Fuel performance characteristics

Desired burner fuel performance characteristics and fuel properties which affect performance are provided in TABLE 3-17. 

Validation and Application. VaUdated CFD examples are emerging (30) as are examples of limitations and misappHcations (31). ReaUsm depends on the adequacy of the physical and chemical representations, the scale of resolution for the appHcation, numerical accuracy of the solution algorithms, and skills appHed in execution. Data are available on performance characteristics of industrial furnaces and gas turbines systems operating with turbulent diffusion flames have been studied for simple two-dimensional geometries and selected conditions (32). Turbulent diffusion flames are produced when fuel and air are injected separately into the reactor. Second-order and infinitely fast reactions coupled with mixing have been analyzed with the k—Z model to describe the macromixing process. 

Table 9 lists the chief performance characteristics of the most important delay compns. In general, the bum time is controlled within the stated limits by adjustment of the fuel fraction. Other variables are the particle size of the fuel and the presence of additives such as Pb chromate, silica and Viton. Many perchlorate containing mixts are friction and spark sensitive,... 

Figure 20. Performance characteristics of the International Fuel Cells 10-cell DMFC stack. (After Ref. 112 reproduced by permission of The Electrochemical Society, Inc.)...

Although several fuel cell technologies are reaching technical maturity, the economics of a fuel cell are not clear. The commercial potential of fuel cells will depend on the ability to reduce catalyst and other expensive materials costs and to manufacture the units at a competitive cost. Many uses of fuel cells place a premium on specific performance characteristics. The relatively simple alkaline fuel cells (AFC)... 

Figure 46. Performance characteristics of a cathode-supported thin film Ni—YSZ/YSZ/LSM fuel cell at 600 °C in humidified H2 and air with and without a dense protective yttria-doped ceria (YDC) protection layer introduced between the porous LSM cathode and the thin-film electrolyte. (Reprinted with permission from ref 296. Copyright 1997 Elsevier.)...

The performance of SOFCs with Cu—ceria—YSZ anodes has been tested with a wide variety of hydrocarbon fuels, and this has been documented elsewhere.With the exception of methane, which is known to be relatively unreactive in normal heterogeneous reactions as well, all of the hydrocarbons we examined appear to give similar performance characteristics. The fuels that were tested include /2-butane, /2-decane, toluene, and a synthetic diesel. The main difference observed between the various fuels is that some fuels tend to form tars more readily via gas-phase free-radical chemistry. Otherwise, with the exception of CH4, all hydrocarbons that were investigated showed similar power densities. This is shown in Figure 20, which displays the voltage and current densities for /2-decane, toluene, and synthetic diesel as a function of time. In this case, the hydrocarbon fuels were diluted in dry N2 to a concentration of 40 wt % hydrocarbon to prevent condensation of unreacted fuels that leave the cell. (In our studies, the active area for the fuel cell is typically 0.5 cm, and a current density of 1 A/cm would require a flow... 

It is unique because of its powerful hydrogen bonding character and its distinct polarity. However, in fuel systems, these characteristics of water make it a source of a variety of problems. Corrosion of metal fuel system components, emulsification with fuel performance additives, and ice formation in fuel lines are some of the problems directly related to the presence of water in fuel. 

One of the easiest ways to determine the character and sometimes the quality of a fuel is to examine the distillation profile. Certain characteristics of fuel performance and potential fuel problems can be determined from the distillation profile of the fuel. Some important and known examples are provided as follows ... 

The CFPP was developed in 1965-66 to predict the low-temperature filterability performance of diesel fuels. This method is commonly used throughout the world to quickly determine low-temperature fuel filterability characteristics. In more recent... 

To keep pace with advances and changes in the fuel industry, a new chapter has been added. The chapter is titled Synthetic and Alternative Fuels. Contained within this chapter is a review of information about the processing, properties, and performance of synthetic and alternative fuels. Pertinent background information is presented to account for the tremendous amount of work that led to the development of the present-day synthetic and alternative fuel industry. A brief summary of the handling and performance characteristics associated with various alternative fuels provides useful information about the fuels, their strengths, and their shortcomings. 

Primary zone size is important with regard to efficiency and limits also. Within practical limits, a larger primary zone cross-sectional area will provide the best performance 138). Possible reasons arc lower velocities, less wall impingement by fuel, larger zone of low velocity, and less wall quenching of chemical reactions. The best axial distribution of open area of a combustor will depend on required operating conditions, the pressure loss characteristics, and the shape of the air entry ports. It will also depend on fuel-injection and fuel-volatility characteristics, as these factors will affect the amount of vapor fuel present at any location. If proper burning environment is to be obtained, these factors must be matched, and compromises in performance must be expected. 

McCafferty, R. J., Effect of Fuels and Fuel-Nozzle Characteristics on Performance of... 

Besides limits on physical and chemical properties, fuel specifications include tests that evaluate the performance characteristics of a fuel. For example, there are tests to assess the corrosivity of fuels on fuel system materials and performance tests to evaluate vapor pressure, octane number, cetane number, and others. In many cases, additives are used to assist fuels in satisfying the performance test portions of fuel specifications. 

As shown in this review, test equipment integrated with several diagnostic techniques is preferred for a deeper insight into the mechanisms that cause performance losses and spatial non-uniform distribution. As a consequence, more information, which is simultaneously obtained with these diagnostic tools, will strongly support development of empirical models or validate theoretical models predicting performance as a function of operating conditions and fuel cell characteristic properties. 

Figure 3.3.7 Theoretical (dashed dotted) and real (solid) cell voltage (V) - current density (I) performance characteristics of a fuel cell. Overpotentials are responsible for the difference between theoretical and real performance and cause efficiency losses. They split into (i) activation polarization overpotentials at anode and cathode due to slow chemical kinetics, (ii) ohmic polarization overpotential due to ohmic voltage losses along the circuit, and (iii) concentration polarization overpotentials due to mass-transport limitations. The activation overpotentials of the cathode are typically the largest contribution to the total overvoltage.

Damin, B., Faure, A., Denis, J., Sillion, B., Claudy, P., and Letoffe, J. M. 1986. New Additives for Diesel Fuels Cloud-Point Depressants, in Diesel Fuels Performance and Characteristics. In SAE Spec. Publ. SP-675 (Diesel Fuels Performance and Characteristics). Warrendale PA Society of Automotive Engineers (Paper No. 861527). 

---