Automotive Technology: The Engine and Engine Systems

ENGINE BASICS

The engine provides the power to drive the wheels of the vehicle. All automobile engines, both gasoline and diesel, are classified as internal combustion engines because the combustion or burning that creates energy takes place inside the engine.

Combustion is the burning of an air and fuel mixture. As a result of combustion, large amounts of pressure are generated in the engine. This pressure or energy is used to power the car. The engine must be built strong enough to hold the pressure and temperatures formed by combustion.

Diesel engines have been around a long time and are mostly found in big heavy-duty trucks. However, they are also used in some pickup trucks and will become more common in automobiles in the future. Although the construction of gasoline and diesel engines is similar, their operation is quite different.

A gasoline engine relies on a mixture of fuel and air that is ignited by a spark to produce power. A diesel engine also uses fuel and air, but it does not need a spark to cause ignition. A diesel engine is often called a compression ignition engine. This is because its incoming air is tightly compressed, which greatly raises its temperature. The fuel is then injected into the compressed air. The heat of the compressed air ignites the fuel and combustion takes place. The following sections cover the basic parts and the major systems of a gasoline engine.

Cylinder Block

The biggest part of the engine is the cylinder block, which is also called an engine block. The cylinder block is a large casting of metal (cast iron or aluminum) that is drilled with holes to allow for the passage of lubricants and coolant through the block and provide spaces for movement of mechanical parts. The block contains the cylinders, which are round passageways fitted with pistons. The block houses or holds the major mechanical parts of the engine.

Cylinder Head

The cylinder head fits on top of the cylinder block to close off and seal the top of the cylinders. The combustion chamber is an area into which the air-fuel mixture is compressed and burned. The cylinder head contains all or most of the combustion chamber. The cylinder head also contains ports, which are passageways through which the air-fuel mixture enters and burned gases exit the cylinder. A cylinder head can be made of cast iron or aluminum.

Piston

The burning of air and fuel takes place between the cylinder head and the top of the piston. The piston is a can-shaped part closely fitted inside the cylinder. In a four-stroke cycle engine, the piston moves through four different movements or strokes to complete one cycle. These four are the intake, compression, power, and exhaust strokes. On the intake stroke, the piston moves downward, and a charge of air-fuel mixture is introduced into the cylinder. As the piston travels upward, the air-fuel mixture is compressed in preparation for burning. Just before the piston reaches the top of the cylinder, ignition occurs and combustion starts. The pressure of expanding gases forces the piston downward on its power stroke. When it reciprocates, or moves upward again, the piston is on the exhaust stroke. During the exhaust stroke, the piston pushes the burned gases out of the cylinder.

Connecting Rods and Crankshaft

The reciprocating motion of the pistons must be converted to rotary motion before it can drive the wheels of a vehicle. This conversion is achieved by linking the piston to a crankshaft with a connecting rod. As the piston is pushed down on the power stroke, the connecting rod pushes on the crankshaft, causing it to rotate. The end of the crankshaft is connected to the transmission to continue the power flow through the drivetrain and to the wheels.

Valve Train

A valve train is a series of parts used to open and close the intake and exhaust ports. A valve is a movable part

that opens and closes a passageway. A camshaft controls the movement of the valves, causing them to open and close at the proper time. Springs are used to help close the valves.

Manifolds

A manifold is metal ductwork assembly used to direct the flow of gases to or from the combustion chambers. Two separate manifolds are attached to the cylinder head. The intake manifold delivers a mixture of air and fuel to the intake ports. The exhaust manifold mounts over the exhaust ports and carries exhaust gases away from the cylinders.

The engine's pistons fit tightly in the cylinders and are connected to the engine's crankshaft with connecting rods. Piston; Cylinder; Connecting rod; Crankshaft

|||| 8 The valve train for one cylinder of an overhead valve engine. Lifter; Camshaft; Pushrod; Oil return

|||| 9 The blue manifold is the intake manifold and the red manifold is for the exhaust.

ENGINE SYSTEMS

The following sections present a brief explanation of the systems that help an engine run and keep running.

Lubrication System

The moving parts of an engine need constant lubrication. Lubrication limits the amount of wear and reduces the amount of friction in the engine. Friction is heat generated when two objects rub against each other.

Motor or engine oil is the fluid used to lubricate the engine. Several quarts of oil are stored in an oil pan bolted to the bottom of the engine block. The oil pan is also called the crankcase or oil sump. When the engine is running, an oil pump draws oil from the pan and forces it through oil galleries. These galleries are small passageways that direct the oil to the moving parts of the engine.

Oil from the pan passes through an oil filter before moving through the engine. The filter removes dirt and metal particles from the oil. Premature wear and damage to parts can result from dirt in the oil. Regular replacement of the oil filter and oil is an important step in a preventive maintenance program.

|||| Oil flow in a typical engine's lubrication system. Oil pump; Pickup screen Oil pan; Oil filter

|||| A typical engine cooling system. Radiator; Automatic transmission cooler lines; Lower radiator hose; Water pump; Water jackets; Temperature sender; Heat control valve; Heater hoses; Warning light; Heater core; Bypass; Thermostat; Upper radiator hose

Cooling System

The burning of the air-fuel mixture in the combustion chambers of the engine produces large amounts of heat. This heat must not be allowed to build up and must be reduced. This heat can easily damage and warp the metal parts of an engine. To prevent this, engines have a cooling system.

The most common way to cool an engine is to circulate a liquid coolant through passages in the engine block and cylinder head. An engine can also be cooled by passing air over and around the engine. Few air cooled engines are used in automobiles today because it’s very difficult to maintain a constant temperature at the cylinders. If the engine is kept at a constant temperature, it will run more efficiently.

A typical cooling system relies on a water pump, which circulates the coolant through the system. The pump is typically driven by the engine. The coolant is a mixture of water and antifreeze. The coolant is pushed through passages, called water jackets, in the cylinder block and head to remove heat from the area around the cylinders' combustion chambers. The heat picked up by the coolant is sent to the radiator.

The radiator transfers the coolant's heat to the out side air as the coolant flows through its tubes. To help remove the heat from the coolant, a cooling fan is used to pull cool outside air through the fins of the radiator.

To raise the boiling point of the coolant, the cooling system is pressurized. To maintain this pressure, a radiator or pressure cap is fitted to the radiator. A thermostat is used to block off circulation in the sys tem until a preset temperature is reached. This allows the engine to warm up faster. The thermostat also keeps the engine temperature at a predetermined level. Because parts of the cooling system are located in various spots under the vehicle's hood, hoses are used to connect these parts and keep the system sealed.

Fuel and Air System

The fuel and air system is designed to supply the correct amount of fuel mixed with the correct amount of air to the cylinders of the engine. This system also:

• +++Stores the fuel for later use
• +++Delivers fuel to a device that will control the amount of fuel going to the engine
• +++Collects and cleans the outside air
• +++Delivers outside air to the individual cylinders
• +++Changes the fuel and air ratios to meet the needs of the engine during different operating conditions

The fuel system is made up of different parts. A fuel tank stores the liquid gasoline. Fuel lines carry the liquid from the tank to the other parts of the sys tem. A pump moves the gasoline from the tank through the lines. A filter removes dirt or other particles from the fuel. A fuel pressure regulator keeps the pressure below a specified level. An air filter cleans the outside air before it’s delivered to the cylinders.

Fuel injectors mix fuel with the air for delivery to the cylinders or directly to the cylinders. An intake manifold directs the air to each of the cylinders.

|||| The intake system for a V-10 in a Dodge Viper. From Chrysler.

|||| 3 A typical exhaust system on a late-model car. Exhaust head pipe; Exhaust manifold; Catalytic converter; Downstream HO2S sensor (used for catalyst testing); Upstream HO2S sensor (used for fuel control); Gasket Resonator; Muffler; Heat insulator; Intermediate pipe; Tailpipe; Hanger

Emission Control System

In the past one of the chief contributors to air pollution was the automobile. For some time now, engines have been engineered to emit very low amounts of certain pollutants. The pollutants that have been drastically reduced are hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOX). The Environmental Protection Agency establishes emissions standards that limit the amount of these pollutants a vehicle can emit.

To meet these standards, many changes have been made to the engine itself. There also have been systems developed and added to the engines to reduce the pollutants they emit. A list of the most common pollution control devices follows:

+++Positive crankcase ventilation (PCV) system. This system reduces HC emissions by drawing fuel and oil vapors from the crankcase and sends them into the intake manifold where they are delivered to and burned in the cylinders. This system prevents the pressurized vapors from escaping the engine and entering into the atmosphere.

+++Evaporative emission control system. This system reduces HC emissions by drawing fuel vapors from the fuel system and releases them into the intake air to be burned. This system stops these vapors from leaking into the atmosphere.

+++Exhaust gas recirculation (EGR) system. This sys tem introduces exhaust gases into the intake air to reduce the temperatures reached during combustion. This reduces the chances of forming NOX during combustion.

+++Catalytic converter. Located in the exhaust system, it allows for the burning or converting of HC, CO, and NOX into harmless substances, such as water.

+++Air injection system. This system reduces HC emissions by introducing fresh air into the exhaust stream to cause minor combustion of the HC in the engine's exhaust.

Exhaust System

During the exhaust stroke, the engine's pistons move up and push the burned air-fuel mixture, or exhaust, out of the combustion chamber and into the exhaust manifold. From the manifold, the gases travel through the other parts of the exhaust system until they are expelled into the atmosphere. The exhaust system is designed to direct toxic exhaust fumes away from the passenger compartment, to quiet the sound of the exhaust pulses, and to burn or catalyze pollutants in the exhaust. A typical exhaust system contains the following components:

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