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Abstract |
Ionization Current Interpretation for Ignition Control in Internal Combustion Engines
Spark advance setting in spark-ignited engines is used to
place the in-cylinder pressure curve relative to the top dead
center. A feedback scheme, not a calibration scheme, based on
ionization current is proposed here. It is thus related to pressure
sensor feedback schemes, that have reported good results, but have
not yet been proved cost effective, due to the cost of the pressure
sensor. The method proposed here is very cost-effective, since it
uses exactly the same hardware and instrumentation (already used in
production cars) that is used to utilize the spark plug as a sensor
to detect misfire and as a sensor for knock control.
A key idea in the method is to use parameterized functions to
describe the ionization current. These parameterized functions are
used to separate out the different phases of the ionization current.
Special emphasis is laid on getting a correct description of the
pressure development. The results are validated on a SAAB 2.3 l
production engine by direct comparison with an in-cylinder pressure
sensor (used only for validation, not for control), but also by
using a physical model relating the ionization current to the
pressure.
Lars Eriksson and Lars Nielsen
Control Engineering Practice, 1997
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