Engine Mechanic

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Have you ever opened the hood of your car and wondered what was going on in there? A car engine can look like a big confusing jumble of metal,

tubes and wires to the uninitiated.

You might want to know what's going on simply out of curiosity. Or perhaps you are buying a new car, and you hear things like "3.0 liter V-6" and

"dual overhead cams" and "tuned port fuel injection." What does all of that mean?

In this article, we'll discuss the basic idea behind an engine and then go into detail about how all the pieces fit together, what can go wrong and how

to increase performance.

The purpose of a gasoline car engine is to convert gasoline into motion so that your car can move. Currently the easiest way to create motion from

gasoline is to burn the gasoline inside an engine. Therefore, a car engine is an internal combustion engine -- combustion takes place internally.

Combustion of gases like gasoline (mixture of carbon and hydrogen) at high temperature (3316°C), which produces pressure and causes power.

Some unburnt gasoline or partially burnt gasoline are ejected to the air through tailpipe. Gravity, atmospheric pressure & vaccum cause the fuel to enter the cylinder and causes the generation of power. Electricity is required to crank the engine & start it. Electricity operates the fuel system and provide spark at the spark plug. Electric ignition system supplies the spark that ignite the compressed air- fuel mixture in the engine cylinder. To reduce the amount of wiring in the vehicle, the metal engine, chessis and body serve as return circuit. Engine is controlled in two ways: Mechanical and Electrical.

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Many automotive vehicles have electronic engine control (EEC).It usually controls the fuel system and ignition system. This allow engine to operate as fuel efficient as possible. Many other components in the car may be controlled by electronic engine control (EEC).such as charging system,

transmission, suspension, brake, air conditioning, drivers information system etc.

Internal Combustion Engine Working of an engine

An engine is a mechanic that converts heat energy into mechanical energy. The heat from burning the fuel produces power which moves the vehicle. Sometimes the engine is called the power plant.

Automotive engines are internal combustion engine, because the fuel that is burnt internally i.e. inside the engine. They have piston that moves up and down in cylinder. These are called piston engine.

The internal combustion engine was invented by Jean Joseph Etienne Lenoir (Belgian Born). Lenoir made the first internal combustion engine that provides a reliable and continuous source of power, which was the gas engine using coal gas, in 1860, in France.

The creation of the rocket made by the Chinese people is considered to be the simplest kind of internal combustion engine. Also previous pioneers who also worked on the internal combustion engine but failed, also helped in the development of the internal combustion engine.

The first practical internal combustion engine based heavily on experience from the production of steam engines. The engine had a horizontal cylinder; slide valves were used to draw in the fuel-air mixture; and it was double acting, the mixture being fed into the cylinder alternately at either end of the piston. Once it is in the cylinder the mixture was ignited by electric sparks generated at spark plugs by a coil and a battery. This ignition system, a primitive ancestor of modern electric ignition, was unreliable.

Because the first internal combustion engine was unreliable, many later pioneers made improvements of the first internal combustion engine. As a result many new engines were made. Such engines were the two and four stroke engine and the petrol engine. Siegfried Marcus in Austria in 1864 was able to create an engine that uses petrol as a fuel. The first internal combustion engine is the basic form for modern car engines.

The invention of the internal combustion engine made some of man’s most cherished dreams become reality: the aircraft, the motor car, the submarine, the tank and many other inventions before they could be born in there practical form. Nowadays the internal combustion engine is for effective and economical than ever, with reduced gas emissions and lower fuel consumption.

 Piston engines are of two types

Spark – ignition engine (Petrol engine) Combustion – ignition engine (Diesel engine)

The difference between them: Diesel Engines vs. Gasoline Engines

The type of fuel used. The way fuel gets into the cylinders. The way fuel is ignited.

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The spark engine usually runs on a liquid fuel such as gasoline or an alcohol blend. The fuel must be volatile so that it vaporizes quickly. The fuel vapor mixes with air before entering the cylinders. This forms the highly combustible air – fuel mixture that burns easily. The mixture then enters the cylinder and is compressed. Heat from an electric spark produced by the ignition system sets fires to, or ignites the air – fuel mixture. As the mixture burns (Combustion) high temperature and pressure are produced in the cylinder. This high pressure applied to the top of the piston, forces it to move down the cylinder. The motion is carried by gears and shafts to the wheels that drive the car. The wheels turn and car moves.

In the compression – ignition engine, the fuel mixes with the air after it enters the engine cylinder. Compressing the air much raises its temperature to 538°C or higher. A light oil called diesel fuel is then sprayed or injected into the hot air or heat of compression ignites the fuel. The method of ignition – by heat of compression – gives the diesel engine the name compression – ignition engine.

Piston

Reciprocating to Rotary Motion

The reciprocating motion of the piston must be changed to rotary motion to turn the drive wheels. A connecting rod and a crank on the crankshaft make this conversion. The load on the piston due to combustion of fuel in the combustion chamber is transmitted to crankshaft through the connecting rod. One end of connecting rod known as small end and is connected to the piston through gudgeon pin while the other end known as big end and is connected to crankshaft through crank pin. Hence the rotation of the crankshaft leads to the rotate the wheels.( DOR=Direction of rotation.)

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Engine Operation Four Stroke Engine Animation

As their name implies, four-stroke internal combustion engines have four basic steps that repeat with every two

revolutions of the engine:

(1) Intake stroke (2) Compression stroke (3) Power stroke and (4) Exhaust stroke

1. Intake stroke: The first stroke of the internal combustion engine is also known as the suction stroke because the

piston moves to the maximum volume position (downward direction in the cylinder). The inlet valve opens as a result

of piston movement, and the vaporized fuel mixture enters the combustion chamber. The inlet valve closes at the end

of this stroke.

2. Compression stroke: In this stroke, both valves are closed and the piston starts its movement to the minimum

volume position (upward direction in the cylinder) and compresses the fuel mixture. During the compression process,

pressure, temperature and the density of the fuel mixture increases.

3. Power stroke: When the piston reaches the minimum volume position, the spark plug ignites the fuel mixture and

burns. The fuel produces power that is transmitted to the crank shaft mechanism.

4. Exhaust stroke: In the end of the power stroke, the exhaust valve opens. During this stroke, the piston starts its

movement in the minimum volume position. The open exhaust valve allows the exhaust gases to escape the cylinder.

At the end of this stroke, the exhaust valve closes, the inlet valve opens, and the sequence repeats in the next cycle.

Four-stroke engines require two revolutions.

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Basic Engine Construction

Valve ActionIn many engines cylinder has two valves. One is an intake valve, the other is the exhaust valve. The valve is the

series of parts that open and close the valves. The action start at the camshaft. The crankshaft drives the camshaft

through gears, sprockets and chain, or sprockets and a toothed timing belt. Most camshafts have a cam for each

valve in the engine. Each cam is a round collar with a high spot or lob.

The camshaft mounts overhead, on top of the cylinder head. The bucket tappet sits top of the valve stem.

Underneath the bucket is the valve spring that holds the tappet up against the cam. When the rotating cam brings the

cam lobe down against the top of the bucket tappet, the lobe pushes the tappet down. This compresses the spring

and pushes the valve down off its seat. The valve opens. As the cam continues to rotate ,the lobe moves away from

the tappet. The spring pushes the tappet and valve up until the valve seats.

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Multiple-cylinder engines

A single-cylinder four-stroke piston engine spends three- quarters of its running time exhausting burned gas, drawing in fresh mixture and com- pressing it.

On only one of the four strokes—the power stroke—is any energy produced and this makes the output of a single- cylinder four-stroke engine very uneven.

This can be smoothed out if more cylinders, with their pistons driving a common crank- shaft, are used. A twin-cylinder four-stroke, for instance, will produce one power stroke for each revolution of the crank- shaft, instead of every other revolution as on a single-cylinder engine.

If the engine has four cylinders it produces one power stroke for each half-turn of the crankshaft and at no time is the crankshaft free-wheeling’ on one of the three passive strokes.

Even better results can be obtained using six cylinders, as the power strokes can be made to overlap, so that the crankshaft receives a fresh impulse before the previous power stroke has died away—on an in-line six-cylinder engine the crankshaft receives three power impulses each revolution.

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In theory, the more cylinders you can use to drive the crank- shaft, the smoother the power output, and 8-and 12-cylinder engines are used on some of the more expensive cars.

A large number of cylinders can pose practical problems. An engine with eight cylinders in a straight line for instance would have a very long crank- shaft which would tend to twist and be more likely to break at higher engine speeds. The car would also need a long bonnet to enclose the engine.

So in the interests of crank- shaft rigidity and compactness, 8-and 12-cylinder engines have their cylinders arranged in a V, with two cylinder heads and a common crankshaft.

There are also V-6 and V-4 cylinder engines.

The other layout in popular use is where the cylinders are horizontally opposed in two flat banks, with the crankshaft between them. Its low build makes the flat engine particularly suitable for rear installation. In 4-or 6-cylinder form, the flat engine has excellent mechanical balance as movement of a piston assembly in one direction is perfectly.

Basic Engine SystemsA spark – ignition engine requires four basic systems to run. A combustion – ignition engine requires three of

these:

Engine ClassificationAutomotive engines can be classified according to:

1. Number of cylinders.

2. Arrangement of cylinders.

3. Arrangement of valves and valve trains.

4. Type of cooling.

5. Number of strokes per cycle.

6. Type of fuel burned.

7. Method of ignition.

8. Firing order.

9. Reciprocating or rotary.

Most commonly used cylinder arrangement is in-line 4 cylinders engine. After that V-6 engine is commonly used.

Number of strokes per cycle.

Four stroke engine.

Two stroke engine.

Two stroke engineA two-stroke engine is an internal combustion engine that completes the process cycle in one revolution of the crankshaft (an up stroke and a down stroke of the piston, compared to twice that number for a four-stroke engine). This is accomplished by using the end of the combustion stroke and the beginning of the compression stroke to perform simultaneously the intake and exhaust (or scavenging) functions. In this way, two-stroke engines often provide high specific power, at least in a narrow range of rotational speeds. The functions of some or all of the valves required by a four-stroke engine are usually served in a two-stroke engine by ports that are opened and closed by the motion of the piston(s), greatly reducing the number of moving parts. Gasoline (spark ignition) versions are

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particularly useful in lightweight (portable) applications, such as chainsaws, and the concept is also used in diesel compression ignition engines in large and weight insensitive applications, such as ships and locomotives.

Rotary enginesThe rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders

per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated

around it. Its main application was in aviation, although it also saw use in a few early motorcycles and cars.

This type of engine was widely used as an alternative to conventional in-line or V engines during World War I and the

years immediately preceding that conflict, and has been described as "a very efficient solution to the problems of

power output, weight, and reliability".

By the early 1920s, however, the inherent limitations of this type of engine had rendered it obsolete, with the power

output increasingly going into overcoming the air-resistance of the spinning engine itself. The rotating mass of the

engine also had a significant gyroscopic precession: depending on the type of aircraft, this produced stability and

control problems, especially for inexperienced pilots. Another factor in the demise of the rotary was the fundamentally

inefficient use of fuel and lubricating oil caused in part by the need for the fuel/air mixture to be aspirated through the

hollow crankshaft and crankcase.

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Wankel engine working

The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into a

rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside

of an oval-like epitrochoid-shaped housing and a rotor that is similar in shape to a Reuleaux triangle but with sides that

are somewhat flatter. The very compact Wankel engine delivers smooth high-rpm power. It is commonly called

a rotary engine, though this name applies also to other completely different designs. It is the only internal combustion

engine invented in the twentieth century to go into production.

The engine was invented by German engineer Felix Wankel. He received his first patent for the engine in 1929, began

development in the early 1950s at NSU, completing a working prototype in 1957.[1] NSU then licensed the concept to

companies around the world, which have continued to improve the design.

Thanks to their compact design, Wankel rotary engines have been installed in a variety of vehicles and devices

includingautomobiles, motorcycles, racers, aircraft, go-karts, jet skis, snowmobiles, chain saws, and auxiliary power

units. Perhaps the greatest proponent of the Wankel engine has been the Japanese company Mazda.

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In an internal combustion engine, the term indirect injection refers to a fuel injection where fuel is not directly injected into the combustion chamber. Gasoline engines are usually equipped with indirect injection systems, wherein a fuel injector delivers the fuel at some point before the intake valve.

An indirect injection diesel engine delivers fuel into a chamber off the combustion chamber, called a prechamber, where combustion begins and then spreads into the main combustion chamber. The prechamber is carefully designed to ensure adequate mixing of the atomized fuel with the compression-heated air. This has the effect of slowing the rate of combustion, which tends to reduce audible noise and softens the shock of combustion and produces lower stresses on the engine components. The addition of a prechamber, however, increases heat loss to the cooling system and thereby lowers engine efficiency. The engine requires glow plugs for starting. In an indirect injection system the air moves fast, mixing the fuel and air. This simplifies injector design and allows the use of smaller engines and less tightly toleranced designs which are simpler to manufacture and more reliable. Direct injection, by contrast, uses slow-moving air and fast-moving fuel; both the design and manufacture of the injectors is more difficult. The optimisation of the in-cylinder air flow is much more difficult than designing a prechamber. There is much more integration between the design of the injector and the engine.[1] It is for this reason that car diesel engines were almost all indirect injection until the ready availability of powerful CFD simulation systems made the adoption of direct injection practical.

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