Knock Question

[M&D]

I think the Jacobs Energy-pak aftermarket ignition amplifier uses this very
method (sparkplug) to see the condition of the combusting mixture. see
http://www.jacobselectronics.com

Michael Harrington
91coupe at bellsouth.net
91 RX-7 Coupe "Pearl" w/ some mods
N3WJE Ham

-----Original Message-----
From: Robert Harris <bob at bobthecomputerguy.com>
To: diy_efi at esl.eng.ohio-state.edu <diy_efi at esl.eng.ohio-state.edu>
Date: Saturday, March 14, 1998 12:55 PM
Subject: Knock Question


>Whilst re-reading my Heywood trying to figure out how a slower burning open
>chamber is going to make more power without knocking to destruction, I ran
>across something obscure I had forgotten about.
>
>Seems that when "knock" occurs, a high intensity flash is observed and it
is
>accompanied by a sharp increase in ionization.  He then says that optical
>probes and ionization detectors can be used to measure this.  In fact, the
>spark plug itself.
>
>Now my engine builder is a little reluctant to cut a hole through the
>cooling jacket and put a quartz window in for an optical detector, and I am
>rather reluctant to undertake a total redesign of my electronic ignition
>system.  Which leaves sticking a probe into the exhaust and measuring the
>amount of ionization.
>
>Heywood while referring to the measurement of ionization, leaves the
>methodology to do so as an exercise for the student.  So what I am asking
>for help on is any references to how to measure the ionization - SAE
papers,
>Reference books not leaving it as an exercise for the student etc.  Circuit
>Ideas for modifying the ignition would work. One idea that springs to mind
>(I am absolutely positive it has been done before by someone!) is to use a
>separate spark plug in the exhaust as an ionization detector.
>
>The reason for this interest is that acoustic knock sensors do work.
>However, to work well they must be closely tuned to the acoustics of a
>particular engine and speed range and without an excellent processor can
>give false reading (mainly knock when there ain't - fail-safe). If an
>Ionization Detector could be built that resides in the exhaust or a
modified
>ignition, then it could be coupled to the engine management system
>electronically and be virtually platform independent. Self tuning even.  No
>muss fuss dyno time thingee.
>
>Any thoughts, info or references would be appreciated. TIA
>
>
>