Temperature measurement of gases using acoustic means

Traditional temperature measurement devices such as bimetallic strips, thermocouples, RTDs, radiation devices (i.e. Infrared), silicon P-N junctions etc. all have limitations such as range or slow response times due to them having to 'reach' temperature. These limitations, while normally not an issue become so where high speed operation or large temperature ranges are either required and/or likely to be encountered. Kleppe [1, 2] and Stones[3] describe methods based on Acoustic Pyrometry for high speed high temperature measurement in flue gas flows and high pressure burner combustors. However most Acoustic Pyrometric schemes use active acoustics in that an acoustic wave of sufficient power and frequency (usually ultrasonic) is introduced into the medium to be received by an appropriate transducer a distance away. From the resultant time of flight (TOF) of the transmitted signal the speed of sound in that gas region can be determined. The aim of this paper is to discuss the use of passive acoustic sensors that utilise the self generating pressure pulses in a dynamic gas flow.