title: Problems Encountered in Fluctuating Flame Temperature Measurements by Thermocouple.
abstract: Some thermocouple experiments were carried out in order to obtain sensitivity of thermocouple readings to fluctuations in flames and to determine if the average thermocouple reading was representative of the local volume temperature for fluctuating flames. The thermocouples considered were an exposed junction thermocouple and a fully sheathed thermocouple with comparable time constants. Either the voltage signal or indicated temperature for each test was recorded at sampling rates between 300-4,096 Hz. The trace was then plotted with respect to time or sample number so that time variation in voltage or temperature could be visualized and the average indicated temperature could be determined. For experiments where high sampling rates were used, the signal was analyzed using Fast Fourier Transforms (FFT) to determine the frequencies present in the thermocouple signal. This provided a basic observable as to whether or not the probe was able to follow flame oscillations. To enhance oscillations, for some experiments, the flame was forced. An analysis based on thermocouple time constant, coupled with the transfer function for a sinusoidal input was tested against the experimental results.
authors.affiliation: Department of Mechanical Engineering, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA. yilmaznadir@yahoo.com.
authors.forename: Nadir
authors.initials: N
authors.lastname: Yilmaz
authors.affiliation: Sandia National Laboratories, Albuquerque, New Mexico 87185, USA. wgill@sandia.gov.
authors.forename: Walt
authors.initials: W
authors.lastname: Gill
authors.affiliation: Sandia National Laboratories, Albuquerque, New Mexico 87185, USA. bdonald@sandia.gov.
authors.forename: A Burl
authors.initials: AB
authors.lastname: Donaldson
authors.affiliation: Department of Mechanical Engineering, New Mexico State University, Las Cruces, New Mexico 88003, USA. rallucer@nmsu.edu.
authors.forename: Ralph E
authors.initials: RE
authors.lastname: Lucero
keywords: Diffusion flames; Flame thermocouple measurement; Fluctuating flames; Thermocouple transfer function