FUEL AND COMBUSTION
Year:2019 | Volume:12 | Issue:2 |Papers Count:8

In this paper, the results of the two-dimensional and axisymmetric modeling of the methane-air pre-mixed combustion with multi-step kinetics in a porous medium with continuous porosity change have been presented. In order to determine the thermophysical and thermochemical properties of species, the CHEMKIN II program and Basic information used. Continuity equations, Navier Stokes, gas and solid phase heat transfer equations, and chemical species governing equations are solved by using of finite volume method. The SIMPLE algorithm has been used for the relationship between speed and pressure. The burner under the studied includes two preheated and combustible areas. In this paper, we study the effects of divergence angle changes and length of burner preheating area on temperature profiles and emission of pollutants. The results showed that by increasing the divergence angle, the amount of NO contamination in the burner output increases dramatically, while by increasing the length of the preheating region, the amount of emission of this pollutant in the output decreases.

In this study a 1000 MW NGCC power plant has been integrated with post-combustion CO2 capture and compression process to mitigate its emission. The MEA-based CO2 capture process was designed for 90% CO2 separation. The detailed models of the power plant, CO2 capture and compression process were developed in Aspen HYSYS v9 in order to analyse the performance of the integrated system. Three cases of integration have been investigated. In the first case, the power plant net thermal efficiency was decreased from 62. 5% to 53. 4%. This efficiency drop due to steam extraction from the power plant to provide reboiler duty and power consumption by capture and compression process. The effect of exhaust gas recirculation (EGR) on the plant performance was studied in the second case. EGR implementation and waste heat recovery by organic Rankine cycle in the third case led to an increase of 1. 56% in the power plant efficiency in comparison with the first case. The CO2 emission of the power plant was decreased from 324. 71 g/kWh to 36. 71g/kWh in the third case of integration.

The main objective of the present study is to estimate the turbulent Prandtl number in non-premixed combustion of methane-air. In this regard, a turbulent stream of non-premixed combustion in a stoichiometric condition, is numerically analyzed using the (Reynolds averaged Navier-Stokes) (RANS). For modeling the combustion, the Eddy Dissipation Model (EDM), Eddy Dissipation Concept (EDC) and Probability Density Function (PDF) have been applied. The k-ε Realizable model and Discreet Ordinate (DO) also was used for the turbulence modeling and radiation modeling, respectively. To the turbulent heat flux in the energy equation, second order algebraic model (GGDH and HOGGDH) with simple eddy diffusivity model has been applied. Comparing the results of the numerical model SED (with the turbulent Prandtl 0. 85) and second order models with available experimental data show that applying the SO Models significantly led to the modification of predicting the temperature distribution in the combustion chamber. Moreover the NO derived from SO models distribution model has a good agreement with available experimental data. Calculation of Prandtl number turbulence in the combustion chamber shows that the assumption of Prandtl number of 0. 85 is far from reality and based on GGDH model, Prt in different areas varies from 0. 2 to 1. 3. Finally, the Prandtl number of 0. 45 has been proposed for the non-premixed combustion of methane-air.

Recently, RCCI combustion mode has been proposed, and various researches have been done on this kind of combustion. Such combustion mode has improved the emission shortages of diesel engines besides its advantages. Previous studies mostly investigated the performance and emissions of RCCI engines. In this study, RCCI combustion is studied from the viewpoint of production and consumption of important species. In this RCCI engine gasoline injected at the intake port and diesel injected directly into the cylinder. Investigations showed that first, heat release is started by diesel fuel and an initial heat is released; then gasoline fuel energy is released. The appearance of formaldehyde species shows the cool flame combustion and consumption of diesel fuel; then the appearance of hydroxyl radical and the consumption of gasoline happen simultaneously. Also, some portion of formaldehyde is consumed with the appearance of hydroxyl radical. Heat release started by diesel and followed by gasoline has positive effects. First, by this sequential heat release, the in-cylinder temperature does not increase suddenly, so heat losses decreased. Second, due to the low temperature, NOx emissions reduced. Further-64 CA and-74 CA injection timings and 20 and 28 percent diesel mass fractions have been studied. Results show that the start of combustion is not dependent on these two parameters and its occur at a specific crank angle. So the cool flame combustion only dependent on temperature. But the main combustion is dependent on the temperature and equivalence ratio so the injection timing and diesel mass fraction have shown their effect at this section of combustion.

The properties of the biodiesel will be changed by changing the reaction parameters of biodiesel production from vegetable oils that heating value is one of important of them. The aim of this study is to evaluate a new system in order to detect changes in the properties of biodiesel, such as heating value by dielectric spectroscopy with the capacitive sensor. Transesterified palm-based biofuels were synthesized in different weather conditions using the heat loss of a linear parabolic trough solar collector power. At first, a sample of biodiesel was produced with optimized parameters as the basis of evaluation. Then, five samples of biodiesel with the same optimized parameters but with different temperatures were produced by the solar collector as one of the renewable energy systems. After that, the samples were placed in the device and information obtained by dielectric spectroscopy was transferred to software. In order to validate the analysis, some algorithms from the decision tree technique were used. According to the results, the Classification and Regression Tree (CART) algorithm had the highest accuracy (99%) in comparison with others. According to the accuracy of algorithms, it was deduced that the chosen techniques had good potential to determine biodiesel fuel properties.

In recent years, many studies have been done on reusing waste materials like red mud, because it consists of various oxides like iron oxides, alumina and silica that can be used as support for hydrodesulfurization catalysts. The common hydrodesulfurization catalysts are CoMo/Al2O3 and NiMo/Al2O3. Addition of secondary promoter such as zirconia is proposed as a useful solution for increasing catalyst activity and production of standard fuels. In this paper, NiMo nanocatalyst supported on activated red mud was prepared by impregnation method containing various amounts of Zr promoter and its catalytic performance was evaluated for hydrodesulfurization (HDS) process of iso diesel and light diesel in the atmospheric pressure. The red mud support along with synthesized nanocatalysts were characterized with XRF, XRD, FESEM, BET and FTIR techniques. Analytical techniques related to NiMo/ZrO2-ARM nanocatalysts characterization revealed that zirconia addition resulted in uniform dispersion of particles on the support surface and destroying of agglomerate, an increase in the active phase and a decrease in the formation of Ni spineless. The catalytic activity of nanocatalysts in the hydrodesulfurization process showed that NiMo/ZrO2-ARM with 10 wt. % zirconia had the best catalytic activity for iso diesel and 15 wt. % zirconia for light diesel.

Different versions of Perfectly Stirred Reactor (PSR) have been examined in the simulation of a methane-air jet flame, Sandia flame D. These models have been incorporated with a turbulent mixing based combustion model, Eddy Dissipation Concept (EDC), to address the interaction between turbulent flow field and chemical reactions. Turbulent small scale effects were modeled using Reynolds Average Navier Stokes (RANS) approach. A reduced chemical mechanism (DRM) was used in order to calculate the species reaction rates. Velocity profiles were in good agreement with experimental data. The modified model applied the effect of turbulent mixing by altering the PSR’ s species transport equation. Using the modified model resulted in an inevitable enhancement on the reactive scalar’ s distribution along the central axis. However the distribution of the scalar showed a slight over-prediction at the flame location, which was originated from using the reduced mechanism. The model capability in predicting the turbulent flame interaction was examined using a Computational Fluid Dynamic (CFD) toolbox, OpenFOAM.