Papers by Akbar Ghafourian
The unsteady response of a laminar diffusion flame to harmonic mass fraction oscillations and als... more The unsteady response of a laminar diffusion flame to harmonic mass fraction oscillations and also flow velocity fluctuations has been 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 surface, it is possible to obtain the flame zone. In addition, different types of flame structures and transition from overventilated flame to underventilated flame are studied. Assuming that unburnt species have not passed across the flame surface and that the diffusion coefficient is constant, heat release ...
The algorithm of directed relation graph (DRG) recently developed for skeletal mechanism reductio... more The algorithm of directed relation graph (DRG) recently developed for skeletal mechanism reduction is extended to overall linear time operation, thereby greatly facilitating the computational effort in mechanism reduction, particularly for those involving large mechanisms. This algorithm is applied to a spatially homogeneous constant-pressure autoignition of methane combustion and result are compared with CSP method. It is observed that the accuracy of skeletal mechanisms is equivalently bounded by the userspecified error threshold value. DRG method because of directly eliminate unimportant species instead of elementary reactions, computationaly is more efficient. keywords: Directed relation graph; computational singular perturbation; skeletal mechanism
An experimental investigation of premixed methane/air combustion within a novel porous ceramic bu... more An experimental investigation of premixed methane/air combustion within a novel porous ceramic burner is described in this paper. The burner is composed of three rectangular porous ceramic layers stacked on each other and insulated around the circumference. The upstream layer is assumed to be the preheat zone, while the others are served as the combustion zones. The operating parameters include fuel/air mixture flow rate and equivalence ratio. The main objectives of this study are documenting the flame stabilization within the burner and determination of operating range. The burner is tested over the range of lean limit (Φ≤0.65). The experimental data demonstrates the advantages of burning a combustible gas inside the porous ceramic burner. The burner shows a great ability to extend the blow off limit at each equivalence ratio.
Combustion response to acoustic perturbation in liquid rocket engines
An experimental study of the effect of acoustic perturbations on combustion behavior of a model l... more An experimental study of the effect of acoustic perturbations on combustion behavior of a model liquid propellant rocket engine has been carried out. A pair of compression drivers were used to excite transverse and longitudinal acoustic fields at strengths of up to 156.6 dB and 159.5 dB respectively in the combustion chamber of the experimental rocket engine. Propellant simulants were injected into the combustion chamber through a single element shear coaxial injector. Water and air were used in cold flow studies and ethanol and oxygen-enriched air were used as fuel and oxidizer in reacting hot flow studies. In cold flow studies an imposed transverse acoustic field had a more pronounced effect on the spray pattern than a longitudinal acoustic fields. A transverse acoustic field widened the spray by as much as 33 percent and the plane of impingement of the spray with chamber walls moved up closer to the injection plane. The behavior was strongly influenced by the gas phase velocity b...
Analysis of Temperature Distribution Over a Gas Turbine Shaft Exposed to a Swirl Combustor Flue
2010 14th International Heat Transfer Conference, Volume 5, 2010
Gas turbine shaft is generally exposed to high temperature gases and may seriously be affected an... more Gas turbine shaft is generally exposed to high temperature gases and may seriously be affected and overheated due to temperature fluctuations in the combustion chamber. Considering vortex flow in the combustion chamber, it may increase the heat release rate and combustion efficiency and also control location of energy release. However, this may result in excess temperature on the combustor equipments and gas turbine shaft. Vortex flow in the vortex engine which is created by the geometry of combustion chamber and conditions of flow field is a bidirectional swirl flow that maintains the chamber wall cool. In this study a new gas turbine combustion chamber implementing a liner around the shaft and liquid fuel feeding system is designed and fabricated. Influence of parameters such as axial position in the combustor direction and equivalence ratio are studied. Experimental results are compared with the numerical simulation by the existing commercial software. Swirl number i.e. ratio of ...
Analytical Solution of Chamber Effective Length in the Axial Engine
Volume 1: Symposia, Parts A, B and C, 2009
In this research, effective length of one-dimensional combustion in a dilute monopropellant spray... more In this research, effective length of one-dimensional combustion in a dilute monopropellant spray, constant area and fixed volume chamber is analytically predicted. A new evaporation rate in the form of dk+1 relation is introduced. In the case of controlling vaporization by radiative heat transfer, k is equal to zero, and when molecular processes control the vaporization, k will be equal to one and in some cases vaporization data need the value of k greater than one to fit properly to related equation. Development of this approach can be used in the design of combustion chambers with optimum length and with using vaporization rate of R = R0〈r〉0k/〈r〉k. Spray equation and distribution function in one-dimensional coordinate in direction of chamber axis is used as the governing equation. Multiplying velocity and displacement variables by simplified spray equation and some manipulation lead to a final form of integral equation. Definition of β1β3 as criteria will simplify the complex int...
Effect of Entrance Position on Particle Dispersion in Bidirectional Vortex Flow
Volume 1: Symposia, Parts A, B and C, 2009
ABSTRACT
Combustor design for atomization study in liquid rocket engines
30th Aerospace Sciences Meeting and Exhibit, 1992
Dynamic response to acoustic perturbation of an atomizing coaxial jet in a liquid rocket engine
31st Aerospace Sciences Meeting, 1993
ABSTRACT A study of the acoustic perturbations on the atomization of a coaxial gas/liquid rocket ... more ABSTRACT A study of the acoustic perturbations on the atomization of a coaxial gas/liquid rocket engine injector is being carried out. A pair of compression drivers are used to excite a transverse acoustic field at strengths of up to 155.6 dB in an experimental rocket combustion chamber. Ethanol and oxygen enriched air are used as fuel and oxidizer. Chamber pressure is measured to determine the effect of external excitation on the experimental engine. The effects of equivalence ratio and excitation amplitude on atomization and combustion are investigated by varying the equivalence ratio from 7.4 to 3.8 and the excitation amplitude from 155.6 dB to 147 dB. The effect of external excitation at 2950 Hz on chamber pressure fluctuations becomes more pronounced as the value of equivalence ratio is reduced. Larger chamber pressure response is observed at higher external excitation amplitudes.
Swirl Flow Effects on Heat Release/Luminous Radiation in a Vortex Engine
Volume 1: Symposia, Parts A and B, 2006
ABSTRACT Radiation heat transfer as an important phenomenon in combustion applications is an inte... more ABSTRACT Radiation heat transfer as an important phenomenon in combustion applications is an interesting subject for scientists and combustion researchers. Heat release and luminous radiative transfer phenomena in an experimental vortex engine are compared with a similar axial flow type engine. A detector sensitive to emission from C2 * excited radically is utilized for the measurement of chemiluminescence emission at the centerline of chamber along all axial positions. The filtered photographs of flame are used to compare total C2 * emission from flame. Mixtures of Propane and Butane with air enriched by oxygen are used as fuel and oxidizer. The effects of equivalence ratio and oxidizer mass flow rate are investigated as well.
Acoustic analysis of pressure in liquid rocket engines
35th Joint Propulsion Conference and Exhibit, 1999
A review of atomization in liquid rocket engines
29th Aerospace Sciences Meeting, 1991
ABSTRACT The focus of this review is on coaxial and impinging jet atomizers, in which atomization... more ABSTRACT The focus of this review is on coaxial and impinging jet atomizers, in which atomization is due to fluid dynamic instabilities. Appropriate dimensionless numbers are considered to predict the breakup behavior. A review of round liquid jet, liquid sheet and drop breakup is presented. Atomization is strongly influenced by changes in liquid and gas properties, flow conditions and geometrical parameters. The growth of disturbances, generated either within the atomizer or due to aerodynamic interaction with the surrounding gas, is mainly responsible for the formation of sheets and ligaments in the body of the liquid. These sheets and ligaments ultimately break up to produce smaller, more stable liquid globules. Quantitative predictive ability still remain elusive in atomization. Further research is needed to improve quantitative descriptions, so that they can be used in the design of practical atomizers.
Sprays Angle Variation of Liquid-Liquid Swirl Coaxial Injectors
41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2005
Spray angle behavior of a liquid -liquid swirl coaxial injector is experimentally investigated th... more Spray angle behavior of a liquid -liquid swirl coaxial injector is experimentally investigated through cold tests. This type of injector produces two coaxial liquid sprays which interact to form a combine spray. A theoretical model based on momentum balance is developed to predict the combine spray behavior. The spray angles for different operating conditions are obtained from analysis of high resolution digital images. The experimental observations indicate that the two inner and outer sprays are pulled together and interact to form a comb ine spray. Their interaction results in an overall performance that is different from the summation of each individ ual spray characteristic. T heir beha vior is not linear. The combine spray angles are between the inner and outer spray angles. The spr ay angles are calculated by the theo retical relation developed. Comparison of theoretical results with exper imental measurements shows that momentum balance can be used to predict the observed behavior.
A New Approach to the Analytical and Numerical Solution of the Bidirectional Vortex Flow
43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2007
*† ‡ , The solution for bulk fluid motion of a bidirectional coaxial vortex for application in vo... more *† ‡ , The solution for bulk fluid motion of a bidirectional coaxial vortex for application in vortex engine has been derived. The vortex engine is a novel combustion chamber in which swirl motion of reactants are used to maintain the chamber walls cool. The flow field has been considered both analytically and numerically. The model is based on incompressible, steady, axisymmetric, and non-reactive flow conditions. The governing PDEs are reduced to a system of nonlinear ODEs and then, by a coordinate transformation, their singularity has been relaxed. Solution domain has been decomposed into the inner viscous and outer inviscid regions, then, the velocity and pressure fields are obtained analytically. To verify the results, these ODEs are solved numerically via finite element method and by using the Galerkin and modified weighted residual formulations. The analytical and numerical results are in good agreement with each other. In comparison with other studies, the present calculated azimuthal velocity is more supportive of the experimental and numerical results and also confirms the presence of a forced-free vortex flow pattern. Location of the nontranslating vortex layer, mantle, is illuminated as well. Nomenclature i A = inlet area a = chamber radius b = chamber discharge radius Cμ = coefficient for the turbulence viscosity ij K = element stiffness matrix in the finite element formulation L = chamber length e l = an equivalent length scale for the turbulence i N = shape functions P =
45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2009
Experimental Investigation of Heat Transfer Modes in Vortex Combustion Engines
43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2007
ABSTRACT Heat transfer phenomenon in a recently developed vortex engine has been surveyed. Cooler... more ABSTRACT Heat transfer phenomenon in a recently developed vortex engine has been surveyed. Cooler walls, better combustion performance and more stable relative to the other engines, make these engines very interesting. These advantages have been obtained by using a bidirectional swirl flow, containing a cool outer and a hot inner vortex, traveling upstream and downstream respectively. The most eminent benefit of these combustion chambers, having highly reduced wall temperature, is the result of convective heat release from the wall by the outer vortex. A thorough numerically and experimentally investigation has been performed on radiation and convection heat transfer to realize the exact heat transfer behavior of this engine. Results from flame structure observation indicate that flame area is much larger in vortex engine in comparison to regular engines due to vortex stretching of the flame which increases radiation heat transfer to walls. In spite of this increase, heat removal by outer swirl flow is high enough not only to compensate for increased radiation but also reduces the wall temperature substantially.
Investigation of Luminous/Nonluminous Radiation in a Vortex Engine
Volume 1: Symposia, Parts A and B, 2007
Investigation of radiation heat transfer In vortex engine is an important and new phenomenon in c... more Investigation of radiation heat transfer In vortex engine is an important and new phenomenon in combustion for scientists and combustion researchers. In this research some parts of the combustion chamber wall are insulated using Blanket as a high insulating material. The rate of radiative heat transfer to the chamber wall is calculated using temperature difference between inner and outer surface of chamber. In the experiments this parts are protected from direct contact with hot combustion media using quartz window. The luminous radiative transfer per volume of chamber and also volume of flame in a vortex engine are compared with that in a similar axial flow type engine. A detector sensitive to emission from C2* excited radically is utilized for the measurement of chemiluminescence emission at the centerline of chamber along all axial positions. The filtered photographs of flame are used to compare total C2* emission from flame.
Journal of Combustion, 2012
A Dynamic model of Homogeneous Charge Compression Ignition (HCCI), based on chemical kinetics pri... more A Dynamic model of Homogeneous Charge Compression Ignition (HCCI), based on chemical kinetics principles and artificial intelligence, is developed. The model can rapidly predict the combustion probability, thermochemistry properties, and exact timing of the Start of Combustion (SOC). A realization function is developed on the basis of the Sandia National Laboratory chemical kinetics model, and GRI3.0 methane chemical mechanism. The inlet conditions are optimized by Genetic Algorithm (GA), so that combustion initiates and SOC timing posits in the desired crank angle. The best SOC timing to achieve higher performance and efficiency in HCCI engines is between 5 and 15 degrees crank angle (CAD) after top dead center (TDC). To achieve this SOC timing, in the first case, the inlet temperature and equivalence ratio are optimized simultaneously and in the second case, compression ratio is optimized by GA. The model’s results are validated with previous works. The SOC timing can be predicted...
Experimental investigation of combustion instability in rocket motors
Symposium (International) on Combustion, 1953
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Papers by Akbar Ghafourian