Numerical study on effect of CO2 addition in flame structure and NOx formation of CH4-air counterflow diffusion flames

Abstract

SUMMARYNumerical study with detailed chemistry has been conducted to investigate the e!ect of CO addition on #ame structure and NO V formation in CH }air counter#ow di!usion #ame. Radiation e!ect is found to be dominant especially at low strain rates. The addition of CO makes radiation e!ect more remarkable even at high-strain rates. It is, as a result, seen that #ame structure is determined by the competition between the radiation and strain rate e!ects. The important role of CO addition is addressed to thermal and chemical reaction e!ects, which can be precisely speci"ed through the introduction of an imaginary species. Thermal e!ect contributes to the changes in #ame structure and NO formation mainly, but the e!ect of chemical reaction cannot be neglected. It is noted that #ame structure is changed considerably due to the addition of CO , in such a manner, that the path of methane oxidation prefers to take CH PCH PC H PC H instead of CH PCH PCH PCH.

Evaluation of chemical effects of added CO2 according flame location

“…One reason may be the reduction of flame temperature, which is absolutely associated with thermal NO, due to high heat capacities of recirculated major combustion products such as carbon dioxide and water vapour, while the high temperature of recirculated gases can cause an increase in NO x emission. It should be additionally, kept in mind that there exist chemical effects of recirculated major gases, thereby affecting flame structure and NO x emission behaviour considerably (Park et al, , 2002aLee et al, 2001;Liu et al, 2001;Kim et al, 2002). Because of these conflicting effects, it is difficult to optimize combustors for achieving best performance with minimum emissions.…”

NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar

“…This is con"rmed from the fact that the di!erence between the maximum #ame temperatures of cases with and without the radiation term decreases with increasing strain rate. This phenomena has been well known elsewhere (Maruta et al, 1986;Ju et al, 1997;Lee et al, 2001). The maximum #ame temperatures become globally low according to the increase of the CO quantity and the di!erences between maximum #ame temperatures with and without radiation term are much larger especially at low strain rates.…”

“…Previous research ) have shown implicitly from the numerical simulation with a relatively simpli"ed chemistry that considerable quantities of CO can breakdown through thermal dissociation and then the formed hydrocarbon product such as HCO can alter a reaction mechanism partly. Lee et al (2001) displayed clearly that CO addition to the oxidizer side in CH /air counter#ow di!usion #ame makes the C -branch reaction path be remarkable as much as to be comparable to the C -branch reaction path. Based on the those researches, in the present study the Fenimore NO should not be formed unless the added CO to fuel side plays a role of only a diluent.…”

Numerical study on NO formation in CH4-O2-N2 diffusion flame diluted with CO2

“…The temperatures at both fuel-and oxidizer-sides are 300 K, respectively. It was well recognized in the previous researches (Ju et al, 1997;Lee et al, 2001;Kim et al, 2002;Park et al, 2001) that especially at low strain rates the reduction of flame temperature was due to radiative heat loss. This was so because radiative heat loss is proportional to the volume of reaction zone and reaction zone thickness is physically inversely proportional to square root of strain rate.…”