Controlling combustion with ionisation feedback

Ionisation probes are frequently used to measure in-cylinder combustion characteristics of Otto cycle engines. The output from these probes can be processed for the calculation of flame propagation times or for the identification of knock or preignition. Adaptive control systems based on ionisation probes can also be used. These utilize correlations between flame arrival time and air to fuel ratio or spark timing. Such control systems are becoming increasingly important for meeting the fuel economy, emissions and driveability constraints of future engines. The paper describes an analysis which was carried out on a control system during the early stages of development. It helped to provide initial values for the control parameters of gain and update time for subsequent use in the initial software calibration