Experimental Investigation of Performance of an Air Blast Atomizer by Planar Laser Sheet Imaging Technique

Abstract

It is widely recognized that the fuel-air mixing process is a critical factor in improving combustion efficiency and in minimizing pollutants such as NOx. Enhancement of fuel-air mixing can lead to lower pollutant emissions and greater efficiency. However, swirl-ing flows in lean combustors play the role of fuel-air mixing and flame stability. The complex fluid dynamic phenomena encountered in swirling two-phase flow contribute to the difficulty in complete understanding of the different processes occurring in combus-tors. Fortunately, optical and laser-based visualization techniques available in our lab are important nonintrusive tools for visualizing flow process, especially for fuel injection and fuel-air mixing. To provide for a better understanding of effects of counter-rotating flow on droplets in atomization process, this study is a detailed characterization of the spray generated by an airblast atomizer by planar laser sheet imaging method. Optical facility for spray diagnostics with fuel planar laser induced fluorescence (fuel-PLIF) method for fuel distribution and particle image velocimetry (PIV) method for the velocity of droplets is used to evaluate the performance of an airblast atomizer. The results show that the performance of secondary atomization is influenced by swirling flow and pri-mary atomization simultaneously; the swirling flow exhibits significant influence on the droplet size and space distribution relative to that of primary atomization. The primary swirling air reopens the spray cone generated by pressure-swirl atomizer, and the sec-ondary swirling air affects the fuel distribution by forming the recirculation zone. The results provide critical information for the design and development of combustion chambers. [DOI: 10.1115/1.4025235

Planar liquid volume fraction and SMD distribution of Jatropha vegetable oil spray: effect of ethanol blending and GLR

“…The spray cone angle reduced from 63 at GLR 3 to 56 at GLR 5. This may be due to the increase in the axial velocity of the atomizing air with the increase in GLR [37]. The spray cone angles of the blended fuels are similar to those of SVO, showing a negligible effect of ethanol addition.…”

Experimental and numerical study of the effect of main stage stratifier length on lean blow-out performance for a stratified partially premixed injector

“…For both the PIV and kerosene-PLIF measurements, the laser sheet was placed through the center of the combustor with the recording CCD camera placed normal to this plane. More details about the optic system can be found in Liu et al 19 The RP-3 kerosene is used both in the spray and combustion experiments. For the PIV measurements, the air is seeded with TiO 2 particles, which are nominally 3-5 mm in diameter and about 4.2 g/cm 3 in density.…”

Improvement on ignition and lean blowout performances of a piloted lean-burn combustor

“…The f/a of ignition limit for both pilot fuel nozzles decrease with the increase of reference velocity of combustor (Figure 17(a)), and kept constant after a fixed reference velocity (about 7.5 m/s for nozzle #1 and 4.5 m/s for nozzle #2), indicating that the dependence of ignition performance on the velocity of swirling air decreases for the new designed pilot fuel nozzle. As the velocity of swirling air are the key factor in determining the droplet size and spray pattern for the airblast atomizer with venturi prefilmer, 14 the spray performance of the pilot injector of nozzle #2 is better than that of nozzle #1, even at relative low reference velocity. At reference velocity of 4.5 m/s, the f/a of ignition limit decreases from 0.02 of nozzle #1 to 0.013 of nozzle #2.…”

“…The pilot stage of the lean-burn injector is a typical swirl cup design which uses a pressure swirl atomizer with two coaxial, counter-rotating swirlers to atomize the fuel. The spray of swirl cup have been studied by many researchers, [10][11][12][13][14] most of the works center on flow structure. Indeed, only few experiments are preformed to characterize the spray.…”

“…Becker and Hassa 13 studied fuel placement in the swirl cup where it was found that fuel placement is governed by the presence or absence of a recirculation zone. Recently, Liu et al 14 investigated the interactions between swirling air and primary spray in swirl cup, liquid fuel placement is determined by both of relative pressure loss of swirling air and spray cone of primary atomization. The evaluations of combustion performances of the primary design for the lean-burn injection in this study have been completed in our previous work, 15 in order to further improve the ignition and LBO performance of the fuel-staged lean-burn combustor, the pilot fuel injector is redesigned to improve the performance of pilot spray, basing on the deeply understanding of physical processes in prefilming atomization of swirl cup.…”