Temperature measurement of end gas under knocking condition in an S.I. engine by laser interferometry

Knock is one of the most significant problems that limit the efficiency of an internal combustion engine. It is caused by autoignition of the unburned gas ahead of the flame. In order to understand the knock phenomenon, it is important to measure the temperature of unburned gas. In this study, with polarization maintaining optical fibers, the laser interference measurement of unburned gas temperature was performed in a constant volume vessel and a specially designed engine which could be ignited only once. The engine fueled with n-butane, oxygen and argon, was operated under knocking conditions. When the density of the gas changes, the change of the optical path length of test beam corresponds to the change of refractive index. The temperature history of the unburned gas was determined by measuring the pressure and the change of interference signal. The optical fiber interference system had the advantage of resisting mechanical vibration because test and reference beams were transmitted in the same optical fiber and were separated only in the test section.