Pressure Effects on Structure and Temperature Field of Laminar Diffusion Flames

Abstract

This study addresses the influence of elevated pressures up to 10 bar on the flame geometry and two-dimensional soot temperature distribution of ethylene-air laminar co-flow diffusion flame. Narrow band photography and two-colour pyrometry in the Near Infra-red (NIR) region have been used to gain a better understanding on effects of pressure on these parameters. Theoretical background, discreet considerations in the choice of two narrow band filters at 780 nm and 1064 nm and calibration of the instrument factor are also described. 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 and soot formation dramatically increased. The flame luminosity at the flame centerline increases, first by axial position 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 2 bar and above. The soot temperature results obtained by applying twocolor method in the NIR region are shown to be consistent with the pyrometry results. Soot temperature measurements show that in ethylene diffusion flame the overall temperatures 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. The average temperature drop of about 177 K is recorded along the flame centerline for a pressure increase from atmospheric to 2 bar and also from 2 bar to 4 bar. However, at higher pressures the rate of temperature drop decreases to 1/3 of the previous temperature drop. It is found that, applying two-color pyrometry method in the NIR region, utilizing a commercial digital camera, is capable of nonintrusive measurement of two-dimensional soot temperatures with a simple and relatively high accuracy technique. The maximum recorded error of the method was found to be about 8%. It mainly occurred at the regions with the lowest concentration of soot particles.

Study of the Flame Structure and Dynamics Using Non-intrusive Combustion Diagnostic Techniques

“…In this experiments the cross-sectional area of the flame (was measured from the radius defined by the outer edges of the sooting region at each height showed an average inverse dependence on the pressure. 18 The normal, color pictures of Ethylene (0.15 l/min)-air (15 l/min) diffusion flame at different pressures are presented in Figure 3. At atmospheric pressure the presence of the soot particles is mainly limited at the flame tip and in an annular band near the burner rim.…”