Chemical effects of CO2 addition to oxidizer and fuel streams on flame structure in H2-O2 counterflow diffusion flames

Abstract

SUMMARYNumerical simulation of CO 2 addition effects to fuel and oxidizer streams on flame structure has been conducted with detailed chemistry in H 2 -O 2 diffusion flames of a counterflow configuration. An artificial species, which displaces added CO 2 in the fuel-and oxidizer-sides and has the same thermochemical, transport, and radiation properties to that of added CO 2 , is introduced to extract pure chemical effects in flame structure. Chemical effects due to thermal dissociation of added CO 2 causes the reduction flame temperature in addition to some thermal effects. The reason why flame temperature due to chemical effects is larger in cases of CO 2 addition to oxidizer stream is well explained though a defined characteristic strain rate. The produced CO is responsible for the reaction, CO 2 +H=CO+OH and takes its origin from chemical effects due to thermal dissociation. It is also found that the behavior of produced CO mole fraction is closely related to added CO 2 mole fraction, maximum H mole fraction and its position, and maximum flame temperature and its position.

Evaluation of chemical effects of added CO2 according flame location

“…The study of Feese and Turns might pass over the fact that the strain rate varied while they maintaining the fixed nozzle exit velocities or the fixed mass fluxes. The explanation with a characterized strain rate (Park et al, 2003b) might ignore the difference in fuel-and oxidizer-side boundary conditions; that with flame location (Park et al, 2003c) described NO emission behaviour well with the propriety of flow residence time according to the distance from the stagnation point to the flame location, even if it is not a basic answer. This may imply that even chemical reaction effects should also be affected by relative flame location to the stagnation point.…”

Hydrogen utilization as a fuel: hydrogen-blending effects in flame structure and NO emission behaviour of CH4–air flame

“…showing a well-known C-curve. The decrease of maximum flame temperature at low global strain rates is due to flame radiation (Park et al, 2003;2005;Ju et al, 1997). It is also shown that the global strain rate at the maximum of maximum flame temperature shifts to lower one as X CH 4 decreases.…”

“…The increase of the forward reaction rate is relevant to the remarkable formation of H atom, despite of the decrease of methane mole fraction. It has been also well known that the populations of the chain carrier radicals (H, O, and OH) increase with the increase of strain rate (Park et al, 2003). Figure 5 shows the variation of maximum (a) CO and (b) CO 2 mole fractions with global strain rate for various blended fuels with hydrogen and methane.…”

Comparative study of flame structures and NOx emission characteristics in fuel injection recirculation and fuel gas recirculation combustion system

“…Subsequently the existence of hydrocarbon products inhibits chain branching since the rate of the major chain branching reaction, H+O 2 =O+OH, is much less than the rate of reaction between H atoms and hydrocarbons, so that the major chain branching reaction, H+O 2 =O+OH, is prohibited. Recent researches on the chemical effects of carbon dioxide addition to both the fuel-and the oxidizer-sides of a diffusion flame (Liu et al, 2001;Park et al, 2003) displayed that the reaction CO 2 +H->CO+OH was found to be the major starting point of the chemical effects of added CO 2 , and the chemical effects of added CO 2 were also seen to suppress NO x formation. Park et al, (2003) also recognized that the reason why flame temperatures with CO 2 addition to the fuel-side were lower compared with those with CO 2 addition to the oxidizer-side was closely associated with a characterized strain rate, and the chemical effects were much more prevailing with CO 2 addition to the oxidizer-side.…”