نشریه سوخت و احتراق
سال چهارم شماره 2 (پیاپی 8، پاییز و زمستان 1390)

In this article, the reacting gas flow heat transfer is numerically studied in the thrust chamber of a liquid rocket engine. The gas flow in the thrust chamber is considered as a quasi one-dimentional mathematic model in which the effects of friction, the convection heat transferred to the wall, gas radiation, and non-equalibruim chemical reactions were taken into account. The gas governing equations are solved with a fully implicit finite volume method. The Brabbs air-hydrogen chemical model, which includes 9 species and 18 finite rate elemntary reactions, is used for modeling the combustion processes. The coolant flow in the cooling channels and the heat conduction through the wall are modeled as a quasi one-dimentional mathematical model. Numerical results show that the method used for solving the governing equations can appropriately simulate the gas flow field, the wall temperature, the heat flux through the wall and can calculate the increase in the coolant temperature in the cooling channels, as well. Besed on these results, the wall temperature and the heat flux through the wall on the hot gas side reaches a maximum aboat the throat. The maximum heat flux by gases radiation is about 30% of total heat flux to the wall of the combustion chamber. Comparing the results obtained for this code that is considered as the effect of chemical reactions in the chamber with the numerical calculations, it can be seen that the differencess in the maximum heat flux to the wall, the maximum wall temperature, the tempreature increase, and pressure drop of the coolant in the cooling channels are 30%, 7%, 29%, and 3%, respectively.

Since natural gas has become a very important energy source in most parts of the industrialize world, it is necessary to study the flame structure and the effect of its exhausts on the environment. In this paper, the combustion of natural gas, which is a combination of different hydrocarbons such as CH4, C2H6,and C3H8, and gasses like N2, CO2, and O2 and H2 has been investigated using the counterflow diffusion flame model. In this research, the profiles of temperature, species concentration, and NOx mixtures are determined using numerical solution and the CO2 diluent effect on temperature distribution and rate of species production are investigated. GRI3.0 mechanism is selected as the chemical kinetic in modeling natural gas combustion. Increasing the CO2 diluent in the fuel causes a reduction in the peak combustion temperature, which is caused by decreased concentration of reactants and consequently reduction in the general reaction rate. It also reduces the peak of mole fraction species of C2H2 and NO.

Microalgaes, with high growing capability and high level of oil yield can be considered as a new source for biodiesel production. In this research, Chlorella vulgariss microalgae was used for biodiesel production. Biodiesel fuel produced was added to diesel fuel with different volume percentages (B2,B5, and B8) and used in the M8/1 diesel engine. The diesel engine was tested at three loads (8.6, 82.9, and %100) and constant engine speed (730 rpm) conditions based on the ECE R-96 standard. Experimental results indicated that using B2, B5, and B8 biodiesel blends does not have a significant effect on brake power and brake Specific fuel consumption. Using B8 at 8.6, 82.9, and %100 loads, the CO emission respectively decreased to 40, 20,and 18%; and the HC emission decreased to 20, 27.2, and 20%, respectively. However,the NOX emission increased to 20, 13.7, and 12.2%, respectively.

In this paper, the requirements of accurate simulation of the cellular structure and triple wave configuration of a weakly unstable detonation wave have been studied. Two-dimensional reactive Euler equations and a one-step Arrhenius form chemical mechanism have been solved using the well-known PPM scheme and the exact Riemann solver for a gas mixture of H2/O2/Ar. Introducing harmonic density perturbation ahead of ZND profile, detonation wave with regular structure would be produced. The flow field is restricted to a narrow patch containing detonation wave and moves with it during time and along the channel. Using the narrow patch, instead of the entire channel, leads to enormous computational cost and time saving, without losing the accuracy. At the first step, grid resolution study was conducted. Using the mentioned scheme and one-step chemical mechanism, it was shown that for capturing the cellular structure properly, a grid resolution of about 24 points per half reaction length is required. At the next step, the effects of initial perturbation parameters including perturbation amplitude factor, distance from perturbation to downstream boundary condition and perturbation thickness on the evolution and final cellular structure was examined. This way, permitted domain of variation for the parameters mentioned with the aim of precise simulation of celluar structure would be achieved. Finally, increasing the grid resolutions up to 36 points per half reaction length, capability of one-step Arrhenius chemical mechanism for capturing the second triple-point and the shear layer in triple-wave configuration has been investigated.

The purpose of this article is thermodynamic analysis of a hybrid system to provide simultaneous electrical and thermal energy. In this paper, a hybrid system of solid oxide fuel cell and micro gas turbine is investigated with all accessories and then, thermodynamic analysis for all components of the cycle is done. Also, an electrochemical analysis is separately performed for the fuel cell. Then, with parametric study for the mentioned hybrid system, the effect of cell temperature, working pressure and air to fuel flow ratio on efficiency, power, and entropy generation in the hybrid system are studied. Finally, a case for optimum performance is presented. The results indicate increased efficiency of hybrid system with increasing cell temperature and working pressure (up to 80 percent). Determining the optimum air to fuel flow ratio and the full calculations of fuel cell at three separate parts (reforming, electrochemical, thermal) are the other items presented in this study.

Pulse combustors are simplest form of combustor with low cost and operating with different fuels. In this research a non-premixed pulse combustor is constructed and some factors affecting the NOX, CO, flame temperature and frequency of combustion are experimentally investigated. The key variables of the experiments are the inlet mass flow rate of fuel and the tailpipe length. The results show that with decreasing the mass flow rate of fuel, the concentrations of NOX and CO are reduced and reached to its minimum values of 17 and 65 ppm, respectively. This level of NOX emission from pulse combustors is quoted to be generally lower than from conventional burners which reported to be 58-138 ppm. Increasing the tailpipe length causes the concentrations of NOX and CO to be decreased and the frequency of combustion is also decreased. The results are compared with the results of other researchers and are in good agreement.

This paper is dealing with the development of a new version of an existing burning model for predicting the burning rate of different pyrotechnic mixtures of magnesium and sodium nitrate. Modifying some parts of the model including burning time of magnesium particles, thermophysical properties of combustion products, and the mixture density, the burning rate has been predicted for different values of mixture composition and combustion pressure. Comparison of the predicted and available experimental values of the burning rates shows good agreements, especially in pressure dependency.