Measurement of GT exhaust gas temperature by acoustic pyrometry: Preliminary error investigation

Acoustic pyrometry uses the variations of the speed of sound in a medium to determine its temperature. One of the assumptions at the base of this technique is that the flow velocity component in the direction of the acoustic path is negligible in comparison to the speed of sound. However, if the temperature of the medium is known, the acoustic pyrometry approach can be used to determine flow speed, as long as the flow is not perpendicular to the acoustic path. The combined approach of temperature and velocity determination is also known as acoustic tomography. This technique allows the determination of velocity and temperature maps in a flow region. Even though this is an interesting result, the mathematical approach to solve the velocity and temperature fields might be very complex and sensitive measurement set-up. In this study, a preliminary investigation is carried out to determine the flow velocity by starting from the time of flight of an acoustic signal moving along different acoustic paths in a constant temperature field. For this purpose, a simplified geometry is considered. The developed mathematical approach at the base of the methodology is presented in this study.

Section: Figure 3 Velocity Profile Used As Case Studymentioning

confidence: 99%

Acoustic pyrometry for flow velocity estimation: preliminary analysis

Caposciutti

Ferrari

2023

“…The results suggested how both the size of the devices used in the computational procedure and the emitter-receiver couple (ERC) number significantly affect the estimation accuracy and the computational burden. The reliability of the acoustic pyrometry with respect to the number of ERCs used and TOF uncertainty was further investigated by Ferrari et al [9][10][11] through a statistical approach. As a general result, they found that if the TOF estimation is not affected by uncertainty, the estimation accuracy may be improved simply by increasing the number of ERCs.…”

Section: Introductionmentioning

confidence: 99%

Time-of-flight estimation in acoustic pyrometry: sensitivity to pulse characteristics

Pettinari

Ferrari

2023

Self Cite

Acoustic pyrometry is a non-intrusive measurement technique that may have several applications in turbomachinery. This methodology estimates the gas temperature by measuring the time of flight of an acoustic wave moving through a medium. It can be accomplished by placing a sound source (emitter) and a set of microphones (receivers) on opposite sides of a section. The emitter generates a sound pulse, and the receivers detect it. Since the emitter-receiver distances are known and fixed, the average temperatures of the paths traversed by the acoustic pulse can be computed by estimating the time-of-flight through deconvolution techniques. However, despite the straightforward principle, an acoustic wave suffers a variation of amplitude when propagating within a medium because of energy losses and ambient noise. Hence, time-of-flight estimation becomes a critical task, especially when considering high-frequency waves or short distances between sensors. It is then fundamental to select proper acoustic waves to maximise the cross-correlation between the signals of the emitter-receiver couples, thus improving the accuracy of the time-of-flight measurements and, consequently, the estimation of the spatial temperature distribution within a specific area. This study is a preliminary investigation, based on a modelling approach, to estimate the impact of different acoustic waves on the accuracy of the time-of-flight measurement. The results of this analysis will be useful to design and setup an acoustic pyrometry application.

“…Since then, there have been developments in reconstruction algorithms and the capabilities of electronic processing systems, allowing for reduced reconstruction times and increased spatial and temporal resolution of the method. Recently, several studies investigated the feasibility of using acoustic pyrometry in turbomachinery applications, as reported in [17]- [20]. In a previous study the authors investigated the potential of velocity estimation in a simplified arrangement [21].…”

Section: Introductionmentioning

confidence: 99%

Acoustic tomography for velocity estimation in high temperature flows

Ferrari,

Sugaroni

2023

Accurately measuring the temperature of a gas flow is essential for monitoring purposes in many energy conversion applications. Typically, this is achieved using either contact measurement techniques, like thermocouple sensors, or radiation-based methods, like optic pyrometry. In harsh conditions, contact measurement techniques are prone to degradation due to the high oxidizing and high-temperature environment, thus reducing sensor lifespan. Radiation-based methods, on the other hand, rely on expensive and highly non-linear transduction systems. Acoustic pyrometry is attracting an increasing interest as it allows the estimation of the temperature distribution in a section by computing the time of flight of acoustic waves. If two measurement sections, at different axial positions, are considered, the same theoretical approach can be adapted to also compute the velocity map of the flow (acoustic tomography). However, the complexity of the mathematical problem to be solved for such a calculation needs a careful analysis. In this study, starting from a known temperature and velocity profile, a reconstruction algorithm was developed and tuned with a particular focus on velocity estimation. Relevant guidelines for a proper application of this measurement technique were also derived.