scholarly journals Ultra-Lean Gaseous Flames in Terrestrial Gravity Conditions

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 21
Author(s):  
Ivan Yakovenko ◽  
Alexey Kiverin ◽  
Ksenia Melnikova
Keyword(s):  
Fire Safety ◽  
Flame Structure ◽  
Combustion Process ◽  
Spatial Structures ◽  
Flammability Limits ◽  
Gaseous Mixtures ◽  
Terrestrial Gravity ◽  
Flame Dynamics ◽  
Preferential Diffusion ◽  
The Impact

Development of the combustion process in the gaseous mixtures of near-limit composition is of great interest for fundamental aspects of combustion theory and fire-safety applications. The dynamics of ultra-lean gaseous flames in near-limit mixtures is governed by many effects, such as buoyancy, preferential diffusion, radiation, and instability development. Though ultra-lean combustion was extensively studied in microgravity conditions, the influence of gravity on the ultra-lean flame structure and stability is still poorly understood. The paper is devoted to deepening the knowledge of ultra-lean flame dynamics in hydrogen-air mixtures under terrestrial gravity conditions. The spatial structures of the flame developing under the effect of buoyancy forces are investigated employing detailed numerical analysis. Different modes of near-limit flame evolution are observed depending on the mixture concentration. In particular, we registered and described three distinct spatial structures: individual kernels tending to extinguish in leanest compounds, complex multi-kernel structures in marginal compositions, and stable cap-shaped flames in more chemically active mixtures. We apply the flame-bubble analogy to interpret flame dynamics. On this basis, the diagram in the Re-Fr plane is developed. That allows classifying the emerging flame structures and determine flame stability. Additionally, different ignition modes are studied, and the mechanisms determining the impact of ignition mode on the flammability limits are distinguished. Obtained results provide useful insights into the processes of flame quenching and development in near-limit hydrogen-air mixtures under real gravity conditions and can be applied in the design of contemporary fire-safety systems.

STABILITY OF ULTRALEAN HYDROGEN FLAMES IN TERRESTRIAL CONDITIONS

2020 ◽  
Author(s):  
I. Yakovenko ◽  
◽  
K. Melnikova ◽  
A. Kiverin ◽  
◽  
...  
Keyword(s):  
Large Scale ◽  
Burning Velocity ◽  
Flame Structure ◽  
Combustion Products ◽  
Flammability Limits ◽  
Flame Kernel ◽  
Terrestrial Gravity ◽  
Convective Flows ◽  
Flame Dynamics ◽  
Scale Motion

The paper is devoted to the study of specific features of flame dynamics in ultralean hydrogen-air mixtures in terrestrial gravity conditions. By means of numerical methods, it is shown that gasdynamic flows, which develop due to the buoyancy force acting on the hot combustion products, play a crucial role on the overall ultralean flame dynamics from the earliest stage after ignition and up to the large-scale motion of the developed flame. Immediately after ignition, convective flows determine the stability of flame kernel. It is shown that, on the one hand, despite the “superadiabatic” temperature of the flame products that is considered as one of the main stability factors of the ultralean flames in microgravity conditions, the influence of convective flows on the ultralean flames in terrestrial gravity conditions can alter flammability limits from that measured in microgravity. On the other hand, the propagation dynamics of the stable flame kernels is also mainly determined by the buoyancy forces. Rising velocity of the flame kernel in the ultralean mixture occurs to be much greater than the burning velocity and correlates well with estimations obtained for the bubble rising in liquid. Apart from the upward rising, the developed flame is shown to be expanding laterally; so, the complex large-scale flame structure is observed which could be a possible threat for explosion and fire safety for many industrial environments.

scholarly journals Influence of Eddy-Generation Mechanism on the Characteristic of On-Source Fire Whirl

2019 ◽  
Vol 9 (19) ◽  
pp. 3989 ◽  
Author(s):  
Cheng Wang ◽  
Anthony Chun Yin Yuen ◽  
Qing Nian Chan ◽  
Timothy Bo Yuan Chen ◽  
Qian Chen ◽  
...  
Keyword(s):  
Flame Structure ◽  
Flame Temperature ◽  
Combustion Process ◽  
Flame Height ◽  
Reacting Flow ◽  
Detailed Chemistry ◽  
Eddy Generation ◽  
Fire Whirl ◽  
Generation Mechanisms ◽  
The Impact

This paper numerically examines the characterisation of fire whirl formulated under various entrainment conditions in an enclosed configuration. The numerical framework, integrating large eddy simulation and detailed chemistry, is constructed to assess the whirling flame behaviours. The proposed model constraints the convoluted coupling effects, e.g., the interrelation between combustion, flow dynamics and radiative feedback, thus focuses on assessing the impact on flame structure and flow behaviour solely attribute to the eddy-generation mechanisms. The baseline model is validated well against the experimental data. The data of the comparison case, with the introduction of additional flow channelling slit, is subsequently generated for comparison. The result suggests that, with the intensified circulation, the generated fire whirl increased by 9.42 % in peak flame temperature, 84.38 % in visible flame height, 6.81 % in axial velocity, and 46.14 % in velocity dominant region. The fire whirl core radius of the comparison case was well constrained within all monitored heights, whereas that of the baseline tended to disperse at 0.5   m height-above-burner. This study demonstrates that amplified eddy generation via the additional flow channelling slit enhances the mixing of all reactant species and intensifies the combustion process, resulting in an elongated and converging whirling core of the reacting flow.

scholarly journals Modeling diesel combustion with tabulated kinetics and different flame structure assumptions based on flamelet approach

2019 ◽  
Vol 21 (1) ◽  
pp. 89-100 ◽  
Author(s):  
Tommaso Lucchini ◽  
Daniel Pontoni ◽  
Gianluca D’Errico ◽  
Bart Somers
Keyword(s):  
Soot Formation ◽  
Flame Structure ◽  
Combustion Process ◽  
Computational Cost ◽  
Pollutant Emissions ◽  
Diesel Combustion ◽  
Flamelet Generated Manifold ◽  
Tabulated Chemistry ◽  
Computational Fluid Dynamics Analysis ◽  
The Impact

Computational fluid dynamics analysis represents a useful approach to design and develop new engine concepts and investigate advanced combustion modes. Large chemical mechanisms are required for a correct description of the combustion process, especially for the prediction of pollutant emissions. Tabulated chemistry models allow to reduce significantly the computational cost, maintaining a good accuracy. In the present work, an investigation of tabulated approaches, based on flamelet assumptions, is carried out to simulate turbulent Diesel combustion in the Spray A framework. The Approximated Diffusion Flamelet is tested under different ambient conditions and compared with Flamelet Generated Manifold, and both models are validated with Engine Combustion Network experimental data. Flame structure, combustion process and soot formation were analyzed in this work. Computed results confirm the impact of the turbulent–chemistry interaction on the ignition event. Therefore, a new look-up table concept Five-Dimensional-Flamelet Generated Manifold, that accounts for an additional dimension (strain rate), has been developed and tested, giving promising results.

scholarly journals Design of a Fluidic Actuator with Independent Frequency and Amplitude Modulation for Control of Swirl Flame Dynamics

Fluids ◽  
2021 ◽  
Vol 6 (3) ◽  
pp. 128
Author(s):  
Amrit Adhikari ◽  
Thorge Schweitzer ◽  
Finn Lückoff ◽  
Kilian Oberleithner
Keyword(s):  
Flow Control ◽  
Large Scale ◽  
Combustion Process ◽  
Precessing Vortex Core ◽  
Flame Dynamics ◽  
Efficient Combustion ◽  
Control Authority ◽  
Swirl Flame ◽  
Actuator Design ◽  
The Impact

Fluidic actuators are designed to control the oscillatory helical mode, called a precessing vortex core (PVC), which is often observed in gas turbine combustors. The PVC induces large-scale hydrodynamic coherent structures, which can considerably affect flow and flame dynamics. Therefore, appropriate control of this structure can lead to a more stable and efficient combustion process. Currently available flow control systems are designed to control the PVC in laboratory-scale setups. To further develop these systems and find an approach applicable to the industrial scale, a new actuator design based on fluidic oscillators is presented and studied in this paper. This actuator allows for independently adjusting forcing frequency and amplitude, which is necessary to effectively target the dynamics of the PVC. The functionality and flow control of this actuator design are studied based on numerical simulations and experimental measurements. To verify the flow control authority, the actuator is built into a prototype combustor test rig, which allows for investigating the impact of the actuator’s forcing on the PVC at isothermal conditions. The studies conducted in this work prove the desired functionality and flow control authority of the 3D-printed actuator. Accordingly, a two-part stainless steel design is derived for future test conditions with flame.

Effects of Emulsified Fuel on the Performance and Emission Characteristics of Aeroengine Combustors

2019 ◽  
Author(s):  
M. G. De Giorgi ◽  
E. Pescini ◽  
S. Campilongo ◽  
G. Ciccarella ◽  
D. Fontanarosa ◽  
...  
Keyword(s):  
Flame Structure ◽  
Combustion Process ◽  
Optical Filters ◽  
Diagnostic Techniques ◽  
Jet Fuels ◽  
Test Case ◽  
Performance And Emission ◽  
Emulsified Fuel ◽  
Spectral Ranges ◽  
The Impact

Abstract The aim of the present work is the experimental investigation of the effects of the addition of water and urea into jet fuels, on the reduction of nitrogen oxides (NOx) emissions and eventually improvement of the lean flame stability in aeroengine combustors. Experiments have been carried out using a 300-kW liquid-fueled swirling combustor. Various urea and/or water concentrations have been tested at the same fuel/air ratio. In order to study the flame behavior, non-invasive optical diagnostic techniques, as charge-coupled device (CCD) cameras in different spectral ranges (Visible and UV ranges, with different optical filters), have been adopted to analyze the shape and the brightness of the flame structure. Measurements of exhaust emissions (NOx, SO2, CO, CO2 and O2) have also been performed in order to evaluate the impact of emulsification on the entire combustion process. Finally, the thermal efficiency losses with respect to the neat jet test case were also analyzed for each emulsified fuel condition.

Instability Control by Premixed Pilot Flames

2008 ◽  
Author(s):  
Peter Albrecht ◽  
Stefanie Bade ◽  
Arnaud Lacarelle ◽  
Christian Oliver Paschereit ◽  
Ephraim Gutmark
Keyword(s):  
Gas Turbines ◽  
Flame Structure ◽  
Premixed Flames ◽  
Combustion Process ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Pilot Injection ◽  
Acoustic Instabilities ◽  
Flame Behavior ◽  
The Impact

Premixed flames of swirl-stabilized combustors (displaced-half-cone) are susceptible to thermo-acoustic instabilities which should be avoided under all operating conditions in order to guarantee a long service life for both stationary and aircraft gas turbines. The source of this unstable flame behavior can e.g. be found in a transition of the premix flame structure between two stationary conditions that can be easily excited by fuel fluctuations, coherent structures within the flow and other methods. Pilot flames can alleviate this issue by either improving the dynamic stability directly or by sustaining the main combustion process at operating points where instabilities are unlikely. In the present study, the impact of two different premixed pilot injection on the combustion stability is investigated. One of the pilot injector (pilot flame injector, PFI) was located upstream of the recirculation zone at the apex of the burner. The second one was a pilot ring (PR) placed at the burner outlet on the dump plane. A noticeable feature of the pilot injector was that an ignition device allowed for creating pilot premixed flames. The present investigation evidenced that these premixed pilot flames were able to suppress instabilities over a wider fuel/air ratio range than when the conventional premixed pilot injection alone. Furthermore, it was possible to prevent instabilities and maintain the flame burning near the lean blow out when a percentage of the fuel was premixed with air and injected through the pilot ring. In the mean time, NOx emissions were significantly reduced.

Effects of Emulsified Fuel on the Performance and Emission Characteristics of Aeroengine Combustors

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
M. G. De Giorgi ◽  
E. Pescini ◽  
S. Campilongo ◽  
G. Ciccarella ◽  
D. Fontanarosa ◽  
...  
Keyword(s):  
Flame Structure ◽  
Combustion Process ◽  
Optical Filters ◽  
Diagnostic Techniques ◽  
Jet Fuels ◽  
Test Case ◽  
Performance And Emission ◽  
Emulsified Fuel ◽  
Spectral Ranges ◽  
The Impact

Abstract The aim of this work is the experimental investigation of the effects of the addition of water and urea into jet fuels, on the reduction of nitrogen oxides (NOx) emissions and eventually improvement of the lean flame stability in aeroengine combustors. Experiments have been carried out using a 300-kW liquid-fueled swirling combustor. Various urea and/or water concentrations have been tested at the same fuel/air ratio. In order to study the flame behavior, noninvasive optical diagnostic techniques, as charge-coupled device (CCD) cameras in different spectral ranges (visible and UV ranges, with different optical filters), have been adopted to analyze the shape and the brightness of the flame structure. Measurements of exhaust emissions (NOx, SO2, carbon monoxide (CO), CO2, and O2) have also been performed in order to evaluate the impact of emulsification on the entire combustion process. Finally, the thermal efficiency losses with respect to the neat jet test case were also analyzed for each emulsified fuel condition.

Instability Control by Premixed Pilot Flames

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Peter Albrecht ◽  
Stefanie Bade ◽  
Arnaud Lacarelle ◽  
Christian Oliver Paschereit ◽  
Ephraim Gutmark
Keyword(s):  
Gas Turbines ◽  
Flame Structure ◽  
Premixed Flames ◽  
Combustion Process ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Lean Blowout ◽  
Acoustic Instabilities ◽  
Flame Behavior ◽  
The Impact

Premixed flames of swirl-stabilized combustors (displaced half-cone) are susceptible to thermo-acoustic instabilities, which should be avoided under all operating conditions in order to guarantee a long service life for both stationary and aircraft gas turbines. The source of this unstable flame behavior can be found in a transition of the premix flame structure between two stationary conditions that can be easily excited by fuel fluctuations, coherent structures within the flow, and other mechanisms. Pilot flames can alleviate this issue either by improving the dynamic stability directly or by sustaining the main combustion process at operating points where instabilities are unlikely. In the present study, the impact of two different premixed pilot injections on the combustion stability is investigated. One of the pilot injector (pilot flame injector) was located upstream of the recirculation zone at the apex of the burner. The second one was a pilot ring placed at the burner outlet on the dump plane. A noticeable feature of the pilot injector was that an ignition device allowed for creating pilot premixed flames. The present investigation showed that these premixed pilot flames were able to suppress instabilities over a wider fuel/air ratio range than the conventional premixed pilot injection alone. Furthermore, it was possible to prevent instabilities and maintain the flame burning near the lean blowout when a percentage of the fuel was premixed with air and injected through the pilot ring. NOx emissions were significantly reduced.

scholarly journals Comprehensive Thermodynamic Analysis of the Humphrey Cycle for Gas Turbines with Pressure Gain Combustion

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3521 ◽  
Author(s):  
Panagiotis Stathopoulos
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Combustion Process ◽  
Ideal Gas ◽  
Point Of View ◽  
Pressure Gain Combustion ◽  
Combustion Technology ◽  
Secondary Air ◽  
And Performance ◽  
The Impact

Conventional gas turbines are approaching their efficiency limits and performance gains are becoming increasingly difficult to achieve. Pressure Gain Combustion (PGC) has emerged as a very promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine thermodynamic cycles. Up to date, only very simplified models of open cycle gas turbines with pressure gain combustion have been considered. However, the integration of a fundamentally different combustion technology will be inherently connected with additional losses. Entropy generation in the combustion process, combustor inlet pressure loss (a central issue for pressure gain combustors), and the impact of PGC on the secondary air system (especially blade cooling) are all very important parameters that have been neglected. The current work uses the Humphrey cycle in an attempt to address all these issues in order to provide gas turbine component designers with benchmark efficiency values for individual components of gas turbines with PGC. The analysis concludes with some recommendations for the best strategy to integrate turbine expanders with PGC combustors. This is done from a purely thermodynamic point of view, again with the goal to deliver design benchmark values for a more realistic interpretation of the cycle.

Reduction of Fuel Utilization Through Oxygen-Enriched Combustion in a Reheat Furnace Pusher-Type

2021 ◽  
Author(s):  
Francisco J. Martinez Zambrano ◽  
Armin K. Silaen ◽  
Kelly Tian ◽  
Joe Maiolo ◽  
Chenn Zhou
Keyword(s):  
Heat Flux ◽  
Fuel Injection ◽  
Combustion Process ◽  
Oxygen Enrichment ◽  
Rolling Temperature ◽  
Heating Zone ◽  
Reheat Furnace ◽  
Steel Slabs ◽  
The Impact ◽  
Reheating Process

Abstract Steelmaking is an energy-intensive process. Thus, energy efficiency is highly important. Several stages of steelmaking involve combustion processes. One of the most energy-consuming processes in steelmaking is the slab reheating process in a reheat furnace (RF). The energy released by fuel combustion is used to heat steel slabs to their proper hot-rolling temperature. The steel slabs move through the reheat furnace passing the three stages of heating called: Preheating Zone (PZ), Heating Zone (HZ), and Soaking Zone (SZ) to finally leave the discharge door at a rolling temperature of 2375 °F. One way to improve a reheat furnace’s fuel consumption is by implementing oxygen-enriched combustion. This study investigates the implementation of oxygen-enriched combustion in a pusher-type reheat furnace. The increment of oxygen in the combustion process allows for increasing the furnace gas temperature. Consequently, the oxygen enrichment approach allows for the reduction of fuel injection. The principal goal of this investigation is to model the combustion-based on oxygen-enrichment and develop parametric studies of fuel injection rates. The different simulations aim to match the slab heat flux profile of the industrial reheat furnace pusher-type. Computational fluid dynamics are used to generate the slab heat flux distribution. To reach more uniform slab heating, oxygen and fuel ports were alternated. Also, injection angles were modified to optimize slab heating and avoid the impact of hot spots. Thermocouple readings of the industrial reheat furnace are compared to simulation results. The results determined that 40–45% fuel reduction can be achieved.

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