High revving engines - endurance

[hansforum]

Hi!

Can someone explan why F1 engines break after only few hundred miles, I mean what parts are the weakest link and why do they fail? What is the most often reason they broke?

I read that some civil sport car engines (Audi R8 V10 for example) have average piston speed higher than F1 engine. Why don't they break so fast?

Thanks!

 

[BrianGar]

The Audi is 5.2L, and 518hp with a rev limit of 8,700.

An F1 engine is very different. It has just 3.0l and makes around 950hp, with a rev limit of oh...18,000

Consider what both engines each weigh that you are comparing also.

Perhaps this will start to explain why they break.

If you have never seen one in person, you should have a look, they are also disappointingly small. All the more reason as to how they are so impressive from an engineering point of view.

Also, piston speed and max piston acceleration at tdc so be looked at, lot of reading there...

G-forces within an F1 engine are insane, with hot bike engines a close second. Same goes for piston velocities.

Brian,

 

[BrianGar]

Here is a thread I remembered reading from a few yrs back(time is flying!) that may provide you with more material, you will find more Im sure by searching,

http://www.eng-tips.com/viewthread.cfm?qid=85349

Brian,

 

[hansforum]

I found and calculated some interesting facts.

F1 engine (2003 BMW F1 engine) - at 19000 RPM, average piston speed is about 25m/s, max. piston acceleration is around 10000g.

Audi R8 V10 5.2L 560hp - at 8700 RPM, average piston speed is 26.9m/s, max. piston acceleration is around 5000g.

Ferrari 458 Italia V8 4.5L 570hp - at 9000 RPM, average piston speed is 28.2m/s, max. piston acceleration is somewhere around 5400g.

We can see that Audi and Ferrari have greater average piston speed than F1 engine. What does this fact tell us in terms of reliability? Why so many car magazines quote this number if it is greater than F1 engine numbers.

Now, it is clear that F1 engine piston has a lot greater acceleration, but it would be nice if someone have piston mass numbers for those car so we can calculate real force that is acting on piston mechanism.

It is obvious that Audi and Ferrari have bigger engines with less hp than F1 and they could be cooled easier because of that but it would be nice if someone can answer what is the most common failure in F1 engines and why?

 

[BrianGar]

Did you read the above link also?

One of the main problems with such speeds is keeping the big ends round, and the hydrodynamic oil film complete. - Bare in mind doing all this with minimum conrod material.

Pneumatic valve trains are another weak point, the gas escapes and the valve train suffers.

Brian,

 

[Lou Scannon]

Something to keep in mind is that F1 and other race engines have a much higher duty cycle at the upper end of their performance envelope than do high powered passenger cars. Consequently, BSFC at the upper end of their power range is relatively more important than for high powered passenger cars. BSFC tends to increase with piston speed. So F1 and other racing classes' piston speeds may not be pushing the envelope.
The need for light weight, and especially for low reciprocating & rotating inertia, will drive extremely light, high rpm solutions, in F1 and other racing environments. This will result in high g forces, that are readily met by the appropriate design solutions.

 

[LionelHutz]

Simple answer - There are many, many hours of R&D put into a F1 engine to build the lightest, most powerful engine possible. Part of that R&D is to ensure that the parts are just strong enough to run the distance required for the race weekend before breaking because that is as light as you can make the part. Sometimes, they go to far or have a material defect and the part fails too soon.

There are 2 basic areas where failure occur - the rotating assembly and the valvetrain. I'd suspect that valvetrain failures are the most common.

 

[L4189]

If you ran the Audi and Ferrari engines at their rated speeds and power they wouldn't last very long either. Mostly they are stuck in traffic or if running under 100 mph probaly don't exceed 100 hp. or run between 2000 and 3000 rpm. So in average conditions the piston speed is at a reasonable rate.

 

[GregLocock]

Dunno about that. All three companies I have worked for regard 100 hours at full power from a prototype as the STARTING point for a successful production engine. Until then you don't have an engine for your program.

Cheers

Greg Locock


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[BrianGar]

Full power, or full rpm?

Brian,

 

[pontiacjack]

I agree with Greg regarding the 100 hour peak-power dyno test being typical for U.S. automotive engine development, at least for the last half century. Bunkie Knudsen initiated this minimum requirement for model year 1958 of Pontiac V8 engines.

 

[140Airpower]

Generally, F1 engines do not break within the design lifetime. The design lifetime is set by the rules. The manufacturers are able to minimize the weight and durability of parts to last just long enough. A few years ago, before the FIA limited the maximum RPMs, you would see regular failures usually from rod and piston breakage. Because pneumatically sprung valve trains removed that as a limiting factor, F1 engines were usually rev and power limited by the bottom end, -rods and pistons.

 

[WGJ]

A past employer used a 55/5 cycle (55 mins rated max speed/rated max load, followed by 5 min idle) for 1500 hours as a so-called "sign-off" for many engines.

Running in simulated city/traffic conditions is not necessarily an easy ride as there may well be more coolant and oil temperature variation and rich running during accelerations.

Bill

 

[SomptingGuy]

We've been doing quite a lot of work on a contemporary high performance engine recently. The durability testing sounds awesome.

- Steve

 

[pwildfire]

I spent some time at a manufacturer where we built family car style 4-cylinders. I was not particularly surprised by the QC tests regarding various load cycles, but the thermal shock test was amazing to me. The engine was run at a constant medium load/speed condition for 80 hours, during which coolant was exchanged every xx minutes, alternating between 100C coolant and 15C? coolant. Surprisingly most engines survived.

As far as F1, as has been mentioned, the rules dictate the design. Currently, each driver is allowed 8 engines per season. The rules also dictate the material for each major component (mostly NOT exotic materials), as well as the lack of most 'advanced' features such as variable timing and geometry.

The load cycle is pretty severe for F1 too. Full load/speed is often not as detrimental to components ans a wide load/speed cycle such as an F1 race where the engines are constantly cycled from full load to full braking load amidst various environmental conditions.

 

[Lou Scannon]

The F1 rules do less to keep the development cost down than to limit maximum performance. Development expenditures for a first rate team will be dictated by sponsors' return on investment calculations (and/or strategic investment in a brand), not the cost of raw materials, processing thereof, or exotic (or not) technology. Whether or not the raw material or basic technology for a particular component or subsystem is considered conventional or exotic, when it's realized in an F1 application, it's exotic by definition, considering the unit cost including NRE.
In a nutshell, ultimately the rules limit theoretical maximum performance, and the teams strive with each other to approach that theoretical maximum, by expending the all funds they have available, as wisely as possible.

 

[patprimmer]

As wisely as possible or as wisely as they think they can.

I agree, no matter how tight the rules, someone with the desire and budget can get an advantage from investing more in development within the rules or by finding ways around the rules.

A case in point. In a turbo class with maximum allowable boost, some manufacturers spent a lot of time developing the best location in the manifold for the pressure sensor to get the lowest possible reading. Things like in a side chamber with the entrance facing away from direction of airflow.

I think one may even have created a side chamber with a somewhat restricted inlet to it and a bleed of from it. I think they got disqualified for a few years when caught.

Point being that extensive testing for the best legal position costs.

Regards
Pat
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[Lou Scannon]

Exactly. They will always put their effort where (they think) they can get the most bang for the buck.

 

[140Airpower]

I agree with Pat, "...no matter how tight the rules, someone with the desire and budget can get an advantage from investing more in development within the rules or by finding ways around the rules...".

This is more true with a designer/constructor's formula, like F1, where rules makers may not anticipate unintended opportunities for innovation, than it is with spec or preparers' formulas, like NASCAR.

Al

 

[romke]

the reason is quite simple - they are designed that way.

the requirement in F1 is pretty straightforward: as high as possible a power output as possible with as little weight as possible that lasts a full race and some preliminary training time. anything longer will result in either less power or more weight or both and less change to be successful in the race.

to get to that point calls for extensive testing, careful design, QC and exotic materials, but all that effort in the end is geared towards that one goal: power combined with lightness.