Flame exhaust emissions

A laboratory combustor containing porous media and burning atomized Jet-A fuel was tested for exhaust emissions and flame temperatures. The major findings of this study are as follows ... 

The results in Figure 1 imply that the abundance of chemiions initially present in the exhaust is 109/cm3. As noted by Yu and Turco [75], this number is consistent with the measurement of charge concentrations in flames, and with known ion-ion recombination coefficients, when the time scale of the exhaust emission into the atmosphere is taken into account. More recently, direct sampling of massive ion clusters (greater than 9500 amu) in fresh jet exhaust confirms that the chemiion concentration near the exit plane is of the order of 109/cm3 [90-92]. 

The data for this reaction has recently been thoroughly reviewed by Baulch and Drysdale [178]. Not only is it an important reaction in relation to exhaust emission and air pollution studies (cf. slowness of CO oxidation stage in flames, Sect. 10.2.3), but it is also a useful reference reaction for the measurement of OH reaction rates by competitive methods [213]. An example of this approach is the use of the ratios 1/ 2 3 given in Table 36 and Fig. 37 in order to deduce eqn. (71) for fej. 

Flame tunnel emissions which have been measured with the exhaust gas probes are presented in Table IV. 

The aromatic hydrocarbon content of diesel fuel affects the cetane number and exhaust emissions. One test method (ASTM D-5186) is applicable to diesel fuel and is unaffected by fuel coloration. Aromatics concentration in the range 1-75 mass% and polynuclear aromatic hydrocarbons in the range 0.5-50 mass% can be determined by this test method. In the method, a small aliquot of the fuel sample is injected onto a packed silica adsorption column and eluted with supercritical carbon dioxide mobile phase. Mono- and polynuclear aromatics in the sample are separated from nonaromatics and detected with a flame ionization detector. The detector response to hydrocarbons is recorded throughout the analysis time. The chromatographic areas corresponding to the mononuclear aromatic constituents, polynuclear aromatic constituents, and nonaromatic constituents are determined, and the mass-percent content of each of these groups is calculated by area normalization. 

Chlorophenols, 1989 Diethylhexylphthalate, 1992 Polychlorinatedbiphenyls and Terphenyls, 1992 Diesel fuel and exhaust emissions, 1996 Chlorinated paraffins, 1996 Flame retardants, 2000... 

In principle, emission spectroscopy can be applied to both atoms and molecules. Molecular infrared emission, or blackbody radiation played an important role in the early development of quantum mechanics and has been used for the analysis of hot gases generated by flames and rocket exhausts. Although the availability of FT-IR instrumentation extended the application of IR emission spectroscopy to a wider array of samples, its applications remain limited. For this reason IR emission is not considered further in this text. Molecular UV/Vis emission spectroscopy is of little importance since the thermal energies needed for excitation generally result in the sample s decomposition. 

Nitrogen Oxides. From the combustion of fuels containing only C, H, and O, the usual ak pollutants or emissions of interest are carbon monoxide, unbumed hydrocarbons, and oxides of nitrogen (NO ). The interaction of the last two in the atmosphere produces photochemical smog. NO, the sum of NO and NO2, is formed almost entkely as NO in the products of flames typically 5 or 10% of it is subsequently converted to NO2 at low temperatures. Occasionally, conditions in a combustion system may lead to a much larger fraction of NO2 and the undeskable visibiUty thereof, ie, a very large exhaust plume. 

The Danish Environmental Protection Agency has started work to draft a national plan to control brominated flame retardants, and has published what officials claim to be the most exhaustive national survey analysing the flow of such substances and assessing possible substitutes for specific applications. The survey found that the major source of BFRs emissions in Denmark was from evaporation from products already in use, and underlines previous concerns about the possible harm due to bioaccumulation. Denmark is to join Sweden in urging international action to curb the use of brominated flame retardants. 

Several methods have been developed to estimate the exposure to such emissions. Most methods are based on either ambient air quality surveys or emission modeling. Exposure to other components of diesel emissions, such as PAHs, is also higher in occupational settings than it is in ambient environments. The principles of the techniques most often used in exhaust gas analysis include infrared (NDIR and FTIR), chemiluminescence, flame ionization detector (FID and fast FID), and paramagnetic methods. 

Other issues of importance to combustor performance include soot production, pressure loss, and mechanical lifetime of the material. Too much soot in the exhaust could indicate poor combustion efficiency and unwanted particulate (smoke) emissions. For the baseline case without any inserts in the combustor, a slightly sooting flame was found. When one or two porous layers were inserted into the flame, no soot residue was found in the porous foams. It was thought... 

Catalytic combustion has been commercially demonstrated to reduce NO.. emissions to below 3 ppm while keeping CO and UHC emissions below 10 ppm without the need for expensive exhaust clean-up systems. In addition, a catalytic combustor reduces typical DLN problems such as risk of blow-out and flame instability. Also, the economic advantage of primary methods including catalytic combustion as opposed to secondary clean-up measures (SCR and SCONOx) has recently been assessed [1]. 

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