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The effect of the electrodes on the early signal of the ionization sensor has been studied experimentally and with a model for the sensor. Experiments in a constant-volume combustion chamber with a generic electrode configuration allowed to investigate the role of electrode contact and the main path of the current. A framework for a model allowing the inclusion of electrode processes is introduced, and a first implementation of this model is presented. The results from the simulations are in good qualitative agreement with the experimental observations. Our conclusion is that electrode processes can limit the current during early combustion, and that the geometry of the electrodes, and especially the cathode, govern the characteristic shape of the first current peak.

The location of the peak pressure can serve as a control parameter to adjust ignition timing and optimize engine performance. The ionization sensor, an electrical probe for combustion diagnostics, can provide information about the peak pressure location. However, the reliability of such information is rather poor. In-cylinder gas flow at the electrodes may be one reason for this. We present results from an investigation of the relationship between ionization sensor current and pressure under various gas flow conditions. The gas flow velocity in the vicinity of the electrode gap was measured by LDA. From the results one may infer how the in-cylinder gas flow affects the reliability of the prediction of pressure peak location from the ionization sensor signal. One finding is that high bulk gas flow impairs the precision of the prediction in certain configurations.