining emissions of carbon monoxide and nitric oxide from a kerosene-fueled atmospheric-pressure burner. Nonuniformaties are allowed for by assuming that burnt gas eddies have a normal distribution of equivalence ratios about the mean value. Mixedness is characterized by the ratio of the standard deviation of this distribution to the mean value and is related to combustor operating variables. A simple one-dimensional flow model is coupled with the mixing model to predict the variation of CO and NO concentrations with atomizing pressure and distance along the burner. The data obtained agree with the predictions and show clear mixing effects on both CO and NO concentration levels.