Mixing enhancement in a lobed injector

Abstract

A study on a lobed jet mixing flow by using stereoscopic particle image velocimetry technique An experimental investigation of the non-reactive mixing processes associated with a lobed fuel injector in a coflowing air stream is presented. The lobed fuel injector is a device which generates streamwise vorticity, producing high strain rates which can enhance the mixing of reactants while delaying ignition in a controlled manner. The lobed injectors examined in the present study consist of two corrugated plates between which a fuel surrogate, CO 2 , is injected into coflowing air. Acetone is seeded in the CO 2 supply as a fuel marker. Comparison of two alternative lobed injector geometries is made with a straight fuel injector to determine net differences in mixing and strain fields due to streamwise vorticity generation. Planar laser-induced fluorescence ͑PLIF͒ of the seeded acetone yields two-dimensional images of the scalar concentration field at various downstream locations, from which local mixing and scalar dissipation rates are computed. It is found that the lobed injector geometry can enhance molecular mixing and create a highly strained flowfield, and that the strain rates generated by scalar energy dissipation can potentially delay ignition in a reacting flowfield.

Numerical simulations of a lobed fuel injector

“…In these experiments, acetone-seeded CO 2 is used as the fuel surrogate, and PLIF images of the mixture fraction of CO 2 for different flow conditions and at different locations downstream of the injectors' exit planes are obtained. 16 Calculations were first performed for each lobed injector geometry to obtain the magnitude of the circulation ⌫ produced by the injector over a half wavelength. The circulation ⌫, scaled by and W, can be shown to be only a function of y m / and tan ␣ by careful examination of the governing equations.…”

“…The lobed injector flow field ͑Fig. 1͒ has been demonstrated in recent experiments at UCLA to have the potential to improve molecular fuel-air mixing over that for a nonlobed injector 16 as well as to have the potential for reducing NO x emissions. 17 The mixing experiments in particular are able to demonstrate the evolution of the flow field and the degree of local and global mixing as well as the rate of scalar energy dissipation ͑related to local strain rate͒ through detailed planar laser-induced fluorescence ͑PLIF͒ imaging.…”

“…In the present application, since vorticity and fuel are by nature initially confined to specific regions of the flow ͑along the injector lobes͒, the scalar transport method is highly suitable for tracing the evolution of the injectant, replicating the type of study done in the associated gas phase PLIF experiments. 16 …”

Jet impingement heat transfer from lobed nozzles

“…Many studies have been conducted to enhance mixing, such as the works of Tilman and Presz [23], Power et al [24], Presz et al [25], Hu et al [26] or Smith et al [27]. Research into the physics of mixing within these devices has been the subject of numerous works.…”

An extended Reynolds analogy for excited wavy instabilities of developing streamwise vortices with applications to scalar mixing intensification

“…Lobed injectors and secondary flows in combustion systems are also found useful (Schadow et al 1989;Swithenbank et al 1989). The control of the sequence of mixing and combustion in order to lower pollutant levels from air-breathing engines has been steadily advanced by Smith et al (1997), Strictland et al (1998), Majamaki et al (2003) and Mitchell et al (2004). In certain vortex generation techniques, it is possible to estimate the relatively large penalty due to drag of the vortex generators relative to the benefit attained: a doubling of heat transfer enhancement ratio could incur a quadrupling of the drag penalty ratio (e.g.…”