FUEL AND COMBUSTION
Year:2018 | Volume:11 | Issue:1 |Papers Count:7

In the present study, a steady state three-dimensional simulation of the pulverized coal combustion inside tuyere of a blast furnace in presence of natural gas in Esfahan Steel Company has been investigated and the effects of the blast air parameters, such as the oxygen percentage and temperature of the blast air at the outlet of the tuyere has been investigated. Auxiliary fuels in the blast furnace are used to increase productivity, reduce production costs and increase efficiency in the steel industry. In the first case, the simulation is carried out without the pulverized coal and only natural gas was considered. In the second case, the gas is removed and the combustion behavior of pulverized coal is simulated. The combustion model used for these cases is non-premixed combustion. In the third case, combustion behavior of natural gas and pulverized coal together is simulated using the eddy dissipation model. The results show that increasing the oxygen content and the blast air temperature increases the maximum temperature and maximum velocity at the outlet. The standard k-e model is used for turbulence and the DO radiation model solves the radiative heat transfer equation.

The aim of this study is to investigate the effects of chemical kinetics and radiation model on the combustion of natural- gas- oxygen mixture using flamelet combustion model. For this purpose, C1_C3, DRM22 and GRI3.0 chemical kinetics mechanisms are combined with DO and P1 radiation models in the simulations. In addition, results with and without modelling radiative heat transfer are compared. The results of flamelet combustion model are also compared with the experimental data and PaSR combustion model. The most important advantage of using flamelet combustion model over the PaSR model is significant reduction in the cost of calculation. According to the obtained results, C1_C3 chemical mechanism predicts the temperature distribution in the furnace with highest accuracy and the predicted flame shape is a good match with that obtained using PaSR model. The flame length obtained using DRM22 and GRI3.0 chemical mechanisms, however, is very small. In addition, using P1 radiation model in comparison with DO leads to more computational errors in calculating the temperature distribution and the length of the high temperature region in the furnace, due to over- predicting the radiation losses.

In this study, the effects of EGR on the combustion behavior, and NOX and soot emissions of a diesel engine fueled by biodiesel is investigated. To do so, a compression ignition engine, diesel fuel, biodiesel fuel blend (B20) obtained from waste cooking oil, three EGR rates (0, 10 and 20%) and 7, 14 and 21Nm engine loads are used. The results show that the addition of biodiesel to diesel fuel increases the cylinder pressure and the maximum increase is 1.97%. In addition, the cylinder pressure increases with increasing EGR rate. Also, the ignition delay of B20 is lower than diesel and the maximum decrease of the ignition delay is 7.3%. The in-cylinder temperature is decreased with increasing EGR rate and ultimately, it can be stated that the maximum heat release rate increases with increasing EGR rate. The NOX emissions decrease with increasing EGR rate for both types of fuels.

Ultrasonic Ram- Jet and Scram- Jet are high technology engines in aerospace industries. Scram- Jet engines can achieve higher velocity than the common Ram-Jet engines, because the combustion in these engines occur in ultrasonic velocity. Combustion in ultrasonic velocity needs stability. Since cavities are very important in the stability of ultrasonic reacting flows, different parameters affecting the wall shear layer in ultrasonic cavity flow is investigated in this paper using numerical simulations with various turbulence modeling approaches. Firstly, the best turbulence model in accuracy and speed is introduced for wall shear layer solution in ultrasonic cavity flow. Then, the solution is used for various cavity wall angles and the results are presented, that show the SST-k-e turbulence model is the best model in accuracy and speed for the problem under investigation. In addition, the results of different angles for back normal wall shows that in a cavity with steep angle, the temperature increases sharply. Therefore, the temperature is a very important parameter in indicating the value of the angle and the limitation of the melting point may affect the angle selection.

In this paper, the effects of directly heating fuel (natural gas) in a gas- fired furnace equipped with a pre-combustor on soot production, luminosity, flame temperature and NOx emissions are investigated numerically and experimentally. Changing F1 and F2 (feeding) fuel rates, in constant total fuel flow rate, are conducted for various F1/F total ratios. A probability density function (PDF) which is parameterized by the mean and variance of mixture fraction was used to model the chemical reactions. To describe the effects of turbulences on soot formation, a Moss- Brooks model and a b-PDF in terms of normalized temperature is employed. The results reveal that for F1/F total<50%, the luminosity of flame increases due to the incomplete combustion of the feeding fuel ensuing soot production. This causes carbon monoxide (CO) emission to significantly increase. On the other hand, for F1/F total=85%, the maximum solid carbon mass fraction and the flame radiation increases by 9% and 15%, respectively. In addition, nitrogen oxides (NOx) emissions reduce to 52 ppm.

Ignition process in a shear- less mixing layer is studied in this paper and the main goal is to investigate the effects of initial temperature on the flame propagation phase of ignition process. The investigation is done using large eddy simulation method, coupled with thickened flame approach and DRM19 chemical mechanism. Mean and RMS axial velocities from both coarse and fine grids and mean mixture fraction are validated against experimental results. Most upstream and downstream positions of the flame edge are in good agreement with the experimental data. By increasing the initial temperature from 323K to 1000K, the mean edge flame propagation velocity increases from 1 to 4.2m/s. The same trend exists for flame kernel volume. Comparing the calculated edge flame propagation velocity and laminar flame speed and its root density correction shows that corrected laminar flame propagation can better predict the edge flame propagation velocity. Also, by increasing the initial temperature, bibrachial edge flame converts to a triple flame.

The turbulent burning velocity of air- fuel mixture depends on the laminar burning velocity and turbulent aspects. The main factors influencing the laminar burning velocity are the fuel type, pressure, temperature and equivalence ratio of the mixture. In the current work, a constant volume spherical bomb and its related equipment are used to capture the experimental pressure-time data during combustion. The data is defined as input to a multi- zone thermodynamic model to calculate the laminar burning velocity. The velocity is evaluated for gasoline-air and natural gas (NG) -air mixtures at stoichiometric equivalence ratio and NG- gasoline- air mixtures with NG mass fraction of 25%, 50%, 75% and 100% at stoichiometric conditions with initial pressure and temperature of 500kPa and 333K, respectively. The obtained results of laminar burning velocity of gasoline- air in comparison with NG-air mixtures shows that the NG-air laminar burning velocity in the range of 5 to 20bar is higher than that of gasoline- air mixture. For dual fuel NG- gasoline it is observed that at the stoichiometric conditions and when the bomb pressure is lower than 20bar, the laminar burning velocities of 25% and 50% NG in dual case are lower than in the case of 100% NG.