Honda Power Unit Hardware & Software

[PlatinumZealot]

Notice the 50% burn angle (a number often quoted by researchers and called "CA50") ends up being very similar (about 7* ATDC) at different AFRs, ignition systems and burn rates. Likewise CA50 stays about the same for different engine speeds (bottom image). CA50 is clearly a preferred metric for "people who really know" and is obviously one that is more reliable than PCP as a predictor of MBT.

@SS and @godlameroso.
Any talk of "cylinder pressure occurring at optimum crank angle/geometry/mechanical advantage" is rubbish. Work done during the power stroke is the integral of PdV. It doesn't matter what the mechanism below the piston does. If a more favourable mechanical advantage is able to extract more work early in the stroke, there will be less work extracted later in the stroke - period!





CITATION: Attard, W. and Blaxill, H., "A Gasoline Fueled Pre-Chamber Jet Ignition Combustion System at Unthrottled
Conditions," SAE Int. J. Engines 5(2):2012, doi:10.4271/2012-01-0386.

Guru... The eponymous guru....

Yes very enligthening comments there. You said it and actually it can be viewed another way: The mere fact that these testst were OPTIMIZED for igntion timing yet still all of the 50% burn off occuring at almost the same crank angle tells us Precisely that the best power is when your middle of your combustion occurs at this angle in this specific engine... No matter how advanced your timing or fast your combustion or state of fuel it all squares up at the same spot.
We can see how quick the TJI is here if you compare the gaps between the "spark" and burn angle plots we can see how small the gap is for TJI.. And yet it still gives best output when the middle of the combustion reaction occurs the same as standard spark. Not to be confused with peak pressure mind other readers..

[gruntguru]

On mechanical advantage, think of a swing, there's a specific moment in the swing where someone pushing you will will add the most momentum(especially important if you want to get really high and impress all the playground girls.) This moment is just as the swing is going away from you(the person pushing).

No No No No No. It is simple mechanics.
W = Integral P.dV (Pressure, Volume) Area under the PV curve
W = Integral F.dx (Force, distance) Area under the Fx curve
W = Integral T.dTheta (Torque, Crank angle) Area under the T Theta curve

If you observe the PV diagram and maximise the area under the curve, you will maximise the work done on the top of the piston. Apart from a small loss to friction, that is EXACTLY the same amount of work available at the crankshaft. It doesn't matter what sort of mechanism you use to convert the pressure energy to rotational energy or where the pressure peaks occur - it is simply area under the PV curve.

Likewise each combustion event is a push on the piston, you do not want the push to come on half way through the power stroke where piston speed is already greatest, and where CC volume is high, and compression ratio is low. You want the push to come when piston speed is low relative to other parts of the stroke. Ie at the start of the down swing.

Your first sentence is correct although it has nothing to do with piston speed - it is piston POSITION. The best place to apply pressure is as close as possible to TDC (minimum volume) where the maximum work can be extracted by expansion of the gas.

~14° ATDC is the best compromise between compression ratio, expansion volume, piston speed, and piston momentum, thus the ideal place to give a piston a push(especially important if you're trying to impress the girls at the race track).

It is particularly false to relate the 14* (or 15*) PCP number to any kind of crank-rod geometry. Not only is 14* ATDC a position of very low mechanical advantage, it is irrelevant as I showed in the first paragraph of this post. The ideal location for PCP (as I said in my reply to SS) is actually at TDC - if it were possible to do the entire burn at TDC.

[PlatinumZealot]

@ goldie..

I see why people may think that it can equate to swing.. There is one big difference. For a swing you only push for a short period. Almost an impulse. In the engine the combustion gases apply a consistent push. You want to maximise the expansion work because you wont be able to use up all the energy from the gas anyway.

I think the peak pressure at 14deg thing is for mechanical reliability reason and physical limitations in combsution more than anything to do with kinetics.

[gruntguru]

I think the peak pressure at 14deg thing is for mechanical reliability reason and physical limitations in combsution more than anything to do with kinetics.

The 14* is mostly to do with combustion duration. To reduce the number below 14 you have to get the combustion done in less than - say 28*. That is difficult with conventional ignition. You also run into problems when rate of pressure rise gets too high. Conventional ignition starts slowly and speeds up with a sharp peak when the flame front is at its broadest. TJI burns quickly from start to finish - the problematic peak is less pronounced.

[saviour stivala]

Must say a very pleasant interesting and informative discussion by highly informed people around this here “combustion process” subject. Appreciated are the graphs produced the research work of qualified people which cannot be disputed. The only thing that can be disputed is their interpretations. And that will be nothing more than a personal opinion. So having said all that and with all respect to others I will forge ahead and say that those graphs, and their interpretations plus some opinions expressed does not change anything from my personal expressed opinion/s on this here subject for the following reasons. My opinion/s expressed centered mostly around the present F1 engine which spends most of its working life at a maximum power speed of 10500RPM and when not on the move idles at a mandated 4000RPM, an engine that thrives on extracting the maximum combustion burn potential and transforms that potential into maximum power, torque and efficiency possible. At some point the effect/s of con-rod length to crank radius ratio was touched upon, this in itself is a very interesting subject. I have a treasured list of very complete engine specification for what was regarded as the greatest 50 racing engines from 1913 to 1994 of which I am willing to share with fellow interested posters on here, but the list is long, it will be of topic, and permission will be needed from site administration to post.

[Big Tea]

Guys, not genned up on this, so it may sound a stupid question, but does the timing of the fuel injection have any affevt on the lubrication of the rings?

If, what amounts to solvent is above the ring on the up stroke, is the oil film on the cylinder wall affected, diluted or washed off/ vaporised?

[saviour stivala]

Guys, not genned up on this, so it may sound a stupid question, but does the timing of the fuel injection have any affevt on the lubrication of the rings?

If, what amounts to solvent is above the ring on the up stroke, is the oil film on the cylinder wall affected, diluted or washed off/ vaporised?

A good read:- “impact of fuel injection on dilution of engine crankcase oil for…jestor.” “jestor.org/stable/26278010” April 14 2015.

[Big Tea]

Guys, not genned up on this, so it may sound a stupid question, but does the timing of the fuel injection have any affevt on the lubrication of the rings?

If, what amounts to solvent is above the ring on the up stroke, is the oil film on the cylinder wall affected, diluted or washed off/ vaporised?

A good read:- “impact of fuel injection on dilution of engine crankcase oil for…jestor.” “jestor.org/stable/26278010” April 14 2015.

Thanks, interesting (even though I only read the Abstract so far). This though is concerned with the 'sump oil' being 9% diluted, I was thinking of the top few mm of the bore, which would I assume be far more diluted?

Then again I suppose if it 'that wet' the fuel would be a lubricant its self?

[saviour stivala]

Guys, not genned up on this, so it may sound a stupid question, but does the timing of the fuel injection have any affevt on the lubrication of the rings?

If, what amounts to solvent is above the ring on the up stroke, is the oil film on the cylinder wall affected, diluted or washed off/ vaporised?

A good read:- “impact of fuel injection on dilution of engine crankcase oil for…jestor.” “jestor.org/stable/26278010” April 14 2015.

Thanks, interesting (even though I only read the Abstract so far). This though is concerned with the 'sump oil' being 9% diluted, I was thinking of the top few mm of the bore, which would I assume be far more diluted?

Then again I suppose if it 'that wet' the fuel would be a lubricant its self?

The top of the bore is were the dilution or wash-up starts and being a dry sump might be of a tiny little help from being a wet sump. another bit of help is that the F1 engine highest possible mileage on oil is no more than a race length (2hours).

[Tommy Cookers]

regarding rod ratio and F1 etc ac mentioned by s s .....
grandprixengines.co.uk is (I imagine) the source of such material - conrod length/stroke CRL/S

Note 62 conflates BRM F2 and F1 gains via 'short rod' 1.7 RRs - in F1 stroking to stretch to 2+ litre V8 with unchanged block
(the BRM and Weslake 3 litre V12s were based on this - did they use similar or different RRs ?)
and of course the F1 2.5 litre Coventry-Climax that won everything - stretched to 2.5 by using a RR of only 1.44
or maybe the tipo 60 ? 2.8 litre Maserati
ok the likeliest driver of short rod ratio is stroking within an unchanged block deck height
the opposite effect, destroking eg the 3.5 litre F1 Honda V10 to 1990 3 litre F1 Mugen ('Honda') needed a 2.7 rod ratio
and postfreeze NA F1 had only 39mm stroke - a low RR unlikely (the big-end eye almost touching the small-end eye)

[saviour stivala]

regarding rod ratio and F1 etc ac mentioned by s s .....
grandprixengines.co.uk is (I imagine) the source of such material - conrod length/stroke CRL/S

Note 62 conflates BRM F2 and F1 gains via 'short rod' 1.7 RRs - in F1 stroking to stretch to 2+ litre V8 with unchanged block
(the BRM and Weslake 3 litre V12s were based on this - did they use similar or different RRs ?)
and of course the F1 2.5 litre Coventry-Climax that won everything - stretched to 2.5 by using a RR of only 1.44
or maybe the tipo 60 ? 2.8 litre Maserati
ok the likeliest driver of short rod ratio is stroking within an unchanged block deck height
the opposite effect, destroking eg the 3.5 litre F1 Honda V10 to 1990 3 litre F1 Mugen ('Honda') needed a 2.7 rod ratio
and postfreeze NA F1 had only 39mm stroke - a low RR unlikely (the big-end eye almost touching the small-end eye)

An important note on this subject. Some people express themselves in a way that can leads to confusion such as “con-rod length to stroke ratio” some others takes a very short cut and express themselves as just “RR”. People that matters and can speak with authority express themselves as “con-rod length ‘center to center’ to crank radius ratio”.

[63l8qrrfy6]

An important note on this subject. Some people express themselves in a way that can leads to confusion such as “con-rod length to stroke ratio” some others takes a very short cut and express themselves as just “RR”. People that matters and can speak with authority express themselves as “con-rod length ‘center to center’ to crank radius ratio”.

Not only you are pedantic, you are also factually wrong. You suggest that the rod to stroke ratio is the same as the “con-rod length ‘center to center’ to crank radius ratio”. This is incorrect since the crank radius is half the stroke.

So for example in your post below:

Formula 1 engines has always used/favored higher rod length to crank radius ratio, always used a ratio higher than 2.0:1 as opposed to what seems the preferred lower than 2.0:1 used for fast road engines.

you should have said that f1 engines have favoured a rod length to crank radius ratio higher than 4 for the statement to be corrent.

I think the only one here confusing matters is yourself.

[gruntguru]

Guys, not genned up on this, so it may sound a stupid question, but does the timing of the fuel injection have any affevt on the lubrication of the rings?

If, what amounts to solvent is above the ring on the up stroke, is the oil film on the cylinder wall affected, diluted or washed off/ vaporised?

One of the main factors determining fuel wetting of port and chamber walls is atomisation. The smaller the droplets the less likely to wet surfaces. The higher the fuel pressure the smaller the droplets.

The mechanism is simple. The smaller the droplet, the higher the surface area (and silhouette area) to mass ratio. this results in the spray (droplets) behaving more like a gas as they get smaller. The gas slows down (or turns) as it approaches any wall. Large droplets take longer to slow down (or turn), continue forwards and hit the wall. Ultra-small droplets slow down (or turn) with the gas and are less likely to hit the wall.

And yes, the timing of the injection has an effect. Earlier injection gives the droplets more time to fall out or continue forwards and hit the wall.

[gruntguru]

An important note on this subject. Some people express themselves in a way that can leads to confusion such as “con-rod length to stroke ratio” some others takes a very short cut and express themselves as just “RR”. People that matters and can speak with authority express themselves as “con-rod length ‘center to center’ to crank radius ratio”.

Engineering text books, kinematic formulae and papers usually refer to "l/r".

[saviour stivala]

Re my note about the different ways of expressing con-rod length as a ratio to crank radius that can lead to possible confusion. My first touched on the subject was expressed as “con-rod length to crank radius ratio” I even expressed length as “center-to-center”. Thereafter both “rod to stroke ratio” and just “RR” were being expressed. These different ways to express “con-rod length to crank radius ratio” all leads those up to speed on the matter to the same point, being C-R length to crank radius ratio 4.0:1 or C-R length to stroke ratio 2.0:1 is one and the same value. But it might make it a bit harder for those interested and following but (with all due respect to them) might not be up to speed on such matters as others. But on the other hand trying to make things a shade easier for those interested and following but not being fully up to speed on such matters risks upsetting those allergic to the lower rungs of academy and they go in overdrive nit-picking.