Fuel combustion, maximum

In principle, the equatorial maximum in CO2 should diminish during an El Nino, and the secular increase of atmospheric CO2 from fossil fuel combustion should be counterbalanced by the diminution of the equatorial oceanic flux. That this did not occur during the strong El Nino of 1972-73 is shown in Figure 10. During 1982-83 the secular increase in CO2 likewise appears not to have been affected by the diminution of the equatorial oceanic flux (Keeling and Revelle, 1985). A possible explanation is given... 

The oxidation reaction comprises three ranges of reaction, i.e. low temperature oxidation LTO, fuel deposition, and fuel combustion, which manifest discrete peaks at different temperatures. For example Fig. 4-165 presents the DSC plot of the oxidation of n-hexacontane in 1 bar air at a heating rate )3= 5 K/min. An increase of the heating rate shifts the peak maximum temperatures towards higher values, as expected. As a consequence additional peaks appear in the range of fuel deposition, as Fig. 4-166 shows for the example of oxidation of the dispersion medium in 1 bar air at a heating rate )8= 20 K/min. An increase of the pressure causes an increase of the area of the LTO peak, whereas peaks in the range of fuel deposition disappear and display only a shoulder on the flank of the LTO peak. The peak of the fuel combustion also becomes wider and flatter (Fig. 4-167, -hexacontane in 50 bar air, = 20 K/min). 

Table 4-199 Relation of the maximum temperature (°C) of the fuel combustion peak on the pressure in oxidation in air Heating rate )5 = 10 K/min...

In principle Differential Scanning Calorimetiy and Thermogravimetry are suitable methods for investigation of the kinetics of pyrolysis and oxidation reactions of heavy crude oils and heavy petroleum products. The repeatability of selected values i.e. onset and offset point temperatures, and DSC (DTA) and DTG peak maximum temperatures, is excellent. For the pyrolysis reaction the coefficient of variation is 2 % maximum. In the oxidation reaction this is also true for the regions of low temperature oxidation and of fuel combustion. For the fuel deposition region of reaction the repeatability is worse. 

The thermodynamic analysis of NO formation during fuel combustion is additionally improved by inclusion of trajectory construction problem in it, which is illustrated in Fig. 2,a and b. The Fig. 2 presents the calculation results for the Kansk-Achinsky coal pulverized combustion. Residence time for the reacting agent in combustion zone is taken equal to a second. Fig. 2,a shows solutions to the problem of determining attainable states the state with maximum possible concentration of nitrogen oxide and the state of final equilibrium. The latter was calculated not at the complete system of conditions (29), (30) that determine the region Dj (y), but with an accoimt of the condition for monotony (29) only. Application of the notion of equilibrium that is not related to kinetics in this case... 

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. 

When the partial pressures of the radicals become high, their homogeneous recombination reactions become fast, the heat evolution exceeds heat losses, and the temperature rise accelerates the consumption of any remaining fuel to produce more radicals. Around the maximum temperature, recombination reactions exhaust the radical supply and the heat evolution rate may not compensate for radiation losses. Thus the final approach to thermodynamic equiUbrium by recombination of OH, H, and O, at concentrations still many times the equiUbrium value, is often observed to occur over many milliseconds after the maximum temperature is attained, especially in the products of combustion at relatively low (<2000 K) temperatures. 

Flame Temperature. The adiabatic flame temperature, or theoretical flame temperature, is the maximum temperature attained by the products when the reaction goes to completion and the heat fiberated during the reaction is used to raise the temperature of the products. Flame temperatures, as a function of the equivalence ratio, are usually calculated from thermodynamic data when a fuel is burned adiabaticaHy with air. To calculate the adiabatic flame temperature (AFT) without dissociation, for lean to stoichiometric mixtures, complete combustion is assumed. This implies that the products of combustion contain only carbon dioxide, water, nitrogen, oxygen, and sulfur dioxide. 

Thus if combustion can be effected in two stages, with or without the intermediate heat rejection for thermal NO control discussed above, the conversion of fuel N to NO can be largely ckcumvented by first, a primary stage at 0 = 1.5-2 with a modest residence time to allow formation of N2 in the hot primary products, followed by rapid addition of secondary ak to complete the combustion at an effective [Pg.529]

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