A Compact Tunable Diode Laser Absorption Spectrometer to Monitor CO2 at 2.7 μm Wavelength in Hypersonic Flows

Since the beginning of the Mars planet exploration, the characterization of carbon dioxide hypersonic flows to simulate a spaceship’s Mars atmosphere entry conditions has been an important issue. We have developed a Tunable Diode Laser Absorption Spectrometer with a new room-temperature operating antimony-based distributed feedback laser (DFB) diode laser to characterize the velocity, the temperature and the density of such flows. This instrument has been tested during two measurement campaigns in a free piston tunnel cold hypersonic facility and in a high enthalpy arc jet wind tunnel. These tests also demonstrate the feasibility of mid-infrared fiber optics coupling of the spectrometer to a wind tunnel for integrated or local flow characterization with an optical probe placed in the flow

Rocket Motor Diagnostics using Tunable Diode Laser Spectroscopy for Chemically Non-Reacting Air/Water Vapor Mixture in Internal Flow

This research is for the implementation of non-intrusive measurement techniques in the study of high temperature pipe flow. A low pressure, laboratory scale hybrid rocket motor simulator was built to achieve high temperatures with various gases. A quartz test section was designed, built, and implemented into the existing test setup to accommodate the laser beam of the existing Tunable Diode Laser Absorption Spectrometer (TDLAS) system which was designed to observe water vapor. A super-heated water vapor injector was designed to obtain the desired water vapor concentrations. Flow characteristics were simultaneously recorded using the existing TDLAS system and the DAQ system for temperatures for later comparison. A numerical study using a commercial CFD package was used to predict the flow characteristics at certain locations for experimental comparison. Based on this study, it is concluded that the TDLAS can be used to make real time temperature measurements of heated internal gas flows

Rocket Motor Diagnostics using Tunable Diode Laser Spectroscopy for Chemically Non-Reacting Air/Water Vapor Mixture in Internal Flow

This research is for the implementation of non-intrusive measurement techniques in the study of high temperature pipe flow. A low pressure, laboratory scale hybrid rocket motor simulator was built to achieve high temperatures with various gases. A quartz test section was designed, built, and implemented into the existing test setup to accommodate the laser beam of the existing Tunable Diode Laser Absorption Spectrometer (TDLAS) system which was designed to observe water vapor. A super-heated water vapor injector was designed to obtain the desired water vapor concentrations. Flow characteristics were simultaneously recorded using the existing TDLAS system and the DAQ system for temperatures for later comparison. A numerical study using a commercial CFD package was used to predict the flow characteristics at certain locations for experimental comparison. Based on this study, it is concluded that the TDLAS can be used to make real time temperature measurements of heated internal gas flows

Fluoroindate glass co-doped with Yb3+/Ho3+ as a 2.85 μm luminescent source for MID-IR sensing

This work reports on the fabrication and analysis of near-infrared and mid-infrared luminescence spectra and their decays in fluoroindate glasses co-doped with Yb3+/Ho3+. The attention has been paid to the analysis of the Yb3+ ! Ho3+ energy transfer processed ions in fluoroindate glasses pumped by 976 nm laser diode. The most effective sensitization for 2 um luminescence has been obtained in glass co-doped with 0.8YbF3/1.6HoF3. Further study in the midinfrared spectral range (2.85 um) showed that the maximum emission intensity has been obtained in fluoroindate glass co-doped with 0.1YbF3/1.4HoF3. The obtained efficiency of Yb3+ ! Ho3+ energy transfer was calculated to be up to 61% (0.8YbF3/1.6HoF3), which confirms the possibility of obtaining an efficient glass or glass fiber infrared source for a MID-infrared (MID-IR) sensing application

Optical Microresonator-Based Flow-Speed Sensor

Optical sensors have become more prominent in atmospheric measurement systems, with LiDAR instruments deployed on a variety of earth-bound, air-borne, and space-based platforms. In recent years, the interest in the human exploration of Mars has created a substantial push towards reliable and compact sensing elements for Mars exploration missions, particularly during a spacecraft’s entry, descent, and landing stages. Real-time sensors able to reliably measure the craft’s speed relative to the surrounding atmosphere during these stages are thus of great interest. In this dissertation, a proof-of-concept for an optical microfabricated sensor, which leverages the whispering-gallery-mode (WGM) and Doppler shift principles, is developed to measure wind speed from atmospheric particles through light scattering. WGM micro-resonators could replace Fabry–Perot interferometers and other optical frequency discriminators often employed in remote sensing applications, thereby significantly reducing the size and weight of the measurement system. The capabilities of the presented sensor concept are first studied under the aerosol scattering regime, and the measurement resolution of the WGM resonators is assessed. An optical system is developed, and velocity measurements near the exit of a seeded air jet nozzle are carried out to validate the velocity measurement capabilities from aerosol streams. The feasibility of employing WGM resonators for molecular scattering-based measurements of atmospheric properties is also investigated. A modified mathematical model for coherent and spontaneous scattering is implemented in the performance analyses of the resonators for different altitudes of Earth and Mars atmospheres. Spectral profiles generated from the model are compared to those in the literature under similar conditions. An analysis for photon count under various atmospheric conditions and altitudes is also carried out. The analyses indicate that WGM resonator-based spectral instruments may be viable as part of future compact and lightweight atmospheric sensors

Diode Laser Absorption Measurements of Gas Diffusion Coefficient in the Transition Gas Regime

Mass diffusion coefficients of gas mixtures have been measured for more than 100 years. However, experimental data for the effective diffusion coefficient (Deff) of gas mixtures in the rarefied gas regimes at Knudsen numbers (Kn) above 0.1 are few and remain uncertain due to the increased effect of gas-wall collision behaviour. Due to growing demand in rarefied gas regime applications like microfluidic and vacuum systems, accurate Deff measurements are needed to validate available diffusion theories and empirical relations in the rarefied gas regimes. This thesis is the first to report the non-intrusive, in-situ, direct measurement of Deff of gas mixtures in the Kn range 0.1 < Kn < 6. The experimental investigation of Deff for gas mixtures in the transition gas regime where no direct measurements were available earlier has been made possible due to the implementation of the tunable diode laser absorption spectroscopy (TDLAS) technique using a hollow-core photonic crystal fiber (HCPCF) as the diffusion environment. First, different experiment methodologies used in the literature to measure the diffusion coefficient of gas mixtures were investigated. Information is synthesised to determine the limits of the current state of the art for measuring Deff in the transition gas regime, and reasons for the lack of Deff measurements at Kn above 0.1 were identified. As a result, the two-bulb (TB) diffusion configuration having the HCPCF combined with the TDLAS gas concentration measurement technique is proposed to measure the Deff of gas mixtures in the transition and free molecular gas regimes at Kn above 0.1. Second, this experiment methodology was implemented, and the Deff of binary and ternary gas mixtures containing CO2 as one of the gas species were measured in the transition gas regime. CO2 has strong absorption features near the wavelength of 2005 nm, corresponding to a wavelength range of one of the laboratory’s lasers that would propagate without significant attenuation through the available HCPCF. Selected rotational-vibrational transitions of CO2 near 2005 nm are probed using the TDLAS technique to monitor the change in the mole fraction of CO2 through the change in the path-integrated absorbance (∫Aexp) of CO2 absorption lines in real time as the diffusion progresses. The change in ∫Aexp as a function of time has been used to estimate the Deff of a gas mixture from the diffusion time constant. He and Ar were chosen as gas species in a gas mixture containing CO2 for simplicity and to avoid potential adhesion and surface reaction with the silicon dioxide (SiO2) wall surface of the HCPCF used in the study. Initially, the Deff of He-CO2 was measured closer to the continuum gas regime at Kn ≈ 0.01 and compared with literature to validate the Deff measurement using the TB-TDLAS methodology against more traditional measurements and empirical correlations. Then, the measurement was extended to the transition gas regime at 0.1 < Kn < 6 and the Deff of binary gas mixtures He-CO2, Ar-CO2, and ternary gas mixture He-Ar-CO2 were measured using the TB-TDLAS methodology. Third, continuing the in-situ and direct measurement of Deff, the advantage of species-specific diffusion measurement was demonstrated by reporting for the first time the simultaneous measurement of Deff of both gas species in a diffusing N2O-CO2 gas mixture in the transition gas regime. The measured Deff of binary and ternary gas mixtures in the transition gas regime is compared against the predicted Deff using the Bosanquet empirical relation. The comparison between the measured and predicted Deff of gas mixtures is discussed in detail. Finally, the measured Deff of He-CO2, Ar-CO2, and He-Ar-CO2 gas mixtures were validated against the direct simulation Monte Carlo (DSMC) calculations in the transition gas regime. The DSMC simulated Deff are closer to the measured Deff values if fully diffuse reflection of particles from the gas wall is assumed. Both the measured and DSMC simulated Deff demonstrate the viability of TB-TDLAS methodology as a convenient technique to obtain a non-intrusive, in-situ, direct measurement of Deff for gas mixtures in the transition gas regime. The research outcomes point out the possibility of further extending the TB-TDLAS experiment methodology to obtain the Deff of gas mixtures in the free molecular gas regime at Kn > 10. In addition, the TB-TDLAS methodology opens up the possibility of real-time monitoring of the change in the mole fraction of multiple gas species during the diffusion process, leading to the simultaneous measurement of Deff of multiple gas species involved in a gas mixture, applicable to all gas regimes from continuum to free molecular

H2O LASER ABSORPTION AND OH* CHEMILUMINESCENCE MEASUREMENTS OF H2-NO2 OXIDATION IN A SHOCK TUBE

The mitigation of NOx pollutants continues to be a matter of environmental and economic interest in the gas-turbine industry, and an improved understanding of fundamental NOx chemical kinetics has led to reductions in NOx emissions. However, the exhaust gas recirculation (EGR) method necessitates an accurate understanding of NOx/fuel interactions, and few experimental data with NOx as the sole oxidizer exist. New measurements of this kind would provide unique target data for the continuing design and optimization of NOx chemical kinetics mechanisms. To this end, new combustion data in the H2-NOv2 system were acquired. Experiments were performed behind reflected shock waves near 1 atm and at temperatures between 917 and 2003 K. Fuel-lean, near-stoichiometric, and fuel-rich mixtures of H2-NOv2 diluted in approximately 99 percent Ar were studied. A laser absorption diagnostic near 1.39 µm measured H2O time histories, while an emission diagnostic near 307 nm measured exited-state OH (OH asterisk) time histories. Kinetic modeling of the H2O data revealed the species HONO and NO3 are important in the H2vO reaction pathways. Newer mechanisms predicted the experimental H2O profiles quite well at fuel-lean and high-temperature conditions, but discrepancies persisted at fuel-rich and low-temperature conditions despite variation of the most-sensitive reactions. The kinetic models were unable to predict the experimental OH asterisk profile shapes with any sort of accuracy, suggesting the need for a new OH asterisk-forming reaction. By fitting the OH* profile shapes and considering exothermicity, the reaction NH + NOv2 ⇄ N2vO + OH asterisk was identified, and a tentative rate constant of kv13 = 5.0×10^^16·exp(- 40,000/RT) was proposed (units of [cal], [mol], [cm^3 ], [s])

Laser-based temperature diagnostics in practical combustion systems

Today’s energy supply relies on the combustion of fossil fuels. This results in emissions of toxic pollutants and green-house gases that most likely influence the global climate. Hence, there is a large need for developing efficient combustion processes with low emissions. In order to achieve this, quantitative measurement techniques are required that allow accurate probing of important quantities, such as e.g. the gas temperature, in practical combustion devices. Diagnostic techniques: Thermocouples or other techniques requiring thermal contact are widely used for temperature measurements. Unfortunately, the investigated system is influenced by probe measurements. In order to overcome these drawbacks, laser-based thermometry methods have been developed, that are introduced and compared in this work. Special emphasis is set on a recently developed multi-line technique based on laser-induced fluorescence (LIF) excitation spectra of nitric oxide (NO). This calibration-free temperature imaging method was optimized within this thesis such that accurate temperature measurements are possible in practical, harsh environments. Numerical and experimental studies were conducted to identify ideal spectral excitation and detection strategies. The limited accuracy of this time-averaging technique in turbulent systems was investigated. In cooperation with T. B. Settersten (Sandia, USA), energy transfer processes during quenching of NO LIF were quantified. These processes are not understood so far and hamper the application of saturated LIF spectroscopy. In collaboration with Prof. R. K. Hanson (Stanford University, USA) a two-line thermometry sensor based on tunable diode-laser absorption spectroscopy (TDLAS) of water was optimized. Applications: NO LIF and H2O TDLAS were applied to quantitatively measure the gas temperature over a wide range of pressures (3 – 500 kPa) and temperatures (270 – 2200 K). With multi-line NO-LIF thermometry, gas-temperature fields in spray flames were obtained that have been used to validate numerical models for spray combustion developed by Prof. E. Gutheil (Heidelberg University). In cooperation with the Robert Bosch GmbH, Germany, this technique was used to quantify the evaporative cooling in internal-combustion (IC) engine-relevant pulsed fuel-sprays. NO-LIF thermometry was compared to soot pyrometry, has been applied to sooting high-pressure flames, and the data was taken to calculate soot-particle sizes with laser-induced incandescence. In collaboration with Toyota Central R&D Labs, Japan, the temperature distributions in boundary layers of solid-wall quenched flames were measured. This data enables quantitative LIF species measurements and optimization of the IC engine thermal management. In a nano-particle flame-synthesis reactor, both techniques were applied to measure the gas temperature, which is taken to validate numerical simulation codes for nano-particle formation developed at the University of Duisburg-Essen. In cooperation with Shinko Electric Industries, Japan, and Prof. J. Warnatz (Heidelberg University), H2O TDLAS was applied to optimize a direct-flame solid-oxide fuel cell system. The versatile measurement techniques developed and improved within this thesis enable quantitative probing of the gas temperature in practical combustion devices. Accurate knowledge of this important quantity allows developing efficient power plants and engines with low emissions of green-house gases and toxic pollutants

High Temperature and Pressure Measurements from TDLAS Through the Application of 2nd Derivative Fitting and the Aggregate Boltzmann Method

This work expands Tunable Diode Laser Absorption Spectroscopy (TDLAS) measurement and data processing techniques. Specifically, it introduces new data acquisition and data reduction techniques that improve scanned direct absorption spectroscopy measurements. Current data acquisition techniques are limited in temporal and spatial resolution. Some of these limitations are resolved by extending measurements from a single point to a plane by the introduction of a novel instrumentation method, the Linear Array Camera (LAC). The use of an LAC allows for simultaneous imaging of absorption spectra on multiple points, from which the spatial distribution of pressure, temperature and species fraction can be inferred. Example measurements are presented to demonstrate the capability of a planar measurement approach. Some practical challenges are identified, and corrections are given for common design problems, as well as models to help with the design of an LAC system. TDLAS is typically used to generate measurements of temperatures, pressures and species fraction. Their accuracy is limited by errors introduced in the measurement of the absorption profile and by the accuracy of the spectral parameters used to related absorbance to the thermochemical state. Some of these limitations are overcome by the introduction of a novel application of the second derivative fitting of the absorption spectrum, the wavenumber-domain equivalent of Wavelength Modulation Spectroscopy (WMS), a Fourier domain technique. Because the WMS technique requires fast acquisition, it is impractical for use with state-of-the-art LAC systems, which have limited scan rates. The second derivative reconstruction method allows for insensitivity to baseline errors and increases sensitivity to small variations in the spectral absorbance, which allow for more accurate measurement of temperatures and vastly improve the measurement of pressure through spectral fitting. The second derivative scheme, a spectral fitting technique, is dependent upon the accurate knowledge of the spectral parameters, which are typically taken from a spectral database. One common database is the HITRAN spectral database, which lists parameters for the spectral transitions and includes collisional parameters for air and self broadening. In actual applications, such as in combustion environments, the collisional partners are frequently far more numerous than air and self collisions. The lack of these parameters can introduce errors into the reconstructed measurements. This can be addressed through the use of the Boltzmann Plot method, which makes use of the integrated area under a number of isolated transitions to negate the dependence on accurate broadening parameters. To overcome the necessity for isolated features an extension is introduced, referred to as the Aggregate Boltzmann Plot method, based on the concept of aggregate spectrum within a Boltzmann Plot framework to expand its applicability to high pressure and temperature conditions where spectral blending has prevented the application of the traditional Boltzmann Plot method. The Aggregate Boltzmann Plot requires accurate measures of spectral profiles, which are affected by baseline errors resolvable by second derivative fitting. Therefore, through the combination of second derivative fitting and the Aggregate Boltzmann Plot method, a robust measurement technique is obtained. This technique applies the second derivative fitting to obtain baseline insensitive spectral profiles, which are then applied in the Aggregate Boltzmann Plot method to mitigate the effects of missing broadening parameters. This results in a robust measurement technique capable to generate accurate measurements under conditions that were previously inaccessible by traditional approaches based on scanned direct absorption methods.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/149901/1/jjfrance_1.pd