07-04-2012, 12:09 PM
ROLE OF TURBOCHARGER &SUPERCHARGER IN AUTOMOBILE
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INTRODUCTION
To increase the output efficiency of any engine we have to burn more fuel and make bigger explosion in every cycle. When age two options for this. Onaway to add power is to build bigger engine but bigger engines, more and cost more to build and maintain, are not always better. Another way to add power is to make normal-sized engine more efficient. We can accomplish this by forcing more air into the combustion chamber. More air means more fuel can be Added, and more fuel eans a bigger explosion and greater horsepower. This can be done with the help of supercharger. As u perch larger is basicallyanaircompre s sore used for forced induction of an internal combustion engine. It does the same work a that of a compressor, i.e. it compresses the air being delivered to the combustion chamber ofan engine.The greater mass flow-rate provides more oxygen to support combustion than would beavailable ina naturally-aspirated engine,which allows morefu el to be providedand morework to be done per cycle, increasing the power output of the engine.
WHY SUPERCHARGER
A supercharger is used in an engine for various reasons.
Some of theadvantages of superchargersareas follows
Increases the power of an engine
A supercharger spinning at 50,000 RPM translates toa boost of about six to nine pounds per square inch (psi). Increases the torque produced. An efficiently working engine with supercharger can achieve the same speed in one third of the time taken by the same engine without supercharger. Necessary in air planes and jetsas theyh aveless oxygenathigh altitudes. So they provide the sufficient amount of air by compressing it tohigher pressure and ensure complete combustion.
SUPERCHARGER VS TURBOCHARGER
The thermal efficiency, or fraction of the fuel/ air energy that is converted to output power, is less with a mechanically driven supercharger than with a turbocharger, because turbochargers are using energy from the exhaust gases that would normally be wasted. For this reason, both the economy and the power of a turbocharged engine are usually better than with superchargers.
High Temperatures
Not only is this heat from the exhaust useful to us but it also has a down side, in that temperatures well over the 1,000ºC mark are not uncommon and that plays havoc with the turbine wheel. This helps the turbine to spin up at low engine speeds. Exhaust manifold design too, plays an important part in this whole process.
Turbocharger Intercooler
Whenever air is compressed, it gets hot—witness to that is the bicycle pump after pumping up a tire. As the air temperature increases, the density of that air (at that pressure) is less dense, meaning that the air molecules are further apart. This also means that there will be less oxygen in that sample of air that will be around to help with the combustion process. Enter the Turbocharger Intercooler. No, this is not just a marketing ploy to sell more planes (we’ve all seen the phrase, Turbocharger with Intercooler).
Altitude effects
The Rolls Royce Merlin, a supercharged aircraft engine from World War II
Superchargers are a natural addition to aircraft piston engines which are intended for operation at high altitudes. As an aircraft climbs to higher altitude, air pressure and air density decreases. The efficiency of a piston engine drops because of the reduction in the weight of air that can be drawn into the engine; for example the air density at 30,000 ft (9,100 m) is 1⁄3 of that at sea level, thus only 1⁄3 of the amount of air can be drawn into the cylinder and not enough oxygen can be delivered to the engine cylinders to provide efficient combustion for the fuel/air mixture; so, at 30,000 ft (9,100 m), only 1⁄3 of the fuel can be burnt one advantage of the decreased air density is the airframe only experiences about 1/3rd of the aerodynamic drag, plus there is decreased back pressure on the exhaust gases.
Two-stage and two-speed superchargers
In the 1930s, two-speed drives were developed for superchargers. These provided more flexibility for the operation of the aircraft, although they also entailed more complexity of manufacturing and maintenance. The gears connected the supercharger to the engine using a system of hydraulic clutches, which were manually engaged or disengaged by the pilot with a control in the cockpit. At low altitudes, the low-speed gear would be used in order to keep the manifold temperatures low. At around 12,000 feet (3,700 m), when the throttle was full forward and the manifold pressure started to drop off, the pilot would retard the throttle and switch to the higher gear, then readjust the throttle to the desired manifold pressure.