MFUMO WA MAFUTA KWENYE GARI.
Diesel Fuel Systems
Topics
1.0.0 Diesel Fuel Systems
2.0.0 Methods of Injection
3.0.0 Superchargers and Turbochargers
4.0.0 Cold Starting Devices
5.0.0 Diesel Fuel System Maintenance
6.0.0 General Troubleshooting
Objectives
When you have completed this chapter, you will be able to do the following:
1. Understand the different types of diesel fuel systems, how the components
function to provide fuel to the engine, and how to service diesel fuel systems.
2. Identify the properties of diesel fuel.
3. Understand the function and operation of governors and fuel system
components.
4. Understand the principles and operation of the different diesel fuel systems.
5. Understand the operation of and the differences between superchargers and
turbochargers.
6. Identify the different types of cold weather starting aids.
7. Understand the basic maintenance required for a diesel fuel system.
8. Understand general troubleshooting techniques used in the maintenance of a
diesel fuel system
Prerequisites
None
This course map shows all of the chapters in Construction Mechanic Basic. The
suggested training order begins at the bottom and proceeds up. Skill levels increase as
you advance on the course map.
Automotive Chassis and Body
Brakes
Construction Equipment Power Trains C
Drive Lines, Differentials, Drive Axles,
and Power Train Accessories M
Automotive Clutches, Transmissions,
and Transaxles
Hydraulic and Pneumatic Systems
Automotive Electrical Circuits and
Wiring
B
A
Basic Automotive Electricity S
Cooling and Lubrication Systems I
Diesel Fuel Systems C
Gasoline Fuel Systems
Construction of an Internal Combustion
Engine
Principles of an Internal Combustion
Engine
Technical Administration
Features of this Manual
This manual has several features which make it easy to use online.
• Figure and table numbers in the text are italicized. The figure or table is either
next to or below the text that refers to it.
• The first time a glossary term appears in the text, it is bold and italicized. When
your cursor crosses over that word or phrase, a popup box displays with the
appropriate definition.
• Audio and video clips are included in the text, with italicized instructions telling
you where to click to activate it.
• Review questions that apply to a section are listed under the Test Your
Knowledge banner at the end of the section. Select the answer you choose. If the
answer is correct, you will be taken to the next section heading. If the answer is
incorrect, you will be taken to the area in the chapter where the information is for
review. When you have completed your review, select anywhere in that area to
return to the review question. Try to answer the question again.
• Review questions are included at the end of this chapter. Select the answer you
choose. If the answer is correct, you will be taken to the next question. If the
answer is incorrect, you will be taken to the area in the chapter where the
information is for review. When you have completed your review, select
anywhere in that area to return to the review question. Try to answer the question
again
1.0.0 DIESEL FUEL SYSTEMS
Like the gasoline engine, the diesel engine is an internal combustion engine using either
a two- or four-stroke cycle. Burning or combustion of fuel within the engine cylinders is
the source of the power. The main difference in a diesel engine is that the diesel fuel is
mixed with compressed air in the cylinder.
Compression ratios in the diesel engine range between 6:1 for a stationary engine and
24:1 for passenger vehicles. This high ratio causes increased compression pressures of
400 to 600 psi and cylinder temperatures reaching 800°F to 1200°F. At the proper time,
the diesel fuel is injected into the cylinder by a fuel-injection system, which usually
consists of a pump, fuel line, and injector or nozzle. When the fuel oil enters the
cylinder, it will ignite because of the high temperatures. The diesel engine is known as a
compression-ignition engine, while the gasoline engine is a spark-ignition engine.
The speed of a diesel engine is controlled by the amount of fuel injected into the
cylinders. In a gasoline engine, the speed of the engine is controlled by the amount of
air admitted into the carburetor or gasoline fuel injection systems.
Mechanically, the diesel engine is similar to the gasoline engine. The intake,
compression, power, and exhaust strokes occur in the same order. The arrangement of
the pistons, connecting rods, crankshaft, and engine valves is about the same. The
diesel engine is also classified as in-line or v-type.
In comparison to the gasoline engine, the diesel engine produces more power per
pound of fuel, is more reliable, has lower fuel consumption per horsepower per hour,
and presents less of a fire hazard.
These advantages are partially offset by higher initial cost, heavier construction needed
for its high compression pressures, and the difficulty in starting which results from these
pressures.
1.1.0 Diesel Fuel
Diesel fuel is heavier than gasoline because it is obtained from the residue of the crude
oil after the more volatile fuels have been removed. As with gasoline, the efficiency of
diesel fuel varies with the type of engine in which it is used. By distillation, cracking, and
blending of several oils, a suitable diesel fuel can be obtained for all engine operating
conditions. Using a poor or improper grade of fuel can cause hard starting, incomplete
combustion, a smoky exhaust, and engine knocks.
The high injection pressures needed in the diesel fuel system result from close
tolerances in the pumps and injectors. These tolerances make it necessary for the
diesel fuel to have sufficient lubrication qualities to prevent rapid wear or damage. It
must also be clean, mix rapidly with the air, and burn smoothly to produce an even
thrust on the piston during combustion.
1.1.1 Diesel Fuel Oil Grades
Diesel fuel is graded and designated by the American Society for Testing and Materials
(ASTM), while its specific gravity and high and low heat values are listed by the
American Petroleum Institute (API). Each individual oil refiner and supplier attempts to
produce diesel fuels that comply as closely as possible with ASTM and API
specifications. Because of different crude oil supplies, the diesel fuel may be on either
the high or low end of the prescribed heat scale in BTU per pound or per gallon.
Because of the deterioration of diesel fuel, only two grades of fuel are considered
acceptable for use in high-speed heavy-duty vehicles. These are the No. 1D or No. 2D
fuel oil classification. Grade No. 1D comprises the class of volatile fuel oils from
kerosene to the intermediate distillates. Fuels within this classification are applicable for
use in high-speed engines in service involving frequent and relatively wide variations in
loads and speeds. In cold weather conditions, No. 1D fuel allows the engine to start
easily. In summary, for heavy-duty high-speed diesel vehicles operating in continued
cold-weather conditions, No. 1D fuel provides better operation than the heavier No. 2D.
Grade No. 2D includes the class of distillate oils of lower volatility. They are applicable
for use in high-speed engines in service involving relatively high loads and speeds. This
fuel is used more by truck fleets due to its greater heat value per gallon, particularly in
warm to moderate climates. Even though No. 1D fuel has better properties for cold
weather operations, many still use No. 2D in the winter, using fuel heater/water
separators to provide suitable starting, as well as fuel additive conditioners, which are
added directly into the fuel tank.
Selecting the correct diesel fuel is a must if the engine is to perform to its rated
specifications.
Generally, seven factors must be considered in the selection of a fuel oil:
• Starting characteristics
• Fuel handling
• Wear on injection equipment
• Wear on pistons
• Wear on rings, valves, and cylinder liners
• Engine maintenance
• Fuel cost and availability
Other considerations in the selection of a fuel oil are as follows:
• Engine size and design
• Speed and load range
• Frequency of load and speed changes
• Atmospheric conditions
1.1.2 Cetane Number
Cetane number is a measure of the fuel oil’s volatility; the higher the rating, the easier
the engine will start and the smoother the combustion process will be within the ratings
specified by the engine manufacturer. Current 1D and 2D diesel fuels have a cetane
rating between 40 and 50.
Cetane rating differs from the octane rating used in gasoline in that the higher the
number of gasoline on the octane scale, the greater the fuel resistance to self ignition,
which is a desirable property in gasoline engines with a high compression ratio. Using a
low octane fuel will cause premature ignition in high compression engines. However, the
higher the cetane rating, the easier the fuel will ignite once injected into the diesel
combustion chamber. If the cetane number is too low, you will have difficulty in starting.
This can be accompanied by engine knock and puffs of white smoke during warm-up in
cold weather.
High altitudes and low temperatures require the use of diesel fuel with an increased
cetane number. Low temperature starting is enhanced by high cetane fuel oil in the
proportion of 1.5°F lower starting temperature for each cetane number increase.
1.1.3 Volatility
Fuel volatility requirements depend on the same factors as cetane number. The more
volatile fuels are best for engines where rapidly changing loads and speeds are
encountered. Low volatile fuels tend to give better fuel economy where their
characteristics are needed for complete combustion, and will produce less smoke, odor,
deposits, crankcase dilution, and engine wear.
The volatility of a fuel is established by a distillation test where a given volume of fuel is
placed into a container that is heated gradually. The readiness with which a liquid
changes to a vapor is known as the volatility of the liquid. The 90 percent distillation
temperature measures volatility of diesel fuel. This is the temperature at which 90
percent of a sample of the fuel has been distilled off. The lower the distillation
temperature, the higher the volatility of the fuel. In small diesel engines higher fuel
volatility is needed than in larger engines in order to obtain low fuel consumption, low
exhaust temperature, and minimum exhaust smoke.
1.1.4 Viscosity
The viscosity is a measure of the resistance to flow of the fuel, and it will decrease as
the fuel oil temperature increases. What this means is that a fluid with a high viscosity is
heavier than a fluid with low viscosity. A high viscosity fuel may cause extreme
pressures in the injection systems and will cause reduced atomization and vaporization
of the fuel spray.
The viscosity of diesel fuel must be low enough for it to flow freely at its lowest
operational temperature, yet high enough to provide lubrication to the moving parts of
the finely machined injectors. The fuel must also be sufficiently viscous so that leakage
at the pump plungers and dribbling at the injectors will not occur. Viscosity also will
determine the size of the fuel droplets, which in turn govern the atomization and
penetration qualities of the fuel injector spray.
Recommended fuel oil viscosity for high-speed diesel engines is generally in the region
of 39 SSU (Seconds Saybolt Universal), which is derived from using a Saybolt
Viscosimeter to measure the time it takes for a quantity of fuel to flow through a
restricted hole in a tube. A viscosity rating of 39 SSU provides good penetration into the
combustion chamber, atomization of fuel, and suitable lubrication.
Topics
1.0.0 Diesel Fuel Systems
2.0.0 Methods of Injection
3.0.0 Superchargers and Turbochargers
4.0.0 Cold Starting Devices
5.0.0 Diesel Fuel System Maintenance
6.0.0 General Troubleshooting
Objectives
When you have completed this chapter, you will be able to do the following:
1. Understand the different types of diesel fuel systems, how the components
function to provide fuel to the engine, and how to service diesel fuel systems.
2. Identify the properties of diesel fuel.
3. Understand the function and operation of governors and fuel system
components.
4. Understand the principles and operation of the different diesel fuel systems.
5. Understand the operation of and the differences between superchargers and
turbochargers.
6. Identify the different types of cold weather starting aids.
7. Understand the basic maintenance required for a diesel fuel system.
8. Understand general troubleshooting techniques used in the maintenance of a
diesel fuel system
Prerequisites
None
This course map shows all of the chapters in Construction Mechanic Basic. The
suggested training order begins at the bottom and proceeds up. Skill levels increase as
you advance on the course map.
Automotive Chassis and Body
Brakes
Construction Equipment Power Trains C
Drive Lines, Differentials, Drive Axles,
and Power Train Accessories M
Automotive Clutches, Transmissions,
and Transaxles
Hydraulic and Pneumatic Systems
Automotive Electrical Circuits and
Wiring
B
A
Basic Automotive Electricity S
Cooling and Lubrication Systems I
Diesel Fuel Systems C
Gasoline Fuel Systems
Construction of an Internal Combustion
Engine
Principles of an Internal Combustion
Engine
Technical Administration
Features of this Manual
This manual has several features which make it easy to use online.
• Figure and table numbers in the text are italicized. The figure or table is either
next to or below the text that refers to it.
• The first time a glossary term appears in the text, it is bold and italicized. When
your cursor crosses over that word or phrase, a popup box displays with the
appropriate definition.
• Audio and video clips are included in the text, with italicized instructions telling
you where to click to activate it.
• Review questions that apply to a section are listed under the Test Your
Knowledge banner at the end of the section. Select the answer you choose. If the
answer is correct, you will be taken to the next section heading. If the answer is
incorrect, you will be taken to the area in the chapter where the information is for
review. When you have completed your review, select anywhere in that area to
return to the review question. Try to answer the question again.
• Review questions are included at the end of this chapter. Select the answer you
choose. If the answer is correct, you will be taken to the next question. If the
answer is incorrect, you will be taken to the area in the chapter where the
information is for review. When you have completed your review, select
anywhere in that area to return to the review question. Try to answer the question
again
1.0.0 DIESEL FUEL SYSTEMS
Like the gasoline engine, the diesel engine is an internal combustion engine using either
a two- or four-stroke cycle. Burning or combustion of fuel within the engine cylinders is
the source of the power. The main difference in a diesel engine is that the diesel fuel is
mixed with compressed air in the cylinder.
Compression ratios in the diesel engine range between 6:1 for a stationary engine and
24:1 for passenger vehicles. This high ratio causes increased compression pressures of
400 to 600 psi and cylinder temperatures reaching 800°F to 1200°F. At the proper time,
the diesel fuel is injected into the cylinder by a fuel-injection system, which usually
consists of a pump, fuel line, and injector or nozzle. When the fuel oil enters the
cylinder, it will ignite because of the high temperatures. The diesel engine is known as a
compression-ignition engine, while the gasoline engine is a spark-ignition engine.
The speed of a diesel engine is controlled by the amount of fuel injected into the
cylinders. In a gasoline engine, the speed of the engine is controlled by the amount of
air admitted into the carburetor or gasoline fuel injection systems.
Mechanically, the diesel engine is similar to the gasoline engine. The intake,
compression, power, and exhaust strokes occur in the same order. The arrangement of
the pistons, connecting rods, crankshaft, and engine valves is about the same. The
diesel engine is also classified as in-line or v-type.
In comparison to the gasoline engine, the diesel engine produces more power per
pound of fuel, is more reliable, has lower fuel consumption per horsepower per hour,
and presents less of a fire hazard.
These advantages are partially offset by higher initial cost, heavier construction needed
for its high compression pressures, and the difficulty in starting which results from these
pressures.
1.1.0 Diesel Fuel
Diesel fuel is heavier than gasoline because it is obtained from the residue of the crude
oil after the more volatile fuels have been removed. As with gasoline, the efficiency of
diesel fuel varies with the type of engine in which it is used. By distillation, cracking, and
blending of several oils, a suitable diesel fuel can be obtained for all engine operating
conditions. Using a poor or improper grade of fuel can cause hard starting, incomplete
combustion, a smoky exhaust, and engine knocks.
The high injection pressures needed in the diesel fuel system result from close
tolerances in the pumps and injectors. These tolerances make it necessary for the
diesel fuel to have sufficient lubrication qualities to prevent rapid wear or damage. It
must also be clean, mix rapidly with the air, and burn smoothly to produce an even
thrust on the piston during combustion.
1.1.1 Diesel Fuel Oil Grades
Diesel fuel is graded and designated by the American Society for Testing and Materials
(ASTM), while its specific gravity and high and low heat values are listed by the
American Petroleum Institute (API). Each individual oil refiner and supplier attempts to
produce diesel fuels that comply as closely as possible with ASTM and API
specifications. Because of different crude oil supplies, the diesel fuel may be on either
the high or low end of the prescribed heat scale in BTU per pound or per gallon.
Because of the deterioration of diesel fuel, only two grades of fuel are considered
acceptable for use in high-speed heavy-duty vehicles. These are the No. 1D or No. 2D
fuel oil classification. Grade No. 1D comprises the class of volatile fuel oils from
kerosene to the intermediate distillates. Fuels within this classification are applicable for
use in high-speed engines in service involving frequent and relatively wide variations in
loads and speeds. In cold weather conditions, No. 1D fuel allows the engine to start
easily. In summary, for heavy-duty high-speed diesel vehicles operating in continued
cold-weather conditions, No. 1D fuel provides better operation than the heavier No. 2D.
Grade No. 2D includes the class of distillate oils of lower volatility. They are applicable
for use in high-speed engines in service involving relatively high loads and speeds. This
fuel is used more by truck fleets due to its greater heat value per gallon, particularly in
warm to moderate climates. Even though No. 1D fuel has better properties for cold
weather operations, many still use No. 2D in the winter, using fuel heater/water
separators to provide suitable starting, as well as fuel additive conditioners, which are
added directly into the fuel tank.
Selecting the correct diesel fuel is a must if the engine is to perform to its rated
specifications.
Generally, seven factors must be considered in the selection of a fuel oil:
• Starting characteristics
• Fuel handling
• Wear on injection equipment
• Wear on pistons
• Wear on rings, valves, and cylinder liners
• Engine maintenance
• Fuel cost and availability
Other considerations in the selection of a fuel oil are as follows:
• Engine size and design
• Speed and load range
• Frequency of load and speed changes
• Atmospheric conditions
1.1.2 Cetane Number
Cetane number is a measure of the fuel oil’s volatility; the higher the rating, the easier
the engine will start and the smoother the combustion process will be within the ratings
specified by the engine manufacturer. Current 1D and 2D diesel fuels have a cetane
rating between 40 and 50.
Cetane rating differs from the octane rating used in gasoline in that the higher the
number of gasoline on the octane scale, the greater the fuel resistance to self ignition,
which is a desirable property in gasoline engines with a high compression ratio. Using a
low octane fuel will cause premature ignition in high compression engines. However, the
higher the cetane rating, the easier the fuel will ignite once injected into the diesel
combustion chamber. If the cetane number is too low, you will have difficulty in starting.
This can be accompanied by engine knock and puffs of white smoke during warm-up in
cold weather.
High altitudes and low temperatures require the use of diesel fuel with an increased
cetane number. Low temperature starting is enhanced by high cetane fuel oil in the
proportion of 1.5°F lower starting temperature for each cetane number increase.
1.1.3 Volatility
Fuel volatility requirements depend on the same factors as cetane number. The more
volatile fuels are best for engines where rapidly changing loads and speeds are
encountered. Low volatile fuels tend to give better fuel economy where their
characteristics are needed for complete combustion, and will produce less smoke, odor,
deposits, crankcase dilution, and engine wear.
The volatility of a fuel is established by a distillation test where a given volume of fuel is
placed into a container that is heated gradually. The readiness with which a liquid
changes to a vapor is known as the volatility of the liquid. The 90 percent distillation
temperature measures volatility of diesel fuel. This is the temperature at which 90
percent of a sample of the fuel has been distilled off. The lower the distillation
temperature, the higher the volatility of the fuel. In small diesel engines higher fuel
volatility is needed than in larger engines in order to obtain low fuel consumption, low
exhaust temperature, and minimum exhaust smoke.
1.1.4 Viscosity
The viscosity is a measure of the resistance to flow of the fuel, and it will decrease as
the fuel oil temperature increases. What this means is that a fluid with a high viscosity is
heavier than a fluid with low viscosity. A high viscosity fuel may cause extreme
pressures in the injection systems and will cause reduced atomization and vaporization
of the fuel spray.
The viscosity of diesel fuel must be low enough for it to flow freely at its lowest
operational temperature, yet high enough to provide lubrication to the moving parts of
the finely machined injectors. The fuel must also be sufficiently viscous so that leakage
at the pump plungers and dribbling at the injectors will not occur. Viscosity also will
determine the size of the fuel droplets, which in turn govern the atomization and
penetration qualities of the fuel injector spray.
Recommended fuel oil viscosity for high-speed diesel engines is generally in the region
of 39 SSU (Seconds Saybolt Universal), which is derived from using a Saybolt
Viscosimeter to measure the time it takes for a quantity of fuel to flow through a
restricted hole in a tube. A viscosity rating of 39 SSU provides good penetration into the
combustion chamber, atomization of fuel, and suitable lubrication.
Maoni