ABSTRACT
Abstract: This paper presents the application of a digital imaging system to the three-dimensional (30) quantitative characterisation of luminous propel1ies of gaseous flames. The system comprises three monochromatic CCO cameras, three short-wave-pass optical filters, a frame grabber and a computer with dedicated software. The three cameras, placed cquidistantly and equiangular ITom each other around the flame, capture 20 images of the flame simultaneously from three different directions. Various image processing techniques including posterization, contour extraction and mesh generation are applied to reconstruct the 3D models of a flame from the 20 imagcs, 3D luminous characteristics of a flamc such as luminosity distribution, brightness and non-uniformity are quantified from the models generated, A series of experiments was conducted on a gas-fired combustion rig to evaluate the performance of the system. The results obtained demonstrate that the system is capablc of measuring 3 D luminous parameters of a flame over a range of combustion conditions,
1. Introduction
A flame is the central reaction zone of a combustion process and its geometrical, luminous and thermodynamic characteristics provide instantaneous infonnation on the quality and performance of the combustion process. Monitoring and characterisation of combustion flames have, therefore, become increasingly important to combustion engineers for an improved understanding and subsequent on-line optimisation of combustion conditions. A number of instrumentation systems bas cd on digital imaging and image processing techniques have recently been developed for the measurement of a range of parameters of fossil fuel fired flames [I], Such systems have been tested under real plant conditions [2]. However, the systems use a single CCD camera, the information obtained is therefore limited to two-dimensions - the third dimension has not been taken into account. Since a flame is generally an asymmetrical 3D flow field, a two-dimensional (2D) imaging system does not provide overall information on the structure and dynamic propertics of the flame [3]. This entails that the flame should be characterised three-dimensionally.
