Investigation on Soot Characteristics of Gasoline/Diesel Blends in a Laminar Coflow Diffusion Flame

Gasoline addition in diesel fuel could not only improve the overall energy efficiency, but also could reduce the soot emission on diesel engine. However, the influence of gasoline on the soot forming characteristics has not been revealed fundamentally. A liquid burner system, modified from a Gülder burner, was applied to create strict laminar diffusion flame to carry out the related study. Also, optical diagnostics technologies including digital camera imaging and high speed two-dimension line-of-sight attenuation (2D-LOSA) were used to record the natural luminosity flame structure, smoke point, and soot volume fraction. During the experiments, the diesel ratio was varied as 0%, 20%, and 40% by volume, while the fuel flow rate was varied from 6 to 9 g/h. The results show that diffusion flames of blends can be distributed into three typical parts, soot free region, soot growth region, and soot oxidation region. With the fuel flow rate increasing, more soot was generated and the flame height was lifted. With the diesel ratio increasing in gasoline/diesel blends, the visible flame height decreased, the flame luminosity intensity decreased, the smoke point increased, and the 2D soot volume fraction value reduced, which indicates that diesel is less likely to produce soot than is gasoline in the laminar diffusion flame. The soot reducing effect of diesel is regarded because diesel can enhance the cool flame combustion in the free soot region due to its more obvious NTC (negative temperature coefficient) effect. It is also reasonable to expound that the soot emission reduces with addition of gasoline in diesel on engines mostly because of its volatility rather than its chemical characteristics.