[Diy_efi] Ion Sensing project

Ville Vartiovaara vvartiov at cc.hut.fi
Wed Jul 3 20:51:23 GMT 2002


Sorry in advance for the reposts to come.. I had a wrong e-mail address in
my subscription.. But now it should work.


> Could this be used to detect knock?  I assume it could be done by 
> sampling in the 100Khz range.  Just look for a sinewave that would
> change frequency based on gas density and cylinder volume.

For me it's enough - to be sure the engine in not knocking - to keep the
PPP constant (e.g. 18 degrees ATDC).

But taking advantage of the vibration of the pressurized gas you asked
about can sure be done, the only problem is that it needs a bit faster ADC
than is on board. It's only spec'd to conversion times of "<10ms"
resulting in maximum samplerate of 100kHz.. But that's one of the minor
problems..;)


> I assume this could be calibrated for absolute pressure readings as 
> well? If that could be done, then a realtime horsepower could be
> calculated.

Yep. The only problem, I think, is that the "calibration" is quite
difficult, as it needs a table of other factors involved. But possible;)


> Would these parts work for the ion project?  How much voltage is too
> much before arcing becomes a problem?

As someone's said, the _useful_ range is up to somewhere 400Volts. I
haven't tried higher voltages, but I suppose that the problem caused by
too high a voltage accross the plug instantly after ignition is not
spontaneous arcing but the same effect as CDI systems use to extend
spark. It is that the once-ignited arc continues burning, whereas we want
it to extinguish (as soon as possible) before ion signal can be seen..

If someone has info about the arc-maintaining voltages of capacitor
discharge systems, it could help.. I'd stay at 400V..;)


-------------------------------------------------------
Ville Vartiovaara    Ville.Vartiovaara at hut.fi
 Helsinki University of Technology
 Dept. of Electrical and Communications Engineering



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