Abstract:Energy storage is one of the highest priority challenges in transitioning to a low-carbon economy.Fluctuating, intermittent primary renewable sources such as wind and solar require low-carbon storage options to enable effective load matching, ensuring security of supply. Chemical storage is one such option, with low or zero carbon fuels such as hydrogen, alcohols and ammonia having been proposed.Ammonia provides zero-carbon hydrogen storage whilst offering liquefaction at relatively low pressures and atmospher… Show more
“…In terms of utilizing ammonia in combustion equipment, pertinent studies have tested and applied ammonia in internal combustion engines, 10‐12 gas turbines, 13‐15 etc. Meanwhile, in order to support the application and have better understanding of ammonia combustion, fundamental studies also have been performed using ammonia fuels 16‐19 .…”
Summary
Ammonia mixed with methane is a potential clean fuel for engine applications toward a low carbon economy. Studies are scarce on ignition phenomenon for ammonia/methane fuels in literature. In the present study, the ignition characteristics for ammonia–methane–air mixtures have been investigated by both experimental measurements and numerical simulations. Ignition processes of a 60%ammonia/40%methane (mol%) fuel blend were investigated with shock‐tube experiments. Measurements of the ignition delay times were performed behind reflected shock waves for such fuel/air mixtures with different equivalence ratios of 0.5, 1, and 2, at pressures around 2 and 5 atm within the temperature range of 1369 to 1804 K. Experimental results were then compared with numerical prediction results employing detailed kinetic mechanism, which showed satisfactory agreement within most of the range of the temperatures, equivalence ratios, and pressures investigated. Within the temperature range of 1300 to 1900 K, pressure range of 1 to 10 atm, equivalence ratio range of 0.5 to 2, and methane proportion range of 0% to 50% in fuel blends, the impacts of temperature, pressure, equivalence ratio, and methane additive were simulated on the ignition delay times of the fuel blends based upon the numerical model. It was found that the improvement of ammonia/methane ignition is significant with the increase of temperature, pressure, and methane additive while it is relatively not sensitive to equivalence ratio within the studied conditions. This suggests a promising potential of such fuel blends in real engine application. In addition to the calculations, reaction sensitivity analyses were also performed to have a deep insight into the observed differences between ammonia/methane/air ignition delay times with variation of conditions.
“…In terms of utilizing ammonia in combustion equipment, pertinent studies have tested and applied ammonia in internal combustion engines, 10‐12 gas turbines, 13‐15 etc. Meanwhile, in order to support the application and have better understanding of ammonia combustion, fundamental studies also have been performed using ammonia fuels 16‐19 .…”
Summary
Ammonia mixed with methane is a potential clean fuel for engine applications toward a low carbon economy. Studies are scarce on ignition phenomenon for ammonia/methane fuels in literature. In the present study, the ignition characteristics for ammonia–methane–air mixtures have been investigated by both experimental measurements and numerical simulations. Ignition processes of a 60%ammonia/40%methane (mol%) fuel blend were investigated with shock‐tube experiments. Measurements of the ignition delay times were performed behind reflected shock waves for such fuel/air mixtures with different equivalence ratios of 0.5, 1, and 2, at pressures around 2 and 5 atm within the temperature range of 1369 to 1804 K. Experimental results were then compared with numerical prediction results employing detailed kinetic mechanism, which showed satisfactory agreement within most of the range of the temperatures, equivalence ratios, and pressures investigated. Within the temperature range of 1300 to 1900 K, pressure range of 1 to 10 atm, equivalence ratio range of 0.5 to 2, and methane proportion range of 0% to 50% in fuel blends, the impacts of temperature, pressure, equivalence ratio, and methane additive were simulated on the ignition delay times of the fuel blends based upon the numerical model. It was found that the improvement of ammonia/methane ignition is significant with the increase of temperature, pressure, and methane additive while it is relatively not sensitive to equivalence ratio within the studied conditions. This suggests a promising potential of such fuel blends in real engine application. In addition to the calculations, reaction sensitivity analyses were also performed to have a deep insight into the observed differences between ammonia/methane/air ignition delay times with variation of conditions.
“…Initial results were conducted to validate the CFD model against previous experimental data [34,39,50]. The results in Figures 3 and 4 show good correlations.…”
Section: Resultsmentioning
confidence: 95%
“…A numerical study was conducted to determine the exhaust gases obtained from the combustion of a 70-30 (mol%) ammonia-hydrogen blend under rich conditions (equivalence ratio of 1.2) and medium swirl (0.8), thus providing details for further thermodynamic analyses of a combustor previously evaluated using these settings [34,39]. Validation of the model was performed using the results from Valera-Medina et al [39] and Pugh et al [34]. Correlations were established between experimental and numerical concentrations of NOx, NH 3 , and H 2 emissions.…”
Section: Methodsmentioning
confidence: 99%
“…Different to the Eddy dissipation concept (EDC), which integrates chemistry for a time scale close to Kolmogorov's timescale, thus delivering slower reaction rates, LFC integrates the chemistry with respect to the residence time in the cell. The selection was based on results from previous campaigns and findings that denoted the high reactivity of this ammonia-hydrogen blend, with high NH 2 , OH, and H/O pools close to the flame front that increase the reactivity of the former [34,39]. Finally, the LFC model is appropriate for premixed, partially premixed, and unsteady flames [48].…”
Section: Methodsmentioning
confidence: 99%
“…Unfortunately, one of the markers that scored the lowest for ammonia was the specific energy of the fuel (MJ/kg), whilst in comparison, hydrogen showed the highest. The approach applied by the group only briefly raised the potential of ammonia-hydrogen blends, which are well-known to be more efficient for combustion purposes whilst having higher specific energies and the potential of the production of hot, unburned hydrogen [34,39]. Simultaneously, hydrogen, a well-known substitute for many power applications, has the potential to generate clean power whilst ensuring the distribution and storage of large renewable energy sources.…”
Ammonia, a chemical that contains high hydrogen quantities, has been presented as a candidate for the production of clean power generation and aerospace propulsion. Although ammonia can deliver more hydrogen per unit volume than liquid hydrogen itself, the use of ammonia in combustion systems comes with the detrimental production of nitrogen oxides, which are emissions that have up to 300 times the greenhouse potential of carbon dioxide. This factor, combined with the lower energy density of ammonia, makes new studies crucial to enable the use of the molecule through methods that reduce emissions whilst ensuring that enough power is produced to support high-energy intensive applications. Thus, this paper presents a numerical study based on the use of novel reaction models employed to characterize ammonia combustion systems. The models are used to obtain Reynolds Averaged Navier-Stokes (RANS) simulations via Star-CCM+ with complex chemistry of a 70%–30% (mol) ammonia–hydrogen blend that is currently under investigations elsewhere. A fixed equivalence ratio (1.2), medium swirl (0.8), and confined conditions are employed to determine the flame and species propagation at various operating atmospheres and temperature inlet values. The study is then expanded to high inlet temperatures, high pressures, and high flowrates at different confinement boundary conditions. The results denote how the production of NOx emissions remains stable and under 400 ppm, whilst higher concentrations of both hydrogen and unreacted ammonia are found in the flue gases under high power conditions. The reduction of heat losses (thus higher temperature boundary conditions) has a crucial impact on further destruction of ammonia post-flame, with a raise in hydrogen, water, and nitrogen through the system, thus presenting an opportunity of combustion efficiency improvement of this blend by reducing heat losses. Final discussions are presented as a method to raise power whilst employing ammonia for gas turbine systems.
The effect of NH, NH 2 , and HNO on NO x and De-NO x chemistry of a NH 3 /H 2 /air mixture at a pressure of 20 bar is investigated. Results suggest that the increase in pressure reduces NO x emissions and increases HO 2 radical production through the reaction H + O 2 (+M) HO 2 (+M). In contrast with OH and O radicals, the HO 2 radical is less reactive, which prevents NO formation. The fuelbound NO x emissions mainly depend on the reactions NH + OH NO + H, HNO(+M) NO + H(+M), HNO + OH NO + H 2 O, and HNO + O 2 NO + HO 2 , and thermal NO x depends on the reactions N + O 2 NO + N and N + OH NO + H. At a pressure of 20 bar, the N 2 O is further converted to NO 2 and N 2 through the reaction N 2 O + NO NO 2 + N 2 . The abundance of HO 2 radicals at high pressure also initiates the conversion of NO to NO 2 via the reaction NO + HO 2 NO 2 + H.
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