Honda Power Unit Hardware & Software

[hurril]

Doesn't increasing PC volume reduce CC compression ratio?

You mean 5 on the tip and 7 on the cap periphery?

I don't think I can buy the 25% figure because that's a lot of gasses that must cross those "flame in-/ outlets." Basically the combined area of those channels must be in some relation to half a valve.

Depends on the size of your CC, if you have a nearly flat head with 3 degrees, and your piston crown is your CC, then making the PC 25% of that volume is not excessive, nor requires as much flow as you imagine.

That makes it worse though because the volume is the same. Compressing it with a greater ratio just means that the more volume will have to travel through the "membrane".

No compression at all -> no travel; 2:1 ratio -> 50% of the PC-volume travels through twice. With rising geometric CR, you will see a correspondingly greater volume of intake mass having to cross the "membrane" (and twice.)

[godlameroso]

I don't think I can buy the 25% figure because that's a lot of gasses that must cross those "flame in-/ outlets." Basically the combined area of those channels must be in some relation to half a valve.

Depends on the size of your CC, if you have a nearly flat head with 3 degrees, and your piston crown is your CC, then making the PC 25% of that volume is not excessive, nor requires as much flow as you imagine.

That makes it worse though because the volume is the same. Compressing it with a greater ratio just means that the more volume will have to travel through the "membrane".

No compression at all -> no travel; 2:1 ratio -> 50% of the PC-volume travels through twice. With rising geometric CR, you will see a correspondingly greater volume of intake mass having to cross the "membrane" (and twice.)

We talking about gear oil or air? How fast can air move, have you ever used pneumatic tools?

[hurril]

Depends on the size of your CC, if you have a nearly flat head with 3 degrees, and your piston crown is your CC, then making the PC 25% of that volume is not excessive, nor requires as much flow as you imagine.

That makes it worse though because the volume is the same. Compressing it with a greater ratio just means that the more volume will have to travel through the "membrane".

No compression at all -> no travel; 2:1 ratio -> 50% of the PC-volume travels through twice. With rising geometric CR, you will see a correspondingly greater volume of intake mass having to cross the "membrane" (and twice.)

We talking about gear oil or air? How fast can air move, have you ever used pneumatic tools?

Gear oil? What do you mean?

The entire engine is a pneumatic tool; have you seen the size of the tubing? Your argument implies that all the piping can be reduced in size (which you certainly don't mean or think.) My doubts are founded in this, however.

PC:s in old diesel engines are of considerable size but the channeling between the PC and the CC is very different.

[Sasha]

Also with bigger PC and more flame outlets. You can go even leaner in main chamber because there is the the energy to so with enough flame patterns to ignite everywhere in the CC.

Less fuel needed
Less unburned fuel
Less hot silt/ particles
Less knock
Better heat control( where you want it not the cylinder walls)
= Better efficiency

Question???

Leaner you go does that also mean more heat?
The heat you lose with better combustion and efficiency.
And if it is hotter. Then that is way to get more energy recovery thru MGU-H that you lost with better combustion.

[Sasha]

With a big PC I would look into reverse flow and double ignition events.
Then you could get away with lean mixture in PC too with excellent scavenging.

The Jet engine boys are going that way because of very high efficiency gain.
And the next big leap is second CC after losing most of the energy to the turbine.
In the future will they need the 1000 pound a minute fuel burn afterburner or the 10 pound a minute secondary CC.
It will almost match an afterburner thrust( they don't go crazy with trust with afterburner anymore).
And will surpass a 7-10,000 thrust afterburner

[gruntguru]

. . . Put 25% of CC volume in the PC and that solves alot engineering headaches with very high CR with better CC control with no knock worries. . . .
I know nothing and people just laughed at a PC larger than 3-4%. They be state too much heat loss to PC walls.
Nope if that happened, you just have a bad CC design

The large PC you are describing is yesterday's technology eg Hond CVCC. The problem (especially in a high speed engine) is the high velocity gas flow required through the PC nozzles simply to get that 25% of the charge to do work on the piston. Energy losses are unacceptably high, not to mention delay in converting the expansion of that 25% of the charge into useful work (remember, pressure applied at TDC is expanded most efficienty - later expansion does less work and simply increases exhaust temperature).

These engine all use the Mahle TJI style prechamber - less than 5% of total charge volume at TDC. (with 18:1 CR the percentage at TDC is 18 times higher than at BDC) The charge in the PC serves little purpose in expansion terms, it is simply an igniter that:
1. Generates almost simultaneous ignition at all points of the C.
2. Allows rapid ignition and complete combustion of much leaner mixtures than is possible with any number of spark plugs.

[gruntguru]

Leaner you go does that also mean more heat?

No - same amount of heat and lower gas temperatures.

[hurril]

. . . Put 25% of CC volume in the PC and that solves alot engineering headaches with very high CR with better CC control with no knock worries. . . .
I know nothing and people just laughed at a PC larger than 3-4%. They be state too much heat loss to PC walls.
Nope if that happened, you just have a bad CC design

The large PC you are describing is yesterday's technology eg Hond CVCC. The problem (especially in a high speed engine) is the high velocity gas flow required through the PC nozzles simply to get that 25% of the charge to do work on the piston. Energy losses are unacceptably high, not to mention delay in converting the expansion of that 25% of the charge into useful work (remember, pressure applied at TDC is expanded most efficienty - later expansion does less work and simply increases exhaust temperature).

These engine all use the Mahle TJI style prechamber - less than 5% of total charge volume at TDC. (with 18:1 CR the percentage at TDC is 18 times higher than at BDC) The charge in the PC serves little purpose in expansion terms, it is simply an igniter that:
1. Generates almost simultaneous ignition at all points of the C.
2. Allows rapid ignition and complete combustion of much leaner mixtures than is possible with any number of spark plugs.

This is exactly what I was thinking about. There is most definitely an alternate cost to the size of the PC.

A few years ago there was talk about Honda having the PC in the piston crown. Did anything come out of that?

[godlameroso]

Yeah, the PC is in the head and CC is the piston crown itself.

[godlameroso]

Leaner you go does that also mean more heat?

No - same amount of heat and lower gas temperatures.

Depends how lean you go. If you're lean as in approaching stochiometric vs a safe 12:1/1.2:1eq ratio then temperatures will only increase, if you go leaner than stochiometric then it will do as you say.

[trinidefender]

Leaner you go does that also mean more heat?

No - same amount of heat and lower gas temperatures.

Depends how lean you go. If you're lean as in approaching stochiometric vs a safe 12:1/1.2:1eq ratio then temperatures will only increase, if you go leaner than stochiometric then it will do as you say.

They are definitely running on the lean side of stoichiometric.

[godlameroso]

No - same amount of heat and lower gas temperatures.

Depends how lean you go. If you're lean as in approaching stochiometric vs a safe 12:1/1.2:1eq ratio then temperatures will only increase, if you go leaner than stochiometric then it will do as you say.

They are definitely running on the lean side of stoichiometric.

You can't go too far or combustion simply doesn't happen. Also, maximum power will always happen at phi. If you want to increase crank power getting closer to phi at high speeds and loads is the goal.

Now I agree, that these engines can operate on the lean side of phi, but it does so because it is "safer" and more efficient than being on the other side of the curve, regardless the goal is to get closer to the peak.

[gruntguru]

You can't go too far or combustion simply doesn't happen.

Which is the reason for TJI. It lets them combust mixtures approaching 2.0 lambda. The pre-chamber and spark plug is at 1.0 for reliable and rapid combustion. (onther reason the PC must be as small as possible - keep the overall AFR as lean as possible)
.

Also, maximum power will always happen at phi.

Almost never the case. Depends entirely on what the constraints are. Most engines are "air limited" - constrained by how much air they can breathe. In this case, the AFR is adjusted to the ratio that best utilises the limited amount of oxygen available. This will always be at an AFR richer than stoichiometric. At stoichiometric there is only just enough fuel to burn all the oxygen so thanks to:
- imperfect mixing
- formation of NOx
- dissociation
all the possible combinations of fuel and oxygen molecules simply do not happen.

If the engine is "fuel limited" (eg current F1), the AFR for best power will be lean of stoiciometric for exactly the same reasons. In addition - running super-lean (out towards lambda 2.0) reduces combustion temperatures and therefore heat loss to the cylinder.
.

If you want to increase crank power getting closer to phi at high speeds and loads is the goal.

No, every engine is different and the best AFR for power will vary, but it is never 1.0.
.

Now I agree, that these engines can operate on the lean side of phi, but it does so because it is "safer" and more efficient than being on the other side of the curve, regardless the goal is to get closer to the peak.

F1 PUs run a long way from 1.0 (1.8 to 2.0 is my guess) and it is mostly about efficiency not safety.

[gruntguru]

A few years ago there was talk about Honda having the PC in the piston crown. Did anything come out of that?

Likely just a rumour. The spark plug needs to be in the PC.

[godlameroso]

You can't go too far or combustion simply doesn't happen.

Which is the reason for TJI. It lets them combust mixtures approaching 2.0 lambda. The pre-chamber and spark plug is at 1.0 for reliable and rapid combustion. (onther reason the PC must be as small as possible - keep the overall AFR as lean as possible)
.

Also, maximum power will always happen at phi.

Almost never the case. Depends entirely on what the constraints are. Most engines are "air limited" - constrained by how much air they can breathe. In this case, the AFR is adjusted to the ratio that best utilises the limited amount of oxygen available. This will always be at an AFR richer than stoichiometric. At stoichiometric there is only just enough fuel to burn all the oxygen so thanks to:
- imperfect mixing
- formation of NOx
- dissociation
all the possible combinations of fuel and oxygen molecules simply do not happen.

If the engine is "fuel limited" (eg current F1), the AFR for best power will be lean of stoiciometric for exactly the same reasons. In addition - running super-lean (out towards lambda 2.0) reduces combustion temperatures and therefore heat loss to the cylinder.
.

If you want to increase crank power getting closer to phi at high speeds and loads is the goal.

No, every engine is different and the best AFR for power will vary, but it is never 1.0.
.

Now I agree, that these engines can operate on the lean side of phi, but it does so because it is "safer" and more efficient than being on the other side of the curve, regardless the goal is to get closer to the peak.

F1 PUs run a long way from 1.0 (1.8 to 2.0 is my guess) and it is mostly about efficiency not safety.

Safety of the mechanical components, not human health.