Diesel engine testing

merlin

merlin

merlin

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This is work related but maybe some engine geeks can help me understand.

3 weeks ago a car manufacturing plant got a little upset as they were testing an engine which failed before it should have failed.

In a nutshell, this engine was set up to run at 7,500rpm constantly. It blew apart after 1140 hours. It should have lasted 1200 hours.

Reason for the failure isn't really relevant - I just can't get my head around why/how this engine was being run at 7,500rpm because it's actually a Diesel engine.

I've no idea whether the engine was just free revving or under load.

Twice now I've asked for confirmation of the set rpm for the test and twice I've been told 7,500rpm so there's no way I've misheard.

Data protection & all that rubbish so I can't give any more info on who is involved etc but maybe someone can explain why the engine was running at 7,500 rpm?
 
I should explain - it's not a race engine and the capacity is 2.0 and it goes into family type cars.

It's your regular dull diesel engine for your regular dull family type car.
 
Dolph said:
Sounds like a stress test tbh. That sort of speed would show accelerated wear over standard operating speeds and therefore reduce the length of time the test would take, or alternatively act as a worst case scenaro. It's fairly standard to test things well outside their usual operating range to see what happens.
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Yes, they say it simulates 100,000 miles.
 
DreXeL said:
I know you can't go into details J, but I find this really bizzare. Surely a test is just that, a test. Why did they 'get upset' when it failed the test? A test, by it's very nature, is going to involve ether passing or failing :confused: :confused:
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They said it was "unacceptable" the engine did not hit 1200 hours.

Their engineers have calculated that 1200 hours = 100,000 miles.
 
kaiowas said:
As some of you may know I spend my days sitting in the middle of an engine test facility. Never heard of doing overspeed tests (assuming it is actually operating outside it's normal range) to that kind of extent though.

1200 hours pretty much sounds like a full engine life durability test where the engine would usually cycle over it's full range of speeds and loads. If they were testing the effects of inadvertantly running at 7.5k I wouldn't expect the test to last any longer than a few hours.
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I can't really comment on whether the test is a reasonable durability test, i'm not clued up on that sort of stuff, I just know they equate 1200 hours @ 7.5k to be 100,000 = pass, but the engine failed.

What I don't understand (because again I'm pretty clueless on these things) is whether the engine would have just been free revving @ 7,500 or whether it would have been under load? Diesel doesn't burn quickly enough for 7,500rpm & this is just a bog standard 2.0 D engine.
 
kaiowas said:
Is there any chance that the engine was just being used as a mule to test a particular component (piston rings, bearings etc)?

In that case it may be that the engine was being motored (ie driven by the dyno in a similar way to when you coast down a hill) in order to increase engine speed and reduce the time taken to put a certain amount of wear on the relevant components.

Edit, having though about it you couldn't test rings in this way as they would need to see realistic combustion pressures for the test to be valid. They could concievably be testing bearings though.
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It was an "engine test", so I guess they were just expecting no problems up to 1200 hours. They intended to simply run it for as long as possible but so long as it hit 1200 hours it's a pass.

The top end failed.

Engine being "motored" to 7,500 rpm makes sense!
 
kaiowas said:
Any of the big players would be running a lot more engines that that before going to production. Even if an existing design is put into a different vehicle there'd be at least 2-3 validation engines to ensure that changes to the ECU calibration haven't caused any issues. An all new design would go through anything up to a couple of hundred engines.
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These are big players! Huge in fact.

Bear in mind I only have the information that's been fed to me though. This test could have been one in a series of tests. I just don't know the absolute full story.

Certainly I know for an absolute fact that they were ready to start making engines, then they had the failure, then they were not best pleased as the track stood still untill a revision was made and finally the engine let go AFTER 1200 hours.
 
[TW]Fox said:
Is it just me who thinks that sustained 7500rpm on a diesel engine without exploding until it had covered a simultated what.. 95,000 miles, is damn good?
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Yes and no.

Yes in that 7,500 rpm in a diesel is impressive as it's waaaay outside usual trim.

No in that it failed at 95,000 miles, well, that's if you agree that 7,500 rpm over 1200 hours = 100,000 miles. Their engineers have always worked to this formula.
 
Stonedofmoo said:
Sure I saw a post of his yesterday!

I gotta agree with Fox, seems to be to get that far at those revs is amazing. Surely even the modern diesels don't go much beyond 5500rpm.

I wonder if they use special engine oil for such a test, must run a big fuel tank! :)
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I think we're swaying towards the engine not actually "running" at 7,500 rpm.

In other words - it's being powered externally to run at that speed.

The engine probably wasn't been fuelled, just turned, if that makes sense.
 
It's pretty obvious diesel will not burn quickly enough with 7,500rpm cycles.

Hence it'll be making virtually no power if it was gobling air and drinking fuel at those revs. If it's making no power that's pretty pointless as a stress test, which leads me to believe this was a durability test with the engine just being spun up to 7,500rpm rather than running at 7,500rpm.

Stress test you'd do with the engine under load and producing power i.e 4,000rpm. Or simply throw stupid amounts of boost at it, or both!
 
Simon said:
I'd be pretty sure the valvetrain would struggle at 2500rpm over the max engine speed.
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Maybe that was the whole point of doing 7,500rpm?

To purposely see how long the top end could cling on to dear life.
 
Cool. :)

Do you agree the engine would be producing negligible amounts of power @ 7,500rpm if it was actually "running"?
 
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