The Prediction of Flame Pattens by Droplet Ignition Model And Droplet Evaporation Model in A liquid-fueled Spray Combustor

• Main Authors: Yang, Li-Jia, 楊禮嘉
• Other Authors: Ma h.k.
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/18363255814550347149

碩士 === 國立臺灣大學 === 機械工程學系研究所 === 86 === This paper discussed the effects of inlet mean droplet size, Group combustion number (Gc), and fuel-air ratio on combustion efficiency and flame patterns in a liquid-fueled spray combustor through implementation of droplet ignition model (DIM) and droplet evaporation model (DEM). The predicted combustion modes indicate that fuel is consumed by the complementary processes of the three flame patterns which are droplet combustion, gas-phase combustion, and mixed gas/droplet-vaporizing combustion are significantly influenced by both spray angle, injected mean droplet size and Gc number. The numerical results show that small droplet spray is characterized by a diffusion flame separating the fuel and air, while large droplet spray yields intense mixed droplet and gas-phase combustion near the combustion wall. The optimum sized droplet spray for maximum combustion efficiency exists in a large spray angle and occurs at the transition between these three flame patterns. Two different combustion models, namely, DIM and DEM, were used in this study to predict combustion phenomena and compare differences between the two models given different F/A ratios and fuel droplet diameter. The numerical results show that given the same F/A ratio, the larger the fuel droplet diameter, the greater the difference between the two models. Besides, from numerical simulation we have done, we find out that, under fuel-lean condition, there are chance for more fuel droplets to ignite; however, DEM cannot simulate this. So we suggest using DIM to predict when fuel-lean. Except for fuel-lean, we use DEM which can decrease the code complexity. But, if we want to observe the flame patterns of combustion chamber, we can only use DIM..