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|其他題名: ||A Study on Carbon Nano-Structures in Inverse Diffusion Flames of Mixed Fuels|
Inverse Diffusion Flame
|Issue Date: ||2010-03-06 18:09:48 (UTC+8)|
The formation and growth of carbon nano-structures including carbon nanotubes (CNTs) and carbon nanocapsules in inverse co-flowing diffusion flames of mixed fuel were experimentally studied. The influences of volumetric methane concentrations in ethylene/nitrogen mixture from the outer jet, sampling position and substrate (uncoated or coated with Ni(NO3)2-36.4% by weight) upon the yield of carbon nano-structures were particularly emphasized. The flame appearance, flame structure, and flame stability under the influences of inner/outer velocity ratios, volumetric oxygen concentrations in nitrogen of the inner jet and methane concentrations in ethylene/nitrogen mixture of the outer jet were firstly studied using image processing techniques. The results showed that increasing the injection velocity of oxygen/nitrogen mixture, the sooty zone becomes narrower, leading to an increase in the critical methane concentration require for the occurrence of yellow flame (sooty zone). However, raising oxygen concentration of inner jet or fuel (methane or ethylene) concentration of outer jet resulted in an increase in flame height and a wider range of sooty zone, and in turn a decrease in the critical fuel concentration required for the occurrence of yellow flame.
Thereafter, we employed a sampling Ni grid as the catalytic metal substrate for the carbon nano-structures growth. The sampler was mounted on a two-dimensional micro-positioner with the plane normal to the burner axis. The sampling time of the substrate inside the flame was kept at 120 sec. The SEM and TEM images showed that carbon nano-structures depositted on the substrates were mainly CNTs and carbon nanocapsule. Curved and entangled tubular multi-walled CNTs (MWCNTs) were harvested, which had both typical straight tubular and bamboo-like structures. Besides curved CNTs, carbon nanocapsules were also synthesized, inside which metal particles were encapsulated. It is of interest to note that only MWCNTs were generated when the mixture of 5% methane/5% ethylene/90% nitrogen and the mixture of 10% methane/5% ethylene/85% nitrogen were separately used as the fuel. Both the growth range and yield of CNTs of the former are smaller than those of the latter. However, carbon nanocapsules synthesized on Ni(NO3)2-coated substrates were found when the methane concentration of outer fuel jet was equal to 30% (i.e. 30% methane/5% ethylene/65% nitrogen). Furthermore, for the same sampling approach, the sampling positions on or near the flame front had a greater carbon nano-structures harvest than those far from the flame front. Using Ni(NO3)2-coated substrates had advantages over uncoated Ni(NO3)2 substrates, which can increase the range, quantity and length of carbon nano-structures.
|Appears in Collections:||[機械工程系所] 博碩士論文|
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