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The spray formation and mixing processes in a direct-injection gasoline engine are examined by using a sophisticated air flow calculation model and an original spray model. The spray model for a spiral injector can evaluate the droplet size and spatial distribution under a wide range of parameters such as the initial cone angle, back pressure and injection pressure. This model also includes the droplet breakup process due to wall impingement. The arbitrary constants used in the spray model are derived theoretically without using any experimental data. Fuel vapor distributions just before ignition and combustion processes are analyzed for both homogeneous and stratified charge conditions.

Turbulent flows in a model engine having a square piston were analyzed in detail by using a numerical simulation method with higher-order accuracy to perform simulations on an orthogonal homogeneous grid without grid motions. Calculations were performed during several continuous engine cycles. A better understanding of the cycle-by-cycle differences, i.e., cyclic variations, in flow fields may lead to more effective ways of stabilizing combustion.

Large Eddy Simulation of the turbulent premixed-flame in engine is performed in a wide range of the operating conditions such as engine speed, air-fuel ratio, and ignition timing. Firstly, a mathematical formulation suitable for Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) of the compressible turbulence and combusting flows is derived, which is the Multi-Level formulation. And a numerical algorithm based on the formulation is developed in order to calculate precisely the supergrid fluctuations of the physical quantities. As the determinations of the subgrid-turbulence and flame wrinkling, the Yakhot-Orszag turbulence model based on the Renormalization Group theory(RNG theory) and a flame-sheet model are combined with the numerical code. Computations are performed for a real engine with dual intakeport and valves. Obtained computational data agrees well with the experimental data on turbulence-intensity and pressure history.

A theoretical model based on a nonlinear ordinary differential equation was developed, which can estimate the atomization process of fuel droplets after the wall impingement. The phase-space trajectory of the equation for droplet deformation and oscillation varies from oval to parabola with increasing impact velocity. Four different regimes for droplet diameter distribution are derived from this complex feature of the equation. The amount of liquid film remaining on the wall and the number of droplets are estimated from the related mass and energy conservation laws. The model is called the Oval-Parabola Trajectories (OPT) model in the present report. Comparisons made with some fundamental experimetal data confirm that this mathematical model is effective in a velocity range from 2m/s to 40m/s and in a diameter range below 300 micrometers.

Numerical simulation of two-dimensional and three-dimensional air flow in automobile passenger compartments is described. The flow can be expressed by means of an incompressible Navier-Stokes equation for a narrow temperature range. The results were represented visually using animation and a color graphics system. The two-dimensional simulation showed that heat ansfer takes place chiefly by convection in vortices, and that the effects of heat transfer are minimal. In the three-dimensional analysis, shading was used to show the shape inside the compartment, and instantaneous stream lines and temperature distribution were depicted. The three-dimensional stream lines swirl upward at the front seat, and do not reach the back seat. The results gained from this study show that present theoretical flow analysis methods are close to being perfected. Further advances will require additional refinement of supercomputers and graphic engineering workstations.