LES Analysis of Mixture Formation and Ignition in a Diesel Spray

Numerical calculation based on large eddy simulation was carried out to investigate mixture formation process in a spray formed by injecting n-heptane into a constant volume vessel under high-temperature and high-pressure conditions. Liquid phase of fuel was described by discrete droplet model. The results show that the shape of spray is similar to that of visualized image and spray tip penetration corresponds well to experimental results. In addition, distributions of fuel concentration and local non-homogeneous distribution were discussed by comparing the calculation results with the mixture distributions measured using planer laser induced fluorescence technique. The local distributions were well described except around downstream spray boundary. Calculations were also carried out for lower injection pressure condition and smaller nozzle orifice diameter condition. Although fuel concentration in a spray does not quantitatively reproduce the experimental results, the effects of the injection conditions qualitatively agreed with the experiments. Furthermore, ignition and combustion processes were investigated using Schreiber's model for calculating the progress of oxidation reactions.