Flow rate fuel properties

Koistinen et al observed the parabolic relationship between air flow and combustion rate as well as ignition rate. The combustion rate is a complex function of several factors (a) fuel properties - moisture content and particle size (b) fuel bed configuration, that is countercurrent or cocurrent combustion (c) grate size and (d) the fuel bed depth. 

The input requirements for post-flashover types of models can be quite broad. Besides the compartment and vent dimensions, detailed fuel combustion characteristics are often needed. The fuel characteristics include the fraction of carbon, hydrogen, nitrogen, and oxygen that make up the fuel, the burning efficiency, and the quantity of fuel available for burning. Mechanical ventilation flow rates and the material properties of the compartment boundaries may be necessary. Some models can account for the heat transfer through the boundaries in detail, and may even allow the user to supply time-dependent material properties. An example of a post-flashover fire model is COMPF (Babrauskas, 1979). 

Flow ratio control is essential in processes such as fuel-air mixing, blending, and reactor feed systems. In a two-stream process, for example, each stream will have its own controller, but the signal from the primary controller will go to a ratio control device which adjusts the set point of the other controller. Figure 3.17(a) is an example. Construction of the ratioing device may be an adjustable mechanical linkage or may be entirely pneumatic or electronic. In other two-stream operations, the flow rate of the secondary stream may be controlled by some property of the combined stream, temperature in the case of fuel-air systems or composition or some physical property indicative of the proportions of the two streams. 

The specific values of exponents a, b, and c determined for the two distillate fuels are presented in Table II. The correlation of SMD with mass flow rate, pressure, and viscosity are in generally good agreement with typical values for petroleum fuels (11). Due to the limited properties variation available with these three fuels, the effects of surface tension and density could not be determined independently. 

Similarly to gaseous fuels, an important role is played by the instrumentation allowing for precise measurements of process values. However, in comparison with gaseous fuels, there are much higher requirements for the robustness of individual measuring instruments, especially as regards to pressure sensors and flow rate meters that not only have to be resistant to pressure shocks but also have to resist temperatures and physical-chemical properties of liquids. In the case of manometers and pressure sensors it is necessary to avoid that sludge settles down and solidifies inside their bodies. Separators filled with silicon oil are used for that purpose. 

In consequence of the high flow rate and rapidly dropping temperature of the exhaust gas, there remain combustible components as well as oxygen. For this reason one achieves potential differences between electrodes which are placed on a solid electrolyte side by side in the exhaust gas if their catalytic properties (for example in the case of Au and Ft) differ. Their use for the control of the air/fuel mixture, however, causes problems because the equivalence point cannot be exactly indicated [82] and the signals become vanishing small with increasing temperature. 

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