Optimising a piston

30th November 2012, 15:05

I've put this here as I know a few people who regularly browse this part of the forum may be able to help me

Basically, in uni, we've got a FEA project to optimise the following marine piston. We have to model the piston in Solidworks under a specific cooling condition i.e. liquid cooled piston through the cooling cores, blocked cooling cores etc. Then we have to optimise the piston i.e. remove as much material as possible while keeping the thermal properties and stress distributions similar.

The gudgeon pin slots through the quarter model as show in the diagram below. I've modeled the piston and now just running some analyses with the current cooling properties and convection parameters. Any ideas where to start removing material from considering the following:

The optimisation of the piston must remain below the crown region
The outer dimensions of the piston must remain the same

Is there any typical procedures for removal or certain shapes that are used? I haven't looked into the project fully as I'm still busy doing other projects. Any info would be much appreciated so I can focus my research etc.

Cheers

30th November 2012, 15:34

Have you got any images of the piston design overall? Hard to tell where material is with that cross section. Is it perfectly symmetrical? Common areas are around the pin holes. If you calculate the force they will be put under (pretty complicated to calculate exactly due to massive variables) then you can optimise them fairly easily.
What is the material?
Are you limited by manufacturing restraints? e.g. Can it be ALM, EDM made or does it have to be conventionally machined?
Have they specified the "crown region" as that 82mm deep section on the diagram?

30th November 2012, 15:37

Also, if it is symmetrical then the one to jump at straight away is to create piston skirts on the thrust and opposing side and remove the other skirts making the pin supports in the centre. Although i'm not sure you are allowed to do that as it changed the stress distribution a fair bit, and will hinder the oil cooling you are aiming for.

30th November 2012, 15:50

Quote:

Originally Posted by adamskiTNR

Have you got any images of the piston design overall? Hard to tell where material is with that cross section. Is it perfectly symmetrical? Common areas are around the pin holes. If you calculate the force they will be put under (pretty complicated to calculate exactly due to massive variables) then you can optimise them fairly easily.
What is the material?
Are you limited by manufacturing restraints? e.g. Can it be ALM, EDM made or does it have to be conventionally machined?
Have they specified the "crown region" as that 82mm deep section on the diagram?

Yeah I'll post the solidworks shots below. Bare in mind its only a quarter model making it quicker and more beneficial for FEA. So the full piston would just be the same but revolved through 360 degrees (I've shown an image of the full piston too).

No limited manufacturing restraints, basically it could potentially be unable to be manufactured, its just showing the steps you've taken to optimise the piston and the various procedures of the FEA process (mesh convergence, mesh control etc).

The material is a custom silicon alloy. We are given the properties where the UTS changes with temperature etc. The crown region doesn't appear to be specified nope

, I'm guessing it literally means the top of the piston!

This is the statement given for the optimisation stage:

"The design of piston presented above is rather old. In order to increase the power output the engine is required to run at a higher speed which can only be achieved if the mass, and hence inertia, of the piston is reduced. Optimization of the piston to achieve the above requirement should be limited to the under crown region of the piston, the outer geometry of the piston should not be changed in any way.You are required to undertake an optimization of the piston both on an individual
and group basis (see below for details of how this is to be presented). The optimization should aim to produce a piston with a considerably reduced mass but which will not fail in service."

SW images:

30th November 2012, 16:08

Remember when you put it through FEA that it is not a simple quarterly revolve. Look at it and you will notice if you do this the FEA will go berserk as the pin hole cant be revolved obviously. So make sure it is a half model and then halved again, if that makes sense. So the software is doing a quarter of the actual model it should be doing.
Please bare in mind that i have no experience of "marine" engine design" So i have no idea what requirements are needed. e.g piston rings.
You could do as i said above, by making central pin mounts (really don't know the name lol) then this will allow you to remove the outer skirts between the thrust and opposing face. Remember that the only function of the piston skirts are to transfer heat to the block and to support the piston in the axis of the cylinder. In the second instance the sides of the piston serve no function to an extent.
To remove more you could assess the situation and possibly remove a ring land to push the skirt higher still. Note this will increase piston temperature due to reduced surface area for heat transfer. So the remaining faces (especially the thrust face) may need coating to reduce friction and in turn generated heat.
After doing this the piston will look nothing like it does now so i cant comment on the other internal areas.
Of course this is all in reference to massively over square race car engine designs, so all this may be impossible with this (big?) marine piston. And engine design isn't something that i am particularly focussed in, I'm a suspension and packaging man myself, so dont compromise your degree lol.

30th November 2012, 20:08

I would initially start with all the standard areas such as piston skirt design in addition to the design around the pin.

The next steps are harder to explain try looking up design houses and companies on google they are a good references

4th December 2012, 12:31

Any progress?