Reasons for varying performance at high altitude

All that has to do with the power train, gearbox, clutch, fuels and lubricants, etc. Generally the mechanical side of Formula One.
User avatar
Steven
Owner
Joined: Mon Aug 19, 2002 5:32 pm
Location: Belgium

Reasons for varying performance at high altitude

Post

Last weekend's Mexican GP has thrown some surprises in terms of performance, not only for fans, but also for the engine manufacturers themselves.

A few things of note:
- Renault were strong but unreliable (ERS and MGU-H issues).
- Renault said they were too aggressive in relation to the climate
- Renault believe Mercedes were very conservative for the altitude
- Honda were stronger than they expected

So, I'm curious how this can actually happen. How can power unit suppliers still be surprised of themselves and their competition when running on a known circuit?

Does anybody have any idea on what is actually being adjusted? I'm aware there are certain measurements to be taken due to the lower cooling capacity, but do they need to work the Turbo harder with the MGU-H? Or slow it down even?

NL_Fer
NL_Fer
66
Joined: Sun Jun 15, 2014 8:48 am

Re: Reasons for varying performance at high altitude

Post

Turboshaft rpm, to compensate for the thinner air, the turbo’s have to spin faster and the bearings are overheating. Renault has pushed the turbo’s to far and they blew, bearing/seals failed.

I can think of 2 causes.

1. The split turbo because of it’s mounting positions, it’s bearings rely on watercooling and somehow they could increase the cooling capacity. (bigger radiators, faster waterpumps?) The Renault is mounted behind the engine and relies more on air cooling, through the top air intake and this is harder to increase.

2. Because of the better mounting position, the split turbo has a bigger compressor and can spin much slower and will have less bearing stress at all. Where the Renault turbo is limited in size, because of the position above the gearbox and the it interferes with the aero.

It is either 1 or 2, or a little of both.

gruntguru
gruntguru
453
Joined: Sat Feb 21, 2009 6:43 am

Re: Reasons for varying performance at high altitude

Post

The air density is about 75% of sea level density so a PU optimised for a PR of 3 at sea level would need to run a PR of 4 at Mexico City to see the same MAP (and therefore the same AFR). Assuming the compressor and turbine were selected for best efficiency at PR = 3, the efficiency at PR = 4 would be somewhat less. Shaft speed would have to increase by 15%.
je suis charlie

User avatar
henry
261
Joined: Mon Feb 23, 2004 7:49 pm
Location: England

Re: Reasons for varying performance at high altitude

Post

If the turbine runs at lower efficiency it will extract less lower from the exhaust stream, and similarly the compressor will take more power to drive it. This leaves less power for the MGU-H to harvest and so less need for cooling, unless it too is running less efficiently.
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus

sosic2121
sosic2121
18
Joined: Wed Jun 08, 2016 11:14 am

Re: Reasons for varying performance at high altitude

Post

I noticed from ERS telemetry(blue bars) that Hamilton deployed significantly less than Sainz while they battled.

Also FI deployed less than Ferrari.

Am I missing something here? What exactly that blue bar represents?
ES > MGU-K
ES + MGU-H > MGU-K
?

User avatar
MrPotatoHead
55
Joined: Thu Apr 20, 2017 6:03 pm
Location: All over.

Re: Reasons for varying performance at high altitude

Post

At it's most basic level on a turbocharged vehicle running at higher altitude (thinner air) you are able to recover the power lost due to the thinner air by running the turbo faster to achieve the same air pressure that you would normally run at sea level and thus almost the same performance.
But - along with running faster you will have higher mechanical loading - and we have already seen how on the edge some of the power units are in the MGU-H reliability.

So if you can make the choice to run higher turbo shaft speeds to get the boost back you then have to worry about the fact that with the thinner air you have far less cooling ability from the air when moving at speed. And these cars are already on the edge cooling wise. This was the biggest problem to manage this weekend.

Basically Renault were too aggressive this weekend - and it showed. It's no coincidence that the Renault powered car of Verstappen that spent most of the race in clean air was also one of the only Renaults to survive.

notsofast
notsofast
7
Joined: Wed Oct 10, 2012 1:56 am

Re: Reasons for varying performance at high altitude

Post

Not to hijack the thread, but what changes could be made to the track to lessen the impact of high altitude?

User avatar
strad
265
Joined: Sat Jan 02, 2010 12:57 am

Re: Reasons for varying performance at high altitude

Post

I just keep thinking of how lean they must be running.
To achieve anything, you must be prepared to dabble on the boundary of disaster.”
Sir Stirling Moss

User avatar
Mudflap
220
Joined: Wed Feb 17, 2016 8:36 pm

Re: Reasons for varying performance at high altitude

Post

gruntguru wrote:
Tue Oct 31, 2017 3:38 am
The air density is about 75% of sea level density so a PU optimised for a PR of 3 at sea level would need to run a PR of 4 at Mexico City to see the same MAP (and therefore the same AFR). Assuming the compressor and turbine were selected for best efficiency at PR = 3, the efficiency at PR = 4 would be somewhat less. Shaft speed would have to increase by 15%.
It's probably worth mentioning that a drop in compressor efficiency translates into an increase in compressor outlet temperature for the same PR. Combined with the reduced charge air cooler performance this probably forces teams to derate ?
How much TQ does it make though?

User avatar
dren
285
Joined: Wed Mar 03, 2010 1:14 pm

Re: Reasons for varying performance at high altitude

Post

Mudflap wrote:
Wed Nov 01, 2017 12:03 am
gruntguru wrote:
Tue Oct 31, 2017 3:38 am
The air density is about 75% of sea level density so a PU optimised for a PR of 3 at sea level would need to run a PR of 4 at Mexico City to see the same MAP (and therefore the same AFR). Assuming the compressor and turbine were selected for best efficiency at PR = 3, the efficiency at PR = 4 would be somewhat less. Shaft speed would have to increase by 15%.
It's probably worth mentioning that a drop in compressor efficiency translates into an increase in compressor outlet temperature for the same PR. Combined with the reduced charge air cooler performance this probably forces teams to derate ?
Yes, I'd say cooling was the major reason for derating. Running the PU to obtain the same sea level power creates more heat and the thin air decreases your overall cooling efficiency. Everyone was likely derated, just some willing to accept more risk than others.
Honda!

User avatar
MrPotatoHead
55
Joined: Thu Apr 20, 2017 6:03 pm
Location: All over.

Re: Reasons for varying performance at high altitude

Post

notsofast wrote:
Tue Oct 31, 2017 8:25 pm
Not to hijack the thread, but what changes could be made to the track to lessen the impact of high altitude?
Pick it up and move it to a lower altitude. :D

notsofast
notsofast
7
Joined: Wed Oct 10, 2012 1:56 am

Re: Reasons for varying performance at high altitude

Post

Or build a dome over it and increase the air pressure.

But seriously. If I understand the situation correctly, there was a lack of grip, and the tires lasted quite long. So, how about paving the track with a more abrasive substance? Would that allow for better racing? Just wondering...

NL_Fer
NL_Fer
66
Joined: Sun Jun 15, 2014 8:48 am

Re: Reasons for varying performance at high altitude

Post

notsofast wrote:
Tue Oct 31, 2017 8:25 pm
Not to hijack the thread, but what changes could be made to the track to lessen the impact of high altitude?
Make it a street circuit wih more slow corners and shorter straights.

OT: It looks like Renault is really on edge with turbochargers rpm. And the problem with Honda’s split turbo is something else. Or we just saw the superior cooling setup a split turbo offers, because of less IC piping clutter.

roon
roon
445
Joined: Sat Dec 17, 2016 6:04 pm

Re: Reasons for varying performance at high altitude

Post

Do the engine test stands adjust their plenum pressure, or drop the pressure in the entire room? To simulate elevation.

User avatar
MrPotatoHead
55
Joined: Thu Apr 20, 2017 6:03 pm
Location: All over.

Re: Reasons for varying performance at high altitude

Post

roon wrote:
Wed Nov 01, 2017 9:19 pm
Do the engine test stands adjust their plenum pressure, or drop the pressure in the entire room? To simulate elevation.
Adjusting the plenum pressure would not simulate the different air density.
The only way to do it would be to lower the air pressure being fed to the turbo inlet. But that is troublesome because you have to lower the pressure but still maintain enough volume of air for the engine.