i.c. engines

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

• Apparatus• Engine• Indicator• Planimeter

Indicated Power Pi

• 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

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 for engine working on the four stock cycle

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

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

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