Qasim Sarwar Khan

EXPERIMENTAL STUDY ON BINARY DROPLET EVAPORATION AT ELEVATED PRESSURES AND TEMPERATURES

The evaporation characteristics of single and multicomponent droplets hanging at the tip of a quartz fiber are studied experimentally at the different environmental conditions under normal gravity. Heptane and Hexadecane are selected as two fuels with different evaporation rates and boiling temperatures. At the first step, the evaporation of single component droplet of both fuels has been examined separately. At the next step the evaporation of several blends of these two fuels, as a binary component droplet, has been studied. The temperature and pressure range is selected between 400 and 700°C, and 0.1 and 2.5 MPa, respectively. A high-temperature environment was provided by a falling electrical furnace. The initial diameter of droplet was in the range of 1.1 and 1.3 mm. The evaporation process was recorded by a high-speed CCD camera. The results of binary droplet evaporation show the three-stage evaporation. In the first stage the more volatile component evaporates. The droplet temperature rises after an almost non-evaporative period and, in the third stage, a quasi-linear evaporation takes place. The evaporation of the binary droplet at low pressure is accompanied with bubble formation and droplet fragmentation and leads to incomplete microexplosion. The component concentration affects the evaporation behavior of the first two stages. The bubble formation and droplet distortion does not appear at high environment pressure.

EXPERIMENTAL STUDY ON EVAPORATION OF KEROSENE DROPLETS AT ELEVATED PRESSURES AND TEMPERATURES

Kerosene is a common liquid fuel in many industrial applications. However, there is little useful data on high pressure and high temperature evaporation for kerosene. In this research, the vaporization of kerosene droplet was experimentally investigated at high temperatures (between 500 and 1000°C) and high pressures (between 0.1 and 3.0 MPa) under normal gravity. High temperature environment has provided by a furnace. Droplet with initial diameter between 1.0 and 1.2 mm was suspended at the tip of a quartz fiber. The evaporation process was recorded by a high-speed CCD camera. The evaporation rate was extracted from the recorded movie by determining temporal rate of changing of droplet diameter. Despite its multicomponent nature, the evaporation of kerosene droplet followed the d 2 -law after heating-up period. The evaporation rate of kerosene droplet increased monotonically with an increase in gas temperature. At low temperature, when ambient pressure increased, the evaporation rate also increased. But at high temperature, evaporation rate shows a maximum around 2.0 MPa and then decreases. Also, the formation of dense fuel vapor cloud around the droplet was observed under conditions with higher evaporating rate.

ON THE AUTOIGNITION AND COMBUSTION CHARACTERISTICS OF KEROSENE DROPLETS AT ELEVATED PRESSURE AND TEMPERATURE

Abstract The effects of high ambient pressure and temperature were experimentally investigated on the autoignition delay times of isolated kerosene fuel droplets. The droplet was hanged at the tip of a quartz fiber and suddenly exposed to high ambient temperature by the help of falling electric furnace at desired ambient pressures under normal gravity. The ignition was detected visually by the use of high-speed photography. Results have shown that the autoignition delay time decreases with an increase in both temperature and pressure. Also an increase in ambient pressure reduces the ignition location distance from the droplet. The experimental results of autoignition delay times were correlated with the equation τ = APBexp(D/T). The combustion of the kerosene droplet was also investigated at various ambient temperatures and at atmospheric pressure. The droplet burning rate was calculated using temporal histories of droplet diameter. The droplet combustion followed d 2-law. And a comparison between evaporation and burning rate constants has shown that their difference reduces at higher ambient temperatures.