A Dimensionless Criterion for Predicting the Onset of Knock in Spark Ignition Engines

An approach for predicting the onset of knock and estimating its intensity in spark ignition engines is described. It is based on evaluating a dimensionless energy functional group, K_n, formulated to provide a numerical criterion to test continually, while using predictive models of the performance of spark ignition engines, for the onset of knock and its relative intensity at any instant during the combustion process. The basis for the derivation of this knock criterion and its significance are described. Examples involving gaseous fuels and their mixtures under different operating conditions show how the criterion can be employed for the prediction of the onset of knock and the associated knock- limited performance. Experimental results validating this predictive approach are also included. It is shown that this approach can be made an integral part of modeling spark ignition engine operation to be used for optimizing engine performance while ensuring throughout the avoidance of the onset of knock.