A detailed soot emission model for Direct Injection diesel engines has been developed. The model can predict both in-cylinder and exhaust soot concentrations from the engines. Accurate predictions of flame temperature, equivalence ratio and engine cylinder pressure are made for the soot model using a two-dimensional, multi-zone, phenomenological spray mixing combustion model.
The net soot concentration in diesel exhaust results from the soot formation and oxidation processes in the combustion chamber. Both these processes occur within the turbulent eddy structure of the charge. Soot formation occurs in the large scale eddy structure in two stages - radical nuclei formation and the formation of the soot particulates from these nuclei. In the fuel rich spray elements, soot is considered to form in both the burning zone and the surrounding fluids. The oxidation or combustion rate of nuclei and soot particulates is kinetically controlled and takes place in the fine eddy structure. The exhaust soot concentration is the net soot formed in all the spray elements from the onset of combustion to the exhaust valve opening.
The predicted and experimental in-cylinder and exhaust soot data, obtained from three sources at various engine design and operating conditions, are compared. The results concerning the effect of injection timing, fueling rate and swirl ratio are presented. The predicted and experimental results show very good agreement.