method to control frictional power in engines
TRANSCRIPT
Method to Control Frictional Power in Engines
P M V SubbaraoProfessor
Mechanical Engineering Department
A Parametric Study of Curse ….…
Effect of Speed on Boundary Friction ForceF fr
ictio
n,b
Effect of Speed on Hydrodynamic Friction ForceF fr
ictio
n,h
Power loss at top piston ring at 5000 rpm, no load (pcyl = 0)
Power loss at top piston ring at 5000 rpm, (pcyl = 30bar)
Piston and Ring Friction
Distribution of the total mechanical losses of an engine
Diesel EnginePetrol Engine
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.
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
Free body/kinetic diagram of forces acting on piston pin
Pressure Distribution Diagram
Combined Bearing Pressure Diagram Vs Gas Pressure
Stribeck Curve for Bearings
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.
Indicative Pressure Profile During Compression
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dQ
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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:
piston
fringsf A
Fp ,
Combined Bearing Pressure Diagram Vs Gas Pressure
Break Pressure Profile During Compression
CS
IVC
CS
IVC
dVpWW bnogenncompressio
,
TDC
CS
TDC
CS
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Work Consumed by compression Process
dVpW
Valve Train Friction
Valve Train Friction
Auxiliary Component Friction
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.
dxFW ifif )(,,
2321 NCNCCWtf
Friction:Measurement Methods
• Measurement of FMEP from IMEP.• Direct Motoring Tests.• Willans Line.• Morse Test.
Willans Line
• The Willan’s 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.
• It’s advantages lie in it’s 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 Willan’s Line Model, the energy conversion efficiency is
represented as the ratio between the input and output power.
Willans Line
2
100005.0
100015.097.0
NNFMEPt
Correlation:
SI Engines
Effect of Load on FMEP SI Engines
CI Engines
CI Engines
221 04.0
100048 pmt SNCFMEP
Engine Power Performance Curves : SI Engine
Engine Power Performance Curves : CI Engine