نشریه سوخت و احتراق
سال سیزدهم شماره 1 (پیاپی 30، بهار 1399)

In this paper, the effect of the magnetic field with decreasing and increasing gradients on the non-premixed methane flame has been investigated. To examine the impact of the magnetic field, Arrhenius combustion model and the one-stage methane-air mechanism have been used for simulation. The simulated results of the flame temperature are in a good agreement with experimental measurements. Results show the flame deformation and its temperature increase is affected by the magnetic field gradient. By applying the flame in the magnetic field with decreasing and increasing gradients, the flame temperature increases, and the flame height decrease. By using a decreasing gradient magnetic field, the maximum temperature at the top of the burner reaches a height of 4.5 mm and in the absence of field, position at the height of 2.5 mm. While under the influence of increasing gradient magnetic field, this value is 4 mm, indicating a decrease in the height of the flame. These changes are more evident in the area with a decreasing gradient. The magnetic field effects on methane and combustion products mass fraction's decrease. In decreasing and increasing gradients, unburned methane declined respectively 99% and 52% in comparison with no field.

In this paper, air gasification of Tehran’s refinery Mazut is investigated. First, Mazut gasification is modeled by the equilibrium method and then, the thermal operating of an entrained flow gasifier is studied experimentally. An entrained flow gasifier is designed and manufactured for 7 kg/h flow rate of heavy fuel oil. The physical/chemical properties of this heavy fuel oil are determined via standard laboratory experiments. In Aspen plus, a parametric study is conducted by the equilibrium model in order to investigate the effects of equivalence ratio on syngas composition, gasification temperature, and higher heating value for the steady-state condition. Temperature distribution along the gasifier and the solid carbon consumption are effective parameters on syngas composition and gasification performance. In an experiment, the gasification temperature is measured at different locations of a gasifier. The modeling results show that the values of H2, CO, and HHV have a maximum which is accompanied with complete consumption of solid carbon at equivalence ratio 0.39. By increasing equivalence ratio, gasification temperature increases which are supported by experimental results. The comparison of modeling and experimental result shows that difference between model and experimental temperature increases by increasing equivalence ratio. Also, after a short distance from the injector, the temperature is decreased along the gasifier with a constant rate. Finally, in order to provide the optimum gasification operation, the proportion between an appropriate gasifier length and operating equivalence ratio is presented based on one of the gasification reaction.

Concerns about increasing environmental pollution and increasing greenhouse gas emissions from fossil fuels have led researchers to use renewable energy. In this research, the environmental impacts of bioethanol production from potato waste were investigated from the agricultural stage to the production stage of bioethanol (crushing and malt production, enzymatic hydrolysis, fermentation and dehydration). Investigation of environmental impact of the data collection was done using a life cycle assessment method in the form of 15 impact groups and 4 final indicators, and its functional unit was considered to produce 1 kg of bioethanol. The results obtained from the impact groups in two stages of agriculture and bioethanol production showed that the agricultural stage in all the affected groups except the carcinogenicity group had higher values than the stages of bioethanol production (malt production, hydrolysis, fermentation and dewatering). Also the results showed that the highest contribution to creating different impact groups is related to energy consumption of electricity, steel, agricultural machinery, nitrogen, phosphate and direct emission of pollutants from the field and manufactory. The comparison between different environmental endpoints indicator shows that the human health index is 9.90 times higher than ecosystem quality, 1.28 times higher than climate change and 1.48 times higher than that of resources with destructive effects on bioethanol fuel production.

Zeolite Y was successfully synthesized using alkali-fused pyrophyllite as the source of Si and Al without using template. Surfactant (CTAB) was used in order to create the mesopores in the synthesized Y zeolite. Physicochemical properties of the synthesized samples were investigated using XRD, FESEM, BET, FTIR, NH3-TPD, EDX and TGA characterizations. The properties and catalytic performance of the synthesized zeolites using pyrophyllite were compared with commercial Y zeolite. The results of XRD analysis showed that a pure Y zeolite has been synthesized using alkali-fused pyrophyllite in the presence of CTAB. Furthermore, the use of CTAB resulted in improving the textural and acidity properties of the synthesized sample. Moreover, the catalytic activity of the synthesized zeolites was tested in a fixed bed reactor. The synthesized sample with CTAB, for the case of heavy oil conversion to light fuels showed a conversion of up to ca. 60%. It was observed that the light fuels selectivity such as gasoline and gasoil as well as gaseous production over modified zeolite with CTAB was higher than the other samples. Due to the presence of mesopores and better accessibility of the feed molecules to the catalytic active sites, the CTAB-synthesized sample showed higher catalytic activity as well as gaseous products formation.

This study investigates the stability of a surface flame burner using a photodiode and data acquisition system. The light intensity fluctuations were measured by the photodiode and, using fast Fourier transform, they were transferred from the temporal to the frequency space. To illustrate the dynamic behavior of premixed flames, flames are divided into two regions of cellular flames and surface flames. This classification is dependent on the flow rate and the equivalence ratio. In surface flames, as the flow rate increases, the oscillation frequency also increases because the hot burned gas velocity increases. In cellular flames, as the flow rate increases, oscillation frequency decreases. At identical flow rates, the sharp decrease in the oscillation frequency indicates the appearance of cellular flames so we can find the transition from the surface flame to the cellular flame. At a constant flow rate, with an increase in the equivalence ratio, there is no increase in the oscillation frequency, the transition from the cellular flame to the surface flame occurs. The initiation of the transition from the cellular flame to the surface flame occurs at flow rates of 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 m3 / h and at equivalence ratios of 0.6 , 0.62, 0.62, 0.64, 0.66, and 0.67, respectively. The location of the transition corresponds to the start of the liftoff zone based on image processing. This research is innovative because it is possible to evaluate flame stability using a non-intrusive method without disturbing the flame shape and damaging the flame regime.

In this study, the effect of coal dust particle size on the intensity of coal dust explosion was investigated using an explosion test in a 2-liter chamber. Samples of coal have been collected from various coal mines in the country and they are used for coal dust preparation. To determine the index of explosion capability (KST), the distribution of the explosion intensity of each sample should be evaluated by measuring the maximum pressure (Pmax) and the maximum explosion pressure rise rate (dp/dtmax) in different experiments. Coal dust particles at constant concentrations and different sizes (149µm, 125µm, 105µm, 74µm, 63µm, 53µm, 44µm, 37µm) were evaluated. The results of the sieving analysis show that almost all samples of the prepared coal dust have a minimum optimum explosive concentration (250 g/m3 ). In this analysis, all tests were carried out at 1.5 bar and the initial temperature was 25 °C. According to the results, coal dust particles with dimensions of 44 and 37 microns have higher explosive index than other dimensions. Therefore, both parameters of maximum explosion pressure (Pmax) and the maximum explosion pressure rise rate (dp/dtmax) show an increasing trend with decreasing particle size. Also an increasing concentration of coal dust shows an increasing trend at the first and then a decrease in the intensity of the explosion. The presence of small coal particles increases the effective level, thus increasing the explosion rate and the rate of instability, which accelerates the process of coal dust explosion. Therefore, according to the results obtained in the process of checking coal dust explosion, in addition to the inherent characteristics of coal dust, particle size coal dust should also be taken into account. The results obtained in this mechanism are useful not only in the research and development of knowledge of coal dust blasting processes, but also in taking the necessary measures to prevent the explosion of coal dust in coal mines.

In the present research work, computational simulation of the multi cavity scramjet combustor has been performed by using the two-dimensional compressible Reynolds-Averaged Navier Stokes (RANS) equations coupled with two equations standard k-ɛ turbulence model as well as PaSR model for combustion modeling. In this combustion chamber, the supersonic air with Mach number of 2.05 flows in the enclosure, and the transverse hydrogen fuel injection is employed at sonic condition. The cavity is used to stabilize the flame in the combustor and the effect of cavity location and also the number of cavities on flow structure, combustion efficiency, and pressure recovery factor are studied. The results show that by increasing the number of cavities from one to four, the combustion efficiency is increased but the pressure recovery factor decreases. For the four-cavity configuration, the combustion efficiency is around 98% and the pressure recovery factor is 46.13%, which shows 26% increase in the combustion efficiency and 10% decrease in the pressure recovery factor as compared with the single-cavity. In the considered configurations, the best performance is achieved by the parallel dual-cavity with two-injection combustor.