ENGINE PERFORMANCE

PARAMETRS

Energy Flow in engine

Indicated Thermal Efficiency■ =

■ Indicated Power (IP) – power produced in cylinder

■ IP (KW) = n = k= no. of cylinders

■ =

Brake Thermal Efficiency

■ =

■ Brake Power (BP) - power available at crankshaft

■ IP (KW) = n = k= no. of cylinders

■ BP (KW) =

■ =

Mechanical efficiency

■ = =

■ Friction Power (FP) = Indicated power – Brake power

Volumetric Efficiency

■ =

■ =

■ = mass flow rate in kg/sec■ = Density of air

Mean effective pressure■ Average pressure inside cylinder based on measured or calculated

power output.

■ Imep – indicated mean effective pressure

■ Bmep – brake mean effective pressure

■ Used for comparing different engines

Mean speed of piston■ = Piston Speed (m/sec)

■ = 2■L= Length of stroke■N= revolution per second

■8 to 15 m/sec

Specific power input■ SPI =

■SPI = constant

■Effect of bmep and piston speed

Specific fuel consumption■ Fuel characteristics of engine – KG/KWH

■Sfc = = =

■ Depending upon power■ Bsfc – brake specific fuel consumption■ Isfc – Indicated specific fuel consumption

■ It is inversely proportional to thermal efficiency

Air- fuel ratio■Chemical correct or Stoichiometric air fuel ratio

(15:1)■Just enough air for complete combustion of fuel

■Equivalence ratio = φ = ■φ 1 --- Lean mixture■φ 1 --- Rich mixture■SI (Petrol) - 11:1 to 20:1■CI (Diesel) - 18:1 to 80:1

Calorific value■Thermal energy released per unit quantity of

fuel.

■HCV- Water vapors present are condensed

■LCV- Water vapors present are not condensed

Inlet value Mach index■ = Z =

■ = gas velocity at inlet value at smallest flow area■ = Area of Piston■ = Velocity of piston■ = Inlet value flow coefficient■ = Nominal intake value opening area■ = sonic velocity■ Z = Mach number

0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.30

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Inlet Value Mach Number (Z)

Volu

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