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Title: Miniature rainbow schlieren deflectometry system for quantitative measurements in microjets and flames

Abstract

Recent interest in small-scale flow devices has created the need for miniature instruments capable of measuring scalar flow properties with high spatial resolution. We present a miniature rainbow schlieren deflectometry system to nonintrusively obtain quantitative species concentration and temperature data across the whole field. The optical layout of the miniature system is similar to that of a macroscale system, although the field of view is smaller by an order of magnitude. Employing achromatic lenses and a CCD array together with a camera lens and extension tubes, we achieved spatial resolution down to 4 {mu}m. Quantitative measurements required a careful evaluation of the optical components. The capability of the system is demonstrated by obtaining concentration measurements in a helium microjet (diameter, d=650 {mu}m) and temperature and concentration measurements in a hydrogen jet diffusion flame from a microinjector(d=50 {mu}m). Further, the flow field of underexpanded nitrogen jets is visualized to reveal details of the shock structures existing downstream of the jet exit.

Authors:
; ; ;
Publication Date:
OSTI Identifier:
20929734
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Optics; Journal Volume: 46; Journal Issue: 15; Other Information: DOI: 10.1364/AO.46.002954; (c) 2007 Optical Society of America; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CAMERAS; CHARGE-COUPLED DEVICES; COMBUSTION; EQUIPMENT; EVALUATION; FLAMES; HELIUM; HYDROGEN; LENSES; MEASURING METHODS; NITROGEN; SPATIAL RESOLUTION; TEMPERATURE MEASUREMENT

Citation Formats

Satti, Rajani P., Kolhe, Pankaj S., Olcmen, Semih, and Agrawal, Ajay K. Miniature rainbow schlieren deflectometry system for quantitative measurements in microjets and flames. United States: N. p., 2007. Web. doi:10.1364/AO.46.002954.
Satti, Rajani P., Kolhe, Pankaj S., Olcmen, Semih, & Agrawal, Ajay K. Miniature rainbow schlieren deflectometry system for quantitative measurements in microjets and flames. United States. doi:10.1364/AO.46.002954.
Satti, Rajani P., Kolhe, Pankaj S., Olcmen, Semih, and Agrawal, Ajay K. Sun . "Miniature rainbow schlieren deflectometry system for quantitative measurements in microjets and flames". United States. doi:10.1364/AO.46.002954.
@article{osti_20929734,
title = {Miniature rainbow schlieren deflectometry system for quantitative measurements in microjets and flames},
author = {Satti, Rajani P. and Kolhe, Pankaj S. and Olcmen, Semih and Agrawal, Ajay K},
abstractNote = {Recent interest in small-scale flow devices has created the need for miniature instruments capable of measuring scalar flow properties with high spatial resolution. We present a miniature rainbow schlieren deflectometry system to nonintrusively obtain quantitative species concentration and temperature data across the whole field. The optical layout of the miniature system is similar to that of a macroscale system, although the field of view is smaller by an order of magnitude. Employing achromatic lenses and a CCD array together with a camera lens and extension tubes, we achieved spatial resolution down to 4 {mu}m. Quantitative measurements required a careful evaluation of the optical components. The capability of the system is demonstrated by obtaining concentration measurements in a helium microjet (diameter, d=650 {mu}m) and temperature and concentration measurements in a hydrogen jet diffusion flame from a microinjector(d=50 {mu}m). Further, the flow field of underexpanded nitrogen jets is visualized to reveal details of the shock structures existing downstream of the jet exit.},
doi = {10.1364/AO.46.002954},
journal = {Applied Optics},
number = 15,
volume = 46,
place = {United States},
year = {Sun May 20 00:00:00 EDT 2007},
month = {Sun May 20 00:00:00 EDT 2007}
}
  • The rainbow schlieren deflectometry (RSD) technique is used to determine the liquid boundary and the fuel volume fraction distributions in the vapor region of a high-pressure fuel spray. Experiments were conducted in a constant pressure flow vessel, whereby a customized single-hole common-rail diesel injector is used to introduce n-heptane fuel into a coflow of low-speed ambient air at two different test conditions. Only the quasi-steady period of the fuel spray is considered, and multiple injections are performed to acquire statistically significant data at an image acquisition rate of 20 kHz. An algorithm to identify the liquid boundary using intensity recordedmore » by the RSD images is presented. The results are compared against measurements obtained by the Mie scattering technique. Our results demonstrate that the RSD can be a powerful optical diagnostics technique to simultaneously quantify both the vapor and liquid regions in the high-pressure fuel sprays.« less
  • We present the results of an implementation of a refractive diagnostic to study fast dynamics in capillary discharges. It consists of a moire-schlieren deflectometry technique that provides a quantitative analysis of the refractive index gradients. The technique is composed of an angular deflection mapping system (moire deflectometry) and a spatial Fourier filter (schlieren). Temporal resolution of 12 ps, 50 {mu}m of spatial resolution and minimum detectable gradient of ({nabla}n{sub e}){sub min}=6x10{sup 18}cm{sup -4} were obtained. With these parameters, a large aspect ratio capillary discharge of 15 ns half period current was studied; the diagnostic was implemented axially along the aluminamore » tube of 1.6 mm inner diameter and 21 mm length. The detectable electron density for these conditions was 1x10{sup 17}cm{sup -3}. From the interpretation of the fringe displacement, we are able to measure the velocity of the radial compression wave and the compression ratio due to the Lorentz force. On axis, electron densities of the order of 5x10{sup 17}cm{sup -3} were obtained at the time of maximum soft x-ray emission.« less
  • The heat convection generated by micro filaments of a self-organized non-thermal atmospheric pressure plasma jet in Ar is characterized by employing laser schlieren deflectometry (LSD). It is demonstrated as a proof of principle, that the spatial and temporal changes of the refractive index n in the optical beam path related to the neutral gas temperature of the plasma jet can be monitored and evaluated simultaneously. The refraction of a laser beam in a high gradient field of n(r) with cylindrical symmetry is given for a general real refraction index profile. However, the usually applied Abel approach represents an ill-posed problemmore » and in particular for this plasma configuration. A simple analytical model is proposed in order to minimize the statistical error. Based on that, the temperature profile, specifically the absolute temperature in the filament core, the FWHM, and the frequencies of the collective filament dynamics are obtained for non-stationary conditions. For a gas temperature of 700 K inside the filament, the presented model predicts maximum deflection angles of the laser beam of 0.3 mrad which is in accordance to the experimental results obtained with LSD. Furthermore, the experimentally obtained FWHM of the temperature profile produced by the filament at the end of capillary is (1.5 {+-} 0.2) mm, which is about 10 times wider than the visual radius of the filament. The obtained maximum temperature in the effluent is (450 {+-} 30) K and is in consistence with results of other techniques. The study demonstrates that LSD represents a useful low-cost method for monitoring the spatiotemporal behaviour of microdischarges and allows to uncover their dynamic characteristics, e.g., the temperature profile even for challenging diagnostic conditions such as moving thin discharge filaments. The method is not restricted to the miniaturized and self-organized plasma studied here. Instead, it can be readily applied to other configurations that produce measurable gradients of refractive index by local gas heating and opens new diagnostics prospects particularly for microplasmas.« less
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