ABSTRACT
When a fossil fuel is burned, oxygen in the air chemically reacts with combustible elements of the fuel to produce heat. Since nitrogen is nearly inert, it is mainly a diluent that carries away some of the energy released during the combustion process and produces pollutants. Oxygen-enhanced combustion has been considered as an attractive alternative in order to increase efficiency, to reduce volume of the flue gas, to lower emissions of NOx and CO2, and to improve heat transfer and flame stability characteristics. With decreasing costs involved in production of oxygen from air, oxygen-enhanced combustion may not only be limited to glass-melting and steel-making furnaces but also may have potential in the power-generation industry using fossil fuels such as coal and natural gas. Substantial research has been conducted to evaluate the effects of oxygen enrichment on overall efficiency, fuel savings, heat transfer rates, and pollutant emissions. However, only limited fundamental research has been performed to understand the physical changes in the flame structure when using oxygen-rich oxidizer containing more than 21% oxygen. Laser-based techniques can be used to obtain nonintrusive velocity, temperature, and concentration measurements relevant to the combustion process, thus providing nearly complete description of the coupling among the fluid flow, thermal, and chemical transport in reacting flows. Several laser-based diagnostic methods are available, each having its own advantages and limitations; detailed description of these techniques and their application to combustion has been reported
in the literature by Eckbreth and Kohse-Hoinghaus and Jeffries.1,2 In this chapter, we will describe specific examples of laser-based measurements in the following areas relevant to oxygen-enhanced combustion: (a) soot, (b) temperature and major species, and (c) minor pollutant species such as nitric oxide.
