Experimental and numerical investigation on effect of butanol isomers additions in iso-octane sooting transition chemistry

Abstract

The effects of four butanol isomers additions on sooting transition process were studied in iso-octane counterflow diffusion flame combining flame luminosity characteristics and gas-phase combustion chemistry. Flame luminosity characteristics was obtained to determine the sooting transition points of all investigated flames with homemade image processing and transition point extraction methods. The results indicated that the delay effect has occurred on sooting transition point in four blended flames with a little difference. Gas-phase combustion chemistry of the different flames in sooting transition process was studied experimentally by an online GC system as well as numerically by kinetic analysis realized with two distinct kinetic mechanisms. In addition, soot formation characteristics have also been qualitatively analyzed with soot model. Experiments and simulations show that, depending on the butanol isomer, the intermediate species production is clearly different. These different species pools play an important role on soot formation pathways as demonstrated by the simulations. Although n-butanol and sec-butanol were weaker in benzene formation, stronger C₂H₂ production capacity was dominant in PAHs growth. Tert-butanol had the highest C₆H₆ concentration with a ratio of 7 %−15 % higher than the other isomers due to the strongest IC₄H₈ production capacity. Therefore, its flame also has the highest PAHs concentration. Both effect mechanisms existed in iso-butanol blended flame.