Characteristics of spray generated by effervescent atomizer.

conference paper

English

In some technical applications (e.g. fuel atomization in gas turbine combustors or burners) effervescent atomizers are more frequently being used. Effervescent atomization is a method of twin-fluid atomization that involves bubbling a small amount of gas into the liquid before it is ejected from the atomizer. The advantages in comparison with common twin-fluid injectors are simple design and fine spray under low pressure and low mass air-liquid ratio. Nevertheless unstable behaviour of atomizer occurs at some operational modes. Little effort has been so far made to resolve this problem, although spray stability in the large turndown ratio is usually one of the basic demands for atomizer design. The stability of the spray can significantly impact on the stability of the flame and on the formation of NOx. The objective of the submitted paper is a design of suitable method for spray instability measurements. It means to find an appropriate quantity for description of instabilities and their quantification and evaluation. One of the possible unsteadiness evaluation method is the method developed by Luong and Sojka, which uses PDPA analyser. The droplet arrival time data in measurement position are used in calculation of interparticle arrival time gaps. The spray is determined to be steady or unsteady by comparing experimental and theoretical interparticle time distribution function. In our approach we are using a different method with measurement of some of integral values of atomisation process. Two techniques are used. The first one is based on fast miniature pressure sensor placed close to the nozzle orifice. Time record of the signal after FFT is statistically analysed. The result is quantitative information on global instability. The other technique employs measuring microphone. Also laser diagnostic system PLIF (optical patternator) will be used to study instabilities. In this case, instabilities will be evaluated from time series of spray picture recording. Developed methods will serve as a basic tool while developing new effervescent atomizers. All methods will be cross-checked and compared with results acquired with PDPA system. As a result we obtain identification of source instabilities and quantification and evaluation of design and operational parameters impact.

drop size, spray, Effervescent Atomizer

JEDELSKÝ, J.; JÍCHA, M.; SLÁMA, J.

2003

1. 1. 2003

Institute of Hydrodynamics AVCR

Praha, Česká republika

80-239-0644-5

18. Sympozium o anemometrii, Úvaly u Prahy

47

54

8