Experimental Studies on Combustion and Microexplosion Characteristics of N-Alkane Droplets

A detailed experimental investigation on the effect of thermal properties on single droplet combustion characteristics has been performed at room temperature and atmospheric pressure under normal gravity with four n-alkanes (n-octane, n-dodecane, n-tetradecane, and n-hexadecane). The evolution of suspended droplet diameter and the global flame over time were obtained using microscopic and direct photography simultaneously. The results show that the n-alkane droplets used in this study exhibited similar D-2-law curve characteristics and the droplet shape of single component is quasi-spherical throughout the whole combustion duration. The n-alkanes with lower boiling point and high volatility present a higher burning rate and shorter combustion duration, and there is no expansion process during the evaporation period. Strong microexplosion and fluctuation on droplet diameter were observed when the thermal properties of the multicomponent are sufficiently different. The reason is that the bubbles nucleate, grow, and rupture continuously by heating the components of lower boiling point and high volatility in multicomponent droplets. The thermal properties and mixing ratio of the components in the multicomponent droplet and the formation position of the bubbles have an important influence on the microexplosive combustion and its intensity. Besides, there is an inverse power relationship between the burning rate constant of n-alkane droplets and initial droplet diameter (D-0 > 1 mm).