Method to Control Frictional Power in Engines

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Method to Control Frictional Power in Engines

• P M V Subbarao
• Professor
• Mechanical Engineering Department

A Parametric Study of Curse .
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Effect of Speed on Boundary Friction Force
Ffriction,b
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Effect of Speed on Hydrodynamic Friction Force
Ffriction,h
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Power loss at top piston ring at 5000 rpm, no
load (pcyl 0)
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Power loss at top piston ring at 5000 rpm, (pcyl
30bar)
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Piston and Ring Friction
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Distribution of the total mechanical losses of an
engine
Diesel Engine
Petrol Engine
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BEARING FRICTION

• Bearing friction comes from many different
  sources including the crankshaft main bearings,
  connecting rod big-end bearings, connecting rod
  small-end bearings, camshaft bearings, and rocker
  arm bearings.
• As previously discussed engine bearings typically
  represent 20 to 30 of the total engine
  frictional losses.
• Of the many different bearings in a diesel engine
  none are more critical or highly stressed than
  the connecting rod big/small-end bearings and the
  crankshaft main bearings.

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Big-End Bearing Friction

• The connecting rod big-end bearings are subject
  to varying loads, speeds, and angular velocities
  throughout the cycle of engine operation.
• In these bearings the journal rotates steadily
  while the sleeve oscillates back and forth.
• The magnitude of these bearing loads at any point
  is the resultant of three main forces
• 1. Combustion gas force
• 2. Inertia force of the reciprocating parts
• 3. Centrifugal force on the crankpin created by
  the big-end of the connecting rod

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Free body/kinetic diagram of forces acting on
piston pin
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Pressure Distribution Diagram
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Combined Bearing Pressure Diagram Vs Gas Pressure
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Stribeck Curve for Bearings
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Geometrical Solutions to Contain Friction in
Bearings

• The loads on the bearings vary significantly with
  crank angle, the connecting rod geometry and the
  combustion gas pressure.
• Size of a bearing
• Diameter of crankshaft main bearing 65 of bore.
• Connecting rod bearings 55 of bore.
• Bearing lengths are sized at 35 to 45 of bore.

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Indicative Pressure Profile During Compression
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The Total Friction Pressure due to Piston rings
The total friction force Ff, acting on the ring
in tangential direction, is the sum of the
friction force between the asperities and the
shear force about the HDL regime
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Combined Bearing Pressure Diagram Vs Gas Pressure
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Break Pressure Profile During Compression
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Work Consumed by compression Process
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Valve Train Friction
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Valve Train Friction
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Auxiliary Component Friction
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Total Friction

• The work per cycle for each component I of the
  total friction is given by integrating the
  friction force Ff,I times its displacement dx
  around the cycle.
• The friction force components are either
  independent of speed or proportional to speed or
  to speed squared.

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FrictionMeasurement Methods

• Measurement of FMEP from IMEP.
• Direct Motoring Tests.
• Willans Line.
• Morse Test.

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Willans Line

• The Willans line model is a scaling technique
  used to create numerical models of IC Engines of
  virtually any desired size.
• It is a good quasi-static representation of the
  fuel efficiency of CI/SI Engines.
• Its advantages lie in its scalability within
  engines of a certain class.
• However, this technique does not take into
  account several aspects of IC engines such as
  detailed engine geometry, fuel injection, thermal
  effects, engine dynamics, etc.
• Modeling
• In the Willans Line Model, the energy conversion
  efficiency is represented as the ratio between
  the input and output power.

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Willans Line
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SI Engines
Correlation
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SI Engines
Effect of Load on FMEP
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CI Engines
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CI Engines
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Engine Power Performance Curves SI Engine
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Engine Power Performance Curves CI Engine