Philip A. Martin

Phase-shift off-axis cavity-enhanced absorption detector of nitrogen dioxide

Phase-sensitive, off-axis cavity-enhanced absorption spectroscopy techniques with a rectangular pulse current modulated violet diode laser (~404 nm) were applied to measurement of nitrogen dioxide (NO2) in diluted standard mixture and laboratory air. An optical cell of an NO2 detector was bounded by two plano-concave mirrors with a diameter of 7.75 mm and a reflectivity of 0.999, separated by a distance of 43 cm. The phase shift measurements due to Rayleigh scattering extinction were used for calibration of the detector. NO2 sensitivities were extracted from synchronous measurements of either the cavity output light intensity or the phase shift induced by the cavity. NO2 noise equivalent detection limit (S/N = 1) of 1–2 ppbv was demonstrated for the intensity measurements with a lock-in amplifier time constant of 1 s. From the Allan plot of the intensity measurements the NO2 minimum concentration was estimated to be 0.24 ppbv in 80 s at atmospheric pressure.

In situ vehicle engine exhaust measurements of nitric oxide with a thermoelectrically cooled, cw DFB quantum cascade laser

This paper describes the application of a thermoelectrically cooled, continuous wave (cw), single mode distributed feedback (DFB) quantum cascade laser (QCL) to the real-time, in situ vehicle engine exhaust monitoring of nitric oxide. Experiments have been carried out on a static gasoline engine test bed where the engine operating conditions can be varied in a controlled manner. Results show the response of the nitric oxide concentration to engine conditions. The prospects for further multispecies in situ measurements are discussed.

Multispecies in situ monitoring of a static internal combustion engine by near-infrared diode laser sensors

A multispecies near-infrared diode laser spectrometer has been constructed for measurements of carbon monoxide, carbon dioxide, and methane directly in the exhaust of a static internal combustion engine. A wavelength modulation-division multiplexing scheme was implemented for the two distributed feedback diode lasers. Gas concentration variations were observed for changes in operating conditions such as increasing and decreasing the throttle, adjusting the air-fuel ratio, and engine start-up.

FTIR and QCL diagnostics of the decomposition of volatile organic compounds in an atmospheric pressure dielectric packed bed plasma reactor

Non-thermal atmospheric plasmas can be used to decompose toxic volatile organics. A dielectric packed bed plasma reactor was used to decompose dichloromethane (DCM) in a flowing gas mixture of nitrogen and oxygen. The effect of varying the oxygen concentration on the decomposition of dichloromethane was investigated. A comparison has been made of spectroscopic diagnostics based on FTIR (Fourier Transform Infrared) spectroscopy and infrared quantum cascade laser spectroscopy for the detection of nitric oxide produced in the plasma reactor.

The Production of Methane, Acetone, “Cold” CO and Oxygenated Species from Isopropyl Alcohol in a Non-Thermal Plasma: An In-Situ FTIR Study

This paper reports in situ Fourier transform infrared (FTIR) spectroscopic studies on the nonthermal plasma reaction of isopropyl alcohol in dinitrogen at Macor (a ceramic containing oxides of Al, Mg, and Si) and the analogous thermally driven process. While isopropyl alcohol did not react at the Macor at temperatures up to 600 °C, the study of the nonthermal plasma-driven process at the ceramic led to unexpected chemistry hitherto not observed, primarily the reaction of IPA in dinitrogen at short time scales to produce methane, HCN, acetone and cold CO at ca. 115 K. The CO, methane, and HCN rapidly established steady state concentrations, pointing to the need for faster FTIR studies: at longer times, isophorone and a polymethylacetylene-like polymer were formed as a brown oil. The observation of the steady-state gases and brown oil suggested parallel pathways in the plasma, the latter taking place at the plasma/catalyst interface, and the former in the plasma remote from the catalyst. Replacing dinitrogen with argon completely inhibited or negated the production of the oil, had no effect upon the processes taking place in the plasma remote from the Macor, and instead resulted in the production of acetylene.

2D Species Concentration Mapping of Thermal AP-CVD Reactors for Monitoring, Control and Design

This paper describes progress towards the two-dimensional mapping of chemical species in an atmospheric pressure chemical vapour deposition (AP-CVD) reactor during the deposition process. The approach uses tunable infrared laser absorption spectroscopy to measure line-of-sight optical absorbance data for specific chemical species. 2D distributions can then be obtained by tomographic inversion techniques. The developed techniques will have advantages for monitoring, control and design of reactors.

Naphthalene Decomposition by Dielectric Barrier Discharges at Atmospheric Pressure

Naphthalene decomposition in O₂/N₂ gas mixture with different O₂ concentrations has been studied in a dielectric barrier discharge reactor at atmospheric pressure. O₂ played an important role in the decomposition of naphthalene, especially in the selectivities of CO and CO₂. There was an optimal naphthalene decomposition rate at an O₂ concentration of about 3%. The CO_x selectivity increased up to 83.3% gradually with the O₂ concentration increasing from 1% to 20%. Nanoparticles were found in the gas samples, concentrations of which can be reduced greatly through raising the O₂ concentration. The decomposition byproducts of naphthalene were obviously different under different O₂ concentrations. Some nitrogenous compounds reduced but some oxygenous compounds increased with increasing O₂ concentration. The mechanism of naphthalene decomposition was proposed as that naphthalene was first initiated by dehydrogenation and oxidation, and then followed by deep oxidation to CO and CO₂.

Observations of Light Emission From the Surface of the Paraxial Diode Cathode Fielded on the Superswarf 5-MV Pulsed Power Accelerator

Light from the region around a cathode in a radiographic diode, used for the generation of X-rays, was imaged using a gated camera array. Optical images of the resulting plasma are presented in this paper.

The Production of Ketene and C 5 O 2 from CO 2 , N 2 and CH 4 in a Non-thermal Plasma Catalysed by Earth-Abundant Elements: An In-Situ FTIR Study

In situ Fourier Transform Infra Red spectroscopy was employed to study the plasma glow region of a non-thermal plasma between two Macor dielectrics and fed with CO2, CH4 and N2. CO, HCN and formaldehyde were produced and rapidly attained steady-state conditions. In addition, the chain oxides C5O2 and ketene were observed (the first time such species have been seen in the dry reforming of methane) and a liquid film was produced comprising multiple components, one of which was acetamide. The data were interpreted in terms of catalysis by the Macor dielectric and a wholly novel, multizone model in which the liquid film plays a direct and important role. The data obtained in the plasma experiments were compared to an analogous, thermal experiment. Importantly, the results from this work could have major implications across the fields of catalysis, synthesis and origin-of-life chemistry.