Honda Power Unit Hardware & Software

[JonoNic]

Injector is always in pre-chamber under the rules of only one per cylinder.

Probably this a is a stupid question, but is it possible that the one injector could span two chambers, with two exits? What exactly constitutes a second injector?

If possible, that could help with filling the pre-chamber.

[MrPotatoHead]

With those fine nozzle holes in the pre-chamber.. Why would the fuel mist move inside the pre-chamber easier than the main chamber which has no such restrictions to moovement? Worse it is driving against a dead end and possible high concentration gradient. Not sure getting inside the pre-chamber richer would happen without alot of momentum in that direction..

Exactly. You can't beat physics.

[MrPotatoHead]

Injector is always in pre-chamber under the rules of only one per cylinder.

Probably this a is a stupid question, but is it possible that the one injector could span two chambers, with two exits? What exactly constitutes a second injector?

Possible and extremely likely.
You're not going to convince 3% of the fuel to magically go hide in a secret chamber with tiny entrance holes otherwise
At least not with the precision and repeatability required for it to happen under these kinds of loads.

[MrPotatoHead]

Injector is always in pre-chamber under the rules of only one per cylinder.

I believe the only way to get around the rules is for the pre chamber to be part of the injector.
Otherwise it would be a separate chamber.

This also explains the new for 2018 engine rules that would limit this to 10%.

[mwillems]

Injector is always in pre-chamber under the rules of only one per cylinder.

Probably this a is a stupid question, but is it possible that the one injector could span two chambers, with two exits? What exactly constitutes a second injector?

Possible and extremely likely.
You're not going to convince 3% of the fuel to magically go hide in a secret chamber with tiny entrance holes otherwise
At least not with the precision and repeatability required for it to happen under these kinds of loads.

It's not possible for the flow to be directed to one opening or or the other depending on where it is in the cycle? A single injector with dual feeds? Or is that outside the realms of possible or legal?

[MrPotatoHead]

Probably this a is a stupid question, but is it possible that the one injector could span two chambers, with two exits? What exactly constitutes a second injector?

Possible and extremely likely.
You're not going to convince 3% of the fuel to magically go hide in a secret chamber with tiny entrance holes otherwise
At least not with the precision and repeatability required for it to happen under these kinds of loads.

It's not possible for the flow to be directed to one opening or or the other depending on where it is in the cycle? A single injector with dual feeds? Or is that outside the realms of possible or legal?

It's not very likely to happen that way in my opinion and my experience.

[sosic2121]

If injector is in prechamber, is it possible that small "tip" on piston is entering prechamber and closing it?
Could it be used to create different A/F ratio in prechamber and maybe different pressure compared to the main chamber?

[godlameroso]

What if the injector nozzle is perpendicular or close to such an angle relative to the passage between the main and pre-chamber? Then it's only a matter of having a spray nozzle for the pre-chamber fire from one half of the injector, and a spray nozzle for the main chamber with the other half. That's probably why dual anchor injection makes sense. You have enough resolution with dual anchor to have two precise spray patterns instead of just one. That way the pre-chamber gets it's own small precisely directed squirt of fuel, and the main chamber gets it's own while adhereing to the one injector rule.

Something like in this lazy edited picture


Then also one has to wonder how it is that this actually works when the holes are so small.


It's no hidden part of the combustion chamber, when the cylinder pressure increases, the pressure is distributed relatively evenly everwhere that is part of the chamber. If main chamber pressure increases so does pre-chamber pressure in some ratio defined by the chamber geometry, pressure charging and resulting back pressure.

[Frank_]

which i think is what gg is implying when he mentions injecting on the intake AND compression strokes

[Sasha]

And another clue......make the injector two-stage.

[restless]

Injector is always in pre-chamber under the rules of only one per cylinder.

I believe the only way to get around the rules is for the pre chamber to be part of the injector.
Otherwise it would be a separate chamber.

This also explains the new for 2018 engine rules that would limit this to 10%.

10% of what ?!

[n4rf]

Pre-Ignition occurs LESS in Direct Injected engines by nature of how they work.
As far as oil causing pre-ignition this would be less of a problem than a Port Injected engine also.
Some of the theories presented here make me scratch my head.

Raise your hand if you have built and tuned a high strung high boost engine because experience in these things tells you a lot more than the Internet does.

Raising my hand. Been involved part-time in R&D as a student since 2010, full-time in scientific research since 2015 doing my PhD .
I'm not particularly involved in the design part per se, but in the thermodynamic testing, combustion concepts and specifically in calibration and function development. However, feedback to the design usually comes from thermodynamic testing, so there's that.
I have no idea how you arive at the conclusion of your first sentence. As mentioned by others, it is general knowledge in engine development, that pre-ignition is a common issue in highly boosted, high bmep gasoline DI engines.
Knocking is also an issue, I didn't mean to say that it isn't. It's just, that knocking is really well understood and, to a certain degree, easy to cope with. Obviously, dealing with knocking usually is detrimental to the thermal efficiency of the engine, so there's that. There's also always different categories of "knock limit". The one most people that have been at an engine test bench will know is the safe limit. Depending on the manufacturer they define some limit that, in their experience, will ensure that there's no longterm problems with mechanical defects or unsatisfactory NVH behaviour in the vehicle. Then there's the thermodynamic limit. This is usually quite a lot higher and much more dangerous to test, because it usually is only a small distance from causing broken parts. The thermodynamic limit is defined by the point, where allowing increased knocking doesn't yield any benefits anymore. Basically, it is running into combustion instabilities to an extent, where the better center of combustion (MFB50) doesn't is counteracted by these instabilities.
In general, knocking is less of a problem with increased engine speed. But all of the "in general" has to be viewed as exactly that. Engine specific problems can be surprisingly simple and yet at the same time difficult to overcome.

On the other hand we have pre-ignition. This can easily destroy an engine within one combustion cycle, though that's not the usual situation. But the really worrying part is, that it can often not really be controlled. At least not from one cycle to the next, like knocking with retarding the spark. Since the F1 teams run with pressure transducers in the cylinders, at least they should be able to react to pre-ignition events, because they actually see them. In road cars it's usually not possible for the ECU to detect them.

Regarding the pre-chamber spark plug. The main difficulty is the injector design, specifically the spray target. I do not know, what exactly the teams are doing. But research engines with pre-chamber spark plugs have been operated successfully with conventional injectors with injection during the suction stroke and homogeneous charge operation. I remember a dissertation from RWTH Aachen from somewhere around 2008 (I think), where this was tested extensively. One of the results was, that a scavenged pre-chamber will work much better, but that's not allowed under current F1 regulations. However, the focus was not necessarily maximum thermal efficiency.
An influx of fuel/air mixture into the pre-chamber from the main combustion chamber has to happen during the combustion stroke, because there is a pressure difference between the pre-chamber and the main-chamber (due to the compression). I don't know, however, if that can be sufficient for achieving desirable lambda values in the pre-chamber for the whole operating range.
I actually like the idea of an injector that sits sort of in-between the two chambers. If that is mechanically feasible is another question. Maybe one single injector spray aimed directly towards a whole in the pre-chamber could also work. It is certainly possible to design an injector in that fashion.
What I do know from reliable sources is, that the teams are running homogeneous lean charge in the main combustion chamber. The same sources also tell me, that there's no real "super-lean" stuff going on, certainly nothing above 2.0, usually some way below that. Also makes sense, when you remember that the fuel mass is fixed. That means, that increasing the air/fuel ratio leads to an increased boost pressure demand. So you need to balance the thermodynamic benefits in the cylinder (if there are any left above lambda 1.5-ish) against the losses due to higher compression work. That then also depends on your choice of turbocharger and your MGU-H strategy.
As ever with these engines, after thinking about it for more than 15 Minutes, you arrive at the simple conclusion, that it is much more difficult to get the best design, than you would initially think.

That's enough rambling for today, I think

[MrPotatoHead]

Pre-Ignition occurs LESS in Direct Injected engines by nature of how they work.
As far as oil causing pre-ignition this would be less of a problem than a Port Injected engine also.
Some of the theories presented here make me scratch my head.

Raise your hand if you have built and tuned a high strung high boost engine because experience in these things tells you a lot more than the Internet does.

Raising my hand. Been involved part-time in R&D as a student since 2010, full-time in scientific research since 2015 doing my PhD .
I'm not particularly involved in the design part per se, but in the thermodynamic testing, combustion concepts and specifically in calibration and function development. However, feedback to the design usually comes from thermodynamic testing, so there's that.
I have no idea how you arive at the conclusion of your first sentence. As mentioned by others, it is general knowledge in engine development, that pre-ignition is a common issue in highly boosted, high bmep gasoline DI engines.
Knocking is also an issue, I didn't mean to say that it isn't. It's just, that knocking is really well understood and, to a certain degree, easy to cope with. Obviously, dealing with knocking usually is detrimental to the thermal efficiency of the engine, so there's that. There's also always different categories of "knock limit". The one most people that have been at an engine test bench will know is the safe limit. Depending on the manufacturer they define some limit that, in their experience, will ensure that there's no longterm problems with mechanical defects or unsatisfactory NVH behaviour in the vehicle. Then there's the thermodynamic limit. This is usually quite a lot higher and much more dangerous to test, because it usually is only a small distance from causing broken parts. The thermodynamic limit is defined by the point, where allowing increased knocking doesn't yield any benefits anymore. Basically, it is running into combustion instabilities to an extent, where the better center of combustion (MFB50) doesn't is counteracted by these instabilities.
In general, knocking is less of a problem with increased engine speed. But all of the "in general" has to be viewed as exactly that. Engine specific problems can be surprisingly simple and yet at the same time difficult to overcome.

On the other hand we have pre-ignition. This can easily destroy an engine within one combustion cycle, though that's not the usual situation. But the really worrying part is, that it can often not really be controlled. At least not from one cycle to the next, like knocking with retarding the spark. Since the F1 teams run with pressure transducers in the cylinders, at least they should be able to react to pre-ignition events, because they actually see them. In road cars it's usually not possible for the ECU to detect them.

Regarding the pre-chamber spark plug. The main difficulty is the injector design, specifically the spray target. I do not know, what exactly the teams are doing. But research engines with pre-chamber spark plugs have been operated successfully with conventional injectors with injection during the suction stroke and homogeneous charge operation. I remember a dissertation from RWTH Aachen from somewhere around 2008 (I think), where this was tested extensively. One of the results was, that a scavenged pre-chamber will work much better, but that's not allowed under current F1 regulations. However, the focus was not necessarily maximum thermal efficiency.
An influx of fuel/air mixture into the pre-chamber from the main combustion chamber has to happen during the combustion stroke, because there is a pressure difference between the pre-chamber and the main-chamber (due to the compression). I don't know, however, if that can be sufficient for achieving desirable lambda values in the pre-chamber for the whole operating range.
I actually like the idea of an injector that sits sort of in-between the two chambers. If that is mechanically feasible is another question. Maybe one single injector spray aimed directly towards a whole in the pre-chamber could also work. It is certainly possible to design an injector in that fashion.
What I do know from reliable sources is, that the teams are running homogeneous lean charge in the main combustion chamber. The same sources also tell me, that there's no real "super-lean" stuff going on, certainly nothing above 2.0, usually some way below that. Also makes sense, when you remember that the fuel mass is fixed. That means, that increasing the air/fuel ratio leads to an increased boost pressure demand. So you need to balance the thermodynamic benefits in the cylinder (if there are any left above lambda 1.5-ish) against the losses due to higher compression work. That then also depends on your choice of turbocharger and your MGU-H strategy.
As ever with these engines, after thinking about it for more than 15 Minutes, you arrive at the simple conclusion, that it is much more difficult to get the best design, than you would initially think.

That's enough rambling for today, I think

I should have added more clarification to my initial comments.
I was not referring to DI engines in general, but to these high rpm race engines.
In these engines LSPI is less likely to occur due to the rpm and time involved.
Sorry if that caused some confusion.

As far as the lambda they are running at I tend to agree with you that it is probably lower than many have speculated.

[PlatinumZealot]

What if the injector nozzle is perpendicular or close to such an angle relative to the passage between the main and pre-chamber? Then it's only a matter of having a spray nozzle for the pre-chamber fire from one half of the injector, and a spray nozzle for the main chamber with the other half. That's probably why dual anchor injection makes sense. You have enough resolution with dual anchor to have two precise spray patterns instead of just one. That way the pre-chamber gets it's own small precisely directed squirt of fuel, and the main chamber gets it's own while adhereing to the one injector rule.

Something like in this lazy edited picture
http://i.imgur.com/Mz1JMqS.jpeg

Then also one has to wonder how it is that this actually works when the holes are so small.
http://www.enserv.de/wp-content/uploads ... 9vpvr4.jpg

It's no hidden part of the combustion chamber, when the cylinder pressure increases, the pressure is distributed relatively evenly everwhere that is part of the chamber. If main chamber pressure increases so does pre-chamber pressure in some ratio defined by the chamber geometry, pressure charging and resulting back pressure.

There. You said it.. "passage" to the main chamber. For the "Jet" term in TJI there are no big passages... Just small lazer cut nozzles.

Unless you wanna put sort of poppet valve to close the passage after the first injections diverting the ingnited fuel spray through the fine TJI holes. The poppet valve can easily be mechanically timed and of fixed duration. As the closed period would more than overlap with the following injection and ignition periods..

Say:
first injection .. 90 deg BTDC

Second injection ... 60 deg BTDC

Pre-chamber valve closes... 40 deg BTDC

Third injection.... 25deg BTDC

Igntion.... 20 deg BTDC

Flames jets... 15 deg BTC

Pre-chamber valve opens.. 10 deg ATDC

Repeat for next cycle..

NOTE : the injector and spark plug is located in the pre chamber..

The pre-chamber valve is pnematically operated just like the intake and exchaust valves. It would have a diameter of about 8mm. Its stem is cantered at an angle to allow room for spark plug and injector.

[Sasha]

In un-educated terms.

Under load Honda's CC Design isn't working.The fuel isn't going where it is suppose to go in the main chamber that leads to very very lean areas in the main chamber=eating pistons and destroyed engine.

The bandage fix is running the engine rich=no power and bad MPG.

Mid-term fix is new CC design(Heads, pistons and injectors)

Long term fix is almost a whole new PU design.(because of vibrations)