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Soot Formation

Soot Formation Modelling
in Diffusion Combustion


In the diffuse combustion, fuelin the high temperature zone will be decomposed by heat into various organic components. The heavy organic components forming centers accumulating light organic elements, making these initial centers of solid particles, called basic nucleating phase. Then, these nuclei are linked together to form larger particles in parallel with the development of the particle surface and volume. Due to the convection-diffusion process, the soot particles after formation will be flowed by the gas stream. Through the zones of oxygen excess and the temperature high enough, the soot particles are oxidized. If they get out of those zones, where the soot particles are not burned completely, the remaining soot parts will escape out. In diesel engines, the soot parts themselves present in the exhaust gas area source causing environmental pollution.
Derived from the above mentioned formation mechanism of soot particles, Tenser has proposed a two-phase model: the first phase is the formation of basic nucleus and the final phase is the development of the soot particles. Magnusson completed this model by accelerating the speed of burning soot particles. According to Magnusson, the general diffusion combustion and combustion of soot particles in particular, can be described by the model edgy-dissipation. According to this model, the flame intensity decides combustion speed because it affects the fuel-air mixing which requires much a longer time than the time for chemical reaction.
Based on the soot formation model by Tenser-Magnusson we need to define two new variables, which are the concentration of basic particles and soot. So for making the equations close, it is needed to add two conservation equations for nuclear elements n and soot s that these quantities locally depend on the concentration of fuel, oxygen and heat.
This study presents a comparison between experiments and models of soot formation in flame diffused freely in the air.


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English Translation by Gec