Chapter 1 engine components and classification

CHAPTER 1 – ENGINE

COMPONENTS & CLASSIFICATION

Prepared by: MUHAMMAD HILMI BIN ZAID

SUMMARY The topic covers basic theoretical

knowledge and understanding of engine components, classifications and terminologies. Areas involving engine construction, operating principles and valve train

SYLLABUS Understand engine construction

Explain various types of internal combustion engines construction and operation: two-stroke petrol and diesel four-stroke petrol and diesel rotary/Wankel

Understand basic engine terminologiesExplain basic engine terminologies such

as TDC, BDC, stroke, bore, displacement, compression ratio etc.

Understand cylinder head and valve train construction State the purpose of cylinder head Describe various type of valve train:

OHV OHC Multivalve

Explain typical valve timing diagram Explain basic operating principles of:

VTEC MIVEC VVTI CPS DVVT

INTRODUCTION TO ENGINES Engine provides the power to drive the

vehicle’s wheel. Biggest part of the engine is the cylinder

block. The cylinder block is a large casting of metal 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.

The cylinder head fits on top of the cylinder block to close off and seal the top of the cylinder.

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 through which the air-fuel mixture enters and burned gases exit the cylinder and the bore for the sparkplug.

The 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 the ports.

A camshaft controls the movement of the valves.

Springs are used to help close the valves.

The up-and-down 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.

The upper end of the connecting rod moves with the piston.

The lower end of the connecting rod is attached to the crankshaft and moves in a circle.

The end of the crankshaft is connected to the flywheel.

ENGINE CLASSIFICATIONS Operational cycles. (4 stroke or 2 stroke) Number of cylinders. (3,4,5,6,8,10,12

cylinders) Cylinder arrangement. (Flat, inline, V-

type) Valve train type. (OHC,OHV, DOHC) Ignition type (Spark, Compression) Fuel type (gasoline, natural gas,

methanol, diesel, propane, fuel cell, electric, hybrid)

ENGINE CONSTRUCTION Types of internal combustion engines

construction:4 Stroke petrol and diesel2 Stroke petrol and dieselRotary/wankel

4 STROKE PETROLIntake Stroke

Compression Stroke

Power Stroke

Exhaust Stroke

INTAKE STROKE The first stroke of the cycle is the intake stroke. As the piston moves away from top dead center (TDC), the

intake valve opens. The downward movement of the piston increases the volume of

the cylinder above it, reducing the pressure in the cylinder. Low pressure (engine vacuum) causes the atmospheric pressure to push a mixture of air and fuel through the open intake valve.

As the piston reaches the bottom of its stroke, the reduction in pressure stops, causing the intake of air-fuel mixture to slow down. It does not stop because of the weight and movement of the air-fuel mixture.

It continues to enter the cylinder until the intake valve closes. The intake valve closes after the piston has reached bottom dead center (BDC).

This delayed closing of the valve increases the volumetric efficiency of the cylinder by packing as much air and fuel into it as possible.

COMPRESSION STROKE The compression stroke begins as the piston

starts to move from BDC. The intake valve closes, trapping the air-fuel

mixture in the cylinder. The upward movement of the piston compresses

the air-fuel mixture, thus heating it up. At TDC, the piston and cylinder walls form a

combustion chamber in which the fuel will be burned.

The volume of the cylinder with the piston at BDC compared to the volume of the cylinder with the piston at TDC determines the compression ratio of the engine.

POWER STROKE The power stroke begins as the

compressed fuel mixture is ignited. With the valves still closed, an electrical

spark across the electrodes of a spark plug ignites the air-fuel mixture.

The burning fuel rapidly expands, creating a very high pressure against the top of the piston.

This drives the piston down toward BDC. The downward movement of the piston is transmitted through the connecting rod to the crankshaft.

EXHAUST STROKE The exhaust valve opens just before the piston

reaches BDC on the power stroke. Pressure within the cylinder causes the exhaust gas

to rush past the open valve and into the exhaust system.

Movement of the piston from BDC pushes most of the remaining exhaust gas from the cylinder.

As the piston nears TDC, the exhaust valve begins to close as the intake valve starts to open.

The exhaust stroke completes the four-stroke cycle. The opening of the intake valve begins the cycle

again. This cycle occurs in each cylinder and is repeated

over and over, as long as the engine is running.

It takes two full revolutions of the crankshaft to complete the four-stroke cycle.

One full revolution of the crankshaft is equal to 360 degrees of rotation; therefore, it takes 720 degrees to complete the four-stroke cycle.

During one piston stroke, the crankshaft rotates 180 degrees.

4 STROKE DIESEL The operation of a diesel engine is comparable to a gasoline

engine. They also have a number of components in common,

(crankshaft, pistons, valves, camshaft, and water and oil pumps. However, diesel engines have compression ignition systems.

Rather than relying on a spark for ignition, a diesel engine uses the heat produced by compressing air in the combustion chamber to ignite the fuel.

The compression ratio of diesel engines is typically three times (as high as 25:1) that of a gasoline engine.

As intake air is compressed, its temperature rises to 700°C to 900°C. Just before the air is fully compressed, a fuel injector sprays a small amount of diesel fuel into the cylinder. The high temperature of the compressed air instantly ignites the fuel.

The combustion causes increased heat in the cylinder and the resulting high pressure moves the piston down on its power stroke.

4 STROKE DIESEL ENGINE

2 STROKE ENGINE This engine requires only two strokes of the

piston to complete all four operations: intake, compression, power, and exhaust.

This is accomplished as follows: Movement of the piston from BDC to TDC completes

both intake and compression. When the piston nears TDC, the compressed air/fuel

mixture is ignited, causing an expansion of the gases. During this time, the intake and exhaust ports are closed.

Expanding gases in the cylinder force the piston down, rotating the crankshaft.

With the piston at BDC, the intake and exhaust ports are both open, allowing exhaust gases to leave the cylinder and air-fuel mixture to enter.

2 STROKE ENGINE

2 STROKE ENGINE Although the two-stroke-cycle engine is

simple in design and lightweight because it lacks a valve train, it has not been widely used in automobiles.

It tends to be less fuel efficient and releases more pollutants into the atmosphere than four-stroke engines.

ROTARY/WANKEL ENGINE The rotary engine, or Wankel engine, is

similar to the standard piston engine in that it is a spark ignition, internal combustion engine.

Its design, however, is quite different. For one thing, the rotary engine uses a rotating motion rather than a reciprocating motion.

In addition, it uses ports rather than valves for controlling the intake of the air-fuel mixture and the exhaust of the combusted charge.

ROTARY/WANKEL ENGINE

CHARACTERISTICS OF ROTARY ENGINE The rotating combustion chamber

engine is small and light for the amount of power it produces, which makes it attractive for use in automobiles.

However, the rotary engine at present cannot compete with a piston gasoline engine in terms of durability, exhaust emissions, and economy.

BASIC ENGINE TERMINOLOGIES Bore – cylinder diameter measured in

inches(in) or milimeters (mm). Stroke – length of the piston travel between

TDC & BDC. TDC – Top dead center BDC – Bottom dead center If bore = stroke, the engine is called a

square engine. If bore > stroke, the engine is called a

oversquare engine. If bore < stroke, the engine is called a

undersquare engine.

Cylinder Displacement – volume of the cylinder when the piston is at BDC.

Engine displacement – sum/total of the displacement of each of the engine cylidners. Typically, an engine with a larger displacement

produces more torque than a smaller displacement engine.

Compression ratio – comparison of a cylinder’s volume when the piston is at BDC to the cylinder’s volume when the piston is at TDC. The higher the compression ratio, the more power

an engine theoretically can produce.

ENGINE EFFICIENCY Volumetric efficiency describes the

engine’s ability to have its cylinders filled with air-fuel mixture.

If the engine’s cylinders are able to be filled with air-fuel mixture during its intake stroke, the engine has a volumetric efficiency of 100%.

Typically, engines have a volumetric efficiency of 80% to 100%.

CYLINDER HEAD & VALVE TRAIN Purpose of cylinder head

The cylinder head fits on top of the cylinder block to close off and seal the top of the cylinder.

The cylinder head also contains ports through which the air-fuel mixture enters and burned gases exit the cylinder and the bore for the sparkplug.

TYPE OF VALVE TRAIN Overhead Valve (OHV) Overhead Cam (OHC) Multivalve

OVERHEAD VALVE (OHV) The intake and exhaust valves in an OHV engine

are mounted in the cylinder head and are operated by a camshaft located in the cylinder block.

This arrangement requires the use of valve lifters, pushrods, and rocker arms to transfer camshaft rotation to valve movement.

OVERHEAD CAM (OHC) An OHC engine also has the intake and exhaust

valves located in the cylinder head. But the cam is located in the cylinder head. In an OHC engine, the valves are operated directly

by the camshaft or through cam followers or tappets. Engines with one camshaft above a cylinder are

often referred to as single overhead camshaft (SOHC) engines.

MULTIVALVE A multivalve design typically has three, four,

or five valves per cylinder to achieve improved performance.

Any four-stroke internal combustion engine needs at least two valves per cylinder: one for intake of air and fuel, and another for exhaust of combustion gases.

Multi-valve engines tend to have smaller valves have lower reciprocating mass, can reduce wear on each cam lobe, more power from higher RPM without the danger

of valve bounce.

MULTIVALVE Three-valve cylinder head

This has a single large exhaust valve and two smaller intake valves

Four-valve cylinder headThis is the most common type of multi-valve

head, with two exhaust valves and two similar (or slightly larger) inlet valves.

Five-valve cylinder headLess common is the five-valve head, with

two exhaust valves and three inlet valves. All five valves are similar in size.

VALVE TIMING Valve timing is the precise timing of the opening and closing of

the valves. One way to look at this diagram is to think of these events in

terms of the position of the crankshaft and 360 degrees rotation.

VALVE TIMING With traditional fixed valve timing, an engine will have a

period of valve overlap at the end of the exhaust stroke, when both the intake and exhaust valves are open.

The intake valve is opened BTDC because to give enough time for air-fuel mixture to get into the cylinder.

The intake valve is allowed open ABDC because to get advantages of inertia created by velocity assists in drawing in the fresh charge.

The exhaust valve is opened BBDC because the gases inside the cylinder posses a higher pressure even after the expansion stroke. This higher pressure enables it to reduce the work that needs to be done by the engine piston in pushing out these gases.

The exhaust valve close ATDC because to give sufficient time for exhaust gas exit through the exhaust valve. If the exhaust valve is closed like in actual timing diagram, a certain amount of exhaust gases will get compressed and remain inside the cylinder and will be carried to the next cycle also.

VARIABLES VALVE TIMING At low speed, a little valve lift already sufficient for

air/fuel to enter the cylinder. The fuel consumption is better and enough for

cruising and low speed. But at high speed, the valve need to open and

close very fast and need more longer time for air/fuel to enter the cylinder.

Therefore, the valve lift must be higher and the timing is longer.

If the engine has fixed valve lift and valve timing, the performance will be bad.

To increase the performance of the engine and better fuel consumption, variable valve timing is introduced.

VARIABLES VALVE TIMING How it works?

As the camshaft spins, the lobes open and close the intake and exhaust valves in time with the motion of the piston.

VVT is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions.

Some cars use a device that can advance the valve timing. This does not keep the valves open longer; instead, it opens them later and closes them later.

VIDEO

VARIABLES VALVE TIMING Type of variables valve timing

VTEC (Honda)MIVEC (Mitsubishi)VVTI (Toyota)CPS (Proton)DVVT (Perodua)

VIDEO How an Engine Works - Comprehensive T

utorial Animation featuring Toyota Engine Technologies

EXERCISE1. Explain how 4-stroke engine works?2. Compare 2-stroke and 4-stroke engines.3. Compare petrol and diesel engine.4. Sketch and explain 4 process in the rotary

engine.5. An engine has 4 cylinders. Each cylinder

has a bore of 5.15cm and its stroke is 6cm. Calculate the engine displacements.

6. Draw and explain a typical valve timing diagram for 4-stroke petrol engine.

7. What is ‘valve overlap’?

QUIZ 1Chapter 1

9 July 2013 (Tuesday)

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