Sharif Digital Repository

Solid fuel ignition transient in dump combustor geometry is numerically studied. The objective of this work is to gain insight into the ignition of the fuel and its controlling parameters in back-step turbulent flow. The system of governing equations is solved with a finite volume approach using a structured grid in which the AUSM+ scheme is used to calculate the gas phase convective fluxes. The Spalart-Allmaras turbulence model is used in these simulations. First, the auto-ignition of solid fuel subject to an inlet oxidizer flow at elevated temperatures is considered and distinct intervals in ignition delay time are studied. We have demonstrated that for inlet oxidizer streams with high... 

Low emissions combustion V-flame combustors are exceptionally prone to combustion instabilities. These systems for land based gas turbines rely on a premixed or partially premixed combustion process. As V-flames do not anchored on the lip of combustor, an experimental study of the transfer function of these flames shows that they are more sensitive to fuel oscillations and in the range of frequencies, they behave like an amplifier. This paper presents an experimental study of the transfer function of a ducted, laminar, premixed V and M-flames. V-flame, laminar, propane/air premixed flame stabilised at the rim of the burner. The limit of M and V-flame are identified without excitation, then... 

In this work, the unsteady response of a laminar diffusion flame to harmonic mass fraction oscillations and also to flow velocity fluctuations is investigated. Flame-sheet assumption is utilized to model the laminar unsteady two-dimensional co-flow diffusion flame mathematically. The initial combustion of most combustion chambers is through diffusion mechanism. Therefore, developing analytical model of diffusion combustion is of great importance. The flow is assumed subsonic (incompressible), inviscid, and uniform. The convection-diffusion equation for conserved scalar variable with appropriate boundary conditions is solved. Considering stoichiometric mass fraction surface to be the flame... 

In this investigation, cellular structure of a weakly unstable detonation wave in H2/O2/Ar mixture is studied. The detonation is simulated using 2D reactive Euler equations and one step Arrhenius type reaction model developed by Mr. Barkhordari. The numerical technique is the high order Piecewise Parabolic Method on the basis of Godonov method. The numerical fluxes are computed based on a high-order extension of the Godunov's method; the piecewise parabolic method (PPM). The initial cell formation processes and different machanisms involved in cell size changes are studied. This study shows that the form of initial perturbation used to intrigate the instability of detonation is not important... 

Although Pulsed Plasma Thruster (PPT) has first been utilized in a space mission in 1964 but after more than four decades, it is still a space rated technology which has performed various propulsion tasks from stationkeeping tasks to three-axis attitude control for a variety of former missions. With respect to the rapid growth in the small satellite community and the growing interest for smaller satellites in recent years, PPT is one of the promising electric propulsion devices for small satellites (e.g. CubeSats) as the following advantages: simplicity, lightweight, robustness, low power consumptions, low production costs and small dimensions. In spite of the fact that the issues relating... 

Flameless Combustion was experimentally studied. In this combustion mode, inlet air is preheated and products are recirculated inside the chamber. Therefore, the reaction zone is spread from a limited front to a wider area with that of a lower peak temperature and very lower Nitrogen Oxides (NOx) production. Controllable parameters are preheating temperature, equivalence ratio, and fuel and air mass flow rates. Applying similar conditions, the flameless combustion was compared to the diffusion flame. Measurable parameters are exhaust temperature and composition, including NOx. Reaction zone homogeneity is observed by photographing inside the combustion chamber through its visual access... 

One of the problems associated with lean premixed combustion is their stability. Low swirl flame is a modern technology for reducing NOx emissions and increasing stability.In this thesis, first, the effect of geometric parameters on the flame stability was investigated. This study was carried out in high fuel and oxidizer mixture flow rate. Having find, the most stable burner, two other burners with the same geometrical parameters were built. Stability of these three burners were analyzed. Second, they were located in a ring together in three different relative positions. In each configuration stability and NOx emissions of the burners were determined.The study shows that NOx and CO... 

Experimental studies of regular cell structure of a weak detonation wave in a gaseous mixture of hydrogen and oxygen diluted with argon have shown that for a constant initial thermodynamic condition, the final cell size differs by repeating the tests. The question is that if these different final cell sizes for a constant initial condition are because of test errors, or the experiments would lead to a domain of solution in the form of different final cell sizes? Therefore, the aim of this study is to investigate, numerically, the evolution process and domain of variation of cellular structure of a weak detonation, and their dependency to unstable wavelengths obtained from linear instability... 

The goal of this research is the simulation of the annular combustion chamber of the turbine engine utilized by liquid fuel. The achievement to this goal will lead to create numerical tools for parametric study, analysis and combustion chamber designing.For this reason simple geometry has been considered. This simplicity of geometry causes to facilitate in parametric study and decrease in saving time for modeling and meshing. This combustion chamber is a simplified model of engine CF6. In recent study, the k – ε realizable model has been used for turbulence modeling. For non-adiabatic condition, chemical reaction is dissolved by utilizing probability density function along with laminar... 

The objective of current research is to investigate the effects of Twin Swirler Injector on performance of turbine combustor. For this purpose, the swirlcup is assessed in a dump combustion chamber. The resultant simplicity in geometry leads to a facilitation in parametric studies as well as a reduction in modeling and meshing time. The target swirlcup, is a simplified model of CFM56 engine’s swirlcup.
Standard k-ε model is established to take into account turbulence effects. The non-reacting flow is at first simulated for capturing and recognising different phenomena. Adiabatic reacting flow simulations are conducted with Probability Distribution Function using Steady Laminar Flamelet... 

Combustion in supercritical conditions (thermodynamic) is one of the most important applications of today's systems. One of the reasons for the increased use of combustion in supercritical conditions is the need to develop high pressure combustion systems, such as liquid fuel engines, gas turbines and internal combustion engines. Combustion is a technique in which the fuel is injected into the combustion chamber with its supercritical state (Any substance at a temperature and pressure above its critical point). Fuels in the supercritical conditions exhibit new features such as low viscosity, high diffusivity and low surface tension, which lead to higher efficiency, high power generation and... 

In this dissertation, based on the method of recurrence plot and its application in dynamic system analysis we examine the behavior and dynamic analysis of a swirl burner. Though retrospective studies on thermoacoustic instability have been performed on single-blown premixed cone shape flames and several combustion systems but so far this method has not been considered for a real combustion system. There have also been more work on phenomena known as the flame separation from the burner (blowout) and its propagation into the burner (flashback), which is almost conscious of their process. In fact, selecting a single flame has been to eliminate the flame-flame interactions in the... 

Lean premixed flames bring both benefits and challenges to combustion systems. While they have low emission levels and high efficiencies, they are also very susceptible to combustion instabilities. Low swirl burners have been shown to be very capable in stabilizing lean premixed flames.
In this thesis, behavior of low swirl flames under conditions of variable equivalence ratio (0.6 – 0.8), mean flow velocity (3.5 – 5.5 m/s), and excitation frequency is investigated. In static stability diagram of the flame, a region is observed in which stability mode of the flame is dependent on the path that takes the flame to its operating point (hysteresis region). Increasing the recess distance of... 

Flame Response to acoustic excitation which plays an important role in combustion chamber stability state may be found through numerical simulation. A finite volume code of higher order accuracy developed for compressible flows was adopted. Species equations along with a single-step irreversible reaction model were added to this non-reacting program. Changes were also made to the energy equation. Premixed methane/air flame in tubes was studied and the same problem was solved with FLUENT software. It was found that whether the Lewis number is considered constant or temperature dependent has a strong effect on flame structure and shape and that using mean values for gas properties yields out... 

Lean premixed combustion is highly susceptible to thermoacoustic instabilities. Such instabilities are compounded in low swirl flames by the fact that low swirl flames are stabilized aerodynamically at a relatively considerable distance downstream of the burner rim, such stabilization mechanism makes the flame more prone to both vertical and acoustic perturbations. The main objective of the present thesis is to evaluate effects of acoustic and hydrodynamic perturbations on low swirl flame features. To such aim, first, low swirl flame characteristics and stabilization mechanism are studied using large eddy simulations along with thickened flame combustion model. The obtained results show that... 

The aim of the present research is to investigate the combustion chamber cooling with vortex method in presence of kerosene and liquid oxygen as propellants. For this purpose, a part of oxidizer is entered into the cylindrical combustion chamber tangentially (from bottem of the chamber), and creates a vortex flow (outer vortex). With motion of created outer vortex along the wall and eventually hit its top wall (the head of the chamber), secondary vortex (inner vortex) occurs along the center line, with a downward direction (opposite to the primary vortex). The fuel and other part of the oxidizer injection is also carried in the head of chamber, so by mixing the fuel and oxidizer that happens... 

Up to early seventies, Gas turbine combustor design was very time consuming and costly process including trial and errors through test rigs. Over the time analytical-experimental relationships take place as one of the key rules in the design processes. With the increasing power of computer calculations, computational fluid dynamics find its way in the procedure. Obtaining a deeper understanding of flow conditions and geometry inside the chamber, a great reduction in production time and cost of revisions to rigs and samples were achieved. Finding a precise prediction of polluting elements like NOx (less than 10 ppm) after many run hours and enormous computing resources, CFD methods must... 

Flameless combustion in combustion technology is an innovative method with low nox production that few years provided it passes. In this paper the effects of various parameters on flameless combustion chamber with separate fuel and air jets, has been modeled numerically with the help of Fluent 6.3 software. Differences between traditional combustion and flameless combustion were determined and the flame structure has been studied in different scenarios. In numerical modeling, approach were used to modeling turbulence and eddy dissipation concept (EDC) approach use to modeling combustion and turbulence interaction effects. A global Two-step reaction mechanism for propane and a global... 

Excited jet flow has many physical and industrial applications, e.g. in aeroacoustics and the combustion instability. Analysis of this type of flow needs an accurate simulation of flow dynamics. This work presents the large eddy simulation of this type of flow. The numerical method used in the large eddy simulation must have low numerical dissipation and high order of accuracy. Compact methods which satisfy these requirements and have high resolution of frequency, are favorable ones for the large eddy simulation. A fourth-order compact finite volume method which had been developed in the MSc thesis of the author is extended and completed in the present work. This extension includes the... 

During the last six decades, there were remarkable developments in the field of gas turbines. In the early 1950’s, the effciency of gas turbines was 20% and it is improved up to more than 40% for modern gas turbines. In addition, due to the implementation of the combined power cycles, the thermal effciency have been reached to 60%. According to the recent developments, further improvements in this field seem to be more costly and diffcult to obtain. Rotating detonation combustor (RDC) is a new generation of detonation combustors which has simpler design and several advantages compared to jet engine combustors, but it has its intrinsic problems which seem resolvable. Given that the RDC...