Analysis: blown diffusers, before the cut
Further ahead, the FIA is also planning a ban on the blown diffuser as exhaust exit positions will be restricted.
As early as the beginning of 2010, kinetic energy of exhaust gases have been a hot topic in Formula One. Red Bull's Adrian Newey initially pioneered the new generation of blown diffusers as the exhaust outlet was positioned low above the floor of the Red Bull RB6. In the age of double deck diffusers, this was extremely beneficial to energise airflow going through the upper deck of the diffuser.
As things moved on, gaps were opened in the diffuser to also blow the lower deck, eventually triggering the governing body to clamp down on the practice and ban double diffusers, as well as any possibility to blow exhaust gases directly into the diffuser.
Alternatives to blow the diffuser
Obviously, with such energy being pushed out of the exhaust, teams were looking feverishly to work around the new regulations and still use the fast and hot exhaust gases for downforce generation. Different teams took different routes, but 7 races into the season, only two different design paths are being followed.
The first and most popular route is that introduced by, again, Adrian Newey. This system is often dubbed an exhaust blown diffuser (EBD). On the new Red Bull RB7, he decided to use the outer 50mm of the diffuser - close to the inner wall of the rear tyres - to try to still end up with exhaust gases underneath the car's floor (illustration by AbbaleRacing77).
Red Bull channeled the ovalled exhaust pipe over the car's floor and ends the exhaust pipes just ahead of the 50mm opening. With air pressure lower and air speed higher underneath the floor - due to the diffuser "sucking air" from underneath the car - some of the exhaust flow get bent under the diffuser and is expanded further, hence creating additional downforce.
In addition to the gasflow bending, and perhaps more importantly is the sealing effect of these exhaust gases. The high speed nature of the exhaust flow creates what one could call an air-wall, preventing outside air from flowing into the diffuser.
The second option, but certainly the most revolutionary are the front exit exhausts (FEE) that are run by Renault. This effectively created an exhaust blow floor (EBF) as exhaust gases are routed towards the leading edge of the sidepods, and released their transversally into the path of the regular airflow.
There are various different theories as to how this effectively works, but just like with the Red Bull system, the exhaust gases create a skirt alike flow that fights airflow through that exhaust stream. At the pipe exits, the flow acts similar to a barge board where coming from the front wing will be diverted to the outside. Further along the exhaust stream, the same can be achieved along the car's floor up to the rear wheel.
In any case, Renault's technical director James Allison has confirmed that this system creates its effect close to the car's centre, hence generating downforce all over the car and not affecting aero balance.
A third option, and in fact a much simpler one is that currently used by Mercedes GP and HRT. Both are taking a similar route to the Red Bull RB6 solution as the exhaust pipes exit low above the car's floor, but much further ahead than on the RB7. This solution is less optimal but is believed to be less sensitive to throttle, and hence requires less extreme engine mappings to create an effect on the diffuser.
Hot blown diffuser clampdown
With the effect of exhaust gases becoming more and more important for downforce generation, teams and engine manufacturers started to develop special engine mappings that allowed for an exhaust flow, even when the driver is off the throttle.
Such engine map is put into the ECU by connecting a computer to it. These newly developed engine settings retard the ignition so much that fuel is burned in the exhaust pipes. While Renault have said they have been using a similar technique for years now to cool the exhaust valves within the engine, this hot-blowing is facing a considerable restriction as of the race at Silverstone.
After giving in on its proposal to restrict hot blowing for the Spanish GP, the FIA confirmed it will restrict this practice as of the GP of Great Britain. With formal wording not yet finalised, throttle openings will likely be restricted to just 10% of their maximum when the driver is not pushing the throttle. Although most teams appear to be opposed to this change mid-season, all will be effected, but it remains to be seen which cars will suffer most from the change.
In addition to that, race director Charlie Whiting also recently sent a letter to teams, nothing that switching engine maps between qualifying and race is not allowed anymore. This will prevent teams from running engine maps that are targeted for extreme performance, no matter what amount of fuel is used. Red Bull Racing are expected to suffer most from this change as they have dominated each qualifying session so far in 2011 but are usually less dominant in races.
Further along the road: 2012
As for next season, word has it that the FIA have agreed with teams that exhausts will have to exit above the sidepod, hence returning to the periscope exhausts all teams were using from 2002 (McLaren was the last to adopt the Ferrari pioneered system) until the switch to blown diffusers.
There was an earlier proposal to mandate exhaust exits at 330mm behind the rear wheel centreline, but it is understood that teams preferred the periscopes, most likely because it allows for shorter exhaust pipes and hence provides an advantage for the engine manufacturers.
While rules about this are not finalized, it is certain that exhausts are they are now will not be seen again in 2012, once more deeming it necessary for cost reductions.Steven De Groote Images courtesy of Mercedes GP, Red Bull Racing, LRGP