Size Distribution of Nascent Soot in Premixed n-Hexane, Cyclohexane, and Methylcyclohexane Flames

The evolution of particle size distribution function (PSDF) of nascent soot in premixed flames of n-hexane, cyclohexane, and methylcyclohexane was studied on the burner-stabilized stagnation flame platform. The cold gas velocities were changed to keep the maximum flame temperatures of different flames approximately constant. The PSDFs of all fuels tested transited from the unimodal (nucleation mode only) to the bimodal (both nucleation and accumulation modes) distribution with increased particle residence time. Soot nucleation and growth in the n-hexane flame were found to appear later than those in the cyclohexane and methylcyclohexane flames. In addition, the methylcyclohexane flame exhibited the highest nucleation and accumulation rate at the early stage of soot formation. However, the particle nucleation strength and the soot mass growth rate of the cyclohexane flame exceeded those of the methylcyclohexane flame at long particle residence times.