# Knowledge base: Warsaw University of Technology

Back

## Gas-flame propagation in a short channel-numerical simulation using FLUENT code

### Damian Łupiński

#### Abstract

The problem of gas-flame propagation in a channel, both smooth and rough-walled tubes, or filled with obstacles, is an important issue for modern science. Due to common use of gas fuels, safe transport of different mixtures, that may vary in level of reactivity, is necessary. Mechanisms of propagation and combustion are very complex. Modern science enables observation of these phenomena. Available numerical methods can be used to simulate combustion, heat transfer and flame propagation. Obtained data can serve as a guidance in later experimental research. The aim of this work was to realize a series of numerical simulations of gas-flame propagation in short, square sectioned channels with different configurations of obstacles. There were three 0,6m long channels chosen for the analysis. The first one was smooth, while the second and third were equiped with barrier type obstacles and differ only in blockage ratio. In the first part of this study, simulations for stechiometric propan-air mixture were carried out. Later, the analysis was repeated for stoichiometric hydrogen-air mixture. To achieve this goal CFD program (FLUENT) was used. A numerical model selected for the combustion was Premixed Combustion. Since the generation of turbulence has a significant effect on the propagation of the flame, the choise of the turbulent model was very important. After many tests, realisable k-eps model was chosen, as the most suitable for this simulation. Above that, 3D mesh was generated in GAMBIT. After the simulation, obtained data were compared with experimental results. Although results of the simulation and of the experiment vary, some similarities can be found. The general character of the flame propagation, maximum velocities of the flame and the shape of the flame front in the numerical analisys were found to be close to those, seen in the experiment. The propagation mechanism of the flame in a smooth channel is controled mainly by turbulence. When the gas burns, it expands and pushes unburned mixture ahead of the flame front. The movement of the gas mixture causes the turbulent boundary layer to grow, due to friction on channel walls. The generation of turbulence is the reason of turbulent mixing increase and, in consequence, hgher reaction rate. At first the shape of the flame will be similar to a “mushroom”, mainly because of the ignition conditions. The flame speed will be highest in the axis of the channel. Later, turbulence generated close to the walls will cause the acceleration of the flame in these regions. The effect of this acceleration will be the change of the flame shape into a “tulip”. The situation with the obstacle filled channels is a bit different. Turbulence remains a main reason of flame acceleration, but the form of barriers can be the cause of a unique gas-dynamic mechanism. Due to a sudden rise of the tube diamater behind the barrier, we are witnessing an abrupt expansion. This situation can be compared to case,when the combustion front propagates into unlimited space. As a result the flame accelerates immediately. Zones of unburned mixture remain between the barriers, close to the channel walls. They will burn slowly long after the main flame front has passed. It was found that the blockage ratio has a significant effect on the flame propagation. In general, the highest flame speeds were recorded in a channel with obstacles 10mm high. The reactivity of the mixture is also an important issue of the flame propagation. Simulation results for both examined fuels show that with the rise of the reactivity, propagation velocities are higher. In conclusion, numerical methods are methods of approximate calculations. Even though the results obtained in this study are not exact, numerical analysis still remains a useful tool for engineers. The simplicity of the model used in this work can encourage further development of these methods.
Diploma type
Engineer's / Bachelor of Science
Diploma type
Engineer's thesis
Author
Damian Łupiński (FPAE) Damian Łupiński,, Faculty of Power and Aeronautical Engineering (FPAE)
Title in Polish
Propagacja płomienia gazowego w kanale-symulacja numeryczna przy użyciu programu FLUENT
Supervisor
Andrzej Teodorczyk (FPAE/IHE) Andrzej Teodorczyk,, The Institute of Heat Engineering (FPAE/IHE)Faculty of Power and Aeronautical Engineering (FPAE)
Certifying unit
Faculty of Power and Aeronautical Engineering (FPAE)
Affiliation unit
The Institute of Heat Engineering (FPAE/IHE)
Study subject / specialization
, Mechanika i Budowa Maszyn
Language
(pl) Polish
Status
Finished
Defense Date
01-02-2008
Issue date (year)
2007
Pages
93
Internal identifier
MEL; PD-532
Reviewers
Janusz Piechna (FPAE/IAAM) Janusz Piechna,, The Institute of Aeronautics and Applied Mechanics (FPAE/IAAM)Faculty of Power and Aeronautical Engineering (FPAE) Andrzej Teodorczyk (FPAE/IHE) Andrzej Teodorczyk,, The Institute of Heat Engineering (FPAE/IHE)Faculty of Power and Aeronautical Engineering (FPAE)
Keywords in Polish
paliwa gazowe, spalanie, symulacja numeryczna, fluent
Keywords in English
xxx
Abstract in Polish
urn:pw-repo:WUT3606dc800b274445a4a78960dadc0239