An Experimental Study Of Multiple Jet Mixing

Author : Mohamed Boutazakhti
Publisher : Library and Archives Canada = Bibliothèque et Archives Canada
ISBN 13 : 9780612944237
Total Pages : 304 pages
Book Rating : 4.9/5 (442 download)

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Download or read book Experimental Study of the Flow Downstream of a 3 X 3 Square Matrix of Swirling Droplet Laden Air Jets [microform] written by Mohamed Boutazakhti and published by Library and Archives Canada = Bibliothèque et Archives Canada. This book was released on 2004 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to the small fuel and air channels of the nozzle used, seeding the airflow with solid particles to perform PIV experiments was not an option. Instead liquid was injected in the air stream and a MATLAB routine was developed to identify the size of the seeding drops and filter out those that were larger than 3 x 3 pixels. The key to reducing combustion emissions such as nitrogen oxides (NOx) and carbon monoxide (CO) is fast and thorough mixing of fuel and air. The aim of multi-point lean direct injection (LDI) technique is to improve mixing and atomization by injecting fuel in small amounts through multiple injection ports. Multiple small injectors are used instead of a main injector introducing fuel and air streams in the combustion chamber. Various combustion studies reported in the literature showed that multi-point lean direct injection (LDI) nozzles had lower emissions compared to other ordinary nozzles. Besides these overall combustion performance studies there are no detailed investigations of the nozzle flow and the role of mixing and atomization in achieving the low emission performance. The objectives of this study were: (1) Characterize turbulence and spray fields; and (2) Investigate the effect of lateral jet interaction on spray quality and mixing. This work is an experimental investigation of the flow downstream of a multi-point LDI nozzle. The nozzle is a 3 x 3 square matrix of 9 small swirling air jets with fuel inject at the center of each jet. The design swirl number was 0.8 and the Reynolds number of the flow was 40 000. The experiments were conducted under non-burning conditions at atmospheric conditions. Particle image velocimetry (PIV) and Phase Doppler particle anemometry (PDPA) were used to map the velocity and spray properties. The investigation covered the region within the first 18 jet diameters downstream of the nozzle exit plane. The results showed that: (1) Lateral jet interaction slows the spreading rate of the jets and improves turbulence, thus mixing. The improved turbulence is due mostly to the opposing direction of the tangential component; (2) Increased spray number density and droplets relative velocity in the matrix favors coalescence; (3) Although smaller injectors achieve better atomization than ordinary nozzles, jet-jet interaction occurring when matrices of small jets are used offsets this gain in atomization quality; and (4) Results suggest that the emission reduction is due to improved mixing.