Numerical investigation of a spark ignition engine turbulent flow

Numerical calculations have been carried out to investigate the transient flow structure inside a four valves, 1.8L Lotus cylinder at an engine speed of 1500rpm. A dynamic mesh CFD simulation has been conducted to represent the real movement of the piston and valves. The main advantage of the dynamic mesh modelling is that it provides the time history of individual flow realisations. Calculations included the inlet port and moving valves so that the flow field can be analysed in detail. The eddy viscosity k-ε RNG turbulence model was used throughout this study. The predicted results were validated against experimental LDA measurements. In this experiment, only air is inserted through the ports into an optically accessible cylinder. Velocity measurements were obtained at different crank-angles and cutting-planes for a standard spark ignition settings and valve lift. The maximum inlet valve lift is 8.5mm with a valve duration of 278º. The maximum exhaust valve lift is 8mm with a duration of 272º. The inlet valves open (IVO), inlet valves close (IVC), exhaust valves open (EVO) and exhaust valves close (EVC) occured at -29º, 249º, 490º and 762º respectively. The volume compression ratio is 10.5. The engine bore is 80.5mm, the stroke is 88.2mm with a connecting rod length of 131mm. In this paper, results are presented and discussed for the variation of turbulence parameters such as turbulence intensity, kinetic energy and its dissipation rate during the intake and compression strokes at various crank-angle positions. The calculation results are in good agreement with the LDA measurements. Moreover, the results have revealed the formation of a strong tumble flow motion during the inlet stroke as well as the creation of a clockwise vortex at the bottom of the cylinder.