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

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.