maximum piston speed? 11

[bigtomwcp]

in my quest for more useful knowledge i am wondering what kind of piston speeds are the limit? i know some of you guys out there deal in F1 and such. i had jotted a number on a small piece of paper an F1 guy told me a few months ago but i have misplaced it and it is important now. i think it was 28m/s or was it f/s? thanks for the help i am really looking for a max this engine will only run for 200 miles then be rebuilt. i am trying to maximize breathing with the best trade off of stroke and rpm.

 

[doejohn]

Trying again...

Here's some equations for piston kinematics I had worked out some time ago. They might even be correct!

let c = conn rod length
let s = stroke
let r = ½s
let p = "rod ratio" = c/s
let Q = crank angle from TDC
let w = dq/dt = engine speed (radians/time, not rev/time)
let x = piston position from mid-stroke)
let y = du/dt = piston velocity
let z = d²u/dt² = piston acceleration
let a = 2p (twice rod ratio)
let b = (a² - 1 + cos²Q)^½

And first note that for infinitely long conn rod, piston motion approaches sinusoidal, where
max x = r
max y = rw
max z = rw² for constant engine speed (dw/dt = 0)

Actual motion for pistion (finite conn rod length) can then be expressed as ratio to max sinusoidal motion:

x/r = -a + b + cosQ
y/rw = -sinQ[1 + (cosQ)/b]
z/rw² = -(cosQ + [(sin²Q)/b]•[(cosQ)/b - 1])•[(cosQ)/b - 1]

These normalized motion equations approach sinusoidal for larger rod ratios, with max/min values of ±1. The amount that the normalized velocity and acceleration max/min values exceed ±1 represent the amplification due to non-infinite conn rod length. Again, engine acceleration was neglected in deriving normalized acceleration equation.

Note that maximum piston acceleration is amplified over sinusoidal max (aw²) by factor of (1 + 1/a) = (1 + ½/p). Trends pointed out by Norm above can be seen (what's with the Structurals hanging out here?....)

FWIW, I've heard max piston accelerations for near-current F1 engines as being around 10,000g, as mentioned above. Same source reported engine accelerations of 25,000rpm/sec.

 

[NormPeterson]

Originally posted by ivymike

position = a*cos(o)+sqrt(r^2 - a^2*sin(o)^2)

That's the basic position formula that I used (piston pin offset being taken as an algebraic correction against 'a*sin(o)'). I've been looking for some old derivation notes that may still be around somewhere. But I recall having used the rod angle as well as the crank angle in working the various velocity and acceleration components. Seemed simpler at the time . . .

Have to admit, I hadn't considered the possibility of crankshaft offset.

Norm

 

[Nothegger]

To cnova: That's very interesting. Is there any more info on those ceramic-aluminum liners?

 

[WilliamH]

Nothegger:

Metal/matrix/composite (MMC) cylinder applications can be found if you do a search in Google. Porsche and I believe, Toyota use this material currently.

I worked in the engineering/testing dept. for a piston manufacturer a few years back that was experimenting with the material as a piston alloy. Machining is a real challenge.

Will