On the roles of humidification and radiation during the ignition of ammonia–hydrogen–air mixtures

Zheng, Sining; Líu, Hao; Wang, Yiqing; Chen, Xinyi; Sui, Ran; Lü, Qiang

doi:10.1016/j.combustflame.2023.112832

Cited by 10 publications

(1 citation statement)

References 32 publications

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“…Since the experimental temperature and pressure range of the kinetic mechanism proposed by Mei et al is close to the research in this work, and it is a relatively new research study on the reaction mechanism of ammonia combustion, this mechanism was selected for the numerical calculation of the ammonia/air mixture at the flammability concentrations. Since the thermal radiation of ammonia has a strong influence on the mechanistic analysis of ammonia flames, − and the influence of radiation reabsorption on the flame velocity is mainly determined by free radicals, the changes of free radicals are also discussed.…”

Section: Discussionmentioning

confidence: 99%

Flammability Limits of Ammonia in Air from 298 to 423 K at Elevated Pressures

Fu,

Zhou,

et al. 2024

Energy Fuels

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The flammability limit (FL) data of ammonia at elevated temperatures and pressures are useful for fire prevention and control of the storage, transportation, and bunkering process of a large amount of ammonia, as well as for the detailed study of the reaction kinetics of ammonia-containing alternative fuels. In this work, the FLs of ammonia were measured in the temperature range from 298 to 423 K and in the pressure range from 0.05 to 0.5 MPa based on the ASTM E918 and EN 1839 standards, and the ammonia concentrations at the FLs were characterized using the mole fraction and volume fraction, respectively. The FLs of ammonia varied linearly with the temperature and logarithmically with the pressure. The combined effect of the temperature and pressure expanded the FLs of ammonia and increased the likelihood of an explosion. By correlating the FLs of ammonia, the correlated results of ammonia FLs varying with the temperature and pressure were obtained. The mean absolute deviation between the fitted values and the experimental values of ammonia at the lower FLs (LFLs) was 0.22%, while at the upper FLs (UFLs) it was 0.37%. The influence of the temperature and pressure on the ammonia FLs was explained by using the reaction kinetics of ammonia combustion. The presence of OH radicals was crucial for the LFLs in the ammonia/air mixture, followed by NH2 radicals. The UFLs in the ammonia/air mixture were highly dependent on the change of NH2 radicals. The formation of NH2 radicals primarily relied on the elementary reaction NH3 + OH⇔NH2 + H2O at the lower and upper FLs. The peak value of the free radical mole fraction gradually decreased with increasing experimental pressure. The increase in pressure resulted in a significant increase in the change rate of radical ROP, while the increase in temperature resulted in a slight decrease in the rate of change.

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Section: Discussionmentioning

confidence: 99%

Flammability Limits of Ammonia in Air from 298 to 423 K at Elevated Pressures

Fu,

Zhou,

et al. 2024

Energy Fuels

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Stochastic Modeling of Partially Stirred Reactor (PaSR) for the Investigation of the Turbulence-Chemistry Interaction for the Ammonia-Air Combustion

Yu,

Cai,

Chen

2023

Flow Turbulence Combust

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The Partially Stirred Reactor (PaSR) model is carried out for the ammonia-air combustion system by means of stochastic modeling, namely by solving the transport equation for the joint Probability Density Function (PDF). The turbulent mixing is accounted for by the Linear Mean-Square Estimation (LMSE) mixing model. Notwithstanding the simplified nature of the PaSR modeling, the transported-PDF method enables capturing the effect of mixing frequency on the combustion system, especially the NOx emission. Since the chemical source term is in a closed form in the transported-PDF method, it allows us to apply different chemical mechanisms to explore, whether the set of elementary reactions that are identified as important for the prediction of NOx in the PaSR model is sensitive to the choice of chemical mechanisms. Furthermore, the effect of the residence time in the PaSR model has also been studied, and compared with those in the Perfectly Stirred Reactor (PSR) model (infinite large mixing frequency). Moreover, since the ammonia under oxygen enrichment shows some similar combustion behaviors in terms of e.g. laminar burning velocity as the ammonia under hydrogen enrichment, how large the difference of thermo-kinetic states (e.g. temperature and NOx emission) predicted by PaSR models and in laminar premixed flame configuration is also investigated. A further discussion focuses on the effect of thermal radiation, where the radiative heat loss roles in the prediction of NOx for the turbulent simulation is examined. By using the optically thin approximation model, it is shown that the thermal radiation exhibits little effect on the considered combustion systems within a typical turbulent time-scale.

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