TURBOCHARGER: TURBINE WHEEL AND TURBINE HOUSINGREPORT SUBMITTED BY SAJI, JERIN THOMAS (5438079)Contents

1. List of Pictures

2. Introduction 1

3. Working Objectives 1

4. Turbocharger 24.1. Working 2

5. Functions of Turbine Components 35.1. Turbine Housing 35.2. Turbine Wheel 4

6. In-service conditions and loading 56.1. Turbine Housing 56.2. Turbine Wheel 5

7. Material selection for turbine components using CES software 67.1. Turbine Wheel 67.2. Turbine Housing 8

8. Surface consideration and treatments of turbine wheel And turbine housing 10

9. References 11LIST OF PICTURES

Figure1. Turbocharger. (Ecopoint, 2012) 2

Figure 2. Working of a Turbocharger in an engine. (Howstuffworks , n.d.) 3

Figure 3. Illustration of turbine housing showing A/R characteristics. (Honeywell International, 2012). 3

Figure 4. Turbocharger turbine wheel. (Diesel Power, 2013) 4

Figure 5. Graph of e / Versus K1c / 7

Figure 6. Graph of Price versus Density. 8

Figure 7. Graph of E / versus strain/ 9

Figure 8. Graph of Price versus Density. 10

Advanced Manufacturing Processes and MaterialsM11EKM

Advanced Manufacturing Processes and MaterialsM11EKM

Jerin Saji Thomas: 54380798Jerin Saji Thomas: 5438079

1. INTRODUCTION

Since 1945, due to the development in turbo charging technology the power output of the automobile engines has increased in a rapid manner. Turbochargers are mainly used in internal combustion engines with an idea of less fuel consumption, reduced noise level, high torque at low speed and increased engine performance. It is commonly used in engines designed for automobiles, ship and rail propulsion and industrial power generating sets. (Watson and Jonata, 1982).This course work discusses the functions of a turbocharger turbine wheel and turbine housing and shows how material is selected for the turbine components using CES software. Surface considerations affecting the component surface and appropriate surface treatments are also explained.

2. WORKING OBJECTIVES

To describe a turbocharger and discuss the functions of a turbocharger turbine components.

To understand the in-service conditions and loading modes of the turbine components operating under and evaluate the material characteristics.

To perform a material selection of turbine components using CES software.

Evaluate the surface considerations during the working cycles of the component and suggest appropriate surface treatments.

3. TURBOCHARGERA Turbocharger is an exhaust gas driven device which is used to make an engine more efficient and produce more power by burning extra amount of air-fuel ratio in the combustion cylinder of an engine. Turbocharged engines are more powerful than naturally aspirated engines since it burns more air and fuel in to the engine cylinders and thereby delivering more engine output.It is used in automobiles such as racing cars, ship and rail propulsion etc. (Watson and Jonata, 1982).

Figure1. Turbocharger. (Ecopoint , 2012)

3.1. WorkingA turbocharger consists of a turbine, central hub and a compressor. The turbine coverts the energy of exhaust gas into rotational motion of the shaft which in turn drives the compressor. The exhaust gas entering is concentrated at the center of the turbine by nozzle blade rings. The movement of the turbine wheels rotates the shaft and the compressor.

As the compressor rotates, air is sucked into the center of the impeller and due to heavy rotational motion an outward circumferential velocity is experienced. A radial velocity is gained and pushes the air further on to the inducer. Thereby, ambient air from the surrounding is compressed to high pressure and density and driven to inlet manifold of the engine cylinders. (Bright hub, 2012)

Figure 2. Working of a Turbocharger in an engine. (Howstuffworks, n.d.)

4. FUNCTIONS OF TURBINE COMPONENTSThe function of a turbocharger turbine is to convert the energy of exhaust gas from engine to mechanical energy to drive the turbocharger compressor. The turbocharger turbine mainly consists of turbine housing and a turbine wheel.

4.1. Turbine HousingThe turbine housing encloses the turbine wheel and acts as a protective shield. The exhaust gas enters the turbine wheel through the turbine housing and a temperature up to 950is generated. The turbine performance is greatly influenced by variation in A/R (Area/Radius) ratio of the housing as it is used to adjust the flow capacity of the turbine.

Figure 3. Illustration of turbine housing showing A/R characteristics.(Honeywell International, 2012).Smaller A/R ratio is used to increase the velocity of exhaust gas flowing in to the turbine wheel resulting in increased turbine power at low engine speeds. However the ultimate turbine wheel is flow capacity is reduced since the flow entering the wheel is tangential due to smaller A/R value. Thereby engines ability to produce better power at high speed is shattered due to increase in exhaust back pressure generation. Conversely using larger A/R ratio will lower exhaust gas velocity and the flow will be radial in fashion resulting in increase in turbine wheel flow capacity and reduced back pressure. Thus better power is achieved at high RPM.Turbocharger housing for commercial vehicles such as trucks are designed as double flow housing in which jet of two streams joins before entering the turbine wheel. Water cooled turbine housing is used for marine applications. Housing is coated with insulating materials to avoid creation of hot surfaces because hot surfaces can increase the risk of fire. (Honeywell International, 2012).

4.2. Turbine Wheel The turbocharger wheel is enclosed in a conical housing and converts the exhaust gas energy in to rotational energy of the shaft. The exhaust gas is made to concentrate on the center of the turbine wheel by a nozzle making the wheel to rotate which in turn rotates the shaft to drive the compressor. The amount of air entering the turbine wheel depends on the shape and size of the wheel. Turbine wheel gains higher speed of rotation when large amount of exhaust gas enters the wheel.

Figure 4. Turbocharger turbine wheel. (Diesel Power, 2013)Turbines are classified according to the flow patterns as axial flow turbines and radial flow turbines. Radial flow turbines are used in small turbochargers up to a wheel diameter of about 160mm and generate an engine output of approximately 1000KW per turbocharger. Axial flow turbines are used for larger units of wheel diameter from 300mm onwards. (BorgWarner Turbo Systems 2014)

5. INSERVICE CONDITIONS AND LOADING MODES

5.1. Turbine HousingThe turbo charging is getting more popular in connection with diesel and gasoline engines. Nowadays, by the advancement in engine technology the air ratio can be increased to a value between 0.9 and 1.0 by cooling a portion of air inside the engine and resulting in an achievement of fuel saving up to 20%. However, these can lead to an increase in exhaust gas temperature of up to 950in diesel engines and 1050 in gasoline engines. Thus, turbine housing should be designed to operate at high temperature environment and melting point of the material should be higher than the operating temperature. (BorgWarner Turbo Systems, n.d.).In addition during the working period of a turbocharger, turbocharger housing is continuously subjected to repeated heating and cooling cycles. When the engine is not started the temperature is at ambient temperature but this temperature may vary once the engine is ignited and increases to maximum value at higher working loads. The rise in temperature causes the housing to expand. After the engine is switched off, housing begins to cool down and contracts. The repeated contraction and expansion produces thermal fatigue cracking on the turbine housing. Thus, the housing material should have high thermal fatigue resistance, lower coefficient of expansion and high strength. (Anon., 2008).

5.2. Turbine WheelFrom the above study of working conditions of a turbine housing it is clear that the turbine wheel should be designed to withstand a high operating temperature as same as that of the housing since the air entering the turbine wheel has same temperature. The speed of the wheel depends on its size. A smaller wheel can rotate faster than a larger wheel and can reach a circumferential tip speed of 530 meter/sec. Thus a centrifugal stress is generated on the wheel and imposes huge tensile load as well as bending and vibratory loads.Materials with high density may be heavy and can create high centrifugal stress for higher speed of wheel rotation. In addition heavy weight can lead to turbo lag. Commonly used material is Titanium alloys and has significantly lower density (about 4g/) and thus produce lower inertia and reduced turbo lag compared to other materials (Anon., 2013).Thus it can be inferred that the turbine wheel material should be of low density, high heat resistant, high strength to withstand high stress and highly ductile.

6. MATERIAL SELECTION FOR TURBINE COMPONENTS USING CES SOFTWARE

6.1. Turbine Wheel

Material Indices Used:{K1c /} and {e /}

Where, K1c is the Fracture Toughness in ksi.in^0.5 is the Density in lb/ft^3 e is the Fatigue Strength at 10^7 cycles in ksi.

For all the following graphs: Maximum Service Temperature is taken to be 950 (Honeywell International Inc 2012).

Density of the turbine conventional wheel material vary from 180 to 480lb/ft^3 and an average value 250lb/ft^3 is taken (Anon., 2013).

Price is in (USD/lb).

Figure 5. Graph of e / Versus K1c /

Figure 6. Graph of Price versus Density.

From the above graphs we can infer, in the order of decrement relative to cost/lb, Aluminium nitride, Boron carbide, Silicon nitride, Silicon carbide and Alumina are among the wide range of materials that can combat the various mechanical and thermal loads of turbine wheel. Hence the most dependable material out of all the above determined would be Silicon carbide.

6.2. Turbine Housing

Material Indices Used:{E /}

Where,E is the Youngs Modulus in 10^6 psi. is the Density in lb/ft^3.Price is in (USD/lb).

For all the following graphs: Maximum Service Temperature is taken to be 950 (Honeywell International, 2012).

Density is assumed to be greater than turbine wheel. Therefore the minimum density is taken as 250 lb/ft^3.

Price is in (USD/lb).

Figure 7. Graph of E / versus strain/Figure 8. Graph of Price versus Density.From the above graphs for the turbine housing it can be interpreted that Tungsten alloys, Nickel-based superalloys and Tungsten carbides exhibits the material characteristics required to withstand high mechanical loads and temperature variations. Hence considering all material properties and also the price, the best material for the turbine housing would be Nickel-based superalloys.

7. SURFACE CONSIDERATIONS AND TREATMENTS OF TURBINE WHEEL AND TURBINE HOUSINGTurbocharger turbine wheel and housing are subjected to operate at high temperature and corrosive environment. The gas entering the turbine may be corrosive in nature. Nickel based superalloys provide adequate resistance to corrosion at elevated temperatures above 950 but fails at low temperature as 650.Materials are made applicable to operate at certain conditions by adequate providing surface treatments. For high performance application, turbocharger turbine material is subjected to shot peening process. Shot peening involves controlled bombardment of spherical steel balls or ceramic blades on the material to produce plastic yield at the surface.Shot peening removes residual stresses induced during material manufacturing. Sand blasting is done to remove contaminants and to smooth the rough surfaces. (Waterhouse and Niku-Lari, 1988)

8. REFERENCESAnon. (2008) Turbine housing for a turbocharger [online] available from https://www.google.com/patents/WO2008009936A1?dq=turbocharger+turbine+housing+materials&ei=2yX9UomLMZOqhAf7p4DgDw&cl=en [15 February 2014]Anon. (2013) A low steel turbocharger turbine wheel having a threaded through bore mount [online] available from https://www.google.com/patents/WO2013165840A1?cl=en&dq=turbocharger+turbine+wheel+materials&hl=en&sa=X&ei=BSP9UpqENc2qhQf48IDQAQ&ved=0CDMQ6AEwAA%20 [15 February 2014]BorgWarner Turbo Systems (2014) Design and Function of a Turbocharger: Turbine [online] available from http://www.turbos.bwauto.com/en/products/turbochargerTurbine.aspx [12 February 2014]Bright hub (2012) Components of a Turbocharger [online] available from http://www.brighthubengineering.com/marine-engines-machinery/41368-components-of-a-turbocharger/ [05 February 2014]BorgWarner Turbo Systems (n.d.) Turbocharger for an exhaust temperature of 1050C [online] available from http://www.3k-warner.de/products/turbochargerExhaustTemperature.aspx [12 February 2014]Diesel Power (2013) Turbochargers: How They Work Photo Gallery [online] available from http://www.dieselpowermag.com/tech/1311_november_2013_basic_training_turbochargers_how_they_work/photo_02.html [10 February 2014]Ecopoint (2012) Turbocharger Fundamentals [online] available from https://www.dieselnet.com/tech/air_turbocharger.php [02 February 2014] Honeywell International (2012) Turbine housing A/R and sizing [online] available from http://www.turbobygarrett.com/turbobygarrett/turbine_housing_AR_and_housing_sizing [05 February 2014]Howstuffworks (n.d.) How Turbochargers Work [online] available from http://auto.howstuffworks.com/turbo2.htm [10 February 2014] Waterhouse, R.B. and Niku-Lari, A. (1988) Metal, Treatments Against Wear Corrosion, Fretting and Fatigue. England: Pergamon Press.Watson, N. and Janota, M.S. (1982) Turbocharging the Internal Combustion Engine. London: Macmillan Education ltd.