# Fuel Effects on Aviation Engine Emissions: A Chemical Reactor Network Modeling Study

## TL;DR

This study uses chemical modeling to compare emissions from traditional and sustainable aviation fuels, showing significant reductions in harmful pollutants.

## Contribution

The study introduces a chemical reactor network model to evaluate the impact of sustainable aviation fuel and cycloalkane substitutions on engine emissions.

## Key findings

- Replacing Jet-A with SAF reduces PAH emissions by 93% and CO emissions increase slightly when aromatics are substituted with cycloalkanes.
- Cycloalkane substitution in Jet-A reduces PAH emissions by up to 96% when all aromatics are replaced.
- The CRN model accurately predicts combustion characteristics and aligns with experimental data on ignition delay and flame speed.

## Abstract

The present study investigates the formulation of surrogates
for
Jet-A and sustainable aviation fuel (SAF) by means of a chemical reactor
network (CRN) to predict emissions in gas-turbine combustors. The
modeling framework is used to analyze the effects of fuel composition,
specifically the replacement of Jet-A with SAF as well as the substitution
of aromatics in Jet-A with cycloalkanes. This approach enables the
examination of the effects of the fuel class and molecular structure
independently of global exhaust emission trends. A comprehensive chemical
kinetic mechanism incorporating 8478 species and 33,318 reactions
was used to model jet fuel surrogates. This mechanism, validated against
ignition delay times, laminar flame speeds, and extinction strain
rates, accurately predicted combustion characteristics for iso-cetane
and iso-dodecane, key components of SAF. Surrogate fuels for Jet-A
and alternative fuels were formulated targeting critical properties
such as density and cetane number. Surrogate simulation results show
strong alignment with experimental data on ignition delay and flame
speed, further confirming the reliability of the surrogates. The CRN
model was developed using the CFM56 engine data and validated against
the International Civil Aviation Organization emission benchmarks.
After that, two different fuel replacement scenarios, involving Jet-A,
are investigated. In the first one, Jet-A is compared to 100% SAF,
which helps assess expected differences in combustion performance
if a fully renewable fueling supply is followed. Results show that
NO
x
emissions are unaffected by SAF, aligning
with previous experimental studies. Polycyclic aromatic hydrocarbons
(PAH) decrease by 93% for SAF compared to Jet-A, while Jet-A produces
more CO due to its aromatic content. Substituting aromatics with cycloalkanes
in Jet-A reduces PAH emissions by up to 96 or 92%, depending on whether
all aromatics are replaced or only diaromatics. In a second scenario,
aromatics are removed from conventional Jet-A and replaced with cycloalkane
species, which can still hold the swelling properties needed by the
fueling system. In terms of combustion, cycloalkane substitution leads
to slightly increased CO emissions and reduced flame temperatures.
These results demonstrate the potential of SAFs and cycloalkanes in
reducing soot precursors while maintaining a highly similar performance
in the combustion process. Overall, the proposed CRN framework provides
a good example of how a predictive and computationally efficient tool
can help in the early evaluation of alternative aviation fuels under
realistic gas-turbine combustor conditions.