Study on Particulate Formation in Diffusive Combustion

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The formation of carbonaceous particulates in the diffusive combustion is a matter of great concern from removing not only imcomplete combustion but also health hazards. For this reason, much efforts have been concentrated to elucidate the mechanism of soot formation. In the present study, the process of the formation and extinction of soot particlates in the heterogeneous states of fuel concentration during combustion was theoretically and experimentally investigated. The main points of the study may be sumarized as follows. (1). The formation of both dry soot and polycyclic aromatic hydrocarbons (PAH) was discussed to enable prediction of their concentrations at elevated temperatures that prevail in flames. This is based on multicomponent thermochemical equilibrium considerations, in which only gaseous intermediate substances of soot are considered. This allows qualitative description of particulate formation measured with a heated flow reactor, suggesting that the carbon-hydrogen ra … More tio of fuel and the fuel formation enthalpy are main factors that govern particulate formation. Furthermore, a partial-equilibrium model for soot formation based on the homogeneous condensation and the cluster formation was proposed for prediction of time-dependent soot yields and final soot yield. (2). Thermal decomposition and oxidations in the earlier stages of diesel combustion were studied with simulated direct-injection diesel engine using high-speed photography and a fast in-cylinder gas-sampling technique. The measured results show the detailed behavior of fuel spray and thermal cracking of the fuel before ignition. Also, the local gas composition in the deep-bowl type combustion chamber were investigated to know how soot formation proceeds. The results show that within time allowable for fuel-air mixing, gas flow from the combustion bowl into the clearance, and combustion in this space greatly affect soot formation. (3). A picture processing technique was applied to study the flame notion in a direct-injection diesel engine, with a special attention to turbulence which significantly affects the turbulent mixing and soot formation. The analysed results showed that the turbulent flow field is almost uniform and isotropic over the space. Furthermore, the effects of the swirl and chamber geometry on the flame behavior were discussed in detail. (4). Based on the experimental findings and chemical-equilibrium considerations, the turbulent mixing model was applied to describe the combustion process in high-speed direct-injection diesel engines. This model enables us to predict the effect of several engine variables on the pollutant emissions. Less