نشریه سوخت و احتراق
سال چهاردهم شماره 2 (پیاپی 35، تابستان 1400)

In this study, the computational fluid dynamics (CFD) simulation of an experimental 350 kg cast iron rotary furnace was conducted for the aim of optimizing its fuel consumption and pollutants reduction. The furnace is divided into 3 distinct simulation zones: a) solid charge zone with liquid-solid phase, b) combustion zone with gas phase, and c) solid rotating zone or furnace refractory wall. These three zones are three-dimensionally and transiently modeled in terms of the leading phenomena within each zones and interfaces. The simulation in each region is based on the simultaneous solution of hydrodynamic equations, including vortex dissipation and chemical reaction kinetics equations. The simulation results for the outside wall temperature of the furnace body are in close agreement with the data obtained from experimental units. Furthermore, melting rate, NOx and CO pollutant generation, specific fuel consumption, rotating speed, preheating of combustion air, excess air percentage, and pollutant production were all evaluated in this simulation. Changing the furnace configuration decreases fuel consumption by 5%, which is important in terms of improving fuel consumption and alloy product quality in this furnace.  The results of this study can be used to optimize the industrial rotary furnace operations.

This paper aims to numerically investigate the effect of blockage ratio on the mechanisms governing the deflagration to detonation transition (DDT) in inhomogeneous mixtures of H2-air. The study combustion chamber is a closed rectangular cross-section channel with obstacles that have been studied in three blockage ratios of 10, 30, and 60 percent and at different obstacle spacing. The present numerical simulation was performed using the SST-K-ω turbulence model and the combustion model of the Weller flame wrinkling and the HLLC method was used to shock-capturing. The results show that for the 10% blockage ratio, the onset of detonation occurred in the unobstructed part of the channel and for the blockage ratios of 30% and 60% DDT occurred in the obstructed section of the channel. The mechanisms governing the DDT process change as the blockage ratio and obstacle spacing change. The Mach reflection from the lower wall of the channel and the formation of the reactive Mach stem, the reflection of the Mach stem from the wall of the lower obstacles, and the reflection of incident shock from the wall of the upper obstacles are the most important governing mechanisms observed. The results also show that flame acceleration and the occurrence of DDT in the channel occur faster as the blockage ratio increases. The fastest onset of detonation occurred at the blockage ratio of 60% and the space to height ratio of S/H = 2.5.

A numerical study has been performed to evaluate the cryogenic injection and mixing characteristics of a real transcritical bi-shear injector. With this aim, a dynamic one-equation eddy-viscosity subgrid-scale model (for large eddy simulation), the Peng-Robinson equation of state (for calculating the thermodynamic properties), the NIST database (for estimating the transport properties) and the PISO algorithm (for velocity-pressure coupling) have been used to analyze various features of the transcritical turbulent bi-shear flow. Observations indicate that there is a good agreement between the results of the present work and previous experimental and numerical studies. Simulations show that due to the remarkable effects of pseudo-boiling and density stratification phenomena in preventing the sustained growth of the transcritical mixing layer, the potential core of the inner dense jet is much longer than that of the outer jet. However, due to the high sensitivity of isobaric specific heat to temperature, especially around the pseudo-boiling temperature, small temperature fluctuations drastically reduce the isobaric specific heat and in turn result in local distortion and weakening of the thermal shield. Subsequently, the vorticity generating mechanisms, including the baroclinic torque and volume dilatation, catch up and efficiently enhance the mixing quality.
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In this paper, the performance of a triple pressure heat recovery boiler with gaseous fuels from biomass is discussed in terms of power output, efficiency and pollutions at oxygen, air, and steam gasification processes. The main parameters to optimization of heat recovery boiler by using genetic algorithm method are water and steam mass flow rates, high to low pressure pinch points temperatures, and temperature difference between the superheat steam and gas flows. It was found that the use of steam gasification in comparison with oxygen gasification increases the power output and efficiency of cycle 117 MW and 3.24%, respectively. However, the NOx production in oxygen gasification process is 790 gr/s less than steam gasification. Also different types of biomasses are compared in terms of power generation, efficiency and emissions production with each othe.In this paper, the performance of a triple pressure heat recovery boiler with gaseous fuels from biomass is discussed in terms of power output, efficiency and pollutions at oxygen, air, and steam gasification processes. The main parameters to optimization of heat recovery boiler by using genetic algorithm method are water and steam mass flow rates, high to low pressure pinch points temperatures, and temperature difference between the superheat steam and gas flows. It was found that the use of steam gasification in comparison with oxygen gasification increases the power output and efficiency of cycle 117 MW and 3.24%, respectively. However, the NOx production in oxygen gasification process is 790 gr/s less than steam gasification. Also different types of biomasses are compared in terms of power generation, efficiency and emissions production with each othe.

Investigation the combustion pattern when the flame hits with obstacles is very important to increase safety in various industries. In this paper, the flame quenching behavior with the presence of porous barriers and perforated plates is investigated. In this study, a closed chamber with the presence of porous barriers and 2 mm perforated plates and a high-speed video camera were used to capture the flame propagation behavior process. All experiments were performed at atmospheric pressure. According to the recorded images, the flame quenches in two modes; side wall and head on, after hitting the obstacles. In this study, the effects of the position of obstacles from the ignition system on the flame quenching distance, flame quenching pattern, and flame propagation speed have been investigated. The position of the porous barriers and 2 mm perforated plates is effective in the flame quenching distance. When the perforated plate is 16.6 cm away from the ignition system, the flame quenches after hitting the first obstacle. However, when the porous barrier is located at a distance of 16.6 cm from the ignition system, the flame passes through the barrier after hitting the barrier. According to the results, the presence of porous barriers in a closed chamber compared to perforated plates increases the quenching distance and the speed of the flame tip. For example, with the presence of porous barriers relative to perforated plates, the flame quenching distance increases from 16.6 cm to 25 cm. Also, the flame tip speed has increased by about 128% from 2.5 to 5.7 m/s using porous obstacles.

The purpose of the present study was to investigate the susceptibility of NOx and CO pollutants due to the change of stabilizing jets characteristics in a gas turbine model combustion chamber. The change of stabilizing jet characteristics were analyzied according to their interactions. To simulate the two-phase flow inside the combustion chamber, the Eulerian method was used for gas flow and the Lagrangian method was used for spraying the fuel. For simulating the combustion The purpose of the present study was to investigate the susceptibility of NOx and CO pollutants due to the change of stabilizing jets characteristics in a gas turbine model combustion chamber. The change of stabilizing jet characteristics was analyzed according to their interactions. To simulate the two-phase flow inside the combustion chamber, the Eulerian approach was used for gas flow and the Lagrangian approach was employed for spraying the fuel. For simulating the combustion process inside the combustion chamber, the RANS approach, the Realizable k-ε model for turbulence, Discrete Ordinates Model (DOM) for radiant heat transfer and steady flamelet combustion model were applied. NOx modeling was done by post-processing with a finite rate model. Using a sensitivity analysis, the effects of variations of input variables including diameter, angle and position of the stabilizing jets on output variables were studied. Numerical data were generated by using Design of Experiments (DOE) and full factorial model. The results were inspected by the means of analysis of variance (ANOVA). The results indicated that with considering the interaction among jets characteristics, the trends of pollutants changes could be observed more accurately. Nevertheless, this was not possible without considering the interactions.  The purpose of the present study was to investigate the susceptibility of NOx and CO pollutants due to the change of stabilizing jets characteristics in a gas turbine model combustion chamber. The change of stabilizing jet characteristics was analyzed according to their interactions. To simulate the two-phase flow inside the combustion chamber, the Eulerian approach was used for gas flow and the Lagrangian approach was employed for spraying the fuel. For simulating the combustion process inside the combustion chamber, the RANS approach, the Realizable k-ε model for turbulence, Discrete Ordinates Model (DOM) for radiant heat transfer and steady flamelet combustion model were applied. NOx modeling was done by post-processing with a finite rate model. Using a sensitivity analysis, the effects of variations of input variables including diameter, angle and position of the stabilizing jets on output variables were studied. Numerical data were generated by using Design of Experiments (DOE) and full factorial model. The results were inspected by the means of analysis of variance (ANOVA). The results indicated that with considering the interaction among jets characteristics, the trends of pollutants changes could be observed more accurately. Nevertheless, this was not possible without considering the interactions.  .

The purpose of this study is investigating the effect of fuel to air ratio on the flow characteristics and NO emission in a model double swirler combustion chamber. The air in this combustion chamber passes inversely through the liner. In this research, by defining the boundary conditions and producing adequate mesh, and using standard K-Ɛ model for methane fuel, combustion simulations have been performed. The simulations are performed in four different equivalence ratios, all of which are for the dilute phase of the fuel. The physics of the flow inside the chamber showed that in the higher equivalence ratios than 1, the mass flow air in entrance is not enough to keep the vortex breakdown and the stability of the flame, and thus prevents the formation of flame. By examining the vorticity and the amount of power of each vortex breakdown inside the chamber, the results showed that reducing the equivalence ratio increases the intensity of the vortex. It was found that reducing the equivalence ratio not only reduces the maximum flame temperature, but can also reduce the flame length to some extent. Finally, it was concluded that the NO production behavior is highly depend on the fluid temperature and its change graph is very similar to the temperature change diagram in the chamber, which results in a significant positive effect of decreasing the equivalence ratio on reduce the production of combustion emissions.