Investigating Soot Parameters in an Ethane/Air Counterflow Diffusion Flame at Elevated Pressures

Soot emissions from diesel engines and gas turbines are influenced by the combustion environment. Pressure is one of the parameters, which affects particulate emissions, and these effects are poorly understood on soot parameters. In this work, pressurized counterflow diffusion flame of ethane and air has been investigated using two angle light scattering and extinction technique. A counterflow diffusion flame has been stabilized from 2 to 5 atm in a pressure vessel, which can provide optical access from 10 to 165° in angular direction. Global strain rate (a) of 30 s⁻¹ is maintained at all pressures by adjusting the inlet flows. Scattering measurements are performed at two angles (45° and 135°) and Rayleigh-Debye-Gans theory for Fractal Aggregates (RDG-FA) has been used to determine soot parameters from light scattering and extinction data. By combining the scattering at 135° with laser extinction measurements, path averaged soot volume fraction (f_v), mean primary particle diameter (dp¯¯¯¯¯) and particle number densities (n_p), along the axis of the counterflow flame are calculated. Local soot volume fraction (f_v,local) profiles are also measured using diffuse light 2D line of sight attenuation technique. Peak value of f_v increases from 0.3 to 8 ppm as the pressure is raised from 2 to 5 atm. Primary particle size (dp¯¯¯¯¯) also increases with pressure where peak primary particle size of 11 nm at 2 atm rises to 38 nm at 5 atm. Population average radius of gyration (R_g) increases with pressure while the number densities (n_p) of primary particles decrease due to coalescence.