WEC (World Endurance Championship) 2014

[machin]

Thanks again for running the numbers. I expected there to be less of a speed disadvantage, not an advantage at Le Mans. Was that scaling factor in the rules pre-homologation? If so it could be what lead Audi to choose the 2MJ option in spite of the rest of the championship.

It is worth showing the full diesel vs Petrol energy allowance to avoid confusion:-



The 2, 4, and 6MJ Diesels get relatively more fuel energy per lap in accordance with the "K-Factor" which balances the respective ICE weights... i.e. because the Diesel engine weighs more, they get more fuel energy per lap as a compensation...

I don't understand why the K-factor is 1 for 8MJ cars... as this implies that the engine weights are suddenly the same when you have the biggest hybrid system....

To my mind, this graph suggests that, due to the different engine weights, if we assume that all competitors will run at the 870kg limit, and run with the biggest hybrid system possible within that limit, a 2MJ Diesel is equivalent (in lap time terms) to a 6.5 to 7MJ Hybrid Petrol... which would be fair enough if that is what the ACO have determined... except we know that a 6MJ Petrol is "allowed" to do more laps on a single fuel tank (at max fuel consumption) than a 2MJ Diesel.... so there is no parity on that front...

????

[Callum]

Just to clarify, Machin, is red diesel and blue petrol?

If so, what i'm getting from the graph is that for the 2,4 and 6 MJ class the diesels have nearly a 1MW advantage in usable energy per lap. - This is to offset the heavier car when compared to the 'lighter' petrol engine. But, when we get to the 8MJ class, suddenly the diesels are not given an advantage over the petrols and they basically have equal energy allowances per lap.

Am I understanding this correctly?

Would you also please be able to explain how turbos fit into this (for each class)? Does the N/A Toyota petrol get the same KE per lap as a turbo Porsche? (if they were in the same hybrid class)

Thanks for the graphs, again.

CT

[machin]

Yes, Sorry, red is diesel, and blue is petrol.

what i'm getting from the graph is that for the 2,4 and 6 MJ class the diesels have nearly a 1MW advantage in usable energy per lap. - This is to offset the heavier car when compared to the 'lighter' petrol engine. But, when we get to the 8MJ class, suddenly the diesels are not given an advantage over the petrols and they basically have equal energy allowances per lap.

Exactly.... weird isn't it? But that is exactly as per the published FIA numbers; not something I've generated from assumed numbers:- See here the value of the K-Technology-factor is 0.987 for 2, 4 and 6MJ and 1 for 8MJ (and non-Hybrid) cars (ignore the coloured circles; they're from another post):-



Where the KT-factor is described as:-

KTF balances fuel and gasoline engine weights. The heaviest technology is handicapped because it does not allow embedding the same amount of ERS as the lightest technology.

And the KTF is used to calcualte E-Additional, where E-Additional is referred to as:-

the additional allocated Diesel Energy due to technology differences.

[machin]

Would you also please be able to explain how turbos fit into this (for each class)? Does the N/A Toyota petrol get the same KE per lap as a turbo Porsche? (if they were in the same hybrid class)

The engine architecture makes absolutely no difference... you can have as many cylinders as you want, NA or turbo... all that matters is that you arrive at an engine that is small, lightweight, reliable and has the best BSFC (efficiency) as possible over the engine's operating range*.

That is what makes the Toyota vs Porsche comparison so interesting considering that their engines are so completely different!

(* -Unless you are the only competitor in your fuel class, in which case BSFC doesn't really matter seeing as you will be balanced (either up or down) to the performance of the best Petrol engine.)

[PorscheLMp1Fan]

Are those graphs, (namely the petrol diesel comparison) based on the latest appendix B numbers?

[machin]

Are those graphs, (namely the petrol diesel comparison) based on the latest appendix B numbers?

Yes, but I've had to estimate the BSFC's (which is used to determine the amount of Kinetic energy that can be obtained from each kg of fuel) which are not publicly declared; the Diesel BSFC is taken from a draft version of Appendix B, and the Petrol BSFC is set so that the non-hybrid petrol and diesel cars have the same Kinetic energy per lap, as per my full, expanded, Appendix B table below:-

Well, I've had a go and putting some figures to the "unknown" values:-

Figures in black are directly from the latest FIA Appendix B.
Figure in blue are estimated figures
Figures in red are calculated using the black and blue figures.

[FW17]

Why are Toyota still running a NA 3.5 L engine? Is there no difference in efficiency between an NA and turbo engine for a given fuel flow?

[Pierce89]

Why are Toyota still running a NA 3.5 L engine? Is there no difference in efficiency between an NA and turbo engine for a given fuel flow?

Its 3.7L but in a RCE article Toyota claimed it was better(and more efficient) than a turbo motor. I don't see how that could be true but they seem to be the fastest in a fuel flow formula. Go figujre.

[machin]

As I see it there are some advantages to a large capacity NA petrol engine, if it is tuned for economy rather than out-and-out power:

Large capacity = lower revs = less friction
NA = Higher compression ratio = high expansion ratio = higher efficiency
NA = simpler ancillary systems = easier packaging
NA = no intercooler = better aerodynamics

Possibly the decision was also helped by keeping the engine something that they know is reliable, and then concentrating development budgets on the Energy recovery systems...?

[FW17]

If that were the case why are manufacturers down sizing?

[machin]

Because there are also advantages of using small capacity turbo engines...

Turbo = Higher volumetric efficiency = less revs (for a given power) = less friction.
Turbo = better mixing in cylinder = better burn = more efficient
Small capacity = smaller and fewer parts = less friction
small capacity = smaller ICE = more aerodynamic and weight distribution freedoms.

I suspect that when you weigh up the two different arrangements there probably isn't too much difference between them... which is why we're seeing little difference in the performances of the two petrol cars....

I just wish they would declare the BSFC's so we would have a better idea!

[machin]

"small capacity turbo vs large NA engine efficiences" may be a good title for a separate discussion? I'd love to hear more views on the subject.... ????

[AnthonyG]

If that were the case why are manufacturers down sizing?

EU-emission cycles, but in real life such a turbo engine doesn't give that much (or none) advantage, certainly if you start driving "fast".

[zonk]

So far no one mentioned the Ligier JS P2 chasis a closed LMP2 will be raced by two teams
33 Oak racing Team Asia HPD engine(honda) Michelin tires
46 Thiriet By TDS Racing Nissan engine Dunlop tires


http://sportscarracingnews.com/2014/05/ ... he-sarthe/

[cokata]

"small capacity turbo vs large NA engine efficiences" may be a good title for a separate discussion? I'd love to hear more views on the subject.... ????

In race conditions i think a big NA engine is more efficient,since it can run a lot higher CR,have less pumping losses,and i believe at high load and RPM turbo petrol engines need to run slightly rich to cool the exhaust so that the turbo doesn't melt.In civil cars however there are several advantages to turbo engines that make them more appealing:
1.Faster warm-up - this is often overlooked but it makes a huge difference especially if you drive mostly in town
2.Reduced pumping losses at low load/low rpm - since the boost pressure is dependent on load and rpm if you are just cruising at a steady speed or crawling in traffic the engine runs with almost no boost , and you get to have all the advantages of an engine with small displacement
3.Most people like to drive their cars at low rpm for economy and noise purposes, and shift as rarely as possible.So you average joe would assume that a turbo engined car is much quicker.

All in all i would still prefer a NA car because the small advantages that turbo engines offer do not offset the extra complexity and maintenance that require.