Ultraviolet filtered Rayleigh scattering temperature measurements with a mercury filter

We report the development of ultraviolet filtered Rayleigh scattering as a diagnostic tool for measurements of gas properties. A frequency-tripled narrow-linewidth Ti:sapphire laser illuminates a sample, and Rayleigh scattered light is imaged through a mercury-vapor absorption filter. Working in the ultraviolet improves the signal-to-noise ratio compared with that previously obtained in the visible as the result of an enhanced scattering cross section as well as the nearly ideal properties of the mercury filter. Tuning the laser through the absorption notch of the filter is a means of probing the scattering line shape, which contains temperature information. Temperature measurements of air are shown to have uncertainties of less than 3%.     

Spray thermometry using thermographic phosphors

In this study a novel technique for 2D spray temperature measurement is presented. For this purpose the thermographic phosphor (TP) Mg₄GeO_5.5F:Mn was dispersed in n-dodecane and atomised using a conventional semi solid-cone nozzle. The thermographic phosphor was excited electronically by a frequency tripled Nd:YAG laser (355 nm). An ICCD-camera in combination with an image doubler detected the subsequently emitted phosphorescence at both peak emission wavelengths located at 633 nm and 659 nm, respectively. Utilising suitable calibration measurements, the local spray temperature was determined by evaluating the intensity ratio of both emission wavelengths. To the knowledge of the authors this is the first approach of spray temperature measurement exploiting the temperature dependent intensity ratio of thermographic phosphors. PACS 07.20.Dt; 32.50.+d     

分子过滤瑞利散射技术测量火焰温度和密度

 为了解决瑞利散射光易受米散射和背景杂散光干扰的问题,发展了结合窄线宽激光器、分子过滤器以及像增强器等技术的分子过滤瑞利散射技术。在图像诊断的基础上,依据测量的碘蒸气吸收光谱曲线,对CH₄/air预混火焰进行了诊断,获得了密度场和温度场分布。距炉面15 mm火焰中心区域处,分子过滤瑞利散射(FRS)技术测量的温度为1 827 K±84 K,密度为0.19 kg/m³,其测温结果与CARS法的测温结果基本吻合。最后分析了FRS技术测温不确定度。实验表明FRS技术具有较高的信噪比,可以定量测量温度和密度信息,有望应用于超音速燃烧流场、紊流场等复杂流场的诊断。     

Simultaneous 2D flow velocity and gas temperature measurements using thermographic phosphors

In this paper a new approach for simultaneous 2D velocity and temperature measurements using phosphoric particles is presented. The phosphoric particles respond to the temperature changes in the flow while acting as tracers for velocity mapping. The temperature sensitive particles were seeded into a heated flow and were excited by a pulsed UV laser. The subsequent red shifted emission was detected and analyzed to infer temperature using calibration procedures for lifetime and emission spectra against temperature. The diameter of the temperature sensitive particles, usually in the range of 1–10 μm, makes them useful for velocity measurements using particle image velocimetry (PIV). As such, simultaneous measurement of temperature and flow velocity of a gaseous flow were performed and presented. PACS  42.62.-b; 47.80.Cb; 47.80.Fg     

A research bibliography on the temperature dependencies of thermographic phosphors

We have prepared a comprehensive research bibliography on the fundamental physics and engineering applications of thermographic phosphors. It is available upon request.     

2D-temperature imaging of single droplets and sprays using thermographic phosphors

A novel 2D-technique for temperature visualization of single droplets and sprays is presented. Laser induced emission from thermographic phosphor seeded to the investigated liquid was detected by a fast framing camera. The subsequent phosphorescence images measured by seven consecutively gated CCD detectors allowed pixel-to-pixel lifetime evaluation of the phosphorescence emission. The temperature at each pixel position was evaluated using a calibration procedure of temperature against lifetime. These measurements were applied first to a free falling water based droplet, then to a suspended droplet in an ultrasonic levitator. Finally, the technique was applied to spray. PACS 07.20.Dt; 46.65.Fi; 32.50.+d; 43.25.Uv; 34.50.Gb     

Two-dimensional cycle-resolved exhaust valve temperature measurements in an optically accessible internal combustion engine using thermographic phosphors

Phosphor thermometry was employed to measure the temperature distribution of the exhaust valves in an optically accessible direct injection internal combustion engine. A CMOS high-speed camera was used to two-dimensionally resolve the temperature dependent luminescence decay of the phosphor Gd₃Ga₅O₁₂:Cr. Measurements were performed under motored and fired conditions for several degrees crank angle to determine the temperature distributions within cycles. Additionally, several binders have been tested in terms of survivability and signal strength to guarantee ideal phosphor coating.     

Progress towards absolute intensity measurements of emissions from high temperature thermographic phosphors

Phosphor thermometry has been successfully used in a number of applications ranging from turbo-machinery, pyrolysis, supersonic and hypersonic studies in the past few decades. There are a number of issues related to high temperature, which include faster decays, decreasing emission intensity and increasing blackbody radiation. Although absolute lifetime decay values are readily available, there has been no known work presenting absolute intensity measurements throughout the phosphors operating temperature range. This additional information could help design engineers facilitate phosphor and instrument selection, optimise system setup, and help estimate the performance of the technique at higher temperatures, for any given optical setup. A number of well known high temperature thermographic phosphors were investigated including YAG:Tm, YAG:Tb and Y₂O₃:Eu from 20 °C in an excess of 1000 °C. Both 355 and 266 nm excitation wavelengths from a Q-switched Nd:YAG laser were used. The subsequent emissions were passed through a narrowband interference filter to isolate the peak emission wavelengths, and were collected using PMT. The methodology for an absolute measurement, which requires a sound understanding of the PMT, including solid angle, collection efficiency, dynode gain, calibration and electronic temporal response for intensity measurements is presented and discussed. The results clearly indicate a variation in phosphor intensity with an increasing temperature, which is considerably different amongst different phosphors under different excitation wavelengths. The combined standard uncertainty of measurement was estimated to be approximately ±10.7%. The existing system was able to monitor intensity values up to 900 °C for Mg₃F₂GeO₄:Mn phosphors, 1100 °C for Y2O3:Eu, 1150 °C for YAG:Tb and up to 1400 °C for YAG:Tm thermographic phosphors. Y₂O₃:Eu using 266 nm excitation was found to exhibit the highest peak intensity per mJ of laser excitation from all the phosphors investigated at 20 °C. However, at high temperatures (900 °C+) YAG:Tm using 355 nm excitation was found to exhibit the highest peak intensity per mJ of an excitation energy.     

Instantaneous temperature measurement in a rapid-compression machine using laser Rayleigh scattering

The instantaneous local temperature is measured in a Rapid-Compression Machine (RCM) after the compression. The technique that we have used is the laser Rayleigh scattering at 532 nm. Despite the important background noise due to the very confined RCM chamber, optimum optical conditions lead to a single-shot temperature accuracy of 30 K at the end of compression. The temperature history is sampled at the laser pulse rate, and it exhibits large temperature fluctuations just after the end of compression. Comparison with the extensively used calculated adiabatic core gas temperature shows excellent agreement, at least in the time interval corresponding to ignition delays ( < 100 ms). This first experimental assessment of core-gas assumption is important for chemical-kinetics numerical predictions in RCMs.     

Planar imaging thermometry in gaseous flows using upconversion excitation of thermographic phosphors

Temperature measurement in gaseous flows is of significant practical importance for determining convection coefficients for heat transfer calculations, validating computation fluid dynamic simulations, and understanding the fundamentals of turbulent mixing and transport in flows. Here, we report on a new diagnostic technique for measuring temperature in gaseous flows which relies upon upconversion luminescence from inorganic phosphors. The phosphor used for the study consists of erbium (Er³⁺) and ytterbium (Yb³⁺) ions doped into a yttrium oxysulfide host material. The theoretical background behind the upconversion diagnostic is presented and spectral emission data taken using upconversion excitation are used to design a temperature diagnostic which is quite sensitive for temperatures ranging from approximately 300–600 K. Demonstration temperature measurements were performed in an air jet heated to temperatures ranging from 295–523 K. Single-shot images of temperature were obtained with a temperature precision of approximately ±5 K (1 standard deviation basis). This is the first known application of upconversion excitation to imaging temperatures in gaseous flows.     

Characterization of premixed swirling methane/air diffusion flame through filtered Rayleigh scattering

Characteristics of a premixed, swirl methane/air diffusion flame at atmospheric pressure are measured by filtered Rayleigh scattering (FRS). Three operating conditions are investigated with the equivalence ratios of the methane/air flame covering a range of 0.67—0.83. Under each condition, single-shot and averaged FRS images over a region measured 39.3×65.6 mm² at seven cross sections of the flame are collected to demonstrate the flame behavior. A gradient calculation algorithm is applied to identify reaction zone locations and structures in the instantaneous FRS measurements. Statistical analysis for the mean FRS measurements is performed by means of joint probability density functions. The experimental results indicate that thermochemical state of the swirl flame is strongly influenced by equivalence ratio, leading to varieties of flame structures and temperature distributions. The gradient of the instantaneous FRS images clearly illustrates the characteristics of the reaction zone. The results also demonstrate that FRS can provide detailed insights into the behavior of turbulent flames.     

Investigation of potential laser-induced heating effects when using thermographic phosphors for gas-phase thermometry

The spectral emission from thermographic phosphors in free flow and its dependence of laser energy per cross section area (laser fluence [J/cm²]) has been investigated. Temperature measurements in gaseous flows using thermographic phosphors require higher laser energy than measurements performed on surfaces, due to lower particle density. A troublesome systematic error associated with high fluences would be introduced if the excitation laser heats the particles. In the presented work, three different types of the thermographic phosphor BaMg₂Al₁₀O₁₇:Eu (BAM) are investigated. Spectra of the phosphorescence are achieved for a range of laser fluences. The results show no indications of the laser heating the particles, making further development of phosphor thermography in free-flow applications feasible.     

Quantitative temperature imaging at elevated pressures and in a confined space with CH_4/air laminar flames by filtered Rayleigh scattering

Laminar methane/air premixed flames at different pressures in a newly developed high-pressure laminar burner are studied through Cantera simulation and filtered Rayleigh scattering(FRS).Different gas component fractions are obtained through the detailed numerical simulations.And this approach can be used to correct the FRS images of large variations in a Rayleigh cross section in different flame regimes.The temperature distribution above the flat burner is then presented without stray light interference from soot and wall reflection.Results also show that the extent of agreement with the single point measurement by the thermocouple is 6%.Finally,this study concludes that the relative uncertainty of the presented filtered Rayleigh scattering diagnostics is estimated to be below 10% in single-shot imaging.     

Mapping the surface temperature of ceramic and superalloy turbine engine components using laser-induced fluorescence of thermographic phosphor

An excimer laser-based system for mapping the surface temperature of turbine engine parts coated with thermographic phosphors has been developed. The intensities measured for Y₂O₃:Eu over the temperature range 500–750°C are presented. In addition, the data correction and error analysis algorithm is discussed. The overall accuracy of this intensity-based surface temperature measurement technique was estimated to be ±5%. Furthermore, surface temperature measurements obtained from a ceramic matrix composite and superalloy components are presented.     

Measurement of second-harmonic optical susceptibility using Rayleigh scattering

We report a simple method to measure relative second-harmonic optical susceptibilities of crystals by use of Rayleigh scattering. We use two crystals with fixed alignments: one is a phase-matched crystal with varying degrees of phase matching, which serves as a reference point of the phase relationship and a source for the second-harmonic beam to be incident on the sample crystal, and the other is a sample crystal for measurement. The second-harmonic signals generated from each of the two crystals are superposed in the sample crystal to give Rayleigh scattering at the second-harmonic frequency, the analysis of which can determine the relative values of the second-harmonic optical susceptibilities of the sample crystals. We have applied this method to obtain d ₁₄ (KDP)1.8 d ₃₆ (KDP), d ₃₆ (ADP)1.1 d ₃₆ (KDP), d ₃₁ (KTP)15 d ₃₆ (KDP), d ₃₂ (KTP)13 d ₃₆ (KDP), where d ₃₆ of KDP crystals was taken as a reference.     

Neutron Rayleigh and Brillouin scattering in normal 4He

Rayleigh and Brillouin peaks have been observed in neutron scattering by normal fluid ⁴He at 4.2 K and saturated vapour pressure in the wavevector transfer range from 0.06 Å^?1 to 0.2 Å^?1. The observations can be described by hydrodynamics, but there is a small discrepancy with the thermodynamic parameters.