Two-color pyrometry system to eliminate optical errors for spatially resolved measurements in flames

Reggeti, Shawn A.; Agrawal, Ajay K.; Bittle, Joshua A.

doi:10.1364/ao.58.008905

Cited by 18 publications

(11 citation statements)

References 18 publications

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“…In the case of an external filter wheel and un-cooled camera used in other setups [24,21,17,27,43], additional contributions from the environment reflected by the filter outside of its transmissivity range would have to be considered.…”

Section: Model Component Negligible Quantity Energy Balance Contributionmentioning

confidence: 99%

“…A potential approach to overcome this problem is two-color (2C) -or ratio -pyrometry. This technique is commonly used to measure soot concentration [24,25], temperature evolution in turbulent flames [26], or for flame-wall impingement studies [27,28,29]. The basic idea is to measure the sample radiance through two different narrow spectral bands and then use the signal ratio to calculate the object temperature [30,31,32].…”

Section: Introductionmentioning

confidence: 99%

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Surface temperature and emissivity measurement for materials exposed to a flame through two-color IR-thermography

Pelzmann¹,

Dupont²,

Sauté³

et al. 2022

Preprint

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Two-color (2C) pyrometry has long been used for flame temperature and soot concentration studies and is now becoming more widely used to measure surface temperatures of burning materials. With the obvious advantage of being a contact-free method that requires only minimal optical access, 2C pyrometry combined with high-speed acquisition is a promising diagnostic tool to obtain exceptional temporal and spatial resolution of thermally degrading samples. However, its conceptual simplicity relies on a set of basic assumptions that when violated can result in large errors. In this work, we use an experimental configuration representative for fire resistance testing for aerospace and naval applications to analyze the impact of camera parameters and test setup on the accuracy of the surface temperature results obtained. Two types of fibre reinforced polymer composites and a steel plate are used to investigate material specific aspects that effect the measurements. An improved workflow for camera calibration is presented that takes the actual experimental setup into account. The temperature and emissivity mapping obtained trough in-situ IR measurements is compared against data acquired trough thermocouples and post-fire hemispherical directional reflectance measurements at room temperature. This comparison illustrates the necessity for proper post-processing and demonstrates that emissivity values obtained from pristine or burnt samples are not well suited to obtain accurate surface temperatures through conventional (single color) IR thermography. We also present a detailed error budget and suggestions for calibration measurements to keep the overall error well below 50 • C in a temperature range from 400 • C to 1200 • C.

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Section: Model Component Negligible Quantity Energy Balance Contributionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Surface temperature and emissivity measurement for materials exposed to a flame through two-color IR-thermography

Pelzmann¹,

Dupont²,

Sauté³

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…Computing T and KL with radiant emissions from different LsOS, whether caused by an angle of parallax induced by the 2CP optics (blue arrows) or by misalignment of the two wavelength images, would result in measurements with intractable errors in T and KL. Some optical configurations of 2CP systems result in an angle of parallax between the LsOS of the two wavelength images [10,17], which has been shown to misalign flame features [20].…”

Section: Optical Configurationmentioning

confidence: 99%

“…Optical configurations to obtain spatiallyresolved 2CP results include hybrid photodiode/camera systems [9], monochrome camera systems with image doublers and beamsplitters [2,10,15,17], colour cameras with a demosaicing technique [14,18], dual-camera configurations [7,8,19], and others [8]. Some of these optical configurations can yield spatially non-corresponding images at the two wavelengths [17,20] causing intractable errors in computed temperature and KL values. The present 2CP system [20] avoids erroneous imaging at the two wavelengths with a pixel-by-pixel calibration applied to increase measurement accuracy.…”

Section: Introductionmentioning

confidence: 99%

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Robust two-colour pyrometry uncertainty analysis to acquire spatially-resolved measurements

Reggeti¹,

Agrawal²,

Bittle³

2022

Meas. Sci. Technol.

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Two-colour pyrometry (2CP) has been used over several decades to study engine-relevant combustion processes, but results are generally regarded as qualitative or semi-quantitative. In many current 2CP systems, large measurement errors are introduced by parallax because the two measured wavelengths are not from the same line of sight. This work presents a spatially-resolved 2CP system with the objective to quantify and reduce the measurement uncertainty. An optical setup that eliminates parallax in 2CP is used together with pixel-by-pixel calibration of the camera sensor to increase the measurement accuracy. Primary uncertainty terms are identified, and an error propagation analysis is performed to compute uncertainties in the final results of soot temperature, soot concentration parameter, KL, and soot mass. These methodologies are applied to investigate an auto-igniting fuel spray in a constant pressure flow rig at diesel-like conditions of high ambient pressure and temperature. Results show bias uncertainty of around 200 K (~10%) for temperature and about 40-60% for KL. High uncertainty was found to occur on the diffusion flame front where both optical thickness and soot concentrations are small. However, these uncertain measurement zones with relatively low soot concentrations contribute minimally to the total soot mass present in the reacting jet during the temporal evolution of the flame.

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Representative Phenomena of Cyclic Turbulent Combustion in High-Pressure Fuel Sprays

Parker

Agrawal

Bittle

2023

Flow Turbulence Combust

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Cyclic variations in conventional diesel combustion engines can lead to large differences in engine out emissions even at steady operation. This study uses an optically accessible constant-pressure flow chamber to acquire fuel injections in quick succession to analyze mixing, auto-ignition, and combustion of diesel-surrogate n-heptane using multiple high-speed optical diagnostics. Prior studies have utilized fewer injections and/or they rely on analysis of ensemble average behavior. These approaches do not yield information on injection-to-injection variation or provide confidence in utilizing individual injection measurements for high-fidelity computational fluid dynamics(CFD) model validation. In this study, a large set of 500 injections is used to obtain global parameters including liquid length, vapor penetration length, ignition delay time, and lift-off length. Results for multiple injections are presented to illustrate large injection to injection variations. Potential sources for these variations are analyzed to conclude localized, small scale turbulence and rate of injection variations as the likely sources. Then, a statistical method based on z-scores is proposed and implemented to identify instantaneous injections that best represent the bulk data-set of jet boundaries measured independently by three different diagnostics. This synthesis of statistics-guided screening of data set and ensemble-average analysis offers higher confidence for CFD model validation relying upon both a representative single and average injection results.

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Two-color pyrometry system to eliminate optical errors for spatially resolved measurements in flames

Cited by 18 publications

References 18 publications

Surface temperature and emissivity measurement for materials exposed to a flame through two-color IR-thermography

Surface temperature and emissivity measurement for materials exposed to a flame through two-color IR-thermography

Robust two-colour pyrometry uncertainty analysis to acquire spatially-resolved measurements

Representative Phenomena of Cyclic Turbulent Combustion in High-Pressure Fuel Sprays

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