Ali S. Kheireddine

Bio: Ali S. Kheireddine is an academic researcher. The author has contributed to research in topics: Combustion & Turbulent diffusion. The author has an hindex of 1, co-authored 1 publications receiving 4 citations.

Numerical Prediction of Turbulent Diffusion Flames Formed by Cylindrical Tube Injector

Abstract: This work summarizes numerical results for a diffusion flame formed from a cylindrical tube fuel injector, issuing gaseous fuel jet vertically in a quiescent atmosphere. Both pure fuels as well as fuel mixtures are examined. The primary objective is to predict the flame base height as a function of the jet velocity. A finite volume scheme is used to discretize the time-averaged Navier-Stokes equations for the reacting flow, resulting from the turbulent fuel jet motion. The turbulent stresses, and heat and mass fluxes are computed from the Reynolds stress turbulence model. A chemical kinetics model involving a two-step chemical reaction mechanism is employed for the oxidation of methane. The reaction rate is determined from a procedure which computes at each point the minimum (process limiting) rate from an Arrhenius (kinetically controlled) expression and the eddy dissipation (turbulent mixing controlled) model. The Reynolds stress model (RSM), in conjunction with the two-step kinetics and the eddy dissipation model, produces flame base height and other flame characteristics that are in good agreement with experimental results. Numerical results are also in agreement with the hypothesis of Vanquickenborne and van Tiggelen concerning the stabilization mechanism of lifted diffusion flames. Furthermore, computed results also indicate that the flame base location can be approximately located by consideration of the turbulent mixing of the fuel jet in the non-reacting case. For propane, numerical results, obtained using one-step kinetics, show good agreement with the experimental data. Results pertaining to a methane-hydrogen mixture are obtained by using the RSM with three-step kinetics and the eddy dissipation model. The results for pure fuels and fuel mixtures indicate that the lift-off height for all the fuels considered in this study increases linearly with respect to the jet exit velocity. The study also analyzes the effect of swirling motion on the flame stabilization characteristics of the methane jet. The characteristics of methane flame are also determined by another combustion model which employs the probability density function (PDF) in conjunction with the flame sheet model. Results from this model differ in the near field from those predicted from the RSM-eddy dissipation model. However, in the far field the two combustion models yielded results that are in good agreement.

Chemical kinetics computer program for static and flow reactions

Abstract: General chemical kinetics computer program for complex gas mixtures has been developed. Program can be used for any homogeneous reaction in either one dimensional flow or static system. It is flexible, accurate, and easy to use. It can be used for any chemical system for which species thermodynamic data and reaction rate constant data are known.

Numerical Modeling of Flame Lift-Off Phenomenon and Calculation of Thermal Loads on a Methane Fuel Injector With Complex Geometry

Abstract: NUMERICAL MODELING OF FLAME LIFT-OFF PHENOMENON AND CALCULATION OF THERMAL LOADS ON A METHANE FUEL INJECTOR WITH COMPLEX GEOMETRY Taj 0. Mohieldin Department of Mechanical Engineering and Mechanics Old Dominion University Director: Dr. Sushil K. Chaturvedi A numerical study has been conducted to analyze a fuel injector with three in-line cylinder geometry that has been adopted as a model for investigating the combustion phenomenon in the 8-Foot High Temperature Tunnel ( HTT ) combustor at the NASA Langley Research Center. The primary objective here is to analyze the flame lift-off phenomenon in the three cylinder fuel injector geometry in two-dimensions. The fluid mechanics model used in the analysis includes the time-averaged NavierStokes equations that are employed in conjunction with a twoequation k-e model for predicting the effects of turbulence. Calculations were performed with three chemistry models, namely fast chemistry, one-step and two-step reaction kinetics. The coupled elliptic, non-linear, partial differential equations are solved by an existing quadratic upwind scheme. Predictions are made for the flame lift-off, injector surface temperature and thermal load resulting from the combustion phenomenon downstream of the fuel injector. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Effects of fuel jet velocity, chemistry model, inlet turbulent intensity and oxygen enrichment on the flame lift-off phenomenon, and the thermal load on the fuel injector arc analyzed by considering simultaneously combined convection (outside the cylinders) and conduction (inside the cylinders). Results indicate that as the fuel jet velocity is increased, the flame is transformed from a wrap around configuration to a clearly lifted flame configuration. Of the three chemistry models considered in the present study, only the two-step chemistry model predicts a clearly lifted flame. The results indicate that as the fuel injection velocity is increased the thermal load and peak surface temperature decreases sharply (as the flame gets detatched from the injector surface). The effect of oxygen enrichment on the combustion process is very pronounced and causes the establishment of a wrap around flame even at higher injection velocities. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Modeling of turbulent diffusion flame stabilization region

Abstract: The flame base stabilization phenomenon in turbulent diffusion flames, formed by a vertical cylindrical injector operating in still atmosphere, is studied numerically by applying two different turbulent models, namely the Reynolds stress model (RSM) and the k-e model. These two models are used in conjunction with the eddy dissipation model and a two-step reaction kinetics to determine the variation of the flame base height as a function of the fuel jet velocity. The governing equations are solved by a finite volume procedure. Results indicate that the RSM produces results that are in good agreement with experiments. In contrast, the k-e model produces flame base height results that deviate significantly from the observed results. Both the RSM and the k-e model produce results that are consistent with the tangency hypothesis of Van Quickenbourne and van Tiggelen for flame base stabilization. However, the k-e model meets the tangency condition at a point closer to the injection point than indicated by experiments. In the far field, both the RSM and the k-e model yield flow properties, such as k, e, temperature and velocity components that are in good agreement with one another. The large streamline curvature in the vicinity of the flame base suggests that the RSM is the model of choice to use in conjunction with the eddy dissipation model for predicting near field characteristics of diffusion flames considered in the present study.