Ion Current Sensing for HCCI Combustion Feedback

Measurement of ion current signal from HCCI combustionwas performed. The aim of the work was to investigateif a measurable ion current signal exists and if it is possible to obtain useful information about the combustion process. Furthermore, influence of mixture quality in termsof air/fuel ratio and EGR on the ion current signal wasstudied. A conventional spark plug was used as ionizationsensor. A DC voltage (85 Volt) was applied acrossthe electrode gap. By measuring the current through thegap the state of the gas can be probed. A comparisonbetween measured pressure and ion current signal wasperformed, and dynamic models were estimated by usingsystem identification methods.The study shows that an ion current signal can be obtainedfrom HCCI combustion and that the signal levelis very sensitive to the fuel/air equivalence ratio. Themost important result from this study is that the ion current signal proved to be an excellent indicator of the actual combustion timing which is crucial piece of information for HCCI control.