Investigating exhaust aided diffusers

[ringo]

Well here is another diffuser thread, but it has a different spin.

It seems it is general accepted that exhaust driven diffusers increase the suction produced by the diffuser by jet entrainment. However this method to increase down-force is looked down on because of the dependency on the drivers right foot to keep the exhaust flowing.

It is said that in a corner or under braking, the driver is off the throttle and the exhaust velocity is reduced, affecting the diffuser performance. It is this inconsistent behavior, why the exhaust blown diffuser is looked down upon. This train of thought has been carried on throughout the years, and F1 teams simply turn a blind eye to it as a means of improving performance.
What i find interesting is that most of us may have overlooked the difference between the cars from the inception of the exhaust blown diffuser and the cars of today.
We look at a car like the RB6 and say that the technique works because they move the exhausts higher up than where they were on the older cars; in the throat.

It could be a possibility, but i think we need to look at the cars themselves and find out why it is an exhaust blown diffuser is a net gain on a 2010 car, than say a car from the early 90s or late eighties.
What i find stands out is the engine speeds. Cars today rev at 18000~20,000 depending on which year and engines you are looking at.

So this thread is really about investigating, the exhaust velocities at 18,000 and whatever engine speeds occur off throttle in the turns. Versus those of an older car, which maybe 13,000 rpm on full throttle and whatever else in the turns.
Do the higher engine speeds of today's cars and the responsiveness of the engines ensure that the exhaust gas velocity stay above that threshold where the down-force can be drastically affected?
Or is it that the amount of down-force produced today's refined cars is so monstrous that the down-force lost by going off throttle is a small percentage?

[ringo]

Some examples of cars with exhaust driven diffusers, their engine speeds, style of diffuser and what rpms experienced in a downshift or off throttle in a turn, responsiveness and other technical aspects would be helpful. I am not too knowledgeable on the cars of the past.

[tommylommykins]

hmm

Wasn't there some engineer over here that posed another idea?

(don't quote me, but) He said that the exhaust was used to keep the turbulence from the rear wheels from messing up airflow in the back


Considering he appeared to have real experience with real diffusors, I wonder why his ideas were ignored...

He appeared to know more than us

[DaveW]

Are brakes & throttle necessarily mutually exclusive?

[autogyro]

Are brakes & throttle necessarily mutually exclusive?

Not in a series Hybrid they are not but you do not realy want to go there do you?

[aral]

A peculiar title to the thread. No diffuser is DRIVEN by the exhaust. Presumably the thread is supposed to discuss the exhaust exiting into the diffuser area. Yes, this will increase the suction effect of the diffuser, and also help to fill in the low pressure void behind a car, thus creating less drag, and increasing top speed. But a diffuser has no parts requiring to be DRIVEN.
And where is the stigma??

[DaveW]

Not in a series Hybrid they are not but you do not realy want to go there do you?

No, I don't (although I believe most do drive "two footed"). But it depends on how much D/F they gain, I guess (assuming RBR do use the exhaust productively). RBR does appear to have an aero advantage..... & might have experienced brake problems?

[autogyro]

Not in a series Hybrid they are not but you do not realy want to go there do you?

No, I don't (although I believe most do drive "two footed"). But it depends on how much D/F they gain, I guess (assuming RBR do use the exhaust productively). RBR does appear to have an aero advantage..... & might have experienced brake problems?

I remember helping to pioneer left foot braking with my semi automatic racing saloons back in the 1970s. In F1 it started with the auto and semi auto layshaft control in 1988/9. Many of the drivers took a long time to adapt and some still move their right foot across rather than use the left on the brake pedal.
Left foot brake right foot throttle is 'much' faster.
It does allow a certain independence but keeping the throttle on under braking puts a lot more wear onto the brakes. Is this what you mean?

[autogyro]

With my ESERU as the core component and the gearbox in an F1 car. It can be operated either as a parallel or series hybrid/kers at the same time as retaining a seven speed stepped sequential gearbox operation for the regulations.
In series use, the engine can be used idependently to maintain high rpm while letting the ESERU gearbox act as an energy recovery/Kers unit balanced to the rear brakes. This would allow up to full throttle under braking without brake wear from the engine and maintaining full driver feel and control.
An exhaust augmented diffuser would then be a simple matter.

[RH1300S]

Can I make a suggestion? Bringing your tranmission up in this thread will potentially de-rail it (IMHO of course ) simply because the poster is asking about the 'how's' and 'why's' with particular regard to engine revs. And I think the answers should relate to F1 as it currently is or has been - which means stepped transmissions and throttle off situations.

What I WOULD like to see is for you to add that info to your transmission thread - it's actually quite an interesting statement worth discussing.

P.S. - nothing personal, I enjoy many of the little bombs you throw around, they are thought provoking.

[Jon]

It could be a possibility, but i think we need to look at the cars themselves and find out why it is an exhaust blown diffuser is a net gain on a 2010 car, than say a car from the early 90s or late eighties.
What i find stands out is the engine speeds. Cars today rev at 18000~20,000 depending on which year and engines you are looking at.

Well, I believe McLaren abandoned the blown diffuser with the MP4/16 of 2001. The 2000 car still had it, and that engine reved between 17,000 and 18,000 rpms. So, about the same as they are now...and yet they dropped the concept...

Hmmm...what does that mean?

[autogyro]

IMO it is not possible to use the exhaust from a high reving engine to increase DF without making the DF levels and balance alter to much for the driver to deal with.
I do believe that Newey has found a way to use the exhaust gas to improve airflow however.

[DaveW]

IMO it is not possible to use the exhaust from a high reving engine to increase DF without making the DF levels and balance alter to much for the driver to deal with.
I do believe that Newey has found a way to use the exhaust gas to improve airflow however.

You could be right, autogyro. But if rear D/F has been increased by exhaust flow, then the front wing would have been adjusted to achieve (more of) an aero balance at high power. Hence the vehicle would tend to be an aero over-steerer with a closed throttle..... Hence my thoughts re maintaining some power whilst braking.

p.s. A driver would not require full power for a balance at low(er) airspeeds, I guess....

[autogyro]

Manual front wing flap might help, or even a flexi front wing that increases AofA at lower speeds. Regulations might stop that though.
I think it more likely to do with the suspension and dive under braking increasing floor DF and moving the center forward.
Lengthening wheelbase when the suspension closes up powering out of corners has an effect to.
But I could be way wrong.

[mx_tifoso]

It's ok guys, autogyro invented the wheel, sliced bread, the ICE.

Autogyro, no more talk/interjection of the ESERU system or your posts will be moved out of here. I am already contemplating moving a few out. You use other peoples threads to market your product, that's beyond lame.

Oh, and it's not on topic because it's not real nor is it in use in F1. Pediod.