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This thesis presents the research on direct-fuel-injection (DFI) performance analyses of the two-stroke engine using computational fluid dynamics (CFD). The aims of this research are: (1) to generate a finite volume mesh that can be used to simulate the moving of the piston and opening and closing the ports of the cylinder, (2) to achieve an numerical flow pattern of the scavenging process and (3) to study the DFI process using the mesh and the flow pattern obtained from the first two parts. The three parts in the analyses, therefore, are the engine geometry modelling, scavenging process modelling and DFI modelling. CFD software STAR-CD was used to write the programme and perform the analysis. The geometry model used a moving mesh mechanism with variable openings to simulate the piston motion and port area changes. The scavenging model was constructed to calculate 3D, compressible, turbulent, transient flow with heat transfer and changing volume. Results of the calculation provided a large number of data, including flow patterns, pressure and temperature distributions and fresh-charge concentrations. The DFI process was simulated as a gasliquid two-phase flow. Fuel droplets dispersed in the continuous gas phase were calculated using the Lagrangian model. Four DFI cases that differ in position and number of injectors were simulated. Fuel droplet distribution, including droplet size, velocity, temperature and position, and fuel-vapour concentration were obtained. The result of the geometry modelling shows that the finite volume programme performed well for this particular task. Because of the limitation of the computer hardware used, this programme was restricted to be used for the simulation of the engine process before the ignition, i. e., cold running condition, therefore, combustion process was not included. The findings from the analyses, with very limited resources, would help improve the engine design. The results of all four cases indicate that, even only for the period of engine process before the ignition, the DFI two-stroke engine can significantly reduce hydrocarbon emissions compared with the conventional carburettor engine.

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