A laboratory flame established between the opposing fuel and air streams shows the luminous soot zones and flow patterns.
A computational framework that accurately
predicts the formation of particulates and soot when burning hydrocarbon fuels
has been developed by researchers at KAUST and an international research
team. The model takes into account the crucial contributions
of larger hydrocarbon molecules1.
“These have often been neglected
in previous studies,” said Hong Im from the KAUST Clean Combustion Research
Center (CCRC). He noted that consideration of these molecules is essential for accurate
prediction of soot levels.
Small particles emitted into air during the
burning of hydrocarbon fuels damage the human respiratory system and enhance
the greenhouse effect. In their agglomerated form, these particles form soot
that consists predominantly of highly condensed carbon atoms. The formation of
soot is widely studied, but models are often inaccurate because the amount and
size of the carbon particles depends on many factors, including the fuel used
and the combustion conditions.
The researchers improved the way
to predict the formation of soot precursors in the flames, or the so-called
polycyclic aromatic hydrocarbons (PAH).
PAHs are organic molecules containing
rings of carbon atoms with surrounding hydrogen atoms. They form during the
burning process when smaller molecules collide and combine into larger ones. The
molecules themselves cluster and under some conditions form carbon soot
particles. A detailed understanding of the formation pathways for PAH is therefore
essential to reduce soot formation and to improve the efficiency of the burn
Because of their larger number of atoms, previous
computer models have been limited by the size of the PAH considered in the
calculations. In their work, the researchers have identified more accurate chemical
pathways to larger PAHs by carefully examining their complex reaction mechanisms.
The model developed in collaboration with the National University of
Ireland, Galway and Saudi Aramco describes reaction pathways that lead to
the formation of PAH with up to seven rings of carbons—24 carbon atoms in
Deploying the model, the research shows
that accurate predictions must not only take PAH molecules into account, but
that the larger PAH molecules are those that contribute most to the production
Although current computations are based on a simple
fuel, future work will extend other fuel types such as gasoline or jet fuels.
In addition, Im explained, dynamic effects are also important.
“Studies of soot
formation under the influence of turbulent fluctuations are currently being
investigated,” Im said.
Selvaraj, P., Arias, P.G., Lee, B.J., Im, H.G., Wang, Y. et al. A computational study of ethylene–air sooting flames: Effects of large polycyclic aromatic hydrocarbons. Combustion and Flame 163, 427–436 (2016). | article
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