KNOCK IDENTIFICATION USING THE MEASURED CYLINDER PRESSURE TRACE OF A SPARK-IGNITION COMBUSTION ENGINE

This paper focuses on the experimental study of the knock phenomenon in current low-volume supercharged spark-ignition internal combustion engines burning a homogeneous fuel mixture. Specifically, the point of interest is the correct and unambiguous knock identification based on the measured pressure trace from the highpressure indication in the cylinder. The major theories describing the knock phenomenon are presented here. The paper also describes the factors that affect knocking and possible ways of knock detection. There are four most commonly used methods for determining knock from measured pressure traces. Namely the method using the third derivative of the pressure, the method based on the heat release traces, and two methods from the commercial analytical software widely used by manufacturers and researchers involved in the development of internal combustion engines in Europe. The advantages and disadvantages of each of the knock identification methods are also presented. Besides, as cycle assessment appears knocking or non-knocking, the researchers need to approach the problem from a broader perspective. The pre-requisite for the evaluation is the correct high-pressure indication measurement in the engine cylinder, which is already a matter of course, during the experimental development and optimization work. Sensing of the crank angle and determination of the top dead centre (TDC) are inherent parts of the ICE indication. Another key aspect is filtering of the measured signal obtained from the knock sensor because it is important to suppress all other phenomena that are not clearly identifiable as knocking. To evaluate a knock phenomenon is correct, a larger set of data must be measured to allow proper determination of knock limit, from which the working cycle is clearly a knocking cycle. This knock limit is different for each engine, and therefore it is not possible to apply general knock limits to all SI engines.