Gas Temperature Measurements Research Articles

An optical method for the measurement of combustion gas temperature in particle laden flows

Temperature measurements in combustion systems are challenging due to the physical limitations of measurement devices and the complexity of combustion flows. The objective of this work is to investigate the Integrated Spectral Band Ratio (ISBR) method for measuring the temperature of combustion product gases surrounded by radiating walls or within a mixture of gas and particles. Five conditions in a multi-fuel reactor were investigated using an optical probe. A Fourier Transform Infrared spectrometer provided detailed spectral measurements of hot gas and particle emissions at wavelengths of 1.69–2.15 μm, focusing on a spectral region where H2O is the dominant participating gas. These measurements were used to infer the gas temperature of the flows. It was found that the measurement path length needed to be at least 0.25 m in order to obtain a signal large enough to infer temperature accurately. For four of the five operating conditions tested, optically measured gas temperatures were found to be in good agreement with the average temperature along the measured path as taken with a suction pyrometer (aspirated thermocouple). For these four operating conditions the particle media were optically thin. Temperatures for the in-flame fine wood particle condition did not exhibit as good of agreement due to high particle loading causing optically thick zones along the line of sight. Modeling experiments showed that when particles and gasses are optically thin, the optical gas temperature measured with this technique will be near the arithmetic mean of the line of sight temperature.

Single-ended mid-infrared laser-absorption sensor for time-resolved measurements of water concentration and temperature within the annulus of a rotating detonation engine

Abstract A novel single-ended mid-infrared laser-absorption sensor for time-resolved measurements of water mole fraction and temperature was developed and deployed within the annulus of a hydrogen/air-fed rotating detonation engine (RDE). The sensor transmitted two laser beams targeting mid-infrared water transitions through a single optical port on the outer wall of the cylindrical RDE annulus and measured the backscattered radiation from the RDE inner surface using a photodetector for a round-trip path of 1.52 cm. Optimizing the sensor's optical arrangement using numerical ray tracing to minimize interference from optical emission, beam steering, and scattered laser light from window surfaces was essential to sensor performance. Scanned-wavelength-modulation spectroscopy with second-harmonic detection and first-harmonic normalization was implemented to allow for frequency-domain multiplexing of the two lasers and to suppress non-absorbing interference sources such as beam-steering and emission. Tunable diode lasers near 2551 and 2482 nm were modulated at 100 and 122 kHz, respectively, and sinusoidally scanned across the peaks of their respective water transitions at 10 kHz to provide a measurement rate of 20 kHz and detection limit of 0.5% water by mole. Experimentally derived spectroscopic parameters enabled water and temperature sensing with respective uncertainties of 7.3% and 5.3% relative to the measured values. Time-resolved and time-averaged sensor measurements of gas temperature and water vapor mole fraction allow quantitative evaluation of the combustion progress at the measurement location and thus provide a design tool for RDE optimization. Broadly, this single-ended laser sensor should find applications in other combustion systems where optical access is limited.

Gas Temperature Measurement Using Differential Optical Absorption Spectroscopy (DOAS).

A nonintrusive method for flow gas temperature measurement using differential optical absorption spectroscopy (DOAS) was demonstrated. A temperature-dependent spectra (TDS) originated from the DOAS spectra of sulfur dioxide (SO2) in the wavelength range of 276-310 nm was introduced, and the relationship between the TDS and the temperature was built through experimental calibration process. This relationship is found to be independent of SO2 concentration and can be used for temperature measurements. The experimental results indicated that the precision of the TDS method is < ± 0.3% for SO2 concentrations higher than 150 ppm with the optical path length of 170 mm. For lower concentrations, the precision is estimated to be ± 0.4% at 1 ppm. The relative deviation between the temperature measured by the TDS method and that measured by a thermocouple is within 3% in the temperature range of 298-750 K, and the TDS method has a quicker response to the fast-changing temperature than the thermocouple.

Measurement of gas temperature in self‐blast chamber of model gas circuit breaker at high current interruption

Gas circuit breakers have been developed to be small and have low operating energy. To reduce their operating energy, a self‐blast technique has been used. The self‐blast gas circuit breaker obtains high pressure by utilizing arc energy in a fixed‐volume chamber. Consequently, the temperature of the blasting gas rises. However, when the gas temperature rises, the interrupting efficiency of SF6 gas decreases. Therefore, gas temperature is an important parameter that determines the interrupting performance. Gas temperature and pressure in a thermal puffer chamber of a self‐blast circuit breaker using a model circuit breaker were measured by using a parameter of interrupting current and arcing time to estimate the blast gas temperature for a large current. Gas temperature in the thermal puffer chamber of the model circuit breaker was measured by a micro‐gap discharge method in which the gas temperature was calculated by the breakdown voltage of a micro‐gap by using critical electric field strength data. Two micro‐gaps were installed in a thermal puffer chamber. The measured behavior of the hot gas was compared with flow analysis. The hot gas mixing processes with the parameter of interrupting current and arc duration time were estimated. The inlet gas temperature depends on the interrupting current, but the blowing gas did not depend on the arcing time at high currents. Results show that the temperature of the gas flowing out from the thermal puffer chamber reaches 2000 K for a’ large interrupting current of 57 kA. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Plasma-Assisted Biomass Gasification with Focus on Carbon Conversion and Reaction Kinetics Compared to Thermal Gasification

Compared to conventional allothermal gasification of solid fuels (e.g., biomass, charcoal, lignite, etc.), plasma-assisted gasification offers an efficient method for applying energy to the gasification process to increase the flexibility of operation conditions and to increase the reaction kinetics. In particular, non-thermal plasmas (NTP) are promising, in which thermal equilibrium is not reached and electrons have a substantially higher mean energy than gas molecules. Thus, it is generally assumed that in NTP the supplied energy is utilized more efficiently for generating free radicals initiating gasification reactions than thermal plasma processes. In order to investigate this hypothesis, we compared purely thermal to non-thermal plasma-assisted gasification of biomass in steam in a drop tube reactor at atmospheric pressure. The NTP was provided by means of gliding arcs between two electrodes aligned in the inlet steam flow with an electric power of about 1 kW. Reaction yields and rates were evaluated using measured gas temperatures by the optical technique. The first experimental results show that the non-thermal plasma not only promotes the carbon conversion of the fuel particles, but also accelerates the reaction kinetics. The carbon conversion is increased by nearly 10% using wood powder as the fuel. With charcoal powder, more than 3% are converted into syngas.

Resolving multiple combustion parameters from a single transition using degraded deconvolution of Voigt lineshape

A novel algorithm to fast deconvolve a molecular transition for its Gaussian and Lorentzian broadening was reported, and was further used to simultaneously measure multiple parameters, i.e. species concentration, temperature, and pressure, for combustion diagnostics. The proposed method was demonstrated by theory simulation and laboratory verification with combustion experiment. Direct absorption spectroscopy of H2O transition at 7185.6 cm−1 in premixed methane/air flames is used to verify the accuracy. The measurement temperature is agreement with that by two-line thermometry and thermocouple. The method is simple and feasible for non-intrusive simultaneous measurements of gas temperature, concentration, and pressure without calibration or other contact sensors. With an appropriately selected spectral line for analysis, the method can be applied to combustion diagnostics and industrial process control applications.

Experimental and numerical study on thermal-structural behavior of steel portal frames in real fires

This paper presents experimental and numerical investigations on the collapse behavior of a 12 m × 6 m steel portal frame exposed to fire. A real fire test is conducted with a 4 m × 6 m fire compartment at the corner of the frame. Extensive thermal and structural responses of the frame are measured and presented. The experimental results show that the fire compartment collapses after 20-min heating with a critical column temperature of 850 °C. It is found that the measured gas temperatures are higher than the ISO fire, but lower than the parametric fire specified in EN 1991-1-2, indicating the underestimation of the thermal exposure for standard fires and unrealistic estimation for parametric fires. For steel temperatures, the prediction from parametric fires is in a reasonable agreement with the measurements by predicting a similar maximum temperature at a delayed time. The prediction from standard fires significantly underestimated the steel temperatures by up to 300 °C. The significant non-uniform gas temperature distribution along the frame height shows a two-zone model with a temperature gap of 200 °C. The maximum temperature of the members beyond the fire compartment exceeds 500 °C due to the spread of hot smoke. A numerical model is established and validated against experimental results. A potential outward collapse mode of the frame is predicted. It is suggested that a more realistic description of fire scenarios is still needed for a performance-based structural fire design, based on a better consideration of ventilation conditions and thermal properties of boundary enclosure.

FPGA-Based Real-Time Implementation of Temperature Measurement via Tunable Diode Laser Absorption Spectroscopy

In this paper, a real-time temperature measurement system was implemented using a field programmable gate array (FPGA) via tunable diode laser absorption spectroscopy. The system can be used to measure the average temperature along the laser path. The wavelength modulation spectroscopy (WMS) method was applied to realize temperature measurement. First, a recursive peak detection algorithm was proposed to improve the accuracy of main peak detection of WMS signal and reduce the computational complexity. Second, an FPGA was facilitated to realize: 1) a real-time quadrature demodulator to extract the signals at frequencies of $2f $ and $1f$ and calculate the WMS- $2f/1f $ signals on chip and 2) in-situ accurate main peak detection of the WMS- $2f/1f $ signals and hence target gas temperature measurement. Third, experiments were conducted to verify the real-time performance of the system. Experimental results show that the proposed algorithm and hardware design can implement continuous temperature measurement with a temporal resolution of up to 0.25 ms and the measuring rate can reach 4 kHz.

Fire tests on full-scale steel portal frames against progressive collapse

This paper presents experimental investigations on the collapse behavior of a full-scale 36 m × 12 m steel portal frame exposed to natural fires. Extensive thermal and structural responses of the frame are measured and presented. The frame collapses after 15-min fire exposure with a critical temperature of about 1100 °C in the heated column. The measured gas temperature history has a short growth period of 3 min, and reaches its peak temperature of 1100 °C within 8 min (400 °C higher than standard fire). It is found that a two-zone model can be assumed with uniform temperature distribution in the lower and upper half region, respectively. The temperature gap of these two zones reaches 200 °C. The gas temperature at top region decreases due to the deformation-induced opening of roof and fire walls. The surface facing the environment has higher gas temperatures than that inside the fire compartment (more than 200 °C). The temperature of rafters beyond the fire compartment reaches 700 °C due to the spread hot smoke. Outward bending of the external unexposed column and pulling out of corner column base are observed, which should be prevented in practical design to mitigate fire spread to adjacent buildings and ensure life safety of fire fighters. Numerical simulation is conducted and compared to experimental results which can be used for calibrating numerical models.

Numerical Simulation of Fire Exposed Façades Using LEPIR II Testing Facility

The fire behavior of external wall insulation system on facades is assessed during LEPIR II testing. This facility involves a 600 kg wood crib fire in a 30 m3 lower compartment of a two levels high concrete structure. External flames develop in front of the facade from the fire compartment through windows with dimensions 1 × 1.5 m (W × H). In order to predict the fire exposure of a facade during the test, CFD simulations were carried out with the computational fluid dynamics code Fire Dynamics Simulator (FDS) for two full-scale experiments. The main objective of this study was to evaluate the ability of FDS to reproduce quantitative results in terms of gas temperatures and heat fluxes close to the tested facade. This is an important step before the fire performances of any insulation system can be predicted by numerical tools. A good repeatability was observed in terms of measured gas temperatures for experiments. Maximum heat release rate of the fire, close to 5 MW, was achieved after 5 min of test. When experimental results were compared with numerical calculations, good agreement was found for every quantity. The most critical zone on the facade is located above the fire room and is directly impacted by external flame outgoing from the fire compartment. Temperatures up to 500°C were observed in this zone. For the thermocouples located up to the second level opening, these probes were not located directly in the flames, but rather in the hot gases above the fire plume. The maximum temperature achieved was thus close to 400°C. The proposed model gives correct thermal loads and flames shape near the facade during calibration tests and can be used for further evaluation of combustible material on facade.

Analysis of Unsteady Gas Temperature Measurements in the Appendix Gap of a Stirling Engine

This contribution presents the experimental setup and the results of stationary cylinder wall temperature and unsteady gas temperature measurements in the appendix gap of an experimental machine, which can be switched between different regenerative cycles. Direct measurements in the gap are important for the validation and verification of existing analytical modeling approaches for appendix gap losses because these losses may reduce the power of Stirling engines significantly; so far, no direct measurements have been conducted to prove the modeling assumptions. The gas temperatures are measured by newly developed fine-wire thermocouple probes, the design of which is explained in detail. The results show curved axial wall temperature profiles and roughly sinusoidal gas temperature fluctuations, which are dependent on the radial and axial positions. In the axial center of the gap, the assumption of laminar flow conditions is largely fulfilled; whereas at the open end of the gap, intermittent disturbances are observed, presumably due to turbulent eddies entering the gap from the cylinder volume during the inflow period. A comparison to analytically calculated temperatures shows a qualitatively good agreement in the main section of the appendix gap.

Measurement of multispecies concentration and gas temperature in an ammonium-dinitramide-based thruster by tunable diode lasers

In this paper, quantitative experiments were made to measure the concentration of key intermediate products (CO, N2O, and NO) and the gas temperature for combustion flow based on near-infrared and mid-infrared laser absorption spectroscopy. This paper used the developed diagnostic system to study two main ignition modes of a real 1-Newton thruster based on ammonium dinitramide (ADN): steady-state firing and pulse-mode firing over a feed pressure of 5-12bar. The steady-state firing experiments distinguished the whole process into catalytic decomposition stage and combustion stage, experimentally demonstrating the combustion kinetics mechanism of an ADN monopropellant. Experiments for pulse-mode firing showed the measured multispecies concentration and temperature were consistent with pulse trains, verifying good performance for the thruster pulse-mode firing operation. The performance of the thruster was given based on the optical measurements, and characteristic velocity for the ADN-based thruster standard operation was higher than the corresponding 1-Newton hydrazine thruster.

Underresolved absorption spectroscopy of OH radicals in flames using broadband UV LEDs

A broadband absorption spectroscopy diagnostic based on underresolution of the spectral absorption lines is evaluated for the inference of species mole fraction and temperature in combustion systems from spectral fitting. The approach uses spectrally broadband UV light emitting diodes and leverages low resolution, small form factor spectrometers. Through this combination, the method can be used to develop high precision measurement sensors. The challenges of underresolved spectroscopy are explored and addressed using spectral derivative fitting, which is found to generate measurements with high precision and accuracy. The diagnostic is demonstrated with experimental measurements of gas temperature and OH mole fraction in atmospheric air/methane premixed laminar flat flames. Measurements exhibit high precision, good agreement with 1-D flame simulations, and high repeatability. A newly developed model of uncertainty in underresolved spectroscopy is applied to estimate two-dimensional confidence regions for the measurements. The results of the uncertainty analysis indicate that the errors in the outputs of the spectral fitting procedure are correlated. The implications of the correlation between uncertainties for measurement interpretation are discussed.

Measurement of transient gas temperature with two-wavelength laser interferometry

Measurement of transient gas temperature with two-wavelength laser interferometry

Gas Temperature Distribution in Cathode Fall Region of Grimm Glow Discharge

Optical emission spectroscopy technique was used to measure gas temperature along the axis of cylindrical abnormal glow discharge parallel to the copper cathode surface (side-on) in hydrogen-argon mixture at low pressure. The rotational temperature of excited state of H&lt;sub&gt;2&lt;/sub&gt; was determined from the rotational structure of Q branch of Fulcher-α diagonal bands using Boltzmann plot technique while the obtained ground vibrational state temperature is assumed to be equal to gas temperature. The temperature T&lt;sub&gt;0&lt;/sub&gt; determined from the rotational population density distribution in an excited vibrational state can be considered as a valid estimation of the ground state temperatutre i.e. H&lt;sub&gt;2&lt;/sub&gt; gas temperature.

DYNAMIC TEMPERATURE MEASUREMENT BY CONTACT METHOD

The main disadvantage of contact methods of temperature measurement by means of thermocouples is the thermal inertia of a sensitive element, which adds an additional methodological error in the dynamic measurements of temperature. In gas temperature measurement, a researcher deals with approximation of the true temperature. And also, thermocouples have limited range of measured temperature.If the temperature of the object changes with a certain speed, then thermocouple needs time to achieve thermodynamic equilibrium with the object. This time determines the thermocouple reaction rate to incoming temperature change. If the temperature of the object changes at a rate which exceeds the reaction rate of the thermocouple, in this case the thermocouple does not reach the thermodynamic equilibrium with the object of measurement. Thermo EMF of the thermocouple corresponds to the temperature to which the thermocouple sensitive element has heated up, not to the true temperature of the object of measurement.Hence, it is necessary to study the dynamic characteristics of the thermocouple and to develop a method for the temperature values restoration from thermo EMF of the thermocouple in the transient mode of its operation, with relatively low values of the temperature of the sensitive element.The purpose of the article is to improve the method of dynamic temperature measurement by using experimentally obtained dynamic characteristics of the thermocouple to restore the true value of the temperature of the medium based on the methods of solving the inverse measurement problem.The method of determining the gas flow temperature using a thermocouple in the transient mode is considered in the article. The method of nonlinear approximation based on the assumption that the transient characteristic of a thermocouple is the sum of exponentials is applied, and a model of the transient characteristic of a thermocouple is obtained. Applying the deconvolution, the form of the temperature pulse of the gas flow is determined.

Combustion measurements of type-1 pulverized coal flames operating under oxy-fired conditions

The present study addresses the impact of oxy-fired conditions on type-1 flames generated by an oxidant-staged burner operating with pre-dried lignite and applying wet flue-gas recirculation. Investigations were carried out in a laboratory facility where the combustion takes place in a furnace with a rated capacity of 0.40MWth. In-flame measurements were performed for oxy-fired conditions operating at three levels of secondary swirl number (1.15, 1.65, and 2.05), while overall O2 fraction upstream of the burner in oxy-firing was kept at 31vol%. One air-fired condition at 1.65 secondary swirl number was also investigated. Measurements of local gas temperature and gas species concentrations were performed using standard water-cooled probes with focus on the near burner region. Results showed evidence of radial flame stratification consistent with gradual O2 admixing to the central fuel jet. Lower temperatures on the flame axis were obtained under oxy-fired condition. In the same region, as a result of CO2 dissociation and/or gasification reactions by water vapor and CO2, higher CO concentrations were also monitored, which contributed to lower temperatures. Experimental data also suggested great potential for NO abatement through flame stratification due to type-1 flame pattern.

In situ laser measurement of oxygen concentration and flue gas temperature utilizing chemical reaction kinetics

Combustion research requires detailed localized information on the dynamic combustion conditions to improve the accuracy of the simulations and, hence, improve the performance of the combustion processes. We have applied chemical reaction kinetics of potassium to measure the local temperature and O2 concentration in flue gas. An excess of free atomic potassium is created in the measurement volume by a photofragmenting precursor molecule such as potassium chloride or KOH which are widely released from solid fuels. The decay of the induced potassium concentration is followed with an absorption measurement using a narrow-linewidth diode laser. The temperature and O2 concentration are solved from the decay curve features using equations obtained from calibration measurements in a temperature range of 800°C-1000°C and in O2 concentrations of 0.1%-21%. The local flue gas temperature and O2 concentration were recorded in real time during devolatilization, char burning, and ash cooking phases of combustion in a single-particle reactor with a 5Hz repetition rate. The method can be further extended to other target species and applications where the chemical dynamics can be disturbed with photofragmentation.

X3 expansion tube driver gas spectroscopy and temperature measurements

The University of Queensland’s X3 facility is a large, free-piston driven expansion tube used for super-orbital and high Mach number scramjet aerothermodynamic studies. During recent development of new scramjet test flow conditions, experimentally measured shock speeds were found to be significantly lower than that predicted by initial driver performance calculations. These calculations were based on ideal, isentropic compression of the driver gas and indicated that loss mechanisms, not accounted for in the preliminary analysis, were significant. The critical determinant of shock speed is peak driver gas sound speed, which for a given gas composition depends on the peak driver gas temperature. This temperature may be inaccurately estimated if an incorrect fill temperature is assumed, or if heat losses during driver gas compression are significant but not accounted for. For this study, the ideal predicted peak temperature was 3750 K, without accounting for losses. However, a much lower driver temperature of 2400 K is suggested based on measured experimental shock speeds. This study aimed to measure initial and peak driver gas temperatures for a representative X3 operating condition. Examination of the transient temperatures of the driver gas and compression tube steel wall during the initial fill process showed that once the filling process was complete, the steady-state driver gas temperature closely matched the tube wall temperature. Therefore, while assuming the gas is initially at the ambient laboratory temperature is not a significant source of error, it can be entirely mitigated by simply monitoring tube wall temperature. Optical emission spectroscopy was used to determine the driver gas spectra after diaphragm rupture; the driver gas emission spectrum exhibited a significant continuum radiation component, with prominent spectral lines attributed to contamination of the gas. A graybody approximation of the continuum suggested a peak driver gas temperature of 3200 K; uncertainty associated with the blackbody curve fit is ±100 K. However, work is required to quantify additional sources of uncertainty due to the graybody assumption and the presence of contaminant particles in the driver gas; these are potentially significant. The estimate of the driver gas temperature suggests that driver heat losses are not the dominant contributor to the lower-than-expected shock speeds for X3. Since both the driver temperature and pressure have been measured, investigation of total pressure losses during driver gas expansion across the diaphragm and driver-to-driven tube area change (currently not accounted for) is recommended for future studies as the likely mechanism for the observed performance gap.

Validation of the van der Waals broadening method for the determination of gas temperature in microwave discharges sustained in argon–neon mixtures

Gas temperature is a key parameter to understand the processes that take place in a plasma because this temperature is related to the energy of the heavy plasmas particles which participate in the atomization of molecules and the formation of radicals from the substances introduced into the discharges. The method for the measurement of gas temperature in argon-helium plasma at atmospheric pressure, using the van der Waals broadening of spectral atomic lines, is adapted for the case of argon–neon mixtures. The Ar I lines 425.9 nm and 603.2 nm are determined as recommendable for such measurements, especially when the use of OH radicals is difficult or the contribution of these radicals to the plasma pollution is to be avoided.