A combustion model for wall-wetting direct-injection diesel engines

The work presented constitutes an original approach to the phenomenological modelling of combustion in wall-wetting direct injection diesel engines. Starting with the modelling of fuel film development on the piston wall, the model covers essential aspects involved in mixture preparation in the engine and its subsequent combustion. Experiments using optical methods were undertaken to measure various characteristic dimensions of the fuel film along the piston wall. Predicted results are compared with empirical data obtained in engine experiments and used to improve the formulation of wall-jet equations used to describe fuel film flow. Velocity and scalar quantity profiles in the region close to the film surface are described, based on the theory of turbulent boundary layer flow over a porous flat plate with mass injection from the surface. This is done for conditions with and without combustion, thus defining the distribution of mixture strength in the gaseous stream adjacent to the wall. These principles were incorporated in an existing thermodynamic model to illustrate their influence on important engine parameters such as pressure, temperature, and heat release rate. Predictions for the formation of smoke and NOx emissions are carried out to address the problem of poor exhaust emissions associated with wall-wetting diesel engines. A description of the alterations made to improve the computational efficiency of the existing thermodynamic model is also provided. These make the implementation of the program possible on all machines equipped with stamdard FORTRAN 77 Compilers.