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The number that really contrasts to the turbo years is AFR (lambda) and that's what's dictating the boost requirement.

Turbo Years - 0.75 - 0.98
F1 2014 . . . - 1.2 - 1.6

gruntguru wrote:The number that really contrasts to the turbo years is AFR (lambda) and that's what's dictating the boost requirement.

Turbo Years - 0.75 - 0.98
F1 2014 . . . - 1.2 - 1.6

I still doubt it and fail to see why burning 27.8 g/sec should crave 3.5 bar, when 2.5 was enough for 40+ g/sec 25 years ago.

But time will tell I guess

xpensive wrote:

gruntguru wrote:The number that really contrasts to the turbo years is AFR (lambda) and that's what's dictating the boost requirement.

Turbo Years - 0.75 - 0.98
F1 2014 . . . - 1.2 - 1.6

I still doubt it and fail to see why burning 27.8 g/sec should crave 3.5 bar, when 2.5 was enough for 40+ g/sec 25 years ago.

But time will tell I guess

Because instead of running rich you are running lean, so with the same amount of fuel you need more air. More air = more boost.

Would people be able to send me links to decent pictures of the Renault PU, I'm struggling to find the time to search all the car threads of the best pictures. It would help with some analysis I will post up on here along with the Mercedes Comoressor annotations I am working on.

FWIW, if we take rpm for example from Canada’s pole lap (rpm from noise analysis, throttle/brake info from FOM graphics):

and assume density at compressor inlet 1.2kg/m3 and AFR stoichiometric as 14.7, the compression ratio needed to use the allowed fuel rate in WOT areas only, would be:

or, put in another way, here the percentage of full throttle time spent above a give compression ratio for varying AFR (these are references, you can easily see where the curve would be with any other AFR):


Edit: corrected graphs

Reca: you have a nice audio to rpm software (very little drop out at low rpm / noise points on the lap) what s/w is it?

Your data confirms what others are saying: *if* 3.5 Bar *boost* is correct data (I have no idea: I'm only an insider in the sense that I don't get out enough!) then this would imply very high lambda, even at low rpm.

Actually I approached this from the other direction.
1. What AFR would likely give the optimum thermal efficiency for these DI compound engines? Answer lambda = 1.2+
2. What MAP would be required to achieve lambda 1.2+? Answer = 3+ bar.

Interesting analysis reca thanks! You seem to have assumed 100% VE and intercooling to ambient which is sensible if not accurate - but then we would only be guessing if we said 110% and 70* CAT.

The interesting think is how much the boost has to change and how quickly - if the AFR is to remain constant. I think we can safely say the AFR has to vary as the engine accelerates through the gears - at least a little.

gruntguru wrote:Interesting analysis reca thanks! You seem to have assumed 100% VE and intercooling to ambient which is sensible if not accurate - but then we would only be guessing if we said 110% and 70* CAT.

The interesting think is how much the boost has to change and how quickly - if the AFR is to remain constant. I think we can safely say the AFR has to vary as the engine accelerates through the gears - at least a little.

Yeah, that’s obviously a first order estimate with some assumptions made (including that of AFR constant that, as you say, likely is varying), not dissimilar in method from what posted already by others, I just thought that using real rpm data would help seeing the effective application range; playing around with other input variables obviously causes change of comp. ratio but relatively small (+/- 0.1), at least as long as we stay in a range of what should be sensible assumptions.

There's also the issue of that being WOT only (and consequently for basically all time with max fuel rate, <10.5k rpm time at WOT is negligible), even if theoretically throttle info from FOM graphics could be used, the amount of fuel effectively injected at given throttle % and rpm would be basically random guess so I didn't bother. If anybody has suggestions though, we can maybe play a bit with the part throttle areas too.

Brian Coat wrote:Reca: you have a nice audio to rpm software (very little drop out at low rpm / noise points on the lap) what s/w is it?

I use a Matlab routine I wrote myself various years ago and improved every now and then, in particular to have a time resolution compatible with needs of rapidly varying rpm of a racing engine. There should be a thread where I posted the basics of the method long ago.

gruntguru wrote:Interesting analysis reca thanks! You seem to have assumed 100% VE and intercooling to ambient which is sensible if not accurate - but then we would only be guessing if we said 110% and 70* CAT.

The interesting think is how much the boost has to change and how quickly - if the AFR is to remain constant. I think we can safely say the AFR has to vary as the engine accelerates through the gears - at least a little.

The engines have more than 100% VE.

Inter-cooling to ambient is impossible and is breaking the thermodynamic laws.

Basically it's a nice attempt, but too many assumptions, some of which are law breaking.

No big deal.

If the VE is 110% thats 10% extra air mass. If the MAT is 27 degrees above ambient thats 10% less air mass. Combine the two - no change.

(This is VE of the piston engine i.e. charge air not atmospheric)

How many hp will 2015 power units have in addition, compared to the number they have during the current season?

gruntguru wrote:No big deal.

If the VE is 110% thats 10% extra air mass. If the MAT is 27 degrees above ambient thats 10% less air mass. Combine the two - no change.

(This is VE of the piston engine i.e. charge air not atmospheric)

I couldn't agree more!

gruntguru wrote:No big deal.

If the VE is 110% thats 10% extra air mass. If the MAT is 27 degrees above ambient thats 10% less air mass. Combine the two - no change.

(This is VE of the piston engine i.e. charge air not atmospheric)

How did you get 10% less, I got 17% less for 27 deg above ambient (22)?

irsq4 wrote:

gruntguru wrote:No big deal.

If the VE is 110% thats 10% extra air mass. If the MAT is 27 degrees above ambient thats 10% less air mass. Combine the two - no change.

(This is VE of the piston engine i.e. charge air not atmospheric)

How did you get 10% less, I got 17% less for 27 deg above ambient (22)?

Did you use 22 as ambient?ambient air temp is considered 15 degrees Celsius and 29.92 in.Hg/1013 MPa by ISA conditions.