Question

How to calculate brake power of an engine?

Answer 1

Engine Formulas

 

Cylinder Swept Volume (Vc):

 



where:

            Vc= cylinder swept volume [cm3 (cc) or L]

            Ac = cylinder area [cm2 or cm2/100]

            dc = 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 (Ve):

 



where:

            Ve = engine swept volume [cm3 (cc) or L]

            n = number of cylinders

            Vc = cylinder swept volume [cm3 (cc) or L]

Ac = cylinder area [cm2 or cm2/100]

dc =  cylinder diameter [cm or cm/10]

 

* The units of cylinder swept volume is measured in (cm3, cubic centimeter (cc), or liter)

- Ve  for small engines, 4 cylinder engines is (750 cc:1300 cc)

- Ve for big engine, 8 cylinder engines is (1600 cc:2500 cc)

 

 

Compression Ratio (r):

 



where:

            r = compression ratio

            Vs = cylinder swept volume (combustion chamber volume) [cc, L, or m3]

            Vc = cylinder volume     [cc, L, or m3]

 

* 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 (hv):

 



where:

            hV  = volumetric efficiency

            Vair = volume of air taken into cylinder [cc, L, or m3]

            Vc = cylinder swept volume [cc, L, or m3]

 

* 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 (Ti):

 



where:

            Ti = engine indicated torque [Nm]

            imep = indicated mean effective pressure [N/m2]

            Ac = cylinder area [m2]

                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 (Pi):

 

,                        

where:

            imep = is the indicated mean effective pressure [N/m2]

            Ac = cylinder area [m2]

            L = stroke length [m]

            n = number of cylinders

            N = engine speed [rpm]

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

            Vc = cylinder swept volume [m3]

            Ve = engine swept volume [m3]

            Ti = engine indicated torque [Nm]

            ω = engine angular speed [1/s]

 

 

Engine Mechanical Efficiency (hm):

 

 

where:

            hm = mechanical efficiency

            Pb = engine brake power [kW]

            Pi = engine indicated power [kW]

            Pf = 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]

            Pb = brake power [kW]

 

 

Engine Thermal Efficiency (hth):

 

 

where:

            hth = thermal efficiency

            Pb = 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]

 
A whole list of engine formula
hope this helps
mark as a brain list please