| In this work, the effect of intake flow on fuel-air mixing, combustion, and emissions formation in direct injected (DI) diesel engines is investigated. A method for directly utilizing intake flow simulation predictions as initial conditions for combustion calculations is also described. In addition, a number of numerical techniques for evaluating details of the in-cylinder flow field are outlined and applied.; Since the majority of combustion simulations today are undertaken using initial conditions which are assumed to be spatially uniform, the significance of this assumption is tested. Comparisons of in-cylinder velocity fields prior to fuel injection and of heat release rate show that significant differences in prediction of combustion characteristics can result when assumed, rather than computed, initial flow field data are used as initial conditions. These differences include prediction of ignition delay, premixed burn fraction, peak heat release rate, and rate of diffusion combustion.; In order to better understand the role of intake generated flow inhomogeneities, the individual effects of temperature, turbulence, and large scale flow differences on combustion are investigated using a stirred heated combustion bomb. From these results, the most significant gas phase parameter in determining combustion behavior is the turbulent kinetic energy level.; The effects of modification of the intake flow are studied by modifying the valve lift profiles in a heavy-duty DI diesel engine and by variation of the intake port shape. These results show that the effects of intake flow can persist strongly throughout the compression stroke and the combustion event. The key effects of intake, which are felt most strongly at higher loads, include large scale effects, which can be characterized by global quantities such as swirl ratio, and localized effects including local variability in turbulent viscosity. Local effects of intake flow on emissions performance are seen to be the result of the spatial distribution of turbulent viscosity before and during the combustion process, with regions of low viscosity resulting in locally higher NO{dollar}sb{lcub}rm x{rcub}{dollar} production. |
