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- Shahsavari, Mohammad, et al.
(author)
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On nanosecond plasma-assisted ammonia combustion : Effects of pulse and mixture properties
- 2022
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In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 245
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Journal article (peer-reviewed)abstract
- In this study, the effects of nanosecond plasma discharges on the combustion characteristics of ammonia are investigated over a wide range of mixture properties and plasma settings. The results reveal that the impacts of the plasma on ammonia combustion change non-monotonically by altering the reduced electric field value. Within the studied range of the reduced electric field, i.e., 100–700 Td, it is shown that plasma is most effective in the medium range, e.g., 250–400 Td. At lower values, the main fraction of the plasma energy is consumed to excite the diluent to higher vibrational levels. At very high reduced electric field values, a substantial portion of the plasma energy is transferred into the ionization reactions of the diluent, which compromises the effective excitations of fuel and oxidizer species. In terms of the pulse energy density, results indicate that an increase in the range of 0–20 mJ/cm3, at a given reduced electric field, decreases the ignition delay time by five orders of magnitude, and increases the laminar flame speed up to an order of magnitude, depending on the mixture composition. The results show that the plasma discharge produces more radicals, electronically excited and charged species when He is used as the diluent in the oxidizer instead of N2, since NH3 and O2 ionization reactions are strengthened in NH3/O2/He. Moreover, plasma discharge is highly effective in assisting the combustion of preheated lean mixtures. The present study also indicates that ammonia flame thickness is minimum at a critical pulse energy density in the range of 12–14 mJ/cm3. Further increases in the pulse energy density can manipulate the inner structure of the flame, altering the pre-heat zone of the flame to include some levels of chemical reactions toward the flameless mode of combustion.
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| 2. |
- Shahsavari, Mohammad, et al.
(author)
-
Synergistic effects of nanosecond plasma discharge and hydrogen on ammonia combustion
- 2023
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In: Fuel. - 0016-2361. ; 348
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Journal article (peer-reviewed)abstract
- Synergistic effects of nanosecond plasma discharge and hydrogen on the combustion characteristics of ammonia/air are numerically studied under conditions relevant to gas turbine combustion chambers. It is shown that increasing the plasma contribution in assisting the flame results in lower NOX emissions by up to 27% than those in flames assisted by hydrogen for the range of operating conditions considered in this study. Plasma makes the consumption speed of the reactants less prone to the strain rate than that in flames assisted by hydrogen. It is found that discharging plasma with the pulse energy density of 9 mJ/cm3 alongside using 12% hydrogen by volume in the fuel increases the flame speed of ammonia/air to those of conventional fossil fuels such as methane—an improvement that is not achievable by just using hydrogen, even at a high concentration of 30%. Furthermore, raising the pulse energy density beyond a specific value broadens the reaction zones by generating radical pools in the flame preheating zone, which is expedited in fuel-rich conditions with high H2 fuel fractions. Investigations show that the simultaneous utilization of high-energy plasma and hydrogen reduces the NOX emissions by activating the mechanisms of nitrogen oxide denitrification (DeNOX) in preheating and post-flame zones, being more significant under the lean condition as compared with rich and stoichiometric cases. It is shown that increasing mixture pressure significantly deteriorates the impacts of plasma on combustion. Such unfavorable effects are weakly controlled by changes in the reduced electric field caused by pressure augmentations.
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