Sharif Digital Repository

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... 

Many studies on hybrid vehicles have been done in the past few years. The Full hybrid vehicles need a large number of batteries creating up to 300V to meet the required voltage of electric motor. The size and weight of the batteries cause some problems. This research investigates the mild hybrid vehicle. This vehicle includes a small electric motor and a high power internal combustion engine. In most cases the car’s driving force is created by internal combustion part. A small electric motor, which can operate as engine starter, generator and traction motor, is located between the engine and automatically shifted multi-gear transmission (gearbox). The clutch is used to disconnect the gearbox... 

Some researches have been carried out in the last 20 years in order to increase the present IC engines thermal efficiency and their optimum performance. (HCCI) engine is viewed as a combination of spark-ignition (SI) and compression-ignition (CI) engines. This is because HCCI engines use premixed fuel/air mixture like SI engines and have auto ignition combustion after the mixture is compressed like CI engines. Control of combustion and ignition timing are the main challenges of these engines. Ignition delay, compression ratio, fuel air equivalence ratio and intake temperature and pressure are considered to be the most effective parameters on HCCI combustion.HCCI engines have great potentials... 

The partially stratified charge (PSC) approach involves micro-direct-injection of pure fuel or a fuel air mixture, to create a rich zone in the region around the spark plug. A theoretical model is presented in this research to predict ignition delay and combustion process in partially stratified charge engine. It considers flame progress through rich and lean regions. Step by step calculations will be carried out in both regions. The process continues to the point where all the fuel is burned. At each step for one degree rotation of the crank shaft, there is a change in cylinder volume and mole fraction burned due to burning of a fraction of the mixture. Considering heat transfer from the... 

Hydrogen is one of the favorite substitute for fossil fuels due to various properties including the flammability, ubiquity, and easy extraction from plain water. These properties have made it an appropriate alternative source of energy that can be used in internal combustion engines. Compared with fossil fuel energy, in addition to much lower emissions, hydrogen has proved to be much more efficient when applied as a clean source of energy. The main purpose of the present project is to study the effect of applying hydrogen on performance of compression - ignition as internal combustion engines as an alternative fuel. These studies encompass the results derived from the experiment of using... 

Thermodynamic analysis of a system is a method for recognizing the type of energy transmission between system and surrounding environment. It also helps to find how macroscopic properties of the system change during this process. This analysis is based on first and second laws of thermodynamic. The first law expresses conservation of energy and inspects quantity of energy transmission but doesn’t evaluate quality of energy. The second law expresses quality of energy and the ability of doing work. The analysis that uses both of the laws is named exergy analysis. By exergy analysis the place of useful energy losses in the system can be determined. In this research the exergy analysis of... 

The purpose of this research is the design and fabrication of a mobile social robot for children with cancer. This robot is named Arash. Interaction with the robot can improve children's education, as well as their mental condition. Design and development of Arash robot project have been carried out in a number of M.Sc. projects. In the present study, it is specifically focused on three areas of activity:
1. Design and fabrication of the robot head (and the overall appearance of the robot)
2. Design and development of human-robot interactions
3. Social and educational interactions/interventions of the robot with children
In this study, with the cooperation of child... 

The Rotary Combustion Engines are known as Wankel Engines, for the first time designed and built by German inventor, Felix Wankel. In open letrecher, research reports about these engines are much less than piston engines. While, the wankel engine hase many advantages such as lower volume, less weight, less vibration and use of fuels lower octane number in compared with reciprocating engines. Therefore, it has particular importance in industries such as aircraft manufactueres.In this theses after the introduction chapter, Wankel engines and Turbochargers usage are reviewed. Then the Wankel engine and its turbocharging are searched in letrecher. Then, a computer code for simulation the Wankel... 

Nowadays internal combustion engines play an important role in the power generation as well as transportation fields all over the world. By using the turbocharger in internal combustion engine, more power is obtained in compare with aspirated engine having the same size, which is limited for gasoline engines. In this research, by a three-zone computer simulation code and experimental tests, the power boost limitations of the gasoline turbocharged engine are investigated. The results of single cylinder aspirated gasoline engine tests are used for validation the natural aspirated part of the code. For validating the turbocharged engine simulation, the results of a four cylinders gasoline... 

In this study an internal combustion rotary (Wankel) engine and its specifications is analyzed and the proper lubrication system is described. The acceleration acting on apex seals, and engine speed fluctuations together with the leading and trailing cells gas pressure forces are analyzed in the present work using the second Newton law. The research shows that cell gas pressure effects are important and inclusion of these effects will provide results which are more compatible with the reality and lead to a much more accurate analysis of the system. Theoretical calculations reveal that gas cell pressure forces represent about 78% of the overall calculated force and ignoring these pressure... 

Online voltage stability assessment is essential for preventing the failure in power systems. Voltage instability in power systems usually occurs in consequence of contingency situations or continuous load increasing or both of them. A new method for online voltage stability assessment using the data acquired from phasor measurement units (PMUs) and offline trained decision trees is presented in this thesis. The index of voltage stability margin (VSM) is used for security assessment and considering WSCC criterion, different operation points are divided in two classes: safe and unsafe. In order to obtain the voltage stability margin and generate the database, a new method which has been named... 

Research for renewable energy has grown considerably over the last years. Osmotic energy is a form of renewable energy which is not yet used at commercial scale, but have a large potential to used at commercial scale soon. Osmotic power is a technique that converts the difference of molar free energy between fresh water and salt water into electricity. Pressure retarded osmosis (PRO) is the most frequently studied process of osmotic energy. In PRO two solutions of different salinities are brought into contact by a semipermeable membrane that only allows the transport of water and retain the solute. Positive developments in recent years initiated new studies to the exploitation of osmotic... 

The purpose of this dissertation is to experimentally and numerically investigate the effect of molecular structure, composition, and physical and chemical properties of fuel on HCCI combustion. A well-equipped laboratory was set up to perform the required tests, capable of performing HCCI tests with different fuels. All tests used a single-cylinder diesel engine modified to operate in HCCI mode. Also, for numerical simulation, a chemical kinetic multi-zone model was developed to predict HCCI combustion behavior with appropriate accuracy. To investigate the effect of fuel chemical structure on HCCI combustion, three fuels, toluene, iso-octane and normal heptane, with entirely different... 

In atmospheric studies, chemical transport models are formulated to simulate the spatial and temporal distribution of pollutant concentrations. However, the performance of these models is strongly dependent on the input parameters such as emissions. Inverse modeling is a widely used mathematical approach for estimating model parameters by minimizing the discrepancy between model output and observations. For air quality studies, inverse modeling is often used for emission inversion as emissions are associated with significant amount of uncertainties.This research aims to estimate optimal values for anthropogenic PM2.5 emission through a four-dimensional variational (4D-Var) inverse modeling... 

Recent stringent HC and CO emission regulations are because of increasing consciousness of the perilous influences of exhaust emissions. The chief attempt to pass the standards is to decrease the emissions during cold-start, due to catalytic converters are not efficient until they arrive a light-off temperature. It has been discovered that 50% to 80% of the controlled HC and CO emissions are sent out from tailpipe of automotive during the cold-start. Therefore, in order to minimize the cold-start emissions and fast light-off of catalytic converters, it is important to understand the catalytic converter characteristics and techniques for rapid warm-up catalyst. This thesis describes a... 

Many of industrial processes include suspension in their middle section of production, final product or residue. Majority of these two-phase mixtures are unstable due to their large particle size (larger than one micrometer). Therefore, Study of particle distribution in suspensions for generation of stabilized suspension becomes significant. In this study a new mechanism in stabilization of microparticle suspension known as nanoparticle halo mechanism has been assessed. Experiments have been conducted in dilute suspension and two-way coupling range. The effect of the presence of silica nanoparticle on zirconia microparticle suspension has been investigated. The effect of zeta potential of... 

Investigation of flow field and vortex structures in swirl flows and their velocity components, have received widespread interest among the researchers in the field of fluid mechanics. Due to the importance of vortex structures and their applications in combustion chambers, a special type of combustion chamber which is called “bidirectional swirl combustor” has been investigated in this work. Accurate identification of vortex phenomenon and flow structure in vortex engine leads to better design and control of the engine in the field of stability, geometry, cooling and combustion efficiency. Eperimnetal methods in this area are difficult but very valuable and efficient. Numerical methods are... 

In this project, one-dimensional and two-dimensional numerical approaches are used to study the effect of applying electrohydrodynamics on the temperature and species mass fraction profiles along the micro-combustor. A premixed mixture of H2-Air with a multi-step chemistry (9 species and 19 reactions) is used and thermal conductivity of the mixture is considered as a function of species thermal conductivity and temperature by using a set of new relations. Both thermal and radical quenching mechanisms are important in the micro-scale combustion due to increasing of area-to-volume ratio and significant heat loss from the combustor walls. By inserting a number of electrodes into the... 

Due to increasing of internal combustion engine applications in metropolitan, reduction of emission is one of the challenging issues for engine companies. Natural gas is a promising fuel for the strict legislation of emission in many countries. Vast variety of natural gas sources in Iran and also lower carbon to hydrogen content of natural gas motivates us to use this fuel for engine application. Using natural gas also helps to increase the variety of fuel basket in Iran. Present research has focused on mixture formation and injection characteristics of natural gas direct injection engine. Injection and mixture formation in direct injection engines is very important for good combustion and... 

Electroosmosis is the predominant mechanism for flow generation in lab-on-a-chip devices. These microfluidic devices are microscale laboratories on a microchip that can perform clinical diagnoses. Since most biofluids encountered in these devices are considered to be non-Newtonian and the cross section of microchannels in these devices is close to a rectangular shape, In this study, the hydrodynamically and thermally fully developed combined electroosmotically and pressure driven flow of power-law fluids in rectangular microchannels is analyzed. The governing equations are first made dimensionless and then transformed into new ones based on the computational parameters which provide mesh...