Current F1 diffusers, how do they work?

Specifically in relation to all the talk about engine mapping continuing to flow exhaust gases over the diffuser when the driver is on the brakes. Hence the upcoming ban.

http://www.autosport.com/news/report.php/id/91475

Are they just letting brakes overcome the engine HP? That seems unlikely, but I don't claim to have that kind of knowledge.

Are they just dumping fuel so there is the added mass going over the diffuser? Seems as though the headers would be hot enough to ignite the unburned fuel, right? Or maybe that's what they are after?

Even if it burns in the header, it's flowing more mass over the diffuser. THat kind of makes sense.

Sorry, just mumbling out loud.

I think the idea is the rev hangs when on the brakes... I assume the wheels are disconnected while braking.

"they will no longer be allowed to continue flowing gases through the engine when the driver is not on the throttle."

Heh, hope they wrote the rule better then that... or I wonder how they will start the engine every time they get back on the throttle

why don't they just go to a 205/60/15 all season tire and a maximum brake rotor diamter of 10" and let them do whatever the hell they want with the rest of the car?

F that, no wings, no ABS/trac control/launch control, bodywork inside the wheels (no LMS prototype style bodies), Do what you want.

Maybe a wheel size limit of some kind.

BobOfTheFuture wrote: F that, no wings, no ABS/trac control/launch control, bodywork inside the wheels (no LMS prototype style bodies), Do what you want. Maybe a wheel size limit of some kind.

Formula Vee!

Wheel base, track and weight. No other rules necessary. There's no telling what would roll out of the garages then.

For those who want to know how blown diffusers work.

http://www.youtube.com/watch?v=Ui6EDypjZKQ

the way the blown diffusers work is decently simple. they route the exhaust up to the front of the sidepod and out from under the car, to produce a cushion of air to "seal" the bottom of the car to the ground in a similar way that sideskirts do on ground effects cars. with a normal engine operation, there is a HUGE variation in the amount of gas being expelled out the exhaust between idle and full throttle, however, which would play hell with the sealing effect, so the teams are controlling the throttle via the engine map rather than the butterflies in the throttle body in order to keep a consistent amount of gas flowing out of the pipes. once you wrap your head around the basic method they use to do this, it's an ingenious idea that I'm REALLY sad to see go because it is genuinely one of the most interesting innovations to come out of F1 in some time, at least for me

say at full throttle, the engine is flowing 1000cfm of exhaust out of the pipes, and with this type of blown diffuser setup, the engine is tuned to flow damn close to that same 1000cfm of exhaust, regardless of throttle application, in order to retain a more or less constant sealing effect, but under the new regs that go in effect for Barcelona, off throttle, the engine would not be allowed to flow more than 100cfm of exhaust out the pipes (10% of the cfm rate at full throttle, as per the regulations), which obviously will play hell with the blown diffuser idea and will pretty much turn the entire field on its head, except for those select few teams not running a blown diffuser, but they haven't been doing much aero work anyway so they won't be much threat anyway.

^I know how blown diffusers work, if you'll check my first post, I'm curious as to how the engine mapping tricks are implemented. Your post just kinda repackaged all the available info already out there.

How are they still flowing exhaust gases out of the engine with no throttle input (that parts easy), but what are they doing with the revs/power being produced. They aren't just letting it sit in neutral at redline as they slow down.

alfadriver or one of the other engineers have any ideas?

z31maniac wrote: ^I know how blown diffusers work, if you'll check my first post, I'm curious as to how the engine mapping tricks are implemented. Your post just kinda repackaged all the available info already out there. How are they still flowing exhaust gases out of the engine with no throttle input (that parts easy), but what are they doing with the revs/power being produced. They aren't just letting it sit in neutral at redline as they slow down. alfadriver or one of the other engineers have any ideas?

maybe they let off the throttle pedal, but the throttle doesn't close.. the ecm just cuts the fuel and/or spark but keeps air flowing thru the engine because it is still being turned by the transmission. this assumes that they run a "fly by wire" throttle setup in place of a cable, which i'm sure they do.

F1 (and Indy) lost me when they became so rules laden. They will get me back when they scrap the current programs and create a simple elegant ruleset that allows for creativity.

z31maniac wrote: ^I know how blown diffusers work, if you'll check my first post, I'm curious as to how the engine mapping tricks are implemented. Your post just kinda repackaged all the available info already out there. How are they still flowing exhaust gases out of the engine with no throttle input (that parts easy), but what are they doing with the revs/power being produced. They aren't just letting it sit in neutral at redline as they slow down. alfadriver or one of the other engineers have any ideas?

Well, remember, there is more ways than one to limit torque. Since it's a balance of air, fuel, and spark, if you keep the air, you can turn off fuel and spark to keep the air flow very high.

So you may not have the velocity thanks to the heated exhaust, you can come to about 80-85 of peak air flow at a given engine speed (taking out the fuel does that, and even my estimate may be low, since fuel is 8-10%).

Basically, you are turning the fuel and spark off, and letting the engine pump via the gearbox. It's not as if the teams are not doing something like this with engine braking- the whole deal with downshifting and double clutching and whatnot. But modern F1 brakes are so good that you can not even worry about the engine braking and still have more than enough to do the job.

Keep the engine spinning, keep air flow going to places that don't normally get it, and you get downforce.

BTW, that does seem really easy- and the off part is. But getting it going again in a manner that does not upset the car is a trick, and since these conditions are so extreme, I have to hand it to the calibrators who tune these engines. they do a heck of a job.

Oh, and mid-corner when part throttle is used- you can retard the spark quite a bit so that torque is reduced and airflow can stay high- another major calibration trick. Not easy at all to get it really right.

(I'll go out on a limb and point out that I have a patent regarding controlling an engine with a fixed throttle.... one of them is 5,685,277....)

As a calibrator, I like the idea. As a fan, well, not so sure. Still debating it, personally.

^Excellent, thank you!

In reply to z31maniac:

Couple of things- I wasn't the first to post that, just a little more explanation.

Second- from what I'm reading, they will be legal this coming weekend in Spain, but not after that. So expect the pack to tighten a lot for the next races.

Yeah, I didn't skipped right over novaderrik's post. Sorry novaderrik!

Correct, the teams all complained that they didn't have enough time to change setups, engine mapping etc.

http://scarbsf1.wordpress.com/2011/05/19/fia-ban-on-aggressive-off-throttle-engine-maps/

According to the article (Craig Scarborough is the best tech authority on F1 I've seen), teams are timing the engine so that, off throttle, the fuel/air mixture is ignited just as it is leaving the combustion chamber. That way, it expands in and out the exhaust pipes, rather than against the pistons. That way, you still get combusted gases out the pipe while still being able to go off throttle normally, engine brake, etc.

I wonder how a setup like this would work at the relatively low speeds of autocross, or on closed-fender cars? flat-bottoming a production car can't be that hard, a purpose-built race car (eg a prototype/sports racer/tube frame GT/touring car) even easier, and from there it's just a matter of exhaust routing and a bit of trial and error on the engine map and the throttle linkages to keep the butterflies open all the time. I don't know how well it works compared to a physical sideskirt, or how it would work compared to just venting air from the front wheelwheels to roughly the same spot, but if it would work and work well, it might be worth exploring the possibility, especially for sports racers and the small bore formula cars that tend to run a very wide body/sidepods (F500/F600, for example, assuming you could fiddle with the engine mapping enough to get it to work)

EDIT: and for once, my signature is pertinent to the thread

In reply to Slyp_Dawg:

If you read the aero articles in Racecar Engineering, low speed aero is very possible. They have some good montly articles about aero, and some interesting stuff about realatively slow data recently.

In other news, I've read that this new rule change, where the blown diffuser will not be allowed, will not be enforeced until after Canada- so Spain, Monaco, and Canada will all have the current diffuser.

^That's too bad.

Canada would likely be even more exciting than usual with less downforce.

alfadriver wrote: In reply to Slyp_Dawg: If you read the aero articles in Racecar Engineering, low speed aero is very possible. They have some good montly articles about aero, and some interesting stuff about realatively slow data recently. In other news, I've read that this new rule change, where the blown diffuser will not be allowed, will not be enforeced until after Canada- so Spain, Monaco, and Canada will all have the current diffuser.

I really need to get a subscription to that magazine, preferably in electronic form, since there's only so much room in my house and I'm about convinced that there won't be room for other frivlous things like food and drink, lord knows car parts and race tires have started to replace traditional items in my house. you would be amazed how comfortable a 205/50-R15 Kumho V710 is to sit on if your chair is occupied

all joking aside, blown diffusers could be a real interesting prospect in club racing, and it would be awesome to see what backfires look like through a blown diffuser. wonder if the effect would be amplified if you supercharged the engine, then adjusted the map to suit? more air moving through the engine is more air moving through the engine, but at that point I would almost be worried about the added airflow making the car do a mix of a CLK-GTR/Harrier impersonation down the backstraight, especially on the much lighter cars.