Elijah Jans

Progress in Development of a Chemical CO Laser Driven by a Chemical Reaction between Carbon Vapor and Oxygen

A chemical flow reactor is used to study the vibrational population distribution of CO produced by a reaction between carbon vapor generated in an arc discharge and molecular oxygen. The results demonstrate formation of highly vibrationally excited CO, up to vibrational level v=14, at low temperatures, T=400-450 K, with population inversions at v=4-7, in a collision-dominated environment, 15-20 Torr. The average vibrational energy per CO molecule formed by the reaction is 0.6-1.2 eV/molecule, which corresponds to 10-20% of the reaction enthalpy. The results show feasibility of development of a new CO chemical laser using carbon vapor and oxygen as reactants. A supersonic flow CO laser excited by a transverse RF discharge in the plenum is used to determine the effect of adding air species to the laser mixture. Carbon monoxide infrared emission spectra are used to measure CO vibrational level populations and temperature in subsonic CO-He, CO-He-N2, CO-He-O2, and CO-He-air flows excited by the discharge. Laser power and spectra generated in the transverse resonator in the M=3 supersonic flow are measured for each mixture. Nitrogen addition to the baseline CO-He mixture increases energy stored in the CO vibrational mode, resulting in a significant increase in laser power. Addition of oxygen had the opposite effect, reducing both CO vibrational populations and laser power. Adding air resulted in a modest increase of CO vibrational distribution, as well as an increase in laser power, although not as significant as when nitrogen was added to the flow. The results demonstrate feasibility of operating a supersonic flow CO laser in mixtures with significant amounts of air. 1 Graduate Research Assistant 2 Research Scientist 3 Professor Emeritus, Fellow AIAA 4 Professor, Fellow AIAA D ow nl oa de d by I go r A da m ov ic h on J an ua ry 1 4, 2 01 7 | h ttp :// ar c. ai aa .o rg | D O I: 1 0. 25 14 /6 .2 01 719 67 55th AIAA Aerospace Sciences Meeting 9 13 January 2017, Grapevine, Texas AIAA 2017-1967 Copyright

Scaling Up Generation of Vibrationally Excited CO in a Chemical Reaction between Carbon Vapor and Oxygen

Carbon products generated in a DC arc discharge with graphite electrodes sustained in argon buffer are characterized using time-resolved mass spectra measured by a Residual Gas Analyzer (RGA). The results show that atomic carbon vapor is one of the dominant vapor-phase components produced in the discharge. The yield of C atoms is much higher compared to that of C2 molecules. C3 signal exhibits essentially no dependence on the arc current and may be due to carbon particulates accumulated on the walls of the discharge cell from the previous runs. The yield of heavier carbon species (up to C17) is insignificant. However, the atomic carbon vapor yield is approximately two orders of magnitude lower than the net rate of carbon electrode consumption, indicating that carbon may be ablated from the electrodes as solid particulates. Carbon atoms produced in the arc discharge are used to generate highly vibrationally excited CO by a chemical reaction with molecular oxygen, added to the flow downstream of the discharge cell. Based on previous CO laser experiments, it is estimated that the rate of C atom production in the arc discharge needs to be scaled up by approximately three orders of magnitude, to achieve optical gain sufficient for laser power generation. To increase the high-temperature plasma volume up to several cm3, inductively coupled RF discharge is used. Fourier Transform Infrared (FTIR) emission spectroscopy was used to measure temperature in the Inductively Coupled Plasma (ICP) sustained in argon flow seeded with 2.5% CO. Temperatures up to T=2600 K were observed at a discharge power of 1 kW in the ICP. Micron-size carbon particles added to the argon flow using a custom-designed particle seeder are vaporized in the ICP discharge cell, and the products are injected into the main argon flow. Oxygen is injected into the main flow downstream of the ICP discharge cell. Vibrationally excited CO is formed by a chemical reaction between carbon vapor and oxygen in the main flow, at a relatively low temperature of T=400 K. CO vibrational levels up to v=6 are detected from FTIR emission spectra. Further experiments quantifying the yield of vibrationally excited CO are underway. 1 Graduate Research Assistant 2 Research Scientist 3 Undergraduate Research Assistant 4 Professor Emeritus, Fellow AIAA 5 Professor, Associate Fellow AIAA 1 D ow nl oa de d by I go r A da m ov ic h on J an ua ry 1 1, 2 01 8 | h ttp :// ar c. ai aa .o rg | D O I: 1 0. 25 14 /6 .2 01 801 79 2018 AIAA Aerospace Sciences Meeting 8–12 January 2018, Kissimmee, Florida 10.2514/6.2018-0179 Copyright

OH Radical Measurements in Hydrogen-Air Mixtures at the Conditions of Strong Vibrational Nonequilibrium

This work presents time-resolved, absolute measurements of OH number density, nitrogen vibrational temperature, and translational-rotational temperature in nitrogen, air, and lean hydrogen-air mixtures excited in a diffuse filament nanosecond pulse discharge, at a pressure of 100 Torr and high specific energy loading. The main objective of these measurements is to study a possible effect of nitrogen vibrational excitation on low-temperature kinetics of HO2 and OH radicals. N2 vibrational temperature and gas temperature in the discharge and the afterglow are measured by ns broadband Coherent Anti-Stokes Scattering (CARS). Hydroxyl radical number density is measured by Laser Induced Fluorescence (LIF) calibrated by Rayleigh scattering. The results show that the discharge generates strong vibrational nonequilibrium in nitrogen and air for delay times after the discharge pulse of up to ~ 1 ms, with peak vibrational temperature of Tv ≈ 2700 K at T ≈ 550 K (in nitrogen) and Tv ≈ 1900 K at T ≈ 650 K (in air). Nitrogen vibrational temperature in air peaks ≈ 200 μs after the discharge pulse, before decreasing due to vibrational-translational relaxation by O atoms (on the time scale of a few hundred μs) and diffusion (on ms time scale). OH number density increases gradually after the discharge pulse, peaking at t ~ 100-300 μs and decaying on a longer time scale, until t ~ 1 ms. Both OH rise time and decay time decrease as H2 fraction in the mixture is increased from 1% to 5%. OH number density in a 1% H2-air mixture peaks at approximately the same time as vibrational temperature in air. Since vibrational temperature and gas temperature in air and in a 1% H2-air mixture are expected to be close, this suggests that OH kinetics may be affected by N2 vibrational excitation. Additional CARS measurements in H2-air mixtures are necessary to verify this conjecture and obtain further insight. 1 Graduate Research Assistant 2 Research Scientist 3 Professor, Associate Fellow AIAA D ow nl oa de d by I go r A da m ov ic h on J an ua ry 1 4, 2 01 7 | h ttp :// ar c. ai aa .o rg | D O I: 1 0. 25 14 /6 .2 01 715 84 55th AIAA Aerospace Sciences Meeting 9 13 January 2017, Grapevine, Texas AIAA 2017-1584 Copyright

Experimental and Kinetic Modeling Studies of Novel Carbon Monoxide Gas Lasers 1

A chemical flow reactor has been used to study the vibrational population distribution of carbon monoxide produced by a reaction between vapor-phase carbon generated in an arc discharge and oxygen, to determine feasibility of extracting the chemical energy released from this reaction by laser radiation. Additionally, a supersonic flow, electric discharge excited CO laser has been developed and characterized over a range of operating conditions. The same supersonic laser apparatus can be adapted to produce population inversion via oxidation of vapor-phase carbon, generating vibrationally excited CO. Resultant laser power and spectra are compared with the predictions of a kinetic model of a supersonic flow CO laser.