Laminar Burning Speed Measurements of Ammonia-Hydrogen Mixtures at Elevated Pressures for Gas-Turbine Applications

Abstract Ammonia (NH3) has been shown to serve as an effective hydrogen (H2) carrier in both power and transportation applications, as its similar properties to existing fuels like propane (C3H8) allow for relatively easier storage and transportation operations (Veziro and Barbir, 1992, “Hydrogen: The Wonder Fuel,” Int. J. Hydrogen Energy, 17(6), pp. 391–404). Hence, applied turbine-combustion research on NH3 and H2 fuels has been conducted to identify combustion performance parameters to facilitate the development of high-pressure, sustainable turbomachinery and identify the conditions for efficient burning and nitric oxide (NOx) reduction (Chai et al., 2021, “A Review on Ammonia, Ammonia-Hydrogen and Ammonia-Methane Fuels,” Renew. Sustain. Energy Rev., 147, p. 111254). One key combustion parameter is the laminar burning speed (LBS), which provides gas turbine design engineers with knowledge of combustion physiochemistry, flashback propensity, and efficiency. While abundant literature exists on the combustion of NH3 and H2 fuels at lower pressures, there is not sufficient evidence in elevated-pressure environments to provide a comprehensive understanding of NH3 and H2 combustion phenomena and NH3 conversion for practical engine conditions. Therefore, to advance the state of knowledge, NH3 and H2 mixtures were ignited in this work at an initial temperature and pressure of 323 K and 10 atm to understand their performance properties and LBS, which was calculated using a multizone, constant volume combustion model. The effect of H2 dilution on NH3 was studied by comparing the LBS across a range of fuel mixtures and equivalence ratios. Peak LBS values for NH3 and NH3-H2 were located at stoichiometry. Pressure-dependent LBS suppression effects were observed to be stronger in H2-diluted NH3 mixtures relative to pure NH3. Sensitivity analyses revealed the strongest LBS-suppressing reactions were mainly the radical termination reactions [O + H+M↔OH+M] and [H+O2+M↔HO2+M]. Current work provides the crucial knowledge needed to advance the chemical kinetic models for ammonia-hydrogen mixtures at high pressure.