A Predictive Model for Knock in Spark Ignition Engines

The present contribution combines the consideration of the chemical reaction activity of the end gas and engine operating conditions to predict the onset of knock and associated performance in a spark ignition engine fuelled with methane. A two-zone predictive combustion model was developed based on an estimate of the effective duration of the combustion period and the mass burning rate for any set of operating conditions. The unburned end gas preignition chemical reaction activity is described by a detailed chemical reaction kinetic scheme for methane and air.

The variation with time of the value of a formulated dimensionless knock parameter based on the value of the cumulative energy released due to preignition reaction activity of the end gas per unit volume relative to the total energy release per unit cylinder swept volume is calculated It is shown that whenever knocking is encountered, the value of builds up to a sufficiently high value that exceeds a critical value. Under normal operating conditions, the value of remains throughout the whole combustion period at comparatively very low levels.

It is shown that the model and the use of this knock criterion produce results that are in good agreement with experiment when applied to an engine fuelled with methane. The applicability of this approach to operation with other gaseous fuels can be Similarly considered.