CHAPTER 26 diessel injection.PPT

© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
Publisher
The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
by
Russell Krick

 Basic diesel injection system
 Diesel injection system accessories

Diesel Fuel Injection
System
 High-pressure mechanical system that
delivers fuel directly into the
combustion chambers
 Unlike a lower-pressure gasoline
system, which meters fuel into the
intake manifold

Diesel versus Gasoline
 High compression
17:1 to 25:1
 Compression ignition
 No throttle valve
 Compresses air
 Direct injection into
combustion chamber
 Engine power
controlled by the
amount of fuel injected
 Lower compression
8:1 to 10:1
 Spark ignition
 Throttle valve
 Compresses air/fuel
 Fuel metered into
intake manifold
 Engine power
controlled by
regulating air and fuel
flow

Diesel Injection
System
Injection pump
plunger produces
high pressure to
open the injector

Components
 Injection pump
 high-pressure mechanical pump
 meters fuel to each injector nozzle at the
proper time
 Injection lines
 high-strength steel tubing
 carry fuel to each injector nozzle

Components
 Injector nozzles
 spring-loaded valves
 spray fuel into each combustion chamber
 Glow plugs
 electric heating elements
 warm air in the cylinder precombustion
chambers
 aid starting of a cold engine

Components
 Diesel fuel supply system
 feeds fuel from the fuel tank to the
injection pump
 components
 inline electric pump or engine-driven
mechanical pump
 filters and water separator to clean the fuel
 fuel return lines to carry unused fuel back to
the tank

Complete Diesel
System
Supply pump
feeds the
injection pump

Diesel Injection Pumps
 Bolted to the top or side of the engine
 Meter correct amount of fuel to the
injectors
 Time fuel injection
 Control idle speed and maximum
speed
 Provide a means of shutting off the
engine

Diesel Injection Pump
Located on the right
side of
the engine

Inline Injection Pump

Inline Injection Pump
Components
 Camshaft
acts on roller
tappet
 Tappet
pushes on
plunger

Camshaft
 Operates one plunger per cylinder
 When the engine turns the pump
camshaft, lobes push on the roller
tappets to move them up, forcing
plungers up
 Plunger return springs force plungers
back down as the lobes rotate away
from the roller tappets

Pump Plungers
 Small pistons that slide in individual
barrels to push fuel
 Plungers pressurize the fuel, forcing it
through the injector lines and to the
injector nozzles

Inline Pump Components
Control sleeves alter amount of fuel to
each injector nozzle

Control Rod or Rack
 Toothed shaft
 Acts as a throttle to control speed and
power
 Rotates the control sleeves
Delivery Valves
Spring-loaded valves in the outlets to
the injection lines
Ensure quick, leak-free closing of the
injector nozzles

 The fuel supply pump fills the barrel
with fuel
 The camshaft forces the roller tappet
and plunger upward in the barrel
 Fuel is forced through the delivery
valve, through the injection line, and
out the nozzle
 The delivery valve closes when the
plunger reaches the end of its stroke
Pump Operation

Pump Operation
Plunger action in an inline pump

 The rack slides across the control
sleeves to rotate them
 A helix-shaped (spiral) groove and a
slot are cut into the side of the plunger
 When the helix is aligned with the port
(hole) in the side of the barrel, the
plunger cannot develop pressure
 Fuel flows down the slot, through the
helix groove, and out the port
Metering

Metering
Control rack is linked to the gas pedal
and governor

 Amount of plunger movement that
pressurizes the fuel
 When the plunger moves up and the
helix is not aligned with the port, fuel is
trapped and pressurized
 Sleeve rotation regulates how much
fuel is injected
Effective Plunger
Stroke

Inline Pump
Governor
Controls idle
speed and limits
maximum engine
speed

 Uses weights, springs, and levers
 Levers are connected to control rack
 As engine speed increases, weights
are thrown outward (centrifugal force)
 This moves the levers and control rack
to reduce effective plunger stroke
 Engine speed is limited
Governor Operation

 When driver presses the gas pedal,
throttle lever spring pressure
overcomes governor spring pressure
 The control rack is moved to increase
fuel delivery (effective plunger stroke is
increased)
 When engine speed reaches the
desired level, the governor overcomes
throttle lever spring pressure
Governor Operation

Governor Operation

Governor
Operation

Accelerator-Injection
Pump Linkage

Injection Timing
 Relationship between the moment fuel
is injected into cylinder and piston
position
 Controlled by spring-loaded weights in
an inline injection pump
 As engine speed increases, weights fly
outward to advance injection timing,
providing more time to ignite and burn
fuel

Injection Pump
Fuel Flow

Distributor Injection
Pumps
 Only one or two plungers supply fuel
for all the cylinders
 Most common type of pump used on
passenger cars
 There are two common types of
distributor injection pumps:
 single-plunger pumps
 two-plunger pumps

Single Plunger Pumps
 Components
 Operation
 Metering
 Timing

Components

Transfer Pump
 Forces fuel into the injection pump
 Lubricates injection pump
 Fills the pumping chambers
Cam Plate
Rotating lobed disc
Operates plunger
Forces plunger to move and develop
injection pressure

Fuel Metering Sleeve
 Can be slid sideways on the plunger to
change effective plunger stroke
 Surrounds the plunger
Hydraulic Head
Housing around the plunger
Contains passages for filling the barrel
and injecting fuel into the delivery
valves

Centrifugal Governor
 Controls amount of fuel injected and
engine speed
 Flyweight action moves the metering
sleeve to limit top speed

Single Plunger Pump
Note the system fuel flow

Single Plunger
Pump Parts

Operation
 As the shaft rotates, the fill port in the
hydraulic head lines up with the port in
the plunger
 The transfer pump forces fuel into the
high-pressure chamber in front of the
plunger
 The fill port moves out of alignment
 The injection port lines up
 The cam plate lobe pushes the plunger
sideways, forcing fuel to the injector
nozzle

Metering

 As speed increases, injection must
occur sooner
 Transfer pump turns faster, increasing
pressure output
 Increased pressure moves an injection
advance piston
 Cam plate ramps engage plunger
sooner
Injection Timing

Injection Timing
Vane pump pressure can be used to
control injection timing

Two Plunger Pump

Components
 Two plungers
 force fuel to each injector nozzle
 Distributor rotor
 controls fuel flow to each injector nozzle
 Internal cam ring
 acts as a cam to force plungers inward
 Fuel metering valve
 regulates injection quantity by controlling
how far plungers move apart on the fill
stroke

Operation
 The transfer pump pulls fuel into the
injection pump
 When charging ports line up, fuel fills
the high-pressure chamber
 Charging ports move out of alignment
 Discharge ports line up
 Plungers are forced inward by the cam
ring, forcing fuel out of the hydraulic
head and to the injector nozzles

Injection System
Fuel Flow

Injector Nozzles
Spring-loaded
valves that spray
fuel directly into
precombustion
chambers

Injector Nozzle
Construction

Injector Nozzle
Operation
 High pressure fuel flows into the
injector nozzle inlet
 Fuel flows down the fuel passage in the
body into the pressure chamber
 The needle is forced upward,
compressing the spring
 Fuel sprays out in a conical pattern
 Fuel that leaks past the needle returns
to the fuel tank through return lines

With enough
injection pressure,
the needle valve is
pushed up and fuel
sprays into the
precombustion
chamber
Injector Nozzle
Operation

Inward Opening
Nozzles

Nozzle Types
Spray patterns for different
types of injectors

Glow Plugs
 Heating elements that warm air in
precombustion chambers
 Threaded into the cylinder head
 Control circuit automatically
disconnects the glow plugs after a few
seconds of operation

Glow Plug
Tip protrudes into the
precombustion chamber

Current flow through the plug heats
the element to warm air in the
precombustion chamber
Glow Plug

Control Circuit
Components
 Engine coolant temperature sensor
 Glow plug control unit
 Indicator lights

Glow Plug Circuit

Engine Temperature
Sensor
 Senses coolant temperature
 Input to control unit
 If engine is warm, the control unit will
not turn on glow plugs

Indicator Lights
 Operated by control unit
 Inform driver if engine is ready to start
because glow plugs are fully heated

Glow Plug Operation
 Engine cold
 The driver turns on ignition switch
 High current flows from battery to glow
plugs
 Glow plugs heat to a dull red glow
 When the indicator light goes out, the
engine is ready to crank
 Glow plug heat supplements the heat
of compression to ignite mixture

 Water detector
 Fuel heater
 Block heater
 Vacuum pump

Water Detector
 Warns driver of water in fuel
 Water and other contaminants are very
harmful to the fuel injection pump and
injectors
Fuel Heater
May be used to warm diesel fuel
Prevents fuel from jelling in very cold
weather
Electric heating element is located in the
fuel line, ahead of the injection pump

Water Detector and
Fuel Heater

Diesel
Injection
Electrical
Circuit

Block Heater
 May be used to warm the engine in
cold weather
 Cold starting aid
 Heating device plugs into wall electric
outlet

Vacuum Pump
 Diesel engines have little manifold
vacuum since there is no throttle valve
 Provides a source of vacuum for
vehicle systems:
 power brakes
 A/C ventilation controls
 emission control devices (EGR)

Diaphragm Vacuum
Pump

Vane-Type Vacuum
Pump
Mounted in back of the alternator

Computer-Controlled
Diesel
Uses a computer,
sensors, and
actuators to
increase efficiency

Injection Pump
Solenoids
 Control injection timing and quantity
 Controlled by the computer
 When energized or de-energized
electrically, solenoids open or close fuel
passages to alter pump operation

Diesel Injection
Sensors
 Monitor temperature, speed, and other
variables that affect fuel needs
 Similar to those on gasoline systems

Diesel Injection
Computer
 Monitors sensor inputs
 Calculates fuel needs
 Controls outputs such as pump
solenoids and emission control devices
 Precisely controls mechanical high-
pressure plungers inside the injection
pump

CHAPTER 26 diessel injection.PPT

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CHAPTER 26 diessel injection.PPT