A comparative study on droplet characteristics and specific charge of ethanol in two small-scale electrospray systems

An investigation on the droplet characteristics of ethanol in small-scale combustors with two different systems was conducted experimentally and theoretically. The classical capillary-mesh electrode arrangement was applied in Type A electrospray system, and for Type B, an additional ring electrode is included. The droplet size and velocity were measured by a Phase Doppler Anemometer. The electric filed intensity was theoretically calculated in the two electrospray systems. Compared with Type A, Type B system has smaller droplet size and velocity in the same spraying mode. Meanwhile the electrospray process in Type B system is more stable than that in Type A with its smaller root mean square velocity. By measuring the spraying current, the average specific charge of the droplets for the two systems was obtained in different spraying modes. And it was found that the addition of the ring electrode can help to increase the droplet charge, which is the fundamental reason for Type B electrospray system to perform better. The corona charge of the droplets was theoretically calculated for the two electrospray systems. It was found that the calculated specific charge generated by corona charging was in good agreement with the experimental results.

Estimating velocity in Gasoline Direct Injection sprays using statistical pattern imaging velocimetry

Statistical pattern imaging velocimetry (SPIV) is a new technique for the estimation of the planar velocity field from the high-speed videos. SPIV utilizes an ensemble of either backlit or side lit videos to obtain full planar velocities in sprays and flames. Unlike conventional particle imaging velocimetry, statistical pattern imaging velocimetry does not require well-resolved images of particles within turbulent flows. Instead, the technique relies of patterns formed by coherent structures in the flow. Therefore, SPIV is well suited for the estimating planar velocities in sprays and turbulent flames, both of which have well-defined patterns embedded in the flow videos. The implementation of the SPIV technique is relatively quite straightforward since high-speed videos can be readily obtained either in a laboratory or production floor setting. The biggest challenge for the SPIV techniques is that the procedure is computationally expensive even with an ordinary mega-pixel camera. To improve the computation speed, a successive partitioning scheme was employed. In addition, to improve spatial resolution to subpixel dimensions, a weighted central averaging scheme was used. With these two enhancements, the SPIV method was used to obtain planar radial and axial velocities in a spray emanating from a GDI injector. Sprays from GDI injectors are very dense (with obscuration levels close to the injector being greater than 99%), and velocity measurements are difficult. However, further away from the nozzle, a Phase Doppler Anemometer can be used to obtain velocity measurements. The velocities obtained using these two methods showed reasonable agreement.

Investigation of Fuel Atomization with Density Functions

Atomization involves mass, energy, and impulse transfer, in such a complex way that the overall process can only be described by empirical and semi-empirical correlations to date. The phenomenon of atomization is used in numerous applications, e.g., in combustion technology and metallurgy. However, many formulae are available in the literature to derive mean diameters of the spray, size distribution functions are barely discussed. Based on the measurement results performed earlier by a Phase Doppler Anemometer, twenty probability density functions were evaluated and seven are discussed in detail over the course of the present paper. The atomization pressure was varied, and characteristic regimes of the spray were measured. Interestingly, the analysis showed that not only the three most commonly used probability density functions (Nukiyama-Tanasawa, Rosin-Rammler, and Gamma) are eligible for describing the size distribution of the spray.