Abstract
A fiber optical heterodyne interferometry system was developed to obtain high temporal resolution temperature histories of unburned gas in an SI engine cylinder non-intrusively. The effective optical path length of the test beam changes with the gas density and corresponding changes of the refractive index. Therefore, the temperature history of the gas can be determined from the pressure and phase shift of the interference signal. The fiber optical heterodyne interferometry has the advantage of resisting the mechanical vibration. In this study, this system was applied to a homogeneous charge compression(HCCI) engine. The measured temperature history of unburned gas in a HCCI engine just before generation of cold flame was almost equal to the calculated value using the equation of state of ideal gas.
