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Below is an animation of the piston motion equations with the same values of rod length and crank radius as in the graphs above. Piston motion animation with the various half strokes from the graph above (using the same color code)
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.
For speed the corrected value is corr = / Example: [17] An engine is running at 100% speed and 107 lb of air is entering the compressor every second, and the day conditions are 14.5 psia and 30 deg F (490 deg R).
The formula was calculated from total piston surface area (i.e., "bore" only). The factor of 2.5 accounts for characteristics that were widely seen in engines at the time, such as a mean effective pressure in the cylinder of 90 psi (6.2 bar) and a maximum piston speed of 1,000 feet per minute (5.1 m/s).
As piston engines usually have their maximum torque at a lower rotating speed than the maximum power output, the BMEP is lower at full power (at higher rotating speed). If the same engine is rated 72 kW at 5400 min −1 = 90 s −1 , and its BMEP is 0.80 MPa, we get the following equation:
Oversquare engines (a.k.a. "short stroke engines") are very common, as they allow higher rpm (and thus more power), without excessive piston speed. Examples include both Chevrolet and Ford small-block V8s; the GMC 478 V6 has a bore/stroke ratio of 1.33. The 1.6 litre version of the BMW N45 gasoline engine has a bore/stroke ratio of 1.167.
In piston engines, static compression ratio is determined using the cylinder volume when the piston is at the top and bottom of its travel. The compression ratio is the ratio between the maximum and minimum volume during the compression stage of the power cycle in a piston or Wankel engine .
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 73.17615° after TDC. Then, using the triangle sine law , it is found that the crank to connecting rod angle is 88.21738° and the connecting rod angle is 18.60647° from vertical ...