313190877-1-FSAE-Turbocharger-Design-and-Implementation.pdf | Turbocharger | Internal Combustion Engine

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FSAE Turbocharger Design and Implementation Kumar Joy Nag Indian Institute of Technology, Kharagpur ABSTRACT Formula SAE (FSAE) is a student design competition, organized by the Society of Automotive Engineers (SAE International). Teams from around the world compete to create the best, small, formula-style race car, which is meant to be evaluated from many differ
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  FSAE Turbocharger Design and Implementation Kumar Joy Nag Indian Institute of Technology, Kharagpur ABSTRACT Formula SAE (FSAE) is a student design competition, organized by the Society of Automotive Engineers (SAE International). Teams from around the world compete to create the best, small, formula-style race car, which is meant to be evaluated from many different perspectives as a production item. The goal of this project is to determine the performance gains associated with adding a turbocharger to a naturally aspirated engine, used in a Formula SAE race car. This involves selecting the correct turbocharger for the engine, designing and fabricating the entire turbo-system, selecting and configuring an engine management system, tuning various engine variables, and performing before and after tests to determine any performance gains. INTRODUCTION The primary goal of the project is to produce a working turbocharged system that meets all FSAE rules and can be implemented on our next car. This involves fully designing the system, acquiring all the necessary parts and assembling the system. The secondary goal of the project is to maximize the horsepower-to-weight ratio of the engine. This can be accomplished by maximizing the horsepower of the engine throughout the power band while minimizing the overall weight of the system’s components.   1.   TECHNICAL BACKGROUND This section contains the technical information about a turbocharger and the underlying rules to follow in FSAE. 1.1 Internal Combustion Engine The internal combustion engine is the powerhouse of a variety of machines and equipment ranging from small lawn equipment to large aircraft or boats. Given the focus of this paper, the most important machine powered by an internal combustion engine is the automobile. The engine literally provides the driving force of the car while also directly or indirectly powering just about every other mechanical and electrical system in the modern automobile. While there are several types of internal combustion engines that cover the aforementioned large range of applications, they all basically do the same thing. They all convert the chemical energy stored in a fuel of some kind into mechanical energy, which can then be converted into electrical gasoline engine are shown in Fig. 1. While the arrangement and number of the cylinders in an engine tends to vary, the parts that make up an individual cylinder remain pretty constant. The most significant component is the piston which is connected to the  crankshaft via a connecting rod. The motions of the piston and crankshaft are always related, with one always forcing the other to move. The two valves, intake and exhaust, at the top of the cylinder are opened and closed by separate camshafts that precisely control the timing of each valve’s movement. The spark plug at the top of the cylinder is powered by the engine battery and activated by the engine computer at the appropriate time. Finally, the entire cylinder is surrounded by coolant channels that run through the engine block to remove the massive amount of heat generated by the running engine energy. The 4-stroke gasoline engine is the most frequently used engine in cars and light trucks as well as in large boats and small aircraft. The major components of the cylinder of a 4-stroke gasoline engine are shown in Fig. 1. While the arrangement and number of the cylinders in an engine tends to vary, the parts that make up an individual cylinder remain pretty constant. The most significant component is the piston which is connected to the crankshaft via a connecting rod. The motions of the piston and crankshaft are always related, with one always forcing the other to move. The two valves, intake and exhaust, at the top of the cylinder are opened and closed by separate camshafts that precisely control the timing of each valve’s movement. The spark plug at the top of the cylinder is powered by the engine battery and activated by the engine computer at the appropriate time. Finally, the entire cylinder is surrounded by coolant channels that run through the engine block to remove the massive amount of heat generated by the running engine.   Figure 1- Components of a 4- stroke gasoline engine The four strokes of a 4-stroke gasoline engine, illustrated in Fig. 2, are intake, compression, power and exhaust. During the intake stroke, the camshaft opens the intake valve as the crankshaft lowers the piston, which allows the cylinder to be filled with a precise mixture of air and gasoline. Once the piston reaches the bottom of the cylinder, the camshaft closes the  intake valve. The piston is now at what is known as bottom dead centre, and the cylinder is completely filled with the air/fuel mixture. Figure 2- Engine cycle of a 4-stroke gasoline engine The compression stroke comes next. With both intake and exhaust valves closed, the crankshaft raises the piston, compressing the air/fuel mixture. When the piston has been raised to the top of the cylinder, it is said to be at top dead centre. Once the cylinder has reached top dead centre, the air/fuel mixture has been compressed as much as possible. The power stroke is next up. With the piston still at top dead centre and both valves closed, the spark plug fires, igniting the compressed air/fuel mixture. Once ignited, a flame begins to move through the mixture, causing it to expand downward smoothly. This expansion downward forces the piston to move down. This means that the piston is rotating to the crankshaft, whereas the rotation of the crankshaft moves the piston in the other three strokes. The fact that the piston is driving the crankshaft means that energy is being transferred to the crankshaft. This is how an internal combustion engine transforms chemical energy in the fuel into mechanical energy. The power stroke is completed once the expanding gases have forced the piston to bottom dead centre. The final stroke is the exhaust stroke. The camshaft opens the exhaust valve as the crankshaft raises the piston, which pushes the exhaust gases out of the cylinder. Once the piston has reached top dead centre, all of the exhaust gases have been removed from the cylinder. The cylinder is now ready to start the cycle over again with another intake stroke.  1.2   Forced Induction In automotive applications, forced induction quite literally means to force air into the engine. Under standard atmospheric conditions, the engine will naturally consume a volume of air equal to its engine displacement each time it completes its 4-stroke cycle and is said to be naturally aspirated. When some form of forced induction is added, the engine will be forced to consume a volume of air greater than its engine displacement each time it completes its 4-stroke cycle. While this may seem trivial, it is very significant and can result in large power gains for the engine. The method by which a 4-stroke gasoline engine converts chemical energy into mechanical energy is discussed in Section 1.1. It should be stated plainly that the chemical energy is found entirely within the fuel, and thus the power generated by the engine is directly related to how much fuel is in the cylinders during the power stroke. However, simply flooding the cylinder with gasoline will not result in more power but will manage to seriously damage the engine. The engine is designed to operate at a specific air/fuel ratio (AFR). What this means is that for every particle of fuel there needs to be a corresponding number of air molecules. If this ratio is disturbed, the engine will run lean (too little fuel) or rich (too much fuel), either one of which is bad for engine. The engine control unit (ECU) monitors the airflow into the engine and adjusts fuel injection accordingly to maintain a proper AFR. Thus the only way to really get more fuel into the cylinders, and enjoy the added power, is to increase the airflow into the engine, hence the importance of forced induction. Forced induction systems make use of a compressor to force more air into the cylinders of the engine. In order to maintain a proper AFR, the ECU tells the fuel injectors to spray more fuel into the cylinders, resulting in more power. The compressor is able to force more air into the cylinders by increasing the pressure of the ambient air before it enters the intake ports. With a constant cylinder volume, a lot more air can fit into the cylinder at 20psi than at atmospheric pressure, 14.7psi. An unavoidable therm odynamic result of increasing the air’s pressure is to also increase its temperature. The compressor thus raises both the pressure and the temperature of the air. The two most common types of forced induction are turbocharging and supercharging. Turbochargers and superchargers both use compressors to raise the pressure of the intake air as described above. These devices differ in the way by which they power the compressor. A turbocharger uses exhaust gases expelled from the cylinders to spin a turbine, which in turn powers the compressor. Figure 3 shows a cutaway view of a typical turbocharger. The black housing with red highlights on the left is the turbine. The grey housing with blue highlights on the right is the compressor. The yellow and green section in the middle contains the connecting shaft between the turbine and compressor with its bearings.
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