Sharif Digital Repository

The idea of improving performance of internal combustion engines has always been important for researchers and manufacturers. In recent decades, due to limited resources of fossil fuels and introduction of vehicle emission regulations, researchers have undertaken more efforts to achieve goals such as increased horsepower, reduced fuel consumption and pollutant emissions reductions. Homogeneous charge compression ignition engine is a modern and efficient design that has attracted attention of many researchers. In[[ these engines, homogenous mixture of fuel and air enters into the combustion chamber and with a mechanism of self ignition, produces more power and has less fuel consumption... 

HCCI engines have lower NOX and PM emissions and higher thermal efficiency compared to spark ignition engines. But these engines have some deficiencies which up to now have prevented their widespread employment. These engines have not been very successful at high loads and speeds and in these conditions normally produce high pollution and noise. In order to solve this problem the present research proposes to equip the HCCI engines with fuel injection system so that at low loads and speeds operate at HCCI engine mode and at loads and speeds higher than pre-set limits, use the fuel injection system in order to operate at a combined HCCI and compression ignition engine mode and provide a... 

Combustion and NOx emissions were simulated by quasi-dimensional and ratereaction methods respectively in a turbocharged CNG engine. Mean-value turbulence modeling was carried out during compression and combustion processes to simulate combustion process better. The most appropriate NG flame speed for the CNG turbocharged engine was applied and ignition delay was ended when flame radius became more than turbulence integral length scale. Hemispherical flame propagated from spark gap center and its intersection with reciprocating Mexican-hat piston bowl was calculated analytically. Thermal boundary layer, as a novel approach, was considered in the simulation and a better agreement of predicted... 

Because of advantages of using new sources of energy in the country, especially for generating green energy, the use of wind energy for power generating in wind Fields is of great interest of current communities. For developing a wind power plant the first step is to locate and confirm the areas which possess enough potential for installing the wind turbines. For this purpose in the first chapter of this thesis an introduction to the basic principles of wind energy is noted then in the next chapter the physical relations to calculate the estimated reachable energy in the area is mentioned and in the third chapter the empirical methods for selection of the suitable sites are exhibited .in the... 

In the modern world, one of the largest concerns is the ever depleting supply of oil. The automotive industry is especially impacted. In recent years the price of gasoline has fluctuated substantially and the price of crude oil has reached record highs. The high price of gasoline coupled with the uncertainty of its availability and future price have put a high priority on fuel economy of an engine. In addition the emissions released from internal combustion (IC) engines are polluting the atmosphere. Many studies have linked the greenhouse gases produced by an automobile engine to the partial destruction of our atmosphere and to global warming. As a result the US government is passing... 

To estimate vehicle fuel consumption and emissions in Tehran mega city, air pollution in urban tunnels, parkings, determination of speed limits on highways and produce required inputs of softwares that forecast dispersion and distribution of air pollution, Hot exhaust emissions model of Iranian manufactured gasoline fueled personal cars of Tehran developed. Emission factors is the most important element of model, that obtained from portable emission measurement of 30 vehicles with suitable type and mileage distribution. By averaging the results, total emission factors and fuel consumption of fleet designated, used to annual estimation. in addition with curve fit to data, emission functions... 

Because of advantages of using new sources of energy in the country, especially for generating green energy, the use of wind energy for power generating in wind Fields is of great interest of current communities. For developing a wind power plant the first step is to locate and confirm the areas which possess enough potential for installing the wind turbines. For this purpose in the first and second chapters of this thesis an introduction to the basic principles of wind energy is noted then in the third chaptermethods of grid connection, conversion systems and turnover problems in windfarm is evaluated.in the fourth chapter with the use of Windographer software and empirical data of standard... 

The number of operating vehicles has increased in recent years and as a result global pollutants have widely spread. Therefore, the regulations on the vehicle exhaust emissions have become much stricter. For an automobile to pass the emission tests successfully an accurate calibration of the ECU tables is needed, especially the tables which have direct impact on the amount of pollutant emissions. To achieve the optimum performance of the catalyst existing in the exhaust system of the engine, the fuel/air ratio must have nearly stoichiometric value. The present research studies the ECU strategies for implementing this objective by appropriate management and control of catalyst and oxygen... 

A 3-D CFD model was developed to study effects of early/late intake valves opening/closing on flow field characteristics in the Intake Manifold (IM) of a spark-ignited gasoline 1.5 Litre, 4-cylinder engine. The main task of IM is to prepare essential air for combustion process into cylinder which should distribute air to total runners of IM properly. In this modeling, combustion process and valve behaviors and how to pass fluid flows through intake valves are simulated separately and they are added to it.HyperMesh, Fluent, GT-Power, and MATLAB were used to create a mathematical model on the geometries of IM in TIBA engine, one National Engine of Iran, obtained from MEGA motor Company. The... 

Dissemination of an analyte under the laminar flows plays a major role in measuring and assessment of biological fluids such as sample preparation in the context of microfluidic systems. Due to the development of manufacturing technology in the Lab-on-a-chip devices, the production of rectangular microchannels with finite aspect ratios and micron and submicron sizes has been provided by which the effect of electrokinetic phenomena on concentration distribution will be magnified in these systems. On the other hand, these biofluids are viscoelastic and show extraordinary flow behaviors, not existing in Newtonian fluids and adopting appropriate constitutive equations these exotic flow behaviors... 

Unglazed Transpired Solar Collectors, recently called "Solar Wall", are known as the most efficient solar air heating system for the past two decades. The equator faced collector which is installed in this system has many tiny perforations to suck in the air with a fan and gain the absorbed heat by the collector. Convection and Radiation heat losses from the absorber to surrounding and other design factors have different influents to the heat gain of this system. In this study, Continuity, Momentum and Energy equations are written with proper boundary conditions, solved with computational fluid dynamics methods and validated in order to model Solar Wall system. Thus we could compare all... 

Lamniar flow through porous media has been investigated using finite volume staggered grid. In order to study turbulent flow modelling turbulent flow using RANS models with the aid of Fluent software has been done. And the microscopic and macroscopic results are compared with LES results. None of the RANS models used (k-e, RNG, k-wv2f, v2f and RSM) were able to model the flow through porous media properly, although k-e and RSM gave the best microscopic and macroscopic results  

In recent years, mesoporous nanocrystalline TiO2 films have been regarded extensively. This kind of materials due to having unique surface area, structural and bulk properties, is used in many technological applications. In this work, a stable TiO2 sol was prepared using F127 Copolymer template and evaporation induced self-assembly method (EISA). The mesoporous TiO2 powders and thin films were then prepared. The as-deposited thin films were aged under five different conditions for 72h. Finally the samples were heat treated at 350°C, 400°C and 450°C. N2 adsorption/desorption results verified formation of mesoporous structure. Moreover, x-Ray diffraction patterns exhibited that the synthesized... 

In recent years, there have been huge advancements in fabrication of micron-sized devices such that they enabled engineers to create a wide range of miniaturized systems, each of which is utilized in mechanical, electrical, and thermal applications. Micromixers are one of these devices with the role of mixing various micro flows. These devices are broadly used for chemical, biological, and biomedical assays. Among variety of micromixers, one that employs electrokinetic transport phenomenon is of great popularity. For instance, mixing under electroosmotic flow enables accurate process control and eliminates the need for moving components inside micromixer. The very complex nature of electric... 

This is a theoretical study on heat and mass transfer in electrokinetically driven microfluidic devices with particular consideration to the lab-on-a-chip (LOC) applications. Special attention is given to disclose the effects of the fluid rheology and the aspect ratio of the rectangular geometry on the surface reaction kinetics and the temperature rise due to the Joule heating. Along this line, two different viscoelastic constitutive equations namely PTT and FENE-P models along with the power-law viscosity model are being considered. The secondary aims also include exploring the influences of the fluid properties variations throughout the channel cross section on the hydrodynamic and thermal... 

Heat transfer to combustion chamber walls is an unwanted phenomenon. Reduction of this heat transfer by using bidirectional swirl flow, as proved in past studies, can result in time and cost saving methods in design and fabrication of combustion chambers. Bidirectional Swirl flow, existing in vortex engine, maintains the chamber wall cool. This characteristic of such flow field, among with many other advantages for it, makes researchers more interested in studying the propulsion of it as well as its other applications. Bidirectional swirl flow in liquid fuel ramjet engines has the proven advantage of keeping the combustion chamber walls cool and in solid fuel ramjet engines in increasing the... 

The use of flash-based Solid State Disks (SSDs) has been increased in the past decades because of their high performance and low power consumption. As SSDs have no moving mechanical parts, they are more reliable than HDDs. SSDs have specific errors, such as read, program, and erase disturbs, data retention, and endurance. It is so common in storage systems to apply an array of disks called Redundant Array of Independent Disks (RAID) together for the aim of reliability and performance. Erasure codes are one of the main methods applied in storage systems for the aim of reliability. Erasure codes increase the reliability of storage systems by protecting them against disk failures and sector... 

Jetsurf is a recreation vessel at sea. It is a surfboard that is equipped with a motor propulsion system and provides surfing, which is an exciting and popular sport, in calm seas, lakes, dams, rivers and natural and artificial canals. This project is divided into four steps. In the first step, the appropriate dimensions for the design of this device are specified. In the second step, to calculate the resistance of jetsurf, at first a model with similar dimensions including experimental results in Star CCM+ software was validated by computational fluid dynamics method and Overset dynamic mesh technique and then jetsurf resistance with dimensions of 1.8x0.6x0.225 meters was calculated. In the...