Probing the gas-phase oxidation of ammonia: Addressing uncertainties with theoretical calculations

Chavarrio, Javier E.; Monge‐Palacios, M.; Zhang, Xiaoyuan; Sarathy, S. Mani

doi:10.1016/j.combustflame.2021.111708

Cited by 21 publications

(6 citation statements)

References 59 publications

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“…A high BF 1b (>74%, see Mech2, Mech4, Mech5, and Mech7) also leads to the underestimation of the IDTs for neat NH 3 and NH 3 fuel blends under RCM conditions with elevated pressures. Recent theoretical calculations 60,66,67 all suggest k 1a should be increased in comparison to the value from Sumathi et al; 65 namely, BF 1b should be lowered. However, the reactivity is significantly underestimated for RCM conditions, when the BF 1b is lower than 23% (see Mech6).…”

Section: Discussionmentioning

confidence: 85%

“…Unlike the well-studied important reactions, e.g., NH 2 + NO and NH 2 + NO 2 , the rate coefficient ( k ) and the branching ratio of NH 2 + HO 2 have not been experimentally studied at combustion-related temperatures. However, several theoretical studies ,− were recently released regarding the calculation of the rate coefficient of R1 ( k 1 ). Therefore, this work focuses on discussing the effect of k 1 on model prediction.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…As shown in Table , the adopted k 1a and k 1b are originally from six works. ,− ,, Sumathi and Peyerimhoff calculated the k of all channels theoretically and proposed that the chain-propagating R1b ( BF 1b = 92%) is the most dominant one (Mech2). Recently, Stagni et al recalculated the rate coefficient of NH 3 + O 2 ⇄ NH 2 + HO 2 (reversed R1a) and increased k 1a by a factor of more than 1 × 10 4 .…”

Section: Numerical Simulationmentioning

confidence: 99%

“…They proposed to adopt k 1b from the recommendation by Baulch et al, resulting in the comparable k 1a and k 1b (Mech1). Zhang et al adopted k 1a from the recent theoretical calculation by Chavarrio Cañas et al and k 1b from the estimation by Glarborg et al (Mech3). Mech3 and Mech1 have similar BF s of R1.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…compares the branching fractions (BF) of each reaction channel and the total k 1 at a specific temperature of 1000 K. The BF of one channel is defined as the fraction of its k in the total k of the reaction, e.g., As shown in Table 3, the adopted k 1a and k 1b are originally from six works. 60,[65][66][67]72,73 Sumathi and Peyerimhoff 65 calculated the k of all channels theoretically and proposed that the chain-propagating R1b (BF 1b = 92%) is the most dominant one (Mech2). Recently, Stagni et al 60 recalculated the rate coefficient of NH 3 + O 2 ⇄ NH 2 + HO 2 (reversed R1a) and increased k 1a by a factor of more than 1 × 10 4 .…”

Section: Numerical Simulationmentioning

confidence: 99%

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Exploring the Effect of Different Reactivity Promoters on the Oxidation of Ammonia in a Jet-Stirred Reactor

Shu

et al. 2023

J. Phys. Chem. A

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The low reactivity of ammonia (NH 3 ) is the main barrier to applying neat NH 3 as fuel in technical applications, such as internal combustion engines and gas turbines. Introducing combustion promoters as additives in NH 3 -based fuel can be a feasible solution. In this work, the oxidation of ammonia by adding different reactivity promoters, i.e., hydrogen (H 2 ), methane (CH 4 ), and methanol (CH 3 OH), was investigated in a jet-stirred reactor (JSR) at temperatures between 700 and 1200 K and at a pressure of 1 bar. The effect of ozone (O 3 ) was also studied, starting from an extremely low temperature (450 K). Species mole fraction profiles as a function of the temperature were measured by molecular-beam mass spectrometry (MBMS). With the help of the promoters, NH 3 consumption can be triggered at lower temperatures than in the neat NH 3 case. CH 3 OH has the most prominent effect on enhancing the reactivity, followed by H 2 and CH 4 . Furthermore, two-stage NH 3 consumption was observed in NH 3 /CH 3 OH blends, whereas no such phenomenon was found by adding H 2 or CH 4 . The mechanism constructed in this work can reasonably reproduce the promoting effect of the additives on NH 3 oxidation. The cyanide chemistry is validated by the measurement of HCN and HNCO. The reaction CH 2 O + NH 2 ⇄ HCO + NH 3 is responsible for the underestimation of CH 2 O in NH 3 /CH 4 fuel blends. The discrepancies observed in the modeling of NH 3 fuel blends are mainly due to the deviations in the neat NH 3 case. The total rate coefficient and the branching ratio of NH 2 + HO 2 are still controversial. The high branching fraction of the chain-propagating channel NH 2 + HO 2 ⇄ H 2 NO + OH improves the model performance under lowpressure JSR conditions for neat NH 3 but overestimates the reactivity for NH 3 fuel blends. Based on this mechanism, the reaction pathway and rate of production analyses were conducted. The HONO-related reaction routine was found to be activated uniquely by adding CH 3 OH, which enhances the reactivity most significantly. It was observed from the experiment that adding ozone to the oxidant can effectively initiate NH 3 consumption at temperatures below 450 K but unexpectedly inhibit the NH 3 consumption at temperatures higher than 900 K. The preliminary mechanism reveals that adding the elementary reactions between NH 3 -related species and O 3 is effective for improving the model performance, but their rate coefficients have to be refined.

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Section: Discussionmentioning

confidence: 85%

Section: Numerical Simulationmentioning

confidence: 99%

Section: Numerical Simulationmentioning

confidence: 99%

Section: Numerical Simulationmentioning

confidence: 99%

Section: Numerical Simulationmentioning

confidence: 99%

See 3 more Smart Citations

Exploring the Effect of Different Reactivity Promoters on the Oxidation of Ammonia in a Jet-Stirred Reactor

Shu

et al. 2023

J. Phys. Chem. A

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MILD Combustion of Ammonia, from Kinetics to Applications

Sabia,

Sorrentino,

Manna

et al. 2024

Energy, Environment, and Sustainability

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Experimental and numerical analyses of nitrogen oxides formation in a high ammonia-low hydrogen blend using a tangential swirl burner

et al. 2022

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Ammonia has been considered as a novel fuel for decarbonization purposes. However, emissions from combustion systems are still posing a problem. Therefore, experimental and numerical simulations have been conducted to study the concentration of exhaust emissions (Nitric oxide “NO”, Nitrous oxide “N2O”) from burning the ammonia/hydrogen (NH3/H2) blend 85/15 (vol%). The effects were measured at various thermal powers ranging 10 to 20 kW and with different Reynolds numbers from 20,000—40,000. The experimental points were numerically investigated in the Ansys CHEMKIN-Pro environment employing seven chemical kinetic mechanisms taken from the literature. All experiments have been undertaken at standard atmospheric conditions. The experimental results showed that both NO and N2O gradually increased when the Reynolds number increased from 20,000 to 40,000. Along with that, the concentration of NO emissions at the exhaust reported minimum level when the Re = 20,000 due to lower reactivity radical formation, all that led to a deterioration of the flame characteristics. Also, the integrated radical intensities of NO*, OH*, NH*, and NH2* demonstrate an increasing trend as Re increased from 20,000 to 40,000. In terms of thermal power, N2O suffered an abrupt decrease when the thermal power increased up to 15 kW, while the opposite occurs for NO. In addition, the radicals intensity of OH*, NH*and NH2* figures show an increase in their concentration when the thermal power increased up to 15 kW then decreased with increasing thermal intensity to reach 20 kW, reflecting into increased NO productions and decreased N2O levels. The numerical analysis showed that Stagni, Bertolino, and Bowen Mei were the most accurate mechanisms as these give a good prediction for NO and N2O. The study also showed that the chemical reaction (HNO + O2 ↔ NO + HO2) is the main source of NO formation. While the chemical reaction (NH + NO ↔ N2O + H) is responsible for the formation of N2O by consuming NO and when there will be abundance in NH radicals. Finally, dealing with a blended fuel of high ammonia concentration encourages ammonia chemistry to become more dominant in the flame. It decreases the flame temperature, hence lowering heat loss between the flame and the surrounding.

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Probing the gas-phase oxidation of ammonia: Addressing uncertainties with theoretical calculations

Cited by 21 publications

References 59 publications

Exploring the Effect of Different Reactivity Promoters on the Oxidation of Ammonia in a Jet-Stirred Reactor

Exploring the Effect of Different Reactivity Promoters on the Oxidation of Ammonia in a Jet-Stirred Reactor

MILD Combustion of Ammonia, from Kinetics to Applications

Experimental and numerical analyses of nitrogen oxides formation in a high ammonia-low hydrogen blend using a tangential swirl burner

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