10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Self-explosion of Lower Alkanes and Alcohols Fine Droplet at the End of Evaporation
Enomoto Hiroshi, Teraoka Yoshikazu, Hieda Noboru, Ota Yoshihide, UESAWA TOMOKI, Kanazawa University
Abstract Number: 699 Working Group: Combustion
Abstract In a usage of the liquid fuel with spray combustion method, a higher fuel pressure is used to produces finer droplets. A finer droplet means a higher droplet number density in the fuel. A developed measurement method with that uses X-ray showed that the Sauter mean diameter of the spray was almost 20 µm. In studies of order to consider the droplet evaporation or combustion, the suspended droplet method is the major method used because the environment could can be easily defined easily. However, it is not easy to investigate droplets of diameter 20 µm because the suspension wire/rod diameters should be larger than 5 µm. The authors developed a single-droplet producer and used the free-droplet method to observe the end of evaporation of 20 µm diameter droplets.
Evaporation of droplets of diameter 20 µm in a high-temperature reducing atmosphere was observed directly with a black/white high-speed camera. A high-speed camera (Photron SA-Z, black/white, 100k fps, 10 µs temporal resolution) with a telecentric lens (VS-Technology, VS-TM10-55CO, 55 mm working distance, 10× magnification) and a rear converter (VS-Technology, SV-2.0X, 2× magnification) was used. The spatial resolution and viewing field area were 1.1 µm/pix and 0.211 mm × 0.275 mm, respectively. A continuous light-emitting diode (SUMITA LS-L109) was used as a backlight. The optical equipment was adjusted so that one droplet locus has more than 50 points (frames). The temporal resolution was 10 µs. A high-temperature reducing atmosphere was produced by a butane diffusion flame of diameter 2.5 mm The butane flow rate was adjusted with a mass flow controller (KOFLOC 8500MC, 0.2 cc/min resolution) and set at 7.0 cc/min at room temperature. The average flow velocity in the outer tube was 0.15 m/s. If Poiseuille flow is assumed, the center flow velocity was 0.30 m/s. The droplet velocities in the observation area were 1.5 m/s near the edge of the outer tube and almost 0.3 m/s near the explosion phenomena. The initial velocity of the droplet varied because a spray gives several droplet velocities. The temperature distribution in the flame was measured with a K-type thermocouple wire of diameter 14 µm. The temperature near the injection tube edge was 315 K, which is lower than the boiling point of gasoline. The maximum temperature of the observed area was 1300 K. Six linear-chain alkanes (99.0% n-heptane, 98.0% n-octane, 98.0% n-decane, 98.0% n-dodecane, 97.0% n-tetradecane, and 97.0% n-hexadecane), four alcohols (99.5% ethanol, 99.7% propanol, 99.0% butanol and 99.0% pentanol) and three commercial fossil fuels (Gasoline No. 2, kerosene, and Diesel oil No. 1) were used.
Except in a few cases, an explosion (self-explosion) was observed. The diameters at the explosion (self-explosion diameter) were 5–10 µm. Larger carbon number alkane gave smaller self-explosion diameters. The initial evaporation rate of faster initial velocity was larger than that of slower initial velocity in any cases. Though the initial evaporation rates of the commercial fuels were almost same at the same initial velocity, these of the alkanes and the alcohols were different with the carbon number. The self-explosion diameters and the initial evaporation rates of the commercial fossil fuels were almost the same for the same initial velocity.