A comparative study on PAH characteristics of ethanol and ammonia as fuel additives in a premixed flame

Due to issues towards polycyclic aromatic hydrocarbons (PAH) emissions and energy security, the renewable and non- or low-sooting tendency fuels are growing increased attention as alternatives to conventional fossil fuels. One feasible approach is to co-fire ethanol and ammonia with hydrocarbons, thus improving their combustion properties and pollutant emissions. This study presents a comparative study about the influence of ethanol and ammonia addition on PAH formation with the same blending ratios up to 30% by mole fraction in premixed C2H4 flames. The axial fluorescence intensities in three wavelength bands were measured to represent concentrations of 2- and 3-ring, 4-ring, 5-membered-ring aromatic species using the laser-induced fluorescence (LIF) technique. Experimental results indicated that both ethanol and ammonia addition could cause PAH reductions in premixed ethylene flames as their blending ratios increase. Further, ammonia was found more efficient than ethanol at inhibiting PAH formation under the same blending ratio. A chemical kinetic analysis was conducted to reveal the inhibiting role of ethanol and ammonia as substituents to ethylene on PAH formation. It was found that both ethanol and ammonia addition chemically suppress benzene formation and subsequent PAH growth due to the low yield of C2H2 and C3H3. Meantime, the additional C1 and C2 supply from ethanol decomposition could explain the relatively lower inhibiting effects on C6H6 and PAH formation as compared to the NH3 doped flames.

Automated summary

Co-firing ethanol and ammonia with hydrocarbons can reduce the formation of polycyclic aromatic hydrocarbons (PAH), with ammonia being more efficient than ethanol. Chemical kinetic analysis shows that both ethanol and ammonia addition suppress benzene formation and subsequent PAH growth.