# Flow Reactor Study of the Soot Precursors of Novel Cycloalkanes as Synthetic Jet Fuel Compounds: Octahydroindene, p‑Menthane, and 1,4-Dimethylcyclooctane

## TL;DR

This study examines how three cycloalkanes, derived from biomass, form soot precursors when burned, which is important for developing cleaner synthetic jet fuels.

## Contribution

The paper presents novel experimental data on soot precursor formation from octahydroindene, p-menthane, and 1,4-dimethylcyclooctane, which have not been previously studied.

## Key findings

- Octahydroindene (OHI) showed the highest soot formation tendency (YSI 94.5) due to direct dehydrogenation of its ring.
- p-Menthane and DMCO produced fewer aromatic soot precursors but higher concentrations of benzene precursors like 1,3-butadiene.
- Ring-opening pathways dominate benzene formation in p-menthane and DMCO, unlike OHI's dehydrogenation pathway.

## Abstract

Sustainable aviation fuels (SAFs) or Synthetic aviation
turbine
fuels (SATFs) derived from nonpetroleum sources are essential for
energy security and a strong rural and agricultural economy. Airplanes
operating on SAF can have lower particle emissions compared to those
of conventional jet fuel, reducing air quality impacts near airports.
Processing biobased isoprene or wood and agricultural waste can produce
cycloalkane-rich fuels with properties meeting ASTM International’s
SATF requirements. The unique structures of these cycloalkanes yield
lower soot emissions because of their lack of aromatic rings. We measured
the soot formation tendency as yield sooting index (YSI) and used
laminar flow reactor experiments to evaluate soot precursors formed
for isoprene-derived compounds p-menthane and 1,4-dimethylcyclooctane
(DMCO), and octahydroindene (OHI) produced from woody biomass
via catalytic fast pyrolysis. The combustion chemistry of the OHI
and DMCO has not been previously studied. Experiments were conducted
at 10 bar from 800 to 1200 K, equivalence ratios of 1.0 and 3.0, and
residence times of 1.0 and 0.6 s, respectively. Experimentally detected
species were used to elucidate the mechanisms of soot precursor formation.
OHI exhibited the highest YSI (94.5) and formed a high concentration
of benzene primarily by direct dehydrogenation of the six-membered
ring. p-Menthane (YSI 92.0) and DMCO (YSI 85.0) oxidation
products included fewer aromatic components but higher benzene precursors,
including 1,3-butadiene, propyne, and allene. This suggests that the
ring-opening pathway is dominant over the dehydrogenation pathway
in the benzene formation for these compounds. This experimental speciation
provides insight into the influence of the cycloalkane structure on
the sooting tendencies of potential SAF blend components, thereby
aiding in fuel design processes.