i c engines efficiencies
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ENGINE EFFICIENCIES
Prof. (Dr.) M P Poonia Director
NITTTR, Chandigarh
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Revision
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1. Indicated and Brake Mean Effective Pressure2. Indicated Power, IP3. Brake Power, BP4. Mechanical Efficiency5. Friction Power6. Indicated Thermal Efficiency7 Brake Thermal Efficiency
Performance Parameters
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8. Specific Fuel Consumption9.10 Heat Balance11. Fuel Air-Ratio12. Equivalence Ratio
Performance Parameters
Volumetric Efficiency
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IDEAL P-V Diagram
Average IMEP 4-12 bar
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Actual P-V Diagram
PMEP
= IMEP (g)AREA 1
AREA2
IMEP (n)= AREA1-AREA2
BMEP=IMEP (n)-FMEP
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Metric Horse Power1 hp= 735.5 W
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The indicated power is the power actually developed by the engine cylinder.
INDICATED POWER (IP)
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The indicated power is the power actually developed by the engine cylinder.
IP=
Where IP= Indicated Power, WPm= Mean Effective Pressure N/m2
L = Stroke Length , mA = Piston Top Area , m2
N = Engine RPM
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BRAKE POWER :The brake power is the power available at the crankshaft of the engine.
Indicated Power
BP
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BRAKE POWER (BP)
ɳm=
BP= ɳm× IP =
=
BP=Where:T=Torque in N-mN= Rotational Speed in MinutesBP=Brake Power in watt
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BRAKE POWER (BP)
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Mechanical Efficiency
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Mechanical Efficiency(i)
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Mechanical Efficiency
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Friction Losses1.Crank Shaft Bearing
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Friction Losses2. Connecting Rod Bearing
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Friction Losses3. Cylinder Piston Assembly
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Friction Losses4. Piston Rings
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Friction Losses5. Valve Train
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Friction Losses5. Oil Pump
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Friction Losses6. Water Pump
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Friction Losses7. Generator and Starter Motor
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S I Engine Friction
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Friction Power
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Thermal Efficiency
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Typically Gasoline Engines will have an sfc of about 0.3kg/kW-h
Specific Fuel Consumption(SFC)
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Volumetric Efficiency• Volumetric efficiency is
a comparison of the actual volume of air–fuel mixture drawn into an engine to the theoretical maximum volume that could be drawn in.
• Volumetric efficiency is expressed as a percentage
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Volumetric Efficiency
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Heat Balance
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Heat Balance
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Air Fuel Ratio
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Air Fuel Ratio
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Air Fuel RatioRich mixture
- more fuel than necessary(AF) mixture < (AF)stoich
Lean mixture- more air than necessary
(AF) mixture > (AF)stoich
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Air Fuel Ratio
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It shows the deviation of an actual mixture from stoichiometric conditions.
Equivalence Ratio (ɸ)
actual
stoich
stoich
actual
AFAF
FAFA
)()(
)()(
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The ratio of the volume of charge admitted at N.T.P. to the swept volume of the piston is calleda) mechanical efficiencyb) overall efficiencyc) relative efficiencyd) volumetric efficiency
Answer: d
FAQ
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FAQExplanation: Volumetric efficiency is the ratio of the volume of charge admitted at N.T.P. to the swept volume of the piston while mechanical efficiency is the ratio of the brake power to the indicated power and relative efficiency is the ratio of the indicated thermal efficiency to the air standard efficiency whereas overall efficiency is the ratio of the work obtained at the crankshaft in a given time to the energy supplied during the same time.
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Which one of the following event would reduce volumetric efficiency of an engine?a) Inlet valve closing after bdcb) inlet valve closing before bdcc) inlet valve opening before tdcd) exhaust valve closing after tdcAnswer: bExplanation: Volumetric efficiency of an engine is reduced by closing inlet valve before bdc.
FAQ
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Thanks