__Engine Formulas__

__Cylinder Swept Volume __(*V _{c}*

_{}

where:

*V _{c}*=
cylinder swept volume [cm

*A _{c}*

*
d _{c} *= cylinder diameter [cm or cm/10]

*
L *= stroke length (the distance between the TDC and BDC) [cm or cm/10]

* *

BDC = Bottom Dead Center

TDC = Top Dead Center

* Increase the diameter or the stroke length will increase the cylinder volume, the ratio between the cylinder diameter/cylinder stroke called “bore/stroke” ratio.

- “bore/stroke” >1 is called *over square engine,*
and is used in automotive engines

- “bore/stroke” =1 is called square engine

- “bore/stoke” <1 is called= *under square engine*,
and is used in tractor engine

__Engine Swept Volume __(*V _{e}*):

_{}

where:

*V _{e}* = engine swept volume [cm

*n *= number of cylinders

*V*_{c} =
cylinder swept volume [cm^{3} (cc) or L]

*A _{c}*

*d _{c}*

* The units of cylinder swept volume is measured in (cm^{3},
cubic centimeter (cc), or liter)

- V_{e}
for small engines, 4 cylinder engines is (750 cc:1300 cc)

- V_{e} for big engine, 8
cylinder engines is (1600 cc:2500 cc)

__Compression Ratio __(*r*):

_{}

where:

*r* = compression ratio

*V _{s}* = cylinder swept volume (combustion chamber volume) [cc,
L, or m

*V _{c}* =
cylinder volume [cc, L, or m

* Increase the compression ratio increase engine power

- r (gasoline engine) = 7:12, the upper limit is engine pre ignition

- r (diesel engine) = 10:18, the upper limit is the stresses on engine parts

__Engine Volumetric
Efficiency __(_{h}* _{v}*):

_{}

where:

*h _{V }_{ }=*
volumetric efficiency

*V _{air}* = volume of air taken into cylinder
[cc, L, or m

*V _{c}* =
cylinder swept volume [cc, L, or m

* Increase the engine volumetric efficiency increase engine power

- Engine of normal aspiration has a volumetric efficiency of 80% to 90%

- Engine volumetric efficiency can be increased by using:

(turbo and supper charger can increase the volumetric efficiency by 50%)

__Engine Indicated Torque __(*T _{i}*):

_{}

where:

*T _{i}* = engine indicated torque [Nm]

*imep* = indicated mean
effective pressure [N/m^{2}]

*A _{c}*

_{
}*L* = stroke length [m]

*z* = 1 (for 2 stroke engines), 2 (for 4 stroke engines)

*n* = number of cylinders

*θ* = crank shaft angle
[1/s]

__Engine Indicated Power __(*P _{i}*):

_{},
_{}

where:

*imep* = is the indicated
mean effective pressure [N/m^{2}]

*A _{c}* = cylinder area [m

*L* = stroke length [m]

*n* = number of cylinders

*N* = engine speed [rpm]

*z* = 1 (for 2 stroke engines), 2 (for 4 stroke engines)

*V _{c}* =
cylinder swept volume [m

*V _{e}* = engine swept volume [m

*T _{i}* = engine indicated torque [Nm]

*ω* = engine angular speed [1/s]

__Engine Mechanical
Efficiency __(*h** _{m}*):

_{}

where:

*h _{m} *= mechanical
efficiency

*P _{b}* = engine brake power [kW]

*P _{i}* = engine indicated power [kW]

*P _{f}* = engine friction power [kW]

__Engine Specific Fuel
Consumption __(*SFC*):

_{}

where:

*SFC* = specific fuel consumption [(kg/h)/kW, kg/(3600
s x kW), kg/(3600 kJ)]

*FC* = fuel consumption [kg/h]

*P _{b}* = brake power [kW]

__Engine Thermal Efficiency __(_{h}* _{th}*):

_{}

where:

*h _{th}*
= thermal efficiency

*P _{b}* = brake power [kW]

*FC* = fuel consumption [kg/h = (fuel consumption in L/h) x (*ρ*
in kg/L)]

*CV* = calorific value of kilogram fuel [kJ/kg]

*ρ* = relative density of fuel [kg/L]

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