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Since its implementation, exhaust gas recirculation has proven to be a reliable technique to control NOx emissions by lowering combustion temperature. Dilution with exhaust gas recirculation, whether in internal combustion engines or sequential-staged gas turbine combustors, affects flame reactivity and stability, which are related to the heat release rate and engine power. Another way to control emissions is to use hydrogen as a carbon-free alternative fuel, which is considered a milestone in the energy-decarbonization journey. However, the high reactivity of hydrogen is one of its hurdles and understanding this effect on laminar burning velocity is important. Flame propagation and burning velocity control the mixture reactivity and exothermicity and are related to abnormal combustion phenomena, such as flashback and knock. Therefore, understanding the effect of exhaust gas addition on the laminar burning velocity of hydrogen/air mixtures is imperative for engine design. In this work, a constant volume combustion chamber was used to observe the laminar burning velocity of stoichiometric hydrogen/air mixtures diluted with combustion products at 1 bar and 423K. Actual combustion products (35 % H2O + 65 % N2, by mole) were used for dilution at rates of 0-50%. The burned gas Markstein length was calculated for all mixtures. Experimental results of the laminar burning velocities for all mixtures were compared with kinetic modeling results. These measurements showed the monotonic reduction of reactivity and the laminar burning velocity with dilution. The reduced burning rates at higher dilution were reflected on the pressure gradient inside the vessel. Markstein length values decreased with dilution, meaning that flame instabilities increased with dilution.
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A Study of the Effects of Steam Addition on Ammonia Hydrogen Air Combustion
ABSTRACT: Ammonia and hydrogen are potential fuels for eliminating direct CO2 emissions considering climate change. The volumetric energy density of ammonia is 11,333 kJ/m3, and the volumetric energy density of hydrogen is 2,101 kJ/m3. The ignition energy of ammonia is 8 MJ, and the ignition energy of hydrogen is 0.08 MJ. Ammonia hydrogen mixtures in the right proportions may serve as a practical fuel if the additional challenge related to NOx emissions is addressed. Steam addition is an effective means of controlling the increases in NOx emissions resulting from either the fuel nitrogen and or the high temperatures resulting from the energy density. A computational study of turbulent ammonia + hydrogen burning with air + steam in axisymmetric opposed flow flame configurations is reported. The ANSYS Chemkin-Pro, a commercially available chemical kinetics code with the Konnov ammonia hydrogen-air reaction mechanism, is utilized. In this article, results are reported of combustion of ammonia and hydrogen with air and steam. Two mole fractions of ammonia in the fuel flow (0.9 and 1.0) and multiple mole fractions of steam (in the range 0.0 to 0.20) in the oxidizer flow in an opposed flow flame configuration at a constant mean pressure of 101 kPa and an initial fuel temperature of 298 K are considered. Six steam-air mixture temperatures in the range 473 K to 973 K for the multiple steam mole fractions are considered. The NO mass fractions decreased with the mole fraction of steam in the incoming oxidizer. Stable combustion is observed when a small amount of hydrogen is added.
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- Award ID(s):
- 2027740
- PAR ID:
- 10356442
- Date Published:
- Journal Name:
- 2022 Spring Technical Meeting Central States Section of The Combustion Institute
- Page Range / eLocation ID:
- 1-9
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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