Effects of Intake Ports on In-Cylinder Flow and Lean Combustion in a 4-Valve Engine 981048
Intake-generated in-cylinder flow and subsequent combustion characteristics were studied respectively in a 4-valve spark ignition engine. The flow characteristics of four-valve cylinder head were examined under a steady flow condition for intake ports with three different entry angles; θ=15°, 20° and 25°. The velocity and angular momentum distributions in the tumble adaptor were measured with PIV (Particle Image Velocimetry). Subsequent effects of tumble flow generated by various intakes ports on the lean burn characteristics were also investigated. The lean burn performances were examined in a four-valve pentroof engine. The combustion duration under lean mixture conditions was calculated by heat release analysis of the pressure trace.
The results show that flow structure is complicated by valve interference at low valve lift. As the flow rate in the direction of tumble increased with increasing valve lift, in-cylinder flow pattern changed to large vortex structure with tumble direction. Intake ports with different entry angles have different tumble centers. Therefore there is a correlation between the stronger tumble during induction and faster, more stable combustion under lean mixture conditions. Combustion duration also revealed faster flame propagation in the stronger tumble port under lean mixture conditions, than that in weak tumble port. By comparing tumble intensities and combustion duration, the design of intake port with the optimal entry angle was discussed.