Atmospheric primary reaction zone

The structure of the flame itself consists of two major zones, the primary reaction zone and a secondary reaction or postheating zone. The primary reaction zone, the area of the flame just above the burner surface, is the region where combustion, atomization, and excitation occurs. Some typical flame combustion products formed in this region are CO, C02, H2, N2, and H20 molecules, as well as O, H, OH-, and C- radical species. The secondary reaction zone is a much cooler region where the flame gases mix with atmospheric components that may include impurities and emission interferants. Between these two zones lies a smaller, but important, intermediate region, where little reaction occurs. In this region of the flame, the fraction of the atoms in the ith excited state, a is controlled only by the prevalent temperature and can be represented by the Boltzmann distribution ... 

A flame front is characterized by steep temperature and concentration gradients. As previously mentioned, it is these gradients which make the processes of thermal conduction and diffusion so important in flame fronts and account for the existence of a characteristic burning velocity. In a typical flame—at atmospheric pressure and with a 100 cm per second burning velocity— the primary reaction zone will be a few tenths of a millimeter thick, the maximum temperature gradient will approach 100,000°C per cm, and the gas acceleration will approach a hundred times gravity. It should be noted that despite the high acceleration the pressure drop is still small 10 atm) and... 

Many of the problems connected with the study of flame structure stem from the narrowness of the spatial region to be studied, for example the stoichiometric acetylene-air flame at atmospheric pressure has a primary reaction zone smaller than one-tenth of a millimeter (0.004 inch). It is not possible with present-day techniques to measure the properties of such a flame with sufficient spatial resolution to obtain meaningful second derivatives. The thickness of the reaction zone, however, depends inversely on both pressure and burning velocity. This behavior is... 

Combustion. The primary reaction carried out in the gas turbine combustion chamber is oxidation of a fuel to release its heat content at constant pressure. Atomized fuel mixed with enough air to form a close-to-stoichiometric mixture is continuously fed into a primary zone. There its heat of formation is released at flame temperatures deterruined by the pressure. The heat content of the fuel is therefore a primary measure of the attainable efficiency of the overall system in terms of fuel consumed per unit of work output. Table 6 fists the net heat content of a number of typical gas turbine fuels. Net rather than gross heat content is a more significant measure because heat of vaporization of the water formed in combustion cannot be recovered in aircraft exhaust. The most desirable gas turbine fuels for use in aircraft, after hydrogen, are hydrocarbons. Fuels that are liquid at normal atmospheric pressure and temperature are the most practical and widely used aircraft fuels kerosene, with a distillation range from 150 to 300 °C, is the best compromise to combine maximum mass —heat content with other desirable properties. For ground turbines, a wide variety of gaseous and heavy fuels are acceptable. 

H20 and free radicals such as. Above the primary zone is the outer cone or secondary reaction zone. In this region, cooling occurs as a result of mixing with the surrounding atmosphere. This may lead in turn to the entrainment of impurities, such as sodium compounds which will increase... 

Another ionization technique, which seems closely related to TSI and ESI, is atmospheric-pressure chemical ionization (APCI). In APCI, the solvent stream, e.g., the effluent from an LC column, is pneumatically nebuhzed into a heated vaporizer zone, where (almost) complete evaporation of the aerosol droplets is achieved [71-73]. Analyte ionization is initiated by electrons from a downstream corona discharge needle. The electrons act as primary source of ionization of the solvent or mobile-phase constituents, which in turn by gas-phase ion-molecule reactions in the API source ionize the analyte molecules, mostly by proton-transfer reactions, i.e., formation of [M-hH]+ in positive-ion and [M-H] in negative-ion mode. There are also some results, indicating the Na -cationization can take place under APCI conditions. Atmospheric-pressure photoionization (APPI) is an ionization technique closely related to APCI. In APPI, the analyte ionization is initiated by light from a vacuum-ultraviolet lamp, e.g., a Kr-lamp, instead of by means of a corona discharge. Next to direct photoionization of the analytes, gas-phase ion-molecular reactions greatly contribute to the ionization in APPI [74,75]. 

During accelerator operation radioactive nuclides are produced by the interaction between the primary and secondary particles E 30 MeV) from the machine and the atmospheric air in the accelerator halls. Spallation reactions in solid machine parts can also lead to the formation of radioactive nuclides. If the air is confined in the accelerator hall there will be no release of radioactive nuclides into the outside zones during operation of the machine. When the machine is stopped an unexpected concentration of radioactive nuclides may be present in the air. Table 2.11 lists all the radioactive nuclides with a half-life >1 s (in decreasing half-life order) which can be produced by irradiation of the atmospheric air in a proton ac-... 

In Figure 10.13, the combustion of the flare grain (1) yields an anaerobic core zone of conical shape (2) that contains the primary combustion products such as vaporized metal, its fluorides, condensed metal particles, particulate carbon and fluorocarbon species. Owing to momentum transfer mixing of the primary combustion products with the atmosphere and subsequent afterbum, reactions takes place in zone (3) [16]. Thus the aerobic zone typically displays a higher temperature than the core zone [17]. 

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