Engine%20Parameters

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Engine Parameters
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Cylinder
3
Compression ratio (r)

• VC Clearance volume
• VS Swept volume ?/4 D2 L
• where L (stroke) 2 ?, ? is the crankshaft
  radius
• - Increasing the compression ration increases the
  thermal efficiency, compression is limited by the
  knock limit.

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Engine Displacement, Swept Volume or Engine
Capacity (Ve)

• Ve VS n
• Ve (?/4) D2 L n
• WhereVe engine capacity, Vs cylinder swept
  volume
• n number of cylinders, L stroke, D bore
  diameter

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Volumetric Efficiency ?V
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Volumetric Efficiency ?V (cont.)

• Engines are only capable of 80 to 90 volumetric
  efficiency.
• Volumetric efficiency depends upon throttle
  opening and engine speed as well as induction and
  exhaust system layout, port size and valve timing
  and opening duration.
• High volumetric efficiency increases engine
  power.
• Turbo charging is capable of increasing
  volumetric efficiency up to 50.

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Indicated mean effective pressure (imep)

• Factors affecting imep
• Compression ratio
• Air/fuel ratio
• Volumetric efficiency
• Ignition timing
• Valve timing and lift
• Air pressure and temperature

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Factors affecting (imep)-
Retarded ignition - Weak mixture -
Compression ratio - Super charged
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Pressure, Force, Work Power
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Engine Indicated Power (Pi)

• Engine power factors
• Engine capacity (Ve)
• Engine Speed (rpm) (Ne)
• Number of strokes k
• k2, four stroke engine
• k1, two stoke engine
• (imep)
• volumetric efficiency, compression ratio,
  ignition quality, mixture strength, temperature

• Pi imep.Ve.Ne / (60. k)

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Engine friction

• Three types of friction-bearing surfaces in
  automobile engines
• Journal
• Guide
• Thrust

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Engine Brake Power (Pb)

• -This is the power developed at the crankshaft or
  flywheel.
• -The term brake originated from the method used
  to determine an engines power output by
  measuring the torque using some form of friction
  dynamometer.

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Engine Mechanical Efficiency ?m

• Pb Pi - Pf
• Where
• Pi indicated power
• Pb brake power
• Pf friction power
• ?m Pb / Pi

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Engine Brake Power (Pb)

• Pb Pi ?m
• Pb (imep Ve Ne / 60 k) ?m
• Pb (imep ?m)Ve Ne / 60 k
• Pb bemp Ve Ne / 60 k
• Where
• bmep brake mean effective pressure
• bmep imep ?m
• bmep is indication of engine efficiency
  regardless of capacity or engine speed, 1000 kPa
  represent high efficiency.

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Gross Net Brake Power

• Gross brake power is measured without the
  following items
• Cooling fan, coolant pump, radiator,
  alternator, exhaust system. (SAE)
• Net brake power is measured with all the above
  items. (DIN)
• Gross power is 10-15 more than net power.

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Engine Torque Te

• Torque and crankshaft angle
• Work is also accomplished when the torque is
  applied through an angle.
• Distance xy r?
• W F . xy F r ? T ?
• W per one revolution T (2?)
• P W/t T (2?)/t T?/1000
• Where ? 2? Ne/60

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Engine Torque Te (Cont.)

• Pb T ? Te (2? Ne/60) Te Ne / 9550 (kW)
• bmep . Ve . Ne / k 60 Te (2? Ne/60)
• Te bmep . Ve / 2? . K
• Where
• Pe Engine power (kW)
• Ne Engine speed (rpm)
• Te Engine torque (N m)
• bemp brake mean effective pressure (Pa)
• Ve engine capacity (m3)
• k 2, for 4-stroke engines
• 1, for 2-stroke engines

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Engine Torque Te (Cont.)

• - There is a direct relationship between BMEP
  and torque output.
• - The torque curve with engine rpm is identical
  to the bmep curve, with different values.

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Engine Fuel consumption (FC)

• The amount of fuel an engine consumes can be
  measured by
• volume (cm3 or liter) per (sec. or mint, or hr)
• or
• mass (kg) per (sec, or mint, or hr).

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Engine Specific Fuel Consumption (SFC)

• Specific fuel consumption represents the mass or
  volume of fuel an engine consumes per hour while
  it produces 1 kW of power.
• Typical gasoline engines will have an SFC of
  about 0.3 kg/(kW.h).
• SFC is an indication of the engines thermal or
  heat efficiency.
• (kg/h)/kW or kg/(kW h)

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Engine Thermal Efficiency (?th)

• The efficiency of an engine in converting the
  heat energy contained in the liquid fuel into
  mechanical energy is termed its thermal
  efficiency.
• The petrol engine is particularly inefficient and
  at its best may reach 25 efficiency.
• The thermal efficiency of a diesel engine can
  reach 35 due to its higher compression ratio.

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Thermal Efficiency (Cont.)
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Thermal Efficiency (?th) (Cont.)

• where is the fuel consumption (kg/h)
• is the fuel consumption (L/h)
• CV is the calorific or heat value of 1 kg of
  the fuel (kJ/kg or MJ/kg). (CV for gasoline is
  40000 kJ/kg)
• ? is the relative density (kg/L) of the
  fuel.

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Specific Fuel Consumption (SFC) Thermal
efficiency (?th)

• Where
• ?th thermal efficiency
• fuel consumption (kg/h)
• Pb brake power (kW)
• CV calorific value (kJ)
• SFC specific fuel consumption (kg/(kW.h))

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Specific Fuel Consumption (SFC) Thermal
efficiency (?th)

• A mirror reflection of the SFC curve shows the
  shape of the engines thermal efficiency curve.
• The lowest point on the SFC curve becomes the
  highest point on the thermal efficiency curve.

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Power Units

• BHP (bhp) 550 ft lb/s
• PS 75 kg m/s
• kW 1000 (N m/s)
• BHP British and American horse power
• PS "PferdeStärke is "horse power in
• German
• PS 0.986 bhp, BHP 1.0142 PS
• kW 1.36 PS, PS 0.73529 kW
• kW 1.341 bhp, BHP 0.7457 kW

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Engine Performance Curves

1. Imep
2. Bemp and torque
3. Indicated power
4. Brake power
5. Indicated thermal efficiency
6. Brake thermal efficiency
7. Specific fuel consumption