INSIGHTS

  • THE POWER OF ALTITUDE

Report

28 October 2018

You might not realise it on television, but the Mexican Grand Prix always takes place in extremely demanding conditions due to the race’s location. Often you can tell when it’s extremely hot or very wet just by looking at a television screen, but there is an unseen challenge in Mexico City that you can only appreciate by physically being there.

At 2,285 metres above sea level, the Autodromo Hermanos Rodriguez is the highest circuit on the calendar by some distance. If you skip up a flight of stairs here, you will often find yourself feeling light-headed at the top, because there is a lower concentration of oxygen compared to at sea level.

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Working on site, deputy technical director Masamitsu Motohashi admits even the Honda engineers notice an impact on their bodies during their time at the circuit.

“It is very hard for us!” Motohashi-san says. “We feel more tired at altitude. Plus Mexico is a back-to-back race after the US so it is a tiring schedule. But we have to stay strong physically in order to be able to do a good job at the track.

“To be honest, some engineers are training every day and so are in good shape, because our physical performance is important to work in the Formula 1 championship. It’s not only about your brain, but also the body as well.”

What affects the human side of the team also has an impact on the mechanical components, with the power unit performing differently at altitude. It all stems from the combustion process, where fuel and oxygen are mixed at a desired ratio. The ignition of that mixture - from a spark plug or similar - causes an explosion in the combustion chamber that forces the pistons to move and creates the power output.

To get the correct ratio of air and fuel, a compressor will ensure the right amount is delivered to the combustion chamber, but this is where Mexico is unique.

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“At high altitude, the oxygen density is very low, so we need the compressor to work more to deliver the proper air-fuel ratio,” Motohashi explains.

“We have a target that we call the boost, which is the proper oxygen volume needed for optimal combustion. So if there is a low density of oxygen, we need the air to be compressed even more to go into the internal combustion engine, so that means the compressor working harder and more high-speed rotation.”

If the compressor was working at the same level in Mexico compared to the previous race in Austin - which took place at a much lower altitude - then the result would be obvious: less power. But there are knock-on effects to having to run the components more aggressively.

“We need more high-speed rotation of the compressor, and this has a big impact on reliability. Centrifugal forces have a very big impact on the compressor wheel and turbine wheel, so it can have an impact on the reliability side.

“On the other side it could also have an impact on performance as well, because the effect of high compressor work means the temperature of the compressed air is increased. The higher temperatures can result in knocking - when there is irregular timing of the combustion - so we have to reduce the power in order to avoid that.”

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With the majority of races taking place much closer to sea level, there is little to be gained from designing a power unit with Mexico in mind. That means optimal performance comes down to the way the power unit is run, with special preparation taking place in the build-up to the race.

“The hardware side is always the same as other tracks, so we need special calibrations for Mexico and its high altitude. This is work we do on the dyno. We replicate the Mexican conditions, so create low pressure before the air goes into the compressor, for example, so we can calibrate it under similar conditions.

“The operating conditions are different, so sometimes the compressor efficiency and the turbine efficiency decreases as well. So we have to check the electrical energy such as the MGU-H power and how that will be affected. The tests are not only for the combustion process but also for energy management, so it’s a lot of preparation.”

It’s not just the power unit that will perform differently at altitude, however. The car’s aerodynamics also see the impact, with a high downforce set-up delivering lower downforce overall. Teams liken it to getting  low Monza levels of downforce from maximum wing angles, which will result in high straight-line speeds.

Once we have the power unit calibrated for Mexico, we have to work together with Toro Rosso to optimise the overall set-up to increase cooling without hurting the aerodynamic performance.

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“Of course, the high altitude will have a big impact on the cooling - because less dense air is going into the cooling systems - but that will also have an aero impact as well. The conditions have an impact on the water and oil cooling too, so we have to collaborate with the team in terms of bodywork.”

Top speeds are also high because of an extremely long straight on the run to Turn 1, with drivers at full throttle for some 1.2 kilometres. Such a long time flat-out would place an emphasis on power unit performance at any venue - let alone one at such altitude - but Motohashi says it doesn’t mean the impact on the power unit wouldn’t still be noticeable if the circuit was much more tight and twisty.

“If we have some long straights, the performance impact is very big. But if that wasn’t the case and the track was like Monaco, I still think we would need more work from the compressor and turbine.

“Mexico is very different to anywhere else on the calendar, so we have to take care in these conditions. We see something similar in Austria and Brazil as well, but those venues have much less of an impact than Mexico.”

Ultimately, the challenge of Mexico is just another height that must be scaled in order to be successful in the most demanding of racing environments.

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