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

Area of Science:

• Combustion chemistry and modeling
• Aviation fuel research
• Chemical kinetics and reaction mechanisms

Background:

• Accurate prediction of emissions from gas-turbine combustors is crucial for aviation sustainability.
• Understanding the impact of fuel composition, including sustainable aviation fuel (SAF) and alternative hydrocarbon structures, on combustion performance is essential.
• Existing models require validation against experimental data and established emission benchmarks.

Purpose of the Study:

• To formulate and validate surrogates for Jet-A and SAF using a chemical reactor network (CRN) model.
• To analyze the independent effects of fuel class and molecular structure on emissions, particularly polycyclic aromatic hydrocarbons (PAH) and carbon monoxide (CO).
• To evaluate the combustion performance and emission trends of SAF and cycloalkane-substituted Jet-A under realistic gas-turbine conditions.

Main Methods:

• Development of a CRN model incorporating a comprehensive chemical kinetic mechanism (8478 species, 33,318 reactions).
• Validation of the kinetic mechanism against ignition delay times, laminar flame speeds, and extinction strain rates.
• Formulation of surrogate fuels targeting key properties (density, cetane number) and simulation of two fuel replacement scenarios: Jet-A vs. 100% SAF, and Jet-A with aromatics replaced by cycloalkanes.

Main Results:

• SAF demonstrated a 93% reduction in PAH emissions compared to Jet-A, with no significant impact on NOx emissions.
• Replacing aromatics in Jet-A with cycloalkanes reduced PAH by up to 96%, though it slightly increased CO emissions and decreased flame temperatures.
• The CRN model, validated against CFM56 engine data and ICAO benchmarks, showed strong alignment with experimental ignition delay and flame speed data.

Conclusions:

• The CRN framework effectively predicts aviation fuel combustion performance and emissions, offering a computationally efficient tool for evaluating alternative fuels.
• SAFs and cycloalkane-substituted fuels show significant potential for reducing PAH and soot precursors in aviation combustion.
• The study confirms that SAF can be a viable alternative without compromising NOx emission standards, while offering substantial reductions in other harmful emissions.