FUEL AND COMBUSTION
Year:2012 | Volume:5 | Issue:1|Papers Count:6

In this paper the effect of burners tilt angle on gaseous flows and combustion process is numerically investigated. The furnace of the Bandar Abbas power plant boiler was comprehensively simulated using FLUENT software on the actual scale. The three dimensional Navier-Stokes, the energy and the chemical species transport equations were solved in the computational domain. The standard k-eturbulence model for fluid flow and the eddy dissipation model for turbulent combustion were utilized and radiation heat transfer was considered using the PJ model. The effects of tilt angle on the fluid flow and combustion parameters were analyzed at a constant air and fuel flow rate. Results show that changing the burners tilt angle is an appropriate way to control the flames and the temperature of different boiler parts. The obtained results were compared with the corresponding results in the literature which showed good agreement.

Large eddy simulation (LES) was used to investigate the H2/CH4 flame structure under MILD condition. Effects of the fuel inlet Reynolds number and the oxygen mass fraction in the oxidizer stream on the flame structure were studied. In this regard, the simulation was performed for two Reynolds numbers of 5000 and 10,000 and three oxygen mass fractions of 3,6 and 9%. Numerical results were compared with experimental measurements of Dally. The turbulence-chemistry interaction in numerically unresolved scales was modeled using the PaSR model and the full mechanism GRI-2.11 was used to precisely represent the methane hydrogen reactions. Accuracy of the LES simulation results was evaluated by a set of criteria indicating acceptable predictions. The results show that increasing the oxygen mass fraction in the oxidizer stream decreases the flame thickness, limits the species fluctuations to a smaller zone near the nozzle’s exit plane, decreases local extinctions in the flame structure and limits the partially premixed to a zone near the shear layer line and in summary improves the flame stability especially near the nozzle exit zone. Since decreasing the Reynolds number increases the residence time of fuel and oxidizer elements, it has a favorable effect on flame stability and decreasing its susceptibility to combustion instability.

The present paper concerns an experimental investigation of the flashback phenomenon of flame in a porous media burner made of two SiC-porous media. Regarding the importance of flame stabilization on the surface of these types of burners to achieve the highest efficiency, some influential parameters that affect the flame flashback, such as the firing rate and the pore density, were studied. The reactive mixture comprisednatural gas and air with an equivalence ratio of 0.65. The temperature profile along the burner was measured by thermocouples installed at different locations of the burner, including the porous media. Results show that by increasing the firing rate at a constant porosity, the flashback temperature is increased and the flashback time is reduced. An increase in the porosity results in reduction of flashback temperature and its associated time.

Pulse combustors are simple, low-cost and can operate with different fuels .. In this research, a non-premixed pulse combustor was constructed and some factors affecting NOx, CO, flame temperature and frequency of combustion were experimentally investigated. The key variables of the experiments were the inlet mass flow rate of fuel and the tailpipe length. The results show that with decreasing the mass flow rate of fuel concentrations of NOx and CO reduce and reach to their minimum values of 17 and 65 ppm, respectively. This level of NOx emission is considerably lower than conventional burners which are reported to have NOx. emissions of 58-138 ppm. Increasing the tailpipe length decreased concentrations of NOx. and CO emissions and also reduced the frequency of combustion. The results were in good agreement with previous research reported in the literature.

In a vapor cloud explosion, flame propagation phenomenon and turbulence flow field occur simultaneously. At the same time, the existence of obstacles in the flame propagation direction, leads to wrinkling of the flame front. The mechanism of flame wrinkling phenomenon occurs due to the effect of the flame-vortex interactions. Large scale vortices deform the flame front and increase its surface area. Increasing flame surface area ends in an increase of burning velocity and intensification of pressure build-up. The major challenge in modeling of large scale vapor cloud explosion is calculation of turbulent flame speed. In this paper a combined model of Weller’s wrinkling factor transport equation and SCOPE3 model was utilized to calculate this parameter. The SCOPE3 model considers high intensity turbulence. Therefore. the combined model is suitable for modeling of the vapor cloud explosion in presence of significant obstacles. Numerical results also confirm. the ability of this model to accurately predict pressure history.

Porous media (PM) combustion has interesting advantages compared with free flame burners due to raised burning rates, increased power ranges, extended lean flammability limits, and reduced pollutant emissions. in future internal combustion engines pollutant emissions and fuel consumption should be minimized under a wide range of speed and loads. These parameters strongly depend on mixture formation and combustion processes which are difficult to control in a conventional engine. This may be achieved by realization of a homogeneous combustion process in engine. This paper deals with the simulation of a direct injection internal combustion engine equipped with a chemically inert PM of hemispherical geometry used to homogenize and stabilize the combustion. A 3D numerical model for PM engine is presented in this study based on a modified version of the KIVA-3V code. Due to lack of any published data about the PM engine, numerical combustion wave propagation in the porous medium were compared with experimental data of methane-air mixture under filtration in a packed bed which showed very good agreement. Methane was injected directly inside the hot PM which was assumed to be mounted on the cylinder head. A lean mixture was formed and volumetric combustion occurred in the PM. The mixture formation, pressure and temperature distribution in both phases of PM and in-cylinder fluid, the production rates of co and NO, and effect of injection time in the closed part of the cycle were studied.