How much can the MGU-K recover per lap?

[AJI]

Realistically, how much can the MGU-K recover per lap? I've been working on the assumption that 2MJ was a reasonable target for a +/-120kW K for the 2014/15/16 cars, but I don’t think it’s achievable at most tracks for the 2017 cars as they don’t hit the speeds that they previously did and also the ’17 cars carry much more speed through corners, so, less opportunity to recover.

Now, with the 2021+ suggestion that the H could be scrapped, I have some questions:
How will they recover the required energy? A larger K is obviously the answer, but how big can this unit realistically get?
Could the K be asymmetric in its M-G relationship (say 240kW recovery, 120Kw deployment)?

To my mind, 4MJ per lap recovered from a 240kW K would only be achievable if the cars go back to less DF. Even then I’m doubtful...

[wuzak]

How long will they be on the brakes, where the rear wheels can brake at 120kW or over, on a lap?

We ran some numbers a couple of years ago, and found that tracks such as Albert Park, Monza, etc, struggled to get much over 1MJ. Silverstone couldn't even get that.

If I recall correctly, the only track that exceeded 2MJ was Singapore.

Monza is often seen as a good track for recovery, because of a couple of heavy braking zones. But the reality is that the cars aren't on the brakes for very long. And less so this year.

[wuzak]

I think that for more recovery they will need to use the front wheels. They could recover at higher power than they deploy if they only deploy from the front wheels.

The benefit of this is that it would help to balance the braking, needing less of the electronic brake distribution system.

[AJI]

...But the reality is that the cars aren't on the brakes for very long. And less so this year.

My thoughts precisely wuzak. I did some calcs using Barcelona as a reference and I couldn’t get 2MJ from the 2016 cars let alone the 2017 cars…

It was actually your post about this subject in the 2021 engine thread that got me thinking. Losing the H might be all very well and good to save costs in that area, but I can see this daft 2021 proposal starting a K arms race... I’m not sure what the new K recovery target is, but one thing is clear, the H currently does the ‘heavy lifting’ for recovery and I doubt the K will ever be able to match it unless the front axle is used too.

[wuzak]

I think the K and ES are to be standard components in the 2021 rules.

[AJI]

I think the K and ES are to be standard components in the 2021 rules.

The 2021 ‘spec’ is vague to the point of worthlessness at the moment.

I started this thread to try and calculate the goldilocks K/ES combo (with the help of the big brains on this site).

[henry]

In addition to braking the MGU-K can also drive against the ICE to charge the ES.

So at part throttle the driver’s throttle demand can be translated to ICE - MGU-K. They would have to use a little more fuel but this would be offset to some extent by running at higher efficiency, including less ES power to the MGU-H.

“Torque fill” could be done by less MGU-K to ES rather than more ES to MGU-K. This behaviour would read over to non MGU-H engine configurations.

If you can do this for 10 seconds that’s 1.2 mJ. Depending on fuel allowances it might lead to earlier lifting at the end of straights.

[NL_Fer]

What is wrong with use the amount of braking time as available boost time?

I’m afraid teams will use the negative torque on throttle as a way of traction control.

[henry]

What is wrong with use the amount of braking time as available boost time?

A few possibilities.

Not all braking events can extract 120 kw for their full duration.

The route K -> ES -> K is not 100% efficient.

The H provides a significant proportion of the “boost”

The ES can also be charged by the H.

I’m afraid teams will use the negative torque on throttle as a way of traction control.

Quite likely.

Maybe not eliminating wheelspin but reducing the jerk events that would precipitate it.

[AJI]

I’m afraid teams will use the negative torque on throttle as a way of traction control.

Do they not do this already? IIRC, the K is excluded from use for the first 100m(i think?) of the race to prevent it being used as traction control.

[AJI]

In addition to braking the MGU-K can also drive against the ICE to charge the ES.

Sure, but this would only be truly beneficial if the car is overfilled with fuel.
Surely, for weight reduction, the team want the car to cross the finish line with exactly the 1 litre required for testing and not a single drop more. If there’s a false start or a safety car then charging the ES under power makes sense to use the extra fuel, but would it be worth adding the extra weight under any other circumstances? As you say, the ERS is not 100% efficient...
It’s a strategically interesting prospect though.

[henry]

In addition to braking the MGU-K can also drive against the ICE to charge the ES.

Sure, but this would only be truly beneficial if the car is overfilled with fuel.
Surely, for weight reduction, the team want the car to cross the finish line with exactly the 1 litre required for testing and not a single drop more. If there’s a false start or a safety car then charging the ES under power makes sense to use the extra fuel, but would it be worth adding the extra weight under any other circumstances? As you say, the ERS is not 100% efficient...
It’s a strategically interesting prospect though.

It’s a balancing act.

In qualifying it may well be worth burning an extra kilo or so of fuel to extend the length of time they can run full power (electric supercharger)

In the race it may be used more sparingly, if at all.

The use of ERS deployment and what mix of techniques are deployed will be down to simulations. I think it’s impossible for a casual observer to estimate the balance of fuel loads, ERS strategies and tyre wear. We can only speculate on what might be possible and how various modes might be used.

[carisi2k]

I think if the FIA want to level the playing field then maybe they should allow more K recovery to allow Honda and Renault to overcome shortcomings in this area.

[AJI]

...I think it’s impossible for a casual observer to estimate the balance of fuel loads, ERS strategies and tyre wear. We can only speculate on what might be possible and how various modes might be used.

Well, I don't think it's impossible for us to estimate. That's one of the reasons I started this thread, to get people's opinions on what might be achievable. I'll concede that it is very difficult for us to actually know what the teams are doing, but that statement can be applied to the vast majority of topics on this site.

[gruntguru]

KERS on front axle only sounds great.
- Better harvesting potential
- Deployment possible at all speeds (not just higher speeds where the car is not traction limited)
- AWD for better acceleration at lower speeds (where cars are currently traction limited)
- AWD in corners for increased lateral adhesion.