javad khadem

Reduction of chemical mechanisms is of particular importance to decrease the computational time of combustion simulations. The main goal of this research is to reduce the chemical mechanism of JP-10. To achieve this, an innovative approach was applied, which combined various mechanism reduction methods, including sensitivity analysis, directed relation graphs (DRG), and directed relation graphs with error propagation (DRGEP). Using this approach, the detailed JP-10 mechanism, consisting of 7,740 reactions and 320 species, was reduced to 257 reactions and 48 species. In this regard, ANSYS CHEMKIN was employed for mechanism reduction and combustion simulation. The combustion simulation results for JP-10 in a homogeneous reactor model were then compared using both the detailed and reduced mechanisms. The results exhibited a high level of agreement, with simulation errors below 10%. Furthermore, the results demonstrated that DRG and DRGEP methods are both fast and accurate in identifying less significant species in the mechanism, whereas the sensitivity analysis method is comparatively slower. Validation of the results with experimental data from other researchers confirmed that the model used in this study is highly accurate, making the proposed mechanism reliable for use in combustion simulations.

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.

In this paper, a bidirectional single unit air compressor equipped with two reciprocating pistons and operating with a new mechanism of semi gear and rack type in power transmission has been made, developed and analyzed. In this structure, there are two reciprocating pistons in two opposite positions to produce compressed air, therefore, there are two compressed air strock in each rotation of the output shaft. In the power transmission mechanism, a rack gear and a semi gear have been used, so that The rotation of the compressor shaft causes the rotation of the semi gear and finally, the reciprocating movement of the rack and the pistons. The results show that in the experimental situation, the amount of energy consumed to reach the tank pressure of 4 bar is equal to 142.6 kJ, while the minimum theoretical work of the compressor in the isotherm state to reach the same pressure is equal to 72.5 kJ and this represents 51% efficiency of this structure in the form of working in compressor mode. Also, the results show that using heat from waste sources to increase the tank pressure from 4 bar to 5 bar will lead to an increase in efficiency of about 60 percent.

In recent decades, low temperature combustion engines have been the focus of researchers as an effective strategy to achieve the optimal combustion model. In this method of combustion, initially, the fuel with high octane is sprayed in the inlet manifold and then another fuel with a high cetane number is injected into the combustion chamber at a different time. Combustion in reaction-controlled compression ignition engines does not use direct control tools and depends on the reactions' initial conditions and chemical kinetics. Considering the importance of ignition timing and its control in low-temperature combustion engine performance, in this study, using the control variables of ignition delay, fuel injection time and maximum pressure inside the cylinder, along with the fuel injection system as the ignition control operator, to the experimental investigation of the performance of a direct injection low temperature combustion engine has been discussed. The results show that the injection time of diesel fuel inside the cylinder is one of the most important factors influencing the performance and efficiency of the engine. For low methane injection rate (15 slm), with increasing delay in pilot fuel (diesel) injection time, the value of the maximum heat release rate and specific fuel consumption decreased, while the mean effective pressure and gross indicator efficiency increased. By controlling the reactivity of the mixture and the fuel injection time with more reactivity, it is possible to achieve the appropriate ignition time, which indicates the importance of the fuel injection time as an essential control parameter in the ignition control of a low-temperature engine. In general, the methane rate has a secondary effect on ID compared to SOI.

Mathematical modeling is used as a tool to predict the combustion behavior of fuels. The use of detailed chemical kinetics mechanisms in combustion models increases computational time. Metaheuristic optimization algorithms are one of the methods used to reduce the detailed mechanisms. The purpose of this paper is to investigate the possibility of using continuous metaheuristic algorithms in binary space to reduce the combustion mechanism of dimethyl ether fuel. For this purpose, particle swarm optimization and differential evolution algorithms have been used in a combination with angular modulation to map the continuous space to binary one and reduce the dimensions of problem from 351 to 6. Finally, a detailed mechanism with 79 species and 351 reactions is reduced to 17 species and 43 reactions. It has been showed that the reduced mechanism predicts the results of detailed mechanism in constant pressure and laminar premixed flame reactors very well with maximum error less than % 0.95.
 
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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.

The fast filling process is the main process that occurs in the CNG refueling station. The main objective of the present study is to apply a thermodynamic analysis for a complete modeling of a CNG refueling station with several consecutive refueling . The results of the thermodynamic analysis have been validated against the experimental data and previous studies. The AGA8 Equation of State has been used to calculate the thermodynamic properties of CNG. There are many researches concentrated on the thermodynamic modeling of CNG refueling station, but didn't address the optimal algorithm of priority panel. Filling time minimizing, filling mass maximizing and average specific energy consumption minimizing have been employed as the objective function for the optimization problem. Finally, the optimal algorithm of priority panel has been determined as the main goal of the present study. The conclusive results of the optimization problem are presented. Achieving more accurate modeling and modeling the process of several consecutive refueling is one of the most important results of the present study. The optimal algorithm of priority panel are obtained for PPM225 algorithm . An economic analysis is performed to see the results more clearly. The results of the economic analysis show that 65,700,000,000 Rials (43,800,000 kWh) can be saved in one year.

The influence of magnetic field on combustion has attracted many researchers. Since the effect of the magnetic field on the gas flow and the combustion process is through volumetric electromagnetic force, the need for a numerical solution and electromagnetic simulation of the flow field is necessary to obtain the distribution of the magnetic field. The present study investigates the numerical variations in the shape and temperature of the diffusion flame of methane in the presence of a non-uniform magnetic field. For this purpose, two groups of electromagnetic equations and fluid mechanics and combustion are solved simultaneously. The results show that magnetic force volumetric influences on paramagnetic (oxygen, air) and diamagnetism (methane and combustion products) effects on flame shape, flame temperature, and mixing of fuel and air. Also, the use of a decreasing magnetic field causes Slim and drawn flame shape and increase flame temperature and the application of an increasing magnetic field causes the shape of flame to be shortened and diffused (Mushroom-shaped) and the flame temperature decreases relative to the non-magnetic field.

It is necessary to study the flame structure from the approach of its temperature, species consumption rate and pollutants emission. In this paper, the combustion of Methane/Air was investigated with the counterflow diffusion flame model using OpenFoam software. In order to model the problem, Multi-step GRI3.0 mechanism in 324 steps and 53 radical species was used. In this solution, the convergence of unsteady states was considered 10-6 for each time step and residual physical parameters. With the maximum error of 21%, it is an acceptable agreement in the comparison between numerical model and experimental data in the similar state. The results show that in this type of heating system, the amount of the production of carbon emissions that are harmful to human's health are almost critical.