TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /1 Unit 7Title: Turbo charging and SuperchargingGeneral objective:To understand the basic knowledge of supercharging andoperation of a turbochargerSpecific objectives:At the end of this unit you should be able to: 1. state the definition of supercharging. 2. identify the parts and operation of the mechanical root- type blower. 3. identify the parts and operation of a turbocharger. 4. draw a graph of turbo charging performance.
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /2 InputThis section introduces the subject matter that you are going to learn.7.0 Introduction In this unit we will discuss and study the evolution of automobile technology on how to increase the power output of a car. Many automobile engines today use superchargers to increase the amount of air going into the engine. Supercharging also helps to increase the horsepower characteristics of the engine. The most common type of supercharger is called a turbocharger. In addition, in some racing engines, mechanical roots-type blowers are used to increase the amount of air going into the engine. Unit 7 introduces the principle of turbocharging and explains the basic operations of the mechanical blower.7.1 Why Supercharging is being use in automobile industry today? With the increase use of fuel injection and computer controlled combustion systems, turbocharging have become common components in gasoline and diesel engines. In the past, only large engines had turbochargers. Today, with the precise control afforded by computers, turbochargers are making smaller engines more efficient and capable of producing more power. In this unit we will look at volume efficiency, factor of volume efficiency, head efficiency, turbochargers and supercharging.
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /37.2 Volume efficiency Another way to measure the efficiency of an engine is related to how easily air flows in and out of the engine. As the piston starts moving down on the intake stroke, air and fuel flow into the engine. As the engine increases in revolutions per minute, the intake valves are not opened for long. This means that the amount of air per time period may be less. Volume efficiency measures this condition. The formula for measuring volume efficiency is ; Volume efficiency = actual air used X 100 Maximum air possible 7.1 Example One engine speed 40 cubic inches of fuel mixture enters the cylinder but to completely fill the cylinder of 55 cubic,it needs volume efficiency; calculate the volume efficiency. As we know the formula is ; Volume efficiency = actual air used X 100 Maximum air possible 40 = × 100 55 = 90 %.
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /47.3 Factors of volume efficiency. The following are other factors that affect volume efficiency . 1. exhaust restriction. 2. air cleaner restriction. 3. carbon deposits on cylinder and valve. 4. shape and design of valve. 5. amount of restriction in the intake and exhaust port by curve. 6. shape of the intake exhausts manifolds. 7. temperature of the air.7.4 Supercharging What is supercharging?. This is the process of forcing air into an engine cylinder with an air pump. The forced air can come from a blower or turbocharger. The operation is, when the piston moves downward on the intake stroke, a vacuum is created. This vacuum causes air and fuel to be drawn into the engine. This process is called a naturally aspirated or normally aspirated engine. The amount of air that enters the engine is based on atmospheric pressure. Most engines are considered to be naturally aspirated. However, in smaller engines, there may be a lack of power for certain driving conditions. To overcome this lack of power, an engine can be supercharged. Supercharging an engine means to deliver a greater volume of air to the cylinders than the air delivered from the suction of the pistons alone. The engine is not naturally aspirated, it is supercharged. When more air is forced into cylinders, there must be a corresponding increase in fuel to maintain a 14.7 to 1 air-fuel ratio. If both these conditions occur, then a great increase in power will occur. In some cases, this system can increase 50% more power by supercharging an engine.
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /57.4.1 Parts and operation Supercharging have two important parts and they are: 7.4.1 Blower. Either a blower or turbocharger can be used to supercharge an engine. A blower is a mechanical air pump that forces air into the engine. It is driven by a set of gears or belts from the crankshaft. It produces a substantial friction loss on the engine because it requires horsepower from the engine to operate. Figure 7.3.1: Blower 7.4.2 : Root-Type blower There are several types of mechanical blower which can be used on engines. One most common blower is named after its inventor, the root- type blower. (Figure 7.4.2), the rotors act like a positive displacement air pump, drawing in huge amount of air, and forcing this air into the intake manifold.
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /6 Figure : 7.4.2 : The root –type blower
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /7 InputThis section introduces the subject matter that you are going to learn.7.5 Turbo charging principles A turbocharging is a device that uses exhaust gas, rather than engine power to turn an air pump or compressor. The air pump then forces an increased amount of air into the cylinders. Both diesel and gasoline engines in the automotive market use turbochargers. Figure 7.5.1a,b shows a typical schematic of air and exhaust in a turbocharged engine and Figure 7.5.2 is a complete turbo charging unit for the automobile. High velocity exhaust gases are released from the exhaust part. From here they pass through a turbine driven pump. Here the exhaust gas causes the exhaust turbine to turn rapidly. The exhaust turbine causes the intake compressor to turn rapidly too. As the compressor turbine turns, it draws in a large amount of fresh air. The intake of air is pressurized and forced into the intake port. The increase in pressure in the intake manifold is called boost. Boost may produce pressure in the intake manifold of about 6 to 10 psi or more, depending on the manufacturer. 7.5.1 Turbocharger contruction. Figure 7.5.3 shows a complete turbocharger. The shafts on the intake and xhaust turbines are connected together. The intake turbine acts as fan, causing the shaft to turn. Housing surrounds both turbines. Flanges are attached to the housing for mounting
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /8 Figure 7.5.1a: Blower housing Figure 7.5.1b: A turbocharging uses the exhaust gases to turn an air pump or Compressor. The compressor turbine forces extra air into the engine.
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /9 Figure 7.5.2: A complete turbocharger unit for an automobile.
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /10 Figure 7.5.3: A cutaway view of a turbocharger. Figure 7.5.4: Turbocharger located on the side the engine
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /11 Graph 7.1 : Graph of turbo charging performanceLegend of graph; Normal aspirated engine Turbocharged engine
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /127.6 Graph of turbo charging performance Graph 7.1 shows a comparison between a turbocharged and normally aspirated engine. Note that both the torque and horsepower have been increased at all RPM. For example, at 5,000 RPM the normally aspirated engine produces about 80 hp. At this RPM, the turbocharged engine can produce about 140 hp.
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /13 Activity 7BThe questions in this section test your understanding of the subjectmatter. You have to complete this section by following the instructionscarefully.7.1 Draw the Graph of turbo charging performance7.2 Label the components in Figure A.7.2 below; a f g b c j h d i e Figure A.7.2 : Turbocharger Check your answers…….
TURBOCHARGING AND SUPERCHARGING J3182 / UNIT7 /14 Self –AssessmentSelf-assessment evaluates your understanding of each unit.Question 7-1.List 7 factors of volume efficiencyQuestion 7-2.Define superchargerQuestion 7-3.Explain the principle of turbo chargingQuestion 7-4.Explain the out put graph of turbo charging performance Congratulations!!!! If your answers are correct you can proceed to the next unit. Good Luck!.