The Basics A jet engine can be divided into several distinct sections: intake， compressor， diffuser， combustion chamber， turbine， and These sections are much like the different cycles in a four-stroke reciprocating engine: intake， compression， power and In a four-stroke engine a fuel/air mixture is is brought into the engine (intake)， compressed (compression)， and finally ignited and pushed out the exhaust (power and exhaust) In it's most basic form， a jet engine works in much the same * Air comes in the front of the engine where it enters the The air is compressed by a series of small spinning blades aptly named compressor blades and leaves at a high The pressure ratio between the beginning and end of the compressor can be as much as 48:1， but almost always 12:1 or * The air now enters the diffuser， which is nothing more than an area where the air can expand and lower it's velocity， thus increasing its pressure a little bit * The high pressure air at the end of the diffuser now enters the combustion chamber where it is mixed with fuel， ignited and * When the fuel/air mixture burns， the temperature increases (obviously) which makes the air * This expanding gas drives a set of turbine blades located aft of the combustion At least some of these turbine blades are connected by a shaft to the compressor blades to drive Depending on the type of engine， there may be another set of turbine blades used to drive another shaft to do other things， such as turn a propeller or * The left over energy not extracted by the turbine blades is pushed out the back of the engine (exhaust section) and creates thrust， usually used to drive an airplane The types of jet engines include: * Turbojet * Turbofan * Turboprop * Turbo shaft Turbojet The turbojet is the simplest of them all， it is just as described in "The basics" This style was the first type of jet engine to be used in It is a pretty primitive style used mostly in early military jet fighters such as the F- Its use was discontinued， for the most part， in favor of the more efficient Actually， I should clarify Each type of engine is most efficient under certain Turbojets are most efficient at high altitudes and speeds above the speed of See the diagram at the end of this page for relative efficiencies of each style Turbofan Turbofans make up the majority of jet engines being produced and used A turbofan engine uses an extra set of turbine blades to drive a large fan， typically on the front of the This fan differs from a propeller in that there are many small blades and they are inside of a The fan sits just in front of the normal intake， some of the air driven by this fan will enter the engine， while the rest will go around the The amount of air that bypasses the engine is different for each type of The different styles are called high and low bypass Bypass ratio is the ratio of how much air goes through the fan， to how much goes through the Typical bypass ratios would be 1:1 for a low bypass and 5:1 or more for a high Low bypass engines are more efficient at higher speeds， and are used on planes such as military aircraft， while high bypass engines are used in commercial Turboprop Turboprops are similar to turbofans in that they incorporate an extra set of turbine blades used to drive the Unlike the turbofan engines， nearly all the thrust produced by a turboprop is from the propellor， hardly any thrust comes from the These engines are used mostly on smaller and slower planes such as commuter aircraft that fly to the smaller As you can see from the efficiency chart below， turboprops are very efficient over a fairly wide range of They would probably be used more often on large transport aircraft， except for one problem: they have The general public does not like propellors， as they appear to be old-fashioned and However， the military knows better and uses them on several large transport Turbo shaft Turbo shaft engines are very similar to turboprop engines， but instead of driving a propellor， they are used to drive something Many helicopters use them to drive their rotors， and airliners and other large jets use them to generate Also， the Alaska Pipeline uses them at the pump stations to pump Overall Overall the big difference between these engines is how they take a chunk of air and move Newton's third law states that Force equals mass times Applying this to turbine engines: the turboprop takes a large chunk and accelerates it a little bit， while the turbojet takes a small chunk and accelerates the heck out of it， and the turbofan is somewhere in between these These different methods of moving air also have to do with how much noise each engine The turbojet makes the most noise because there is a large difference in velocities of the blast of air coming out the exhaust and the surrounding The air from the fan on a turbofan engine "shields" the blast in the center by having the slower moving air from the fan surround Then the turboprop is the quietest of all because the air it's moving is relatively A pressure - volume diagram (or a P-V diagram) is a useful tool in In this case， it relates the pressure and volume of the gas moving through the engine at different A P-V diagram can also be helpful in finding the work output of an Work equals the integral of pressure with respect to Or is simpler form， work equals the area enclosed in the diagram The above cycle is the Brayton cycle， or the cycle used by aircraft gas turbine Explanation of the above cycle: * Air enters the inlet at point 1 at atmospheric * As this air passes through the compressor (from point 1 to 2)， the pressure rises adiabatically (no heat enters or leaves the system) * Now the air enters the combustion chamber (from point 2 to 3)， is mixed with fuel， and burned at a constant * Finally， the air goes through the turbine and out the exhaust (point 3 to 4) where the gases expand and do Thus， the pressure drops and the volume The Compressor There are two main styles for turbine compressors: the axial and the The Axial Compressor * The axial type compressor is made up of many small blades， called rotor vanes， arranged in rows on a cylinder whose radius gets larger towards the back (as can be seen from the above picture) These blades act much like small * In between these rotor vanes are stator vanes which stay in a fixed spot and straighten the air coming out of the previous stage of rotor vanes before it enters the next * On some newer engines， the angle of these stator vanes can be adjusted for optimum * Each stage (1 row of rotor and stator vanes) generally provides for a pressure rise of about 3:1 (so after the first stage， the pressure would be 3 above atmospheric， after the second it would be 69， 2， ) The Centrifugal Compressor * Air enters the centrifugal compressor at the front and The blades then sling the air radially outwards where it is once again collected (at a higher pressure) before it enters the * Pressure rise per stage is usually about 4 to 8:1 (higher than axial) These can be sombined in series (that is the exit of the first leads to the entrance of the next) to produce a greater pressure But more than two stages is not - Jet engines are rated in "pounds of thrust，" while turboprops and turboshaft engines are rated in "shaft horsepower" (SHP) This is because it is difficult to hook up a dynamometer (power measuring device) to the column of air coming out of a jet engine， while it is easy to hook one to the shaft of a - An equivalent measure to horsepower is thrust horsepower (THP) THP = (Thrust x MPH) / or THP = SHP x 80% in the case of turboprop engines (the 80% is because the propeller "slips" a little in flight) - Exhaust gases exit the exhaust at upwards of 1000 mph or more and can use 1000 gallons of fuel/hour or - Turbine engines run Unlike gasoline engines， turbines take in more air than they need for - Fuel can be injected into the exhaust section to burn with this unused air for extra This is called an - A water/methanol mixture can be injected into the intake to increase the air density， and thus increase - Turbine engines can be built on a small scale as The turbine pictured below has a diameter of 4mm and runs at 500，000 It was built by at MIT for purposes of powering an aircraft with a wing span of about 5 inches that was projected to fly about 35 - 70 mph with a range of about 40 - 70 micro turbine - The ignition system on turbine engines is only necessary for starting， afterwards it is self In jets， the ignition system is also turned on for added saftey in "critical" stages of flight， such as takeoff and - A device similar to a spark plug is used for the ignition process， but it has a larger The spark is about 4 to 20 Joules (watts/second) at about 25000 volts and occurs between 1 and 2 times per - Turbine engines will run on just about anything， they prefer Jet-A (AKA diesel， kerosene， or home heating oil)， but can burn unleaded， burbon， or even very finely powdered coal! - The above snowmachine uses an Allison turbine engine， a very common engine in helicopters (such as the Bell 206 Jet Ranger shown below) A lot of horsepower can be put into a small package! Note the intake and compressor are at the front of the engine， then the two side tubes take the compressed air and bring it around back to the combustion chamber and turbine and the exhaust exits out the There are many engines out there with strange configurations like Communications Technology Your Rights and what the Data Protection Commissioner can do to help Right of Access The personal information to which you are entitled is that held on computer or in a manual filing system that facilitates access to information about You can make an access request to any organisation or any individual who has personal information about For example， you could make an access request to your doctor， your bank， a credit reference agency， a Government Department dealing with your affairs， or your If you find out that information kept about you by someone else is inaccurate， you have a right to have that information corrected (or "rectified") In some circumstances， you may also have the information erased altogether from the database - for example， if the body keeping the information has no good reason to hold it ( it is irrelevant or excessive for the purpose)， or if the information has not been obtained You can exercise your right of rectification or erasure simply by writing to the body keeping your In addition， you can request a data controller to block your data to prevent it from being used for certain For example， you might want your data blocked for research purposes where it held for other If an organisation holds your information for the purposes of direct marketing (such as direct mailing， or telephone marketing)， you have the right to have your details removed from that This right is useful if you are receiving unwanted "junk mail" or annoying telephone calls from You can exercise this right simply by writing to the organisation The organisation must write back to you within 40 days confirming that they have dealt with your Right to complain to the Data Protection Commissioner What happens if someone ignores your access request， or refuses to correct information about you which is inaccurate? If you are having difficulty in exercising your rights， or if you feel that any person or organisation is not complying with their responsibilities， then you may complain to the Data Protection Commissioner， Mr Mead， who will investigate the matter for The Commissioner has legal powers to ensure that your rights are The Data Protection Commissioner will help you to secure your rights: * with advice and information * by intervening directly on your behalf if you feel you have not been given satisfaction * by taking action against those failing to fulfil their SEE APPENDIX 2 FOR CASE STUDY Ergonomics Ergonomics (from Greek ergon work and nomoi natural laws) is the study of designing objects to be better adapted to the shape of the human body and/or to correct the user's Common examples include chairs designed to prevent the user from sitting in positions that may have a detrimental effect on the spine， and the ergonomic desk which offers an adjustable keyboard tray， a main desktop of variable height and other elements which can be changed by the Ergonomics also helps with the design of alternative computer input devices for people who want to avoid repetitive strain injury or carpal tunnel A normal computer keyboard tends to force users to keep their hands together and hunch their To prevent the injuries， or to give relief to people who already have symptoms， special split keyboards， curved keyboards， not-really-keyboards keyboards， and other alternative input devices Ergonomics is much larger than looking at the physiological and anatomical aspects of the human The psychology of humans is also a key element within the ergonomics This psychological portion of ergonomics is usually referred to as Human factors or Human factors engineering in the US， and ergonomics is the term used in E Understanding design in terms of cognitive workload， human error， the way humans perceive their surrounds and， very importantly， the tasks that they undertake are all analysed by [IMAGE] With video conferencing consideration should be taken in positioning of camera and screens so as to avoid neck Codec (COder/DECoder or COmpressor/DECompressor) Hardware or software that encodes/compresses and decodes/decompresses audio and video data The purpose of a codec is to reduce the size of digital audio samples and video frames in order to speed up transmission and save storage The goal of all codec designers is to maintain audio and video quality while compressing the binary data Speech codecs are designed to deal with the characteristics of voice， while audio codecs are developed for Codecs may also be able to transcode from one digital format to another; for example， from PCM audio to MP3 The codec algorithms may be implemented entirely in a chip or entirely in software in which case the PC does all of the They are also commonly implemented in both hardware and software where a sound card or video capture card performs some of the processing， and the main CPU does the When analog signals are entered into a computer， cellphone or other device via a microphone or video source such as a VHS tape or TV， analog-to-digital converters create the raw digital audio samples and video Speech， audio and video codecs are typically lossy codecs that compress data by altering the original format， which is why "codec" means "encoder/decoder" and "compressor/" If a codec uses only lossless compression in which the original data is restored exactly， then it would not be a coder/ This is a subtle point， but the two meanings of the acronym have been LAN A local area network (LAN) is a computer network covering a local area， like a home， office or small group of buildings such as a The topology of a network dictates its physical The generally accepted maximum size for a LAN is LANs are different from personal area networks (PANs)， metropolitan area networks (MANs) or wide area networks (WANs) LANs are typically faster than WAN The earliest popular LAN， ARCnet， was released in 1977 by Datapoint and was originally intended to allow multiple Datapoint 2200s to share disk Like all early LANs， ARCnet was originally vendor- Standardization efforts by the IEEE have resulted in the IEEE 802 series of There are now two common wiring technologies for a LAN， Ethernet and Token R Wireless technologies are starting to evolve and are convenient for mobile computer A number of network protocols may use the basic physical transport mechanism including TCP/IP In this case DHCP is a convenient way to obtain an IP address rather than using fixed LANs can be interlinked by connections to form a Wide area A router is used to make the connection between LAN WAN WANs are used to connect local area networks together， so that users and computers in one location can communicate with users and computers in other Many WANs are built for one particular organisation and are private， others， built by Internet service providers provide connections from an organisation's LAN to the I WANs are most often built of leased At each end of the leased line， a router connects to the LAN on one side and a hub within the WAN on the A number of network protocols may use the basic physical transport mechanism including TCP/IP Other protocols including X25 and ATM Frame relay can also be used for WAN Ethernet Ethernet is normally a shared media LAN All stations on the segment share the total bandwidth， which is either 10 Mbps (Ethernet)， 100 Mbps (Fast Ethernet) or 1000 Mbps (Gigabit Ethernet) With switched Ethernet， each sender and receiver pair have the full When using Ethernet the computers are usually wired to a hub or to a This constitutes the physical transport Fiber-optic Ethernet (10BaseF and 100BaseFX) is impervious to external radiation and is often used to extend Ethernet segments up to 2 Specifications exist for complete fiber-optic networks as well as backbone FOIRL (Fiber-Optic Inter Repeater Link) was an earlier standard that is limited to 6 miles
