A new spray penetration model is suggested. Analytical expressions for spray penetration are derived in two limited cases: the initial stage and the two-phase flow regime. At the initial stage, three types of flow (Stoke flow, Allen flow and Newton flow) are considered. In the case of two-phase flow, it is assumed that the spray droplets had the same velocities as the entrained air. The predictions of our new spray penetration model agree with available experimental observation. A typical fuel injection process is accompanied by the development of a puff structure consisting of a spray jet and a vortex ring. The theoretical model developed by Lugovtsov is applied to explain the observed vortex dynamics. The general consistency of experimental and theoretical results is achieved by appropriate choice of the constant in the expression for turbulent viscosity. A model for liquid fuel evaporation and ignition in the presence of thermal radiation is suggested and discussed. It is pointed out that the effects of thermal radiation are noticeable, especially at high temperature and cannot be ignored in the analysis of this phenomenon. The results of this model are shown to be compatible with predictions of CFD code VECTIS of Ricardo Consulting Engineers. A water-analogue rig was used to study the in-cylinder air motion during the intake process. The PIV technique was used to obtain the velocity field at any crank angle during the intake process. A computation compression model based on the shear stress theory is suggested for investigating the tumble during the compression stroke in a G-DI engine. CFD package VECTIS is used to simulate the flow during the compression stroke. The internal flow characterisation parameters were applied to analyse the result. The tumble during the compression stroke is shown to be well formed and the flow characterisation parameters have the same values as at the moment when the inlet valves are closed.