Sharif Digital Repository

In this thesis, engine performance parameters such as power, torque, fuel consumption and in-cylinder pressure are investigated with considering ignition timing in order to achieve the minimum value of knock index. The implemented methods include engine dynamometer tests and simulating vehicle powertrain in GT- POWER software. Based on the acceptable precision of the GT-POWER model, it can be used to predict the engine performance in other ignition timings. Final results prove that for wide open throttle status altering the ignition timing to reach the minimum possible value impact differently on the engine performance so that in low engine speeds for basic and new ignition timings, a... 

The application of internal combustion engine is vast in different context, such as transportation and power generation. Therefore to investigation of these objects and the importance of flame front development, a combustion chamber with constant volume is designed and manufactured. The chamber designing is based on the experimental knowledge and numerical simulation of chamber and glasses. The combustion chamber made of stainless steel and contained transparent quartz glasses in both side of it to provide the ability of using schlieren photography method and investigation of flame. The great advantage of present chamber is the capability of different type of combustion, including fuel and... 

In the present study, a 3D combustion chamber was simulated using FLUENT6.32. The objectives were to obtain detailed information on the combustion characteristics and NO formation in the furnace, and also to examine the effect of Oxygen enrichment on the combustion process. The combustion chamber has internal dimensions of 60 cm wide, 90 cm high and 190 cm long. The fuel pipe diameter is 1.25 cm and the air pipe diameter is 3.5 cm. The 3-D Reynolds Averaged Navier Stokes (RANS) equations together with standard k-ε turbulence model are solved by Fluent 6.3. Air/fuel flow rate ratio is varied as 1.3, 3.2 and 5.1 and the oxygen enriched flow rates are 28, 54, 68 lit/min. NO emission was... 

In this work, wind farm layout optimization problem is dealt with a new approach. The aim of this work is maximizing the output power of a wind farm by considering wake loses. Layout optimization minimizes the wake loses regarding the wind direction. Three different wind scenarios including different wind direction angles, wind direction blowing probabilities and Weibull distribution parameters for wind speed are assumed. Since, the problem is nonlinear and constrained, imperialist competitive algorithm is used as a modern and powerful algorithm for continuous optimization problems. The optimization outcomes indicate that imperialist competitive algorithm yields promising results.... 

Sustainable development is a general concept in all aspects of human life, including social, economic, environmental, etc. Since one of the pillars of achieving sustainable development is the optimization of energy consumption, and on the other hand, energy consumption in buildings accounts for one third of the country's annual energy consumption, so it is very important to provide solutions that can reduce energy consumption in this sector. Therefore, in this research, with the aim of optimizing energy consumption in buildings, examples in different climates of Iran are selected and effective strategies to reduce energy consumption are identified according to each climate and used to... 

For optimum designing of dry friction clutch, we should taking into account a lot of parameters, in order to the clutch have good efficiency in torque transmission and power train. These parameters include: the type of friction plate and the mechanical properties, Clutch geometry, diaphragm spring and its ability to make pressure. In this project, the goal is the analysis of effect of different parameters in clutch's temperature distribution and effect of these issues in torque transmission. In next step, the clutch's temperature distribution analyzed by changing the friction plate (ceramic), pressure applied and relative round in order to gain optimum properties of clutch. These works done... 

The purpose of present work is to study the effect of different parameters on the solar chimney used in ventilation. Experimental model and numerical model were used to achieve this goal. First, the model was numerically analyzed by Fluent software using Boussinesq approximation. The results of numerical modeling were validated by the empirical model. Finally, the numerical model can be used to investigate the effects of parameters which modeling is not possible by the empirical model for any reason. Experimental modeling was performed on a chimney with height and width of 180 and 62 cm, respectively. The thickness and angle of chimney in both experimental and numerical methods varied from 5... 

Design hybrid systems to supply electrical energy for off grid domestic consumer in the remote villages in Iran are the main objective of this work. The hybrid systems considered in this study consist of photovoltaic array, wind turbine, battery and diesel generator. Measured wind speed data used for wind turbine energy production model. The hybrid system optimized to supply 6, 14, 20, 40 and 60 families in Bojnoord, Moorchehkhoort, Kish, Langrood, Khash and Meshkinshahr. The main purpose of optimization is to find the economic system, able to fulfill the energy requirements of a given load distribution; so Iran’s current economy and cost, considered. The optimized results for studied cities... 

The purpose of this study is to determine a function which estimate fuel/air equivalence ratio distribution inside combustion chamber of spark ignition engine for pollution minimization and maximum efficiency. To do this, we developed a code by which, we are able to model one SI engine cycle.
Seven distributions for fuel/air equivalence ratio were examined which include: Homogeneous, linearly decreasing, linearly increasing, sinusoidal increasing and decreasing, sinusoidal decreasing and increasing, cosinusodal decreasing, and cosinusodal increasing. The average fuel/air equivalence ratio for all of these distributions was 0.85.
The results for indicated power showed that,... 

Three-dimensional cell culture and forming multicellular aggregates is superior over traditional monolayer approaches due to better mimicking in vivo conditions and hence functions of a tissue. A considerable amount of attention has been devoted to devising efficient methods for the rapid formation of uniform sized multicellular aggregates. Restoring cartilage to healthy state is difficult due to low cell density and hence low regenerative capacity. Currently used platforms are not compatible with clinical translation and require dedicated handling of trained personnel. However, when engineering and implanting cell microaggregates in a higher concentration, new cartilage is efficiently... 

Droplet-based microfluidic logic gates have many applications in diagnostic tests and biosciences due to their automation and cascading ability. Although most biological fluids, such as blood, exhibit non-Newtonian properties, all previous studies in this field have been with Newtonian fluids. Additionally, none of the previous work has studied the functional area of logic gates. In the present work, AND-OR logic gate with power-law fluid is considered. The effect of important parameters such as non-Newtonian fluid properties, droplet length, capillary number, and geometrical properties of the microfluidic system on the operating region of the system has been investigated. The results show... 

Significant advances in biotechnology have led to the emergence of a cost-effective way with less ethical issues to study disease, organ functions, tumors, and their response to drugs besides studying on animals. Microfluidic devices and organ on a chip (tumor on a chip) were introduced to remove those obstacles. Organ on a chip is a powerful tool for studying different types of tissues and simulating diseases, especially cancers, for biological and medical applications. Organ (tumor) on a chip is considered as a smaller scale of the real organ or tumor and it causes to the real-time study of tissues and their functions more accurately. In this study, to fabricate a droplet-based... 

One of the critical challenges in droplet based micro- and nanofluidic devices is handling the droplet breakup such that a controllable droplet size is produced. The experimental and numerical investigations at the microscale indicate that the droplet size can be well controlled by T junction geometries. In the present study we use non-equilibrium molecular dynamics (NEMD) simulations to investigate this phenomenon at the nanoscale. In order to generalize the study the Lennard-Jones type potential between the fluids and the walls have been considered and the strength and the effective range of the potential are changed to consider a wide variety of materials. Our results reveal that the... 

Rapid growing use of energy resources in recent decades, caused to focus on combined heat and power generation systems according to their high efficiencies. Energy efficiencies with these technologies will be up to 90 percent. Some benefits of Co-generation systems are their high efficiencies, omitting of transmission and distribution lossesin the electricity grid, fuel consumption reduction, moving to ward privatization,independent and decentralized production of electricity and heat, increase competition in the power generation and reduction theemission of greenhouse gases, particularly carbon dioxide. In This article theeconomicsof combined heat and power generator stobe installed... 

The actuation mechanism of the tip of the laparoscopic instrument is the main problem in designing the process of miniature scale motorized instruments especially when high level of functionality and multi degrees of freedom (DOF) are concerned. Previous studies suggest local actuation as the best design for this kind of end effectors. In the present study, different actuation methods of needle holders were reviewed, related capabilities and drawbacks were evaluated and a hybrid local actuated design was appointed. The hybrid design included a micro DC motor and a PZT actuator. The main idea behind it was to combine the advantages of DC motors and piezoelectric (PZT) actuators in providing... 

The design of inlet ports for spark ignition internal combustion engines has a direct and well-known influence on performance and emissions as a result of changes in volumetric efficiency and fuel burn rate.The design of ports is becoming more critical as SI engines are developed further to meet increasingly stringent exhaust emissions legislations. Lately further emphasis has been placed on port design by the re-emergence of the direct injection gasoline engine.
Due to lean burning, combustion instability and increasing the cycle to cycle variations, in the direct injection engine, combustion charactersitics will be improved by increasing the tumble in-cylinder flow and the turbulence... 

Electric Arc Furnaces" are of the most important industries in energy field. High energy consumption leads us to improve model for optimizing energy demand in electric arc furnaces. Melting and refining are two processes which need high amounts of energy. There are several different energy resources in electric arc furnaces. Materials can receive energy from electric arc or from chemical reactions that takes place between molten steel and slag. In addition, some slag formers should be added to the furnace. There are complicated relations between mass transfers, heat transfer and energy balance in EAF. In order to solve energy conservation problem in EAF, we should first extract equations to... 

In this paper, we introduced two methods for producing unequal sized droplet from an initial one that don’t have the disadvantages of the available methods. We developed a comprehensive analytical theory for the T-junction with valve method. Also the geometry was simulated using a VOF algorithm and a comparison was performed between numerical and analytical results and very good agreement was observed. The accuracy of numerical results was confirmed by doing the grid independency and time step independency and comparing the results with two analytical benchmarks. We derived accurate analytical relations for calculating the droplet volume ratio, droplet length (L1, L2 and Lwhole) and pressure... 

In this project, transport and absorption of magnetic particles for the purpose of water purification has been simulated. The used magnetic particles must be collected; otherwise they would cause additional pollution. Therefore, separation and absorption of particles is vital. The particles can be collected with an applied magnetic field. In this study different kinds of magnetic fields are applied and effect of different parameters, such as particle diameter, Reynolds number and magnetic field are considered. By increasing particle diameter and magnetic filed strength, the absorption efficiency increases. But by increasing Reynolds number absorption efficiency decreases. The particle with... 

Ultrasonic flowmeters are one of the common and profitable measurement tools and applied in many industrial fields.Ultrasonic flowmeters work based on transit-time technique. The transit-time utilizes the propagation time of the ultrasonic signal in the fluid. Since ultrasonic signals can also penetrate solid materials, a pair of transducers is installed on the surface of tube. Each transducer works alternatively as both transmitter and receiver of ultrasonic signals.In this study, effect of temperature gradient on flowmeter measurements by applying constant temperature and uniform heat flux on the boundary is investigated numerically for methane gas in laminar flow regime and the results...