الفهرس 
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Abstract
An experimental study was carried out, to investigate the combustion performance of
inverse diffusion flames, with elliptic double swirlers and cross flow. A set of six
double swirlers were used, to study the effect of the swirl relative direction mode (co
swirl and counter swirl), the primary and secondary swirl angles, and aspect ratio of
elliptic swirl, on combustion characteristics of commercial LPG inverse diffusion
flames. All test runs and measurements were conducted at the same firing conditions,
regarding air and fuel flow rates. It was found that counter swirl mode enhances the
combustion process more than co swirl mode, which is presented in the form of a
reduction in flame length by about 10%, a decrease in exhaust gases emissions in the
level of 19% for CO, 32% for UHC and 3% in the case of NOx emissions. As a result,
the combustion efficiency in the case of counter swirl mode is higher than that in co
swirl mode (94.8% for counter swirl flame against 92.2% for the co swirl flame). It
is also highlighted that heat transfer to the walls is enhanced by the counter mode.
Increasing the secondary (outer) swirl angle from 30° to 45°, while reducing the
primary angle to 30°, results in a considerable enhancement in the combustion
performance. The flame length is reduced by 7%, a decrease of about 16% in CO
levels, 12% in UHC levels, and 11% in case of NOx emissions is observed. The
combustion efficiency is reported to increase from 91.2% to 92.2%. This indicates
that intensifying the secondary swirl angle for large scale swirled inverse diffusion
flames with intensive cross flow is of favorable effect.
Using elliptic profile swirlers enhances the combustion characteristics. A circular
swirler (aspect ratio =1) was compared with three elliptic swirlers of 1.25, 1.4 and 1.5
aspect ratios. It was found that generally the use of elliptic swirlers leads to a shorter
flame length, higher flame temperature levels in the case of 1.5 aspect ratio swirler,
and reduced emissions. In the present work, the 1.25 aspect ratio swirler represented
an optimum value of aspect ratios, as the flame length is decreased by 30%, and a
decrease of emissions in the level of 62% for UHC, and 24% for NOx emissions is
reported; when compared to the circular base swirler. However, the 1.4 aspect ratio
swirler achieved the lowest CO emissions with a decrease in the level of 53% when
compared to the circular base swirler. The 1.25 aspect ratio swirler flame achieves
the highest combustion efficiency among the group of the tested swirlers with a value
of 95.2%. The 1.4 aspect ratio swirler comes in the second place with a combustion
efficiency of 92.2%, followed by the 1.5 aspect ratio swirler flame that achieved
89.5%; and finally the circular swirler with an 87.6% combustion efficiency. The 1.5
aspect ratio swirler indicated the highest flame temperature among the group of
studied swirlers.