A turbocharger consists of a compressor and a turbine linked by a shared axle so if the turbine rotates, the compressor also rotates. The turbine inlet receives exhaust gases from the engine causing it to rotate. This rotation in turn drives the compressor, which compresses the ambient air and delivers it to the intake manifold of an engine at higher pressure, resulting in greater amount of air entering the cylinder.
Now to some basics before we go ahead. There are two ways of increasing the power of an engine. One of them would be to make the fuel-air mixture richer by adding more fuel. This will increase the power but at the cost of fuel efficiency and increase in pollution levelsÂ¦ prohibtive! The other would be to somehow increase the volume of air entering into the cylinder and increasing the fuel intake proportionately, increasing power and fuel efficiency without hurting the environment or efficiency. This is exactly what Turbochargers do, increasing the volumetric efficiency of an engine.
In a naturally aspirated engine, the downward stroke of the piston creates an area of low pressure in order to draw more air into the cylinder through the intake valves. Now because of the pressure in the cylinder cannot go below 0 (zero) psi (vacuum) and relatively constant atmospheric pressure (about 15 psi) there will be a limit to the pressure difference across the intake valves and hence the amount of air entering the combustion chamber or the cylinder. The ability to fill the cylinder with air is its volumetric efficiency. Now if we can increase the pressure difference acorss the intake valves by someway we can make more air enter into the cylinder and hence increasing the volumetric efficiency of the engine. A turbocharger does exactly this, it increases the pressure at the point where air is entering the cylinder, thereby increasing the pressure difference across the intake valves and thus more air enters into the combustion chamber. The additional air makes it possible to add more fuel, increasing the power and torque output of the engine, particularly at higher engine speeds.
If the pressure in the cylinder goes too high it will cause the fuel to pre-ignite (remember more pressure == more temperature) in turn causing serious physical damage to the engine. To regulate pressure or boost, a wastegate is used. A wastegate controls the boost by routing some of the exhaust flow away from the exhaust side turbine. This controls the speed at which the axle rotates and in turn regulates the boost pressure by the compressor at the other end. The application of a compressor to increase pressure at the point of air intake is also commonly refferred to as forced induction.
The turbocharger application in an engine also introduce ËœLagâ„¢ which is a symptomatic of the time taken by the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its rotational inertia and reach the speed necessary to supply boost pressure. That is why in turbocharged cars, you feel the turbo kicking in after ceratin rpm is reached, at which point the exhaust system overcomes the rotational inertia of the turbine and speed it up to supply boost pressure.
1. More power compared to the same size naturally aspirated engine.
2. Better thermal efficiency over natually aspirated engine and supercharged engine because the engine exhaust is being used to do the useful work which otherwise would have been wasted.
3. Better Fuel Economy by the way of more power and torque from the same sized engine.
1. Lack of response called the Turbo Lag. If the turbo is too big, the boost will build up slowly because more exhaust pressure will be needed to overcome the rotational inertia on the larger turbine reducing throttle response but more peak power. If the turbo is too small the turbo lag wont be as big but the peak power would be lesser. So the turbocharger size is a very important consideration when deciding on it for a particular engine.
2. Non liner rise in power and torque.
4. Complexity: Turbocharger spins at very very high revolutions ( 1 lakh + per minute!!!) so proper cooling and lubrication is essential if it not to destroy the engine.
Functions of a Turbo Charger
1. A turbo charger is a device that uses the energy of exhaust gases coming out from an engine to compress the air going into the engine. It must have at least 4 openings: 1 for the engine exhaust gas to enter; a 2nd for the exhaust gas to exit; a 3rd opening for intake air to enter the turbocharger; and a 4th for the intake air to exit the turbo charger on its way to the engine intake. A turbo charger will also have 1 additional opening to vent excess air pressure. Increasing the intake air pressure going into an engine can increase the engine's power, but too much air pressure can damage the engine. Increasing the pressure increases the power of the engine because of the increased density of the air. Increased air density means more oxygen molecules, which means the engine can respond by increasing the amount of fuel it mixes with that oxygen. When the fuel and oxygen are burned, the result is a more powerful explosion with each piston stroke, and thus more power coming out of the engine.
Function of a Turbo Charger
2. The function of a turbo charger is to increase the power output of an engine without adjusting the engine itself. Typically, an engine would have to be made larger and consequently heavier to gain power; on the other hand, a turbo charger is much smaller and lighter. Additionally, a turbo charger is powered by the exhaust gases of the engine, which would normally just leave the engine and vehicle unused.
3. The function of a turbo charger can be thought of as beginning at the exhaust opening. Exhaust gases from the engine go through the turbo charger before exiting through the exhaust system of the vehicle. The flow of these gases causes a turbine wheel inside the turbo charger to spin. On the other side of this turbine, on the same axis, is a different wheel at the intake opening of the turbo charger.
4. At the intake opening of the turbo charger is a 2nd wheel that spins whenever with the exhaust-side turbine wheel spins, since they are connected by the same shaft. This 2nd wheel is called the "compressor" or "impeller wheel" because its spinning compresses the air coming into the turbo on the intake side. This compressed air is fed into the engine intake and, because of the higher density of oxygen molecules in compressed air as opposed to uncompressed, the engine throws in more fuel for each piston stroke, resulting in increased power.
Exhaust Opening (Again)
5. The compressed air coming in the intake of the engine is burned off inside and becomes exhaust gas. This exhaust gas has more energy than it would had the intake air not been compressed and burned with more fuel, and thus spins the exhaust-end turbine of the turbo charger faster than before. In turn, this spins the compressor wheel faster than before, which compresses the intake air more than before. The increase in compression of the air results in even more oxygen molecules and even more fuel for each piston stroke. As this cycle continues, the turbo charger can easily continue to further increase the compression of the intake air. However, at some point, too much air compression combined with too much fuel can result in too much power that can damage the engine.
Controlling Air Pressure
6. To limit the amount of air pressure a turbocharger generates by compressing the intake air, a control system must be used. Typically, this happens through a mechanism called a "waste gate" that, when open, allows some exhaust gas to bypass the exhaust-side turbine wheel, which limits how fast the wheel can spin. Limiting the speed of the turbine wheel limits the speed of the intake-side compressor wheel, which limits the amount of air compression.
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