12 replies to this topic

[Alex]

We all know that F1 engines turn to over 17000rpm.

But what about idle speed?
From the sound, I'm predicting something like 5000rpm, or maybe more. F1 Engines in video games "idle" at 2500rpm, but I think that's little too low.

I've heard somewhere that F1 engines can't run below 6000, because of specific valve timing, etc.

Any truth in this?

[Christiaan]

they can't run at low speeds because they have a very small flywheel, and thus they do not have the inertia to keep themselves running at low speeds. Martin Brundle explained at Suzuka 1998.

[tak]

Another idling problem is the size of the fuel injectors--F1 appear to have two fuel injectors per cylinder. Figure that they are calibrated to flow enough fuel to produce 800 HP--so they are very large. At idle, they will be metering in MUCH MUCH less fuel, and the fuel wont atomize well. The result is poor fuel mixture at low RPM that is hard to ignite--raising the risk of fouling spark plugs....

[Christiaan]

hmmm, I thought atomisation was a inversly proportional to pressure and concentration?

What affects the atomisation tak?

[DangerMouse]

The main reasons for a high tickover is thet are are optimised for peak power at high revs by having a large valve overlap time which plays havoc with scavenging at low revs as does the huge inlet and exhaust ports which in turn leads to very low air velocity through the ports causing poor fuel atomisation and scavenging.

Even if you put a heavy flywheel on an F1 engine it would still run terribly at low revs due to the problems outlined above.

To fix the above problems you would need camshaftless valve actuation to reduce valve overlap at low revs as well as two inlet ports and butterfly valves per cylinder so only one port opens at low revs increasing the velocity of the incoming air or fuel/air charge (depending of whether you're direct injection or not.) Or course the latter will not occur because it doesn't matter about ultra low speed response in an F1 car!

[Christiaan]

DM, as for as I know F1 engines don't have camshafts at all. They have hydrualic valves operated by liquid nitrogen, which needs to be refilled every 4hrs or so. Imaging designing a cam which would have to have a profile flexible enough to deliver good power and torque from 4000-17000rpm: thats hell!

[MattC]

Christian:
No Camshafts? You sound pretty confident about this. However, 4000-17000rpm sounds far too narrow. I had imagined that they had a MUCH narrower power band. The cars have 6/7 gears, so they shouldn't need such a wide range. It would be like racing my road car using a rev-range of 1700-6800, and I _know_ how little torque I've got at 1700rpm!
If I keep extrapolating (dodgy, I know) we get an F1's power band of no more than 8000-17000.
Anybody know more accurately?

Matt

[Christiaan]

I am not too confident about that because I also read it on this BB. It does make sense to me however, because designing pnumatically operated valves have infinitely better flexibility than cams. I have also heard that they tested electromagnetic valves as well. I don't think that could have done well.

[Kapu7]

I have understood that valves are opened by camshaft, and closing is done with pneumatics. Using coils for closing valves at high RPM:s makes problems because inertia of coils causes vibrations as they bounce back.

If pneumatics were used for both opening and closing valves, it would require some kind of pneumatic servo-system, right? Sounds quite experimental.

And about atomization of fuel: when fuel is injected into intake-air, atomizing gets better when injector-nozzle gets small and injecting pressure gets high (as it creates smalled fuel-drops). At idle speed injection pressure drops, because much less fuel is needed (and nozzle-size remains constant) so it affects atomization.

[MikeA]

First of all; Didn't even a few of the different F1-engine makes turn above 18.000 rpm already in the early '99-season?

I suggest that the modern F1 engine still have a mechanical camshaft, but the valvesprings are of pneumatic design of at least two reasons
* No/less material fatigue (i.e. longevity)
* less valvetrain mass (I.e. more possible lobearea & valve acceleration)

I also believe that the pneu valvesprings emulate the caracteristics of a "real-world valvespring" i.e. linearity, etc.

I also believe that the used rpm-range is quite narrow just like a few thousand rpm's wide i.e. 2-3000 rpm.

I also believe that some of the engines at least has their camshafts NOT fixed in relation to the crank i.e. the are variable on both intake & exhasut and thus have provisions for a variable overlap/area which allow improvement of the rpm-range (if needed...?) and better idle quality.

BTW: Didn't Honda use variable timing valvetrain already in the early nineties?

BR

Mike

[DangerMouse]

Christiaan,
I should imagine just about every manufacturer has been working on a camshaftless engine for years - as far as I know there isn't one racing, the pneumatics are there to eradicate valve bounce by sucking the valve against the cam lobe, I should imagine the camshaftless engine would use electro magnetic valve actuation as it would be a straight forward exercise to map these devices to an engine management system.

I'm fairly confident all F1 engines have camshafts and at best have variable valve timing which although improves throttle response and fuelling lower down in the rev range VVT systems do not provide enough flexibility to change the cam timing too radically - they simply advance and ****** the fixed lift/duration camshafts which is miles away from the flexibility of a camshaftless engine, how can we be sure? If a manufacturer has a camshaftless design with the valve timing controlled at the whim of a computer rather than the by the constraints of a cam lobe imagine the torque punched out by a £100,000 3 Litre engine tuned to push out maximum power at 4000 RPM then you get the idea, F1 cars would have excess power everywhere and F1 teams would drop heavy 6 or 7 speed boxes for lighter 4 or 5 speed boxes and rely on the engines flexibility, as every F1 car always sounds like it screaming its guts out (even out of medium speed turns) we can be fairly certain the camshaft is still in F1!
The current Honda road type VVT and variable valve lift system, which actually lifts the inlet camshaft carrier complete with cam away from the inlet valves at low revs to speed up the inlet charge, isn't worth the technical hassle for the marginal gains it gives in F1, when a camshaftless engine does appear we'll all know because the car in question will trounce everything in sight and will not sound peaky.

[Christiaan]

Mike A, unfortunately if pnuematic valves operate with Nitrogen, their "spring" behaviour will be anything but linear. You see, Nitrogen's "elastic" behaviour is dependant on pressure, temperature and most of all :strain rate. So what could be the advantage of using pnuematic valves, well first of all this behaviour of nitrogen is understood and can thus be easily manipulated in the design to produce a desired effect. Second the inertia and weight savings. Also frictional savings as well.

[MikeA]

Christian:

"unfortunately if pnuematic valves operate with Nitrogen, their "spring" behaviour will be anything but linear. You see, Nitrogen's "elastic" behaviour is dependant on pressure, temperature and most of all :strain rate."

Introgen or not, I think I recall that much work was done in order to emulate a linear spring behaviour.

" So what could be the advantage of using pnuematic valves, well first of all this behaviour of nitrogen is understood and can thus be easily manipulated in the design to produce a desired effect. Second the inertia and weight savings. Also frictional savings as well."

Indeed. And this is the key to improved VE @ elevated rpm's. Plus the very needed longevity issues, as well.

BR

Mike