# Re: Conrod force/acceleration

```>> If both acceleration and velocity are 0 at the same time, it is a
>> clear indication that the engine isn't running at all.

Absolutly correct. :)

>Come again? Is there not a point in time where acceleration and
>velocity are zero? I certainly think so. When there is no velocity,
>there is no acceleration. Acceleration can be zero while velocity is
>constant, but if velocity = 0, acceleration = 0;

>acceleration is nothing more than the rate of change in velocity.

Right, and the acceleration is highest at TDC.

>At TDC velocity is
>zero, and therefore acceleration is zero, too. Yet the engine is most
>definitely running.

If velocity is ZERO and acceleration (rate of change in velocity) is
ZERO, then the velocity will remain at ZERO, and It's IMPOSSIBLE for
the engine to be running.

>Are you suggesting a perfectly parabolic acceleration curve with no
>zero point? (1) There will be a time when acceleration is zero; (2)
>You have massive acceleration/deceleration approaching/leaving TDC,
>as a function of rapid reversal of travel. You also have zero
>velocity, and therefore zero acceleration, at one micor-instant in
>time (at TDC).

Acceleration curve as an function of the crankshaft angle.

A  7   -!                                               !    7  A
C  6   -!*                                             *!    6  C
C  5   -!   *                                       *   !    5  C
E  4   -!                                               !    4  E
L  3   -!      *                                 *      !    3  L
E  2   -!                                               !    2  E
R  1   -!        *                             *        !    1  R
A  0 ---!---------*---------------------------*---------!--- 0  A
T -1   -!          *            _            *          !   -1  T
I -2   -!            *     *         *     *            !   -2  I
O -3   -!               *               *               !   -3  O
N -4   -!                                               !   -4  N
-5   -!-----------!-----------!-----------!-----------!   -5
0          90          180         270         360
DEGREE             CRANKSHAFT ANGLE            DEGREE

>more constant crank velocity, lower piston velocity overall? Eg in a
>I-4 vs. I-5 vs. V8 vs. V12?

The piston acceleration and velocity is an function of
crankshaft/pistonrod lenght and the crankshafts angular velocity.
and is the same for 4,6,8 and 12 cyl. engines.

The 4 cyl. has an higher oscillating peak to peak value
(difference in angular velocity at a constant RPM during one
revolution) than an 6,8 and 12 cyl. who have a higher oscillating
frequencies but lower peak to peak values. => running smoother with
less viberations.

BRGS

--
John Torset
johnt@borre.mail.telia.com
Amiga 4000

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