Statistical approach to characterize combustion knock in the hydrogen fuelled SI engine

Combustion knock in a hydrogen fuelled engine has many different characteristic as compared to knock occurring in the gasoline engine. This is a result of differences in the gasoline and hydrogen combustion mechanisms which lead to knock. Hydrogen as the engine fuel is able to produce combustion knock of significant intensity. This intensity can be determined by measurements, which have been successfully applied for examining knock generated by the gasoline fuelled engine. This paper describes the engine test bed, in-cylinder pressure traces and methods for determining knock intensity. Further, the statistical approach for characterizing combustion knock is also presented. It concentrates on applications of several probability distributions for expressing individual knock intensity metrics of hydrogen port fuelled spark ignited engine. It is assumed that knock metrics for engine working cycles are considered as random variables. The knock metrics are based on the fluctuation component of the in-cylinder pressure traces sampled at 100 khz and are calculated for 300 consecutive engine working cycles. It was noticed that the knock metrics distribution profile changes as the knock intensity varies from light to heavy knock. In the paper, modelling of this knock distribution profile using several known stochastic distributions is also presented. Finally, usefulness of statistical distributions for characterizing combustion knock is shown.