Keywords

combustion, fuels, natural gas, ammonia, gas turbines

Abstract

Natural Gas/Ammonia (NG/NH3) fuel blends are a promising route to reduce CO2 emissions from gas turbines while leveraging existing NG infrastructure, but their autoignition behavior at elevated pressures is not yet well constrained. This work reports high-pressure shock tube ignition delay time (IDT) measurements for NG/NH3/Air mixtures at gas turbine-relevant conditions. Experiments were performed at pressures of 5, 10, and 25 bar, temperatures from 1500 to 2100 K, with equivalence ratios of Φ = 1.0, 1.2, and 1.4, and argon-diluted fuel compositions spanning pure NH3 to NG-rich blends. Experiments were carried out in two shock tube facilities at the University of Central Florida, with ignition being monitored via OH* emission chemiluminescence. The experimental data is compared against simulations using a widely employed nitrogen chemical kinetic mechanism by Glarborg et al. and a newly developed UCF NG/NH3 mechanism. Across all mixtures, IDTs decrease monotonically with increasing temperature and pressure. Increasing pressure from 5 to 10 and 25 bar reduced IDTs for similar temperatures by up to 40% and 60%, respectively, depending on mixture composition. The addition of NG substantially shortens the IDT relative to pure NH3, with the largest incremental benefit at the lowest NG fractions and diminishing returns at higher NG fractions. The pressure sensitivity of ignition is strongest for NH3-rich mixtures and weakens as the NG fraction increases, while changes in equivalence ratio have a comparatively modest effect over the range of Φ = 1.0 to 1.4. Both mechanisms reproduce the overall temperature and composition trends but show systematic deviations for NG-rich mixtures and some disagreements at specific pressure and temperature points in NH3-rich mixtures. Sensitivity analyses based on OH* production indicate that ignition is primarily controlled by CH3 and C2 radical chain-branching pathways in mixtures with NG, while NH3 chemistry mainly influences ignition through radical scavenging and NOx-forming channels. The present measurements provide new high-pressure validation targets for NG/NH3 kinetic mechanisms and help identify specific reaction classes that require further refinement for predictive simulations of low-carbon gas turbine combustion.

Completion Date

2026

Semester

Spring

Committee Chair

Vasu, Subith

Degree

Master of Science in Aerospace Engineering (M.S.A.E.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Document Type

Dissertation/Thesis

Identifier

DP0053221

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