WHAT IS SUPERCHARGING
Supercharging acts as an air compressor. It is used to increase the density and pressure of the air that is supplied to the internal combustion engine. In the engine, during the intake of the cycle it takes more oxygen and burn more fuel to accomplish the work. This is due the power increase. By using the belts, gears, shafts,chain all of these are connected to the engines crank shafts to produce super charge. We can see two types of super chargers. To make matter after super charging, the air enters into the engine. After compression the pressure in the air is compressed and it super charges the system by 1.5 to 2 times to increases the entry of the pressure. superchargers of internal combustion engines is in practice for a long time as a method for improving engine power output. Entering the millennium a new trend is appearing. The trend points to small displacement engines in order to meet emission legislation of fuel on fuel consumption and emission control.
The consumers, however still demand equally the same o better performances they are used to. A good way to meet theses needs is to have supercharging which may be called force induction. As already stated, the purpose of supercharging in engine is to raise the density of the air charge, before it enters the cylinders.Thus, the increased mass of air will be inducted which will then be compressed in each cylinders. This makes more oxygen available for combustion than the conventional method of drawing the fresh air charge into the cylinder (naturally aspirated). Consequently, more air and fuel per cycle will be forced into the cylinder, and this can be effectively burnt during the combustion process to raise the engine power output to a higher valve than would otherwise be possible.
In one type of the supercharger the engine shafts is mechanically linked to the shaft. The shaft energy must turn into useful work input for the super charger. In another type of the super charger the compressor is attached to the turbine . Exhaust gas must be allowed to enter into the turbine. The turbine drives the supercharger. This type of supercharger is known as the turbo.
The points to be noted in supercharging an engine summarized as:
1. Supercharging increases the power output of the engine. It does not increase the fuel consumption, per brake kw hour.
2. Certain percentage of power is consumed in compressing air. This power has to be taken from the engine itself. This will lead to some power loss. However, it is seen that the net power output will be more than the power output of an engine of the same capacity , without supercharging.
3. The engine should be designed to withstand the higher forces due to supercharging.
4. The increased pressure and temperature as a result of supercharging, may lead to denotation, therefore the fuel used must be have better antiknock characteristics. In practice, racing car engines use supercharging. The most important areas where supercharging is to vital importance are:
- Marine and automotive engines where weight and space are important.
- Engines working at high altitudes. The power loss due to altitude can be compensated by supercharging.
In supercharging, to increase the output efficiency we have to bun more fuel and makes bigger explosion in every cycle. We have two options for this
One way to add power is to build a bigger engine. But bigger engines, which weigh more and cost more to build and maintain are not always better.
Another way to add power is to make a 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 means a bigger explosion and greater horsepower. This can be done with the help of a supercharger.
HISTORY OF SUPERCHARGERS
The Roots superchargers is the oldest design of superchargers used in any type of engine. Philander and Francis Roots, in 1860, introduced the concept of such type of equipment. Though they patented the design as a machine that would help in ventilating minecrafts, later this turned out to be a miraculous invention for automotive engineers.
In 1990, Gottleib Daimler for the first time included a root supercharger in a car engine which improved the output of the engine. This was the first step towards its development.
WORKING PRINCIPLE OF SUPERCHARGER
More fuel + More air = Bigger explosion = Greater horsepower
Every superchargers works on the same above mentioned statements. It is quite evident that to get more output from any engine, we need to burn more fuel. More fuel will result in a bigger explosion in every cycle, which will then push the piston with more thrust and consequently this thrust will be transmitted to the wheels with the help of crankshaft. Wheels will rotate faster and with more power and that is how it works.
But, to burn more fuel in an engine, we need more air in it (the chemically correct mixture - 14: 1 air-fuel is essential for an engine to operate perfectly). Thus a supercharger compresses the air being delivered to the engine so as to supply more air in the same. limited volume of the cylinder. This ensure complete combustion of fuel and no unburn fuel comes out of the exhaust. Thus the supercharger increases the power output of any engine.
TYPES OF SUPERCHARGERS
Nowadays, there are several types of superchargers used in the engines. The following are some of the most commonly used superchargers.
1. Roots superchargers
2. Twin-screw superchargers
3. Centrifugal superchargers.
1. Roots Superchargers:
Construction features: It consists of two meshing lobes that are fitted on two parallel shafts. Those lobes resembles to a lobe gear that are in continuous mesh. Both the lobes mesh in such a manner that the air pockets between these lobes and the side walls goes on decreasing as air moves from the fill side to the discharge side. Thus the passing air gets squeezed.
Working Of Root supercharger: As the meshing lobes spin air trapped in the pockets between the lobes is carried between the fill side and the discharge side and large quantities of air moves into the intake manifold and stack up to create positive pressure. This pressurized air is received at the discharge side.
Roots superchargers are usually large and sit on top of the engine . Roots superchargers are the least efficient superchargers for two reasons:-
i. They add more weight to the vehicle.
ii. They provide air in discrete burst instead of providing in a smooth and continuous manner.
2. Twin-screw superchargers
Construction features: Twin-screw superchargers consist of two meshing lobes that resemble a set of worm gear. The two gears meshes in such a way that the air pockets between them goes on decreasing as air moves ahead.
Working of Twin-screw superchargers: A twin screw superchargers operates by pulling air through a pair of meshing lobes that resemble a set of worm gears. The rotors have a conical taper which means the air pockets decreases in size as air moves from the fill side to the discharge side. Thus a twin-screw superchargers compresses the air inside the rotor housing. As the air pocket shrink, the air is squeezed into a smaller space.
i. Thus twin-screw superchargers are more efficient compared to to root superchargers.
ii. They cost more because the screw-type rotor require more precision in the manufacturing process.
iii. They also make a lot of noise.
iv. The compressed air exiting the discharge outlet creates a whine or whistle that must be checked with noise suppression techniques.
Construction features: Centrifugal superchargers consist of an impeller with several blades that rotates at a very high speed at around 50000 rpm. This impeller throws the air outside due to centrifugal force. It also consist of a diffuser which exchange the speed for high pressure.
Working of centrifugal superchargers: As the air is drawn in the hub of the impeller, centrifugal forces cause it to radiate outward. The air leaves the impeller at high speed,but low pressure. A diffuser converts the high-speed, low pressure air to low speed, high pressure air. Thus pressurized air is achieved. The diffuser is placed inside the housing and fixed with an impeller and which converts this centrifugal force into the high pressure and less velocity having the hot air density transported through an outlet of the housing to the intercooler. The intercooler can decrease the air temperature and cool air having the more air molecules and more oxygen sends into the inlet valves of the engine during the suction stroke. More air can burn more fuel to produce huge horsepower from an internal combustion engine.
i. Impeller speeds can reach 50,000 to 60,000 RPM
ii. Centrifugal superchargers are the most efficient and the most common induction systems.
iii. They are small, lightweight and attachable to the front of the engine.
iv. Thus the centrifugal superchargers are the best among the above list.
DRIVES USED IN SUPERCHARGERS
Drives are basically the equipment that are used to transfer power from one shaft to another shaft. In a supercharger, drives are used to transfer part of the engine power to the supercharger. There are several types of drives used to empower a supercharger. These drives are used according to there requirements. Some of them are;
Mechanical
i. Belt (V-belt, toothed belt and flat belt)
ii. Gear drive.
iii. Chain drive
Exhaust Gas turbine
i. Axial turbine.
ii. Radial turbine.
Others
i. Electric motor.
ii. auxiliary power unit
SUPERCHARGER AN EDGE OVER TURBOCHARGER
1. Superchargers do not suffer leg: Superchargers have no lag time because they are driven directly by the crankshaft, whereas turbochargers suffers lag because it takes a few moments before the exhaust gases reach a velocity that is sufficient to drive the impeller/ turbine. Since the supercharger are directly empowered from the engine, so as the engine starts, the superchargers can be activated. But in the case of turbochargers they take some time for the accumulation of exhaust gases.
2. Modification of the exhaust system: Installing a turbocharger requires extensive modification of the exhaust system, but superchargers can be bolted to the top or side of the engine , that makes them cheaper to install and easier to service and maintain. So this becomes a problem in the case of turbochargers. It becomes a tough task to modify the exhaust system as well as it adds an extra cost in vehicle.
3. Shutdown procedures: No special shutdown procedures is required with superchargers as they are not lubricated by the engine oil. They can be shutdown normally. Whereas the turbochargers must be idle for about 30 seconds or so prior to shutdown so the lubricating oil has a chance to cool down. Thus it creates a problem during shutdown procedures as turbochargers can't be shutdown normally.
ADVANTAGES OF SUPERCHARGERS
i. The work output and the overall efficiency of the engine must be increased by 50% of the superchargers.
ii. At the higher heights, the low density air is converted into the normal density air.
iii. In the supercharge engine the specific fuel consumption is saved.
iv. The volumetric efficiency of the superchargers engine will be higher.
v. In the supercharger engine the scavenging is improved .
vi. Higher power output.
vii. Greater induction of charge mass.
viii. Better scavenging of products.
ix. Quicker acceleration of vehicle.
xi More completes and smoother combustion.
xii. Increased cooling requirements of pistons and valves.
DISADVANTAGES OF SUPERCHARGERS
i. On the engine, different moving parts are observed like the thermal stress, mainly on the bearing of the engine shafts.
ii. So it results in the wear and tear in the moving parts.
iii. We need to replace the parts frequently in the engine.
iv. During the time of compression stroked by the piston there is a leakage of the air in the supercharge engine.
v. Due to supercharging, the temperature of the air entering the engine cylinder will be higher.
vi. The denotation tendency of the engine increases.
vii. In the petrol engine, the detonation reduces so inter coolers are used to increases the size of the engine.
.jpeg)
0 Comments