View Full Version : RBR: blown diffuser explained

07-13-2010, 01:17 PM
taken from http://scarbsf1.wordpress.com/2010/07/10/red-bull-map-q-the-secret-to-the-teams-q3-pace/

As explained in my post on ‘EBD’s’ – Exhaust blown diffusers (http://scarbsf1.wordpress.com/2010/06/25/exhaust-driven-diffusers/), teams blowing their diffusers rely on the throttle being open to keep airflow passing to the diffuser. Without this airflow, the diffuser loses downforce and the driver suffers a loss of grip or balance just as he enters the corner.

While careful design and how the exhaust is placed in relation to the diffuser, can alleviate some of the problems, any benefit from blowing the aerodynamics will be reduced when the throttle’s closed and no exhaust gasses are flowing.

It’s been reported that Red Bull are following a practice that was used on turbo cars (i.e. the old F1 turbos and WRC cars) to keep the turbo spooled up. By means of retarding the ignition when the driver is on the overrun as he slows for a corner. If Red Bull can keep the flow out of the exhaust pipe relatively constant, even when the throttle is closed going into a turn, then the diffuser will see a more consistent air flow and maintain downforce. Relieving it of the on\off throttle sensitivity so often a criticism of EBD systems. In effect an antilag system is trying to do the same as the Red Bull EBD mapping, maintaining a constant exhaust gas pressure, on or off the throttle.

Ignition normally occurs within the cylinder, driving the engine

When an engine is running normally, accelerating with the throttle open, the ignition of the fuel and air takes place inside the cylinder above the piston. The expansion of the gasses drives the piston and turns the engine.

After ignition, the exhaust valve opens and the cooler gasses rush down the exhaust pipe

During this process the gasses then escape into the exhaust pipe as the exhaust valves opens. As the burning has already occurred the gasses are some what cooler, the then temperature of the actual ignition. This means the exhaust gasses flow down the exhaust pipe with some speed and energy.

On a closed throttle, little air or fuel are burnt reducing the exhaust gas flow

When a driver lifts off the throttle, the engine does induct much air, nor burn much fuel, as a result the engine slows and the exhaust flow also slows down. It is this problem that affects the diffuser, as it sees less exhaust flowing through it.
With retarded ignition, the mixture burns in the exhaust creating a flow of gasses through the exhaust

What Red Bull do is retard the ignition and maintain some throttle and fuel to allow combustion to continue to take place. However the ignition of the air and fuel mixture now takes place later in the engines revolution, when the exhaust valve has already opened. Rather than driving the piston down, the explosion of the mixture goes into the exhaust, still expanding as it does so. This creates a rush of gas through the exhaust mimicking the effect of running with the throttle open. Thus the diffuser still sees a flow of gas and maintains downforce despite the engine slowing down.

Retarding the ignition overheats the exhaust components (red)

Of course this gain doesn’t come for free, the heat of combustion now takes place in the exhaust port, so that the exhaust valve, cylinder head and exhaust pipe all suffer excessive heat. This will affect them, as they cannot withstand this sort of thermal load for long periods. Equally the process burns additional fuel, in the race this is a negative thing as fuel is limited and no refuelling is allowed.
This ignition retard mapping would be controlled via the SECU via the driver selecting a steering wheel control, using quite normal tuning parameters and not some clever workaround. Of course this is all quite legal.

If the overheating issues can be contained, this would be a relatively simple mapping to introduce for another EBD team. As mentioned Renault Sport, Red Bulls engine supplier would have to know about this. Copying the concept, but not the actual SECU code would be quite easy.

coles version: ignition timing retard in Q3 over a single lap provides exhaust gas pressure to the diffuser even when the driver lifts off throttle, enabling downforce, a problem faced by some teams that have adopted the RBR diffuser, where downforce is lost when the driver lifts off for a corner and stability changes.

EK 2.0
07-13-2010, 01:21 PM
Thanks for the coles version....haha...

07-13-2010, 01:24 PM
Until I saw your Coles I was under the assumption that they were running this for the entire race and it was blowing my mind that they weren't running out of fuel. Makes sense to only do it on Q3 I suppose.

07-13-2010, 01:26 PM
no, this is supposed to be pretty hard on engines, so they can only do it over one lap, hence their Q3 domination this year. It also explains some of the engine reliability problems they've experienced.

This is also the same system the Evo used in Initial D :rofl:

Roaring G60
07-13-2010, 04:03 PM
This is a solution that was derived as a form of anti-lag in the early days of turbo's, as stated exhaust valves and inconel exhaust headers don't take kindly to the rapidly expanding gases. At least some ppl in F1 aren't afraid to look into the past to solve issues. Also note that teh exhaust gases don't actually flow into the diffuser, but in fact over the top section. The Faster moving, less dense exhaust helps to pull more air out the diffuser therefore creating more DF.

07-14-2010, 11:33 AM
I am curious how profound the gains are for this system vs. the downfalls such as lower reliability for critical engine components like exhaust valves .etc

some numbers would be dope! :thumbsup: