Soot Concentration and Temperature Measurements in Co-flow Laminar Propane-Air Diffusion Flames at Pressures up to 7 bar

Abstract

The influence of elevated pressures up to 7 bar on the flame geometry and twodimensional soot temperature and concentration were studied in a propane-air laminar co-flow diffusion flame. Narrow band photography and two-color pyrometry in the visible spectrum have been used to gain a better understanding on effects of pressure on these parameters. The peak radiation from soot particles at 430 nm and 516 nm were collected by applying CH* and C2* narrow band filters in front of a digital CCD camera. It has been observed that the flame properties respond very sensitively to the pressure. As the pressure is increased, the flame diameter decreased at all flame heights. The average cross-sectional area of the flame shows an inverse dependence on pressure. Flame height behavior, however, was observed to be bimodal; initially as pressure rises increasing and then decreasing. The flame luminosity at the flame centerline increases, with distance from the fuel nozzle, then the flame became less intense with height due to cooling of the soot particles by radiative losses, leading to a smoking flame at pressures of 4 bar and above. The soot temperature results obtained by applying the two-color method are shown to be consistent with the pyrometry results. Soot temperature measurements show that in a propane diffusion flame the overall temperature, decreases with increasing pressure. It is shown that the rate of temperature drop is greater for a pressure increase at lower pressures in comparison with higher pressures. Soot formation was dramatically increased by pressure and the location of the peak soot volume fraction moved towards the flame centre line at higher pressures.