2014-2020 Formula One 1.6l V6 turbo engine formula

[Kiril Varbanov]

Matt Sommers has a big write up on different engines architecture - http://somersf1.blogspot.com/2014/06/po ... cture.html with illustrated examples.

[Holm86]

New sensor to replace the Gill sensor could be as early as later this year.
http://www.racecar-engineering.com/news ... 1-and-wec/

[Brian Coat]

[/quote]
It is a lot more than "which AFR". The numbers I have suggested (perhaps 1.4 i.e. 20:1) have never been used in a performance SI engine - these are diesel numbers. To run so lean is a design process - not a mapping decision and every aspect of the engine and ancillaries would reflect that process.

There is no way you could design a turbo compound power unit to operate at say 0.9 then re-map it to 1.4 without redesigning everything in the air path from intake scoop to exhaust outlet.[/quote]

Well if you want to run *20:1* AFR at WOT, that could certainly affect the base engine design but I'm struggling to see how it would make best use of the fuel flow?

I'm not saying you are wrong but what is the chemical/physical mechanism?

[Brian Coat]

"To run so lean is a design process - not a mapping decision and every aspect of the engine and ancillaries would reflect that process."

Maybe so at the very lean AFRs like 20:1+ you have suggested teams are using ...

[gruntguru]

For anyone who hasn't thought about it yet, the difference between running an AFR of 0.9 and 1.4 on this engines is a 55% increase in airflow! (fuel flow doesn't change). That creates a huge difference in requirements for boost pressure, turbo flow capacity etc etc.

[gruntguru]

I put together a couple of charts to help me get an overall picture. Each curve shows the WOT boost required to burn the allocated fuel flow at the AFR (Lambda) value shown. Assumptions were:
Ambient temp = 20*C
Ambient air density = 1.2 kg/m3
Volumetric efficiency = 110% (I know this will vary with rpm but it should be close at 10,000 rpm)

My guess is Lambda = 1.3 and Charge temp = 80*C (green line, bottom chart) This runs close to the 3.5 bar MAP mentioned by Renault.

[Powerslide]

I am assuming drivers can tinker engine set up on the drive for strategic reasons. Since Mercedes-Benz has shown itself to have a power advantage (Hamilton leaving Ricciardo for dead upon entering Monaco tunnel) probably it comes down to setting where Mercedes-Benz will run optimum air fuel ratio when needed for that flier then run lean on parts of the circuit where power is less important. Thing is, other engine manufacturers will be capable of understanding lean as well if we were to think this is where Mercedes-Benz has an advantage. It is just that it seems the edge of Mercedes-Benz is speed and not much a case of how Honda handled it in the last turbo era with a sound speed and economy ratio.

When either Rosberg or Hamilton were driving hard, they would get an occasional call up from their engineers to warn them of fuel usage, this shows they have gotten more from speed out of their given same amount of fuel used rather than being as quick per lap but able to run nearly flat out full distance because of an economical advantage. Even their qualifying to race ratio points towads them having more speed rather than being economical

[dren]

But since this is a fuel flow rate limited formula, being economical is "speed" performance. I just think the Mercedes engine can run closer to full power whenever they want with the way the turbo compounding is working on their PU. This gives them a clear race day advantage. But, they are still quite far ahead during qualifying, a time where everyone will be able to run max PU power for one lap. So, they likely have an overall output advantage, too. Maybe fuel?

They also have a damn good overall car as well.

[Jaap]

I put together a couple of charts to help me get an overall picture. Each curve shows the WOT boost required to burn the allocated fuel flow at the AFR (Lambda) value shown. Assumptions were:
Ambient temp = 20*C
Ambient air density = 1.2 kg/m3
Volumetric efficiency = 110% (I know this will vary with rpm but it should be close at 10,000 rpm)

My guess is Lambda = 1.3 and Charge temp = 80*C (green line, bottom chart) This runs close to the 3.5 bar MAP mentioned by Renault.

This is some great work! really shows how important the fuel restriction is.
The only thing unclear to me, why did you think lambda is 1.3?

[Brian Coat]

"My guess is Lambda = 1.3 and Charge temp = 80*C (green line, bottom chart) This runs close to the 3.5 bar MAP mentioned by Renault."

I understand how you calculated the boost graphs and I also see why you think more pressure is a good thing because ideal Otto and Brayton cycle efficiencies both increase with pressure ratio.

If I understand correctly, your hypothesis is that more boost at very lean AFR will also give a more efficient practical cycle efficiency, even once we add in real world effects like knock limit, fuel flow limit, the combustion-quenching effect of excess air, the relatively low efficiency of the compressor and turbine etc. etc.?

[gruntguru]

Trying to summarise "my hypothesis".

1. Optimum AFR for combustion efficiency is somewhere around 1.1 including WOT operation. I believe that the air-fuel mix region prepared by the direct injection (stratified charge) system will be somewhere around this ratio.

2. To get the best out of a stratified charge system, it is best to have no combustion (and therefore no fuel) near the chamber walls. Combustion near the chamber walls is quenched (slower) and loses more heat to the walls (reducing efficiency). This region of air will cause the overall AFR to be higher ie >1.1

3. It is likely that optimum combustion efficiency occurs at a charge temperature greater than ambient as shown by Honda in the RA126E paper. I believe that this is not unique to toluene rich fuels.

4. Each of the three conditions above calls for leaner AFR and consequently an increase in the required boost pressure. Higher boost means increased detonation tendency and higher cycle temperatures. An easy way to reduce both is to increase excess air. This excess air would not be added to the air-fuel zone but to the region surrounding it. This is standard practice on diesels (to control cycle temps).

5. Increasing boost basically means increasing the power in the turbo-machines (compressor and turbine). Increasing boost (pressure ratio) and reducing intercooling increases the efficiency and power of this "pseudo Brayton cycle" which is especially important with the current engines able to harvest energy from the the turboshaft.

[gruntguru]

. . . . probably it comes down to setting where Mercedes-Benz will run optimum air fuel ratio when needed for that flier then run lean on parts of the circuit where power is less important. . . . .

If running lean improves efficiency (power produced/fuel flow rate) they will run lean for maximum power. If power becomes less important, they may choose to reduce the "fuel flow rate" but they will still run the engine at whatever is the most efficient AFR.

There is a difference between "lean" and "less fuel".

[stevekramer99]

An Axial compressor stage would likely have a higher peak efficiency ~5 points, however it would be difficult to operate correctly over the entire flow range of the engine, it would have surge and choke problems without active management of airflow.

[gruntguru]

The other problem is an axial won't produce enough pressure in a single stage and I think multi-staging is prohibited.

[wuzak]

The other problem is an axial won't produce enough pressure in a single stage and I think multi-staging is prohibited.

Multistaging is prohibited for both turbine and compressor.