To reduce reliance on fossil fuels there has been a global push to minimise fuel consumption, and incorporate the use of bio-derived fuels. In practical combustion systems that use liquid fuels, observing the spray behaviour of these biofuels is key in understanding fuel performance; in particular, droplet size distribution is known to have a strong influence on the fuel energy release and pollutant formation processes. This paper is aimed at the use of the TSI Global Sizing Velocimetry (GSV) interferometric technique as a method to gain detailed understanding of droplet number and size distribution, with a particular focus on ethanol-gasoline fuel blends.
The imaging system for the GSV technique consisted of a Nd:YAG laser and a 4 MP (million pixel) camera, and the spray was generated using a generic automotive port fuel injector. The results showed that the GSV technique was able to effectively measure droplet concentration and diameters for all the fuel blends tested in this study. Ethanol was observed to have larger droplet diameters (both D10 and D32) as compared to fossil gasoline, with droplet diameters generally increasing as the proportion of ethanol in the gasoline was increased. The droplet concentration reduced with increasing radial distance from the spray centreline, but no appreciable change was observed with axial displacement from the nozzle tip. Degradation in the image quality was observed for fuel blends with less than 40% ethanol content. The GSV drop sizing measurements were validated using a mono-disperse droplet generator, and an excellent agreement (within 2%) was observed.