Turbochargers,Final Report of the Seminar

TURBOCHARGERS

1. INTODUCTION A naturally-aspirated engine is one common type reciprocating piston I.C engine that depends solely on atmospheric pressure to counter the partial vacuum in the induction tract to draw in combustion air. In a naturally aspirated engine; air for combustion or an air/fuel mixture is drawn into the engines cylinders by atmospheric pressure acting against a partial vacuum that occurs as the piston travels downwards toward bottom dead centre during the induction stroke. Due to restriction at intake track, a small pressure drop occurs as air is drawn in, resulting in a volumetric efficiency of less than 100 percent - and a less than complete air charge in the cylinder. A supercharger is an air compressor used for forced induction of an internal combustion engine . The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally-aspirated engine, which allows more fuel to be provided and more work to be done per cycle, increasing the power output of the engine. A supercharger can be powered mechanically by a belt, gear, shaft, or chain connected to the engine's crankshaft. It can also be powered by an exhaust gas turbine. A turbine-driven supercharger is known as a turbocharger.

Figure 1: General setup of supercharger is shown.

A turbocharger is a small radial fan pump driven by the energy of the exhaust gases of an engine. A turbocharger consists of a turbine and a compressor on a shared shaft. The turbine DEPARTMENT OF MECHANICAL ENGINEERING

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converts exhaust heat to rotational force, which is in turn used to drive the compressor. The compressor draws in ambient air and pumps it in to the intake manifold at increased pressure, resulting in a greater mass of air entering the cylinders on each intake stroke. The pressure in the atmosphere is no more than 1atm ,there ultimately will be a limit to the pressure difference across the intake valves and thus the amount of airflow entering the combustion chamber. Because 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 manifold pressure increases. The additional air flow makes it possible to maintain the combustion chamber pressure and fuel/air load even at high engine revolution speeds, increasing the power and torque output of the engine. The increase in the inlet pressure of air by any means is called as boost.

Figure 2: General setup of turbocharger is shown. 1 Compressor Inlet 2 Compressor Discharge 3 Charge air cooler (CAC) 4 Intake Valve 5 Exhaust Valve 6 Turbine Inlet 7 Turbine Discharge

2. HISTORICAL PERSPECTIVE The turbocharger was invented by Swiss engineer Alfred Büchi. His patent for a turbocharger was applied for use in 1905. Diesel ships and locomotives with turbochargers began appearing in the 1920s.

2.1 AVIATION: DEPARTMENT OF MECHANICAL ENGINEERING

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During the First World War French engineer Auguste Rateau fitted turbochargers to Renault engines powering various French fighters with some success. In 1918, General Electric engineer Sanford Moss attached a turbo to a V12 Liberty aircraft engine. The engine was tested at Pikes Peak in Colorado at 14,000 feet (4,300 m) to demonstrate that it could eliminate the power losses usually experienced in internal combustion engines as a result of reduced air pressure and density at high altitude. Turbochargers were first used in production aircraft engines in the 1920s before World War II, although they were less common than engine-driven centrifugal superchargers. The primary purpose behind most aircraft-based applications was to increase the altitude at which the airplane could fly, by compensating for the lower atmospheric pressure present at high altitude. Aircraft such as the Fw 190D, B-17 Flying Fortress, and P-47 Thunderbolt all used turbochargers to increase high altitude engine power.

2.2 PRODUCTION AUTOMOBILES: The first turbocharged diesel truck was produced by Schweizer Maschinenfabrik Saurer (Swiss Machine Works Saurer) in 1938. The first production turbocharged automobile engines came from General Motors in 1962. The Y-body Oldsmobile Cutlass Jetfire was fitted with a Garrett Air search turbocharger and the Chevrolet Corvair Monza Spyder with a TRW turbocharger. At the Paris auto show in 1974, during the height of the oil crisis, Porsche introduced the 911 Turbo – the world’s first production sports car with an exhaust turbocharger and pressure regulator. This was made possible by the introduction of a waste gate to direct excess exhaust gasses away from the exhaust turbine. The world's first production turbo diesel automobiles were the Garrettturbocharged Mercedes 300SD and the Peugeot 604, both introduced in 1978. Today, most automotive diesels are turbocharged. 1962 Oldsmobile Cutlass Jetfire 1962 Chevrolet Corvair Monza Spyder 1973 BMW 2002 Turbo 1974 Porsche 911 Turbo 1978 Buick Regal 1978 Saab 99 1978 Peugeot 604 turbo diesel 1978 Mercedes-Benz 300SD turbo diesel (United States/Canada) 1979 Alfa Romeo Alfetta GTV 2000 Turbo delta 1980 Mitsubishi Lancer GT Turbo 1980 Pontiac Firebird DEPARTMENT OF MECHANICAL ENGINEERING

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1980 Renault 5 Turbo 1981 Volvo 240-series Turbo

3 . NOMENCLATURE Early manufacturers of turbochargers referred to them as "turbosuperchargers". A supercharger is an air compressor used for forced induction of an engine. Logically then, adding a turbine to turn the supercharger would yield a "turbo supercharger". However, the term was soon shortened to "turbocharger". This is now a source of confusion, as the term "turbosupercharged" is sometimes used to refer to an engine that uses both a crank shaft driven supercharger and an exhaust-driven turbocharger. Some companies such as Teledyne Continental Motors still use the term turbosupercharger in its original sense.

Figure 4

4. 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 turbine and a compressor on a shared shaft. The turbine converts exhaust heat to rotational force, which is in turn used to drive the compressor. The compressor draws in ambient air and pumps it in to 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 aspirated automobile engine uses only the downward stroke of a piston to create an area of low pressure in order to draw air into the cylinder through the intake valves. Because the pressure in the atmosphere is no more than 1 atm (approximately 14.7 psi), there ultimately will be a limit to the pressure difference across the intake valves and thus the amount of airflow entering the combustion chamber. Because the turbocharger increases the DEPARTMENT OF MECHANICAL ENGINEERING

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pressure at the point where air is entering the cylinder, a greater mass of air (oxygen) will be forced in as the inlet manifold pressure increases. The additional air flow makes it possible to maintain the combustion chamber pressure and fuel/air load even at high engine revolution speeds, increasing the power and torque output of the engine. Because the pressure in the cylinder must not go too high to avoid detonation and physical damage, the intake pressure must be controlled by venting excess gas. The control function is performed by a waste gate, which routes some of the exhaust flow away from the turbine. This regulates air pressure in the intake manifold.

Figure 5

5. COMPONENTS OF A TURBOCHARGER

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Figure 6: Component of turbocharger

The turbocharger has four main components. The turbine (almost always a radial turbine) and impeller/compressor wheels are each contained 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 and shape 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 and sometimes 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 relative efficiency at which they operate. Generally, the larger the turbine wheel and compressor wheel, the larger the flow capacity. Measurements and 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, in automotive applications the CHRA typically uses a thrust bearing or ball bearing lubricated by a constant supply of pressurized engine oil. The CHRA may also be considered "water cooled" by having an entry and exit point for engine coolant to be cycled. Water cooled models allow engine coolant to be the DEPARTMENT OF MECHANICAL ENGINEERING

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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 in more detail in subsequent tutorials; however, it is important to understand the need for a compressor bypass valve (commonly referred to as a Blow-Off valve) on the intake tract and a Waste gates for the exhaust flow.

5.1 TURBINE HOUSING: Turbine housings are manufactured in various grades of spheroidal graphite iron to deal with thermal fatigue and wheel burst containment. As with the impeller, profile machining to suit turbine blade shape is carefully controlled for optimum performance. The turbine housing inlet flange acts as the reference point for fixing turbocharger position relative to its installation. It is normally the load bearing surfaces.

Figure 7: - Turbine housing

5.2 WHEEL: The Turbine Wheel is housed in the turbine casing and is connected to a shaft that in turn rotates the compressor wheel.

Figure 8: Wheel DEPARTMENT OF MECHANICAL ENGINEERING

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5.3 COMPRESSOR COVER: Compressor housings are also made in cast aluminum. Various grades are used to suit the application. Both gravity die and sand casting techniques are used. Profile machining to match the developed compressor blade shape is important to achieve performance consistency.

Figure: - 9 Compressor cover

5.4 COMPRESSOR WHEEL (IMPELLER):-

Figure:-10 Compressor wheel Compressor impellers are produced using a variant of the aluminum investment casting process. A rubber former is made to replicate the impeller around which a casting mould is created. The rubber former can then be extracted from the mould into which the metal is poured. Accurate blade sections and profiles are important in achieving compressor performance. Back face profile machining optimizes impeller stress conditions. Boring to tight tolerance and burnishing assist balancing and fatigue resistance. The impeller is located on the shaft assembly using a threaded nut.

5.5 BLOW OFF VALVES ( BY-PASS):

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Figure 11: by pass system

The Blow-Off valve (BOV) is a pressure relief device on the intake tract to prevent the turbo compressor from going into surge. The BOV should be installed between the compressor discharge and the throttle body, preferably downstream of the charge air cooler (if equipped). When the throttle is closed rapidly, the airflow is quickly reduced, causing flow instability and pressure fluctuations. These rapidly cycling pressure fluctuations are the audible evidence of surge. Surge can eventually lead to thrust bearing failure due to the high loads associated with it. Blow-Off valves use a combination of manifold pressure signal and spring force to detect when the throttle is closed. When the throttle is closed rapidly, the BOV vents boost in the intake tract to atmosphere to relieve the pressure; helping to eliminate the phenomenon of surge.

5.6 WASTE GATES:

Figure 12: waste gate DEPARTMENT OF MECHANICAL ENGINEERING

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TURBOCHARGERS

On the exhaust side, a Waste gate provides us a means to control the boost pressure of the engine. Some commercial diesel applications do not use a Waste gate at all. This type of system is called a free-floating turbocharger. However, the vast majority of gasoline performance applications require Waste gates. There are two (2) configurations of Waste gates, internal or external. Both internal and external Waste gates provide a means to bypass exhaust flow from the turbine wheel. Bypassing this energy (e.g. exhaust flow) reduces the power driving the turbine wheel to match the power required for a given boost level. Similar to the BOV, the Waste gates uses boost pressure and spring force to regulate the flow bypassing the turbine. Internal Waste gate are built into the turbine housing and consist of a “flapper” valve, Crank arm, rod end, and pneumatic actuator. It is important to connect this actuator only to boost pressure; i.e. it is not designed to handle vacuum and as such should not be referenced to an intake manifold. External Waste gates are added to the exhaust plumbing on the exhaust manifold or header. The advantage of external Waste gates is that the bypassed flow can be reintroduced into the exhaust stream further downstream of the turbine. This tends to improve the turbine’s performance. On racing applications, this Waste gated exhaust flow can be vented directly to atmosphere.

5.7 OIL WATER PLUMBING: The intake and exhaust plumbing often receives the focus leaving the oil and water plumbing neglected. Garrett ball bearing turbochargers require less oil than journal bearing turbo. Therefore an oil inlet restrictor is recommended if you have oil pressure over about 60 psig. The oil outlet should be plumbed to the oil pan above the oil level (for wet sump systems). Since the oil drain is gravity fed, it is important that the oil outlet points downward, and that the drain tube does not become horizontal or go “uphill” at any point. Following a hot shutdown of a turbocharger, heat soak begins. This means that the heat in the head, exhaust manifold, and turbine housing finds its way to the turbo center housing, raising its temperature. These extreme temperatures in the center housing can result in oil coking. To minimize the effects of heat soak-back, water-cooled center housings were introduced. These use coolant from the engine to act as a heat sink after engine shutdown, preventing the oil from coking. The water lines utilize a thermal siphon effect to reduce the peak heat soakback temperature after key-off. The layout of the pipes should minimize peaks and troughs with the (cool) water inlet on the low side. To help this along, it is advantageous to tilt the turbocharger about 25° about the axis of shaft rotation. Many Garrett turbo are water-cooled for enhanced durability.

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5.8 BEARING HOUSING:

Figure 13: bearing A grey cast iron bearing housing provides locations for a fully floating bearing system for the shaft, turbine and compressor which can rotate at speeds up to 170,000 rev/min. Shell molding is used to provide positional accuracy of critical features of the housing such as the shaft bearing and seal locations. CNC machinery mills, turns, drills and taps housing faces and connections. The bore is finish honed to meet stringent roundness, straightness and surface finish specifications.

5.9 BEARING SYSTEM:

Figure 14: bearing system The bearing system has to withstand high temperatures, hot shut down, soot loading in the oil, contaminants, oil additives, dry starts. Journal bearings are manufactured from specially developed bronze or brass bearing alloys. The manufacturing process is designed to create geometric tolerances and surface finishes to suit very high speed operation. Hardened steel thrust collars and oil slingers are manufactured to strict tolerances using lapping. End thrust is absorbed in a bronze hydrodynamic thrust bearing located at the compressor end of the shaft assembly. Careful sizing provides adequate load bearing capacity without excessive losses. DEPARTMENT OF MECHANICAL ENGINEERING

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6. CHARGE COOLING Compressing air in the turbocharger increases its temperature, which can cause a number of problems. Excessive charge air temperature can lead to detonation, which is extremely destructive to engines. When a turbocharger is installed on an engine, it is common practice to fit the engine with an intercooler, a type of heat exchanger which gives up heat energy in the charge to the ambient air. In cases where an intercooler is not a desirable solution, it is common practice to introduce extra fuel into the charge for the sole purpose of cooling. The extra fuel is not burned. Instead, it absorbs and carries away heat when it changes phase from liquid to vapor. The evaporated fuel holds this heat until it is released in the exhaust stream. This thermodynamic property allows manufacturers to achieve good power output by using extra fuel at the expense of economy and emissions.

Figure 14: cooling system

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7. PEFORMANCE TURBOCHARGING

CURVES

OF

ENGINES

AFTER

7.1TORQUE & POWER VARIATION

Figure 15

7.2 INTAKE PRESSURE VARIATION

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Figure 16:

7.3 ENGINE SPEED V/S TURBINE SPEED:

Y axes: -Turbine speed (rpm) X axes: -Pressure (bar)

SR. NO

TURBINE SPEED

TURBOCHARGER PRESSURE

1 2 3 4 5 6

0 65 140 300 465 625

0 0.15 0.35 0.75 1.10 1.60

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Figure 17

7.4 ENGINE SPEED V/S TURBOCHARGER OUTLET PRESSURE (bar): X axes: -Engine speed (rpm) Y axes: -Pressure (bar)

SR. NO.

ENGINE SPEED

TURBOCHARGER PRESSURE

1 2 3 4 5 6

0 500 1000 2000 3000 4000

0 0.15 0.35 0.75 1.10 1.60

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Figure 18

8.ADVANTAGES: (1) More specific power over naturally aspirated engine. This means a turbocharged engine can achieve more power from same engine volume. (2) Better thermal efficiency over both naturally aspirated and supercharged engine when under full load (i.e. on boost). This is because the excess exhaust heat and pressure, which would normally be wasted, contributes some of the work required to compress the air. (3) Weight/Packaging. Smaller and lighter than alternative forced induction systems and may be more easily fitted in an engine bay. (4) Fuel Economy. Although adding a turbocharger itself does not save fuel, it will allow a vehicle to use a smaller engine while achieving power levels of a much larger engine, while attaining near normal fuel economy while off boost/cruising. This is because without boost, less fuel is used to create a proper air/fuel ratio.

9. DISADVANTAGES 1. 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 boost slowly otherwise known as "lag". However, doing this may result in more peak power. 2. Boost threshold- A turbocharger starts producing boost only above a certain rpm due to a lack of exhaust gas volume to overcome inertia of rest of the turbo propeller. This results in a DEPARTMENT OF MECHANICAL ENGINEERING

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rapid and nonlinear rise in torque, and will reduce the usable power band of the engine. The sudden surge of power could overwhelm the tires and result in loss of grip, which could lead to under steer/over steer, depending on the drive train 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 wheel spin. 3. Cost- Turbocharger parts are costly to add to naturally aspirated engines. Heavily modifying OEM turbocharger systems also require extensive upgrades that in most cases requires most (if not all) of the original components to be replaced.

4. 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 for properly routing (and sometimes cooling) the lubricating oil, turbo-specific exhaust manifold, application specific downpipe, boosts regulation. In addition inter-cooled turbo engines require additional plumbing, while highly tuned turbocharged engines will require extensive upgrades to their lubrication, cooling, and breathing systems; while reinforcing internal engine and transmission parts.

10. COMPARISON TO SUPERCHARGING A supercharger inevitably requires some energy to be bled from the engine to drive the supercharger. On the single-stage single-speed supercharged Rolls Royce Merlin engine for instance, the supercharger uses up about 150 horsepower (110 kW). Yet the benefits out weigh the costs, for that 150 hp (110 kW), the engine generates an additional 400horsepower and delivers 1,000 hp (750 kW) when it would otherwise deliver 750 hp(560 kW), a net gain of 250 hp (190 kW). This is where the principal disadvantage of a supercharger becomes apparent: The engine has to burn extra fuel to provide power to turn the supercharger. The increased charge density increases the engine's specific power and power to weight ratio, but also increases the engine's specific fuel consumption. This increases the cost of running the aircraft and reduces its overall range. On the other hand, a turbocharger is driven using the exhaust gases. Otherwise wasted heat is extracted from the exhaust gas, and converted to useful power to compress the intake air. The turbine section of the turbocharger is actually a heat engine in itself. It converts the heat of the exhaust into power used to drive the compressor, thereby providing a more efficient compression of the intake air than can happen with supercharger, which uses up net engine power to drive its air compressor.

11. TURBO LAG AND BOOST The time required to bring the turbo up to a speed where it can function effectively is called turbo lag. This is noticed as a hesitation in throttle response when DEPARTMENT OF MECHANICAL ENGINEERING

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coming off idle. This is symptomatic of the time taken for 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. The directly-driven compressor in a supercharger does not suffer from this problem. (Centrifugal superchargers do not build boost at low rpm as a positive displacement supercharger will). Conversely on light loads or at low RPM a turbocharger supplies less boost and the engine acts like a naturally aspirated engine. Turbochargers start producing boost only above a certain exhaust mass flow rate (depending on the size of the turbo) which is determined by the engine displacement, rpm, and throttle opening. Without an appropriate exhaust gas flow, they logically cannot force air into the engine. The point at full throttle in which the mass flow in the exhaust is strong enough to force air into the engine is known as the boost threshold rpm. Engineers have, in some cases, been able to reduce the boost threshold rpm to idle speed to allow for instant response. Both Lag and Threshold characteristics can be acquired through the use of a compressor map and a mathematical equation.

12. CONCLUSION Here the main aim is to effectively utilize the non renewable energy such as petrol and diesel. Complete combustion of the fuels can be achieved. Power output can be increased.Wind energy can be used for air compression. We conclude that the power as well as the efficiency is increasing 10 to 15 % and pollution can also decrease. From the observation we can conclude that when the full throttle valve is open at that time the engine speed is 4000 rpm and by this the turbocharger generate 1.60 bar pressurized air. Generally the naturally aspirated engine takes atmospheric pressurized air to the carburetor for air fuel mixture but we can add the high density air for the combustion so as the result the power and the complete combustion take place so efficiency is increasing.

14. REFERENCES 1. Http://en.wikipedia.org/wiki/Turbocharger (Wikipedia, the free encyclopedia) 2. I.C Engines, Colin, R. Ferguson C. John Wiley & Sons, 1986 3. I C Engines , Shyam K Agarwal , New Age Publications,2006 4. Automobile Engineering By R.B. Gupta 5. Automobile nengineering ,R. K. Rajput , Laxmi Publications

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