| Summary: | 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..
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