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

Abstract

SUMMARYFlame structure and NO emission characteristics in counter#ow di!usion #ame of blended fuel of H /CO /Ar have been numerically simulated with detailed chemistry. The combination of H , CO and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to #ame structure and NO emission characteristics due to the breakdown of CO . A radiative heat loss term is involved to correctly describe the #ame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO , N O and Fenimore are taken into account to separately evaluate the e!ects of CO addition on NO emission characteristics.The increase of added CO quantity causes #ame temperature to fall since at high strain rates a diluent e!ect is prevailing and at low strain rates the breakdown of CO produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N O and NO mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO quantity increase, NO production is remarkably augmented.

Evaluation of chemical effects of added CO2 according flame location

“…The governing equations for mass, momentum, chemical species and energy, and the solution technique can be found in Lutz et al (1997). In this study, we retain the sink term due to the thermal radiation and details of the thermal radiation model, based on an optically thin approximation, can be found in the previous researches (Ju et al, 1997;Kim et al, 2002;Park et al, 2002aPark et al, -c, 2003a. The thermal radiation term is particularly involved due to its importance in the flame dynamics at low strain rates and the high gas radiation absorption coefficient such as CO 2 , CO, H 2 O, and CH 4 .…”

“…The production of C 1 -and C 2 -chemical species, which mainly originated from the reaction CO 2 +H ! CO+OH, was a direct evidence of chemical effects, and thus as a result these chemical effects reduced the flame temperature and affected prompt NO in a complicated manner (Liu et al, 2001;Kim et al, 2002;Park et al, 2002aPark et al, -c, 2003a.…”

“…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.…”

Flame structure and NO emissions in gas combustion of low calorific heating value

“…And then the production rate decreases quickly and becomes negative. Some preliminary studies (Park et al, 2001;Park et al, 2002;Miller and Bowman, 1989;Nishioka et al, 1994) have revealed that the reaction of NO with HCCO, so called HCN recycle route, plays a significant role. The negative production rate is due to the HCN recycle route reaction.…”

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

“…Du et al (1990) showed that addition of CO 2 on either the fuel-or the oxidizer-side has chemical effects on soot formation reduction in addition to dilution and thermal effects. Lee et al (2001) and Park et al (2001a,b) clearly displayed the modification of C 2 -branch species due to added CO 2 , and Park et al (2002a) stressed the modification of C 1 -and C 2 -branch reaction pathway that is directly caused by chemical effects due to thermal dissociation of added CO 2 . Resultantly there existed the considerable change of prompt NO.…”