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Significance Statement
Primary soot particles are known to be dependent on the burnt type of fuel and the combustion chamber. They pose both health and environmental risks and various studies looked at the adverse effects. However, laboratory studies on the effects of these soot particles faces some daunting challenges due to inappropriate soot sources and excessive volume of soot particles which may occupy laboratory space.
A research team led by Professor Sunho Park from Dankook University in South Korea and published in the peer-reviewed journal, Energy & Fuels developed flame-free soot-generating system that has the ability of controlling the primary particle size and the substance of soot by pyrolysis of diverse hydrocarbon fuels.
They sourced soot from liquid n-hexane and gaseous propylene fuel. The liquid fuel and nitrogen flow rates were used to characterize the fuel mole fraction and residence time of the mixture gas in the soot generator. Results showed that a lower setting temperature or low fuel mole fraction led to a decreased amount of soot. An increase in temperature above 12000C showed a higher percentage of fuel conversion to soot at low residence time which was attributed to rapid carbonization of soot precursors.
The measurement results obtained by the authors showed that the normalized soot yield as a function of residence time followed a logistic curve. At a high setting temperature of 1400 0C, the largest concentration of soot formation was present at the start of pyrolysis with a further increase in concentration when the fuel mole fraction increases. A longer time scale for soot formation was discovered when fuel mole fraction and setting temperature were low.
At an increasing residence time, the soot formation process in the soot generator was analyzed. Several combinations of polyaromatic hydrocarbons led to formation of primary soot particles in nanometric sizes. At a longer residence time, larger agglomerates of primary particles formed secondary soot particles.
A more logistic curve was observed at a high residence time and a certain fuel mole fraction which produced a maximum soot yield at a temperature of 1300 0C. At a lower nitrogen flow rate as residence time increases in the soot generator, the sizes of the primary particles also increased concurrently.
The authors were able to get a controllable primary particle size of soot from n-hexane and propylene in the range of 20-60 nm at a certain mole fraction and heating temperature. The soot generator also showed its flexibility on various conditions of different types of fuel.
The developed soot-generating system in this study can be used in the laboratory for fundamental research on characterization and formation mechanisms of soot, providing further assessment of its health and environmental impacts.
