Measurement of the temperature history of unburned gas before knocking in a spark-ignition engine using laser interferometry

It is very important to know the temperature history in a spark-ignition en gine when the phenomenon of knocking is being studied. However, measurement of the gas temperature is not easy and some work has been done using laser diagnostics etc. In this study, the temperature history until the time of occurrence of knocking in a spark-ignition engine was measured by a form of laser interferometry designed especially for use in the combustion chamber . Not only the change in temperature but also the absolute value of the tem perature could be determined with this interferometer, by utilizing the cha nge of the gas density on the reference side. This is a non-intrusive measu rement and high resolution is expected. The temperature resolution is about 5 K near the occurrence of knocking.