Combustion problems

Fuel Additives Control Preburner and Fireside Combustion Problems. Betz Bulletin 713, Copyright 1974, Betz Laboratories, Inc. 

The initial process for molecular conversion was thermal reforming (late 1920s). Thermal reforming at 950 - 1050 F and 600 psi produced gasolines of 70 to 80 octane and heavy naphthas less than 40 octane. Products were olefins, diolefins, and aromatic compounds that were unstable in storage and tended to form heavy polymers and gums, which caused combustion problems. 

In processes involving the combustion of fuels, either pure oxygen or air is supplied in amounts greater than the stoichiometric requirements for complete combustion. The terms "theoretical air or theoretical oxygen are thus frequently encountered in combustion problems. The molar composition of dry air at atmospheric conditions [from International Critical Tables, Volume 1, p. 393 (1926)] ... 

Al. Adams, G. K., et at., Selected Combustion Problems Fundamentals and Aeronautical Applications, p. 277. Butterworths, London, 1954. 

Gl. Geckier, R. D., AGARD Selected Combustion Problems, p. 289. Butterworths, London, 1954. 

This is a general form of the energy equation for a control volume useful in combustion problems. The terms can be literally expressed as... 

As briefly discussed in Section 1.2, chemical-reaction engineers recognized early on the need to predict the influence of reactant segregation on the yield of complex reactions. Indeed, the competitive-consecutive and parallel reaction systems analyzed in the previous section have been studied experimentally by numerous research groups (Baldyga and Bourne 1999). However, unlike the mechanical-engineering community, who mainly focused on the fluid-dynamics approach to combustion problems, chemical-reaction... 

In combustion problems, one is interested in the rate of energy conversion or utilization. Thus it is more convenient to deal with the fractional change of a particular substance rather than the absolute concentration. If (M) is used to denote the concentrations in a chemical reacting system of arbitrary order n, the rate expression is... 

In order to obtain the solution desired, a value of Ts is assumed, the vapor pressure of A is determined from tables, and mAs is calculated from Eq. (6.98). This value of mAs and the assumed value of Ts are inserted in Eq. (6.97). If this equation is satisfied, the correct Ts is chosen. If not, one must reiterate. When the correct value of Ts and mAs are found, BT or BM are determined for the given initial conditions Tx or mAco. For fuel combustion problems, mAcc is usually zero however, for evaporation, say of water, there is humidity in the atmosphere and this humidity must be represented as mAco. Once BT and BM are determined, the mass evaporation rate is determined from Eq. (6.87) for a fixed droplet size. It is, of course, much preferable to know the evaporation coefficient (5 from which the total evaporation time can be determined. Once B is known, the evaporation coefficient can be determined readily, as will be shown later. 

Fineman, S., Some Analytical Considerations of the Hybrid Rocket Combustion Problem, M. S. E. Thesis, Department of Aeronautical Engineering, Princeton University, Princeton,... 

Demirbas, A. 2005a. Potential applieations of renewable energy sources, biomass combustion problems in boiler power systems and eombustion related environmental issues. Progress Energy Combus Sei 31 171-192. 

Wright, F. H., and E. E. Zukoski. 1962. Flame holding Selected engine combustion problems. 8th Symposium (International) on Combustion Proceedings. Baltimore The Williams and Wilkins Co. 933. 

The use of feedback-control techniques to modulate combustion processes in propulsion systems has recently received extensive attention [1-3]. Most of the previous studies involved direct implementation of existing control methods designed for mechanical devices, with very limited effort devoted to the treatment of model and parametric uncertainties commonly associated with practical combustion problems. It is well established that the intrinsic coupling between flow oscillations and transient combustion responses prohibits detailed and precise modeling of the various phenomena in a combustion chamber, and, as such, the model may not accommodate all the essential processes involved due to the physical assumptions and mathematical approximations employed. The present effort attempts to develop a robust feedback controller for suppressing combustion instabilities in propulsion systems. Special attention is given to the treatment of model uncertainties. Various issues related to plant... 

While the control schemes summarized in Table 22.1 have been employed in various combustion problems with some success, direct implementation of these... 

The chemical structure of a polymer can be analysed by many of the techniques used to characterise molecular species (see Chapter 3). Multinuclear NMR, IR and UV-visible spectroscopy, for example, are widely used key characterisation tools. Most polymers will dissolve in at least some readily available solvents (although the rate of dissolution may be slow due to chain entanglement effects). In cases where polymers are insoluble, solid-state NMR techniques can be used to provide excellent structural characterisation. Due to structural imperfections, unknown end groups and incomplete combustion problems as a result of ceramic formation (Section 8.2.5), elemental analysis data obtained by... 

Injector design determines the physicochemical processes occurring in liquid propellant rocket engines. A complete quantitative description of the processes in liquid rockets is impossible because of our limited understanding of chemical reaction mechanisms and rates. The use of similarity principles simplifies the solution of theoretical combustion problems and is described for channel flow with chemical reactions and for diffusion flames over liquid droplets involving two coupled reaction steps. We find the new result that the observed burning rate of a liquid droplet is substantially independent of the relative rates of the coupled reactions. 

Von Karman, Th., Penner, S. S., Selected Combustion Problems, Funda-... 

The relative stabilities of cycloalkanes can be determined by comparing their AH s of combustion (Problem 4.39) on a per-CH2-unit basis. Rings have different AH s of combustion per CH, unit because they have different amounts of ring strain. 

Kumar, R.N., and Stand, L.D. (1975) Combustion problems of nitramine propellants. Proc. 13th Aero. Sci. Meeting, AIAA, Pasadena, 1975. 

Contrary to the experimental techniques discussed above, spatial transport is important in flames. However, the laminar flame presents fewer difficulties than most other spatially varying combustion problems, because the relevant transport parameters are fairly well defined [427], Heat transport takes place primarily by thermal conduction, while transport of chemical species is dominated by molecular diffusion. 

Selected Combustion Problems, Fundamentals and Aeronautical Applicatioi s, AGARD... 

Spalding, D. B., Selected Combustion Problems, AGARD, pp. 340-51, Butterworths... 

Barrere, M., Mestre, A., Selected Combustion Problems—Fundamentals and Aero-... 

Scurlock, A. C., Grover, J. H., Selected Combustion Problems—Fundamentals and... 

The number and variety of fuel combustion problems that are still unsolved suggest that many different fuel additives may still come into use. Petroleum refiners will thereby be able to continue to employ a two-pronged attack when improving their products first, the development of improved refining processes, and second, the use of chemical additives. 

The established correlations and laws of atomization and evaporation are directly applicable to the various combustion problems of ignition delay, performance, stability limits, and design. 

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