Mercedes-AMG achieves 50% thermal efficiency on 2016 F1 engine

What it doesn't show is the portion of the fuel that leaves the chamber from the channels at the bottom into the main cylinder and granted, a different fuel (hydrogen) directly injected is simulated. With gasoline, there is a much greater momentum of the liquid spray and additional processes of spray wall impingement and evaporation, but the principle holds. What ends up at the moment before ignition is nonetheless very homogeneous at a targeted equivalence ratio.

If F1 engines used a gaseous fuel I would have agreed with your analysis from the start. The volume of fuel injected for the main charge would be many times the volume of the pre-chamber. For liquid fuel the situation is reversed. It is possible that the fuel is heated to the point where a greater-than-usual portion vaporises instantly on injection but the majority will remain liquid in the pre-chamber - wetting the walls etc etc.

Your dual function injector that sprays into the pre and main chambers simultaneously sounds more likely. I think most probably, the teams have convinced the FIA to allow an auxiliary injector providing less than 5% of total fuel. (ie Mahle TJI)

Edited by gruntguru, 21 November 2016 - 23:44.

See highlighted.

The highlighted text is too small to be legible here.

The highlighted text is too small to be legible here.

Edited by ray b, 22 November 2016 - 18:41.

Sorry guys, the screenshot was taken at 1920x1080 resolution, it got downsampled either through the image hosting site or the forum software. Here's the text of interest:

 

Mahle is aiming to create a similar effect, albeit 

with a very different tech solution. The Mahle 

Jet Ignition (MJI) system uses a pre-ignition 

chamber, fed by its own fuel injector and 

spark plug. Only a small amount of the 

overall fuel delivery (less than 5%) is injected 

via the MJI system, while the remainder of 

the charge is supplied by a conventional DI or 

PFI system. Once the spark plug fires, it sends 

streams of partially burned mixture outward 

from a series of nozzles in the pre-chamber. 

These ignite the main charge almost 

simultaneously across the whole volume.

This concept made headlines earlier this 

year when it emerged that several engine 

manufacturers were using a similar idea in 

Formula 1 (including Ferrari, whose system 

was reportedly engineered by Mahle). Where 

these differ from the road-going MJI system, 

however, is that they syphon fuel passively 

from the main fuel injector into a pre-chamber 

through a collection of orifices, instead of 

using a dedicated injector unit. ETi has been 

told this is largely done for the sake of the 

Formula 1 technical regulations, which 

prohibit the use of additional injectors. 

Sources close to the project suggest that 

the technology is showing promise. ETi

understands it allows the engine to operate 

stably at very lean equivalence ratios (circa 

λ=2), with multiple high-energy ignition 

points. These can extend right to the 

extremities of the chamber, speeding up 

the combustion and specifically targeting 

the areas where knock tends to occur. This 

allows increased compression ratios – up 

to a four-point increase in some applications, 

according to the company’s website – 

combined with reduced pumping losses.

Almost diesel-like fuel consumption is said 

to be possible as a result. Tests have reportedly 

shown specific consumption below 200g/kWh, 

with considerable reductions in CO2as a 

consequence. NOxemissions on the PFI test 

engine are also understood to have been cut 

by more than 99% in the ultra-lean area, 

with HC emissions comparable to standard 

SI operation. Particulate emissions are 

said to have been somewhat increased 

compared with regular PFI, but they 

remain significantly less than the 

equivalent DI engine.

It’s also understood that 

the system has now been 

miniaturized to the point 

where it can usually be 

packaged in a similar manner 

to a conventional spark plug. 

Casting and machining changes 

are still likely to be required, but 

the fundamental design of the 

cylinder head – at least on PFI 

applications – is thought to be unchanged.

Edited by TDIMeister, 22 November 2016 - 20:56.

Point is that it is better than flat top, flat piston. If a chamber shall contain 500cc of mixture you want it to be round to minimise surface area.

 

We "only" use "flat" top, "flat" piston to get the desired compression ratio. And the only reason they have to be flat top, flat piston is because bore/stroke ratio is more important with this type of engine and application.

 

A ship engine with more stroke and lower rpm runs more hemi like piston and head. I googled to prove my teories and sure enough:

 

http://www.marine-kn...ston-Rings1.jpg

http://www.bcmtourin...0009-jpg.59825/

 

Well i say only but there is also piston speed to consider, weight of the piston and the extra friction that causes, the flame front and all kinds of other variables. Hence modern piston designs.

 

To say it differently..

If i was only chasing Horsepower with unlimited fuel i would run much bigger bore like the old engines. Excess pressure would simply get dumped out so you could make more "peak" pressure to work with. Hence the rpm, overlap on the cams etc.

 

There is a sweetspot where bore/stroke ratio + rpm is optimal for a given fuel type and flow. If they open up the rules F1 engineers will find it..

They probably have some idea where that is. So they made the odd fuel flow ramping  and a locked Bore and stroke ratio to keep the show factor in the sport. "We can not simply be seen dieseling around Monaco can we"

 

Personally i still vote for allowing Straight 5 engines. Some would prob give it a go as it sounds gnarly (ferrari) and it has one less piston so it would be more efficient.

 

Offset for that engine is packaging.

 

Increasing efficiency has the added challenge of giving less reusable energy for the turbo KERS. If all the pressure drop happens in the engine the turbo is simply a back pressure generator. That will never happen ofc.

I guess you have never seen a piston like this then, a high compression piston for a hemi head.

http://raybarton.com...6-hemi-dome.jpg

The surface area of such a piston plus the surface area of the head itself is very large compared to a flat head and flat piston with the same bore and compression ratio. The upside is that it allows rather large valves to be fitted.

https://upload.wikim...mi_chambers.jpg

The piston you linked to is a diesel piston, the bowl in the piston forms the combustion chamber combined with a flat head.

I guess you have never seen a piston like this then, a high compression piston for a hemi head.

 

http://raybarton.com...6-hemi-dome.jpg

 

The surface area of such a piston plus the surface area of the head itself is very large compared to a flat head and flat piston with the same bore and compression ratio. The upside is that it allows rather large valves to be fitted.

 

Yes i have.. But im not talking about that old crap. in addition.. thats not a high boost piston is it? Here is some: http://www.enginelab...tock-and-boats/

Anyway what im talking about is more on the teory side. And looking at diesels is a nice way to look at what ifs.. because they run at lower rpms and can afford more complex designs due to the weight being less of a issue.

Due to limits in bore/stroke and the fuel ramping curve  on the current F1 engines the pistons probably look fairly similar to what you would expect from a turbo engine. Biggest difference is probably in the head.

Interesting theory about being stratified lean - do you have some inside knowledge to know this is a fact, or is it your speculation? It is certainly plausible, but let's straighten out a few things. Lean mixtures would actually promote knocking by reducing the mixture laminar flame speed and thus leaving increased residence time in the end-gas before being consumed by the flame front, thus causing it to spontaneously combust, leading to knock. I admit that it makes for interesting theory, but I have read nothing about knocking at 15000 RPM. I did schlieren imaging on the mixture formation and combustion process in an optically accessible engine at what I believed from the published literature to be unprecedented at 5000 RPM when most were done at 1200, 1500 and 2400 RPM.

 

Charge stratification is certainly one way to address the above. When I have more time I'll do some back of napkin calculations to figure out what the air mass flow of a 15000 RPM 2 litre engine with at 3.5 bar MAP and typical volumetric efficiency of an F1 engine is - we could use the last naturally aspirated engine figures as a rough guide. Then we can know much more accurately the global lambdas these engines are running.

 

I'm extremely hungry for more info like this - whether exotic fuel injection tricks, charge motion and stratification (subjects of my PhD dissertation) or advanced combustion modes. If anyone has articles or papers on the subject, I would be grateful if you would share it and I'll do the same.

 

latest development is that they use somekind of jet ignition, igniting fuel earlier in a pre-chamber to shoot out high velocity charge into the combustion chamber fo rthe rest to burn

Edited by Cynan, 01 June 2017 - 19:41.

See post #105 above.

See post #105 above.

making it obvious ive only gone through two pages of this thread 

  105 is on this page!