Flame surface area models

The fact that the fuel/air ratio is spatially constant in HCSI engines, at least within a reasonably close approximation, allows substantial simplifications in combustion models. The burn rate or fuel consumption rate dm /dt is expressed as a function of flame surface area the density of the unburnt fuel/air mixture Pu, the laminar burning velocity Sl, and the fluctuations of velocities, i.e., E as a measure of turbulence, u. ... 

To estimate the impact of the jet fire on process equipment located 20 m from the source, the point source model can be used to determine the incident heat flux from the jet flame to the equipment. The incident heat flux per unit surface area of target, q" is calculated as follows. 

Since it is difiScuh to obtain diesd soot with constant prop es (the composition dq> ids on the engine load) a model soot was applied (Printex-U, a flame soot kindly provided by Degussa). This soot has a N2-BET surface area of 96 mV and contains approximately 5 wt% of adsorbed hydrocarbons and 0 2-0.4 wt% sulfur. Catalytic soot oxidation temperatures were d ermined in a thermobalance (STA 1500H). About 4 mg catalyst, 2 mg soot and 54 mg SiC were applied as a sample. A heating rate of 10 K/min and a flow rate of 50 ml/min 21 vol% O2 in N2 wa"e used. The maximum of the DSC curve was defined as the oxidation temperature. Samples refored to as tight contact were intensively milled in a ball mill for one hour, before dilution with SiC and thermal analysis, whereas loose contact was established by simply mixing of the catalyst and soot with a spatula. 

In the case of the synthesis of alumina, chrome, nickel, iron and nanocrystalline cobalt oxides using the solution combustion technique, for example, we lack, so far, a deep understanding of the influence of the fuel-oxidant ratios well as a model of the thermodynamic variables associated with enthalpy, adiabatic flame temperature and the total number of moles of gas generated related to the powder characteristics, such as crystallite size and surface area. 

Radiation heat flux is graphically represented as a function of time in Figure 8.3. The total amount of radiation heat from a surface can be found by integration of the radiation heat flux over the time of flame propagation, that is, the area under the curve. This result is probably an overstatement of realistic values, because the flame will probably not bum as a closed front. Instead, it will consist of several plumes which might reach heights in excess of those assumed in the model but will nevertheless probably produce less flame radiation. Moreover, the flame will not bum as a plane surface but more in the shape of a horseshoe. Finally, wind will have a considerable influence on flame shape and cloud position. None of these eflects has been taken into account. 

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