نشریه سوخت و احتراق
سال شانزدهم شماره 1 (پیاپی 42، بهار 1402)

In this article, an investigation is conducted into the impacts arising from variations in the configuration of apertures within a perforated plate employed in the context of low-swirl premixed combustion. To this end, a four-blade burner characterized by a radius of 7 mm is employed, along with a perforated plate possessing a radius of 4.5 mm. The blockage ratio, held at a constant value of 0.88, encompasses a set of 9 orifices, each explored across 5 distinct configurations. Computational analysis is executed utilizing the Ansys Fluent software, encompassing the resolution of the three-dimensional Navier-Stokes equations coupled with the k-ω standard turbulence model. Within this study, the role of oxidizer and fuel is played by air and methane respectively, under an equivalence ratio of 0.65. The outcomes of this investigation reveal a notable constancy in the general flow behavior despite the altered orifice arrangements. At the same time, the maximum total temperature and the average flow rotation change by 1% and 3%, respectively. In addition, in the flame formation area, the location and angles of the flame are changed by 17%, 7% and 19%, Furthermore, a downward shift of the flame by 8.8 mm is discerned consequent to modifications in the spacing between apertures within the perforated plate. Additionally, from an emissions mitigation perspective in combustion processes, it is noteworthy that there exists a discernible disparity of approximately 12% between the maximal and minimal levels of nitrogen oxide emissions generated.

The combustion flow field in domestic gas stove burners plays a fundamental role in the structure and shape of the flame, the distribution of the temperature gradient, and, consequently, the thermal efficiency and emission of pollutants. Obtaining a valid numerical model makes it easier to understand this complex flow and its influencing factors. To provide a valid numerical simulation, the thermal efficiency of the burner was experimentally tested in the pressure range of 12 to 24 mbar. The validity of the numerical results was then examined by comparing them with the experimental results. Additionally, the response surface methodology was utilized to investigate the simultaneous and mutual effects of various factors such as gas source pressure, initial temperature of the mixture, and load height on thermal efficiency, burner thermal power, the ratio of radiant heat flux to total flux, and the amount of CO emission. The algorithm proposed 20 cases that were numerically investigated, and the obtained contours were extracted based on the fitted regression models for the output parameters. The results show that although increasing the pressure increases the thermal power of the burner, it decreases its thermal efficiency. As the pressure of natural gas decreases, the flame temperature increases and the temperature peaks approach each other. In fact, the concentration of the flame increases with the decrease in pressure, and as a result, the thermal efficiency increases. Additionally, the results show that CO gas emission decreases with increasing pressure.
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Reducing fuel consumption, pollutants, and increasing engine power and efficiency are important in the field of internal combustion engine research. Nowadays, reactive control compression ignition engines have attracted the attention of researchers as a new technology in the field of low temperature combustion. One of the problems in the field of low temperature combustion is the control of the combustion process. In this research, the numerical analysis of performance parameters and pollutant emissions of a methane-diesel reactive control compression ignition engine at injection times of -10, -20, -35 and -50 in three equivalence ratios of 0.25, 0.35 and 0.45 has been paid. CONVERGE CFD software was used for simulation. The results show that with advanced injection of diesel fuel, the pressure increases from -10 to -20, and with more advance at injection times of -35 and -50, the pressure decreases, which causes incomplete combustion. Also, advance injection of diesel fuel increases the parameter value of ignition delay and the length of the ignition interval, and at the time of 20 injection, the CA50 parameter value is closer to the top dead point, which is desirable. On the other hand, with the fuel injection advance from -10 to -20, the amount of NOx pollutant increases. Increasing the equivalence ratio, increases the indicator efficiency, ignition delay parameters, the length of the ignition interval, and CA50. Also, increasing this parameter from 0.35 to 0.45 reduces the heat release rate.

This study investigated the effect of grain fuel composition in the ramjet combustion chamber on the ignition delay time and solid fuel regression rate. In this article, a numerical investigation of ignition and stabilization of combustion of a new design of an engine equipped with solid fuel is done. The rod design consists of two solid fuels, maintaining the simple design of the classic ramjet. Numerical simulations of unsteady, turbulent, reactive and disintegration due to solid fuel by simultaneously solving combustion and turbulence models, applying numerical methods in the analysis of the governing equations that are the basis for obtaining some results including the effect of variables, functional characteristics and characteristics Combustion and finally access to the ignition delay time of fuel-rich propellant in solid fuel ramjet systems. In examining the chemical reactions of the combustion chamber, heavy polyethylene is taken into consideration and finally the ignition and combustion process continues. In line with the diagnosis for the correct prediction of the ignition delay time in the two mentioned geometries, the simulation results were in good agreement with the experimental data of the comparison and the selected model. The ignition delay time for the rod geometry was 0.28 seconds, for the classic geometry it was 0.43 seconds. And the design with the rod has increased the fuel regression rate.
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In this research, modeling and numerical simulation of the effect of sudden expansion ratio (ratio of port diameter to inlet diameter) of high-density polyethylene-based solid fuel ramjet combustion chamber in the reactive turbulent flow on the regression rate are presented. The effect of sudden expansion of solid fuel ramjet combustion chamber in three different samples with different port diameters and fixed inlet diameter with ratios of 1.75, 1.875 and 2.125 is investigated on the parameters of temperature and regression rate. The simulation results show that increasing the ratio of port diameter to inlet diameter decreases the temperature. The highest temperature was obtained in the original sample with the ratio of port diameter to inlet diameter equal to 1.75.  Also, the results show that the sudden increase in expansion causes a decrease in the fuel regression rate, which causes a decrease in ramjet performance.

The study of the radiation effects of the pool fire is significant considering the life and financial damages to individuals and facilities of a refinery complex. Therefore, in the present study, the radiation resulting from a pool fire of three common fuels, gasoline, kerosene, and crude oil, in three large fuel storage tanks with diameters of 25, 50, and 75 meters and a fixed height of 15 meters was studied numerically. In this study, FDS software was used, which is based on the finite difference approach with an explicit time discretization. As an innovation, the amount of radiation at a height of 1.5, 3, and 5 meters were studied in order to investigate the level of dangers to humans and firefighters of fire extinguishing machines, and at a height of 10 meters to investigate the effect of radiation on other nearby tanks, at different horizontal distances. The results indicate that when the fuel is gasoline, the highest radiation risk is between the tank wall and 1.7 times the tank diameter, and the minimum allowable distance for the safe zone is 2.6 times the tank diameter, which increases with increasing height above ground level. It was also observed that the radiation received at the same distance from tanks with similar diameters differed depending on the fuel, which has a direct relationship with the heat release rate.
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Numerical simulation of turbulent flames with laminar flamelet models is not easily possible under high turbulence intensity conditions. Experimental results and direct numerical simulations show that introducing strain effects in the production of flamelet tables can significantly increase the accuracy of modeling. In this work, implementing the strain effects in the model results in 30 mm increase in the flame height relative to the unstrained model. In this work, a strained flamlet model has been implemented and evaluated in the simulation of turbulent premixed flames. The premixed counterflow flame has been used to produce the flamelet tables. These tables are used in the computational fluid dynamics solver using two reaction progress variables and the presumed probability density function method. The model obtained in this research has been used in Reynolds-Averaged simulation of a turbulent piloted premixed flame in a bunsen burner. This burner utilized a novel approach to highly increase the input turbulence intensity. The results show that the strained flamelet model predicts the flame propagation speed and consequently the flame length, significantly better compared to the unstrained flamelet model.
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