scholarly journals Numerical investigation of low-velocity filtration combustion instability based on the initial preheating non-uniformity

2019 ◽  
Vol 136 ◽  
pp. 02040
Author(s):  
Yongfang Xia ◽  
Tingyong Fang ◽  
Haitao Wang ◽  
Erbao Guo ◽  
Jinwei Ma
Keyword(s):  
Flame Front ◽  
Equivalence Ratio ◽  
Hydrodynamic Instability ◽  
Packed Bed ◽  
Filtration Velocity ◽  
Thermal Perturbation ◽  
Low Velocity ◽  
Preheating Temperature ◽  
Deformation Behaviors ◽  
Fuel Leakage

The effects of the initial preheating perturbation on the dynamical behaviors of FGC wave propagation instability for low-velocity FGC in packed bed are studied numerically. The behaviors of the flame front inclination, break, and shrinking instabilities are always observed in experiments. Based on the experimental phenomena, an initial thermal perturbation model is numerically proposed as to predict the deformation behaviors of the flame front instabilities. The typical flame shapes are obtained depending on filtration velocity, equivalence ratio, and initial preheating temperature difference. It is demonstrated that the development of flame front inclination instability is proportional to the magnitude of initial preheating perturbation. At a lower equivalence ratio, the initial thermal perturbation of 300 K leads to the evolution of flame front break. Increasing filtration velocity leads to the appearance of flame front break, due to the intensification of the hydrodynamic instability. In addition, a perculiar instability of flame front shifting is also confirmed with the initial thermal perturbation of 400 K, which results in a fuel leakage of incomplete combustion.

Flame Characteristics and Turbulent Flame Speeds of Turbulent, High-Pressure, Lean Premixed Methane/Air Flames

2005 ◽  
Author(s):  
P. Griebel ◽  
R. Bombach ◽  
A. Inauen ◽  
R. Scha¨ren ◽  
S. Schenker ◽  
...  
Keyword(s):  
Flame Front ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Turbulent Flame Speed ◽  
Front Position ◽  
Preheating Temperature ◽  
Lean Premixed

The present experimental study focuses on flame characteristics and turbulent flame speeds of lean premixed flames typical for stationary gas turbines. Measurements were performed in a generic combustor at a preheating temperature of 673 K, pressures up to 14.4 bars (absolute), a bulk velocity of 40 m/s, and an equivalence ratio in the range of 0.43–0.56. Turbulence intensities and integral length scales were measured in an isothermal flow field with Particle Image Velocimetry (PIV). The turbulence intensity (u′) and the integral length scale (LT) at the combustor inlet were varied using turbulence grids with different blockage ratios and different hole diameters. The position, shape, and fluctuation of the flame front were characterized by a statistical analysis of Planar Laser Induced Fluorescence images of the OH radical (OH-PLIF). Turbulent flame speeds were calculated and their dependence on operating conditions (p, φ) and turbulence quantities (u′, LT) are discussed and compared to correlations from literature. No influence of pressure on the most probable flame front position or on the turbulent flame speed was observed. As expected, the equivalence ratio had a strong influence on the most probable flame front position, the spatial flame front fluctuation, and the turbulent flame speed. Decreasing the equivalence ratio results in a shift of the flame front position farther downstream due to the lower fuel concentration and the lower adiabatic flame temperature and subsequently lower turbulent flame speed. Flames operated at leaner equivalence ratios show a broader spatial fluctuation as the lean blow-out limit is approached and therefore are more susceptible to flow disturbances. In addition, because of a lower turbulent flame speed these flames stabilize farther downstream in a region with higher velocity fluctuations. This increases the fluctuation of the flame front. Flames with higher turbulence quantities (u′, LT) in the vicinity of the combustor inlet exhibited a shorter length and a higher calculated flame speed. An enhanced turbulent heat and mass transport from the recirculation zone to the flame root location due to an intensified mixing which might increase the preheating temperature or the radical concentration is believed to be the reason for that.

Characteristic analysis of low-velocity gas filtration combustion in an inert packed bed

2006 ◽  
Vol 10 (4) ◽  
pp. 683-700 ◽  
Author(s):  
G. Zhang ◽  
X. Cai ◽  
M. Liu ◽  
B. Lin ◽  
Y. Chen ◽  
...  
Keyword(s):  
Filtration Combustion ◽  
Packed Bed ◽  
Gas Filtration ◽  
Characteristic Analysis ◽  
Low Velocity

Effects of the Equivalence Ratio and Reynolds Number on Turbulence and Flame Front Interactions by Direct Numerical Simulation

2016 ◽  
Vol 30 (8) ◽  
pp. 6727-6737 ◽  
Author(s):  
Cong Xu ◽  
Zhihua Wang ◽  
Wubin Weng ◽  
Kaidi Wan ◽  
Ronald Whiddon ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Flame Front ◽  
Equivalence Ratio

Micro Combustor Development Using Hydrogen As Fuel

2018 ◽  
Author(s):  
Ronak Shah ◽  
Digvijay Kulshreshtha ◽  
Nisarg Chaudhari
Keyword(s):  
Flame Front ◽  
Reaction Zone ◽  
Equivalence Ratio ◽  
Cross Sectional ◽  
Turbine Engine ◽  
Micro Gas Turbine ◽  
Constant Area ◽  
Stable Flame ◽  
Temperature Levels ◽  
Micro Combustor

Swiss Roll Combustor of 1 W capacity for micro gas turbine engine is operated with premixed hydrogen air mixture at ultra-lean equivalence ratio. The reaction zone under consideration has volume of 60 mm3. The reactant passage and product passage are coiled around the reaction zone facilitating the recovery of heat loss, by preheating the reactants. The reactants are entered through an increasing cross-sectional area passage from 0.6mm × 5mm inlet to 1.5mm × 5mm outlet, thereby reducing the velocity levels in the reactant passage, facilitating stable combustor operation. The combustor performance parameters, temperature levels, pattern factor and emissions are measured is operated at ultra-lean equivalence ratio of 0.12 to lean equivalence ratio of 0.43, for premixed hydrogen air combustion. The results are compared at similar (not same) equivalence ratios for constant area reactant passage. The visual inspection shows stable flame front in the combustion zone for variable area passage and extended flame front in the constant area passage combustor. However, the combustor performance deteriorates drastically above equivalence ratio of 0.43, leading to hot spots generation on walls.

Heat transfer between wall and packed bed crossed by low velocity airflow

2006 ◽  
Vol 26 (16) ◽  
pp. 1951-1960 ◽  
Author(s):  
O. Laguerre ◽  
S. Ben Amara ◽  
D. Flick
Keyword(s):  
Heat Transfer ◽  
Packed Bed ◽  
Low Velocity

Impact of Cooling Air Injection on the Combustion Stability of a Premixed Swirl Burner Near Lean Blowout

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
A. Marosky ◽  
V. Seidel ◽  
T. Sattelmayer ◽  
F. Magni ◽  
W. Geng
Keyword(s):  
Flame Front ◽  
Equivalence Ratio ◽  
Flame Stabilization ◽  
Air Injection ◽  
Combustion Stability ◽  
Nox Emissions ◽  
Test Rig ◽  
Lean Blowout ◽  
Burner Exit ◽  
Cooling Air

In most dry, low-NOx combustor designs of stationary gas turbines, the front panel impingement cooling air is directly injected into the combustor primary zone. This air partially mixes with the swirling flow of premixed reactants from the burner and reduces the effective equivalence ratio in the flame. However, local unmixedness and the lean equivalence ratio are supposed to have a major impact on combustion performance. The overall goal of this investigation is to answer the question of whether the cooling air injection into the primary combustor zone has a beneficial effect on combustion stability and NOx emissions or not. The flame stabilization of a typical swirl burner with and without front panel cooling air injection is studied in detail under atmospheric conditions close to the lean blowout limit (LBO) in a full-scale, single-burner combustion test rig. Based on previous isothermal investigations, a typical injection configuration is implemented for the combustion tests. Isothermal results of experimental studies in a water test rig adopting high-speed planar laser-induced fluorescence (HSPLIF) reveal the spatial and temporal mixing characteristics for the experimental setup studied under atmospheric combustion. This paper focuses on the effects of cooling air injection on both flame dynamics and emissions in the reacting case. To reveal dependencies of cooling air injection on combustion stability and NOx emissions, the amount of injected cooling air is varied. OH*-chemiluminescence measurements are applied to characterize the impact of cooling air injection on the flame front. Emissions are collected for different cooling air concentrations, both global measurements at the chamber exit, and local measurements in the region of the flame front close to the burner exit. The effect of cooling air injection on pulsation level is investigated by evaluating the dynamic pressure in the combustor. The flame stabilization at the burner exit changes with an increasing degree of dilution with cooling air. Depending on the amount of cooling, only a specific share of the additional air participates in the combustion process.

Investigation of Lean Premixed Swirl-Stabilized Hydrogen Burner With Axial Air Injection Using OH-PLIF Imaging

2015 ◽  
Author(s):  
Thoralf G. Reichel ◽  
Katharina Goeckeler ◽  
Oliver Paschereit
Keyword(s):  
Flame Front ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Vortex Breakdown ◽  
Detection Algorithm ◽  
Air Injection ◽  
Swirl Generator ◽  
Air Jet ◽  
Lean Premixed ◽  
Inlet Conditions

In the context of lean premixed combustion, the prevention of upstream flame propagation in the premixing zone, referred to as flashback, is a crucial challenge related to the application of hydrogen as a fuel for gas turbines. The location of flame anchoring and its impact on flashback tendencies in a technically premixed, swirl-stabilized hydrogen burner are investigated experimentally at atmospheric pressure conditions using planar laser-induced fluorescence of hydroxyl radicals (OH-PLIF). The inlet conditions are systematically varied with respect to equivalence ratio (ϕ = 0.2–1.0), bulk air velocity u0 = 30–90m/s and burner preheat temperature ranging from 300K to 700K. The burner is mounted in the atmospheric combustion test rig at the HFI, firing at a power of up to 220 kW into a 105 mm diameter quartz cylinder, which provides optical access to the flame region. The experiments were performed using an in-house burner design that previously proved to be highly resistant against flashback occurrence by applying the axial air injection strategy. Axial air injection constitutes a non-swirling air jet on the central axis of the radial swirl generator, thus, influencing the vortex breakdown position. High axial air injection yields excellent flashback resistance and is used to investigate the whole inlet parameter space. In order to trigger flashback, the amount of axially injected air is reduced, which allowed to investigate the near flashback flame behavior. Results show that both, fuel momentum of hydrogen and axial air injection alter the isothermal flow field and cause a downstream shift of the axial flame front location. Such a shift is proven beneficial for flashback resistance. This effect was quantified by applying an edge detection algorithm to the OH-PLIF images, in order to extract the location of maximum flame front likelihood xF. The temperature and equivalence ratio dependence of the parameters xF is identified to be governed by the momentum ratio between fuel and air flow J. These results contribute to the understanding of the superior flashback limits of configurations applying high amounts of axial air injection over medium or none air injection.

scholarly journals STRUCTURE OF A FLAME FRONT PROPAGATING AGAINST THE FLOW NEAR A COLD WALL

2002 ◽  
Vol 12 (11) ◽  
pp. 2547-2555 ◽  
Author(s):  
VADIM N. KURDYUMOV ◽  
AMABLE LIÑÁN
Keyword(s):  
Flame Front ◽  
Velocity Gradient ◽  
Front Propagation ◽  
Lewis Number ◽  
Critical Value ◽  
Constant Density ◽  
Density Approximation ◽  
Cold Wall ◽  
Low Velocity ◽  
Velocity Region

The flashback or propagation of premixed flames against the flow of a reacting mixture, along the low velocity region near a cold wall, is investigated numerically. The analysis, carried out using the constant density approximation for an Arrhenius overall reaction, accounts for the effects of the Lewis number of the limiting reactant. Flame front propagation and flashback are only possible for values of the near wall velocity gradient below a critical value. The flame propagation becomes chaotic for small values of the Lewis number.

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