02 In Cilinder Charge Motion

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In-Cilinder Charge Motion SWIRL • Structured rotational flow on a plane normal with respect to the cylinder axis, which is formed during the intake process. • It derives from the tangential component imposed to the entering flow by the proper geometry of the intake duct and/or by the shape of the combustion chamber. • Swirl enhances fuel/air mixing in direct-injection engines, when liquid fuel is injected. In PFI, SI engines, it is used to generate turbulence which increase the turbulent flame speed. In CI engine it is useful to mix the burned gases so it should last for all the injector phase, combustion and power stroke. Three different solutions can be used to obtain a desired level of swirl in the inducted flow: 1) Shrouded valve. The air is forced by the shroud to tangentially move, when it is mainly just inside the cylinder. 2) Directed port: designed to give unequal air distribution around the valve periphery, so that a tangential velocity is imposed to the entering flow. In this case, the formation of the air swirl motion is completed by the cylinder wall, but it started inside the intake manifold. 3) Helical port: designed to mainly produce air rotation about the valve axis before it enters the cylinder. Swirl is measured, for each valve lift, under steady-state flow conditions. Swirl ratio: •ωs: paddle wheel rotation speed •D: cylinder bore •vis: velocity due to an ideal iso-entropic expansion under the pressure difference Δpv across the valve. Swirl ratio is mainly a kinematic measure of the swirl, but it is unable to include the effect of the air mass involved in the vortex Swirl number: •Μs: momentum measured by the honeycomb matrix •D: cylinder bore •vis: velocity due to an ideal iso-entropic expansion under the pressure difference Δpv across the valve.…