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      07-13-2015, 01:10 PM   #3081
debom3
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Hey Swamp,

Thanks for your input. I appreciate it. =)
Quote:
Originally Posted by swamp2 View Post
Where did you get the combustion pressure as a function of crank angle? Obviously this is also a function of both rpm and load (the latter is typically assumed to just be full load). This seems to be very difficult information to obtain.
I found that information from page 67 of this document.
http://www.m3post.com/forums/attachm...1&d=1338171744
If you go to page 67, you can find a description of the ion knock detection. I imported this graph into excel, and manually converted it to tabular form so that I could add the combustion pressure in my model. These pressures (peak near 40 bar at about 15 deg ATDC seem to agree with some published curves from my old textbooks) Your right, in that these will vary with load. I'm making the assumption that this is a full load graph, again based that the peak pressure is somewhat similar to values I see publisehd.

Quote:
Originally Posted by swamp2 View Post
Is this essentially a model for a single piston/cylinder, say sort of tilting the V of the block so one bank of pistons are moving vertically? That leads to the related question about the angular reference. Typically the reference point used is that 0° it top dead center just prior to combustion. You clearly used a different standard.
I was treating the Rod as a two force member transitioning between tension and compression. I was neglecting the angle and gravitational effects as well. I wasn't aware of the 0 deg ref angle at TDC, I think that should be easy enough to change.

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Originally Posted by swamp2 View Post
There are forces on the rod at the crank bearing end and at the wrist pin end and they are not equal nor even closely related due to the rod wobble motion. Is your "force" the axial force along the length of the rod on the crank bearing end?
Dont the forces have to be equal because the rod is a two force member? Yes, I was graphing the axial force transmitted through the rod. I know the reaction forces at each end of the rod have an axial and normal component, but the rod force should be completely axial. Im not sure what rod wobble is....

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Originally Posted by swamp2 View Post
The overall magnitude shape of your force curve seems like many assumption or some other parts of your analysis are way off. In particular see fig 2.15 and 2.17 here (I referenced this work way earlier in the thread). This guy, for his Masters Thesis, validated his methodology vs. the well validated and sort of industry standard ADAMS kinematic simulation software for a simple single piston system and it correlated absolutely spot on. Notice that there is always the observed peak tensile load (minimums in graphs) in the rod/rod bearing at the top of the exhaust stroke (360° crank angle with the convention I have described). Here exhaust valve(s) are open, there is almost no cylinder pressure load (it is at atmospheric pressure) and the system is just under inertial loading. The piston stops at TDC but also undergoes its peak acceleration (along with the rod itself) creating this peak tensile load. I can not see any behavior even close to this in your graphs. This indicates a significant flaw to me.

The reference above in 4 should be a solid foundation for you to verify/correct/improve your method.
Thanks for that link. I'm definitely going to check it out and see if I can refine the model. Ill PM you going forward so I don't clutter up this thread, but maybe I can email you my spreadsheet to check out?

I totally think that the engineers here can do just a good of job as some university professor. We are more interested in the topic and have an attachment to finding information and having that information be correct.

If anyone else is interested PM me. Any other ME's out there?

Thanks again
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      07-13-2015, 08:19 PM   #3082
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Quote:
Originally Posted by swamp2 View Post
1% was a rough upper estimate. And no 1% is not by any means a great reliability figure for a single type of flaw in a critical major component/subsystem. But it also is not "oh no, the sky is falling and it is raining S65 blocks and bearings" either.

On the surface more failures (at least a higher failure rate) for a bespoke, 8400 rpm redline, 100+ hp/l motor like the S65 as compared to the N54/N55 is absolutely no surprise to me.

Unfortunately, I think modern engine failure anecdotes, i.e. "data" in the internet age, is just not accurate. What was the failure rate, even an estimate for the M96/M97 engine "debacle"?
According to the class action the IMS bearing failure rate was 8%.

Estimates from various internet sources on catastrophic engine failure overall are 4-7% for '97-'00, around 10% for '01-'05. Keep in mind these engines had more than one common failure mode, not just the IMS bearing.

A more practical way to put it would be that if your relatively low-volume engine design is able to create and support a cottage industry to fix its problems then you screwed up. Troy Jeup already has a healthy S85 business going.
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      07-13-2015, 11:17 PM   #3083
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In looking up the issue with forced induction applications specific to a recent M3 failure (I cannot post the link due to forum rules) about cracked rods/improper casting of the rods as a potential cause of the engine failures (where cracks were seen in the rod itself). The rod bearing wear and ultimate fusion would be a symptom but not the underlying cause. Is there a reason to rule this possibility out completely?
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      07-14-2015, 10:36 AM   #3084
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Most of the bad bearings we see come from cars with perfectly good rods.
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      07-14-2015, 12:39 PM   #3085
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Quote:
Originally Posted by pbonsalb View Post
Most of the bad bearings we see come from cars with perfectly good rods.
+1, There is no evidence pointing to an issue with the rods or rod bolts.
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      07-15-2015, 01:05 AM   #3086
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Quote:
Originally Posted by debom3 View Post
Hey Swamp,

Thanks for your input. I appreciate it. =)
No problem.

Quote:
Originally Posted by debom3 View Post
I found that information from page 67 of this document.
http://www.m3post.com/forums/attachm...1&d=1338171744
If you go to page 67, you can find a description of the ion knock detection. I imported this graph into excel, and manually converted it to tabular form so that I could add the combustion pressure in my model. These pressures (peak near 40 bar at about 15 deg ATDC seem to agree with some published curves from my old textbooks) Your right, in that these will vary with load. I'm making the assumption that this is a full load graph, again based that the peak pressure is somewhat similar to values I see publisehd.
Excellent find! Since knock is generally a high load phenomena I suspect that data is for high/peak load. I think someone here (perhaps kawasaki or regular guy) claimed that combustion pressure varies reasonably strongly with rpm. The source I mentioned prior claims that he found a source (Ferguson, C. R., 1986, “Internal Combustion Engines, Applied Thermosciences,” John Wiley and Sons, Inc.) indicating the the peak pressure is not a function of rpm but the values at lower pressures can differ by around 10%. That specific graph is actually copied into the original thesis source I cited.

Quote:
Originally Posted by debom3 View Post
I was treating the Rod as a two force member transitioning between tension and compression. I was neglecting the angle and gravitational effects as well. I wasn't aware of the 0 deg ref angle at TDC, I think that should be easy enough to change.

Dont the forces have to be equal because the rod is a two force member? Yes, I was graphing the axial force transmitted through the rod. I know the reaction forces at each end of the rod have an axial and normal component, but the rod force should be completely axial. Im not sure what rod wobble is....
No, the forces are not equal and opposite, that is for statics, here the rod is constantly undergoing vertical and horizontal motion and acceleration. The combined motion is wobble. Analytical techniques assign part of the con rod mass as reciprocating and part as rotating whereas kinematic simulation does not require this approximation. Again, read the thesis I posted, it does not use this analytical technique to split the con rod mass.

Quote:
Originally Posted by debom3 View Post
I totally think that the engineers here can do just a good of job as some university professor. We are more interested in the topic and have an attachment to finding information and having that information be correct.
I think the community here can do a reasonable job on some basic kinematics/dynamics/loads. However, the advanced mechanics and hydrodynamics, both analytically and through simulation (FEA) techniques gets pretty involved, pretty quickly. You need to cover a variety of effects, moving oil source inlets, heat generation and thermal viscosity effects, eccentricity and dynamic rod deformation (specifically rpm and crank angle dependent changes in eccentricity from load), computational fluid dynamics, cavitation, etc.
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Last edited by swamp2; 07-15-2015 at 01:26 AM.
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      07-15-2015, 01:08 AM   #3087
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Quote:
Originally Posted by chris719 View Post
According to the class action the IMS bearing failure rate was 8%.

Estimates from various internet sources on catastrophic engine failure overall are 4-7% for '97-'00, around 10% for '01-'05. Keep in mind these engines had more than one common failure mode, not just the IMS bearing.
This data also generally supports the idea that 1% is a low number. Sure engines fail for many reasons but I've not seen much if anything posted on any catastrophic failure mechanisms in the S65 outside of something to do with bearings/oil or some related primary cause (with bearings/oil as a secondary cause).
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      07-16-2015, 04:57 PM   #3088
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Quote:
Originally Posted by swamp2 View Post
No problem.



Excellent find! Since knock is generally a high load phenomena I suspect that data is for high/peak load. I think someone here (perhaps kawasaki or regular guy) claimed that combustion pressure varies reasonably strongly with rpm. The source I mentioned prior claims that he found a source (Ferguson, C. R., 1986, “Internal Combustion Engines, Applied Thermosciences,” John Wiley and Sons, Inc.) indicating the the peak pressure is not a function of rpm but the values at lower pressures can differ by around 10%. That specific graph is actually copied into the original thesis source I cited.

.
I agree with that. Recipricating loads are not the same as cylinder pressure. Highest pressure is not a function line of rpm, this can vary greatly if boosted or whatever but you are correct to say that cylinder pressure doesnt goes up with rpm at a linear rate.
IMEP and PMEP is going to be highest at peak torque, but a engine that is superb at providing that nice flat torque curve will hold cylinder pressure for quite a while, like the s65
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