Mean piston speed
Mean piston speed can be defined as the speed of piston throughout the stroke movement. Since piston is connected to crank shaft then it gets power from it . Piston has reciprocating motion but crank has rotational motion.
If we observe carefully then we can see that , the half rotation of crank shaft gives one way to move forward from BDC to TDC or TDC to BDC. And same for another half rotation. Hence we can see that only one rotation of crank shaft, piston moves linearly twice.So the speed will get two times the speed travelling one stroke during process.
N = rotational motion in rpm L = stroke length of piston in mm v(avg.) = average mean speed of piston
v(avg.) = 2 × speed of piston in one stroke.
But piston need 2 stroke to complete one cycle of rotation (of crank shaft). Piston has a velocity throught the cycle. Hence , it is clear
v(avg.) or total speed = 2.L.N.60/1000 mm.