الفهرس 
TEST RIG AND EXEPRIMENTAL WORKOnly 14 pages are availabe for public view
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Abstract
The present work concerned with microstructure and macrostructure of the inverse diffusion flames produced by different design parameters and aerodynamic variables. An experimental study was devoted to enhance the combustion performance and heat transfer rates from inverse diffusion flames as stabilized on a burner that has a central air jet surrounded by an array of fuel jets. The investigation was performed to explore the effects of changing the inlet air port and the fuel ports’ geometry on the flame thermal structure and the exhaust emissions. In this regard, the features of the circumferentially arranged ports (CAP) were examined where a wide range of velocity and momentum flux ratios was included. Five inverse diffusion flame burners with different air jet ports (of diameters namely 4, 6, and 8 mm) were tested. The 4 mm jet diameter burner was designed with two different center to center distances of 12 and 15 mm. A case was used with circumferentially distributed air ports. Such arrangement of the air ports highlighted the influence of increasing the number of the air ports on the resultant flame features. The fuel flow rate was kept constant while the air flow rate was varied to cover a wide range of the central air Reynolds numbers with a corresponding range of the primary equivalence ratio.
The experiments carried out were divided into four phases. The first part concerned with the experimental determination of the stability limits of each burner. The second part concerned with the investigation of the visual characteristics of the inverse diffusion flames, the illumination of the different reaction zones in addition to the indication of the flame height. The third part concerned with the investigation of the flame structure, including the flame temperature distribution and the exhaust species concentration. The final part dealt with measuring the heat flux during the flame impingement.The results showed that the burner of the smaller dair produced stable bluish flame in wide ranges of Reair and p due to the turbulence induced in the flame neck and the stronger entrainment of the surrounding air in the post-flame region. The smaller dair also produced higher Tf in excess of 1700oC. An enhancement occurred with using the new design of distributed air ports. The centerline flame temperature and the heat flux variation increased. A reduction in the pollutant emissions was obtained. The mixing zone was characterized by the rapid change of the concentrations and the rapid increase in Tf. The CO was efficiently converted into CO2 in the post-flame reaction zone in the presence of the entrained air. The smaller dair reduced the NOx emissions due to the role of turbulence and the suppression of the prompt NOx formation. Concerning the flame impingement onto a flat plate, using smaller air diameters and a number of air jets produced higher levels of heat flux, where the combustion was more efficient than that of the port normal design. As the fuel lean mixture conditions were approached, the flame heat flux variation at any flame height decreases with increasing the air jet Reynolds number Reair. Upon decreasing the center to center distance, the centerline temperature showed higher temperatures. Smaller air diameters in the distributed air ports’ design were associated with higher peak flame temperatures and wider ranges of flame stability.
Increasing the air jet Reynolds number by 30% increased the peak flame temperature by 8.3%. In the primary equivalence ratio range between 0.8 and 2.0, the impingement plate optimum spacing for the maximum heat flux was found to correlate well with Reynolds number. The flame color changed from bluish to yellowish upon switching from the burners of smaller diameters to the burners of larger diameters. The same qualitative features were obtained as the number of the fuel ports increased. The results proved that the nature of the flames issuing from the distributed jets’ burners involving inverse diffusion flames is determined by the combined effect of the burner geometry and the jet aerodynamics. The air Reynolds number and the primary equivalence ratio, p, may be used to describe the performance of a particular burner of invariable geometric parameters. In addition, the burner performance under any conditions of air Reynolds number and primary equivalence ratio cannot be used to predict the performance of another burner unless the conditions of geometric and dynamic similarities are satisfied.