Pan, KL; Wang, CH; Cheng, DY; Yang, JY
The colliding and burning characteristics of freely moving droplets, individually generated by the merging of colliding High-Carbon number Alkanes with Low-Carbon number Alcohols, and Hexadecane with Methanol/Benzene mixture droplets, were investigated. Two stable droplet streams were individually generated by the circular piezoelectric transducer, through properly adjusted their moving trajectories to have the desired droplet collision and orientation, and the merged droplet was then ignited and burned with the aid of a poroustyped flat flame burner. The merging results show that, the High-C alkanes with methanol and ethanol droplets were manifested in an apparently adhesive, unmixed manner, with visible contact surface between the two immiscible droplets for all test conditions; and with 1- and iso-propanol droplets were in mixing mode, a single spherical droplet formed shortly after the collision. By adding a large quantity of benzene into methanol, say, greater than 0.5 volume fractions, the adhesive-merged hexadecane and methanol/benzene droplet could change into the mixed mode. A strong explosion could occur for the merged High-C alkanes with methanol and with methanol/benzene droplets, and a relatively weak explosion for High-C alkanes with ethanol droplets, through the homogeneous nucleation of alcohol at their contact interfaces. The global burning rate could therefore augment by doubled or even tripled. In general, explosion was facilitated for high-C alkanes with Low-C alcohols, and Hexadecane with methanol/benzene with the higher content of alkane in the merged droplets. The co-vaporization of methanol, ethanol, and alkane from their respective hemispherical segments constituting the adhered droplet, of propanol and alkane from the surface of the mixing droplet, led the flame colors more bluish than yellowish, which indicating the reduction of soot from alkane burning by the presence of alcohol vapor. In light of the difficulty of forming stable oil-methanol, -ethanol emulsions, the potential of separate injection of oil and alcohol in opposed jet arrangement, in direct-injection engines in order to facilitate collision, is suggested.