Effect of Dilution, Pressure, and Velocity on Smoke Point in Laminar Jet Flames

Abstract

Smoke point measurements of diluted methane and ethylene flames were made in a co-flowing laminar jet diffusion flame at pressures up to 8 atm. The smoke point corresponds to the fuel flow rate where the soot production is exactly offset by the soot oxidation, and as such is sensitive to changes in rates of production or oxidation. Flame height in these flames was measured as a function of pressure, diluent, and dilution level as well as both fuel exit velocity profile (i.e., plug or parabolic) and fuel=air velocity ratio. As pressure increases, the smoke point became less sensitive to diluent or dilution level. In addition to heat capacity and thermal diffusivity differences between CO 2 and He for example, the large differences in kinematic viscosity was shown to play an important role in the diluent's ability to suppress the fuel's propensity to form soot.

Numerical and experimental study of the influence of CO2 and N2 dilution on soot formation in laminar coflow C2H4/air diffusion flames at pressures between 5 and 20 atm

“…Both the experimental and modelling results indicate that CO 2 is still more effective than N 2 in suppressing soot formation at a fixed fuel:dilutent mass ratio (note that more N 2 is added to fuel on volume basis) between 5 and 20 atm, consistent with the findings of previous studies at atmospheric pressure [4,5,7] and recent studies at elevated pressures [18,23]. The better soot formation suppression ability of CO 2 is due to its thermal effect (higher specific heat) and additional chemical effects [5,7,9,24,25].…”

“…However, only few studies have been conducted so far to investigate the effects of dilution on soot formation at elevated pressures. Berry Yelverton and Roberts investigated the effects of dilution on smoke point through measuring smoke points of diluted methane and ethylene laminar coflow diffusion flames at pressures up to 8 atm [18]. Four diluents were considered, namely helium, argon, nitrogen, and carbon dioxide, to cover a wide range of transport and thermal properties.…”

Soot surface temperature measurements in pure and diluted flames at atmospheric and elevated pressures

“…An iterative approach was used to maintain a velocity matched fuel-to-air ratio in most cases; however, in some cases the fuel flow rate was held constant to compare to previous studies [15]. The burner used for this investigation was modeled after the classic Burke-Schumann over-ventilated laminar diffusion flame, and was enclosed in a pressure vessel capable of continuous operation up to 3.0 MPa.…”

“…As a continuation of previous smoke point investigations, which focused on the effects of pressure, dilution, and fuel exit velocity profile [14][15], the soot surface temperature was measured in flames at their smoke point. For most of the measurements in the co-flow burner, the flames were velocity matched.…”

“…Maintaining a highly over-ventilated flame that was also velocity matched in all cases eliminated one more variable from the smoke point measurements. A one-dimensional (i.e., top-hat or plug) exit velocity profile was utilized [15].…”