Wavelength-agile H2O absorption spectrometer for thermometry of general combustion gases

Using a novel Fourier-domain mode-locking (FDML) laser scanning 1330-1380 nm, we have developed a gas thermometer based on absorption spectroscopy that is appropriate for combustion gases at essentially arbitrary conditions. The path-integrated measurements are particularly useful in homogeneous environments, and here we present measurements in a controlled piston engine and a shock tube. Engine measurements demonstrate a RMS temperature precision of ±3% at 1500 K and 200 kHz bandwidth; the precision is improved dramatically by averaging. Initial shock tube measurements place the absolute accuracy of the thermometer within ∼2% to 1000 K. The sensor performs best when significant H₂O vapor is present, but requires only at 300 K, at 1000 K, or at 3000 K for 2% accurate thermometry, assuming a 4 kHz measurement bandwidth (200 kHz scans with 50 averages). The sensor also provides H₂O mole fraction and shows potential for monitoring gas pressure based on the broadening of spectral features. To aid in designing other sensors based on high-temperature, high-pressure H₂O absorption spectroscopy, a database of measured spectra is included.     

入射角和薄片表面特性对激光干涉测温的影响

以激光干涉为理论基础,采用具有不同表面光学特性的单晶硅片和K-8光学玻璃为样品,针对不同的测量条件,研究干涉条纹对比度变化对温度测量的影响.分析了薄片干涉条纹对比度与测量光束直径、入射角、样品表面粗糙度以及表面镀膜之间的相互关系,研究了薄片的横向温度梯度对干涉对比度的影响.实验结果表明,上述各因素对温度测量参量对比度产生的影响具有规律性,并在一定对比度阈值条件下,能够满足精确测温的条件要求.     

Cavity effects in coiled coil IR reference source

We performed a high resolution imaging of a coiled coil filament used in tungsten lamps, a standard reference source in spectroscopy. The radiometric results using two-wavelength thermometry indicate that its configuration also introduces cavity effects and non-uniformity of filament temperature distribution, with the average temperature calculated to be 2869 K. Considering the tungsten source as an extended body, significant temperature variations of up to +19 K are found above its nominal 2850 K value.     

Modulating Triplet Excited States of Organic Semiconductors via Tuning Molecular Conformation for Dual-ratiometric Thermometers

The dual-ratiometric thermometry is one of highly accurate methods for microscopic thermal measurement in biological systems. Herein, a series of chromone derivatives with noncovalently intramolecular interactions (NIIs) were designed and synthesized for ratiometric thermometers. The triplet states of these organic compounds were systematically tuned upon regulating the conformation with NIIs to yield efficient room temperature phosphorescence and large wavelength difference between fluorescence and phosphorescence simultaneously. As a result, an unprecedent organic 3D dual-ratiometric thermometer was established based on the intensity ratio and lifetime ratio of fluorescence/phosphorescence vs temperature, which was used for in vitro and in vivo bio-thermometry with high accuracy. This work provides a novel method to achieve organic dual ratiometric thermometers via tuning the triplet excited states.     

In-cylinder gas temperature and water concentration measurements in HCCI engines using a multiplexed-wavelength diode-laser system: Sensor development and initial demonstration

A wavelength-multiplexed, fiber-optic-based, line-of-sight, diode-laser absorption sensor is developed for crank-angle-resolved measurements of temperature and water concentration in a homogeneous-charge-compression-ignition (HCCI) engine. An initial demonstration of its use on two optical HCCI engines at Sandia National Laboratories is reported. The measurements encompassed both motored- and fired-engine operation for temperatures between 300 and 1700 K and pressures between 1 and 55 bar. A spectroscopic line selection process identifies the most appropriate water absorption linepair for thermometry under these conditions. Key solutions to suppress crank-angle-dependent noise in the transmitted laser signals are reported, including careful spectroscopic design and optical engineering to accommodate beam-steering, engine vibration and polarization-related interference. Data obtained through this sensor can provide critical engine characteristics such as combustion efficiency, peak combustion temperature, and autoignition temperature. The flexibility of the wavelength-multiplexed architecture allows the straightforward addition of other wavelengths to potentially enable the simultaneous measurement of other important engine parameters such as temperature non-uniformity, and fuel, CO, and CO₂ concentrations.     

Correlation of optical properties and temperature-induced irreversible phase transitions in europium-doped yttrium carbonate nanoparticles

Nanophase europium-doped yttrium carbonate precursors are subjected to heat treatments, ranging from 300 °C to 1100 °C for dwell times of 5 min, 30 min, and 180 min. XRD, TEM, FT-IR, fluorescence, fluorescence excitation, and fluorescence lifetime measurements are used to characterize the materials. Upon heating, the material transitions through several amorphous stages until it reaches the crystalline cubic Y₂O₃ phase. DSC measurements show an exothermic transition at 665.7 °C, indicating the formation of crystalline Y₂O₃. The grain size development is fitted by the relaxation equation and yields an activation energy of 50.3 kJ/mol. The amorphous phases are characterized by inhomogenously broadened optical spectra. Heating up to 700 °C leads to an increased fluorescence lifetime (from about 1 ms to 2.4 ms). As the material is heated to higher temperatures and completes the formation of the crystalline cubic Y₂O₃ phase, the optical spectra become narrower and the fluorescence lifetime decreases to about 1.2 ms.     

Measurement of heat transfer coefficients by nuclear magnetic resonance

We demonstrate an experimental method for the measurement of heat transfer coefficient for a fluid system by magnetic resonance imaging. In this method, the temporal variation of thermally induced nuclear shielding is monitored and the average heat transfer coefficient is measured as a function of fluid velocity. We examine the cases of natural convection and forced convection at fluid velocity up to 0.8 m s(-1). These cases correspond to low dimensionless Biot (Bi) number where the heat transfer is limited by thermal convection. We demonstrate the NMR method for two simple geometries, a cylinder and a sphere, to experimentally determine the heat transfer coefficient (h) in two NMR imaging and spectroscopy systems through measuring three NMR parameters, the chemical shift, magnetization and spin self diffusion coefficient.     

Toward Magneto-Optical Cryogenic Thermometers with High Sensitivity: A Magnetic Circular Dichroism Based Thermometric Approach

Remote temperature probing at the cryogenic range is of utmost importance for the advancement of future quantum technologies. Despite the notable achievements in luminescent thermometers, accurately measuring temperatures below 10 K remains a challenging endeavor. In this study, we propose a novel magneto-optical thermometric approach based on the magnetic-circular dichroism (MCD) technique, which offers unprecedented capabilities for meticulous temperature variation analysis at cryogenic temperatures. The inherent temperature sensitivity of the MCD C-term, in conjunction with both positive and negative signals, enables highly sensitive magneto-optical temperature probing. Additionally, a groundbreaking relative thermal sensitivity value of 95.3 % K⁻¹ at 2.54 K can be achieved using a mononuclear lanthanide complex, [[Ho(acac)₃(phen)], in the presence of a 0.25 T applied magnetic field and using a combination of multiparametric thermal read-out with multiple regression. These results unequivocally demonstrate the viability and effectiveness of our methodology for cryogenic temperature sensing.     

固体火箭发动机羽流辐射光谱测温方法研究

固体火箭发动机羽流具有高温、高速与强辐射特征,羽流温度是发动机工作状态与性能的重要表征参数。准确测量固体火箭发动机羽流温度对了解发动机内部燃烧情况以及发动机综合性能具有重要的参考价值。随着激光与光谱学的发展,激光光谱技术逐步应用于固体推进剂燃烧及发动机羽流温度测量。辐射光谱测温法通过测量火焰辐射光谱来实现温度的非接触在线测量,具有测温范围宽、响应快及可靠性高等优点,可应用于固体火箭发动机羽流温度测量。在此提出了基于火焰辐射光谱的固体火箭发动机羽流温度测量方法,采用350～1 000 nm波段光纤光谱仪搭建了发动机羽流火焰辐射光谱测量系统,利用标准辐射黑体炉开展光谱仪响应系数标定,获得响应系数随波长的变化曲线,并以此用作羽流辐射光谱数据修正。之后将该测量系统应用于标准Φ118固体火箭发动机地面试验,开展典型12%铝质量含量推进剂发动机羽流辐射光谱实验测量,选取不同时刻羽流辐射光谱分析了发动机羽流辐射光谱特征,并利用双色法灰性判断原理对羽流火焰灰体特性进行讨论,验证在675～745 nm波段发动机羽流火焰辐射可近似认为灰体,该波段辐射率随波长变化最大相对偏差为4.01%,相对均方差为1.53%。因此,基于普朗克辐射定律开展辐射光谱拟合参数获得不同时刻羽流温度与辐射率参数,并讨论测量结果与发动机工作状态的关系。最后,开展12%,15%与19%铝质量含量的不同推进剂配方固体火箭发动机羽流辐射光谱测量,将辐射光谱法温度测量值与理论热力计算值进行比较,两者最大偏差值为5.40%,讨论了不同铝含量推进剂发动机羽流辐射光谱特征,并结合温度与辐射率测量结果,分析了固体推进剂铝含量对辐射光谱、羽流温度及辐射率的影响。通过固体火箭发动机羽流辐射光谱测温方法研究,为固体火箭发动机性能评估及推进剂配方优化等研究提供了有效的羽流参数测量手段。分析获得的推进剂铝含量对发动机羽流辐射光谱、温度及辐射率参数的影响,为降低固体发动机羽流特征信号提供了重要的实验数据支撑。     

Simultaneous phosphor and CARS thermometry at the wall-gas interface within a combustor

Phosphor thermometry and vibrational coherent anti-stokes Raman spectroscopy (CARS) were applied simultaneously to examine gas-solid interfaces in a generic combustor. For this purpose, an internally air-cooled obstacle was installed within an optically accessible, pressurized combustion chamber. During the operation of a turbulent, swirled n-heptane flame, the obstacle’s surface temperature and the surface-normal gas temperature distribution were measured. The surface temperature was determined by Thermographic Phosphors, materials whose phosphorescence decay times depend on their temperature. Following a pulsed UV laser excitation (355 nm), the 659 nm emission band of Mg₄FGeO₆:Mn was monitored by a photomultiplier tube.Non-invasive temperature measurements in the flue gas region of the n-heptane spray flame near the surface were performed pointwise by vibrational CARS of diatomic nitrogen. Beams from a frequency doubled Nd:YAG laser (532 nm) and a modeless broadband dye laser (607 nm) were phase-matched within a surface-parallel, planar BOXCARS configuration. This allowed gas phase thermometry as close as 30 μm to the surface.The thermal boundary layer and wall temperature measurements were consistent with each other. This demonstrates the potential of spectrocopic techniques to study gas-solid interfaces with high temporal and spatial resolution. Using the interior surface temperature within the cooling channel measured by a thermocouple, the heat flux through the wall and the local heat transfer coefficient at the front side of the obstacle were estimated.