How Super High Rpm is achevied

[Guest]

Hi berg
it was a good explaination , but i still did not get the first point
and how is that going to help like bore to stroke ratio, see if stroke length is less then a very less powerful stroke right so , ultimately less BHP right.
so y they do that.

thanks
krishna

You're right, less stroke tends to less torque. But it can be healed by minimizing the TDC volume. In F1 engine, the TDC volume is very small since the valve does not have to lift so high. It is because the valve diameter is large and they have to move fast

[T]

don't know if its already been said but its so simple,

to rev high the major limitation is getting the air in! The revs are limited by when the gas speed in the inlet/port reach the speed of sound, which chokes the engine and causes a massive reduction in volumetric efficiency, and therefore torque and power. So to rev high you need to allow as much volume of air into the cylinder as possible at as higher engine speed as possible.

Then comes the valve actuation, combustion theory and structural stuff.

T

[ginsu]

i cannot think of anything radical, which takes engine to that super high rpm.I am missing anything which makes F1 engine move at such high rpm.
any ideas
i think Cosworth came up with first of kind
with this kind of engine

Your missing the biggest factor of all. The Valvetrain!.

Pneumatic valvetrains ushered in the 12k and higher era.

Next up, solenoid actuated valves. Which will do away with camshafts completely. I don't have much data, I know that Renault and McLaren are supposedly working on this tech. But, without camshafts the rotating mass is significantly reduced. No finger followers, no pneumatic pistons, no gears driving the camshafts. All sorts of rotating stuff can be gotten rid of.

[ginsu]

With a fixed displacement, shortening the stroke results in a larger bore. Remember, that despite the bore and stroke, about the same amount of fuel/air is introduced into the combustion chamber, and when ignited, release the same amount iof energy. With a shortened stroke, the crankshaft offset is less, and thus you get a shorter leverage. But there really isn't less power produced. The horsepower and torque characteristics may be altered, and efficiencies may be also changed.

This is true, except to say that a longer stroke allows the combustion process to take place over a longer effective period. This tends to be good for low-end torque characteristics. That's one reason that american V8's produce good low-end.

[ne port man]

There are so many secrets in f-1 engines that wil never be known,but the bottom line of short stroke pneumatic valves are the main contributors to the high engine revs.And yes fuel burn has a small part of total engine output.The quicker the fuel burn the less goes out the exhaust(at 18,000 the piston goes up and down 300 times a second)the variable length trumpets control the power delivery over the rev. range,has nothing to do with fuel rate burning.It tunes by resonance as does the exhaust system.

[riff_raff]

The purpose of shortening the stroke is simply to reduce the inertia loads on the reciprocating components. Logically, if you reduce the stroke dimension, you will need to increase the bore dimension to maintain a given displacement.

The downside to shortening stroke is that intake velocity is proportional to piston velocity. So the point of optimum volumetric efficiency, due to intake inertia, will occur at a higher rpm. That is why long stroke, long rod engines tend to produce peak torque at a lower rpm than a short stroke, short rod engine. You will find that peak engine torque will usually occur at the point of peak volumetric efficiency.

[West]

I can understand less mass equals less inertia, such that it is easier to change direction. But given a force, doesn't less mass mean that the piston will have a higher acceleration (and then higher velocity?)

[DaveKillens]

I can understand less mass equals less inertia, such that it is easier to change direction. But given a force, doesn't less mass mean that the piston will have a higher acceleration (and then higher velocity?)

True, if the piston was allowed to be accelerated by the forces of combustion expansion. But the piston is connected to the rods, crank, etc.
When I was describing piston acceleration, it was in reference against another piston that had a different stroke.
In fact, don't even consider the combustion process, just imagine that a crankshaft is being turned by external forces, the pistons are enjoying a free ride. Starting at top dead center, the piston begins accelerating downwards, to pass the mid-point of the stroke, then begins to decelerate as it reaches bottom. Then it begins it's path upwards, going through acceleration forces, again. If you ask the piston to keep the same RPM, but travel further each stroke, it undergoes higher acceleration forces than the previous shorter stroke. And that's what it's all about, that a shorter stroke has lower acceleration than a long stroke, and thus, less mechanical loads.