Instantaneous Exhaust Temperature Measurements Using Thermocouple Compensation Techniques

Abstract

This paper discusses a method of measuring the instantaneous exhaust gas temperature by thermocouples. Measuring the exhaust gas temperature is useful for a better understanding of engine processes. Thermocouples do not measure the instantaneous exhaust gas temperature because of their limited dynamic response. A thermocouple compensation technique has been developed to estimate the time constant in situ. This method has been commissioned in a simulation study and a controlled experiment with a reference temperature. The studies have shown that the signal bandwidth has to be restricted, since noise will be amplified in the temperature reconstruction. The technique has been successfully applied to some engine exhaust measurements. A comparison between two independent pairs of thermocouples has shown that temperature variations at frequencies up to 80Hz can be recovered. The medium load results agree with a previous study, which used fast response thermometers with a bandwidth of about 50 Hz. However, the results at low load and two different speeds have highlighted the need to do some 1-D unsteady flow simulations, in order to gain more insight into the exhaust process.

Real-Time Monitoring of Combustion Instability in a Homogeneous Charge Compression Ignition (HCCI) Engine Using Cycle-by-Cycle Exhaust Temperature Measurements

“…In Figure 4, the waveform appearance is similar to that reported by other researchers using fine wire thermocouples and [11][12][13]. The exhaust temperature rises abruptly during the period when the exhaust valve is open (due to blowdown and displacement flow of hot exhaust past the probe), then cools at a slower rate while the exhaust valve is closed.…”

An Investigation of Certain Thermodynamic Losses in Miniature Cryocoolers

“…The model validation section later on will verify this assumption. Many twothermocouple techniques have been proposed: Cambray [4], Tagawa et al [5,6,7], Forney and Fralick [8], Hung et al [9,10] and Kar et al [11]. This report will only give a brief overview of these techniques.…”

“…In the limits when N = 1, the estimation become a recursive algorithm. O'Reilly et al [14], Kar et al [11], and Grys and Minkina [15] applied various recursive algorithms for time constant estimation. The major difference in the algorithms lies in which estimators they used.…”

“…Kar et al [11] pointed out that time constant estimation can be compromised by any DC offsets in the raw thermocouple voltages. This is why the amplifier zero voltages were monitored and the thermocouple was calibrated with the zero voltage taken off in advance.…”

A Bias Compensated Cross-Relation approach to Thermocouple Characterisation

“…Since then, numerous approaches for two-thermocouple characterisation have been proposed based on the principle and assumptions of the approach proposed by Pfriem. A range of time-domain methods have been presented by Tagawa et al (1998), Kee et al (1999), O'Reilly et al (2001) and Kar et al (2004). Forney and Fralick (1994) and later Tagawa et al (2003) then tackled the problem in the frequency-domain, thereby avoiding the numerical problems associated with estimating derivatives that were experienced in the timedomain.…”