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Absolute cylinder pressure is used to calculate the dynamic compression ratio, using the following formula: = where is a polytropic value for the ratio of specific heats for the combustion gases at the temperatures present (this compensates for the temperature rise caused by compression, as well as heat lost to the cylinder)
From the geometry shown in the diagram above, the following variables are defined: rod length (distance between piston pin and crank pin) crank radius (distance between crank center and crank pin, i.e. half stroke) crank angle (from cylinder bore centerline at TDC)
The overall displacement for a typical reciprocating piston engine is calculated by multiplying together three values; the distance travelled by the piston (the stroke length), the circular area of the cylinder, and the number of cylinders in the whole engine. [2] The formula is:
The volume ratio / is called the "isentropic expansion ratio". (For the Otto cycle is the same as the compression ratio V 1 / V 2 {\displaystyle V_{1}/V_{2}} ). Mechanically this is the expansion of the hot gaseous mixture in the cylinder known as expansion (power) stroke.
The stroke ratio, determined by dividing the bore by the stroke, traditionally indicated whether an engine was designed for power at high engine speeds or torque at lower engine speeds. [ 2 ] [ 3 ] The term "bore" can also be applied to the bore of a locomotive cylinder or steam engine pistons .
Rolling-element bearings are often used for axles due to their low rolling friction. For light loads, such as bicycles, ball bearings are often used. For heavy loads and where the loads can greatly change during cornering, such as cars and trucks, tapered rolling bearings are used.
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The Peugeot design works by varying the effective length of the con-rods connecting the piston to the crank. When the con-rod is shorter, the compression ratio is lower and vice versa. On the left hand-side of the diagram is the conventional piston of an internal combustion engine. On the right is an hydraulic cylinder with double-acting piston.