Clearance Volume of Cylinder

Posted By: MolaKule

Clearance Volume of Cylinder - 02/03/20 11:44 PM

Riding on the coattails from what we have already explored in:


When the piston is at TDC, the space above the piston is the combustion chamber which may include the compressed gasket. the combustion chamber dome, spark plug space, etc This volume of space is called the clearance volume.

So the clearance volume is the volume of air remaining in the cylinder when the piston is at TDC, due to the shape factors mentioned above.

or stating it another way,

The Displacement Volume, or the "Swept" Volume is the volume displaced by the piston as it moves between top dead center (TDC) and bottom dead center (BDC). This volume determines the capacity of the engine.

The Clearance Volume of the engine is the volume between the cylinder head and the piston top when the piston is at TDC. The relationship of this volume to the swept volume determines the compression ratio of the engine.

If we substitute 180 degrees or 3.1414 Radians into the formula from the previous problem:

x = a + L - [SQRT(L^2 - a^2*sin(ThetaRad)^2] - a*cos(ThetaRad) = 3.48 inches, the piston Stroke distance;

Since V is a function of x as in V(x), we determine total (Swept) cylinder Volume for the x position at 180 degrees of Crank Angle.

V = x*BA = 43.9938 or 44 cubic inches, which is the swept cylinder volume "Vswept" for180 degrees of Crank Angle, or the volume swept by piston from TDC to BDC or from BDC to TDC.

Now since the Compression ratio is a function of Vswept and Vclearance,

Find the Clearance Volume of any one cylinder if the CompressionRatio is 9.2:1 using the formula:

Vclearance = Vswept/(CompressionRatio - 1).

Please show your math, but do not dump any spreadsheets in this thread. Spot answers with values alone are not proper answers.

This question is open to Everyone.

Posted By: CR94

Re: Clearance Volume of Cylinder - 02/04/20 12:09 AM


(Total volume/cylinder at BDC = 49.37 in³)
Posted By: MolaKule

Re: Clearance Volume of Cylinder - 02/10/20 10:16 PM

Looks like CR94 owned this one.

The clearance volume has to be there, otherwise there would be zero volume for combustion during the compression cycle and infinite pressures.

Additionally if you use the piston distance travel formula verses crank angle, the equation

x = a + L - [SQRT(L^2 - a^2*sin(ThetaRad)^2] - a*cos(ThetaRad)

blows up at 0 degrees and 360 degrees.
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