الفهرس 
chapter 1 : SPRAY charACTERISTICS OF EFFERVESCENT ATOMIZEROnly 14 pages are availabe for public view
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Abstract
Liquid atomization is a process of great importance in many medical, environmental, and industrial applications. Nowadays, liquid hydrocarbon fuels contribute by a great amount to the energy production field, due to the ease and flexibility of transporting. However, liquid fuels cannot be used in their bulky form. In most combustion applications, the liquid fuel is mixed with the oxidizer and burned in the form of sprays of small size droplets. This form of combustion is relevant to a variety of the fuel systems in different combustion applications. For developing these systems, the understanding of the basic of physical processes related to the spray combustion is necessary for increasing energy production and reducing emission pollution of liquid fuel combustion. Therefore, great efforts are required to investigate, develop, and then control the combustion processes.
In the present study, the spray and combustion characteristics produced by an effervescent atomizer was experimentally investigated at different geometrical and operating conditions for achieving good fuel atomization with high combustion efficiency. These goals are achieved by employing variables geometry effervescent atomizer. The experimental work investigates spray characteristics (Cold study) and combustion characteristics (Hot study). The spray cone angle and liquid mass distribution throughout the spray cone were investigated in cold study. Furthermore, an empirical correlation of the cone angle with operating and design parameters has been developed. While, the hot study focuses on the combustion process, flame length, temperature distribution, cooling water heat flux, combustion stability and combustion efficiency. A test rig was designed and built up to study the combustion of a light diesel fuel in an experimental horizontal cylindrical furnace cooled by a water jacket.
The investigation showed the influence of the operating and design parameters on the spray and combustion characteristics. In present study, the gas to liquid mass ratio (GLR) varies from 0.3% to 15%, the liquid mass flow rate varies from 0.5 to 10 g/s and the injection pressure varies from 0.5 to 6 bar. The results show that spray cone angles lie in the range of 15-22º for all studied GLR, length to diameter ratios and injection pressures. In the bubbly flow regime, increasing of GLR until 2 % increases the spray cone angle. Furthermore, increasing of GLR changes the flow regime into annular flow. Therefore, the momentum of drops increases in axial direction more than
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the redial one and spray cone angle decreases. While, the increasing of the injection pressure and exit orifice diameter increases the spray cone angle at the different flow regimes. On the other hand, the liquid mass distribution affects local air to fuel ratio in the flame. The liquid mass percentage increases with increasing radial distance until the half distance between the spray axis and the outer edge of the spray. After the main peak, liquid mass percentage decreasing making the tailing. The main peak becomes lower and moves to the outer edge of the spray at higher gas to liquid ratio, large exit orifice, and small injection pressure. While, the mass flux decreases with increasing radial distance; as a result of decreasing the liquid DROP velocity away from spray axis.
The combustion stability of this type of atomizer is more sensitive to the injection pressure and exit orifice diameter, where the flammability zone increases with increasing injection pressure and exit orifice diameter. The increasing of injection pressure, GLR, and air to fuel ratio decreasing the flame length and providing high combustion efficiency. The flame temperature profile in all cases starts with a low temperature and then increases to the peak value then decreases with moving downstream from the burner tip. The maximum temperature of the flame is lies in the range of 15% to 20 % relative to furnace length. The maximum temperature moves to burner tip with increasing A/F ratio, GLR, and injection pressure. There is a good agreement between the temperature distribution in the furnace and the distribution of cooling water heat flux. The increasing of gas to liquid ratio (GLR), exit orifice dimeter, and air to fuel ratio (A/F) decreases the stack temperature.
The combustion efficiency increases at higher air to fuel ratios. At (A/F) ratio higher than 30 the combustion efficiency is over 90%. The increasing of injection pressure provides spray with fine drops and higher evaporating rate. Therefore, the increasing injection pressure from 0.5 to 2 bar increases combustion efficiency. The combustion efficiency at injection pressure 1 bar and A/F ratio 40 is higher than 95%.