Rate of Pressure Rise in SI Engine Cylinder and its Relation to Knock (RESEARCH NOTE)

Tremendous efforts have been devoted to study the complex phenomenon "knock in spark ignition engines. There is an increasing interest in providing some tools to study knock in simulated data. In the previous studies, engine cylinder pressure oscillation has been used to investigate knock. Unless those methods involved highly complex non-detailed chemical relations, the previous studies were dependent on the information derived from oscillations of the engine pressure data. Therefore, in this paper, in order to develop a technique for predicting knock with least dependency on detailed operating information and independent of engine pressure oscillations, rate of pressure rise of individual cycles was measured. This was carried out by measuring the slope of the best straight line fitted to 5-degree steps of experimental engine pressure data in which knock intensity are specified. The experimental data were measured in a research variable compression ratio engine over a wide range of operating conditions using pure iso octane and a commercial fuel at 0.25 degree crank angle intervals. A conversion unit was designed to convert the CUC-DOS measured raw data to MS-DOS data. A new criterion, completely independent of the engine cylinder pressure oscillations, was established to predict the occurrence of knock. Independency of the proposed technique on end-gas temperature and burning rate calculations eliminate the complexity and errors of calculating these parameters in the prediction procedures.