How Brazil's altitude affects the engine

© Renault Sport F1, 22 November 2012
© Renault Sport F1

One week on from the sport’s return to the United States, Formula 1 reaches its highest heights, quite literally, in Brazil.

At nowhere else does Formula 1 race at such high altitudes as in Brazil, and that creates unique problems from an engine perspective.

“We are at 800 metres above sea level in Interlagos. This altitude will degrade engine performance fairly significantly since the pressure is less at higher altitude, so less air will pass into a non-turbocharged engine. As a result you make less power because less oxygen is available to burn with the fuel,” explains Renault Sport F1 engine engineer for Williams, David Lamb. “It’s a fact of life for all engine suppliers. It is in the region of 8 to 10 percent here, so it is quite a significant drop when compared to Austin. The engine was probably at its most powerful all season last Friday because conditions were so cold. The drivers will notice it here, no question.”

Interlagos is a high power circuit, with a long uphill stretch at the conclusion of the lap, but there are countermeasures that can be taken to compensate.

“You’ll have less power and that is a simple fact, however the engines have an easier time internally so you can run them harder for longer. The combustion pressure is less so the pistons and other reciprocating components are put under less stress.

“You will need to use the driver torque pedal maps to make sure that the driver still has the full operating range of the engine under his right foot. There’s a compromise to be made between giving the driver the same physical response from the engine before stepping out to full throttle without losing any pedal resolution. For example, if you took a torque pedal map from Austin where the drivers receive around 300Nm from the engine at full throttle, here they will simply never get that. At maybe 80 percent of the pedal last week we would have asked for 270Nm, 10 percent less than full throttle and roughly equal to the maximum output here. As a result, using the Austin pedal map here would result in him getting maximum engine torque at just 80 percent pedal.”

There are however advantages to the altitude: one of the upswings is reduced fuel consumption.

“As a generalisation a more powerful engine uses more fuel if we assume a constant efficiency. So as a direct consequence of the engine being underpowered here, consumption per kilometre is that bit less.

“Another benefit is that since the air is less dense, there is less drag on the car. End of straight speed isn’t affected hugely because you take the drag off in roughly equal measure to the power, but that also means the drivers have less downforce through the corners, which is why the cars can look quite nervous. We therefore have to work hard to deliver drivability and modulate wheelspin during the second sector where there is a lot of lap time gain to be had.”

And, as if life wasn’t difficult enough for the engineers this weekend, the weather promises to throw a huge curveball.

“Every single forecast says it will be dry and beautiful all weekend with a slight chance of a shower in qualifying, but then Sunday is going to be a washout.”

How then can the teams possibly hope to prepare for such a huge shift in weather?

“You have to make that choice before qualifying as when the car goes into parc fermé you can’t change maps, so you need to have that balance. Realistically there’s no reason why your engine should perform differently in the dry or the wet in terms of its torque response. You may however err on the side of caution and go for a soft pedal map on tip-in to help the driver modulate the wheelspin in the wet. We also have to submit our ignition and torque maps before the event and the difference in climatic conditions between Saturday and Sunday is not insignificant. We’re already thinking about what we submit and how that will affect us this weekend. There’s a lot to think about.”

 

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