Ignition Delay Time Measurements of Natural Gas/Ammonia Mixtures at Gas Turbine Pressures and Temperatures

Abstract

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 F = 1.0, 1.2, and 1.4, and argon-diluted fuel compositions spanning pure NH3 to NG-rich blends. The experimental data is compared against simulations using chemical kinetic mechanisms by Glarborg et al., the CRECK modeling group, and a newly developed UCF NG/NH3 mechanism. Increasing pressure from 5 to 10 and 25 bar reduced IDTs for similar temperatures by up to 40% and 60%, respectively. 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. The mechanisms reproduce the overall temperature and composition trends but show systematic deviations for NG-rich mixtures and some disagreements in NH3-rich mixtures. Sensitivity analyses 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.