Diesel Engine Fundamentals Quiz
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Question 1 of 20
1. Question
The Compression Ratio is,
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The greater combustion pressure is the result of the higher compression ratio used by diesel engines. The compression ratio is a measure of how much the engine compresses the gasses in the engine’s cylinder. In a gasoline engine the compression ratio (which controls the compression temperature) is limited by the air-fuel mixture entering the cylinders. The lower ignition temperature of gasoline will cause it to ignite (burn) at a compression ratio of less than 10:1. The average car has a 7:1 compression ratio. In a diesel engine, compression ratios ranging from 14:1 to as high as 24:1 are commonly used. The higher compression ratios are possible because only air is compressed, and then the fuel is injected. This is one of the factors that allows the diesel engine to be so efficient. Compression ratio will be discussed in greater detail later in this course.
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Question 2 of 20
2. Question
True or False. Diesel Engines are self-speed-limiting because the air (oxygen) entering the engine is always the maximum amount.
CorrectIncorrectHint
Diesel engines are not self-speed-limiting because the air (oxygen) entering the engine is always the maximum amount. Therefore, the engine speed is limited solely by the amount of fuel injected into the engine cylinders. Therefore, the engine always has sufficient oxygen to burn and the engine will attempt to accelerate to meet the new fuel injection rate. Because of this, a manual fuel control is not possible because these engines, in an unloaded condition, can accelerate at a rate of more than 2000 revolutions per second. Diesel engines require a speed limiter, commonly called the governor, to control the amount of fuel being injected into the engine.
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Question 3 of 20
3. Question
True or False. A diesel engine differs from a typical gasoline engine because the fuel that is injected into the diesel engine vaporizes and ignite due the heat created by the compression of the air in the cylinder
CorrectIncorrectHint
Unlike a gasoline engine, a diesel engine does not require an ignition system because in a diesel engine the fuel is injected into the cylinder as the piston comes to the top of its compression stroke. When fuel is injected, it vaporizes and ignites due to the heat created by the compression of the air in the cylinder.
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Question 4 of 20
4. Question
The _________________ provides the structure and rigid frame for the engine cylinders, water coolant and oil passages, and support for the crankshaft and camshaft bearings.
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The cylinder block, as shown in Figure 4, is generally a single unit made from cast iron. In a liquid-cooled diesel, the block also provides the structure and rigid frame for the engine’s cylinders, water coolant and oil passages, and support for the crankshaft and camshaft bearings.
Figure 4 The Cylinder Block -
Question 5 of 20
5. Question
The _________________ provides the engine with the cylindrical structure needed to confine the combustion gases and to act as a guide for the engine’s pistons.
CorrectIncorrectHint
Diesel engines use one of two types of cylinders. In one type, each cylinder is simply machined or bored into the block casting, making the block and cylinders an integral part. In the second type, a machined steel sleeve is pressed into the block casting to form the cylinder. Figure 2 and Figure 3 provide examples of sleeved diesel engines. With either method, the cylinder sleeve or bore provides the engine with the cylindrical structure needed to confine the combustion gasses and to act as a guide for the engine’s pistons.
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Question 6 of 20
6. Question
True or False. A wet cylinder sleeve comes into contact with the engine’s coolant (water) and a dry cylinder sleeve does not.
CorrectIncorrectHint
In engines using sleeves, there are two types of sleeves, wet and dry. A dry sleeve is surrounded by the metal of the block and does not come in direct contact with the engine’s coolant (water). A wet sleeve comes in direct contact with the engine’s coolant. Figure 5 provides an example of a wet sleeve. The volume enclosed by the sleeve or bore is called the combustion chamber and is the space where the fuel is burned.
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Question 7 of 20
7. Question
Each piston has several metal rings around it, these rings help to,
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These rings function as the seal between the piston and the cylinder wall and also act to reduce friction by minimizing the contact area between the piston and the cylinder wall. The rings are usually made of cast iron and coated with chrome or molybdenum. Most diesel engine pistons have several rings, usually 2 to 5, with each ring performing a distinct function. The top ring(s) acts primarily as the pressure seal. The intermediate ring(s) acts as a wiper ring to remove and control the amount of oil film on the cylinder walls. The bottom ring(s) is an oiler ring and ensures that a supply of lubricating oil is evenly deposited on the cylinder walls.
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Question 8 of 20
8. Question
The area round the crankshaft and the crankshaft bearings is called the,
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The crankcase is usually located on the bottom of the cylinder block. The crankcase is defined as the area around the crankshaft and crankshaft bearings. This area encloses the rotating crankshaft and crankshaft counterweights and directs returning oil into the oil pan. The oil pan is located at the bottom of the crankcase as shown in Figure 2 and Figure 3. The oil pan collects and stores the engine’s supply of lubricating oil. Large diesel engines may have the oil pan divided into several separate pans.
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Question 9 of 20
9. Question
The _________________ collects and stores the engine’s supply of lubricating oil.
CorrectIncorrectHint
The oil pan collects and stores the engine’s supply of lubricating oil. Large diesel engines may have the oil pan divided into several separate pans.
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Question 10 of 20
10. Question
The _________________ transforms the energy of the expanding gasses into mechanical energy.
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The piston transforms the energy of the expanding gasses into mechanical energy. The piston rides in the cylinder liner or sleeve as shown in Figure 2 and Figure 3. Pistons are commonly made of aluminum or cast-iron alloys.
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Question 11 of 20
11. Question
The _________________ connects the piston to the crankshaft.
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The connecting rod connects the piston to the crankshaft. See Figure 2 and Figure 3 for the location of the connecting rods in an engine. The rods are made from drop-forged, heat-treated steel to provide the required strength. Each end of the rod is bored, with the smaller top bore connecting to the piston pin (wrist pin) in the piston as shown in Figure 6. The large bore end of the rod is split in half and bolted to allow the rod to be attached to the crankshaft. Some diesel engine connecting rods are drilled down the center to allow oil to travel up from the crankshaft and into the piston pin and piston for lubrication.
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Question 12 of 20
12. Question
The _________________ transforms the linear motion of the pistons into a rotation motion that is transmitted to the load.
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The crankshaft transforms the linear motion of the pistons into a rotational motion that is transmited to the load. Crankshafts are made of forged steel. The forged crankshaft is machined to produce the crankshaft bearing and connecting rod bearing surfaces. The rod bearings are eccentric, or offset, from the center of the crankshaft as illustrated in Figure 7. This offset converts the reciprocating (up and down) motion of the piston into the rotary motion of the crankshaft. The amount of offset determines the stroke (distance the piston travels) of the engine (discussed later).
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Question 13 of 20
13. Question
The _________________ allows for all components of the diesel engine to perform their function at very precise intervals in relation to the motion of the piston.
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In order for a diesel engine to operate, all of its components must perform their functions at very precise intervals in relation to the motion of the piston. To accomplish this, a component called a camshaft is used. Figure 9 illustrates a camshaft and camshaft drive gear. Figure 2 and Figure 3 illustrate the location of a camshaft in a large overhead cam diesel engine.
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Question 14 of 20
14. Question
The _________________ are mechanically opened and closed to admit or exhaust the gasses as needed.
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Figure 10 Diesel Engine Valve Train
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Question 15 of 20
15. Question
What two purposes does the fuel serve in a Diesel Engine?
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In a diesel engine, the fuel system is much more complex than the fuel system on a simple gasoline engine because the fuel serves two purposes. One purpose is obviously to supply the fuel to run the engine; the other is to act as a coolant to the injectors. To meet this second purpose, diesel fuel is kept continuously flowing through the engine’s fuel system at a flow rate much higher than required to simply run the engine, an example of a fuel flowpath is shown in Figure 13. The excess fuel is routed back to the fuel pump or the fuel storage tank depending on the application.
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Question 16 of 20
16. Question
True or False. The highest point of travel by the piston is called top dead center (TDC) and the lowest point of travel is called bottom dead center (BDC).
CorrectIncorrectHint
Bore and stroke are terms used to define the size of an engine. As previously stated, bore refers to the diameter of the engine’s cylinder, and stroke refers to the distance the piston travels from the top of the cylinder to the bottom. The highest point of travel by the piston is called top dead center (TDC), and the lowest point of travel is called bottom dead center (BDC). There are 180o of travel between TDC and BDC, or one stroke.
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Question 17 of 20
17. Question
_________________ is a measure of the engine’s ability to apply the power it is generating.
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Engines are rated not only in horsepower but also by the torque they produce. Torque is a measure of the engine’s ability to apply the power it is generating. Torque is commonly given in units of lb-ft.
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Question 18 of 20
18. Question
True or False. Like the four-stroke engine, the two-stroke engine must go through the same four events: intake, compression, power, and exhaust but a two stroke engine requires only two strokes of the piston to complete one full cycle.
CorrectIncorrectHint
Like the four-stroke engine, the two-stroke engine must go through the same four events: intake, compression, power, and exhaust. But a two- stroke engine requires only two strokes of the piston to complete one full cycle. Therefore, it requires only one rotation of the crankshaft to complete a cycle. This means several events must occur during each stroke for all four events to be completed in two strokes, as opposed to the four-stroke engine where each stroke basically contains one event.
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Question 19 of 20
19. Question
As the diesel engine speeds up or down, the ________________ move in or out, this controls a small piston in the governor’s hydraulic system.
CorrectIncorrectHint
The governor controls the fuel rack position through a combined action of the hydraulic piston and a set of mechanical flyweights, which are driven by the engine blower shaft. Figure 28 provides an illustration of a functional diagram of a mechanical-hydraulic governor. The position of the flyweights is determined by the speed of the engine. As the engine speeds up or down, the weights move in or out. The movement of the flyweights, due to a change in engine speed, moves a small piston (pilot valve) in the governor’s hydraulic system. This motion adjusts flow of hydraulic fluid to a large hydraulic piston (servo-motor piston). The large hydraulic piston is linked to the fuel rack and its motion resets the fuel rack for increased/decreased fuel.
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Question 20 of 20
20. Question
Because a diesel engine relies on compression heat to ignite the fuel, a cold engine can rob enough heat from the gasses that the compressed air falls below the ignition temperature of the fuel. To help overcome this condition, some engines (usually small to medium sized engines) have _______________.
CorrectIncorrectHint
Because a diesel engine relies on compression heat to ignite the fuel, a cold engine can rob enough heat from the gasses that the compressed air falls below the ignition temperature of the fuel. To help overcome this condition, some engines (usually small to medium sized engines) have glowplugs. Glowplugs are located in the cylinder head of the combustion chamber and use electricity to heat up the electrode at the top of the glowplug. The heat added by the glowplug is sufficient to help ignite the fuel in the cold engine. Once the engine is running, the glowplugs are turned off and the heat of combustion is sufficient to heat the block and keep the engine running.