scholarly journals Effects of CO2 Dilution on Methane Ignition in Moderate or Intense Low-oxygen Dilution (MILD) Combustion: A Numerical Study

2012 ◽  
Vol 20 (4) ◽  
pp. 701-709 ◽  
Author(s):  
Zhenjun CAO ◽  
Tong ZHU
Keyword(s):  
Numerical Study ◽  
Low Oxygen ◽  
Mild Combustion

scholarly journals Numerical study of flame structure in the mild combustion regime

2015 ◽  
Vol 19 (1) ◽  
pp. 21-34 ◽  
Author(s):  
Amir Mardani ◽  
Sadegh Tabejamaat
Keyword(s):  
Fuel Injection ◽  
Numerical Study ◽  
Flame Structure ◽  
Combustion Regime ◽  
Low Oxygen ◽  
Mixing Rate ◽  
Jet Flame ◽  
Reduced Mechanism ◽  
Mild Combustion ◽  
O2 Concentration

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.

Numerical Study of the Effect of Nozzle Configurations on Characteristics of MILD Combustion for Gas Turbine Application

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Xiaowen Deng ◽  
Yan Xiong ◽  
Hong Yin ◽  
Qingshui Gao
Keyword(s):  
Gas Turbine ◽  
Numerical Study ◽  
Combustion Efficiency ◽  
Low Noise ◽  
Peak Temperature ◽  
Pollutant Emissions ◽  
Operating Point ◽  
Low Oxygen ◽  
Mild Combustion ◽  
Jet Velocity

The MILD (moderate or intense low-oxygen dilution) combustion is characterized by low emission, stable combustion, and low noise for various kinds of fuel. This paper reports a numerical investigation of the effect of different nozzle configurations, such as nozzle number N, reactants jet velocity V, premixed and nonpremixed modes, on the characteristics of MILD combustion applied to one F class gas turbine combustor. An operating point is selected considering the pressure p = 1.63 MPa, heat intensity Pintensity = 20.5 MW/m3 atm, air preheated temperature Ta = 723 K, equivalence ratio φ = 0.625. Methane (CH4) is adopted as the fuel for combustion. Results show that low-temperature zone shrinks while the peak temperature rises as the nozzle number increases. Higher jet velocity will lead to larger recirculation ratio and the reaction time will be prolonged consequently. It is helpful to keep high combustion efficiency but can increase the NO emission obviously. It is also found that N = 12 and V = 110 m/s may be the best combination of configuration and operating point. The premixed combustion mode will achieve more uniform reaction zone, lower peak temperature, and pollutant emissions compared with the nonpremixed mode.

Premixed Moderate or Intense Low-Oxygen Dilution (MILD) Combustion from a Single Jet Burner in a Laboratory-Scale Furnace

2011 ◽  
Vol 25 (7) ◽  
pp. 2782-2793 ◽  
Author(s):  
Pengfei Li ◽  
Jianchun Mi ◽  
Bassam B. Dally ◽  
Richard A. Craig ◽  
Feifei Wang
Keyword(s):  
Laboratory Scale ◽  
Low Oxygen ◽  
Mild Combustion ◽  
Single Jet

scholarly journals Numerical study of hydrogen mild combustion

2009 ◽  
Vol 13 (3) ◽  
pp. 59-67 ◽  
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.

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

2019 ◽  
Vol 152 ◽  
pp. 686-696 ◽  
Author(s):  
Yihao Xie ◽  
Yaojie Tu ◽  
Hu Jin ◽  
Congcong Luan ◽  
Zean Wang ◽  
...  
Keyword(s):  
Numerical Study ◽  
Mild Combustion ◽  
Combustion Behaviors

Theoretical Study on Chemical-Kinetic Characteristics of Oxy-Coal Mild Combustion

2016 ◽  
Author(s):  
Ruochen Liu ◽  
Enke An ◽  
Kun Wu
Keyword(s):  
Activation Energy ◽  
Oxygen Concentration ◽  
Reaction Pathway ◽  
Chemical Kinetic ◽  
State Theory ◽  
Kinetic Characteristics ◽  
Low Oxygen ◽  
Elementary Reactions ◽  
Mild Combustion ◽  
Low Oxygen Concentration

The chemical-kinetic characteristics of oxy-coal MILD combustion under different initial temperature and oxygen concentration were studied numerically. Aromatic benzene was considered representative for coal molecule. A unique reaction pathway under low oxygen concentration was obtained, the activation energy and reaction rate constant of involved elementary reactions were calculated through classic transition state theory (TST). The results show that low oxygen concentration and high temperature is advantageous for thickening flame front as well as slowing down flame propagation; as oxygen concentration and temperature increase, the global activation energy increases with greater slope; the decomposition of C5H5 dominates under high oxygen concentration, while the decomposition and oxidation of C5H5 become equally important as oxygen concentration decreases, leading to a new pathway that the complexity of overall chemical reactions develops; the radical CH2CHO is easily trigged under low oxygen concentration, its decomposition reaction dominates in the unique pathway C5H5→C5H4O→c-C4H5CH2CHO→CH3 due to larger activation energy, where more CO escapes. The simulation results have theoretical referencing value, laying foundations for the further practical work.

Actuation Studies for Active Control of Mild Combustion for Gas Turbine Application

2014 ◽  
Author(s):  
Emilien Varea ◽  
Stephan Kruse ◽  
Heinz Pitsch ◽  
Thivaharan Albin ◽  
Dirk Abel
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Active Control ◽  
Gas Turbines ◽  
Reverse Flow ◽  
Air Flow ◽  
Combustion Regime ◽  
Nox Emissions ◽  
Low Oxygen ◽  
Mild Combustion

MILD combustion (Moderate or Intense Low Oxygen Dilution) is a well known technique that can substantially reduce high temperature regions in burners and thereby reduce thermal NOx emissions. This technology has been successfully applied to conventional furnace systems and seems to be an auspicious concept for reducing NOx and CO emissions in stationary gas turbines. To achieve a flameless combustion regime, fast mixing of recirculated burnt gases with fresh air and fuel in the combustion chamber is needed. In the present study, the combustor concept is based on the reverse flow configuration with two concentrically arranged nozzles for fuel and air injections. The present work deals with the active control of MILD combustion for gas turbine applications. For this purpose, a new concept of air flow rate pulsation is introduced. The pulsating unit offers the possibility to vary the inlet pressure conditions with a high degree of freedom: amplitude, frequency and waveform. The influence of air flow pulsation on MILD combustion is analyzed in terms of NOx and CO emissions. Results under atmospheric pressure show a drastic decrease of NOx emissions, up to 55%, when the pulsating unit is active. CO emissions are maintained at a very low level so that flame extinction is not observed. To get more insights into the effects of pulsation on combustion characteristics, velocity fields in cold flow conditions are investigated. Results show a large radial transfer of flow when pulsation is activated, hence enhancing the mixing process. The flame behavior is analyzed by using OH* chemiluminescence. Images show a larger distributed reaction region over the combustion chamber for pulsation conditions, confirming the hypothesis of a better mixing between fresh and burnt gases.

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