Super Charging

Super Charging

The power output of an engine depends up on the amount of air indicated per unit time, the degree of utilization of this air and the thermal efficiency of the engine. The amount of air inducted per unit time can be increased by increasing the engine speed pr by increasing the engine speed or by increasing the density of air intake. The method increasing the inlet air density, called supercharging, is usually employed to increase the power output of the engine. This is done by supplying air to a pressure higher than the pressure at which the engine naturally aspirates air from the atmosphere by using a pressure boosting device called a super charger.

OBJECTS OF SUPERCHARGING

The increase in the amount of air inducted per unit time by supercharging is obtained mainly to burn a greater amount of fuel in a given engine and thus increase its power output. The objects of supercharging include one or more of the following.

1. To increase the power output for a given weight and bulk of the engine. This is important for aircraft, marine and automotive engines where weight and space are important.

2. To compensate for the loss of power due to altitude. This mainly relates to aircraft engines which lose power at an approximate rate of one percent 100 meters altitude. This is also relevant for others engines which are used at high altitudes.

A supercharger is an air compressor used for forced induction of an internal combustion engine. The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally-aspirated engine, which allows more fuel to be provided and more work to be done per cycle, increasing the power output of the engine.

A supercharger can be powered mechanically by a belt, gear, shaft, or chain connected to the engine's crankshaft. It can also be powered by an exhaust gas turbine. A turbine-driven supercharger is known as a turbosupercharger or turbocharger. The term supercharging technically refers to any pump that forces air into an engine—but in common usage, it refers to pumps that are driven directly by the engine as opposed to turbochargers that are driven by the pressure of the exhaust gases.

Thermal Barrier Coatings

Thermal Barrier Coatings

Definition

Thermal barrier coatings (TBC) are layer systems deposited on thermally highly loaded metallic components, as for instance in gas turbines. The accompanying figure shows a stator blade of a stationary gas turbine, furnished with a plasma sprayed thermal barrier coating of YSZ (Siemens Power Generation). The cooling of the components causes a pronounced reduction of the metal temperature, which leads to a prolongation of the mechanical component's lifetime. Alternatively, the use of thermal barrier coatings allows to raise the process temperature, obtaining thus an increased efficiency.

Heat engines are based on considering various factors such as durability, performance and efficiency with the objective of minimizing the life cycle cost. For example, the turbine inlet temperature of a gas turbine having advanced air cooling and improved component materials is about 1500oC. Metallic coatings were introduced to sustain these high temperatures. The trend for the most efficient gas turbines is to exploit more recent advances in material and cooling technology by going to engine operating cycles which employ a large fraction of the maximum turbine inlet temperature capability for the entire operating cycle. Thermal Barrier Coatings (TBC) performs the important function of insulating components such as gas turbine and aero engine parts operating at elevated temperatures. Thermal barrier coatings (TBC) are layer systems deposited on thermally highly loaded metallic components, as for instance in gas turbines. TBC's are characterized by their low thermal conductivity, the coating bearing a large temperature gradient when exposed to heat flow. The most commonly used TBC material is Yttrium Stabilized Zirconia (YSZ), which exhibits resistance to thermal shock and thermal fatigue up to 1150oC. YSZ is generally deposited by plasma spraying and electron beam physical vapour deposition (EBPVD) processes. It can also be deposited by HVOF spraying for applications such as blade tip wear prevention, where the wear resistant properties of this material can also be used. The use of the TBC raises the process temperature and thus increases the efficiency.

Structure Of Thermal Barrier Coatings

Thermal Barrier Coating consists of two layers (duplex structure). The first layer, a metallic one, is called bond coat, whose function is to protect the basic material against oxidation and corrosion. The second layer is an oxide ceramic layer, which is glued or attached by a metallic bond coat to the super alloy. The oxide that is commonly used is Zirconia oxide (ZrO2) and Yttrium oxide (Y2O3). The metallic bond coat is an oxidation/hot corrosion resistant layer. The bond coat is empherically represented as MCrAlY alloy where

M - Metals like Ni, Co or Fe.
Y - Reactive metals like Yttrium.
CrAl - base metal.

Coatings are well established as an important underpinning technology for the manufacture of aeroengine and industrial turbines. Higher turbine combustion temperatures are desirable for increased engine efficiency and environmental reasons (reduction in pollutant emissions, particularly NOx), but place severe demands on the physical and chemical properties of the basic materials of fabrication.

In this context, MCrAlY coatings (where M = Co, Ni or Co/Ni) are widely applied to first and second stage turbine blades and nozzle guide vanes, where they may be used as corrosion resistant overlays or as bond-coats for use with thermal barrier coatings. In the first and second stage of a gas turbine, metal temperatures may exceed 850°C, and two predominant corrosion mechanisms have been identified:

Accelerated high temperature oxidation (>950°C) where reactions between the coating and oxidants in the gaseous phase produce oxides on the coating surface as well as internal penetration of oxides/sulphides within the coating, depending on the level of gas phase contaminants

Type I hot corrosion (850 - 950°C) where corrosion occurs through reaction with salts deposited from the vapour phase (from impurities in the fuel). Molten sulphates flux the oxide scales, and non-protective scales, extensive internal suplhidation and a depletion zone of scale-forming elements characterize the microstructure.

Thermal barrier coatings are highly advanced material systems applied to metallic surfaces, such as gas turbine or aero-engine parts, operating at elevated temperatures. These coatings serve to insulate metallic components from large and prolonged heat loads by utilizing thermally insulating materials which can sustain an appreciable temperature difference between the load bearing alloys and the coating surface.In doing so, these coatings can allow for higher operating temperatures while limiting the thermal exposure of structural components, extending part life by reducing oxidation and thermal fatigue. In fact, in conjunction with active film cooling, TBCs permit working fluid temperatures higher than the melting point of the metal airfoil in some turbine applications.

Background

Thermal Barrier Caotings are typically ceramic composites based on zirconia, alumina, and titanium.. The high hardnes, wear resisrance and good chemical stability of TBCs make them very desirable in cutting tool applications. TBCs provide good resistance against the corrosive, high temperature environment of aircraft engines as well. Wear resistance can increase between 200 to 500% with the addition of a TBC to a tool. Chemical vapor deposition (CVD), plasma vapor deposition (PVD), and electron beam physical vapor deposition (EBPVD) are the primary deposition methods for these coatings.


The adhesion quality of the TBC to the substrate is considered to be one of the limiting factors for use of these materials. Previous studies using pull-off methods to determine the adhesion do not sufficiently describe the mechanism of failure. In addition, a large difference in the thermal expansion coefficient between the interface and the substrate is a potential cause for spalling of the coating. This research will attempt to characterize the mechanical properties of the interface, in particular the interface fracture resistance and progressive debonding.

Cutting Tool Applications

The addition of a TBC is credited for increasing cutting speeds of tools and for providing deeper cuts. In particular, TBCs provide excellent wear resistance which is necessary in the harsh tool environment. Wear mechanisms of cutting tools, include crater, attrition, flank, and abrasive wear. It has been shown that TBCs can limit the crater and attrition wear processes.

Multi-layer coatings increase performance as the combination exhibits the best qualities of each coating. These coatings are also known to produce finer grain sizes and minimize chopping. The research will demonstrate the reliability of the combinations already in service.

The Hy-Wire Car

The Hy-Wire Car
Definition

Cars are immensely complicated machines, but when you get down to it, they do an incredibly simple job. Most of the complex stuff in a car is dedicated to turning wheels, which grip the road to pull the car body and passengers along. The steering system tilts the wheels side to side to turn the car, and brake and acceleration systems control the speed of the wheels.

Given that the overall function of a car is so basic (it just needs to provide rotary motion to wheels), it seems a little strange that almost all cars have the same collection of complex devices crammed under the hood and the same general mass of mechanical and hydraulic linkages running throughout. Why do cars necessarily need a steering column, brake and acceleration pedals, a combustion engine, a catalytic converter and the rest of it?

According to many leading automotive engineers, they don't; and more to the point, in the near future, they won't. Most likely, a lot of us will be driving radically different cars within 20 years. And the difference won't just be under the hood -- owning and driving cars will change significantly, too.

In this article, we'll look at one interesting vision of the future, General Motor's remarkable concept car, the Hy-wire. GM may never actually sell the Hy-wire to the public, but it is certainly a good illustration of various ways cars might evolve in the near future.

Hy-Wire Basics

Two basic elements largely dictate car design today: the internal combustion engine and mechanical and hydraulic linkages. If you've ever looked under the hood of a car, you know an internal combustion engine requires a lot of additional equipment to function correctly. No matter what else they do with a car, designers always have to make room for this equipment.

The same goes for mechanical and hydraulic linkages. The basic idea of this system is that the driver maneuvers the various actuators in the car (the wheels, brakes, etc.) more or less directly, by manipulating driving controls connected to those actuators by shafts, gears and hydraulics. In a rack-and-pinion steering system, for example, turning the steering wheel rotates a shaft connected to a pinion gear, which moves a rack gear connected to the car's front wheels. In addition to restricting how the car is built, the linkage concept also dictates how we drive: The steering wheel, pedal and gear-shift system were all designed around the linkage idea.

Ubiquitous computing

Ubiquitous computing names the third wave in computing, just now beginning. First were mainframes, each shared by lots of people. Now we are in the personal computing era, person and machine staring uneasily at each other across the desktop. Next comes ubiquitous computing, or the age of calm technology, when technology recedes into the background of our lives. Alan Kay of Apple calls this "Third Paradigm" computing.

Ubiquitous computing (ubicomp) is a post-desktop model of human-computer interaction in which information processing has been thoroughly integrated into everyday objects and activities. As opposed to the desktop paradigm, in which a single user consciously engages a single device for a specialized purpose, someone "using" ubiquitous computing engages many computational devices and systems simultaneously, in the course of ordinary activities, and may not necessarily even be aware that they are doing so.

Core concept

At their core, all models of ubiquitous computing (also called pervasive computing) share a vision of small, inexpensive, robust networked processing devices, distributed at all scales throughout everyday life and generally turned to distinctly common-place ends. For example, a domestic ubiquitous computing environment might interconnect lighting and environmental controls with personal biometric monitors woven into clothing so that illumination and heating conditions in a room might be modulated, continuously and imperceptibly. Another common scenario posits refrigerators "aware" of their suitably-tagged contents, able to both plan a variety of menus from the food actually on hand, and warn users of stale or spoiled food.

Ubiquitous computing presents challenges across computer science: in systems design and engineering, in systems modelling, and in user interface design. Contemporary human-computer interaction models, whether command-line, menu-driven, or GUI-based, are inappropriate and inadequate to the ubiquitous case. This suggests that the "natural" interaction paradigm appropriate to a fully robust ubiquitous computing has yet to emerge - although there is also recognition in the field that in many ways we are already living in an ubicomp world. Contemporary devices that lend some support to this latter idea include mobile phones, digital audio players, radio-frequency identification tags, GPS, and interactive whiteboards.

In his book The Rise of the Network Society, Manuel Castells suggests that there is an ongoing shift from already-decentralised, stand-alone microcomputers and mainframes towards entirely pervasive computing. In his model of a pervasive computing system, Castells uses the example of the Internet as the start of a pervasive computing system. The logical progression from that paradigm is a system where that networking logic becomes applicable in every realm of daily activity, in every location and every context. Castells envisages a system where billions of miniature, ubiquitous inter-communication devices will be spread worldwide, "like pigment in the wall paint".

Tripwire

A tripwire is a passive triggering mechanism, usually/originally employed for military purposes, although its principle has been used since prehistory for methods of trapping game.

Typically, a wire or cord is attached to some device for detecting or reacting to physical movement. From this basic meaning, several extended and metaphorical uses of the term have developed. For example, the Berlin Brigade stationed in the divided city of Berlin during the Cold War was given the mission to be the "tripwire" for a Soviet incursion into West Germany.

Military usage may designate a tripwire as a wire attached to one or more mines — normally bounding mines and the fragmentation type — in order to increase their activation area. Alternatively, tripwires are frequently used in boobytraps, whereby a tug on the wire (or release of tension on it) will detonate the explosives.

Soldiers sometimes detect the presence of tripwires by spraying the area with Silly String. If the string falls to the ground there are no tripwires. If there is a tripwire, the string will be suspended in the air without pulling the wire. It is being used by U.S. troops in Iraq for this purpose.