Ferrari: Open Fronted Blown Diffuser

The opening in the diffuser (yellow) is blown by the exhausts gasses (red)

On Thursday at Interlagos the F10 was seen with a new diffuser set up, as well as an F-duct with the main plane blown rather than the flap. Ferrari have followed other teams and created an open fronted diffuser.

Ferrari first followed Red Bulls idea of an Exhaust Blown Diffuser (EBD) at Round09 in Valencia. but Ferrari chose to blow the exhaust over the top of the diffuser. Where as Red Bull had created an opening into the diffuser, so that the exhaust blows both over and under it. At Silverstone Red Bull opened the diffuser up in two more places each side.

Closed diffuser: the exhaust gas (red) blows over the top of the diffuser (yellow)

Having an open front to the diffuser and directing exhaust flow into it, speeds up the airflow through the diffuser creating more downforce. As with all EBD’s the trade-off is the variation of downforce according to throttle position. To some extent the positioning of the exhaust well upstream from the inlet reduces this effect, as does the engine mappings that retard the ignition and keep the exhaust flow moving even when off the throttle.

Open Diffuser: the exhaust gas (red) enters the slot and passes inside the diffuser (yellow)

Since Mid season both Williams and Mercedes have created open fronted diffusers. In Mercedes case the 800c heat from the exhaust created problems with the diffuser rigidity. Detail design heat shields and improved materials, such as ceramic composites (i.e. Pyrosil) have allowed the exhaust flow to pass directly over the diffuser surface without thermal problems.

Ferrari’s late introduction of the open fronted diffuser and revised F-duct is at odds with statements from the team back in Singapore that the cars development had finished to focus on 2011. Either Ferrari have reignited their development programme as their championship fortunes have reversed with wins in the late season races. Or perhaps the comments meant that the development of the parts had finished, i.e. the design phase was over, but the manufacturing and testing were still in progress.

Clearly these parts do not come from any 2011 programme as the draft rules will ban openings in the diffuser. Although these rules are aimed at eradicating the double diffuser, the wording prevents 50mm openings in the outer portion of the floor (where the flat floor meets the diffuser). Thus open fronted diffuser are effectively banned as routing exhausts that far outboard are impractical. In 2011 downforce can still gained by having the exhaust blowing over the top towards gurney flap to speed flow the diffuser. Equally the f-duct is banned in 2011 replaced by a driver adjustable rear wing.