Ion current sensing -> spark advance

[mike mager]

David DeHaven <daved at trestle.com> asked about my reply to the "Ion current 
sensing -> spark advance" thread:

>I'm researching a way to use ion current sensing to determine the PPP.

Oh, yeah, I got that, but when I asked . . .

"You have been thinking about pressure measurements, any conclusions 
(besides cost)?"

. . . I was wondering what you had concluded about using mechanical sensors 
for reading pressure (such as used in the big basic engine research 
laboratories).

>There are other things I want to use it for, but that's the main 
>application. The other is knock detection.

I know it, and I sure wish that I just had it done, but, well, we're making 
progress (through you, thanks!).

I said . . .

"I am working with very little information about the 'DeSaxe cylinder
offset', also known as an 'offset cylinder engine';  I wonder about enough 
offset to give a vertical connecting-rod at the PPP."

. . . and you replied . . .

>So, basically, the crank centerline is not lined up with the center of the 
>piston?

. . . Yes, that's just it in the 'offset engine' or DeSaxe offset cylinder;  
the connecting-rod angle is altered at certain (each) point(s) in the 
stroke;  as much as I can tell, the connecting-rod is allowed/made to be 
vertical somewhere near the PPP, rather than being at an angle, so the 
vector would be just down, and not partly (wearing, frictioning) against the 
cylinder wall;  speedway motorcycles and some modern automotive engines (and 
many old engines) use this, but I still haven't found a really good detailed 
explanation of it (and I've been looking in many old books!).

Now, note that this doesn't apply directly to ICS, but, it seems (to me) 
related enough that a guy might want to address the mechanicals (if we are 
designing - or bench racing about designing - engines), as well as the 
fueling and ignition.

> > gudgeon-pin offset, which is still desired.  At the least, the DeSaxe 
>offset appears to noticeably reduce piston friction during the power 
>stroke.

>Or the piston pin is offset from center (for normal engines). Makes
sense, though it seems you could end up wearing one side of the cylinder 
wall more than the other.

The pin offset causes the piston rock (evident in all typical 
reciprocating-piston engines) to go in one step of the skirt touching, then 
the next step of the crown touching, as opposed to one big 'slap' step;  the 
old Hot Rod Magazine trick of installing the stock OEM (offset pin) pistons 
_backwards_, does the opposite - giving horrendous slap! - but reduces the 
friction for drag racing.

One more example of 'engineering, the art of compromise'.

>As long as you know where the PPP should be, the method of calculating the 
>spark advance is no different. This setup just takes uses the power stroke 
>more efficiently.

>-DrD-

Oh, yeah, got it (at least on a cursory level);  sure do wish that I just 
had it an a form to experiment with;  well, some day, one more project . . .

We sure value your input on this,
Mike
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