نشریه سوخت و احتراق
سال هفتم شماره 2 (پیاپی 14، پاییر و زمستان 1393)

Rotary aluminum furnace is used to recycle aluminum from scrap. This is a complex process and consists of many different phenomena such as aluminum smelting and burn-off, gas phase turbulent combustion and radiation in a rotary drum. In this research, a model is presented which divides the furnace into three zones, according to the distinct phenomenon happening in each zone. The three zones are refractory lining, combustion zone and melting zone. Only heat can be transferred through zones’ interfaces and no mass transfer is allowed. Numerical results indicated that molten aluminum is highly affected by furnace rotation and rotation has a significant effect on aluminum melting time. In addition, the rotational speed of 1.2rpm leads to the minimum melting time. The results also showed that radiation is the dominant heat transfer mechanism inside the furnace and 84% of the total heat flux received by melting zone is due to radiation. This portion of radiation heat transfer increases to 88.5% by increasing radiation emissivity of refractory lining from 0.7 to 0.85. As a result, the temperature of exhaust gases decreases which means better performance of the furnace. Therefore, the furnace operation time decreases by 20 minutes.

In this paper, propagation of propane-air premixed flame in a 2D diverging micro channel has been investigated numerically by emphasizing on the role of wall in flame stability. Effect of inlet velocity, wall thermal conductivity, heat loss coefficient and divergence angle on two modes of instability, blowout and extinction, has been studied. Stability maps have been drawn for straight and diverging channel and it has been shown that divergence angle changes stability map pattern and increases critical heat loss coefficient dramatically. In a certain case, heat loss coefficient of a channel with 0.7o divergence angle is about three times larger than the straight one. The variations of flame position with divergence angle and heat loss coefficient have also been presented.

Nowadays, Homogenous Charge Compression Ignition (HCCI) engine is a promising idea to achieve the benefits of the gasoline and diesel engines. An important motivation to the tendency of these engines is due to low pollutions and particulate matters that are affected by exhaust gas temperature. Controlling exhaust gas temperature in HCCI engine can lead to controlling pollution. In the present work, the parameters that have the most effect on exhaust gas temperature are specified and the effects of input variables on the mentioned parameters have been investigated using a thermo-kinetic multi zone model. This model has been coupled to a full kinetic mechanism of PRFs (iso octane and normal heptane) as fuel. The model is validated with a large number of experimental data obtained from a Ricardo engine. The exhaust gas temperature depends on combustion timing, burn duration and fuel input energy. Results show that the mentioned parameters are most affected by variables such as octane number, inlet pressure, engine speed and equivalent ratio. At the end three correlations have been presented to predict the combustion timing, burn duration and exhaust gas temperature. These parameters have been compared with experimental data.

This work is on the thermal decomposition of ammonium perchlorate activated by addition of commercial Magnesium oxide (MgO) nanoparticles. MgO nanoparticles were characterized by X-ray Diffraction (XRD) and Transition Electron Microscope (TEM) which shows an average nanoparticles diameter of 24 and 20nm, respectively. Also, TEM image shows that the MgO nanoparticles have a polyhedral shape. Furthermore, the catalytic properties of the MgO nanoparticles on the thermal decomposition of ammonium perchlorate (AP) were evaluated by Thermo-Gravimetric Analysis and Differential Scanning Calorimeter (TGA/DSC). This method showed in presence of 1, 2, 3 and 4 wt% of MgO nanoparticles, the thermal decomposition temperature of AP decreased by 102.42, 110.52, 116.47 and 121.96°C, respectively. Also, results imply that the heat decomposition of AP was increased by 420.64, 637.18, 647.69 and 821.33J/g in the presence of 1, 2, 3 and 4 wt% of MgO nanoparticles, respectively. The kinetics of the thermal decomposition of AP and catalyzed AP have also been evaluated using model fitting method.

Today communities have approved of strict laws for the limits of air pollutants produced by industrial units. Hydrogen cyanide, known as one of the most important and toxic gases, is the exhaust gas from heat treatment of polymers containing nitrile groups, such as polyacrylonitrile (PAN). In this paper, the mechanism of hydrogen cyanide production from polyacrylonitrile pyrolysis has been presented and also the amount of hydrogen cyanide emitted by furnaces producing carbon fiber has been evaluated in a research center in Iran. The amount of released Hydrogen cyanide was measured and presented for two production stages of 150 and 196 carbon fiber and at three different locations; the oxidation furnace, high temperature furnace and before entering the gas purification unit. As expected, the maximum amount of cyanide was observed in HT furnace and the production of the cyanide emission was doubled in 196 carbon fiber mode. The main goal of this paper is to select an appropriate system to eliminate discharged pollutants from the furnaces which is an important issue in the field of combustion and furnace. For this reason, various systems have been surveyed to reduce the amount of hydrogen cyanide. This method has been selected due to the fact that absorption is the appropriate system for removing pollutants with various concentrations in different flows. Furthermore, it is a much less costly method in comparison to the other ones. Moreover, for eliminating hydrogen cyanide by the absorption strategy, a system which consists of two consecutive packed towers is simulated by the aid of powerful Aspen Plus software and Electrolyte NRTL-RK thermodynamic package. The optimum values of operating parameters such as fluid flow, temperature and equipment parameters like the height of the columns were proposed.

Gas aerothermodynamics is the thermodynamics of a gas in high velocity associated with heat transfer. One of the devices which takes advantage of this field is a rocket system. High velocity flow filed with intensely varying pressure and temperature along the nozzle axis leads to reduction of residence time. This means the balance between chemical and flow time scales is changing in the flow stream. In this study, reacting flow composition variations in combustion chamber and nozzle of a liquid rocket engine is numerically investigated for hydrogen and kerosene fuels regarding combustion efficiency and performance of the engine. Numerical modeling has been conducted with the aid of commercial code FLUENT. k −e turbulence and EDC combustion models have been used to consider turbulence effects on the flow field. 9-step and 14-step skeletal mechanisms have been utilized to represent chemical oxidation of kerosene and hydrogen, respectively. Results show a reasonable accuracy in comparison with experimental measurements. As a result of this study, it can be concluded that in combustion chamber and convergent nozzle, the frozen and finite rate modeling have almost same results in all equivalence ratios. However, in divergent section of the nozzle some reactions proceed in finite rate regarding to fuel type. Finally, it can be noted that maximum Damkohler number occurs in the same axial position for both kerosene and hydrogen fuels.

In this paper, design and calculation method of a swirl injector with tangential inlets has been presented considering some known assumption. The injector designed based on the above method has been manufactured using CNC. Formation and development phenomena of air core within swirl injectors and their simulation is complicated due to two-phase swirl turbulent flow with common free surface. Therefore, in order to predict exit flow properties and investigate test results fitting, internal flow analysis has been performed. The results show agreement between numerical simulations and experiments, and air core has been formed correctly within injector. Two-phase and free surface simulations have been carried out using VOF method and turbulence has been modeled using k-e model. The results have been discussed completely in the text.