16-10-2012, 01:17 PM
AUTOMOTIVE FUEL AND EMISSION CONTROL SYSTEM
AUTOMOTIVE FUEL.ppt (Size: 6.42 MB / Downloads: 270)
OBJECTIVES
After studying Chapter 4, the reader should be able to:
Prepare for ASE Engine Performance (A8) certification test content area “C” (Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair).
Explain how a diesel engine works.
Describe the difference between direct injection (DI) and indirect injection (IDI) diesel engines.
List the parts of the typical diesel engine fuel system.
Explain how glow plugs work.
List the advantages and disadvantages of a diesel engine.
Describe how diesel fuel is rated and tested. Hydraulic Electronic
DIESEL ENGINES
In 1892, a German engineer named Rudolf Diesel perfected the compression-ignition engine that bears his name.
The diesel engine uses heat created by compression to ignite the fuel, so it requires no spark ignition system.
The diesel engine requires compression ratios of 16:1 and higher.
Incoming air is compressed until its temperature reaches about 1,000°F (540°C).
This is called heat of compression.
As the piston reaches the top of its compression stroke, fuel is injected into the cylinder, where it is ignited by the hot air
THREE PHASES OF COMBUSTION
There are three distinct phases or parts to the combustion in a diesel engine.
Ignition delay.
Rapid combustion.
Controlled combustion.
DIESEL ENGINE CONSTRUCTION
Diesel engines must be constructed heavier than gasoline engines because of the tremendous pressures that are created in the cylinders during operation.
The torque output of a diesel engine is often double or more than the same size gasoline powered engines.
FUEL TANK AND LIFT PUMP
A fuel tank used on a vehicle equipped with a diesel engine differs from the one used with a gasoline engine in several ways, including:
A larger filler neck for diesel fuel.
No evaporative emission control devices or charcoal (carbon) canister.
The diesel fuel is drawn from the fuel tank by a lift pump and delivers the fuel to the injection pump.
Between the fuel tank and the lift pump is a water-fuel separator.
Water is heavier than diesel fuel and sinks to the bottom of the separator.
DIESEL INJECTOR NOZZLES
Diesel injector nozzles are spring-loaded closed valves that spray fuel directly into the combustion chamber or precombustion chamber.
Injector nozzles are threaded into the cylinder head, one for each cylinder, and are replaceable as an assembly.
The top of the injector nozzle has many holes to deliver an atomized spray of diesel fuel into the cylinder.
Parts of a diesel injector nozzle include:
Heat shield.
Injector body.
Diesel injector needle valve.
Injector pressure chamber.
GLOW PLUGS
Glow plugs are always used in diesel engines equipped with a precombustion chamber and may be used in direct injection diesel engines to aid starting.
A glow plug is a heating element that uses 12 volts from the battery and aids in the starting of a cold engine.
As the temperature of the glow plug increases, the resistance of the heating element inside increases, thereby reducing the current in amperes needed by the glow plugs.
ENGINE-DRIVEN VACUUM PUMP
Because a diesel engine is unthrottled, it creates very little vacuum in the intake manifold.
Several engine and vehicle components operate using vacuum, such as the exhaust gas recirculation (EGR) valve and the heating and ventilation blend and air doors.
Most diesels used in cars and light trucks are equipped with an engine-driven vacuum pump to supply the vacuum for these components.