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Acousto-optically modulated quantum cascade laser for high-temperature reacting systems thermometry
Abstract
We demonstrate time-resolved temperature measurements in
shock-heated mixtures of carbon monoxide over a temperature
range of 1000–1800 K for two pressure ranges,
2.0–2.9 atm and 7.6–10.7 atm, at rates up to 250 kHz using
a single acousto-optically modulated quantum cascade laser
with mid-infrared output spanning from 1975 to 2260 cm−1.
Measured temperatures were in excellent agreement with values
determined by ideal shock relations, and the temperature
profile after the passage of the reflected shock wave was
found to be well-modeled by an isentropic compression
assumption. Temperature measurements made with this
setup are largely immune to effects of emissions and beam
steering, making the diagnostic system well-suited for studying
high-temperature gas-phase reactions of energetic materials
such as octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine
and hexahydro-1,3,5-trinitro-1,3,5-triazine.
... Therefore, especially for broadband spectroscopy with a large N, the SNR advantage becomes significant. In the MIR region, wavelengthswept lasers such as external-cavity QCLs have been demonstrated 25,26 , but these lasers have shown limited instrumental scan rates up to 250 kHz 27,28 , which provide lower spectral acquisition rates than those of the state-of-the-art dualcomb spectrometers. Now, we recognize that a single-pulse broadband spectroscopy technique called time-stretch (TS) spectroscopy (also known as dispersive Fourier-transform spectroscopy) is an ideal frequency-swept spectroscopy technique that can be operated at a rate of 10 s of MSpectra s −1 with a fs modelocked laser 29 . ...
Improving the spectral acquisition rate of broadband mid-infrared spectroscopy promises further advancements of molecular science and technology. Unlike pump-probe spectroscopy, which requires repeated measurements with different pump-probe delays, continuous spectroscopy running at a high spectral acquisition rate enables transient measurements of fast non-repeating phenomena or statistical analysis of a large amount of spectral data. Recently, Fourier-transform infrared spectrometers with rapid delay scan mechanisms including dual-comb spectrometers have significantly improved the measurement rate up to ~1 MSpectra s−1 that is fundamentally limited by the signal-to-noise ratio. Here, we overcome the limit and demonstrate the fastest continuous broadband mid-infrared spectrometer running at 80 MSpectra s−1 by implementing a wavelength-swept time-stretch spectroscopy technique. Our proof-of-concept experiment demonstrates broadband absorption spectroscopy of phenylacetylene from 4.4 to 4.9 μm (2040–2270 cm−1) at a resolution of 15 nm (7.7 cm−1) with a signal-to-noise ratio of 85 without averaging and a shot-to-shot fluctuation of 1.3%. Decreasing the acquisition time of spectroscopies permits measurement of dynamic systems to be obtained at increasingly high speeds. Here, a time-stretch mid-infrared spectrometer is presented, operating at eighty million spectra per second and tested via absorption measurements of two molecular species.
... DMMP pyrolysis and oxidation experiments were performed using high purity, stainless steel, and heated shock tube at University of Central Florida. Details of the shock tube can be found in our recent work [19][20][21][22][23][24][25][26][27] . Driven section of the shock tube was uniformly heated to 80 °C (pre-shock temperature T 1 ) using custom made heating jackets supplied from Brisk Heat and PID temperature controllers. ...
Dimethyl methyl phosphonate (DMMP) is an organo-phosphorous compound (OPC) used as a fire sup-pressant and a simulant for sarin, a chemical warfare agent. There exists a critical need to gather combustion data at high heating rate and high temperatures conditions, similar to what exists during destruction process of chemical weapons. In the present work, DMMP pyrolysis and oxidation were carried out behind reflected shock waves at temperatures of 130 0-170 0 K and pressures of 1.5-1.8 atm. Lean, stoi-chiometric, and rich DMMP mixtures (= 0.23, 0.5, 1, 2) were investigated for oxidation experiments. Laser absorption spectroscopy utilizing a quantum cascade laser near 4.9 μm was used to measure intermediate CO concentration formed during the pyrolysis and oxidation processes. To the best of our knowledge, we present the first intermediate concentration data at the reported conditions for DMMP. A tentative kinetic model, based on the AramcoMech2.0 mechanism with Lawrence Livermore National Lab (LLNL)'s OPC incineration chemistry, was utilized in Chemkin-Pro to predict CO yield during the processes. The model provided fair prediction of CO yield during DMMP pyrolysis, however, overpredicted the CO yield for oxidation. Sensitivity and rate of production analyses were carried out to understand important reactions leading to CO formation.
... Carbon monoxide time histories and ignition delay times were collected in a double-diaphragm, heated, shock tube facility at UCF with an internal diameter of 0.1417 m, specific details of which can be found in [19][20][21][22][23][24][25][26][27][28][29]. The speed of the incident shock wave was measured through five piezoelectric pressure transducers (wired to four time interval counters). ...
Carbon monoxide time-histories, ignition delay times, and laminar burning velocity measurements are reported for the oxidation of 3-methyl-2-buten-1-ol (prenol) and 3-methyl-3-buten-1-ol (isoprenol). These prenols are fuel candidates outlined by the U.S. Department of Energy’s Co-Optimization of Fuels and Engines (Co-Optima) program. The laminar burning velocity measurements were conducted for two fuels with synthetic air within a constant-volume spherical combustion chamber at initial conditions of 428 K and 1 atm for a range of equivalence ratios from 0.75 to 1.50. The laminar burning velocities of the two fuels were found to be similar, and the maximum value occurred at an equivalence ratio near 1.0. Carbon monoxide time-histories and ignition delay times were recorded behind reflected shockwaves in a double-diaphragm, heated shock tube over the temperature range 1269–1472 K near 9.4 atm with a mixture of 0.05% fuel/0.35% O2/99.6% Ar. Comparisons with predictions of a detailed chemical kinetic mechanism from the literature were provided. Current model predictions overpredicted both the ignition delay time and the max CO yield; however, the model captured the profile of CO formation well. Detailed uncertainty and sensitivity analyses were carried out to identify important reactions that need attention for accurate prediction of these fuel’s chemistry. Further investigation into the rate of C3H3 + O2 = CH2CO + HCO reaction was suggested based on current experiments. The experimental data and analysis presented here is critical in the development, validation and improvement of kinetic models of these promising Co-Optima fuels.
We develop upconversion time-stretch infrared spectroscopy and demonstrate a high-resolution and broadband measurement of mid-infrared absorption spectra of gas-phase molecules at a scan rate higher than 10 MSpectra/s.
Simultaneous time-histories during the pyrolysis of propane were achieved behind a reflected shockwave using a mid-infrared frequency comb. Data was collected at temperatures ranging from 1105 – 1304 K and pressures of about 4 – 5 atm.
Shock tube experiments have been carried out on 2-methyl-1-butene (2M1B), 2-methyl-2-butene (2M2B), and 3-methyl-1-butene (3M1B)-the three isomers of methyl butene compound. Carbon monoxide (CO) time-histories and ignition delay times are obtained behind reflected shockwaves over the temperature range of 1350-1630 K and pressures of 8.3-10.5 atm with stoichiometric mixtures of 0.075% fuel in O2 /Ar. Comparative ignition study reveals that 3M1B ignites significantly faster than the other two isomers, while 2M1B dissociates earlier but ignites later than 2M2B. Possible mechanisms for this behavior are discussed with ignition delay time sensitivity and reaction path analysis. In addition, time-resolved CO measurements are compared with three different reaction mechanisms from the literature. Sensitivity analyses have been carried out to identify important reactions that need attention to accurately predict the chemistry of these isomers. Further investigation into the rates of unimolecular fuel decomposition reactions and C 3 H 3 + O 2 = CH 2 CO + HCO reaction are suggested based on the current investigation.
The direct-fired supercritical carbon dioxide cycles are one of the most promising power generation methods in terms of their efficiency and environmental friendliness. Two important challenges in implementing these cycles are the high pressure (300 bar) and high CO2 dilution (>80%) in the combustor. The design and development of supercritical oxy-combustors for natural gas require accurate reaction kinetic models to predict the combustion outcomes. The presence of a small amount of impurities in natural gas and other feed streams to oxy-combustors makes these predictions even more complex. During oxy-combustion, trace amounts of nitrogen present in the oxidizer is converted to NOx and gets into the combustion chamber along with the recirculated CO2. Similarly, natural gas can contain a trace amount of ammonia and sulfurous impurities that get converted to NOx and SOx and get back into the combustion chamber with recirculated CO2. In this work, a reaction model is developed for predicting the effect of impurities such as NOx and SOx on supercritical methane combustion. The base mechanism used in this work is GRI Mech 3.0. H2S combustion chemistry is obtained from Bongartz et al. while NOx chemistry is from Konnov. The reaction model is then optimized for a pressure range of 30–300 bar using high-pressure shock tube data from the literature. It is then validated with data obtained from the literature for methane combustion, H2S oxidation, and NOx effects on ignition delay. The effect of impurities on CH4 combustion up to 16 atm is validated using NOx-doped methane studies obtained from the literature. In order to validate the model for high-pressure conditions, experiments are conducted at the UCF shock tube facility using natural gas identical mixtures with N2O as an impurity at ∼100 bar. Current results show that there is a significant change in ignition delay with the presence of impurities. A comparison is made with experimental data using the developed model and predictions are found to be in good agreement. The model developed was used to study the effect of impurities on CO formation from sCO2 combustors. It was found that NOx helps in reducing CO formation while the presence of H2S results in the formation of more CO. The reaction mechanism developed herein can also be used as a base mechanism to develop reduced mechanisms for use in CFD simulations.
We demonstrate time-resolved simultaneous measurements of multiple hydrocarbons in high-temperature reacting and non-reacting mixtures using a broadband (instantaneous bandwidth 2.80 – 3.57 μm) subharmonic mid-infrared optical parametric oscillator based on orientation-patterned gallium phosphide. High-temperature absorption spectra and concentration time-histories of methane, ethane, and ethylene are measured at pressures around 2.3 – 2.7 atm and temperatures around 1 5 – 1277 K in single-shot shock tube experiments.
Operation of continuous wave quantum cascade lasers with a frequency-shifted feedback provided by an acousto-optic modulator is reported. Measured linewidth of 1.7 cm-1 for these devices, under CW operating conditions, was in a good agreement with predictions of a model based on frequency-shifted feedback seeded by spontaneous emission. Linewidth broadening was observed for short sweep times, consistent with sound wave grating period variation across the illuminated area on the acousto-optic modulator. Standoff detection capability of the AOM-based QCL setup was demonstrated for several solid materials.
We provide the first demonstration of an acousto-optically modulated quantum cascade laser (AOM QCL) system as a diagnostic for combustion by measuring nitric oxide (NO), a highly regulated emission produced in gas turbines. The system provides time-resolved broadband spectral measurements of the present gas species via a single line of sight measurement, offering advantages over widely used narrowband absorption spectroscopy (e.g., the potential for simultaneous multispecies measurements using a single laser) and considerably faster (>15 kHz rates and potentially up to MHz) than sampling techniques, which employ fourier transform infrared (FTIR) or GC/MS. The developed AOM QCL system yields fast tunable output covering a spectral range of 1725–1930 cm−1 with a linewidth of 10–15 cm−1. For the demonstration experiment, the AOM QCL system has been used to obtain time-resolved spectral measurements of NO formation during the shock heating of mixture of a 10% nitrous oxide (N2O) in a balance of argon over a temperature range of 1245–2517 K and a pressure range of 3.6–5.8 atm. Results were in good agreement with chemical kinetic simulations. The system shows revolutionary promise for making simultaneous time-resolved measurements of multiple species concentrations and temperature with a single line of sight measurement.
In this work, the effects of pre-ignition energy releases on H2O2 mixtures were explored in a shock tube with the aid of high-speed imaging and conventional pressure and emission diagnostics. Ignition delay times and time-resolved camera image sequences were taken behind the reflected shockwaves for two hydrogen mixtures. High concentration experiments spanned temperatures between 858 and 1035 K and pressures between 2.74 and 3.91 atm for a 15% H2\18% O2\Ar mixture. Low concentration data were also taken at temperatures between 960 and 1131 K and pressures between 3.09 and 5.44 atm for a 4% H2\2% O2\Ar mixture. These two model mixtures were chosen as they were the focus of recent shock tube work conducted in the literature (Pang et al., 2009). Experiments were performed in both a clean and dirty shock tube facility; however, no deviations in ignition delay times between the two types of tests were apparent. The high-concentration mixture (15%H2\18%O2\Ar) experienced energy releases in the form of deflagration flames followed by local detonations at temperatures < 1000 K. Measured ignition delay times were compared to predictions by three chemical kinetic mechanisms: GRI-Mech 3.0 (Smith et al.), AramcoMech 2.0 (Li et al., 2017), and Burke's et al. (2012) mechanisms. It was found that when proper thermodynamic assumptions are used, all mechanisms were able to accurately predict the experiments with superior performance from the well-validated AramcoMech 2.0 and Burke et al. mechanisms. Current work provides better guidance in using available literature hydrogen shock tube measurements, which spanned more than 50 years but were conducted without the aid of high-speed visualization of the ignition process, and their modeling using combustion kinetic mechanisms.
The chemical kinetics of n-heptane (n-C7H16) – an important reference compound for real fuels – oxidation are well studied at stoichiometric and lean conditions. However, there is only limited information on the n-heptane chemical kinetics in fuel-rich combustion. In order to verify the accuracy of chemical kinetic models at these conditions, the oxidation of rich n-heptane mixtures has been investigated. Combustion of n-C7H16/O2/Ar mixtures at equivalence ratios, φ, of 2.0 and 3.0 behind reflected shock waves has been studied at temperatures ranging from 1066 to 1502 K and at pressures ranging from 1.4 to 6.2 atm. Reaction progress was monitored by recording pressure and absorption time-histories of ethylene (C2H4) and n-heptane at a location 2 cm from the endwall of a 14-cm inner diameter shock tube. Ethylene and n-heptane absorption time-histories were measured, respectively, using absorption spectroscopy at 10.532 μm from a tunable CO2 laser and at around 3.4 μm from a continuous wave distributed feedback interband cascade laser (ICL). The measured absorption time-histories were compared with modeled predictions from the Lawrence Livermore National Lab (LLNL) detailed n-heptane reaction mechanism. To the best of our knowledge, current data are the first time-resolved n-heptane and ethylene concentration measurements conducted in a shock tube at these conditions.
Infrared laser-absorption spectroscopy (IR-LAS) sensors play an important role in diagnosing and characterizing a wide range of combustion systems. Of all the laser-diagnostic techniques, LAS is arguably the most versatile and quantitative, as it has been used extensively to provide quantitative, species-specific measurements of gas temperature, pressure, composition and velocity in both laboratory- and industrial-scale systems. Historically, most IR-LAS work has been conducted using tunable diode lasers; however, today’s researchers have access to a wide range of light sources that provide unique sensing capabilities and convenient access to nearly the entire IR spectrum (≈ 0.8 to 16 µm). In particular, the advent of room-temperature wavelength-tunable mid-infrared semiconductor lasers (e.g., interband- and quantum-cascade lasers) and hyperspectral light sources (e.g., MEMS VCSELs, Fourier-domain mode-locked lasers, dispersed supercontinuum, and frequency combs) has provided a number of unique capabilities that combustion researchers have exploited. The primary goals of this review paper are: (1) to document the recent development, application, and current capabilities of IR-LAS sensors for laboratory- and industrial-scale combustors and propulsion systems, (2) to elucidate the design and use of IR-LAS sensors for combustion gases through a discussion of the modern sensor-design process and state-of-the-art techniques, and (3) to highlight some of the remaining measurement opportunities, challenges, and needs. A thorough review and description of the fundamental spectroscopy governing the accuracy of such sensors, and recent findings and databases that enable improved modeling of molecular absorption spectra will also be provided.
Propanal is an aldehyde intermediate formed during the hydrocarbon combustion process. Potentially, the use of oxygenated biofuels reduces greenhouse gas emissions; however, it also results in increased toxic aldehyde by-products, mainly formaldehyde, acetaldehyde, acrolein, and propanal. These aldehydes are carcinogenic, and therefore it is important to understand their formation and destruction pathways in combustion systems. In this work, ignition delay times were measured behind reflected shock waves for stoichiometric (Φ = 1) mixtures of propanal (CH3CH2CHO) and oxygen (O2) in argon bath gas at temperatures of 1129 K < T < 1696 K and pressures around 1 and 6 atm. Measurements were conducted using the kinetics shock tube facility at the University of Central Florida. Current results were compared to available data in the literature as well as to the predictions of three propanal combustion kinetic models: Politecnico di Milano (POLIMI), National University of Ireland at Galway, and McGill mechanisms. In addition, a continuous wave-distributed feedback interband cascade laser centered at 3403.4 nm was used for measuring methane (CH4) and propanal time histories behind the reflected shock waves during propanal pyrolysis. Concentration time histories were obtained at temperatures between 1192 and 1388 K near 1 atm. Sensitivity analysis was carried for both ignition delay time and pyrolysis measurements to reveal the important reactions that were crucial to predicting the current experimental results. Adjustments to the POLIMI mechanism were adopted to better match the experimental data. Further research was suggested for the H abstraction reaction rates of propanal. In addition to extending the temperature and pressure region of literature ignition delay times, we provide the first high-temperature species concentration time histories during propanal pyrolysis.
The HITRAN Application Programming Interface (HAPI) is presented. HAPI is a free Python library, which extends the capabilities of the HITRANonline interface (. www.hitran.org) and can be used to filter and process the structured spectroscopic data. HAPI incorporates a set of tools for spectra simulation accounting for the temperature, pressure, optical path length, and instrument properties. HAPI is aimed to facilitate the spectroscopic data analysis and the spectra simulation based on the line-by-line data, such as from the HITRAN database [JQSRT (2013) 130, 4-50], allowing the usage of the non-Voigt line profile parameters, custom temperature and pressure dependences, and partition sums. The HAPI functions allow the user to control the spectra simulation and data filtering process via a set of the function parameters. HAPI can be obtained at its homepage www.hitran.org/hapi.
We report operation of tunable external cavity quantum cascade lasers with emission wavelength controlled by an acousto-optic
modulator (AOM). A long-wave infrared quantum cascade laser wavelength tuned from ∼8.5 μm to ∼9.8 μm when the AOM frequency was changed from ∼41MHz to ∼49 MHz. The laser delivered over 350 mW of average power at the center of the tuning curve in a linewidth of ∼4.7 cm−1. Measured wavelength switching time between any two wavelengths within the tuning range of the QCL was less than 1 μs. Spectral measurements of infrared absorption features of Freon demonstrated a capability of obtaining complete spectral data in less than 20 μs.
An experimental setup for performing rapid thermolysis studies of small samples of energetic materials is described. In this setup, about 8 μL of a liquid sample or about 2 mg of a solid sample is heated at rates exceeding 1500 K/s to a set temperature where decomposition occurs. The rapid heating is achieved as a result of confining the sample between two closely spaced isothermal surfaces. The gaseous decomposition products depart from the confined space through a rectangular slit into the region of detection. The evolved gases are quantified using FTIR absorption spectroscopy by accounting for the instrument line shape. To illustrate the use of this setup, the thermolysis behaviors of three different energetic materials are examined. These materials include HMX, RDX, and HAN, all of which are considered as highly energetic propellant ingredients. The results obtained in this study of the temporal evolution of species concentrations from these ingredients are in reasonably close agreement with results available in the literature.
A much desired, direct, in situ, diagnostics technique is implemented to measure time variations of temperature and water concentration for a reactive mixture in a rapid compression machine (RCM) using quantum cascade laser absorption spectroscopy near 7.6 μm. The temperature measurements in the RCM are successfully conducted for an end of compression pressure of PC ∼ 11.5 bar and an end of compression temperature of TC ∼ 1022 K for H2/O2/Ar mixtures with (0.5% by mole in the reactive mixture) and without water doping. For all cases investigated, the molar percentages of H2 and O2 in the reactive mixture are respectively kept at 3% while the balance is Ar, in order to modulate the extent of post-ignition pressure rise. Absorption lines of water at 1316.55 cm−1 and 1316.97 cm−1 are used in this study for the measurements. A six-pass setup inside the RCM is implemented for the reactive experiments. For determining the line broadening parameters of water in the range of 1316.4–1317.8 cm−1 with H2 or O2 as a bath gas, a six-pass, 50.8 mm Herriott cell is used in the calibration experiments. The broadening parameters are measured in the pressure range of 300–650 Torr, while the Herriott cell is heated uniformly to temperatures of 460, 500, and 530 K, respectively. With the measured line broadening parameters of water in the bath gases of interest, the temperature and water concentration histories in the RCM runs are experimentally determined. In addition, the experimental results are compared with the simulations with detailed chemistry. Reasonable agreement is found, thereby demonstrating the utility of this mid-IR absorption spectroscopy in RCM experiments. The uncertainties of the associated measurements of temperature and water concentration are also discussed.
A new molecular spectroscopic database for high-temperature modeling of the spectra of molecules in the gas phase is described. This database, called HITEMP, is analogous to the HITRAN database but encompasses many more bands and transitions than HITRAN for the absorbers H2O, CO2, CO, NO, and OH. HITEMP provides users with a powerful tool for a great many applications: astrophysics, planetary and stellar atmospheres, industrial processes, surveillance, non-local thermodynamic equilibrium problems, and investigating molecular interactions, to name a few. The sources and implementation of the spectroscopic parameters incorporated into HITEMP are discussed.
A comprehensive analysis of laser-induced ignition of 1,3,5-trinitrohexahydro-s-triazine (RDX) monopropellant has been performed with consideration of detailed chemical kinetics. The model considers the transient development in the entire combustion zone, including the solid-phase, subsurface two-phase, and gas-phase regions. The formulation accommodates detailed chemical kinetics and transport phenomena in the gas phase, as well as thermal decomposition and subsequent reactions in the subsurface two-phase region. Thermodynamic phase transition and volumetric radiant energy absorption are also considered for completeness. The analysis is capable of treating the complete ignition process from surface pyrolysis to steady-state combustion, with the instantaneous burning rate and surface conditions treated as part of the solutions. Numerical experiments were conducted at atmospheric pressure in argon with CO2 laser heat flux from 35 to 600 W/cm2. Excellent agreement was obtained between the calculated and measured ignition delays. The propellant gasification rate increases with increasing laser intensity, which in turn shortens the ignition delay. The entire process can be divided into six stages: inert heating, thermal decomposition, occurrence of primary flame, preparation and formation of secondary flame and, finally, establishment of steady-state combustion. The major process in the primary flame is identified as the consumption of CH2O, HONO, NO2, H2CN, H2CNNO2, and HNO. In the secondary flame, the conversion of NO and HCN to N2, CO, H2O, and H2 is the key exothermic process causing ignition in the gas phase.
A diagnostic for microsecond time-resolved temperature measurements behind shock waves, using ultraviolet laser absorption of vibrationally hot carbon dioxide, is demonstrated. Continuous-wave laser radiation at 244 and 266 nm was employed to probe the spectrally smooth CO2 ultraviolet absorption, and an absorbance ratio technique was used to determine temperature. Measurements behind shock waves in both nonreacting and reacting (ignition) systems were made, and comparisons with isentropic and constant-volume calculations are reported.
- B Koroglu
- S S Vasu
B. Koroglu and S. S. Vasu, Int. J. Chem. Kinet. 48, 679 (2016).