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

Abstract

This work investigates the implementation of non-intrusive optical combustion diagnostic techniques to study the influence of elevated pressures, on the flame structure and dynamics of the gaseous co-flow diffusion flames. Photomultipliers, high speed photography accompanied with digital image processing techniques have been used to study the structure of stable and unstable flame characteristics. Methane and Ethylene laminar flames have been studied at the same flow rates of fuel and co-flow air (0.15 l/min and 15 l/min, respectively) and at elevated pressures of up to 10 bar. It has been observed that the flame properties respond very sensitively to both the fuel type and pressure. In the Ethylene flame as the pressure is increased, the flame diameter decreased at all flame heights i.e. the average cross-sectional area of the flame shows an inverse dependence on pressure. This flame however, remains stable (non-flickering) within the entire pressure range. In contrast, Methane flame started to flicker at the pressures above 2 bar with one dominant frequency and as many as six harmonic modes. It was found that the pressure enhances the outer vortices to induce stronger flame oscillations.