Abstract
An experimental investigation of characteristics of spray generated by a pressure-swirl atomizer (spill-return type) was performed using shadowgraphy and Phase-Doppler Anemometry (PDA). Several different geometries of the spill-return orifice were tested in terms of a spray stability and quality on a cold test bench. PDA measurement yields a drop-size distribution and velocity data while the shadowgraphy unveils a break-up process in detail. Performed measurements reveal significant differences in spray characteristics as well as differences in spray stability. The results suggest that the air core, formed inside the swirl chamber, passes through the spill orifice, which causes instability of the inner flow. These instabilities lead to a chaotic state of sheet breakup resulting in shortening of breakup distance. Obtained findings are used to propose possible changes in the atomizer design for improvement of its performance.
Highlights
A spill-return atomizer is basically a pressure-swirl atomizer that contains a bypass in the swirl chamber known as a spill-line (SL) orifice
The results suggest that the air core, formed inside the swirl chamber, passes through the spill orifice, which causes instability of the inner flow
The first part of this chapter focuses to the flow characteristics such as mass flow rate, discharge coefficient and overpressure in the spill line, the second one deals with the liquid breakup and the third one is concerning Phase-Doppler Anemometry (PDA) measurements
Summary
A spill-return atomizer is basically a pressure-swirl atomizer that contains a bypass in the swirl chamber known as a spill-line (SL) orifice. Fuel is always supplied to the swirl chamber at high pressure providing good atomization over a wide span of injection flow rate. This feature allows using the spillreturn atomizers in applications requiring the wide regulation range such as industrial burners and gas turbine combustors [1]. Nasr et al in [2] tested several different diameters of spill orifice in terms of Sauter mean diameter (SMD) and flow rate Their atomizers were run with open spill line without any regulation, and the spill-feed ratio was controlled by a cross section of SL orifice. Our research is concentrated on test with regulated spill line along with closed spill line to simulate the full power of the atomizer
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