K-1918 Transient Temperature Measurement of unburned Gas in an SI Engine using Fiber Optic Heterodyne Interferometry

Abstract

A fiber optical heterodyne interferometry system was developed to obtain high temporal resolution temperature histories of unburned gas in an SI engine 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 mechanical vibration. The resolution of the temperature measurement is approximately 0.5 K, and is dependent upon both the sampling clock speed of the A/D converter and the length of the test section. This optical heterodyne interferometry system may also be used for other applications that require gas density and pressure measurements with a fast response time, or a transient temperature record.