[Diy_efi] ION sensing question

[Bevan Weiss]

It's not quite as easy to use ION sensing to determine the AFR of the intake
mixture.
In a perfect combustion you will get H20 and C02... and this would be formed
instantaneously, hence there would actually be no ION's to sense.  It's the
intermediate steps and incomplete transformations that actually allow the
ION sense technique to work.
When the combustion begins, oxygen is turned in ozone, and free oxygen atoms
(O3(2-) and O(2-))
this then allows the remainder of the process to take place...
The long hydrocarbons get broken down into slightly smaller hydrocarbons
(perhaps ionic compounds) and water, as well as some CO2 and likely some CO.
The process continues to get refined down until the end product is very
close to complete combustion...
CO2 and H2O, with trace hydrocarbons, carbon monoxide, ozone etc.

Detecting the peak pressure is quite easy, because it's the point with the
greatest ION concentration and hence the highest sense current.  Misfire is
quite easy to detect because it will have a very characteristic pressure
curve, and will have a very low ION concentration overall.  Knock is only
when the peak pressure point occurs before it's desired, the same is true of
all detonation effects.

To detect the mixture you would really have to do a huge number of
calculations...
The only real way I can think of doing it is via a trial and error method.
Just change the fuel/air ratio either up or down, and see whether it changes
the peak pressure at all.  Making sure that the timing is correct, so that
the peak pressure point occurs where desired.
If the peak pressure decreases then you should probably start to go back in
the other direction.


----- Original Message -----
From: "peterw" <peterw at waybeat.com.au>
To: "List for general do-it-yourself EFI talk" <diy_efi at diy-efi.org>
Sent: Saturday, June 14, 2003 4:14 PM
Subject: [Diy_efi] ION sensing question


> As I understand it ION sensing ignition systems can be used to determine,
> combustion pressure, knock, misfire etc and these ignition systems are
used
> to adjust advance on a cycle by cycle basis.
>
> Does anyone know if ION sensing can be used to determine mixture ? If so
> anyone point me to a relevant web link or other literature. My attempsts a
> web serach turned up lots of references to either ignition systems or
other
> chemical exotica. Couldn't find any refrence to fuel mixture
determination.
>
> Thanks
> Peter

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