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INTRODUCTION

A turbocharger, or turbo, is a gas compressor that is used for forced induction of an internal combustion engine. A

form of super charger, the turbocharger increases the pressure of air entering the engine to create more power. A

turbocharger has the compressor powered by a turbine, which is driven by the engine's own exhaust gases rather than

direct mechanical drive. This allows a turbocharger to achieve a higher degree of efficiency than other types of forced

induction compressors which are more vulnerable to parasitic loss. Turbo charging is usually carried out in diesel

engines. This is because turbochargers work using the pressure from the exhaust gas (For diesel engines the

compression ratio is high and hence the pressure.). But it can be used in petrol engines also if the engine is 4

cylindered or more.

Turbocharging a bike, is possible only if it is a 4 cylinder one. Usually only performance bikes are turbocharged. It is

also possible to improve the performance of a bike using nitro injection, bigger carburetors etc, but the advantage of

turbocharging its stock engine is that you save a lot of money and at the same time obtain better performance. Earlier,

using turbochargers to gain performance without a large gain in weight was very appealing.

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OPERATING PRINCIPLE A turbocharger is a small radial fan pump driven by the energy of the exhaust gases of an engine. A turbocharger consists of a

turbins and a compression on a shared shaft. The turbine converts kinetic energy from the engine exhaust's velocity and

potential energy from the exhaust's higher-than-atmospheric pressure into rotational kinetic energy, which is in turn used todrive the compressor. The compressor draws in ambient air and pumps it into the intake manifold at increased pressure,resulting in a greater mass of air entering the cylinders on each intake stroke.

The objective of a turbocharger is the same as a supercharger; to improve the engine's Volumetric efficiency by solving one of its cardinal limitations. A naturally amplified automobile engine uses only the downward stroke of a piston to create an areaof low pressure in order to draw air into the cylinder through the intake valves.

The pressure in the atmosphere is no more than 1 atmp, so there ultimately will be a limit to the pressure difference acrossthe intake valves and thus the amount of airflow entering the combustion Chamber Since the turbocharger increases the

pressure at the point where air is entering the cylinder, a greater mass of air (oxygen) will be forced in as the inlet manifoldpressure increases.

The additional air flow makes it possible to maintain the combustion chamber pressure and fuel/air load even at high enginerevolution speeds, increasing the power and torque output of the engine.

To avoid detonation and physical damage, the pressure in the cylinder must not go too high; to prevent this, the intakepressure must be controlled by venting excess exhast gas so it will bypass the exhaust turbine. This control function isperformed by a wastegate, which routes some of the exhaust flow away from the turbine. This in turn regulates air pressurein the intake manifold. A simpler alternative is to restrict the input area of the compressor.

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TURBO PRINCIPLE To better understand the technique of turbocharging, it is useful to be familiar with theinternal combustion engine's principles of operation. Today, most passenger and

commercial diesel engines are four-stroke piston engines controlled by intake and exhaust valves. One operating cycle consists of four strokes during two complete revolutions of thecrankshaft.

SUCTION (Charge Exchange Stroke) When the piston moves down, air (diesel engine or direct injection petrol engine) or afuel/air mixture (petrol engine) is drawn through the intake valve.

COMPRESSION ( Power Stroke ):The cylinder volume is compressed.

EXPANSION (Power Stroke) In the petrol engine, the fuel/air mixture is ignited by a spark plug, whereas in the dieselengine fuel is injected under high pressure and the mixture ignites spontaneously.

EXHAUST (Charge Exchange Stroke) The exhaust gas is expelled when the piston moves up.

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TURBOCHARGING In the above-described procedures, the engine operates as a naturally aspirated engine.The combustion air is drawn directly into the cylinder during the intake stroke. Inturbocharged engines, the combustion air is already pre-compressed before beingsupplied to the engine. The engine aspirates the same volume of air, but due to thehigher pressure, more air mass is supplied into the combustion chamber. Consequently,more fuel can be burnt, so that the engine's power output increases related to the samespeed and swept volume. Basically, one must distinguish between mechanically

supercharged and exhaust gas turbocharged engines.

1. Compressor Inlet2. Compressor Discharge3. Charge air cooler (CAC)

4. Intake Valve5. Exhaust Valve6. Turbine Inlet7. Turbine Discharge

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The components that make up a

typical turbocharger system are: The air filter (not shown) through which ambient air passes before entering the compressor (1)

The air is then compressed which raises the air’s density (mass / unit volume) (2).

Many turbocharged engines have a charge air cooler (aka intercooler) (3) that cools the compressed air to furtherincrease its density and to increase resistance to detonation.

After passing through the intake manifold (4), the air enters the engine’s cylinders, which contain a fixed volume.

Since the air is at elevated density, each cylinder can draw in an increased mass flow rate of air. Higher air mass flowrate allows a higher fuel flow rate (with similar air/fuel ratio).

Combusting more fuel results in more power being produced for a given size or displacement. After the fuel is burnedin the cylinder it is exhausted during the cylinder’s exhaust stroke in to the exhaust manifold (5).

The high temperature gas then continues on to the turbine (6).

The turbine creates backpressure on the engine which means engine exhaust pressure is higher than atmosphericpressure.

Pressure and Temperature drop occurs (expansion) across the turbine (7), which harnesses the exhaust gas’ energy toprovide the power necessary to drive the compressor

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COMPONENT’S OF TURBO CHARGER

The turbocharger has four main components. The turbine (almost always a radial turbine) and impeller/compressor wheels are eachcontained within their own folded conical housing on opposite sides of the third component, the center housing/hub rotating assembly

(CHRA).

The housings fitted around the compressor impeller and turbine collect and direct the gas flow through the wheels as they spin. The size andshape can dictate some performance characteristics of the overall turbocharger.

Often the same basic turbocharger assembly will be available from the manufacturer with multiple housing choices for the turbine andsometimes the compressor cover as well. This allows the designer of the engine system to tailor the compromises between performance,response, and efficiency to application or preference.

The turbine and impeller wheel sizes also dictate the amount of air or exhaust that can be flowed through the system, and the relativeefficiency at which they operate. Generally, the larger the turbine wheel and compressor wheel, the larger the flow capacity. Measurementsand shapes can vary, as well as curvature and number of blades on the wheels. The center hub rotating assembly houses the shaft which

connects the compressor impeller and turbine.

It also must contain a bearing system to suspend the shaft, allowing it to rotate at very high speed with minimal friction. For instance, inautomotive applications the CHRA typically uses a thrust bearing or ball bearing lubricated by a constant supply of pressurized engine oil.

The CHRA (Center Housing Rotating Assembly) may also be considered "water cooled" by having an entry and exit point for engine coolantto be cycled. Water cooled models allow engine coolant to be the layout of the turbocharger in a given application is critical to a properly performing system. Intake and exhaust plumbing is often driven primarily by packaging constraints. We will explore exhaust manifolds inmore detail in subsequent tutorials; however, it is important to understand the need for a compressor bypass valve (commonly referred to asa Blow-Off valve) on the intake tract and a Waste gates for the exhaust flow

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PROPERTIES AND APPLICATIONS

Reliability

Temperature Consideration

Turbo lag Boost threshold

Intercooler

INTERCOOLER

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Advantages

More specific power over naturally aspirated engine. This means aturbocharged engine can achieve more power from same engine volume.

Better thermal efficiency over both naturally aspirated and superchargedengine when under full load (i.e. on boost). This is because the excessexhaust heat and pressure, which would normally be wasted,

contributes some of the work required to compress the air.

Weight/Packaging. Smaller and lighter than alternative forced inductionsystems and may be more easily fitted in an engine bay.

Fuel Economy. Although adding a turbocharger itself does not save fuel,

it will allow a vehicle to use a smaller engine while achieving power levelsof a much larger engine, while attaining near normal fuel economy whileoff boost/cruising. This is because without boost, less fuel is used tocreate a proper air/fuel ratio

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Disadvantages

Lack of responsiveness if an incorrectly sized turbocharger is used. If a

turbocharger that is too large is used it reduces throttle response as it builds up boostslowly otherwise known as "lag". However, doing this may result in more peak power.

Boost threshold. A turbocharger starts producing boost only above a certain rpm due to alack of exhaust gas volume to overcome inertia of rest of the turbo propeller. This resultsin a rapid and nonlinear rise in torque, and will reduce the usable power band of theengine. The sudden surge of power could overwhelm the tires and result in loss of grip, which could lead to understeer/oversteer, depending on the drivetrain and suspension

setup of the vehicle. Lag can be disadvantageous in racing, if throttle is applied in a turn,power may unexpectedly increase when the turbo spools up, which can cause excessive wheelspin.

Cost. Turbocharger parts are costly to add to naturally aspirated engines. Heavily modifying OEM turbocharger systems also require extensive upgrades that in most casesrequires most (if not all) of the original components to be replaced.

Complexity. Further to cost, turbochargers require numerous additional systems if they are not to damage an engine. Even an engine under only light boost requires a system forproperly routing (and sometimes cooling) the lubricating oil, turbo-specific exhaustmanifold, application specific downpipe, boost regulation. In addition inter-cooled turboengines require additional plumbing, while highly tuned turbocharged engines willrequire extensive upgrades to their lubrication, cooling, and breathing systems; whilereinforcing internal engine and transmission parts.

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TURBO RECOMMENDATIONS

The turbocharger is designed such that it will usually last as long as the engine. Itdoes not require any special maintenance; and inspection is limited to a few periodicchecks.

To ensure that the turbocharger's lifetime corresponds to that of the engine, thefollowing engine manufacturer's service instructions must be strictly observed:

Oil change intervals

Oil filter system maintenance

Oil pressure control

Air filter system maintenance

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FAILURE DIAGONSIS FOR TURBOCHARGER

If the engine does not operate properly, one should not assume that the turbocharger isthe cause of failure. It often happens that fully functioning turbochargers are replacedeven though the failure does not lie here, but with the engine.

Only after all these points have been checked, should one check the turbocharger forfaults. Since the turbocharger components are manufactured on high-precision machinesto close tolerances and the wheels rotate up to 300,000 rpm, turbochargers should beinspected by qualified specialists only.

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THANK YOU

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