I.C. ENGINES
Practical No: 5
(22 Apr, 2014)
Indicated Power Pi
• Indicated Power Pi
• Date
• Definition of Pi
• Is the actual power developed by the
engine
• Burning of fuel ( Chemical Energy) in the
cylinder produces Mechanical Energy
• Objective
• To measure the energy available at
flywheel
Indicated Power Pi
•
•
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•
Apparatus
Engine
Indicator
Planimeter
Indicated Power Pi
•
•
•
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Procedure
Warm up engine
Attach indicator with the engine
Put load
Indicator will generate indicator diagram
Diagram is recording of the pressure and
rate of pressure changes in the cylinder at
all points during the cycle
• It will give record of combustion process
and pressure rise, which will show any fault
in the timing of the ignition or valves
Indicated Power Pi
• Diagram
Indicated Power Pi
• Results
• By using planimeter the area of pv
diagram can be calculated
• The gauge points on the instrument are
adjusted to the length of the diagram
• Now boundary of the diagram is traced
around by the pointer on the instrument
• Reading on its scale is noted
Indicated Power Pi
• Results
• 𝑴𝒆𝒂𝒏 𝒆𝒇𝒇𝒆𝒄𝒕𝒊𝒗𝒆 𝒑𝒓𝒆𝒔𝒔𝒖𝒓𝒆 =
𝒊𝒏𝒔𝒕𝒓𝒖𝒎𝒆𝒏𝒕 𝒓𝒆𝒂𝒅𝒊𝒏𝒈 𝒙 𝑺𝒑𝒓𝒊𝒏𝒈 𝒓𝒂𝒕𝒆
𝑪𝒐𝒏𝒔𝒕𝒂𝒏𝒕𝒔
Indicated Power Pi
By calculation
• Symbols
• p = Mean effective pressure (m.e.p)
kN/m2
• L = Length of the piston stroke, m
• A = Cross sectional area of the piston
• S = Number of working strokes per
second
Indicated Power Pi
By calculation
• S for engine working on the two stock
cycle
• 𝑆=
𝑟𝑒𝑣
(
)
𝑚𝑖𝑛
60
x No of cylinders
• S for engine working on the four stock
cycle
• 𝑆=
𝑟𝑒𝑣
(
)
𝑚𝑖𝑛
60 × 2
x No of cylinders
Indicated Power Pi
By calculation
• Total force on piston = m.e.p. x cross
sectional area
• Work done by the piston in one stock =
force on piston ( N) x length of stock (m)
• W.D = m.e.p. x Area x stock ( kJ)
• W.D. = p x A x L (kJ)
• Work done by piston per sec
•
= p x A x L x S ( kJ)
• Indicated power (Pi ) = p x L x A x S
Indicated Power Pi
By calculation
• Indicated power (Pi ) = p x L x A x S
• b.m.e.p. = 𝜂 x i.m.e.p
Example
• A four cylinder , four stock engine with
100 mm bore and 100 mm stock
develops its maximum power at 3600
rev/min. At this speed the i.m.e.p. is
760 kN/m and mechanical efficiency is
85 %.
• Find indicated power and b.e.m.p
Example
• Data
• p = 760 kN/m2
• L = 0.10 m
• 𝐴=
• 𝑆=
𝜋 2
𝜋
𝑑 = 0.0102
4
4
360 × 4
= 120
60 × 2
Example
• Formula
• Indicated power (Pi ) = p x L x A x S
• Sol
• Pi = (760 x o.1 x 3.1416 x 0.1 x 0.1x 120)/4
•
= 71.63 kN/m2
• b.m.e.p. = 760 x 0.85 kN/m2
•
= 646 kN/m2
Example
• A six cylinder , four stock
engine with 60 mm bore and 85
mm stock develops a break
power at 24 kW at 2200
rev/min. Calculate b.e.m.p at
this speed
• Let 𝜂 p denoted by b.m.e.p.
Example
• Data
• Pb = 24 kW
• L = 0.085 m
• 𝐴=
• 𝑆=
𝜋 2
𝜋
𝑑 = 0.062
4
4
2200 ×6
= 110
60 × 2
Example
• Formula
• Pb = 𝜂 p x L x A x S
• Sol
• 24 = (𝜂 p x 0.085 x 3.1416 x 0.062 x 110)/4
• 𝜂 p = 907 kN/m2