Concentration measurement of injected gaseous fuel using quantitative schlieren and optical tomography

Abstract

In this paper, the quantitative schlieren method is extended to measure the concentration field of an injected gaseous fuel along several planes perpendicular to the jet axis. Background Oriented Schlieren (BOS) is used as a quantitative flow field concentration measurement based on the deflection made by features in the background pattern. The flow field which is located between the camera and the background pattern changes the intensity value of the background points in the transfer medium. The optical flow algorithm, which is used to measure the deflection vectors in the background due to the change in index of refraction, is modified to consider the change in intensity of the background image due to the flow field. Optical tomography is used as a tool to extract the index of refraction of the gaseous field. Mole fraction values at different planes perpendicular to the jet axis are obtained and displayed.

Background-oriented schlieren (BOS) techniques

“…Challenging wind tunnel applications under cryogenic conditions have been reported by Germain and Quest (2005), Loose et al (2006), andFey et al (2010). Combustion research can take advantage of the ability of BOS to visualize and measure heat plumes and flames (Iffa et al 2011), but also to determine concentration levels of different fuel sprays (Bang and Lee 2013; Lee et al 2011Lee et al , 2013Tillmann et al 2014) or gas jets as performed by Iffa et al (2010), Ducasse et al (2010) and Veser et al (2011).…”

Optimal Filter Estimation for Lucas-Kanade Optical Flow

“…The same approach of combining the spatio-temporal filters of Baron and Simoncelli and optimal in the aim of reducing the motion estimation error is presented by Elad et al in [ 11 ]. In order to measure the concentration field of an injected gaseous fuel, Iffa et al [ 12 ] employ a pyramidal Lucas-Kanade flow determination in conjunction with a 5 × 5 kernel Gaussian filter.…”

Temperature and velocity measurements in a fluid layer using background-oriented schlieren and PIV methods

“…The technique consists of recording a background image as a reference and detection of the distortions in the measurement medium relative to the reference image [1,9]. The changes in the refractive index of the medium are caused by the density changes from pressure, temperature or concentration gradients [2,11,12], which result in shifts on the recorded image [9]. So far, the BOS method has been successfully used to estimate the density fields of different flow types, such as shockwaves, wake behind a cylinder and blade tip vortices of a helicopter [3,4,[6][7][8], as well as temperature measurements of an erupting thermal plume with mK precision [13].…”

“…Similar to the schlieren method, BOS is capable of measuring two in-plane, first-order gradients parallel to the background target and the image sensor, which are integrated along the line of sight [2,3,14,17]. Additional procedures can be followed to measure the gradients in the normal direction of the plane [3,12,14,17]. Besides providing quantitative measurements, the other advantages of BOS can be summarized as: the straightforward computation, no restriction on the measurement object size, reduced number of optical elements and simpler adjustment compared to traditional schlieren technique [2,4,9].…”