Some time before the Belgian Grand Prix, Red Bull submitted a query to the FIA regarding the placement of the heat sensors within the Mercedes power unit’s intake plenum. This was initiated after Red Bull had observed from GPS traces that the Mercedes displayed occasional bursts of enhanced power under acceleration out of corners before then reverting to ‘normal’.
Since the pre-season launch of the W12 it has been speculated that the unusually big plenum of the 2021 Mercedes PU (requiring a large blister at the side of the engine cover) has within it a unique cooling system which can be used to make the intake air denser and therefore more combustible.
The air enters through the airbox within the engine cover and is directed to the turbo’s compressor (which, in compressing the air, has the undesirable effect of increasing its temperature a long way above ambient), then to the intercooler (to reduce the temperature again), the plenum, intake trumpets and finally the combustion chamber.
There’s a technical regulation controlling the intake air temperature. It must be at least 10°C above the ambient, as an average over the race. Sensors measure and transmit this temperature to the FIA.
Obviously the closer the engine can be run to that regulation temperature limit, the more power it will be able to produce, but keeping it at or close to that average limit without going beneath it is no easy task in conditions which are forever changing. So the temperatures tend to be quite conservative. But if there was a way of taking advantage of any ‘surplus’ average built up by briefly introducing much cooler air – thus bringing the average closer to the permitted limit – it would give the sort of brief power burst which Red Bull had observed.
“Cooling the plenum on demand would be a powerful tool”
The theory is that the Mercedes has a system whereby a quantity of coolant can be borrowed from the main system, supercooled and fed into the walls of the plenum. These walls would have a maze of hollows and matrices to maximise surface area. These cooled walls would lower the temperature of the air travelling through the plenum chamber.
But once that thermal transfer from the cool walls to the hotter, fast-moving air had taken place, the effect would be over and the no longer supercool coolant would be released back into the main system. It would though have given a brief burst of extra power and could in theory be repeated on demand.
Such a liquid-cooled plenum would give the sort of flexibility required to get closer to the permitted average minimum in variable, dynamic conditions. The cooling effect of the intercooler cannot be varied as required and has just a set effect. A plenum which could be cooled on demand – perhaps through software which recognises a pre-set combination of parameters – would be a potentially powerful tool
A potential limitation to this theory is that the plenums are commonly fashioned in carbon fibre, which is a very poor conductor of heat. Getting the heat transfer from cool interior walls to the warmer (and fast-moving) air inside the plenum would require a good conducting material. A ceramic would be ideal but such materials are banned from the power unit by regulation. The Mercedes plenum appears to be made of carbon fibre, so maybe debunking the whole theory. It’s possibly merely a carbon casing of a metal plenum, however.
There is nothing about such a system which would contravene the regulations, but this is F1 where competitive paranoia is rife – and occasionally justified. What if the temperature sensors were not in a place which would accurately record the wallcooled air? This seems to have been the basis of Red Bull’s query to the FIA.
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“The FIA is regularly in conversations with the teams about technical matters,” said a spokesman. “It’s just part of the normal process.”
Merc’s technical chief James Allison said of the engine cover bulge at the car’s launch: “There’s been a big investment by our friends at HPP to redesign the plan of the intake system of the engine, re-tune the engine around that, and squeeze a lot more power out of the power unit as a consequence.”
It has all added to the intrigue as Red Bull has sought to understand where its championship rival may be gaining an advantage. “We are happy that they are dedicating time to this type of research,” said Merc boss Toto Wolff about Red Bull’s query. “If they are distracted like this, that’s fine. Their every request is welcome for us.”
There is obviously a reason why the Mercedes plenum is so big. But whether it’s this one is far from certain; it could indeed be that Red Bull is chasing a red herring. Which in the ongoing battle between the two entities adds an extra element.