14-07-2012, 11:20 AM
Variable-geometry turbocharger
[attachment=27618]
Variable-geometry turbochargers (VGTs) are a family of turbochargers, usually designed to allow the effective aspect ratio (sometimes called A/R Ratio) of the turbo to be altered as conditions change. This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds. If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. VGTs do not require a wastegate. VGTs tend to be much more common on diesel engines as the lower exhaust temperatures mean they are less prone to failure. The few early gasoline-engine VGTs required significant pre-charge cooling to extend the turbocharger life to reasonable levels, but advances in material technology has improved their resistance to the high temperatures of gasoline engine exhaust and they have started to appear increasingly in, e.g., gasoline-
Homogeneous charge compression ignition
Homogeneous charge compression ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction releases chemical energy into a sensible form that can be transformed in an engine into work and heat.
HCCI has characteristics of the two most popular forms of combustion used in SI (spark ignition) engines: homogeneous charge spark ignition (gasoline engines) and CI engines: stratified charge compression ignition (diesel engines). As in homogeneous charge spark ignition, the fuel and oxidizer are mixed together. However, rather than using an electric discharge to ignite a portion of the mixture, the density and temperature of the mixture are raised by compression until the entire mixture reacts spontaneously. Stratified charge compression ignition also relies on temperature and density increase resulting from compression, but combustion occurs at the boundary of fuel-air mixing, caused by an injection event, to initiate combustion.
Magnetic refrigeration
Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures as well as the ranges used in common refrigerators, depending on the design of the system.
The effect was first observed by the German physicist Emil Warburg (1880) and the fundamental principle was suggested by Debye (1926) and Giauque (1927) The first working magnetic refrigerators were constructed by several groups beginning in 1933. Magnetic refrigeration was the first method developed for cooling below about 0.3 K (a temperature attainable by Herefrigeration that is pumping on the 3He vapors).
Stabilizer (ship)
Ship stabilizers are fins mounted beneath the waterline and emerging laterally. In contemporary vessels, they may be gyroscopically controlled active fins, which have the capacity to change their angle of attack to counteract roll caused by wind or waves acting on the ship.
The bilge keel is an early 20th century predecessor. Although not as effective at reducing roll, bilge keels are cheaper, easier to install, and do not require dedicated internal space inside the hull.
In November 1932 the ship Conte di Savoia made its maiden voyage. It had three huge gyroscopes fitted low down in a forward hold. These rotated at high revolutions and were designed to eliminate rolling - a persistent problem on the rough North Atlantic crossing that affected all shipping lines. Each of the three flywheels was 13 feet in diameter and weighed 108 tons.
The first mention of automatic stabilizers for ships was in 1932, by an engineer working for General Electric.
[attachment=27618]
Variable-geometry turbochargers (VGTs) are a family of turbochargers, usually designed to allow the effective aspect ratio (sometimes called A/R Ratio) of the turbo to be altered as conditions change. This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds. If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. VGTs do not require a wastegate. VGTs tend to be much more common on diesel engines as the lower exhaust temperatures mean they are less prone to failure. The few early gasoline-engine VGTs required significant pre-charge cooling to extend the turbocharger life to reasonable levels, but advances in material technology has improved their resistance to the high temperatures of gasoline engine exhaust and they have started to appear increasingly in, e.g., gasoline-
Homogeneous charge compression ignition
Homogeneous charge compression ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction releases chemical energy into a sensible form that can be transformed in an engine into work and heat.
HCCI has characteristics of the two most popular forms of combustion used in SI (spark ignition) engines: homogeneous charge spark ignition (gasoline engines) and CI engines: stratified charge compression ignition (diesel engines). As in homogeneous charge spark ignition, the fuel and oxidizer are mixed together. However, rather than using an electric discharge to ignite a portion of the mixture, the density and temperature of the mixture are raised by compression until the entire mixture reacts spontaneously. Stratified charge compression ignition also relies on temperature and density increase resulting from compression, but combustion occurs at the boundary of fuel-air mixing, caused by an injection event, to initiate combustion.
Magnetic refrigeration
Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures as well as the ranges used in common refrigerators, depending on the design of the system.
The effect was first observed by the German physicist Emil Warburg (1880) and the fundamental principle was suggested by Debye (1926) and Giauque (1927) The first working magnetic refrigerators were constructed by several groups beginning in 1933. Magnetic refrigeration was the first method developed for cooling below about 0.3 K (a temperature attainable by Herefrigeration that is pumping on the 3He vapors).
Stabilizer (ship)
Ship stabilizers are fins mounted beneath the waterline and emerging laterally. In contemporary vessels, they may be gyroscopically controlled active fins, which have the capacity to change their angle of attack to counteract roll caused by wind or waves acting on the ship.
The bilge keel is an early 20th century predecessor. Although not as effective at reducing roll, bilge keels are cheaper, easier to install, and do not require dedicated internal space inside the hull.
In November 1932 the ship Conte di Savoia made its maiden voyage. It had three huge gyroscopes fitted low down in a forward hold. These rotated at high revolutions and were designed to eliminate rolling - a persistent problem on the rough North Atlantic crossing that affected all shipping lines. Each of the three flywheels was 13 feet in diameter and weighed 108 tons.
The first mention of automatic stabilizers for ships was in 1932, by an engineer working for General Electric.