Combustion System

[R_GoWin]

Just housekeeping - not suggesting one way or the other about HCCI! Perhaps this sits better here:

Can anyone say wHat is the difference between SCCI and HCCI?

Coincidentally an article on HCCI in spark ignited engines has just been published in the latest issue of Engine Tech magazine - on how it works, the challenges, so on and so forth. (click on the article to zoom to read - works well on desktop).

http://viewer.zmags.com/publication/6d1 ... d1d3a22/36

Some interesting things that stood out for me was:

- HCCI is not being approached as a separate engine, but only an engine mode within SI at certain operating points
- that a HCCI + SI gives greater efficiency than just turbocharged SI
- its not HCCI as well - but along with a whole host of other CI strategies are simply called low temperature combustion (LTC) or Gasoline direct injection compression ignition (GDCI)
- the traditional HCCI was down on efficiency due to lower temperatures from going lean - and not having enough heat for complete oxidation of CO species. This was tackled by keeping the charge to the middle and burning hotter in that region, which improved combustion efficiency.
- Hence its not homogenous as well, but the charge is in fact deliberately stratified to improve its efficiency over downsized turbocharged SI
- big torque and fuel efficiency improvements
- about 5 to 10 years of research away for being a production engine. But Mazda, aiming it for its next generation of Skyactive-G, along with GM, Kia, Hyundai etc.

[GoranF1]

i susspect Honda is working on SCCI......

[Abarth]

MTZ (Motortechnische Zeitschrift) Writer Westerhoff has published this Article:
https://www.springerprofessional.de/mot ... ircle_sel=

A Ferrari Chief Developer has spoken at Wiener Motorensymposium, and has shown a graph wich gave evidence of running Lambda = 1.2.
Westerhoff rules out stratified charge because of the high engine speed in F1.

[Brian Coat]

That's an interesting snippet from Ioannis Kitsopanidis which confirms what we believed we knew.

Thanks for posting.

[Tommy Cookers]

doesn't an equivalence ratio of 1.2 correspond to a boost significantly lower than the 3 - 3.2 bar abs that most believe is being used ?

(imo 3 - 3.2 bar looks more like 1.4 - 1.5 equivalence ratio, assuming the air is well 'inter' cooled, and Renault quoted 3.5 bar 2 years ago)

[Brian Coat]

Good point - I've seen 3+ Bar bandied about too.

If that is correct, maybe their Lambda "1.2" is "1.2+", assuming he's not going to reveal actual race data in a public conference?

And same rules of secrecy/ambiguity would apply to boost, I guess?

Question: At bulk-average Lambda 1.2+ do we think the pre-chamber can produce a strong (and fast) enough jet with no auxilliary injector?

[gruntguru]

Good point - I've seen 3+ Bar bandied about too.

If that is correct, maybe their Lambda "1.2" is "1.2+", assuming he's not going to reveal actual race data in a public conference?

Question: At bulk-average Lambda 1.2+ do we think the pre-chamber can produce a strong (and fast) enough jet with no auxilliary injector?

I would say yes.
Lambda 1.2 can be burned efficiently without any tricks - just adequate turbulence, spark advance etc. TJI would enable a shorter burn time and lower detonation tendency.

[Brian Coat]

I imagine the inflow through the jet nozzles will induce pre mixing and short-scale turbulence which will enhance the growth of the flame kernel and subsequent jets.

Thinking about other ways to stoke up this tiny pre chamber - you are allowed 5 sparks and although the ignition systems have to be approved there may be scope to usefully enhance spark energy.

[NL_Fer]

Would de G forces during racing have any effect on the combustion?

[J.A.W.]

Would de G forces during racing have any effect on the combustion?

How would G forces... affect such a high pressure operating system?

Unless of course, the lateral G is utilized to 'deliver' lubricant - as a defacto fuel additive..

[Abarth]

[....]
Mixture strength in the pre-chamber would be heavily dependent on spray direction and controlled to some extent by the timing of the injection pulse.

I just mulled over this.
Might it be legal to have a two-stage injector, either stage having a completely different spray pattern and direction?

So say one stage injects higly atomised into the inlet stroke, to produce an as homogeneous as possible mixture, and the second stage injects a directed spray into a pre-chamber.

Such an injector could work with two coils, one working in one polarity (and preventing current flow when reverse polarity is applied, using eg a diode), and the other one vice versa.

[Frank_]

i think injectors are piezo nowadays ? the single injector only needs 2 pintles (and 1 needle) surely ? one inside the chamber and one extended outside, both sized to ensure a slightly richer afr inside the chamber, regardless of the duration or number of pulses

[Abarth]

i think injectors are piezo nowadays ? the single injector only needs 2 pintles (and 1 needle) surely ? one inside the chamber and one extended outside, both sized to ensure a slightly richer afr inside the chamber, regardless of the duration or number of pulses

What I mean is that the two different injection modes are not simultaneously. The pre chamber injection shortly befor igniting it, the "homogeneous injection" much earlier during the intake stroke, to allow for good AF mixing (as the original Mahle idea is to use a PFI for that, which is not allowed in F1).
Different spray patterns / directions, at different times. Not possible with a conventional injector, being piezo or not.

[NL_Fer]

When i open the garden hose, it starts with a very soft but wide spray. Opening further gives a less wide, but harder spray ending with a hard jet of water, which can reach every corner of the garden.

I imagin this could be done also with a fuel injector. Short vs long bursts or pwm steering?

[Brian Coat]

RE: garden hose There's a 'watering can rose' in there too, remember!

I've seen a few posts suggesting multi-injections and/or multi-mode injectors as a way to get precise fuelling into a pre-chamber and a main chamber at different AFRs without needing a DI/IDI loophole approval from FIA.

Does presence of a TJI jet-hole plate between the chambers make this a bit tricky?

I think it does, but not necessarily impossible.

If you're of the multi-injection or multi-mode-injector way of thinking, what do you think the best detail solution would be?