Rjh Robert Klein-Douwel

Nitric oxide flow tagging in unseeded air

A scheme for molecular tagging velocimetry is presented that can be used in air flows without any kind of seeding. The method is based on the local and instantaneous creation of nitric oxide (NO) molecules from N(2) and O(2) in the waist region of a focused ArF excimer laser beam. This NO distribution is advected by the flow and can be visualized any time later by laser-induced fluorescence in the gamma bands. The creation of NO is confirmed by use of an excitation spectrum. Two examples of the application of the new scheme for air-flow velocimetry are given in which single laser pulses are used for creation and visualization of NO.

Two‐dimensional distributions of C2, CH, and OH in a diamond depositing oxyacetylene flame measured by laser induced fluorescence

Two‐dimensional laser induced fluorescence measurements are applied to the chemical vapor deposition of diamond by an oxyacetylene flame. The fluorescence distributions of C2, CH, and OH are measured for various deposition conditions. The influence of the temperature of the molybdenum substrate and the distance between the substrate and the flame front on the two‐dimensional distributions and on the quality and morphology of the deposited diamond is investigated. A relation is observed between the C2 distribution in the flame and the local growth rate and quality of the diamond layer, therefore C2 is thought to be an important species for diamond growth. The exact role of CH as a growth species is less clear; OH seems to be of minor importance. All measurements are performed during diamond deposition.

Air photolysis and recombination tracking: A new molecular tagging velocimetry scheme

A new scheme for molecular tagging velocimetry in unseeded airflows is presented. The method, called air photolysis and recombination tracking, is based on the photoinduced formation of nitric oxide (NO) in the waist region of a focused ArF excimer laser beam. The distribution of the formed NO molecules is imaged by planar laser-induced fluorescence in the gamma band, using a frequency-doubled dye laser beam. The role of N-2(+) ions in the NO formation process is discussed, and the lifetime of the NO molecules was determined to be at least 10 ms. The new method has been applied to a laminar and a pulsed airflow and a premixed methane/air flame. Velocities could be determined with an accuracy of 5% in the airflows (on a single-shot basis) and 13% in the flame. By the use of averaging over many laser pulses, velocities as low as 1 cm/s could be measured.

Laser-induced-fluorescence imaging of NO in an n-heptane- and diesel-fuel-driven diesel engine

Continuous on-line imaging by 2D-LIF techniques of in-cylinder NO distributions in a running Diesel engine is explored using an ArF-excimer laser at 193 nm operating at low power. For the first time NO excitation spectra could be measured as a result of high optical transparencies during measurements over longer periods of time. The averaged distributions show different combustion behaviour of both fuels proving the potential of the 2D-LIF technique in application to non-intrusive combustion diagnostics in a steady running Diesel engine.

Laser-induced fluorescence of formaldehyde hot bands in flames.

Laser-induced fluorescence and excitation spectra of formaldehyde in the A-X 4(1)(0) band at 370 nm are recorded in the primary flame front of a Bunsen flame. An examination of partition functions shows that this excitation can minimize temperature bias for formaldehyde in situ diagnostic measurements.

Laser-induced fluorescence imaging in a 100 kW natural gas flame

A tunable excimer laser at 248 nm (KrF) and 193 nm (ArF) has been used to monitor two-dimensional OH and NO distributions in the turbulent flame of a 100 kW natural gas burner. Spatially resolved fluorescence (spatial resolution better than 1.0 mm) from a 20 cm×20 cm area is collected under single shot conditions. We describe the problems encountered when laser-induced fluorescence imaging techniques are applied to large scale flames. Special experimental arrangements, imposed by the turbulent behavior of the flame we used, are also described.

Spatial distributions of atomic hydrogen and C2 in an oxyacetylene flame in relation to diamond growth

Two-dimensional laser induced fluorescence measurements are applied to the chemical vapour deposition of diamond by an oxyacetylene flame to visualize the distributions of atomic hydrogen and C2 in the gas phase during diamond growth. Experiments are carried out in both laminar and turbulent flames and reveal that atomic hydrogen is ubiquitous at and beyond the flame front. Its presence extends to well outside the diamond deposition region, whereas the C2 distribution is limited to the flame front and the acetylene feather. The diamond layers obtained are characterized by optical as well as scanning electron microscopy and Raman spectroscopy. Clear relations are observed between the local variations in growth rate and quality of the diamond layer and the distribution of H and C2 in the boundary layer just above the substrate. These relations agree with theoretical models describing their importance in (flame) deposition processes of diamond. Three separate regions can be discerned in the flame and the dia...

CN distribution in flame deposition of diamond and its relation to the growth rate, morphology, and nitrogen incorporation of the diamond layer

Abstract Two-dimensional laser-induced fluorescence (2D-LIF) measurements are applied to the chemical vapour deposition (CVD) of diamond by an oxyacetylene flame to visualize the distribution of CN in the gas phase during the diamond growth process. The obtained diamond deposits are characterized by optical as well as scanning electron microscopy (SEM) and cathodoluminescence topography (CL). Experiments are carried out in both laminar and turbulent flames and show CN to be present mostly at the outer edge of the flame, where ambient air interacts with flame gases. Clear relations are observed between the distribution of CN and the local variation of the growth rate, the morphology, and the nitrogen incorporation as identified by CL in the deposited diamond layer. The observed differences between the laminar and turbulent flame can be attributed to enhanced diffusion of nitrogen into the latter. Significant differences are found between the results of experiments performed with acetylene gas bottles from two different suppliers.

Spatial distributions of H, CN, and C2 in a diamond-growing oxyacetylene flame

Two-dimensional laser-induced fluorescence (2D-LIF) measurements are applied to the chemical vapor deposition (CVD) of diamond by an oxyacetylene flame to visualize the distributions of atomic hydrogen, C2, and CN in the gas phase during diamond growth. Experiments are carried out in laminar flames and reveal that atomic hydrogen is ubiquitous at and beyond the flame front. Its presence extends to well outside the diamond deposition region, whereas the C2 distribution is limited to the flame front and the acetylene feather. CN is found to be present mostly at the outer edge of the flame, where ambient air interacts with flame gases. The diamond layers obtained are characterized by optical as well as scanning electron microscopy (SEM) and cathodoluminescence topography (CL). Clear relations are observed between the local variations in growth rate of the diamond layer and the distribution of H, C2, and CN in the boundary layer just above the substrate. Further relations between CN and the morphology and the nitrogen incorporation as identified by CL of the deposited diamond layer are found as well. These relations agree with theoretical models describing the importance of the mentioned species in (flame) deposition processes of diamond. Three separate regions can be discerned in the flame and the diamond layer, where the gas phase and diamond growth are predominantly governed by the flame source gases, the ambient atmosphere, and the interaction of both, respectively.

Laser diagnostics in flame deposition of diamond

Combustion diagnostics by means of 2D Laser Induced Fluorescence (2D-LIF) is applied to a diamond depositing oxyacetylene flame. The method and results of diamond growth are discussed, as well as the 2D-LIF technique. The distributions of atomic hydrogen, CN, and C2 in the flame are presented together with their relations to diamond growth.