TurboTommy

Konstantin,
Ich glaube Bengt hat recht (I agree with Bengt).
If you have slower combustion, either because of the fuel and/or combustion chamber design, you have no choice but to increase timing in order to maximise power; that is correct. But, if you can improve combustion speed, you will always increase BMEP at the right time with less timing advance. Delay from the spark to maximum BMEP will always cost power.

By the way, there is no relation between the octane of the fuel and its burning speed. High octane is more stable under pressure, but that doesn't mean it burns slower. Very popular misconception.

NZ951

Translation

I think Bengt is right?

NZ951

Pressure drop is .12 bar.

Tomas L

Bengt is definetly right about the fact the slower combustion means less power all other things equal. Any combustion before TDC will cause more pressure acting against the piston when it is on it's way up against TDC.
And since, to do maximum work, you want full pressure a few degrees after TDC, then combustion should be as fast as possible.
As I understand it pressure speed is closely coupled with combustion speed (and cooling effect from the combustion chamber).

This does no necesarily mean that you can't get more power with water injection. If you can increase boost to that amount that you compensate for the slower combustion and then some. But with the same boost you will loose power.
That figure alone isn't very helpful.
At what airflow (power level)? Which ambient temperature? Which after ic temperature?

Tomas

Konstantin

this is teh same thing what I say. you have slower combustion BUT if you adjust your timing so that you have your max pressure at the right time (just after OT) then everything is ok.

It is the pressure after the explosion after the OT which push the piston down and makes power. the more pressure (we call it effective midle pressure) (at the right momment just after OT) the more power. Quite simple

or not that simple if you wnat to know evrything.
here a small part to beginn.
Ignition and flame dispersion are two different things.
even if you ignite the air/gas mixture sooner that do NOT mean that you will reach the max pressure sooner!!!
diferent spark plugs different mixtures, different grade of gas, different temp in the engine, diffent ignition system, other density of the mixture etc etc. make the flame dispersion different and at the end you have a different time from when you start to ignite your mix till you get the max pressure.

the ignitition delay at lambda 1 (14,7:1) at WOT is typical from 0,5 to 1 milisec.
If you use other RPM not WOT but PT or idle, or leaner mixture and you have more unburnt gas in the cylinder (less flow of fresh air) then the ignition delay is much longer.
There are so many variables that can change the ignition the flame dispersion the max pressure. the middle effective pressure, and

BTW The Proffessor and all books in Germany agree that higher octane gasoline needs more energy to burn and burns more difficult. the dificult to burn the better for high boost since it is less detonation sensible.
I am not the one who found this out. I just say what i learned from them. I believe they are right. If they are wrong then I am wrong either.

some data for the gasoline can be found in many books

More dificult to burn means-> more detonation resistant-> more boost can be used-> more power
More Boost ALWAYS give you more power compared to all other PARAMETERS LIKE ENGINE EFICIENCY, max combustion pressure etc etc.
Turbo cars needs boost and this is what we are after. everything else is just a second choice.

anyway enough for now. not easy to transale all these in English

if anyone wants to know more check for the VIBE and the Double VIBE funktion.
Then you can calculate the ignition delay and find the optimum sparkplug for your ignition system or if you change the ignition system you know what kind of preignition you need (ignition before the OT , not detotantion or knocking)

Konstantin

NZ951

Around 300RWHP at 1bar less loss, 14 degrees C ambient with 22 degrees turbo intake temp. Dont have after IC temp.

333pg333

Since I dug up Corleone's 3L thread I found this one as well. Some interesting reading and shows what this particular forum used to be like...ie bit more technical. Not that I lay claim to understanding all this but it's a shame a lot of these guys have long since left the building.

JohnKoaWood

For more reason than finding different cars!

333pg333

Definitely