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The reciprocating motion of a non-offset piston connected to a rotating crank through a connecting rod (as would be found in internal combustion engines) can be expressed by equations of motion. This article shows how these equations of motion can be derived using calculus as functions of angle ( angle domain ) and of time ( time domain ) .
Engine displacement is the measure of the cylinder volume swept by all of the pistons of a piston engine, excluding the combustion chambers. [1] It is commonly used as an expression of an engine's size, and by extension as an indicator of the power (through mean effective pressure and rotational speed ) an engine might be capable of producing ...
It also denotes the ratio of equivalent air volume drawn into the cylinder to the cylinder's swept volume. [5] This equivalent volume is commonly inserted into a mass estimation equation based upon Boyle's Gas Law. When VE is multiplied by the cylinder volume, an accurate estimate of cylinder air mass (charge) can be made for use in determining ...
It is therefore calculated by the formula [10] = + where is the displacement volume. This is the volume inside the cylinder displaced by the piston from the beginning of the compression stroke to the end of the stroke. is the clearance volume. This is the volume of the space in the cylinder left at the end of the compression stroke.
The mean piston speed is the average speed of the piston in a reciprocating engine. It is a function of stroke and RPM. There is a factor of 2 in the equation to account for one stroke to occur in 1/2 of a crank revolution (or alternatively: two strokes per one crank revolution) and a '60' to convert seconds from minutes in the RPM term.
Speed has dropped out of the equation, and the only variables are the torque and displacement volume. Since the range of maximum brake mean effective pressures for good engine designs is well established, we now have a displacement-independent measure of the torque-producing capacity of an engine design – a specific torque of sorts.
The Porter-Allen high-speed engine (ca. 1862) operated at from three to five times the speed of other similar-sized engines. The higher speed minimized the amount of condensation in the cylinder, resulting in increased efficiency. [19] Compound engines gave further improvements in efficiency. [19]
For example, for rod length 6" and crank radius 2", numerically solving the above equation finds the velocity minima (maximum downward speed) to be at crank angle of 73.17530° after TDC. Then, using the triangle sine law , it is found that the crank to connecting rod angle is 88.21832° and the connecting rod angle is 18.60639° from vertical ...