Current Issue : April - June Volume : 2016 Issue Number : 2 Articles : 7 Articles
Oxy-coal combustion is one of the more promising technologies currently under development for addressing the issues associated\nwith greenhouse gas emissions from coal-fired power plants. Oxy-coal combustion involves combusting the coal fuel in mixtures\nof pure oxygen and recycled flue gas (RFG) consisting of mainly carbon dioxide (CO2). As a consequence, many researchers and\npower plant designers have turned to CFD simulations for the study and design of new oxy-coal combustion power plants, as\nwell as refitting existing air-coal combustion facilities to oxy-coal combustion operations. While CFD is a powerful tool that can\nprovide a vast amount of information, the simulations themselves can be quite expensive in terms of computational resources and\ntime investment. As a remedy, a reduced order model (ROM) for oxy-coal combustion has been developed to supplement the CFD\nsimulations. With this model, it is possible to quickly estimate the average outlet temperature of combustion flue gases given a\nknown set of mass flow rates of fuel and oxidant entering the power plant boiler as well as determine the required reactor inlet mass\nflow rates for a desired outlet temperature. Several cases have been examined with this model.The results compare quite favorably\nto full CFD simulation results....
The results of combustion study for high-energy compositions (HECs) based on\nammonium perchlorate (AP), butadiene rubber and ultrafine powder (UFP) aluminum Alex,\nand agglomeration of metal particles on the burning surface and composition of condensed\ncombustion products (CCPs) are presented. It was found that partial replacement 2 wt. % of\nAlex by iron UFP in HEC increases the burning rate 1.3ââ?¬â??1.4 times at the range of nitrogen\npressure 2.0ââ?¬â??7.5 MPa and reduces the mean diameter of CCPs particles d43 from 37.4 m to\n33.5 m at pressure 4 MPa. Upon partial replacement 2 wt. % of Alex by boron UFP in HEC\nthe recoil force of gasification products outflow from burning surface is increased by 9 % and\nthe burning rate of HEC does not change in the above pressure range, while the mean diameter\nof CCPs particles is reduced to 32.6 m at p 4 MPa....
The Positive Crankcase Ventilation (PCV) system in a car engine is designed to lower the pressure\nin the crankcase, which otherwise could lead to oil leaks and seal damage. The rotation of crankshaft\nin the crankcase causes the churn up of oil which conducts to occurrence of oil droplets\nwhich in turn may end in the PCV exhaust air intended to be re-injected in the engine admission.\nThe oil catch can (OCC) is a device designed to trap these oil droplets, allowing the air to escape\nfrom the crankcase with the lowest content of oil as possible and thus, reducing the generation\nand emission of extra pollutants during the combustion of the air-fuel mixture. The main purpose\nof this paper is to optimize the design of a typical OCC used in many commercial cars by varying\nthe length of its inner tube and the relative position of the outlet from radial to tangential fitting to\nthe can body. For this purpose, CFD parametric analysis is performed to compute a one-way coupled\nLagrangian-Eulerian two-phase flow simulation of the engine oil droplets driven by the air\nflow stream running through the device. The study was performed using the finite volume method\nwith second-order spatial discretization scheme on governing equations in the Solid Works-EFD\nCFD platform. The turbulence was modelled using the k- model with wall functions. Numerical\nresults have proved that maximum efficiency is obtained for the longest inner tube and the tangential\nposition of the outlet; however, it is recommended further investigation to assess the potential\nerosion on the bottom of the can under such a design configuration....
Partially Premixed Combustion (PPC) is a combustion concept that aims to\nprovide combustion with low smoke and NOx emissions and a high thermal efficiency.\nExtending the ignition delay to enhance premixing, avoiding spray-driven combustion, and\ncontrolling temperature at an optimum level through use of suitable dilution levels has been\nrecognized as a key factor to achieve such a concept. Fuels with high auto-ignition resistance\ndo extend ignition delay. In this work three ternary blends of an alcohol (ethanol or\nn-butanol), n-heptane and iso-octane with a target research octane number (RON) of 70 are\nstudied. RON70 was earlier found to be close to optimal for PPC over a large load range.\nThe objective of this research is to analyze the sensitivity of the combustion parameters\nto changes in air-excess ratio when using these three blends. The engine was operated at\n1250 rpm and 1000 bar injection pressure with a single injection strategy. Results revealed\nthat efficiency was increased from rich to lean combustion, and these three blends show\ndistinct premixed combustion even in lean PPC operation. The premixed fraction of combustion\nhowever reduces with the increase of air-excess ratio, which is especially apparent\nfor PRF70 which consists of n-heptane and iso-octane alone....
A two-dimensional elliptic computational fluid dynamics model of micro-combustors is solved to study the effects of wall\nthermal conductivity on homogeneous combustion characteristics of premixed methane-air mixtures. Numerical simulations\nwere carried out using detailed chemical reaction schemes, detailed species transport, and heat transfer mechanisms in the solid\nwall. We have found that the wall thermal conductivity is very important as they determine the upstream heat transfer, which is\nnecessary for flame ignition, and the material's integrity by controlling the existence of hot spots. Large transverse and axial\ngradients are observed even at these small scales under certain conditions. Regarding material lifetimes, higher wall thermal\nconductivities reduce the wall temperature gradients and hotspots and should be preferred....
The reported discrepancy between theory and experiment for external combustion Stirling engines\nis explained by the addition of thermal resistance of the combustion gasses to the standard\nCarnot model. In these cases, the Stirling engine ideal efficiency is not as is normally reported\nequal to the Carnot cycle efficiency but is significantly lower. A new equation for ideal Stirling engine\nefficiency when the heat is obtained through external combustion without pre-heating the air,\nis presented and results for various fuels tabulated. The results show that petrol and diesel, internal\ncombustion engines (Otto cycle) have a higher ideal efficiency than the Stirling engine.\nWhen comparing thermoacoustic engines heated by wood, efficiency should not be quoted as a\npercentage of the Carnot efficiency, but against a figure 48% lower than Carnot. The effect is not\nseen with electrically heated rigs, solar or nuclear fission heated engines....
Most of the thermodynamic modeling of gasification for updraft gasifier uses one process of decomposition (decomposition of\nfuel). In the present study, a thermodynamic model which uses two processes of decomposition (decomposition of fuel and char)\nis used.The model is implemented in modification of updraft gasifier with external recirculation of pyrolysis gas to the combustion\nzone and the gas flowing out from the side stream (reduction zone) in the updraft gasifier. The goal of the model obtains the\ninfluences of amount of recirculation pyrolysis gas fraction to combustion zone on combustible gas and tar.The significant results\nof modification updraft are that the increases amount of recirculation of pyrolysis gas will increase the composition of H2 and\nreduce the composition of tar; then the composition of CO and CH4 is dependent on equivalence ratio. The results of the model\nfor combustible gas composition are compared with previous study....
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