Numerical study of laminar nonpremixed methane flames in coflow jets: Autoignited lifted flames with tribrachial edges and MILD combustion at elevated temperatures

In this paper, turbulent non-premixed CH4+H2 jet flame issuing into a hot and diluted co-flow air is studied numerically. This flame is under condition of the moderate or intense low-oxygen dilution (MILD) combustion regime and related to published experimental data. The modelling is carried out using the EDC model to describe turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI2.11 full mechanism are used to represent the chemical reactions of H2/methane jet flame. The flame structure for various O2 levels and jet Reynolds numbers are investigated. The results show that the flame entrainment increases by a decrease in O2 concentration at air side or jet Reynolds number. Local extinction is seen in the upstream and close to the fuel injection nozzle at the shear layer. It leads to the higher flame entertainment in MILD regime. The turbulence kinetic energy decay at centre line of jet decreases by an increase in O2 concentration at hot Co-flow. Also, increase in jet Reynolds or O2 level increases the mixing rate and rate of reactions.

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Numerical study of hydrogen mild combustion

Thermal Science ◽

10.2298/tsci0903059m ◽

2009 ◽

Vol 13 (3) ◽

pp. 59-67 ◽

Cited By ~ 2

Author(s):

Enrico Mollica ◽

Eugenio Giacomazzi ◽

Marco di

Keyword(s):

Numerical Study ◽

Fluid Dynamic ◽

Thermal Gradients ◽

Radiation Model ◽

Dynamic Simulations ◽

Mild Combustion ◽

Preheating Temperature ◽

Nitric Oxide Emissions ◽

Gas Recirculation ◽

Good Agreement

In this article a combustor burning hydrogen and air in mild regime is numerically studied by means of computational fluid dynamic simulations. All the numerical results show a good agreement with experimental data. It is seen that the flow configuration is characterized by strong exhaust gas recirculation with high air preheating temperature. As a consequence, the reaction zone is found to be characteristically broad and the temperature and concentrations fields are sufficiently homogeneous and uniform, leading to a strong abatement of nitric oxide emissions. It is also observed that the reduction of thermal gradients is achieved mainly through the extension of combustion in the whole volume of the combustion chamber, so that a flame front no longer exists ('flameless oxidation'). The effect of preheating, further dilution provided by inner recirculation and of radiation model for the present hydrogen/air mild burner are analyzed.

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Numerical study on a novel burner designed to improve MILD combustion behaviors at the oxygen enriched condition

Applied Thermal Engineering ◽

10.1016/j.applthermaleng.2019.02.023 ◽

2019 ◽

Vol 152 ◽

pp. 686-696 ◽

Cited By ~ 10

Author(s):

Yihao Xie ◽

Yaojie Tu ◽

Hu Jin ◽

Congcong Luan ◽

Zean Wang ◽

...

Keyword(s):

Numerical Study ◽

Mild Combustion ◽

Combustion Behaviors

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Effects of Hydrogen Enrichment on the Reattachment and Hysteresis of Lifted Methane Flames

Volume 1: Fuels and Combustion, Material Handling, Emissions; Steam Generators; Heat Exchangers and Cooling Systems; Turbines, Generators and Auxiliaries; Plant Operations and Maintenance ◽

10.1115/power2013-98031 ◽

2013 ◽

Cited By ~ 1

Author(s):

James D. Kribs ◽

Andrew R. Hutchins ◽

William A. Reach ◽

Tamir S. Hasan ◽

Kevin M. Lyons

Keyword(s):

Burning Velocity ◽

Flame Structure ◽

Flame Stabilization ◽

Dominant Factor ◽

Jet Flame ◽

Lifted Flames ◽

Methane Flames ◽

Hydrogen Enrichment ◽

The Stability ◽

The Impact

The purpose of this study is to observe the effects of hydrogen enrichment on the stability of lifted, partially premixed, methane flames. Due to the relatively large burning velocity of hydrogen-air flames when compared to that of typical hydrocarbon-air flames, hydrogen enriched hydrocarbon flames are able to create stable lifted flames at higher velocities. In order to assess the impact of hydrogen enrichment, a selection of studies in lifted and attached flames were initiated. Experiments were performed that focused on the amount of hydrogen needed to reattach a stable, lifted methane jet flame above the nozzle. Although high fuel velocities strain the flame and cause it to stabilize away from the nozzle, the high burning velocity of hydrogen is clearly a dominant factor, where as the lifted position of the flame increased, the amount of hydrogen needed to reattach the flame increased at the same rate. In addition, it was observed that as the amount of hydrogen in the central jet increased, the change in flame liftoff height increased and hysteresis became more pronounced. It was found that the hysteresis regime, where the flame could either be stabilized at the nozzle or in air, shifted considerably due to the presence of a small amount of hydrogen in the fuel stream. The effects of the hydrogen enrichment, however small the amount of hydrogen compared to the overall jet velocity, was the major factor in the flame stabilization, even showing discernible effects on the flame structure.

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Modeling Soot Formation Using Reduced PAH Chemistry in n-Heptane Lifted Flames With Application to Low Temperature Combustion

ASME 2008 Internal Combustion Engine Division Spring Technical Conference ◽

10.1115/ices2008-1647 ◽

2008 ◽

Cited By ~ 3

Author(s):

Gokul Vishwanathan ◽

Rolf D. Reitz

Keyword(s):

Low Temperature ◽

Soot Formation ◽

Numerical Study ◽

Low Temperature Combustion ◽

Constant Volume Chamber ◽

Soot Mass ◽

Temperature Combustion ◽

Lifted Flames ◽

Polycyclic Aromatic ◽

Species Comparisons

A numerical study of in-cylinder soot formation and oxidation processes in n-heptane lifted flames using various soot inception species has been conducted. In a recent study by the authors, it was found that the soot formation and growth regions in lifted flames were not adequately represented by using acetylene alone as the soot inception species. Comparisons with a conceptual model and available experimental data suggested that the location of soot formation regions could be better represented if polycyclic aromatic hydrocarbon (PAH) species were considered as alternatives to acetylene for soot formation processes. Since the local temperatures are much lower under low temperature combustion (LTC) conditions, it is believed that significant soot mass contribution can be attributed to PAH rather than to acetylene. To quantify and validate the above observations, a reduced n-heptane chemistry mechanism has been extended to include PAH species up to four fused aromatic rings (pyrene). The resulting chemistry mechanism was integrated into the multidimensional CFD code KIVA-CHEMKIN for modeling soot formation in lifted flames in a constant volume chamber. The investigation revealed that a simpler model that only considers up to phenanthrene (three fused rings) as the soot inception species has good possibilities for better soot location predictions. The present work highlights and illustrates the various research challenges toward accurate qualitative and quantitative predictions of soot for new low emission combustion strategies for I.C. engines.

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