Combustion System

[Brian Coat]

OK, here are 3.5 increasingly wacky ideas for living with a single injector.

1) Live with the lean AFR in pre-chamber and rely on turbulence from pre-chamber filling on the piston upstroke to ensure ignitability.

1a) As (1) but with a small and well-timed injection to (maybe) relatively richen the mixture in the pre-chamber?

2) Multi-hole injector with a method to allow independent fuel delivery to main chamber and pre-chamber e.g. one hole bypasses (or exits thru') plate.

3) "Window" in jet hole plate which can be injected through then closed for certain crank angles, for example a piston crown protrusion to fill the window hole.

I did say increasingly wacky ...

Or there may be a loophole ...

[gruntguru]

I'm going with 1(a).
It makes sense that the DI would be set up to produce richer mixture near the spark plug anyway.

[J.A.W.]

Check this curious combustion system, splitting 4V head inlet valve tasks between air-only & rich mixture duties..
( Scroll down - to see cylinder head diagram)

https://oldmachinepress.com/2015/09/10/ ... -3-vk-108/

[Tommy Cookers]

this Klimov engine has an exhaust pressure down to ambient, ie a substantial forward pressure helping scavenge
but all the current lean-running research engines seem to have a backpressure of around 0.25 bar
surely the F1 engine has a similar backpressure ?
(NACA demonstrated around 1942 an absence of underscavenge at BPs higher than this, at standard EV closure 20 deg atdc)

[Brian Coat]

Lawrence Butcher has an article in this month's RET about F1 combustion.

It's a technically informed and well written round-up but for the most part it's as speculative as what you can read on here.

[Brian Coat]

Not new but still interesting ...

http://delphi.com/docs/default-source/2 ... f?sfvrsn=4

http://www.delphi.com/docs/default-sour ... 56-pdf.pdf

... I've seen CI dismissed on here before but are we sure it is not a viable dvelopment path and why?

[godlameroso]

If there is a loophole it's a multi-stage injector with different spray patterns.

5.10.2 There may only be one direct injector per cylinder and no injectors are permitted upstream of the intake valves or downstream of the exhaust valves. Only approved parts may be used and the list of parts approved by the FIA, and the approval procedure, may be found in the Appendix to the Technical Regulations.

The only thing that can shut the door to the multi-stage injector loophole is the last sentence.

Having the injector house a pre-chamber with it's own nozzle, and the second stage sprays into the combustion chamber, and have the spark plug thread into the pre-chamber. Once you get that working, the next step would be to perfect the plasma jet that emanates from the pre-chamber. The nice thing about having a pre-chamber is that the conditions inside the pre-chamber can be vastly different than the main chamber. Then you have to consider the huge pressure ratios and high IAT could change the fuel in the pre-chamber to a super-critical state(In the end the difference between a plasma, and a super-critical fluid is an academic one, and electric charge). If that's the case you wouldn't even need to inject fuel into the pre-chamber, just let a small amount of fuel linger in the pre-chamber from the previous 4 stroke cycle, and use that to ignite the main mixture.

It's a very intriguing concept in theory, but would probably drive you insane to have to actually implement it.

[gruntguru]

Then you have to consider the huge pressure ratios and high IAT could change the fuel in the pre-chamber to a super-critical state(In the end the difference between a plasma, and a super-critical fluid is an academic one, and electric charge). If that's the case you wouldn't even need to inject fuel into the pre-chamber, just let a small amount of fuel linger in the pre-chamber from the previous 4 stroke cycle, and use that to ignite the main mixture.

There are two benefits in the pre-chamber.
1. It can direct high velocity jets to simultaneously ignite mixture throughout the chamber.
2. The mix in the pre-chamber has a different AFR - one that is easily ignited by spark plug and burns rapidly, neither of which can be said of the main chamber and its very lean AFR. I don't believe this condition can be achieved without injecting fuel into or close to the pre chamber.

[Brian Coat]

The lean end gas may also be mitigating the knock "from the other end?".

See p6 - the operating point is only 20 Bar (at low rpm) but I thought the graph was interesting.

http://www.wartsila.com/docs/default-so ... f?sfvrsn=2

[gruntguru]

Nice link.
Apart from the pre-chamber, it is possible that the charge is somewhat stratified in which case the end gas may well be air with no fuel. If achievable, this would be ideal - the air providing a non-combustible end-gas (detonation free zone) and a thermal blanket to reduce convective heat loss to the chamber wall.

[Brian Coat]

That's an interesting question. This fuel-free-end-gas stratification might be extremely hard to achieve at 10,000+ rpm, even with late injection(s) etc.

[J.A.W.]

Honda now claim 45% TE from a long stroke gasoline engine utilizing hi-comp stoichiometry, via shaped chamber design.

https://www.hondarandd.jp/point.php?pid=1178&lang=en

[Brian Coat]

Interesting article in RET on F1 combustion systems this month where there are hints/speculation towards SACI for Merc, possibly with stratified charge by the author, Lawrence Butcher.

In the article, the SACI idea is suggested to A Cowell whose response is not dismissive but too cryptic to be worth reading much into. His response about the combustion could equally be describing SACI or detonation!

"We use a conventional spark to start our combustion. Does the pressure increase that then occurs as a consequence of combustion cuase spontaneous combustion, as opposed to flame from combustion? The answer is 'Yes'." ... "What is random, sometimes welcome, sometimes unwelcome combustion? I think that is the art of taking combustion to another level".

He also comments that getting the right single cylinder instrumentation arrangement with which to correlate the charge motion simulation is a big challenge. No surprises there then; but it would be a particular area of focus for a team attempting charge stratification.

LB also speculates the possibility that Ferrari may be using TJI as an HCCI initiator under certain conditions. Hmmm ...

[gruntguru]

http://www.cse.anl.gov/pdfs/2011_hpc_wo ... on_opt.pdf
Bengt Johannson presentations are easier to understand than most. One interesting set of numbers is 270 bar compression pressure with 300 bar peak combustion pressure.

[Brian Coat]

http://www.cse.anl.gov/pdfs/2011_hpc_wo ... on_opt.pdf
Bengt Johannson presentations are easier to understand than most. One interesting set of numbers is 270 bar compression pressure with 300 bar peak combustion pressure.

Yes I like Lund's stuff too.

I'd read a similar PPC presentation (below) but not the one you posted - thanks.

https://www.erc.wisc.edu/documents/symp13-Johansson.pdf