Diesel Automotive Diesel Automotive EnginesEngines

Energy and Power Technology Energy and Power Technology TextbookTextbook

Chapter 14Chapter 14

As you study this As you study this chapter, you will learn to:chapter, you will learn to:

Explain why the diesel engine has grown in Explain why the diesel engine has grown in popularity as an automobile and truck engine.popularity as an automobile and truck engine.

Identify the two major differences between Identify the two major differences between gasoline and diesel engines.gasoline and diesel engines.

Describe the function and operation of the diesel Describe the function and operation of the diesel engine fuel-injection system.engine fuel-injection system.

Explain the difference between multiple-plunger Explain the difference between multiple-plunger and unit injector fuel-injection systems.and unit injector fuel-injection systems.

Identify the type of diesel engine that requires an Identify the type of diesel engine that requires an air blower.air blower.

Diesel Automotive Diesel Automotive EnginesEngines

Diesel engines have Diesel engines have long been the source of long been the source of power for heavy-duty power for heavy-duty trucks, trains, and ships.trucks, trains, and ships.

During the past few During the past few years, diesel engines years, diesel engines have become more have become more common as power common as power sources for sources for automobiles.automobiles.

Diesel Engines in Diesel Engines in AutomobilesAutomobiles

The main advantage of diesel engines over gasoline The main advantage of diesel engines over gasoline engines is their good fuel efficiency.engines is their good fuel efficiency.

Diesel powered automobiles average about 25% more Diesel powered automobiles average about 25% more miles per gallon than gasoline powered automobiles.miles per gallon than gasoline powered automobiles.

Diesel engines, however, must be made larger, stronger, Diesel engines, however, must be made larger, stronger, and heavier than gasoline engines.and heavier than gasoline engines.

They must withstand combustion pressures two to three They must withstand combustion pressures two to three times higher than those produced in gasoline engines.times higher than those produced in gasoline engines.

The added weight needed for strength reduces the The added weight needed for strength reduces the acceleration of the automobile.acceleration of the automobile.

A diesel engine of the same horsepower as a gasoline A diesel engine of the same horsepower as a gasoline engine is larger.engine is larger.

Types of Diesel EnginesTypes of Diesel Engines

There are two basic types There are two basic types of diesel engines in use of diesel engines in use today:today: Four-stroke cycleFour-stroke cycle Two-stroke cycleTwo-stroke cycle

These engines differ in the These engines differ in the number of piston strokes number of piston strokes required to produce a required to produce a power stroke.power stroke.

Their methods of intake Their methods of intake and exhaust are also and exhaust are also different.different.

Four-Stroke Cycle Diesel Four-Stroke Cycle Diesel EngineEngine

Four-stroke diesel engines are very similar to four-stroke gasoline Four-stroke diesel engines are very similar to four-stroke gasoline engines.engines.

The piston travels from one end of the cylinder to the other four The piston travels from one end of the cylinder to the other four times during each cycle.times during each cycle.

The fuel is ignited at the beginning of the third stroke of each cycle.The fuel is ignited at the beginning of the third stroke of each cycle. Intake air flows into each cylinder through intake valves in the Intake air flows into each cylinder through intake valves in the

cylinder head.cylinder head. Exhaust gases leave through exhaust valves.Exhaust gases leave through exhaust valves. These valves operate the same way as the valves in four-stroke These valves operate the same way as the valves in four-stroke

gasoline engines.gasoline engines. On the intake stroke, atmospheric pressure pushes air into the On the intake stroke, atmospheric pressure pushes air into the

cylinder through the intake valve.cylinder through the intake valve. The exhaust stroke forces burned gases out through the exhaust The exhaust stroke forces burned gases out through the exhaust

valve.valve. During the compression and power strokes, both valves are closed.During the compression and power strokes, both valves are closed.

Two-Stroke Cycle Diesel Two-Stroke Cycle Diesel EngineEngine

Two-stroke diesel engines are similar to two-stroke Two-stroke diesel engines are similar to two-stroke gasoline engines.gasoline engines.

They have only two strokes per cycle.They have only two strokes per cycle. The fuel is ignited on every other stroke of the piston.The fuel is ignited on every other stroke of the piston. In the two-stroke diesel engine, air is forced in and In the two-stroke diesel engine, air is forced in and

exhaust gases are forced out on a single stroke.exhaust gases are forced out on a single stroke. Usually a blower forces air into the cylinder through Usually a blower forces air into the cylinder through

intake ports.intake ports. The incoming air pushes remaining exhaust gases out The incoming air pushes remaining exhaust gases out

of the cylinder through an exhaust valve.of the cylinder through an exhaust valve.

Engine DesignEngine Design

The diesel engine looks much like the gasoline The diesel engine looks much like the gasoline engine.engine.

The operations of the mechanical systems are The operations of the mechanical systems are also similar in both engines.also similar in both engines.

The piston and crankshaft assembly, the valve The piston and crankshaft assembly, the valve assembly, the lubrication system, and the assembly, the lubrication system, and the cooling system operate in the same way.cooling system operate in the same way.

However, diesel systems are built stronger to However, diesel systems are built stronger to withstand higher combustion pressures.withstand higher combustion pressures.

Engine Design ContinuedEngine Design Continued

The two major differences between gasoline and The two major differences between gasoline and diesel engines are the way that fuel is supplied to diesel engines are the way that fuel is supplied to the cylinders and the way the fuel is ignited.the cylinders and the way the fuel is ignited.

The diesel engine does not need an ignition The diesel engine does not need an ignition system.system.

Compression heat ignites the fuel in the cylinder.Compression heat ignites the fuel in the cylinder. A special fuel system supplies fuel to the A special fuel system supplies fuel to the

cylinder.cylinder. Diesel fuel systems are very different from Diesel fuel systems are very different from

gasoline fuel systems.gasoline fuel systems.

Fuel SystemFuel System

In a gasoline engine, fuel is mixed with air in the In a gasoline engine, fuel is mixed with air in the carburetor or in the intake manifold.carburetor or in the intake manifold.

Diesel engines do not have carburetors.Diesel engines do not have carburetors. Only air flows into the combustion chamber through the Only air flows into the combustion chamber through the

intake manifold.intake manifold. Each intake stroke completely fills the cylinder with air.Each intake stroke completely fills the cylinder with air. Special devices inject fuel into the air inside the Special devices inject fuel into the air inside the

cylinder.cylinder. Engine power is controlled by metering the amount of Engine power is controlled by metering the amount of

fuel injected into the cylinders.fuel injected into the cylinders.

Fuel System ContinuedFuel System Continued

At idle, only a small amount of fuel is injected into each At idle, only a small amount of fuel is injected into each cylinder.cylinder.

The ratio of air to fuel may be 40 to 1.The ratio of air to fuel may be 40 to 1. The ratio in gasoline engines at idle is about 18 to 1.The ratio in gasoline engines at idle is about 18 to 1. As power needs increase, the amount of fuel injected As power needs increase, the amount of fuel injected

increases.increases. However the amount of air remains the same.However the amount of air remains the same. Therefore, the ratio of air to fuel decreases.Therefore, the ratio of air to fuel decreases. The intake stroke always takes in enough air to burn all The intake stroke always takes in enough air to burn all

the fuel injected during full-load operation.the fuel injected during full-load operation.

Fuel-Injection SystemsFuel-Injection Systems

The main components in a diesel fuel-injection The main components in a diesel fuel-injection system are the fuel-injection pump and the fuel system are the fuel-injection pump and the fuel injectors.injectors.

The job of the fuel injectors is to inject a The job of the fuel injectors is to inject a measured amount of fuel into the combustion measured amount of fuel into the combustion chamber.chamber.

When pressure is applied to the fuel, the When pressure is applied to the fuel, the injector opens and sprays fuel into the cylinder.injector opens and sprays fuel into the cylinder.

Combustion begins immediately.Combustion begins immediately.

Fuel-Injection Systems Fuel-Injection Systems ContinuedContinued

The fuel-injection pump produces the The fuel-injection pump produces the necessary high fuel pressure.necessary high fuel pressure.

On injection, diesel fuel must be under enough On injection, diesel fuel must be under enough pressure to offset the pressure inside the pressure to offset the pressure inside the combustion chamber (about 1000 psi during combustion chamber (about 1000 psi during combustion).combustion).

If the fuel pressure were not at least as high as If the fuel pressure were not at least as high as the pressure in the combustion chamber during the pressure in the combustion chamber during combustion, the fuel would not inject.combustion, the fuel would not inject.

Instead, pressure would leak from the Instead, pressure would leak from the combustion chamber into the injector nozzle.combustion chamber into the injector nozzle.

Fuel-Injection Systems Fuel-Injection Systems ContinuedContinued

The injection pump has two other functions.The injection pump has two other functions. It must regulate the amount of fuel directed to the It must regulate the amount of fuel directed to the

cylinder.cylinder. It must also control the timing of the fuel injection.It must also control the timing of the fuel injection. Engine power depends on the amount of fuel supplied to Engine power depends on the amount of fuel supplied to

the cylinders.the cylinders. The time at which injectors spray fuel into the cylinders is The time at which injectors spray fuel into the cylinders is

just as important.just as important. The injection pump controls this timing.The injection pump controls this timing. It makes sure that the injectors spray fuel just before TDC It makes sure that the injectors spray fuel just before TDC

(top dead center) of the compression stroke.(top dead center) of the compression stroke. By the time the fuel ignites, the piston will have started its By the time the fuel ignites, the piston will have started its

downward motion.downward motion.

Fuel Injection Fuel Injection ArrangementsArrangements

The injection pump and injectors may not The injection pump and injectors may not be completely separate.be completely separate.

These two parts can be arranged in three These two parts can be arranged in three different ways.different ways. Multiple-Plunger SystemMultiple-Plunger System Unit Injector SystemUnit Injector System Distributor SystemDistributor System

Multiple-Plunger SystemMultiple-Plunger System

In this system, there is a separate pumping unit In this system, there is a separate pumping unit (plunger) and a separate injector for each (plunger) and a separate injector for each cylinder.cylinder.

The plungers are all part of the fuel-injection The plungers are all part of the fuel-injection pump.pump.

A camshaft inside the pump controls the action A camshaft inside the pump controls the action of the plungers.of the plungers.

Fuel lines connect the plungers to the injectors.Fuel lines connect the plungers to the injectors. The amount of fuel to be injected is controlled The amount of fuel to be injected is controlled

at the fuel-injection pump.at the fuel-injection pump.

Unit Injector SystemUnit Injector System

In this system, the injection pump and In this system, the injection pump and injector are combined into one unit and injector are combined into one unit and are driven by the overhead camshaft.are driven by the overhead camshaft.

The plunger is a part of the injector.The plunger is a part of the injector. Pressurization, timing, and metering of Pressurization, timing, and metering of

the fuel all take place in the unit injector.the fuel all take place in the unit injector. An engine with this system has one unit An engine with this system has one unit

injector for each cylinder.injector for each cylinder.

Distributor SystemDistributor System

In this system, a single injection pump In this system, a single injection pump supplies fuel to a distributor. supplies fuel to a distributor.

The distributor directs fuel to the injectors The distributor directs fuel to the injectors in the right firing order.in the right firing order.

The metering of fuel is done at the pump.The metering of fuel is done at the pump.

Fuel-Injection System Fuel-Injection System OperationOperation

Diesel engines use several different injection systems.Diesel engines use several different injection systems. Their operating principles are the same.Their operating principles are the same. The multiple-plunger system contains both high- and The multiple-plunger system contains both high- and

low-pressure fuel systems.low-pressure fuel systems. The low-pressure system consists of a fuel pump, The low-pressure system consists of a fuel pump,

lines, and filters, similar to the parts in a gasoline lines, and filters, similar to the parts in a gasoline system.system.

These parts deliver fuel from the tank to the fuel-These parts deliver fuel from the tank to the fuel-injection pump.injection pump.

The high-pressure system consists of the fuel-injection The high-pressure system consists of the fuel-injection pump and the injectors. pump and the injectors.

These parts supply fuel to the cylinders.These parts supply fuel to the cylinders.

Glow PlugsGlow Plugs

Because there is no spark to ignite the fuel, diesel engines can Because there is no spark to ignite the fuel, diesel engines can be hard to start.be hard to start.

This is especially true in cold weather.This is especially true in cold weather. For improved starting, diesels are often equipped with glow For improved starting, diesels are often equipped with glow

plugs.plugs. Glow plugs have a small wire element that gets red-hot when Glow plugs have a small wire element that gets red-hot when

connected to an electrical source.connected to an electrical source. Each cylinder has a glow plug.Each cylinder has a glow plug. When the diesel is to be started, current from the battery heats When the diesel is to be started, current from the battery heats

the glow plugs.the glow plugs. The glow plugs then heat the fuel as it enters the cylinders.The glow plugs then heat the fuel as it enters the cylinders. This preheating of the fuel lowers its ignition point to improve This preheating of the fuel lowers its ignition point to improve

starting.starting.

Air Blowers and Air Blowers and TurbochargersTurbochargers

Two-stroke diesel engines require an air Two-stroke diesel engines require an air blower.blower.

This device forces air into the cylinder and This device forces air into the cylinder and drives out the exhaust gases.drives out the exhaust gases.

When the piston reaches the bottom of the When the piston reaches the bottom of the power stroke, the air inlet ports are uncovered.power stroke, the air inlet ports are uncovered.

The blower forces air into the cylinder.The blower forces air into the cylinder. The air drives the burned gases out the The air drives the burned gases out the

exhaust valve and fills the combustion exhaust valve and fills the combustion chamber.chamber.

Air Blowers and Air Blowers and Turbochargers ContinuedTurbochargers Continued

Some modern four-stroke diesel engines use a special Some modern four-stroke diesel engines use a special kind of blower called a turbocharger.kind of blower called a turbocharger.

A turbocharger consists of an air impellor and an A turbocharger consists of an air impellor and an exhaust turbine connected to a shaft.exhaust turbine connected to a shaft.

High-pressure exhaust gases leaving the engine drive High-pressure exhaust gases leaving the engine drive the turbine.the turbine.

The turbine, in turn, drives the air impellor.The turbine, in turn, drives the air impellor. The air impellor forces air into the combustion chamber The air impellor forces air into the combustion chamber

at a pressure higher than atmospheric pressure.at a pressure higher than atmospheric pressure. The action puts more air into the cylinder.The action puts more air into the cylinder. This provides higher compression for greater power This provides higher compression for greater power

output.output.

Test Your Knowledge Test Your Knowledge QuestionQuestion

1.1. What factor helped What factor helped diesel engines diesel engines grow in popularity grow in popularity as an automotive as an automotive engine?engine?

Good Fuel EfficiencyGood Fuel Efficiency

Test Your Knowledge Test Your Knowledge QuestionQuestion

2.2. Name the two major differences between gasoline Name the two major differences between gasoline and diesel engines?and diesel engines?

The way fuel is supplied to the cylinders (fuel injection)The way fuel is supplied to the cylinders (fuel injection)

And the way the fuel is ignited (compression ignition).And the way the fuel is ignited (compression ignition).

Test Your Knowledge Test Your Knowledge QuestionQuestion

3.3. What is the function What is the function of the diesel engine of the diesel engine fuel injector?fuel injector?

To inject a measured To inject a measured amount of fuel into amount of fuel into

the combustion the combustion chamber.chamber.

Test Your Knowledge Test Your Knowledge QuestionQuestion

4.4. What is the function of the glow plug?What is the function of the glow plug?

During starting, the glow plug heats the fuel During starting, the glow plug heats the fuel as it enters the cylinder. This lowers as it enters the cylinder. This lowers

the fuel’s ignition point to improve the fuel’s ignition point to improve starting.starting.

Test Your Knowledge Test Your Knowledge QuestionQuestion

5.5. Which type of diesel engine requires an Which type of diesel engine requires an air blower?air blower?

Two-stroke cycle engine.Two-stroke cycle engine.

Any Other Questions???Any Other Questions???