13 replies to this topic

[12.9:1]

One of our central questions is how much power can JM or MS call on, and how much more is possible. Some seem to assume that more rpm will always = grater and grater hp, however combustion is the essential event, and I think these engines are up against the limits of combustion. A friend of mine asks, "I hear that peak torque ignition timing is now over 60degrees BTDC, and I assume this is because they must compromise painfully between compression ratio and combustion speed, just as has always been the case with Yamaha's 5-valve 750 race engines (take your pick - good acceleration with high compression but loss of top end from an over-tight chamber, or good top-end with a more open, faster-burning chamber but lower compression so sayonara acceleration. Is this a correct picture or have I missed something ?"

What do we know of the current bore/stroke ratio? the last confirmed one I know - judd @2.25, also does any one have info on ignition timing?
A lead of 60degrees points to a slow burning chamber - or does it ? maybe at 18000 rpm
that's a fast one ? and ultimately what's up with compression ratios ?

[Aubwi]

Well, a tank of fuel has a limited amount of chemical energy available. Maybe someone knows how to calculate how much power that equates to as a function of # of pitstops, fuel octane and fuel cell size. Power being energy over time. Or is that approach too academic?

[desmo]

It appears bores range from around 91-96mm in F1 at present. Some sources claim CRs aren't much above 12:1, while others reckon they are likely in excess of 13:1.

John Judd in 1998:

"In the end what stops you making the bore size larger is that you have combustion considerations. If youkeep increasing the bore size the flame travel gets longer and the chamber gets thinner. If you look at a chamber at top dead centre, it is pretty horrible, not the ideal shape to burn anything.

"You have a large bore, a shallow chamber and relatively deep valve pockets and the valve pockets form most of the chamber space at TDC. You cannot avoid a relatively high surface:volume ratio and it is difficult to achieve a high CR. At the same time you can't get the maximum valve lift you require without having some lift around the TDC area, which again works against CR. You put up with this because at the end of the day, breathing makes more difference to performance than combustion does."

"A typical Formula 3000 or Super Touring engine would be around 30 degrees [BTDC spark advance], You are probably running a 14:1 CR with that. In F1 now, I guess that most people get 12:1 while 13:1 is very hard to come by. If you get 13:1, the chances are that your bore is too small or your valve lift is insufficient! I imagine that if you suggested to most F1 engine designers that they are running ignition timing of around 50 degrees or more, they probably wouldn't disagree."

I doubt that combustion chamber geometries, stroke/bores and valve lifts have changed much since then. One engineer I talked to reckons that burn time for combustion is not presently limiting max rpm in F1.

[12.9:1]

No not to academic at all, as in a sense it's all about burning as much petrol as possible in the
least time possible.
So it may come to just how fast can petrol burn ?
Though I'm interested in how the environment which contains the burning petrol effects
the speed and efficiency of the burn.
And by extension how the shape of the combustion chamber is arrived at -- a quest for rpm
and high compression, checked by mechanical limitations.

[12.9:1]

desmo thanks for the excellent John Judd quotes

I would like to introduce a concept from aviation, the "coffin corner", where an aircraft flying
at very high altitudes enters a situation where, as altitude increases the minimum flying speed
or "stall speed" increases, also as altitude increases the point of "compressibility" or the
speed of sound decreases.
So to fly higher one must fly faster - or stall the wing, but if you fly faster you will hit the
"sound barrier"- and stall the wing ! For the U-2 the corner was at 78000ft / 23774m or so
depending on payload, the SR-71 avoids all this by operating at super sonic speeds !

I believe the imminent arrival of the limits of F1 power is at hand.
John Judd lays out the dilemma

"You have a large bore, a shallow chamber and relatively deep valve pockets and the valve pockets form most of the chamber space at TDC. You cannot avoid a relatively high surface:volume ratio and it is difficult to achieve a high CR. At the same time you can't get the maximum valve lift you require without having some lift around the TDC area, which again works against CR. You put up with this because at the end of the day, breathing makes more difference to performance than combustion does."

That in 1998.
To continue to increase hp, rpm must rise, but a crank speed of 18000 rpm, allows approximately
0.002 seconds to fill the cylinder, truly impressive breathing, but to increase it - larger valves are
needed and larger valves need a larger bore.

Again - John Judd

"In the end what stops you making the bore size larger is that you have combustion considerations. If youkeep increasing the bore size the flame travel gets longer and the chamber gets thinner. If you look at a chamber at top dead centre, it is pretty horrible, not the ideal shape to burn anything."

I'm not saying we're in the corner now, but certainly inching up to it.

Here Dr. Mario Theissen (director of BMW F1 engine programme) answers some questions.
from 2001

Q- The four valve single plug head : is that the way forward for the foreseeable future, or will we see the revival of five valves or twin plugs?
A- " No I think what we have today is the right concept"
Q- How far are we from a 19000 rpm engine ?
A- "About 1000 rpm !"
Q- In terms of timescale...
A- "The current regulations stay in place through 2007. I expect us to see 19000 rpm within this period."
Q- Do you foesee the need for a basic change in the concept of the engine, to take crankshaft speed to 20,000 rpm and beyond?
A- " I don't know if it will be possible to exceed 20,000 rpm with the curent concept. I don't know if it is even possible at all, although the past shows that there was always a greater possibility than people anticipated."

The only way out of the coffin corner I can think of would be to replace the poppet valve, would
this be allowed ? or will bigger changes be made in 2008 ? ! !

.

[Engineguy]

Originally posted by 12.9:1
The only way out of the coffin corner I can think of would be to replace the poppit valve, would
this be allowed ? or will biger changes be made in 2008 ? ! !

.

I would think that none of the interested parties really wants more power (they just want their competition to have less than they have) because there is the perception or reality (take your pick) that the cars are "too fast" for the venues they run at.

More importantly, I don't think anyone involved would want to upset the status quo. Destabilizing rules changes that would add technical interest for us are not appealing to the majors. Despite the "always-right-around-the-corner" technologies that often appear promising, the same poppet valve engines that have made up 99.9999999% of the engines for street and track for the past century will likely do so for a couple more decades.

I don't mean to sound flip about this, but a better likelyhood is that sometime between now and 2007 a driver will be killed and a cry will go out again that the cars are too fast... we must reduce power, etc. and to maintain the status quo to the greatest extent possible, the same "0.3L per cylinder package" will be kept... i.e 2.4 litre, eight cylinders maximum or something like that.

While the 1960's and '70's were very interesting (front vs rear engine, 4 vs 6 vs 8 vs 12 vs 16 cyl, 2 valve vs 4 valve, big leaps in tires and downforce) the big business aspect of racing now will prevent us from ever again seeing any diversity at all. The majors are undoubtably comfortable in that coffin.

[regenmeister]

12.9:1
How about variable compression.
http://www.saab.com/...AL/en/vepsilon/

[RDV]

....but if you are already at your compression limit how can SVC help???

[12.9:1]

Enginguy

Thanks for the clear thinking, I can not but agree.
Though I'm still very interested in the dimensions of the coffin and the corner.


regenmeister

Oh yes, those SABB engineers very creative guys,and responsible for some of my favorite gizmos.
Though SVC needs a supercharger of some sort to work it's magic. and such things are banned


RDV

Imagine that head flopping up and down 300 times a second


.

[Engineguy]

Originally posted by 12.9:1

regenmeister

Oh yes, those SABB engineers very creative guys,and responsible for some of my favorite gizmos.
Though SVC needs a supercharger of some sort to work it's magic. and such things are banned

RDV

Imagine that head flopping up and down 300 times a second

.

I think the head only moves on command from the ECU, not mechanically in time with the crank as implied by the 300 times per second (18000RPM F1) you cite . eek indeed!

Gizmo seems an appropriate word... if you've got a supercharger on the engine anyway, can't you much more simply alter the effective compression ratio by variablizing the boost (and valve overlap too perhaps)?

[12.9:1]

Engineguy

The recipe, light load = high compression, no boost
high load = low compression, full boost

Of course I was having a bit of fun.
And RDV does ask. ....but if you are already at your compression limit how can SVC help???
SO....


Seriously, SABB really does have interesting tech, though it rarely gets on the road.

.

[BRIAN GLOVER]

I dont quite understand the analogy to the Coffin Corner and internal combustion engines.

"Coffin Corner' refered to the experience of second world war fighter pilots approaching compression gain in a dive when some of the lowest pressure surfaces of theit fighters, encountered the 'shock wave' causing test pilot, 'Cat's eyes' Cunningham', to reverse elevator inputs to recover.
Chuck Yeager in his X1 tested a 'Flying tail' to overcome this transition to supersonic flight . IE: The entire horizontal stabilizer and vertical fin could be rotated to change incidence and therefore angle of attack, which made the elevator effective once more. Stabillators appeared on fighters after that.

The piston sppeds in F1 engines are not much faster than those in 2nd ww fighter plane engines and the compression ratios cant be very high either with such a short stroke. The fuel F1 cars use, is 2004 European pump gas specifications with pretty slow flame fronts. As the chassis depends on the tires for its design, the engine depends on the fuel, so how much further can they go? Anyway, back to airplanes.

Density effects the 'true' airspeed that the wing stalls, but the indicated airspeed remains constant in a static stall. IE: The indicated airspeed obtained from the pitot tube requires a differential pressure to that of the static vent pressure, which it is connected to, to indicate airspeed at a given altitude .

At altitude, the stall takes place at this same indicated airspeed, however, the aircraft must be going faster to allow the same amount of air particles to enter the pitot. The angle of attack remains the same also. If you land your plane on a hot day in Denver, as opposed to New York on a cold day, as you touch down, the airspeed indicator will indicate the same airspeed, but you will require a hell of a lot more runway, because the true airspeed will be equal to the ground speed in zero wind conditions. Denver density altutude can be obtained in New York with the 'right' atmospheric conditions. Notice pitot tubes on F1 cars? Buyrnes waits for a cloud to go over the track, then tells Michael to go for pole position.
In Denver, the plane will feel mushy.
The higher the altitude, indicated and callibtrated airspeeds become unreliable and the plane is flown with angle of attack indicators at flight levels above 30 000 ft and equivalent airspeeds are used below compression gain. Next time you fly the airlines, ask the crew to show you the airspeed indicator, the Mach number, the true airspeed, the angle of attack indiactor and the ground speed reading on his GPS or DME. Unfortunately, you cant do this in a US carrier.

The U2 had very high aspect ratio wings that could take exceedingly high angle of attacks before stalling, like glider wings. The U2 can recover from a stall at that altitude, but the SR71 could not. Thrust keeps it up there.

[QUOTE]Originally posted by 12.9:1
I would like to introduce a concept from aviation, the "coffin corner",

[12.9:1]

BRIAN GLOVER Writes -

"Coffin Corner" refered to the experience of second world war fighter pilots approaching compression gain in a dive
______________________________________________________________________________


It seems that subsequent to WW2, JET pilots redefined "coffin corner", as the point of coincidence
of the high and low speed buffet boundaries.

Many variabules including, weight, turbulence, speed,altitude/density,and large bank angles.
can combine to create the "corner" even at low altitudes.

The U-2 pilots would regularly fly with less than ten knots speed between the high and low
buffet boudaries

.
The piston sppeds in F1 engines are not much faster than those in 2nd ww fighter plane engines and the compression ratios cant be very high either with such a short stroke. The fuel F1 cars use, is 2004 European pump gas specifications with pretty slow flame fronts. As the chassis depends on the tires for its design, the engine depends on the fuel, so how much further can they go? Anyway, back to airplanes.

I agree, piston speeds are rather moderate, as stroke shrinks to accommodate those big valves.

Exactly! fuel is a major player, and "how much further can thay go" is my question.

[BRIAN GLOVER]

I dont know if you fly 12.9.1 (Strange name);) but even at a private pilot level, the student is required to accellerate the stall by banking the light trainer(C150 or other such) at 45 degrees at about 40 % power. The altitude is held untill the wing stalls. This is a dynamic entry as opposed to slowing the plane to a power off stall , achieved by trying to hold altitude with level wings(static). The stall speed is about 10mph different. If one applied full rudder in the latter scenario, a spin would result. If full rudder was applied in the former, this would be a 'snap roll' or a 'whip stall' ,in English terms, which is an aerobatic manouvre. Most advanced aerobatics is done in this flight region. Best results are achieved at about 5000ft ABS on a standard day with modern aerobatic aircraft. 'Aerobatics" by Niel Williams, is a good book to read if you are interested in this subject.
A 60 degree bank at level altitude would result in 2g mass acceleration.

Originally posted by 12.9:1
BRIAN GLOVER Writes -

"Coffin Corner" refered to the experience of second world war fighter pilots approaching compression gain in a dive
______________________________________________________________________________


It seems that subsequent to WW2, JET pilots redefined "coffin corner", as the point of coincidence
of the high and low speed buffet boundaries.

Many variabules including, weight, turbulence, speed,altitude/density,and large bank angles.
can combine to create the "corner" even at low altitudes.

The U-2 pilots would regularly fly with less than ten knots speed between the high and low
buffet boudaries

.
The piston sppeds in F1 engines are not much faster than those in 2nd ww fighter plane engines and the compression ratios cant be very high either with such a short stroke. The fuel F1 cars use, is 2004 European pump gas specifications with pretty slow flame fronts. As the chassis depends on the tires for its design, the engine depends on the fuel, so how much further can they go? Anyway, back to airplanes.

I agree, piston speeds are rather moderate, as stroke shrinks to accommodate those big valves.

Exactly! fuel is a major player, and "how much further can thay go" is my question.