Spray combustion processes

Figure 1.1. Schematic of spray combustion process (a) annular combustion chamber in a single spool turbojet with an axial flow compressor (b) fuel injection and droplet formation in combustion chamber.

Oince the earliest theoretical models by Spalding (I) and Godsave (2) describing the quasi-steady, spherically symmetric combustion of individual fuel droplets in quiescent atmospheres, numerous more elaborate theories have been proposed to provide a better understanding of droplet spray combustion. These theories are based on the premise that the physical and chemical processes involved dmmg single-droplet combustion are fundamental to complex spray combustion processes. 

It is therefore evident that a detailed experimental analysis of the spray flame is necessary for its theoretical characterization. The aerodynamic changes achieved within the modulated swirl combustor, in which it is demonstrated that blue flame combustion of oil can be achieved using this combustor and a Sonicore atomizing nozzle, clearly show the strong effect of flow aerodynamics upon the spray combustion process. 

This is a more advanced partial combustion process. The feed is first preheated and then combusted in the reactor with a limited amount of air. The hot gases containing carbon particles from the reactor are quenched with a water spray and then further cooled by heat exchange with the air used for the partial combustion. The type of black produced depends on the feed type and the furnace temperature. The average particle diameter of the blacks from the oil furnace process ranges between 200-500 A, while it ranges between 400-700 A from the gas furnace process. Figure 4-4 shows the oil furnace black process. 

Figure 1.6. Size ranges of droplets/particles found in nature and generated by atomization of normal liquids and melts in aerosol spray, spray combustion, powder production, and spray forming processes.

Emphasis is placed on the atomization processes used in spray combustion and spray drying from which many atomization processes have evolved. Advantages and limitations of the atomization systems are discussed along with typical ranges of operation conditions, design characteristics, and actual and potential applications. The physical properties of some normal liquids are listed in Table... 

In addition to the designs mentioned above, other atomizer configurations such as those used in spray combustion and spray drying processes may also be considered as an alternative in gas atomization of melts for special purposes after appropriate modifications. 

It should be noted that the dynamic conditions of droplet impact processes discussed above cover a large range of the actual conditions in many industrial processes, such as spray forming, thermal spray, spray combustion, spray cooling, and aircraft flight. Under these conditions, the spreading behavior of droplets on a flat surface is essentially governed by inertia and viscous effects (Fig. 

THE AMBIENT ATMOSPHERIC AEROSOL consists of liquid and solid particles that can persist for significant periods of time in air. Generally, most of the mass of the atmospheric aerosol consists of particles between 0.01 and 100 xm in diameter distributed around two size modes a coarse or mechanical mode centered around 10- to 20- xm particle diameter, and an accumulation mode centered around 0.2- to 0.8- xm particle diameter (1). The former is produced by mechanical processes, often natural in origin, and includes particles such as fine soils, sea spray, pollen, and other materials. Such particles are generated easily, but they also settle out rapidly because of deposition velocities of several centimeters per second. The accumulation mode is dominated by particles generated by combustion processes, industrial processes, and secondary particles created by gases converting to par-... 

Physical properties of the three test fuels are presented in Table I. Except for the surface tension of No. 6 fuel oil, which was a typical value, all properties were measured for the specific samples tested. The primary differences between the SRC-II middle distillate and the No. 2 fuel were the higher specific gravity, surface tension, and viscosity of the SRC-II. The No. 6 grade fuel, a residual fuel oil, had a much higher viscosity than either of the distillate fuels. Both the SRC-II and No. 2 fuel oil were sprayed at a nominal temperature of 80°F to simulate usage in a non-preheat combustion system. The No. 6 fuel oil was sprayed at temperatures ranging from 150° to 240°F in order to assess spray formation processes and spray quality over a broad range of viscosities. 

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