Efficiency, BP, BSFC, BMEP calculation -Two Stroke, Single Cylinder Petrol Engine


1.     Torque, T = 9.81 x W x R Effective Nm.

Where R Effective = (D + d)/2 m,

W (Load) = ( S1 S2) Kg.

2.     Brake Power, B P = ( 2πN T ) / 60, 000 KW

Where N = rpm,

T = Torque Nm,

3.     Indicated Power, I P = n ( Pm x L Stroke x A x N’) / 60,000 KW

Where Pm = Mean Effective Pressure N/ m2,

L Stroke = Stroke m,

A (Cross Section of the Cylinder) = (πD2Bore)/ 4 m2,

N’ (Number of Power Strokes/ min.)

= N/ 2 per min. (For Four Stroke Engine)

=N per min. (For Two Stroke Engine)

N = rpm, and

n = Number of Cylinders.

4.    Fuel Consumption, m f = ( 50 ml x 106 x ρ Fuel ) / ( t ) Kg/Sec.

Here; 1 ml = 10-3 liters, and 1000 liters = 1m3

So 1 ml = 10-6 m3

5.     Brake Mean Effective Pressure, BMEP = (BP x 60,000)/ ( L Stroke x A x N’) N/ m2

Where L Stroke = Stroke m,

A (Cross Section of the Cylinder) = (π D2Bore)/4 m2,

N’ (Number of Power Strokes/ min.)

= N/ 2 per min. (For Four Stroke Engine.)

= N per min. (For Two Stroke Engine)

N = speed in rpm.

6.     Brake Specific Fuel Consumption, BSFC = ( mf x 3600 ) / BP Kg/ KW . hr

7.     Indicated Specific Fuel Consumption, ISFC = ( mf x 3600 ) / IP Kg/ KW .hr

8.     Indicated Thermal Efficiency, η Indicated Thermal = ( IP x 100 ) / (mf x C.V. )%

9.    Brake Thermal Efficiency, η Brake Thermal = ( B P x 100 ) / (mf x C.V. ) %

10. Mass of the Air, m Air = Cd Ao √2 g Δh ρ Air ρ Water Kg/ Sec ;

Where Cd ( Coefficient of Discharge ) = 0.6,

ρAir= ( Pa x 102 ) / ( R x Ta ) Kg/m3

Ao ( Area of Orifice ) = (π do 2)/ 4 m2,

Pa = 1.01325 Bar,

R = 0.287 KJ/ Kg K .

Ta = ( ta + 273 ) K,

ta = Ambient Temperature O C

11.  Air Fuel Ratio, A/F = ( m Air / mf ) Kg/ Kg of Fuel

12.  Volumetric Efficiency, η Volumetric = ( VAir x 100 )/ Vs %

Where VAir ( Volume of air inhaled/ Sec.) = ( m Air / ρ Air ) m3/ Sec.

Vs ( Swept Volume/ Sec.) = n . ( L Stroke . A.. N’ )/ 60 m3/ Sec.,

And Volume of fuel is Neglected (Based on free air conditions),

A (Cross Section of the Cylinder) = (π D2Bore)/ 4 m2,

L Stroke = Stroke in m,

N’ (Number of Power Strokes/ min.)

= N/ 2 per min. (For Four Stroke Engine)

= N per min (For Two Stroke Engine)

N = speed in rpm., and n = Number of Cylinders.

13.    Mechanical Efficiency, ηmechanical = BP / IP

The BSFC calculation (in metric units) (Source: Wikipedia)

To calculate this rate, use the formula BSFC = \frac{r}{P}

Where:

r is the fuel consumption rate in grams per second (g·s-1)

P is the power produced in watts where P = τω

ω is the engine speed in radians per second (rad·s-1)

τ is the engine torque in newton meters (N·m)

The resulting units of BSFC are grams per joule (g·J−1)

Commonly BSFC is expressed in units of grams per kilowatt-hour (g/(kW·h)). The conversion factor is as follows:

BSFC [g/(kW·h)] = BSFC [g/J]×(3.6×106)

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