Abstract

Numerical simulation of biofuel spray flames requires knowledge of the drag coefficient of the burning drops to facilitate tracking of the drops in the spray flame. The objective of this study was to measure the drag coefficient of individual burning biofuel liquid droplets of various sizes.  Two flat ceramic heaters were used to heat the air (150°F to 250°F) between them; a K type thermocouple connected to a temperature controller and a relay switch was used to control the temperature of the heaters.  Another K-type thermocouple positioned above the gap was used to anchor the droplets.  The droplets were ignited by an external flame and underwent free fall through the gap of hot air between the heaters. The hot air ensured that the flame surrounding the droplet was not extinguished.  The images of the free-falling burning droplets were captured using a Redlake MotionPro X3 camera with a 1280 x 1024 pixel resolution and a recording rate of 1000 frames per second.  Analysis of the images was used to determine the drag coefficients of the burning spray droplets along their trajectories.  Three liquid fuels were tested, including petroleum-based No. 2 diesel fuel, canola methyl ester and soy methyl ester.

Experimental setup for measuring the drag coefficients of burning liquid biofuel droplets

Droplet images with different kind of flames.