Turbulent Flame Characteristics of Oxycoal MILD Combustion

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Ruochen Liu ◽  
Enke An
Keyword(s):  
Ignition Temperature ◽  
Turbulent Flame ◽  
Maximum Temperature ◽  
Low Oxygen ◽  
Mild Conditions ◽  
Mild Combustion ◽  
Global Regime ◽  
Higher Temperature ◽  
Cylindrical Furnace ◽  
Flame Behavior

Oxycoal combustion was numerically simulated in a lab-scale cylindrical furnace (Φ200 mm × 2 m) with high-velocity oxygen jets. The mesoscopic characteristics of turbulent flame behavior such as nondimensional numbers ReT, Ka, and Da were calculated under different jet positions and jet spacing. The results show that for coflow burners, large spacing (L = 75 mm) is not favored due to poor radial mixing and the restriction of wall; except L = 75 mm, as jet spacing increases, the oxidizer flow could be internally diluted to a lower concentration and preheated to a higher temperature, at least 1000 K; for L = 60 mm conditions, the maximum temperature increase is lower than the ignition temperature (437 °C), they are, namely, oxycoal moderate or intense low oxygen dilution (MILD) combustion. For MILD conditions, the mesoscopic parameters of the flame front where temperature gradient is the largest locate in the distributed regime corresponding to l/lF > 1, ReT > 1, Kaδ > 1, and Da < 1, the global regime is depicted as 1 < l/lF < 4, 60 < ReT < 150, 50 < Ka < 500, and Da < 1; for flaming conditions, the regime is depicted as 1 < l/lF < 6, 40 < ReT < 110, 10 < Ka < 800, and Da < 1.

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.

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

Stability and emission characteristics of nonpremixed MILD combustion from a parallel-jet burner in a cylindrical furnace

Energy ◽  
2019 ◽  
Vol 170 ◽  
pp. 1181-1190 ◽  
Author(s):  
Kin-Pang Cheong ◽  
Guochang Wang ◽  
Bo Wang ◽  
Rong Zhu ◽  
Wei Ren ◽  
...  
Keyword(s):  
Emission Characteristics ◽  
Mild Combustion ◽  
Cylindrical Furnace

scholarly journals Resistance of Corynebacterium pseudotuberculosis in the Brazilian semiarid environment

2018 ◽  
Vol 38 (6) ◽  
pp. 1091-1096 ◽  
Author(s):  
Maria C.A. Sá ◽  
Samily A.S. Oliveira ◽  
Edmilson M. Dantas Jr ◽  
Gisele V. Gouveia ◽  
João J.S. Gouveia ◽  
...  
Keyword(s):  
Survival Rates ◽  
Control Measures ◽  
Corynebacterium Pseudotuberculosis ◽  
Maximum Temperature ◽  
Caseous Lymphadenitis ◽  
Biofilm Production ◽  
Brazilian Semiarid ◽  
Higher Temperature ◽  
Inoculum Survival

ABSTRACT: The semiarid northeast of Brazil contains a unique biome known as caatinga, with a maximum temperature of 40 ºC and a relativity humidity of 56%. The caatinga is characterized by a variety of plants, including Cereus jamacaru Dc (mandacaru), Poincianella microphylla Mart. ex G. Don (catingueira), Pilosocereus gounellei FAC Weber (xique-xique) and Mimosa tenuiflora (Willd.) Poir (jurema preta). Sheep and goat industries are economically strong in that region, despite the fact that caseous lymphadenitis is highly prevalent. The aim of the present study was to assess the survival and biofilm production of Corynebacterium pseudotuberculosis isolates in the environment and under controlled temperatures (28°C, 37°C and 42°C) under different surfaces (plants, soil, wood, wire and thorns). In addition, we investigated the effects of applying the disinfectants chlorhexidine, hypochlorite and quaternary ammonia in soil, tiles, wood and vegetation cover. Four strains of C. pseudotuberculosis were selected (two from goats and two from sheep) for inoculation according to their in vitro biofilm production. Adherence to microplates was used to assess the biofilm-forming ability of the bacteria. Lower survival rates were observed when isolates of C. pseudotuberculosis were subjected to a temperature of 42°C. In terms of caatinga biome plants, contamination of jurema-preta plants resulted in the lowest survival rates. The disinfectant quaternary ammonia promoted a lower inoculum survival in all surfaces. The disinfectants and the higher temperature contributed to the reduction of biofilm production in isolates of C. pseudotuberculosis. knowledge of these patterns is important for the establishment of disease control measures, given the questionable efficacy of the treatment and the immuno-prophylaxis of caseous lymphadenitis.

scholarly journals Turbulent Flame Shape Switching at Conditions Relevant for Gas Turbines

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Ivan Langella ◽  
Johannes Heinze ◽  
Thomas Behrendt ◽  
Lena Voigt ◽  
Nedunchezhian Swaminathan ◽  
...  
Keyword(s):  
Turbulent Combustion ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Interaction Model ◽  
Numerical Approach ◽  
Reacting Flow ◽  
Combustion Chambers ◽  
Lean Burn ◽  
Large Eddy ◽  
Flame Behavior

Abstract A numerical investigation is conducted to shed light on the reasons leading to different flame configurations in gas turbine (GT) combustion chambers of aeronautical interest. Large eddy simulations (LES) with a flamelet-based combustion closure are employed for this purpose to simulate the DLR-AT big optical single sector (BOSS) rig fitted with a Rolls-Royce developmental lean burn injector. The reacting flow field downstream this injector is sensitive to the intricate turbulent–combustion interaction and exhibits two different configurations: (i) a penetrating central jet leading to an M-shape lifted flame; or (ii) a diverging jet leading to a V-shaped flame. The LES results are validated using available BOSS rig measurements, and comparisons show the numerical approach used is consistent and works well. The turbulent–combustion interaction model terms and parameters are then varied systematically to assess the flame behavior. The influences observed are discussed from physical and modeling perspectives to develop physical understanding on the flame behavior in practical combustors for both scientific and design purposes.

Effect of CO2/N2 Dilution on Premixed Methane–Air Flame Stability Under Strained Conditions

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Joseph S. Feser ◽  
Ashwani K. Gupta
Keyword(s):  
Thermal Stresses ◽  
Strain Rates ◽  
Low Oxygen ◽  
Temperature Dependent ◽  
Lower Strain ◽  
Pollutants Emission ◽  
Stable Flame ◽  
Thermal Intensity ◽  
Flame Behavior ◽  
Low Oxygen Concentration

The effects of adding N2 or CO2 as diluents to a premixed methane–air flames under strain conditions (associated with a stagnation plate) were examined for flame stand-off distance, stability, intensity, and global flame behavior at various equivalence ratios. A stagnation plate was used to simulate the flame behavior near a combustor wall that can help provide some insights into reducing thermal stresses and enhance combustor lifetime. Decrease in equivalence ratio at the same thermal intensity provided larger strain rates while maintaining a stable flame. At stoichiometric condition, a balance was provided between high strain rates and low oxygen concentration flames to mitigate the peak (maximum) flame temperatures, and the associated temperature-dependent pollutants emission, such as NOx, CO, and unburnt hydrocarbons. Higher thermal intensities provided higher strain rates; however, the addition of diluents impacted in destabilization of flame. The flame stand-off behavior occurred at lower strain rates, low thermal intensity, and increased equivalence ratios. CO2 dilution reduced flame intensity, increased flame stand-off distance and overall flame destabilization than that with N2 dilution.

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.

scholarly journals Effect of Low and High Viscosity Composites on Temperature Rise of Premolars Restored through the Bulk-Fill and the Incremental Layering Techniques

2020 ◽  
Vol 10 (22) ◽  
pp. 8041
Author(s):  
Roberto De Santis ◽  
Vito Gallicchio ◽  
Vincenzo Lodato ◽  
Sandro Rengo ◽  
Alessandra Valletta ◽  
...  
Keyword(s):  
Temperature Rise ◽  
High Viscosity ◽  
Single Step ◽  
Maximum Temperature ◽  
Main Concern ◽  
Light Curing ◽  
Higher Temperature ◽  
Temperature Rate ◽  
Dental Cavities ◽  
Flowable Composites

Background: Deep dental cavities can be restored through a single step according to the bulk-fill technique. Due to the great amount of resin to be cured, a main concern is the temperature rise occurring in the pulp chamber, potentially higher than that developed through the incremental layering technique. Temperature rise of bulk-fill composites have been evaluated. Methods: Bulk-fill composites, differing in material composition and viscosity, were used. Maximum temperature and temperature rate occurring in the composites were measured. Mesio-occlusal-distal cavities of human premolars were restored through the bulk-fill or the incremental layering techniques, and peak temperature and temperature rate occurring in the dentin, 1 mm below the cavity floor, were evaluated. Results: Temperature peak and temperature rise of flowable composites were significantly higher (p < 0.05) than packable composites. For both the techniques, higher temperature peaks were recorded in the dentin for flowable composites. Peak temperatures higher than 42 °C were recorded for the incremental layering technique considering flowable composites. Conclusions: For all the composites, the light curing modality of 1000 mW/cm2 for 20 s can be considered safe if the bulk-fill technique is performed. Instead, for the incremental layering technique, potentially dangerous temperature peaks have been recorded for flowable composites.

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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