Comparative study of soot properties and pressure sensitivity in n-dodecane and decalin laminar flames

The main objective of this study is to compare the soot properties and pressure sensitivity of the high-carbon-number n-alkane and cycloalkane in laminar diffusion flames at elevated pressures. As typical high-carbon-number components of aviation kerosene, n-dodecane and decalin have been used in surrogate fuel kinetic models for aviation kerosene such as Jet-A and Chinese RP-3. In this study, quantitative experiments on soot properties are conducted in nitrogen-diluted n-dodecane and decalin laminar diffusion flames at up to 5.0 atm, which has scarcely been reported in the literature. Soot morphology and detailed soot volume fraction distribution are studied by transmission electron microscopy analysis and laser extinction method. Based on the soot volume fraction results, the soot yield is evaluated to compare the pressure sensitivity of the soot propensity between the two fuels. The results show that from 1.0 to 5.0 atm, the primary soot particle diameter, maximum soot volume fraction and soot yield in decalin flames are higher than those in n-dodecane flames. However, with increasing pressure, the growth rates of these soot properties are higher for n-dodecane flames than for decalin flames. The ratio of maximum soot yield of decalin to n-dodecane decreases from 2.2 at 1.0 atm to approximately 1.2 at 5.0 atm. The quantitative results indicate that the pressure sensitivity of soot properties of n-dodecane is stronger than that of decalin. The quantitative experimental results of this work are helpful in understanding the relevant fuel kinetic mechanisms suitable for simulating soot formation at elevated pressures.