Making sense of ion sense technology - Here's a means of assessing the combusion process that may see renewed interest by the OEMs. - Motor Age - Automotive training, certification & parts info
Not too long ago, one of our Motor Age community members wrote excitedly about a new technology he was told about in a training class. The topic of his excitement
was ion sensing ignition systems, and I certainly admire him for his enthusiasm. But as is the case with many things in the
automotive world, not all new ideas are really new. Ion sensing technology has been around for more than a decade — it just
hasn't caught on. But new developments in ion sensing technology may just change all of that.
What Is An Ion?
An ion is an atom or group of atoms that has more (or fewer) electrons than it does protons. If there are more electrons than
protons, it is negatively charged and is called an anion. If there are fewer electrons, it is positively charged and is called
a cation.
The next generation of ion sensing systems from Delphi will house all the circuitry in the coil itself. (ILLUSTRATION: DELPHI
CORP.)
You might have heard of ionization in reference to an ignition system before, but in a different context. If the spark plug
is located in an electrical path, the gap between the center electrode and the ground electrode would certainly have to be
considered open in that circuit. But if enough electromotive force is generated, the atoms in that gap will begin to ionize
to the point of plasma. These ionized particles conduct electricity just fine, and the plug fires. It is this burn line that
many technicians have been using for years to identify problems in the combustion chamber. Compression problems, mixture problems
and ignition problems all can affect this burn line in unique ways.
The chemical and thermal reactions that occur during the combustion process also cause ionization, and according to researchers
like Lars Eriksson (who wrote Spark-Advance Control by Ion-Sensing and Interpretation in 1998), the post combustion phase is both stable and consistent enough to be used for information on the combustion process.
One drawback to early ion sensing systems was plug condition and type. Worn/fouled plugs or installing the incorrect brand
could result in ghost misfire or system codes. (PHOTO: PETER F. MEIER.)
In other words, it can be used to tell the engine control module the same thing it tells technicians viewing the secondary
pattern and even a bit more.
Ion Sensing Ignition Systems
The pencil style coil is deceiving in what it can do. This is the next generation of ion sensing technology offered by Delphi.
(PHOTO: DELPHI CORP.)
Ion sensing systems are based on the principle that electrical current flow in an ionized gas is proportional to the flame
electrical conductivity. In other words, by measuring the current flow in the post combustion ion trail between the plug electrodes,
engineers can get an idea of the combustion efficiency during combustion itself. This turns the spark plug into an intrusive
engine sensor, providing real time information on each cylinder's unique needs.
Originally, ion sensing ignition systems were used primarily for knock detection and misfire detection. Knock creates a pressure
oscillation in the combustion chamber that is reflected in the current measurement. It is more sensitive than conventional
knock sensors and eliminates the need for the additional sensor(s). In the presence of a misfire, no ions are created and
there is no current flow that can be easily detected. Ion sensing misfire detection is more stable and more accurate than
the more common method of monitoring crankshaft speed fluctuations.
This is the coil cartridge from the Saturn. It came in for a misfire issue, recording a P0300 Random Misfire in the ECM history.
And even though it was misfiring badly in the bay, the MIL was off. (PHOTO: PETER F. MEIER)
But there are more possibilities considering the advances in technology and computing power. According to Eriksson, "The spark
plug can, using signal interpretation, function as a sensor for several parameters."
The circuitry for the Compression Sense Ignition (CSI) system is built into the ignition control module. Based on the CSI
signal, the ICM creates a camshaft position signal for the ECM. (PHOTO: PETER F. MEIER)
In addition to the knock and misfire detection, this method could allow the spark plug to provide individual cylinder information
to the ECM on fuel trim and peak cylinder pressure position. This both improves overall engine efficiency and also gives technicians
even more diagnostic detail when they are dealing with customers' engine drivability complaints.
Pete Meier is an ASE certified Master Technician and sponsoring member of iATN. He has over 35 years practical experience as a technician and educator, covering a wide variety of makes and models. Now, as technical editor for Motor Age, his primary goal is to bring working technicians the information they need to succeed.
Articles by Peter F. Meier
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