TS-80
Phase-Separation Inside a Burning Droplet of Oil-in-Water Emulsion
Daisuke SEGAWA*, Hidemitsu TANAKA*, Hiroshi ENOMOTO*, Toshikazu KADOTA* and Hiroshi YAMASAKI**"
ABSTRACT
An experimental study has been carried out to obtain the detail information needed for the deep understanding of the combustion process of an emulsified fuel droplet. The experiments were conducted under microgravity using the JAMIC drop shaft. Photographic observation and temperature measurement were made of single emulsified fuel droplets burning in quiescent gaseous environments at the atmospheric pressure.
The results showed that the agglomeration and separation of the water and the base fuel layers occurred with the lapse of time. The increase in the temperature of the emulsified fuel resulted in the formation of a single water droplet enveloped by a shell of base fuel prior to the microexplosion. After the phase separation, selective evaporation of the base ftiel would occur and the volume of base filel decreased while the water volume did not change.
The relationship between the phase-separation and occurrence of the disruptive microexplosion were also examined by using the statistical analysis.
Key Words: Combustion, Emulsified Fuel, Microexplosion, Droplet Combustion, Microgravity, Water Content
1. INTRODUCTION
Emulsified fuel combustion method has been recognized to cause the improvement of the combustion efficiency and the reduction of pollutant emissions including unburned hydrocarbons, nitric oxides and soot. This has resulted in the increased interest in the study on the combustion of emulsified fuels, especially on the microexplosion (secondary-atomization) phenomena of emulsified fuel (emulsion) droplets, such as breaking up of droplets into smaller secondary-droplets, so-called "disruption" (Fig. 1(a)), and blowing-out of vapors laden with fine droplets, so-called "puffing" (Fig. 1(b)). Evaporation and combustion of a single emulsion droplet have been examined experimentally with free droplets and fiber-suspended droplets or theoretically [1-11]. In most of these studies, the occurrence of the microexplosion has been discussed using the relationship between droplet temperature and the superheat limit based on the homogeneous nucleation theory; The microexplosion would occur in the case that the superheat limit of water is less than the boiling temperature of the base fuel. However, microexplosion or bubble nucleation has been observed at temperatures below the superheat limit for emulsion droplets suspended in heated glycerin [12] and evaporating on a hot surface [11].
The aspects of microexplosion have been found to also depend on the type of the emulsion, or on the properties of the surfactant as mentioned in the previous work [13]. The droplet is disrupted after puffing occurs several times for oil-in-water emulsions.
Fig. 1 Secondary-atomization of emulsion droplets.
