Unit 5: Diesel Fuel
UNIT 5 Diesel Fuel Characteristics Mechanically Controlled Fuel Systems
Unit Objectives: 1. The student will be able to explain the characteristics of diesel fuel and proper fuel system maintenance procedures for Caterpillar engines. 2. The student will be able to identify and explain the operation of the following Caterpillar fuel systems: new scroll, sleeve metering, and mechanical unit injector. 3. The student will be able to remove and install 3406 New Scroll Fuel System, plunger and barrel group, nozzles, timing advance, and injection pump and governor group. The student will demonstrate the ability to test a fuel nozzle.
Unit References: Diesel Fuels and Your Engine 3406E Operation and Maintenance Manual Fuel Contamination Control Caterpillar New Scroll Fuel System Introduction Using 5P4150 Nozzle Tester Group Testing 7000 Series Nozzles 3406B Service Manual 3406C Service Manual
SEBD0717 SEBU6758 PEHP7046 CD-ROM SEHS7292 SEHS9083 SEBR0544 SEBR0550
Unit 5 Lesson 1
Engine Fundamentals
Unit References: (Continued) Fuel Nozzle Testing The Sleeve Metering Fuel System The Sleeve Metering Fuel System CD-ROM 3116/26 Mechanical Unit Injector Presentation Unit 5 Quiz Tooling: 8T0461 Serviceman's Tool Set or equivalent 6V4186 Pin 9S9082 Turning Tool 1P7408 Thermo-hydrometer 5P5195 Fuel Line Wrench 5P0144 Fuel Line Socket 8S2244 Extractor 8T5287 Wrench 5P4150 Nozzle Test Group 6V2170 Tube Assembly 6V2171 Tube Assembly 5P7448 Adapter 8T3139 Spanner Wrench 8T3198 Nozzle Tube 8T3199 Nozzle Screw 6V6983 Adapter 1B4206 Nut 8S2270 Collector Assembly 6V4089 Nozzle Reamer 6V7025 Nozzle Seal Guide 1U9725 Nozzle Adapter Wrench
LEVP9167 LEBQ9802 LERV9802 CD-ROM
Lesson 1: Diesel Fuel
Lesson 1: Diesel Fuel
Objectives: The student will be able to explain diesel fuel characteristics and related maintenance. References: Diesel Fuels and Your Engine 3406E Operation and Maintenance Manual Fuel Contamination Control
SEBD0717 SEBU6758 PEHP7046
Introduction: Diesel fuel is by far the largest expense related to owning and operating a diesel engine. The characteristics, quality, and handling of the fuel affect the performance and life of the engine.
Unit 5 Lesson 1
5-1-2
Engine Fundamentals
Heating Value of Diesel Fuel
HEAT VALUE PER GALLON IN BTU 1D Diesel
137,000
2D Diesel
141,800
Gasoline Butane Propane
125,000 103,000 93,000
Fig. 5.1.1 Heating values of various fuels
The heating value of a fuel is defined as the amount of heat produced by burning a specific weight of fuel. This is an indicator of how much available energy is available in a specific amount of fuel. The chart above shows the heating values for various common fuels. 1D diesel is winter blended diesel, and 2D diesel is summer blended diesel. Notice that both blends of diesel fuel have a significantly higher heating value than any of the other fuels listed. What this means is that in a given amount of diesel fuel there is more energy available to be turned into useful work. This is one of the significant advantages to using diesel power as a source of energy.
Objectives: The student will be able to explain the operation of the Caterpillar New Scroll Fuel System. References: Caterpillar New Scroll Fuel System Introduction
CD-ROM
Introduction: The Caterpillar New Scroll Fuel System has been in production since 1980 on the 3300 series engines. When the 3406B was released in 1983, the New Scroll Fuel System was added to help improve emissions, performance, and fuel economy. Another benefit of the New Scroll Fuel System is that the individual injection pumps do not need adjustment or calibration.
Lesson 2: Caterpillar 3406 New Scroll Fuel System
Lesson 2: Caterpillar 3406 New Scroll Fuel System
Unit 5 Lesson 2
5-2-2
Engine Fundamentals
This presentation covers the Caterpillar New Scroll Fuel System.
Fig. 5.2.1 Caterpillar 3406B Engine
Caterpillar 3406B Engine The Caterpillar 3406A was introduced in 1973. Since then, a number of changes have been made to meet the demand for an even more reliable and economical product, while meeting governmental regulations. The 3406B, released in 1983, is an example of these changes. The major change to this engine was the fuel system. The New Scroll Fuel System had been in production since 1980 on the 3300 engines. This fuel system is a key factor in the emissions, performance and fuel economy improvements in the 3406B. In 1991, the fuel system was changed to incorporate a more aggressive fuel camshaft to improve emissions. In 1992 the 3406C was introduced. There were no changes to the mechanical fuel system.
Fig. 5.2.2
Caterpillar 3406 Fuel Injection Pump Groups In the top view we can see how the 3406A Engine Fuel Injection Pump had a long drive because there wasn’t room for the pump housing under the air compressor. In the lower view we see the 3406B/C Fuel Injection Pump. It is shorter, but more massive. The shorter length of the 3406B/C pump leaves more room for servicing.
Unit 5 Lesson 2
5-2-3
Engine Fundamentals
Fig. 5.2.3 Injection Pump Camshafts
Injection Pump Camshafts Many of the changes and improvements were internal, and can’t be seen. Here we see the fuel injection pump camshafts. The 3406A is at the top. The 3406B camshaft below it is larger and heavier, and is driven by a gear on the left end. The 3406B cams have a different configuration--they have a faster lift and shorter duration, increasing fuel injection pressures and reducing the time of injection, for greater fuel efficiency. An eccentric on the camshaft operates the piston-type fuel transfer pump. With the changes for emissions in 1988, the nose of the camshaft changed. The 10 degrees helix on the front was changed to a 15 degrees helix and the hole in the front was enlarged to accommodate a different timing advance unit. The emission changes for 1991 was a bearing diameter and lobe shape change only.
Unit 5 Lesson 2
5-2-4
Engine Fundamentals
Fig. 5.2.4 3406 Fuel Flow
This is a schematic of the 3406B/C engine fuel system. We’ll use the schematic to follow the flow of fuel from the supply tank to the injector in the cylinder. The transfer pump (5) pulls fuel from the fuel tank (1) through the supply shutoff valve (3) through the primary fuel filter (4) to the fuel transfer pump itself. The transfer pump then pressurizes the fuel and pushes it though the hand priming pump (7), into the secondary fuel filter (6) and into the fuel manifold (8) under moderate pressure. A bypass valve inside the fuel transfer pump maintains moderate fuel pressure. With moderate fuel pressure inside the fuel manifold and the void (vacuum) inside the high pressure pumps, the fuel is loaded into the cavity of the high pressure pump. The high pressure pumps now meter a small amount of fuel and sends it though the high pressure fuel lines (9) and through the head adapter (10) to the injection nozzle (11) at a very high pressure. When the fuel pressure in the high pressure fuel lines gets above the nozzle opening pressure the fuel is injected into the combustion chamber. With both very high pressure and very small holes in the tip of the nozzle, the fuel is atomized and gives complete combustion in the cylinder. Any air and some fuel is sent out of the fuel manifold through the return line (15) back to the supply tank. The tank drain (2) is used to remove water, sediment and foreign material and to drain the supply tank. The fuel tank cap (16) must be vented to atmosphere to keep vacuum from forming inside the fuel tank.
Unit 5 Lesson 2
5-2-5
Engine Fundamentals
Fig. 5.2.5 3306 Fuel Flow
3306 Fuel Flow This is a schematic of the 3306B/C engine fuel system. We’ll use the schematic to follow the flow of fuel from the supply tank to injection in the cylinder. The transfer pump (6) pulls fuel from the fuel tank (9) through the supply shut off valve (3) through the primary fuel filter (4) through the hand priming pump (5) into the transfer pump itself. The transfer pump then pressurizes the fuel and pushes it through the secondary fuel filter (7) and to the fuel manifold in the injection pump housing (8). A bypass valve inside the fuel transfer pump maintains moderate fuel pressure. With moderate fuel pressure inside the fuel manifold and the void (vacuum) inside the high pressure pumps, the fuel is loaded into the cavity of the high pressure pump. The high pressure pumps now meter a small amount of fuel and sends it though the external high pressure fuel lines (9) at a very high pressure to the fuel injection nozzle (10). When the fuel pressure in the high pressure fuel lines gets above the nozzle opening pressure the fuel is injected into the combustion chamber. With both very high pressure and very small holes in the tip of the nozzle, the fuel is atomized and gives complete combustion in the cylinder. A constant bleed valve (11) lets a constant flow of fuel go through the fuel return line (12) back to the fuel tank (1). This helps keep the fuel cool and free of air. There is also a manual bleed valve that can be used when the fuel priming pump is used to remove air from the system. The supply tank drain (2) is used to remove water, sediment, foreign material and to drain the supply tank. The fuel cap must be vented to atmosphere to keep a vacuum from forming inside the fuel tank.
Unit 5 Lesson 2
5-2-6
Engine Fundamentals
Fig. 5.2.6 Fuel System Components
Fuel System Components In this view we can see some of the components of the 3406B fuel injection system on the engine. Visible are the fuel injection pump housing, the governor housing, the fuel transfer pump and the external fuel injection lines.
Fig. 5.2.7 3306 Fuel System Components
3306 Fuel System Components In this view we can see some of the components of the 3306B/C fuel injection system on the engine. Visible are the fuel injection pump housing, the governor housing, the fuel transfer pump, fuel injection lines, the fuel filter and base and the fuel priming pump.
Unit 5 Lesson 2
5-2-7
Engine Fundamentals
Fig. 5.2.8 Fuel Transfer Pump
Fuel Transfer Pump The fuel transfer pump is located on the bottom of the 3406B/C pump housing and on the side of the 3304B or 3306B/C pump housing. It is activated by the eccentric on the fuel pump camshaft inside the housing and can deliver up to 51 gallons of fuel per hour at 25 psi. This is a spring pumping piston type pump where actual fuel pressure on the engine may vary from 20-45 psi depending on engine operating conditions. The pump only supplies what the engine requires, plus the amount returned to tank. (About 9 gallons per hour). It is a single piston, single action pump with three one-way check valves. The check valves are: inlet, pumping and outlet. This drawing shows that pumping and fill occur on the same pump stroke. Here, the tappet is almost completely extended and the return spring has forced the piston to the top of the pump. This upward motion of the piston opens the inlet check valve and fuel enters the inlet cavity (green). The pumping check valve at the top of the piston is closed and the piston pushes fuel into the outlet cavity (red). This pressurized fuel opens the outlet check valve at the outlet port. There is no pressure relief valve in this pump because fuel outlet pressure is controlled by the force of the piston spring.
Unit 5 Lesson 2
5-2-8
Engine Fundamentals
Fig. 5.2.9 3406 Injection Pump
3406 Injection Pump The area shown in red is the fuel gallery of the 3406B/C fuel pump. This area is pressurized by the fuel transfer pump. The cutaway shows the placement of the pump groups within the pump housing. Fuel enters and leaves the pump group by way of the hardened hollow dowel. This dowel is in the housing to protect it from erosion caused by the high pressure spill pulses.
Fig. 5.2.10 3306 Injection Pump
3306 Injection Pump This is a cutaway of a similar area of the 3306B/C fuel pump. Notice the similarity of the two different pumps.
Unit 5 Lesson 2
5-2-9
Engine Fundamentals
Fig. 5.2.11 3406 Fuel Rack
3406 Fuel Rack The area shown in the slide is a cutaway of the engine side of the 3406B/C fuel pump housing. This cutaway shows a complete pump in the center and a cutaway pump on the right. We can see the relationship of the pump groups and the rack as the gear segment engages the rack. Also note the lifters and return springs.
Fig. 5.2.12 Fuel Metering
Fuel Metering We’ll use a cutaway pump to see how fuel is metered and delivered to the fuel injection nozzles. This is a scroll type fuel system with a left-hand cut scroll on the pump plunger. The gear on the bottom of the plunger is engaged into the rack. Rack movement rotates the plunger in the pump barrel and changes the relationship of the scroll to the spill port (arrow). The camshaft/follower/lifter mechanism moves the plunger up and down in the barrel. In this position, the plunger is at the bottom of its stroke. Fuel is coming into the barrel through the spill port in the back side of the barrel and through the fill port.
Unit 5 Lesson 2
5-2-10
Engine Fundamentals
Fig. 5.2.13 Fuel Delivery
Fuel Delivery Now, the cam has lifted the plunger so the fill port and spill port are just closed. This is the start of the effective stroke of the plunger and the beginning of injection. As the fuel in the barrel is pressurized, the reverse flow check valve is lifted off its seat in the pump bonnet. This sends pressurized fuel through the fuel lines to the injection nozzle. Injection continues until the end of the effective stroke, when the scroll in the plunger lines up with the spill port in the barrel.
Fig. 5.2.14 End of Fuel Delivery
End of Fuel Delivery At the end of the effective stroke, the spill port is opened by the scroll, fuel pressure is released and the reverse flow check valve closes. During the entire pumping cycle the groove on the plunger is positioned over the bleed back passage.
Unit 5 Lesson 2
5-2-11
Engine Fundamentals
Fig. 5.2.15 Bleed Passage
Bleed Passage When the groove in the plunger is in this position, it is aligned with the pressure bleed back passage in the barrel. This bleeds of fuel that goes between the barrel and the plunger and prevents fuel dilution in the engine oil.
Fig. 5.2.16 Reverse Flow Check Valve
Reverse Flow Check Valve The reverse flow check valve keeps the fuel injection line full of fuel between injection strokes. Pressurized fuel (approximately 1000 psi) is kept in the injection line, ready for the next pump stroke. When the engine and injection pump are stopped, the groove (arrow) bleeds the pressure in the injection line to equalize with the residual pressure in the pump.
Unit 5 Lesson 2
5-2-12
Engine Fundamentals
Fig. 5.2.17 Reverse Flow Check Valve Operation
Reverse Flow Check Valve Operation When fuel pressure in the barrel above the plunger reaches 100 psi, the valve is lifted off its seat and fuel flows out the cavity through the bonnet to the injection line. The check valve spring keeps the valve seated when fuel is at transfer pump pressure. This means that fuel can enter the injections lines only during the injection stroke, helping to eliminate cylinder wash down if an injection nozzle is stuck open.
Fig. 5.2.18 Reverse Flow Check Valve
Reverse Flow Check Valve Pressurization continues until the scroll opens the spill port and the pressure in the pump barrel is released. This seats the check valve, but the pressurized fuel in the injection line opens the return flow check valve. Fuel will return to the pump barrel and flow out the spill port until pressure in the injection line drops to 1000 psi. At that point, the return flow check valve spring will seat the valve. When the engine is shut off, a small groove in the face of the check valve allows the 1000 psi pressure to bleed off.
Unit 5 Lesson 2
5-2-13
Engine Fundamentals
Fig. 5.2.19 3406 Fuel Manifold Cover
3406 Fuel Manifold Cover The high pressure fuel that exits through the spill ports goes through the hollow dowel into the fuel manifold and hits the cover plate. These highly pressurized fuel pressure pulses cause polish spots that are lined up with the spill ports on the manifold cover plate of the 3406B/C fuel system.
Fig. 5.2.20 3306 Fuel Manifold Cover
3306 Fuel Manifold Cover On the 3300 series engines, a spring steel pulse deflector is provided in the fuel manifold. This protects the aluminum manifold cover from the force of the released fuel pressure pulses.
Unit 5 Lesson 2
5-2-14
Engine Fundamentals
Fig. 5.2.21 Governor Operation
Governor Operation At the point the rack screw (green) first comes in full contact with the torque spring, the rack is at full load point (rated). As demand horsepower increased, with the rack at rated position, the engine speed decreases as the engine goes into lug (full throttle with rpm less than rated rpm). Depending upon the rigidity of the torque spring, at some point, the governor spring causes the rack screw to begin to depress the torque spring. As this occurs, the rack position increases allowing more fuel to be injected per stroke. This increase in rack position continues until the torque screw (violet) contacts the stop lar. This is the full torque position of the rack.
Fig. 5.2.22 Governor Operation
Governor Operation The flyweights swing out as rpm increases. This moves the riser to compress the governor spring and the pivoting lever moves the sleeve and spool toward the "fuel off" direction.
Unit 5 Lesson 2
5-2-15
Engine Fundamentals
Fig. 5.2.23 Valve Spool - "Fuel Off"
Valve Spool - "Fuel Off" As the valve spool moves in the direction shown, a passage in the piston opens and allows pressurized oil to enter the chamber behind the piston. At the same time, the spool closes the passage behind this chamber. The pressurized oil forces the piston and rack toward the "fuel off" position. With no load on the engine, the rack will move until the low idle setting is reached. This setting is determined by the amount of force put on the governor spring by the throttle resting against the low idle stop screw.
Fig. 5.2.24 Governor Operation
Governor Operation If the engine were to slow down, the flyweights would swing in which would move the riser away from the governor spring and the pivoting lever moves the sleeve and spool toward the "fuel on" direction.
Unit 5 Lesson 2
5-2-16
Engine Fundamentals
Fig. 5.2.25 Valve Spool - "Fuel On"
Valve Spool - "Fuel On"This spool movement blocks the passage in the piston and opens the drain passage behind the chamber. Now pressurized oil forces the piston and the rack in the direction shown (fuel on) so fuel delivery is increased until the desired rpm is obtained. The back and forth movement of the rack in the "fuel off" direction and in the "fuel on" direction will continue until there is a balance between the governor spring force and the flyweight force.
Fig. 5.2.26 Valve Spool - Stabilized Fuel Position
Valve Spool - Stabilized Fuel Position This drawing shows the balance point of the servo spool and piston. When flyweight force equals governor spring force, the valve spool blocks the oil in the chamber behind the piston. Rack position does not change and engine rpm is constant.
Unit 5 Lesson 2
5-2-17
Engine Fundamentals
Fig. 5.2.27 Fuel Ratio Control Function
Fuel Ratio Control Function The fuel ratio control mounts on the rear of the governor housing. Its purpose is to limit smoke and improve fuel economy during rapid acceleration. It does this by controlling rack movement in the fuel ON direction until there is enough (boost pressure) to allow complete combustion in the cylinders. With the fuel ratio control properly adjusted, it also minimizes the amount of soot in the engine.
Fig. 5.2.28 Fuel Ratio Control Operation
Fuel Ratio Control Operation A stem extends out of the fuel ratio control. This stem fits in a notch in a lever which contacts the end of the rack in the servo valve. Air inlet pressure (boost) is sensed by a diaphragm in the control. This diaphragm pushes against a spring and spool. The spool movement controls the oil flow which moves a piston connected to the stem. The stem is out of the way during startup, so full rack is available on all mechanical 3406s. The same is true of 3300s, but beginning with the 1994 3306C truck engine, the stem is partially retracted during startup, but does not go to full retraction until the engine develops oil pressure.
Unit 5 Lesson 2
5-2-18
Engine Fundamentals
Fig. 5.2.29 Fuel Ratio Control Operation
Fuel Ratio Control Operation When boost is low, the stem is in the set (cocked) position and the lever limits rack movement in the fuel ON direction. As boost pressure increases, The stem extends and moves away from the lever and the rack can move to the left allowing more fuel to be supplied by the injection pumps. When manifold pressures of approximately one-half rated boost or above is reached, full fuel rack travel is available. Thus. anytime there is sufficient boost, the stem of the fuel ratio control is extended and does not control or affect the movement of the rack. This permits smooth, rapid acceleration but at a rate that allows complete combustion and low emissions.
Unit 5 Lesson 2
5-2-19
Engine Fundamentals
Fig. 5.2.30 Fuel Shutoff Solenoid
Fuel Shutoff Solenoid A fuel shutoff solenoid is located on the rear of the governor. There are two types. One is energized to run, the other is energized to shut down. The one shown is an energized to run solenoid. When the engine’s electrical system is energized (key on), the solenoid is activated and it releases linkage to allow rack movement in any direction (fuel on - fuel off). When the electrical system is shut off (key off), the solenoid is deactivated and movement of the rack is prevented in the fuel ON direction, causing the engine to shut down. A diode is connected between the two terminals of the solenoid. The diode eliminates electric spikes (high voltage generated by the coil of the solenoid when it is de-energized) that might damage other electronic circuitry in the vehicle electrical system.
Objectives: The student will demonstrate the ability to correctly remove and install 3406 fuel system components and test a nozzle. References: 3406B Service Manual SEBR0544 3406C Service Manual SEBR0550 Test Sequence for Caterpillar 7000 Series Fuel Nozzles SEHS9083 Fuel Nozzle Testing LEVN9167 Introduction: The Caterpillar 3406 fuel system normally requires very little adjustment during the life of the engine. Normal maintenance may require replacement of components such as filters, nozzles, and transfer pump. Fuel system repairs may involve removal of plunger and barrel groups from the fuel injection pump, repair of the timing advance, or removal of the complete fuel system from the engine.
Lesson 3: Remove, Inspect and Install Fuel System Components
Lesson 3: Remove, Inspect and Install Fuel System Components
Unit 5 Lesson 3
Engine Fundamentals
Tooling: 8T0461 Serviceman’s Tool Set or Equivalent 6V4186 Pin 9S9082 Turning Tool 5P5195 Fuel Line Wrench 5P0144 Fuel Line Socket 8S2244 Extractor 8T5287 Wrench 8T3139 Spanner Wrench 8T3198 Nozzle Tube 8T3199 Nozzle Screw 6V6983 Adapter 1B4206 Nut 5P4150 Nozzle Test Group 6V2170 Tube Assembly 6V2171 Tube Assembly 5P7448 Adapter 8S2270 Collector Assembly 6V4089 Nozzle Reamer 6V7025 Nozzle Seal Guide 1U9725 Nozzle Adapter Wrench Lab Exercises: Using a lab engine or engine installed in a vehicle, explain the fuel system and components including transfer pump, filter, injection pump, fuel lines and nozzles. Using a 3406 lab engine, remove and disassemble transfer pump noting check valves and piston in pump. Using the tooling and procedures specified in the 3406 Service Manual perform the following: - Remove fuel injection nozzles, test the nozzles using the 5P4150 Nozzle tester group and SEHS9083 Special Instruction, and reinstall the nozzles. - Remove and install (1) injection pump plunger and barrelgroup from the housing. - Remove the timing advance. - Remove injection pump housing from front cover. - Reinstall the fuel injection pump group and timing advance.
Lesson 4: Sleeve Metering Fuel System
Lesson 4: Sleeve Metering Fuel System
Objectives: The student will be able to explain how the Sleeve Metering Fuel System operates. References: The Sleeve Metering Fuel System 3208 Sleeve Metering Fuel System CD-ROM Diesel Fundamentals and Service - Thiessen, Dales
LEBQ9802 LERV9802 Textbook
Introduction: The Caterpillar Sleeve Metering Fuel System was most recently used on the 3208 engine. The 3208 was a popular mid-range on-highway truck engine until 1991 and saw continued use in marine and industrial applications for many more years.
