The discussion revolves around calculating the required inertia of a flywheel when changing from a larger diameter (1.8 m) to a smaller diameter (1.2 m) flywheel for an engine system. Participants explore the implications of this change on the overall system inertia, considering factors such as mass, moment of inertia, and energy loss in reciprocating parts.
Participants express various viewpoints on the importance of mass, thickness, and design considerations for the flywheel. There is no clear consensus on the best approach to maintain the required inertia or the implications of the changes being made.
Participants reference specific formulas and calculations, but there are unresolved assumptions regarding the definitions of inertia and the effects of design changes on performance and vibration.
xxChrisxx said:You need to know the energy loss caused by reciprocating parts when not on a power stroke. The mass of the engine is irrelevent. (as I am assiming that includes block)
Do you have the book Shigley - Mechanical Engineering Design?
Acutally you may not need to do that as all. Do you want to keep the same inertia as the current larger flywheel gives? Why are you chaning flywheel diameter?
So, when i using the smaller flywheel that means the thickness must be higher than bigger flywheel.xxChrisxx said:If that is the case and the engine has similar power outputs all you want is the moment of inertia of the flywheel to be the same.
MOI= 0.5mr^2
for a cylindrical flywheel.
You need to weigh the current flywheel to find its mass and put it in that formula above to find the current MOI.
Use this MOI value to find the mass needed at the new radius flywheel using the same formula above. This will give a thickness needed to maintain the same inertia.
Compare the new thickness to the old, if it's much thinner you may have structural issues.
Ok. But I'm very worried with this flywheel. Because the thickness almost same. It will be effect more vibration or what?xxChrisxx said:Yes, as the rotational inertia depends on radius.
The further away the mass is from the centre the biggesr its effect of MOI.
You will find your new flywheel will weight less than the old smaller one (less diameter)
xxChrisxx said:If you ran the calcualtion and the thickness as almost the same that's fine. There's no problem.
As long as the flywheel is well made and balanced there should be the same or less vibration.
What is the mass/weight of the current flywheel?
xxChrisxx said:Ahhhhh you are going to a smaller diameter, silly me! Sorry I thought you were going from a smaller to a larger!
Ok so you started with a 2000kg 1.8m diamter.
MOI = (2000*0.9^2)/2
= 810 kgm^2
810 = (m*.6^2)/2
m = 4500 kg.
new mass = 4500kg
This is going to be a much heavier flywheel if you keep it as a cylinder. So it'll be much thicker.
new flywheel thicknes. assuming steel.
mass = density * volume
mass = d * csa *h
4500 = 7850 * pi*0.6^2 *h
thickness = 0.5068 m
What you could do is make the flywheel thinner near the centre and thicker near the edge, this would allow the mass to be reduced but keep the moi the same.