| OCR Text |
Show properties and the initial temperature of the unburned reactant. It is a determinant of several aspects of burner performance, most importantly the heat output characteristics that can determine the suitability of a burner for a given application. Flame temperature is also important from the standpoint of NO and SO emissions characteristics, while soot formation and consumption in a flame can rapidly increase the flame luminosity, increasing radiant heat transfer from the flame while reducing the flame temperature. Finally, the laminar flame speed is an important characteristic by itself in some applications (e.g., low-speed burner flow where flashback phenomena may occur) as well as being a useful measure of the reactivity of a fuel. Since laminar flame speed is directly related to the chemical reaction rate, measurements of a laminar flame speed for a variety of inlet flow fuel air ratios and temperatures can be used to estimate the chemical kinetic rate constants for a given fuel. Chemical reaction time (as opposed to ignition delay time) is an important factor in determining the completeness of combustion and NO , SO , and soot emissions. A. A If residence time is less than the reaction time, combustion will not be completed. This will reduce thermal NO emissions, since the fully-reacted temperature is never achieved, but increase CO and HC emissions, and have a deleterious effect on burner efficiency. Residence time is controlled primarily by the burner flowfield aerodynamics and mixing rate, while reaction time is a strong function of fuel-air ratio and temperature. In an industrial burner the flowfield aerodynamics and the chemical kinetic phenomena that determine reaction time are tightly coupled. Usability and durability characteristics - thermal and oxidative stability, fouling, and corrostion - primarily involve the ability of the fuel to withstand long term storage and environmental extremes without major property changes, and the amount of ash and corrosive constituents in the fuel. Overall effects of these usability and durability characteristics on burner performance involve primarily the fuel management system and furnace and boiler components, but each of these characteristics can also affect combustion phenomena. For example, a fuel with poor thermal and oxidative stability characteristics will undergo changes which can affect the viscosity, surface tension, density, and composition of the liquid, thus affecting the droplet and spray formation process as well as subsequent droplet vaporization and burning. Similarly, fouling creates soot and ash buildups on burner and boiler/ furnace components which can affect the burner aerodynamics, while corrosion induced by a fuel can alter fuel injection characteristics and, by eroding parts of a burner, 1.2.4 |
