PURE-ROTATIONAL RAMAN AND ELECTRONIC-RAMAN SPECTRUM OF NITRIC OXIDE

Nitric Oxide (NO) is a combustion pollutant known for its role in the formation of photochemical smog. Nitric oxide is also interesting from the viewpoint of fundamental spectroscopy since it has two closely spaced ground electronic states. Consequently, in addition to pure-rotational Raman spectrum, NO also exhibits electronic-Raman spectrum near 120 cm$^{-1}$. We applied a dual-pump combined CARS system (DPCCS) to investigate the spectrum of NO. In a DPCCS, in contrast to a typical pure-rotational CARS system, all beams have different wavelengths. This allows us to preferentially suppress Q or S branch Raman transitions and investigate the polarization character of a target molecule, in this case NO. Theoretical spectrum of NO was calculated by solving the time-dependent Schrodinger wave equation using perturbation theory. By comparing the measured and the computed spectrum we obtain the anisotropy of the polarizability tensor of NO as well as a quantitative estimate of the strength of electronic-Raman transitions. The figure in this abstract shows comparison between CARS data and calculated NO spectrum with no preferential suppression of either the Q or S branch Raman transitions. Notice the spin-splitting of the 2 $\Pi$$_{1/2}$ and 2 $\Pi$$_{3/2}$ states of NO, evident, near a Raman shift of 80 cm$^{-1}$. \begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.22]{NO Spectrum.eps} \end{wrapfigure

DEVELOPMENT OF COMBINED DUAL-PUMP VIBRATIONAL AND PURE-ROTATIONAL COHERENT ANTI-STOKES RAMAN SCATTERING TECHNIQUE.

Coherent anti-Stokes Raman scattering is a parametric, four-wave mixing process. CARS, as a diagnostic technique, has been used extensively for obtaining accurate temperature and species concentration information in non-reacting and reacting flows. Dual-pump vibrational CARS (DPVCARS) can provide quantitative temperature and concentration information on multiple species in the probe volume. Mole-fraction information on molecules such as N$_{2}$, O$_{2}$, H$_{2}$ and CO$_{2}$ have been obtained in flames with peak temperature in excess of 2000 K. Although DPVCARS provides high accuracy at higher temperatures it has low sensitivity at lower temperatures (below 800 K). Typically, pure-rotational CARS (PRCARS) provides excellent sensitivity and precision at lower temperatures. We have combined DPVCARS and two-beam PRCARS into a single system which employs three laser beams at different wavelengths. The accuracy and precision of the new combined CARS system has been characterized in laminar flames. The system�s single-shot precision is better than 5.5 % between 295-2200 K, indicating its suitability for diagnostics in turbulent flames. The new system has been applied towards understanding flame structure of CH$_{4}$/H$_{2}$/air laminar flames, stabilized in a counter-flow burner. Here, we present results detailing the development and application of the new combined CARS technique

APPLICATION OF COHERENT ANTI-STOKES RAMAN SCATTERING THERMOMETRY IN TURBULENT AND LAMINAR FLAMES

Coherent anti-Stokes Raman scattering (CARS) is a non-linear spectroscopic combustion diagnostic technique used for measurement of temperature and species concentration. Broadband CARS spectra can be acquired with a single laser shot with high spatial and temporal resolution. We present two distinct applications of a nanosecond dual-pump vibrational CARS system. The first experiment aimed to study the effect of simulated exhaust-gas-recirculation, via addition of \chem{CO_2} to the fuel stream, on the flame structure of lean \chem{CH_4}-air pilot-assisted turbulent premixed flames. For this experiment over 20,000 single-shot spectra were acquired and spectrally fitted to develop a detailed temperature map of the flame flow-field. In the second experiment, laminar flames with varying soot loading were stabilized over a “Yale burner”. This burner, in the combustion community, is a canonical system for the development of soot models. The principal challenge in this experiment was obtaining a CARS signal with an adequate signal to noise ratio in the presence of strong soot-emission background. Our measurements in both experiments will serve as benchmark data for the development of combustion computational models

Development of Combined Dual-Pump Vibrational and Pure-Rotational Coherent Anti-Stokes Raman Scattering (DPVCARS and PRCARS) System

Coherent anti-Stokes Raman scattering (CARS) [1,2] is a spatially-resolved, time-resolved spectroscopic technique for quantitative measurements in reacting flows [3 – 6]. This work demonstrates a combination of N2/O2/CO2 dual-pump vibrational coherent anti-Stokes Raman scattering (DPVCARS) system and two-beam pure-rotational coherent anti-Stokes Raman scattering (PRCARS) system. It is based on the previous development of combined VCARS and PRCARS system which was used to obtain temperature measurements in non-premixed H2-air flames. The new combined system will be used to measure the temperature profiles and major species concentrations such as N2/O2/CO2 in laminar counter-flow non-premixed (CH4/Air) and partially-premixed (CH4/H2/Air) flames. The new system is being characterized in H2/Air diffusion flames stabilized over a Hencken burner. CO2 will be added to the oxidizer stream for the system to assess the precision of the system while performing concentration measurements. The new combined system has shown good precision temperature using PRCARS (better than 3%) and N2/O2 mole-fraction ratio (better than 5%) using DPVCARS

Two-Color Polarization Spectroscopy Measurement of Nitric Oxide

Nitric Oxide (NO) is a greenhouse gas that contributes to smog and acid rain. Commercial combustion engines and turbines are significant sources of NO emission. Two-color Polarization Spectroscopy (PS) will be used to measure the collision-induced resonances of NO in gas mixtures. The effect of collision partners, such as He and Ar, on the line-shape of NO molecule will be studied. This experiment requires the use of two dye laser systems to generate 226nm beam from frequency mixing of 355nm and 622nm. This enhanced the scan range and improved the ease of operation. One dye laser will be used to generate circularly polarized pump beam, which will be tuned to excite the transitions across the X-A (0,0) band of NO. Another dye laser will be used to generate linearly polarized 226nm probe beam, which will be used to probe the transitions. A photomultiplier tube will be used to collect the polarization signal. Nitrogen will be mixed with the NO gas mixtures to measure the sensitivity of this technique. In the current stage of the project, the pump beam is aligned and its wavelength is controlled by a LabVIEW programmed motor. Laser induced fluorescence data was collected to calibrate the scanning frequency with NO’s excitation frequency. The excitation spectrum of NO from this specific pump-probe transition pair will help us understand the fundamental collision dynamics of NO and create a more quantitative technique of NO concentration measurement

Thermoacoustic Instability Suppression and Heat-Release Forcing of a Laminar Flame Using Ionic Wind

Advancements in combustion technologies are often impeded by complex combustion dynamics. Active control has proven effective at mitigating these dynamics in the lab, but mass adoption requires more affordable, lightweight, and reliable actuators. Here, a new actuator concept is presented which utilizes sub-breakdown electric fields, the inherent plasma nature of flames, and the electrohydrodynamic effect to create flame stabilization points. These electrically controlled stabilization points allow variable distortion of a laminar flame and bidirectional forcing of the flame heat release. The electric field-based actuator is combined with a simple feedback controller to demonstrate suppression of a thermoacoustic instability. The instability sound pressure level was reduced by 27 dB and in less than 60 ms upon enabling the controller. The use of a sub breakdown electric field requires a mere 40 mW to stabilize a 3.4 kW thermal power flame. The absence of any moving parts and low electrical power required make this a promising actuator concept for many combustion applications.Comment: Supplementary Videos here: https://dustincruise.com/flame-videos

Preliminary Development of a Nearly-Instantaneous Three- Dimensional Imaging Technique for High-Speed Flow Fields

Recent advances in high-repetition rate laser and camera technology present a new opportunity to develop three-dimensional diagnostics for high-speed flows. The design of a three-dimensional imaging system based on a pulse burst laser, a high-speed laser scanner and a high speed camera is described here. The pulse burst laser system is the 5 th of its kind in the world and can produce high energy pulses at up to 10 MHz repetition rates. A highspeed optical deflector, such as a rotating mirror or acousto-optic deflector, can be used to rapidly deflect a laser sheet through the flow field. A high-speed camera can then be used to collect images at different planes in the flow field, from which a three-dimensional image can be reconstructed. The state-of-the-art of these technologies are described. The high-speed characteristics of an acousto-optic deflector were tested using an Nd:YAG laser where it was found that a full sweep through at least 32 resolvable spots could be completed in 10 μsec. Future work will include testing of a galvanometric scanning mirror and assembly of a complete system

Dual-Band Quasi-Coherent Radiative Thermal Source

Thermal radiation from an unpatterned object is similar to that of a gray body. The thermal emission is insensitive to polarization, shows only Lambertian angular dependence, and is well modeled as the product of the blackbody distribution and a scalar emissivity over large frequency bands. Here, we design, fabricate and experimentally characterize the spectral, polarization, angular and temperature dependence of a microstructured SiC dual band thermal infrared source, achieving independent control of the frequency and polarization of thermal radiation in two spectral bands. The measured emission of the device in the Reststrahlen band (10.3-12.7 um) selectively approaches that of a blackbody, peaking at an emissivity of 0.85 at Lx=11.75 um and 0.81 at Ly=12.25 um. This effect arises due to the thermally excited phonon polaritons in silicon carbide. The control of thermal emission properties exhibited by the design is well suited for applications requiring infrared sources, gas or temperature sensors and nanoscale heat transfer. Our work paves the way for future silicon carbide based thermal metasurfaces.Comment: Journal of Quantitative Spectroscopy & Radiative Transfer (2018

Fluid Flow Thermometry Using Thermographic Phosphors

Phosphor thermometry is a non-intrusive thermometry technique that allows for spatially and temporally resolved surface temperature measurements. The thermographic method has been employed in a number of applications that include combustion, sprays, and gas flows. In the current work, we investigate the implementation of thermographic phosphors in liquid flows, which is of interest in a wide range of applications in heat transfer, fluid mechanics, and thermal systems. Zinc oxide doped with Zinc (ZnO:Zn) was the phosphor employed for experimentation due to its high emission intensity and insolubility. In order to explore this application, the phosphor powder was uniformly dispersed in water using a magnetic stirring rod. The phosphor was excited by the third harmonic 355 nm output of a Nd:YAG laser, and the luminescence was examined using a fiber-coupled spectrometer. Analysis of the spectral data showed a significant redshift as the temperature approached boiling point. Further characterization of effects of temperature and experimental parameters such as ZnO:Zn concentration on the luminescence signal was performed

Healthcare Seeking Behaviour of Hospitalised COVID-19 Patients During Second Wave in Tertiary Care Hospital of Northern India

Background: The Coronavirus Disease (COVID-19) pandemic continues its deadly reign all over the world. Devising effective strategies for detecting and controlling the infection has become ever more critical. Effective prevention and control of the pandemic is entirely dependent on human behavior in terms of practicing preventive and curative measures. During the second wave of COVID-19, people’s perceptions of preventive and curative measures changed. Objective: To study healthcare-seeking behavior of hospitalized COVID-19 patients. Methods: Hospitalized patients due to COVID-19 in the month of March, April and May of 2021 were included in the study. Their attendants/close relatives were contacted telephonically to know about the admitted patients’ healthcare-seeking behavior. Verbal consent was taken from attendants before the commencement of the interview, followed by informing them about the purpose of the interview. Results: Amongst the subjects, there were more males than females (67.5 vs 32.4%), age ranged between 18 to 88 with a mean value of 56.61 ± 14.7 years. Self-medication was significantly associated with study subjects’ mortality (p=0.03). Conclusion: Elderly people were having higher mortality rate than their younger counterparts. People were hesitant to visit primary care physicians after having symptoms of COVID-19