Ion Current Dependence on Operating Condition and Ethanol Ratio
This masters thesis investigates the possibility to estimate the
ethanol content in the fuel using ion currents. Flexible fuel cars can
be run on gasolineethanol blends with an ethanol content from0 to 85
percentage. It is important for the engine control system to have
information about the fuel. In todays cars the measurements of the
fuel blend are done by a sensor. If it is possible to do this with ion
currents this can be used to detect if the sensor is broken, and then
estimate the ethanol content until the sensor gets fixed. The benefit
of using ion currents is that the signal is measured directly from the
spark plug and therefore no extra hardware is needed.
To be able to see how the ethanol ratio affects the ion currents, the
dependencies of the operating point have been investigated. This has
been done by a literature review and by measurements in a Saab
9-3. Engine speed, load, ignition timing, and spark plugs effects on
the ion currents are especially studied. A black box model for the ion
currents dependence on operating point is developed. This model
describes the engine speed, load and ignition timing dependencies
well, but it can not be used to estimate the ethanol ratio.
Karin Gustafsson
2006
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