Experimental Investigation of Cool Flame Behavior of Isolated n-Decane/Ethanol Droplet under Microgravity

To investigate the effect of ethanol concentration on the cool flame characteristics of isolated binary fuel droplet, experiments and numerical simulations on n-decane/ethanol droplet were conducted, varying the volume fractions of ethanol. Ambient pressure was set to atmospheric pressure and the temperature was varied from 600 to 660 K. Under these conditions, although cool flame was observed for n-decane, it did not induce hot flame ignition. CCD camera and K-type thermocouple were used to measure the droplet diameter and cool flame temperature, respectively. Moreover, one dimensional numerical simulation was performed with the fully transient numerical model. In addition to the assumptions on species flux, temperature continuity, fugacity equilibrium was assumed to simulate the evaporation process of multicomponent droplet. After the n-decane droplet was inserted into the hot ambience, evaporation was suddenly promoted and the temperature near the droplet surface decreased due to the cooling effect of evaporation. After the ignition of cool flame, the thermocouple nearest to the droplet showed the highest temperature, which implies that large heat release occurred near the droplet. When ethanol was added to n-decane, the cool flame ignition delay became longer. This is probably because the vapor formation of n-decane was delayed due to the high volatility of ethanol. However, the cool flame temperature was not significantly varied by the volume fraction of ethanol. This is probably because n-decane and OC10H19OOH accumulating at the cool flame location was almost the same for all conditions.