Numerical and experimental study of a boosted uniflow 2-stroke engine

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel UniversityEngine downsizing is one of the most effective ways to reduce vehicle fuel consumption. Highly downsized (>50%) 4-stroke gasoline engines are constrained by knocking combustion, thermal and mechanical limits as well as high boost. Therefore a research work for a highly downsized uniflow 2-stroke engine has been proposed and carried out to unveil its potential. In this study, one-dimensional (1D) engine simulation and three-dimensional (3D) computational fluid dynamic analysis were used to predict the performance of a boosted uniflow 2-stroke DI gasoline engine. This was experimentally complemented by the in-cylinder flow and mixture formation measurements in a newly commissioned single cylinder uniflow 2-stroke DI gasoline engine. The 3D simulation was used to assess the effects of engine configurations for engine breathing performance and in order that the design of the intake ports could be optimised. The boundary conditions for 1D engine simulation were configured by the 3D simulation output parameters, was employed to predict the engine performance with different boost systems. The fuel consumption and full load performance data from the 1D engine simulation were then included in the vehicle driving cycle analysis so that the vehicle performance and fuel consumption over the NEDC could be obtained. Based on the modelling results, a single cylinder uniflow 2-stroke engine was commissioned by incorporating a newly designed intake block and modified intake and exhaust systems. In-cylinder flow and fuel distribution were then measured by means of Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) in the single cylinder engine. The numerical analysis results suggested that a 0.6 litre two-cylinder boosted uniflow 2-stroke engine with an optimised boosting system was capable of delivering comparable performance to a NA 1.6 litre four-cylinder 4-stroke engine yet with a maximum 23.5% improvement potential on fuel economy. Furthermore, simulation results on in-cylinder flow structure and fuel distribution were then verified experimentally