Research Papers

A Parametric Model for Ionization Current in a Four Stroke SI Engine

[+] Author and Article Information
Ingemar Andersson

Signal Processing Group, Department of Signals and Systems, Chalmers University of Technology, Gothenburg SE-41296, Sweden

Lars Eriksson

Vehicular Systems, Department of Electrical Engineering, Linkoping University, Linkoping SE-58183, Sweden

J. Dyn. Sys., Meas., Control 131(2), 021001 (Feb 04, 2009) (11 pages) doi:10.1115/1.3023119 History: Received October 20, 2005; Revised September 09, 2008; Published February 04, 2009

A model for the thermal part of an ionization signal is presented that connects the ionization current to cylinder pressure and temperature in a spark ignited internal combustion engine. One strength of the model is that, after calibration, it has only two free parameters: burn angle and initial kernel temperature. By fitting the model to a measured ionization signal, it is possible to estimate both cylinder pressure and temperature, where the pressure is estimated with good accuracy. The model approach is validated on engine data. Cylinder pressure and ionization current data were collected on a Saab four-cylinder spark ignited engine for a variation in ignition timing and air-fuel ratio. The main result is that the parametrized ionization current model can be used to estimating combustion properties as pressure, temperature, and content of nitric oxides based on measured ionization currents. The current status of the model is suitable for off-line analysis of ionization currents and cylinder pressure. This ionization current model not only describes the connection between the ionization current and the combustion process, but also offers new possibilities for engine management system to control the internal combustion engine.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 2

Example of ionization current with its three characteristic phases

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Figure 3

The structure of the ionization current model with its submodels

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Figure 4

Sketch of the ideal Otto cycle that defines states 2 and 3

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Figure 5

Combustion model for calculation of burned gas temperature close to spark plug. The gas kernel is compressed by the surrounding cylinder pressure and does not mix with other gases.

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Figure 6

Temperature sensitivity for NO formation. Simulation is based on 50 bar pressure, stoichiometric AFR, a fixed volume, and temperature.

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Figure 13

Four randomly picked cycles. Measured and simulated ionization currents and the square error of each curve fit. Dotted: measured current; solid: optimized model.

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Figure 14

Estimated parameters, initial kernel temperature, and burn angle. The circle marks the mean value and the bars show the standard deviation within each data set.

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Figure 15

Comparing pressure trace measures from measured and simulated cylinder pressure

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Figure 1

Ion sense system

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Figure 7

NO formation simulated from engine pressure data

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Figure 8

Ionization ratio dependency on temperature (Eq. 24), NO, 20 bar, NO molar fraction of 1000 ppm

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Figure 9

Upper: Characteristic time to reach 90% of equilibrium NO. Lower: Relative NO gradient in temperature.

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Figure 10

The measurement volume according to Saitzkoff–Reinmann model between the electrodes in the spark gap

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Figure 11

The inverse use of the ion current model in Fig. 3

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Figure 12

Ionization current window for parameter estimation. Left: the window angles marked with vertical lines. Right: the cut-out current.



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