A Computational Study of the Effect of Fuel Blends on Pollutants Emissions in Flames

Requirement of significantly reducing NOx and particulate emissions while maintaining combustor performance is one of the main drivers for combustion research. Fuel blending represents a very promising approach for reducing both NOx and particulate emissions from flames. This paper reports an investigation on the effects of using hydrogen blending with different fuels on pollutants emission in counterflow flames. The fuels investigated include methane and n-heptane. Methane-hydrogen flame is computed using the GRI-3.0 mechanism, while n-heptane-hydrogen flame is computed by combining the Held’s oxidation mechanism with the Li and Williams’ NOx mechanism. Results indicate that in methane/hydrogen blends, emission of NOx is increases with hydrogen addition, but the effect is not significant. However, emission of CO and C₂H₂ (which is a very important soot precursor) are affected significantly by the addition of hydrogen. First, addition of hydrogen decreases the carbon content in the fuel for the same strain rate. Second, the chemistry of combustion also changes due to higher reactivity and higher concentration of H, O and OH radicals produced due to hydrogen addition. In heptane/hydrogen blends, all the three pollutant species investigated (NO, CO and C₂H₂) are found to be affected significantly by hydrogen addition. The effect of pressure on pollutants emission has also been investigated.