Transient Modeling of Current I.C. Engines

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Presentation transcript:

Transient Modeling of Current I.C. Engines P M V Subbarao Professor Mechanical Engineering Department Assessment of Pace of Torque Generation….

Intake Process in Current SI Engine & Future CI Engine FUEL Current CI Engine & Future SI Engine

Transient Flow through Intake & Exhaust Systems Exhaust Pipe 3 1 2

Hardware for Air Intake Valve/Port Design 1. Poppet Valve 2. Rotary Valve 3. Reed Valve 4. Piston Controlled Porting Valve Location 1. The T-head 2. The L-head 3. The F-head 4. The I-head: (i) Over head Valve (OHV) (ii) Over head Cam (OHC)

Poppet Valve & Air Passage

Inlet Valve : Operation Schedule Pcyl Patm

Valve Actuation Diagram

Nature of Flow Through Valves The flow is driven by transient pressure difference across the valve. Temporal variation of flow area section. Generally axi-symmetric sections. Truly the flow is Transient and Multi-dimensional. However, Transient zero dimensional modeling is reasonably accurate to predict instantaneous mass flow rate. Flow Mach Numbers is significant and generates a compressible flow. Generation of spatial pressure gradients due to variable flow area section is important.

Geometrical Nomenclature for Valves The instantaneous valve flow area depends on valve lift and the geometrical details of the valve head, seat and stem. There are three separate stages to the flow area development as valve lift increases.

Stages of Valve Lifting

Instantaneous Valve Events : Low Lift For low lift valves, the minimum flow area corresponds to a frustum of right circular cone. The conical face between valve and seat is, perpendicular to the seat, defines the flow area. The minimum area is:

For the second stage, the minimum area is still the slant surface of a frustum of a right circular cone. However, this surface is not perpendicular to the valve seat. The base angle of the cone increases from (900-) toward that of a cylinder. For this stage: Dm is mean diameter of seat :

When the valve lift is sufficiently large, the minimum flow area is no longer between the valve head and seat. It is the port area minus the sectional area of the valve stem. Then,

Valve Lift Curves

Valve Lift in General (Design) Practice : Intake Valve IVO should occur sufficiently before TC which leads to early fall in cylinder pressure during the intake stroke. The maximum valve lift is normally about 12% of the cylinder bore. Inlet valve opening typically occurs at 10 to 250 BTC. IVC should occur sufficiently after BC, to provide more time for cylinder filing under conditions where cylinder pressure is below the intake manifold pressure at BC. IVC usually falls in the range 40 to 600 after BC. IVC one of the principal factors that determines the amount of air taken in high-speed engines.