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Flame Parameters literature review (O2 concertation), affect of carbon…
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affect of carbon source , temperature , H2,N2 & CO
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The temperature effect on CNT growth was studied by measuring Si-substrate surface temperature and temperature profiles along the luminous sheet of co-flow flame and along the counter-flow axis. The measurements show that for CNT to grow, temperature in synthesis region must be within an appropriate range, region must be within an appropriate range, almost the same as that in CVD synthesis
there is a common temperature range (1023–1073 K) for both CVD and flame synthesis within which CNTs could be synthesized
numerical simulation was done on Counter-flow diffusion flame using mixture of CH4 + 33% N2 as a fuel in the off-symmetric configuration at the air-side strain rate of 53.5 s^-1
possible carbon sources which contribute to CNT growth under the current experimental conditions are the major species CO and those intermediate species, C2H2, C2H4, C2H6, and methyl radical CH3. Some studies suggest that species H2, CO2 and H2O present in the synthesis region may activate the catalyst and help the catalyst reaction
Although ethyl radical C2H5 and formyl radical HCO are active radicals for chemical reactions, they do not appear in the synthesis region so they are not carbon sources for CNT formation. It is possible that high-molecular hydrocarbons such as C6 species may also be carbon sources
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The soot formation is inhibited when CO, H2 or N2 is individually added into ethylene flame. The addition of N2 is the most effective in reducing soot production.
With the increasing addition fraction of CO/N2 in ethylene flame, the mean primary particle diameter decreases. However, with the addition of 20% H2, the mean primary particle diameter is approximately the same as the pure ethylene flame at 30 mm HAB and even much greater at 40 mm HAB, demonstrating the soot in H2 enriched ethylene flame has high oxidation resistance.
The morphological analysis suggests that with the addition of CO, the fractal dimension of the aggregates decreases slightly in the middle and upper flame, though the fractal pre-factor increases slightly. Besides, the fractal parameters show reduction tendency with the increasing proportion of CO.
The analysis on soot nanostructure indicates the elongation in fringe length, diminution in fringe tortuosity and inter-fringe spacing with the addition of CO/H2 while opposite behavior is observed for the flame with N2 addition. Furthermore, H2 addition yields more significant variation for these nanostructure parameters than CO addition does, which suggested the soot nanostructure is more graphitized in H2 enriched flame.
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The biogas composition was simulated by blending proper fractions of pure gases of CH4 and CO2. When a small stream of hydrogen was introduced into the flame, the stability is significantly enhanced, and the initial 5% hydrogen addition is more efficient in the stability enhancement than the other 5% hydrogen addition.
Direct comparison of the stability limits of the flames burning CH4–N2 and CH4–CO2 (biogas) shows a lower stability limit of the biogas flame, indicative of a more adverse effect of CO2 than N2 on flame stabilization.
Under identical volumetric flow rate, the CH4–CO2 flame has lower flame temperature and lesser soot emission than the CH4–N2 flame. In both cases, the flame temperature is increased by addition of hydrogen, and the visible flame height is reduced.
Analysis of the heat transfer data shows that the stagnation point heat transfer is increased by hydrogen addition because there is higher flame temperature at higher level of hydrogen addition. While the total heat transfer is impaired because hydrogen has lower energy content per unit volume of fuel in comparison to the biogas substituted.