Sooting propensities of some gasoline surrogate fuels: Combined effects of fuel blending and air vitiation

Abstract

The sooting propensities of binary mixtures of n-heptane and toluene on one hand, and isooctane and toluene on the other hand are evaluated in haust gas recirculation (EGR). The evolution of the sooting propensity as a function of both toluene mole fraction in the binary mixtures and CO 2 content of the air stream can then be revealed. The sooting tendencies of both kinds of blends decrease in a very linear way with increasing CO 2 content of the air stream. On the opposite, the sooting tendencies of isooctane/toluene blends follow a strongly non-linear relationship with the toluene mole fraction due to synergistic effects while YSIs of n-heptane/toluene blends show very linear trends. Interestingly, these trends match those observed on other configurations of diffusion flames, further strengthening the consistency of the YSI methodology. The combined effects of fuel blending and CO 2 dilution are also exhibited. All these trends can be of great importance for further investigations as toluene and isooctane mole fractions found in commercially available gasoline and gasoline surrogate fuels are prone to affect soot formation through a strong synergistic effect as identified in current study.

Numerical study of soot formation in laminar coflow methane/air diffusion flames doped by n- heptane/toluene and iso-octane/toluene blends

“…The soot production tendency of PRF was found to increase linearly with the volume fraction of iso-octane [5]. In contrast, the sooting tendency of n-heptane/toluene and iso-octane/toluene mixtures was found to increase in a non-linear and monotonic fashion with the toluene mole fraction [6]. In other words, the peak soot volume fraction in these binary mixture doped flames was found to be higher than that from a simple linear-per-volume model.…”

“…In other words, the peak soot volume fraction in these binary mixture doped flames was found to be higher than that from a simple linear-per-volume model. In addition, the experimental data showed a larger degree of non-linear behavior in iso-octane/toluene mixtures than that in n-heptane/toluene mixtures [6].…”

“…The laminar coflow diffusion flames studied experimentally by Kashif and coworkers [6] are simulated. In these experiments, measurements of soot volume fraction distribution were conducted in laminar coflow nitrogen-diluted methane diffusion flames doped with binary mixtures of either n-heptane and toluene or iso-octane and toluene at atmospheric pressure.…”

“…The sooting tendencies of gasoline, diesel, jet-A fuels and their surrogates were experimentally investigated in a laminar coflow heated methane/air diffusion flame at atmospheric pressure by doping methane with a small amount of vaporized liquid fuels (2200-2300 ppm) [4]. Kashif et al conducted similar experiments to characterize the fuel sooting propensity of binary mixtures of n-heptane and iso-octane, n-heptane and toluene, and iso-octane and toluene [5,6]. They considered laminar CH 4 /air coflow diffusion flames doped with these vaporized binary mixtures.…”

“…Although it is important to investigate the effects of these factors on soot emissions from GDI engines, it is challenging to isolate the influence of a particular factor, such as fuel chemistry, on soot formation, as the high sensitivity of soot emissions from a GDI engine to various engine parameters can mask the effect of this particular factor on soot formation. In order to circumvent this drawback, well-controlled laminar diffusion flames have been often used [3][4][5][6][7].…”