Range of Fuel Deposition

In this range, oxidation and pyrolysis take place immediately consecutively or even parallel, so there is a choice as to whether the exothermal or the endothermal peak maxima should be evaluated. Since the peaks undoubtedly have an exothermal appearance at low heating rates and at low pressures, the temperatures of the exothermal summits were selected, even when several peaks were present in the range of fuel deposition. Sometimes it was difficult to coordinate the corresponding temperatures of the peaks at alternating heating rates, so each of the reciprocal Kelvin temperatures of adjoining peak maxima were 

The dependence of peak maximum temperatures on pressure is non-uniform as Table 4-198 shows. The peak maximum temperatures decrease due to increasing pressures for n-hexacontane, n-hexylpyrene, and asphaltenes, which indicates that oxidation predominates. For the vacuum residue and the dispersion medium the peak maximum temperatures increase as consequence of increasing pressure, which indicates that pyrolysis predominates. 

The plots of activation energy E and frequency factor log A versus pressure P are given in Fig. 4-172 and 4-173. The half life times at equal temperatures of n-hexacontane, n-hexylpyrene, and asphaltenes decrease as a result of the increase of pressure. On the 

The vacuum residue alone supplies two pairs of Arrhenius coefficients at pressures from 1 bar to 20 bar in the range of fuel deposition (Fig. 4-176 and Fig. 4-177). The half life time exhibits a sharp increase caused by the pressure increase similar to the behavior of the activation energy and the frequency factor (Fig. 4-178). This behavior also indicates the predomination of the pyrolysis reaction. 

DSC Oxidation in Air, Fuel Deposition Range Activation Energy E versus Pressure P Second Value for Vacuum Residue 

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Fig. 3-47 and Fig. 3-48 represent the behavior of n-hexacontane during the tests at 1 bar and 10 bar air pressure. The endothermic fusion peak at approximately 100 °C is not influenced by the increase of pressure. On the other hand, the exothermic oxidation peaks were shifted to lower temperatures. The first peak (low-temperature oxidation LTO) moves from 241 °C at 1 bar to 221 °C at 10 bar. In the range of fuel deposition, the peak at 334 "C (1 bai) disappears almost completely and may be recognized only in the shoulder of the LTO peak at 300 °C (10 bar). Also, the sharp peak present at 407 °C (1 bar) disappears. 

In tests on the higher boiling members of the homologous series of n-alkanes from n-triacontane up to n-hexacontane, two strong peaks are found which are easy to evaluate. These peaks are the LTO peak and the peak in the fuel combustion range. In the range of fuel deposition more than one peak appears. Evaluation of the numerous small peaks is problematic and rarely valuable. Evaluation is normally limited to one or two well-defined peaks. The peak temperatures of eight n-alkanes... 

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). 

The recovery of vanadium from these slags is of commercial interest because of the depletion of easily accessible ores and the comparatively low concentrations (ranging from less than 100 ppm to 500 ppm) of vanadium in natural deposits (147,148). In the LILCO appHcations the total ash contained up to 36% 20 (147). Vanadium is of value in the manufacture of high strength steels and specialized titanium alloys used in the aerospace industry (148,149). Magnesium vanadates allow the recovery of vanadium as a significant by-product of fuel use by electric utiUties (see Recycling, nonferrous LffiTALS). 

The first commercial supersonic transport, the Concorde, operates on Jet A1 kerosene but produces unacceptable noise and exhaust emissions. Moreover, it is limited in capacity to 100 passengers and to about 3000 miles in range. At supersonic speed of Mach 2, the surfaces of the aircraft are heated by ram air. These surfaces can raise the temperature of fuel held in the tanks to 80 °C. Since fuel is the coolant for airframe and engine subsystems, fuel to the engine can reach 150°C (26). An HSCT operated at Mach 3 would place much greater thermal stress on fuel. To minimize the formation of thermal oxidation deposits, it is likely that fuel deflvered to the HSCT would have to be deoxygenated. 

Apart from the direct corrosive action of the gaseous products from burnt fuels, an important effect frequently arises from the deposition of ashes on the metal surfaces involved. Ashes normally consist of complex mixtures or compounds of oxides, the compositions varying very widely and the precise state of combination being uncertain. Ranges of ash compositions reported for different samples of fuels of three broad classes are given in Table 7.2 (see... 

Using a "home made" aneroid calorimeter, we have measured rates of production of heat and thence rates of oxidation of Athabasca bitumen under nearly isothermal conditions in the temperature range 155-320°C. Results of these kinetic measurements, supported by chemical analyses, mass balances, and fuel-energy relationships, indicate that there are two principal classes of oxidation reactions in the specified temperature region. At temperatures much lc er than 285°C, the principal reactions of oxygen with Athabasca bitumen lead to deposition of "fuel" or coke. At temperatures much higher than 285°C, the principal oxidation reactions lead to formation of carbon oxides and water. We have fitted an overall mathematical model (related to the factorial design of the experiments) to the kinetic results, and have also developed a "two reaction chemical model". 

A wide range of fhese materials has been investigated for fuel cell use, usually as supports for PfRu particles for DMFC testing (presumably due to the ease of experimenfafion). The fheoretically inerf surfaces of CNTs pose some difficulties for mefal cluster deposition because no sites exist for deposition or stabilization. Therefore, clusters fend to be deposited onto defecf and amorphous portions of samples (see Figure 1.18). 

Saha et al. [109] have proposed an improved ion deposition methodology based on a dual ion-beam assisted deposition (dual IBAD) method. Dual IBAD combines physical vapor deposition (PVD) with ion-beam bombardment. The unique feature of dual IBAD is that the ion bombardment can impart substantial energy to the coating and coating/substrate interface, which could be employed to control film properties such as uniformity, density, and morphology. Using the dual lABD method, an ultralow, pure Ft-based catalyst layer (0.04-0.12 mg Ft/cm ) can be prepared on the surface of a GDL substrate, with film thicknesses in the range of 250-750 A. The main drawback is that the fuel cell performance of such a CL is much lower than that of conventional ink-based catalyst layers. Further improvement... 

There are few reported analyses of the thermodynamics of carbon deposition in the ATR of liquid fuels. Though typically not stated in these analyses, the calculations were presumably carried out using the thermodynamic properties of elemental carbon e.g., as formed in reactions (6)-(8) above), rather than any coke species (which consist of a wide range of polynuclear aromatic compounds with quite different thermodynamic properties). This is an important difference, since the results apply only to elemental carbon, not coke deposition in general. 

To avoid excessive fragmentation of the feed, which could result in the formation of unsaturated hydrocarbons and carbon deposits on the catalyst, feed preheat temperatures for liquid fuels range from ambient to just above their boiling point. Reaction temperatures are typically in the range of 700 to 900°C. If organic sulfur is present in the feed, then the reactor is typically operated at higher temperatures, where metal sulfides are less stable. The O2 in... 

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