Modern Automotive Technology PowerPoint for by Russell Krick Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

Chapter 25 Diesel Injection Fundamentals

Contents Basic diesel injection system Diesel injection system accessories Piezo diesel injectors

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 Injection lines 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 Glow plugs 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 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

Located on the right side of the engine Diesel Injection Pump Located on the right side of the engine

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 Delivery Valves 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

Pump Operation Fuel supply pump fills the barrel with fuel 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 Delivery valve closes when the plunger reaches the end of its stroke

Plunger action in an inline pump Pump Operation Plunger action in an inline pump

Metering 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

Control rack is linked to the gas pedal and governor Metering Control rack is linked to the gas pedal and governor

Effective Plunger Stroke 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

Controls idle speed and limits maximum engine speed Inline Pump Governor Controls idle speed and limits maximum engine speed

Governor Operation 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

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

Single-Plunger Pump Components

Transfer Pump Cam Plate 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 Hydraulic Head 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

Note the system fuel flow Single-Plunger Pump Note the system fuel flow

Single-Plunger Pump 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

Injection Timing 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

Vane pump pressure can be used to control injection timing

Two-Plunger Pump

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

Two-Plunger Pump 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

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

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

Inward Opening Nozzles

Spray patterns for different types of injectors 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

Tip protrudes into the precombustion chamber Glow Plug Tip protrudes into the precombustion chamber

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

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

Glow Plug Circuit

Engine Temperature Sensor Senses coolant temperature Feeds data 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

Diesel Injection System Accessories Water detector Fuel heater Block heater Vacuum pump

Water Detector Fuel Heater 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

Mounted in back of the alternator 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

Piezo Diesel Injectors Use piezoelectric crystals to meter fuel Provide precise fuel metering Reduce exhaust emissions Produce smoother engine operation

Piezoelectric Crystals Used to open or close injector needle When current is applied, crystal expands and forces injector needle open When polarity is reversed, crystal contracts and closes injector needle Rapid operation allows for more precise timing

Piezo Diesel Injector Current flow causes piezoelectric element to open or close needle valve