Topics:
Calculating Piston Speed:
The speed at which the piston moves within the cylinder is referred to as piston speed. The piston moves from top to bottom (the top dead center TDC) downward (bottom dead center BDC) and up again. Every time the piston reaches TDC or BDC, it stops because the direction of motion changes. This is illustrated in the image below:
The piston speed is highest when it is halfway through the cylinder. This is also related to the secondary piston movement. From the middle, the movement will slow down again until TDC is reached. When the crankshaft makes one full rotation, the piston moves down and up once. The distance between TDC and BDC is referred to as the stroke volume. If the actual crankshaft speed is also known, the average piston movement can be calculated.
V = 2 x s x n
V = average piston speed [meters per second]
2 = twice the piston movement
s = stroke; the distance the piston travels [meters]
n = crankshaft speed [Hertz]
Example:
An engine has a stroke of 90 mm. The stroke volume can be found in the manufacturer’s data for the engine. The engine speed is 3000 revolutions per minute (as read from the tachometer). With this data, the average piston speed can be calculated.
To begin, the stroke given in millimeters must be converted to meters (divide by 1000). So it is 0.09 meters. The crankshaft speed must also be converted from revolutions per minute to revolutions per second (divide by 60). That is 50 Hertz.
The calculated data can be filled into the formula:
V = 2 x 0.09 x 50 = 9 m/s