Thermal growth

[Dhondt]

How can i determin (or make an educated guess at)the thermal growth of an engine in the vertical plane (upward), when no specifications are available? More specificly i'm looking for the exact thermal growth of the MTU 2000 & 4000Marine diesel engine. I'm trying to determin the amount of offset necessary to compensate for thermal growth, flywheel sag and oil film lift of the crankshaft.

 

[GregLocock]

Figure on a block temperature of 100 degrees C and take it from there.

How on earth can you get an 'exact' figure from an 'educated guess' is beyond me.

Cheers

Greg Locock

 

[patprimmer]

How can you get an exact figure on constantly varying values.

Every component is receiving and rejecting heat, and receiving cyclic stresses as the engine runs. All components also have a temperature profile accross the component.

You can do pages full of very precise calculations for various conditions, and come up with an answer with very wide min and maximum possible limits, or you can draw on best guess experience and get it pretty close if you have access to experience..

I guess you are trying to set piston to head clearance, or calculate static compression ratio

Regards
pat

 

[EngJW]

Not all the temperature change goes into growth. For example, with an aluminum head it may want to expand a lot, but the steel head bolts prevent it. So instead of thermal growth you get thermal stress.

 

[EdDanzer]

The only way to obtain what you want is to measure it. This will be difficult but results may be obtainable with a portable CMM. The trick will be to have a known location cold, and hot, that is in the plane you are trying to measure.

 

[Chumley]

From my AISC Manual (American Institute of Steel
Construction) I use the table for coefficients of
lineal thermal expansion which are listed in inches
per inch per 100°F change in temperature provided
as jlwoodward states, the materials are free to expand.
But, be careful. Because materials are restrained in
one dircetion does not imply they are restrained in
all directions. Cylinder block/cylinder head/exhaust
manifolds come to mind.


Here are a few values from the table:

Aluminum, wrought .00128
Bronze .00101
Copper .00093
Iron, cast grey .00059
Iron, wrought .00067
Lead .00159
Magnesium .0016
Nickel .00070
Steel, mild .00065
Steel, stainless .00099
Zinc, rolled .00173

The coefficient of surface expansion is approx. twice
the above, the coefficient of volume expansion is
approx. three times the linear coefficient. Probably
an easier way, if possible, is to find a similar sized
engine that has been around for a while and see what
they did.

Hope this helps,

Chumley

 

[patprimmer]

More food fore thought.

Pistons rock in the bore, in fact offset gudgeons are specifically designed to control when this happens.

This rocking action also effects piston to head clearance, and this changes with wear.

You know you got it right in a race engine when there is no sign of impact, but the top of the piston is clean in the quench area.

in engines that require extensive service life, I guess you got it right if the piston tops are clean in the quench area, but with no actual impact when the bores are at maximum wear tollerance.


Regards
pat