Do
you ever lifted the hood of your car and noticed what was happening in there? The
car engine below the hood look like complicated jumble of tubes, metal and
wires. Sometimes out of curiosity you want to know what is going inside or
sometimes when you are buying a car or in traffic you notice something written
on backside of the car in front of you like ‘CRDI’, ‘1.5 Litre V-6’, ‘ABS’ etc. What does all of them mean?
In
this article, we will know the concept in detail behind the making of car
engine, its assembly and its working.
Wheels
may be 5500 years old, but the cars we drive round in today made their debut
only in 1885. That was when German engineer Karl Benz (1844–1929) fastened a
small gasoline (petrol) engine to a three-wheeled cart and made the first
primitive, gas-powered car. Although Benz developed the automobile, another
German engineer, Nicholas Otto (1832–1891), was arguably even more important—for
he was the man who'd invented the gasoline engine in the first place, about two
decades earlier. It's a testament to Otto's genius that virtually every car
engine made ever since has been inspired by his "four-stroke" design.
What
is a car?
That's not quite such an obvious question as it seems. A
car is a metal box with wheels at
the corners that gets you from A to B, yes, but it's more than that. In
scientific terms, a car is an energy converter: a machine that releases
the energy locked
in a fuel like gasoline (petrol) or diesel and
turns it into mechanical energy in moving wheels and gears. When the wheels
power the car, the mechanical energy becomes kinetic energy: the energy that
the car and its occupants have as they go along.
How do we get power
from petroleum?
Cars,
trucks, trains, ships, and planes—all these things are powered by fuels made
from petroleum. Also known as "crude oil", petroleum is the
thick, black, energy-rich liquid buried deep underground that became the
world's most important source of energy during the 20th century. After being
pumped to the surface, petroleum is shipped or piped to a refinery and
separated into gasoline, kerosene, and diesel fuels, and a whole host of
other petrochemicals—used to make everything from paints to plastics.
Petroleum
fuels are made from hydrocarbons: the molecules inside consist mostly of
carbon and hydrogen atoms (with a fewer other elements, such as
oxygen, attached for good measure). Wood, paper,
and coal also contain hydrocarbons. We can turn hydrocarbons into useful energy
simply by burning them. When you burn hydrocarbons in air, their molecules
split apart. The carbon and hydrogen combine with oxygen from the air to make
carbon dioxide gas and water, while the energy that held the molecules together
is released as heat. This process, which is called combustion, releases
huge amounts of energy. When you sit round a camp fire, warming yourself near
the flames, you're really soaking up energy produced by billions of molecules
cracking open and splitting apart!
People
have been burning hydrocarbons to make energy for over a million years—that's
why fire was invented. But ordinary fires are usually quite inefficient. When
you cook sausages on a camp fire, you waste a huge amount of energy. Heat
shoots off in all directions; hardly any goes into the cooking pot—and even
less into the food. Car engines are much more efficient: they waste less energy
and put more of it to work. What's so clever about them is that they burn fuel
in closed containers, capturing most of the heat energy the fuel releases, and
turning it into mechanical energy that can drive the car along.
What are the main
parts of a car engine?
Car
engines are built around a set of "cooking pots"
called cylinders (usually anything from two to twelve of them, but
typically four, six, or eight) inside which the fuel burns. The cylinders are
made of super-strong metal and
sealed shut, but at one end they open and close like bicycle pumps: they have
tight-fitting pistons (plungers) that can slide up and down inside
them. At the top of each cylinder, there are two valves (essentially "gates" letting
things in or out that can be opened and closed very quickly). The inlet
valve allows fuel and air to enter the cylinder from a carburetor or
electronic fuel-injector; the outlet valve lets the exhaust gases
escape. At the top of the cylinder, there is also a sparking plug (or
spark plug), an electrically controlled device that makes a spark to set fire
to the fuel. At the bottom of the cylinder, the piston is attached to a
constantly turning axle called a crankshaft.
The crankshaft powers the car's gearbox which, in turn, drives the wheels.
Let's look at some key engine parts in
more detail.
Spark plug
The spark plug supplies
the spark that ignites the air/fuel mixture so that combustion can occur. The
spark must happen at just the right moment for things to work properly.
Valves
The
intake and exhaust valves open at the proper time to let in air and fuel and to
let out exhaust. Note that both valves are closed during compression and
combustion so that the combustion chamber is sealed.
Piston
A
piston is a cylindrical piece of metal that moves up and down inside the
cylinder.
Piston rings
Piston
rings provide a sliding seal between the outer edge of the piston and the inner
edge of the cylinder. The rings serve two purposes:
· They prevent the fuel/air mixture and exhaust in
the combustion chamber from leaking into the sump during compression and
combustion.
· They keep oil in
the sump from leaking into the combustion area, where it would be burned and
lost.
Most cars that "burn oil" and
have to have a quart added every 1,000 miles are burning it because the engine
is old and the rings no longer seal things properly.
Connecting rod
The
connecting rod connects the piston to the crankshaft. It can rotate at both
ends so that its angle can change as the piston moves and the crankshaft
rotates.
Crankshaft
The
crankshaft turns the piston's up and down motion into circular motion just like
a crank on a jack-in-the-box does.
Sump
The
sump surrounds the crankshaft. It contains some amount of oil, which collects
in the bottom of the sump (the oil pan).
How many cylinders
does an engine need?
One
problem with the four-stroke design is that the crankshaft is being powered by
the cylinder for only one stage out of four. That's why cars typically have at
least four cylinders, arranged so they fire out of step with one another. At
any moment, one cylinder is always going through each one of the four stages—so
there is always one cylinder powering the crankshaft and there's no loss of
power. With a 12-cylinder engine, there are at least three cylinders powering
the crankshaft at any time—and that's why those engines are used in fast and
powerful cars.
Car engine is an internal
combustion engine -- combustion takes place internally.
Internal Combustion
The principle behind any reciprocating
internal combustion engine: If you put a tiny amount of high-energy fuel (like
gasoline) in a small, enclosed space and ignite it, an incredible amount of
energy is released in the form of expanding gas. You can use that energy to
propel a potato 500 feet. In this case, the energy is translated into potato
motion. You can also use it for more interesting purposes. For example, if you
can create a cycle that allows you to set off explosions like this hundreds of
times per minute, and if you can harness that energy in a useful way, what you
have is the core of a car engine!
Almost all cars currently use what is
called a four-stroke combustion cycle to convert gasoline into
motion. The four-stroke approach is also known as the Otto cycle, in honor
of Nikolas Otto, who invented it in 1867. The four strokes are
- Intake stroke
- Compression stroke
- Combustion stroke/ Power stroke
- Exhaust stroke
You can see in the picture that a device called a piston which is in cylindrical shape. The piston is connected to the crankshaft by
a connecting rod. As the crankshaft revolves, it carries the power of the engine to the wheels. Here's what happens as the engine goes
through its cycle:
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- The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work. (Part 1 of the figure)
- Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful. (Part 2 of the figure)
- When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes, driving the piston down. (Part 3 of the figure)
- Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tailpipe. (Part 4 of the figure)
Now the engine is ready for the next cycle, so it intakes
another charge of air and gas.
Engine Configurations:
The core of the engine is the cylinder, with the piston moving
up and down inside the cylinder. The engine described above has one cylinder.
That is typical of most lawn mowers, but most cars have more than
one cylinder (four, six and eight cylinders are common). In a multi-cylinder
engine, the cylinders usually are arranged in one of three ways: inline, V or flat (also
known as horizontally opposed or boxer), as shown in the following figures.
Different configurations have different advantages and
disadvantages in terms of smoothness, manufacturing cost and shape
characteristics. These advantages and disadvantages make them more suitable for
certain vehicles.
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Fuel System (Injectors):
A fuel injector is nothing but
an electronically controlled valve. It is supplied with pressurized fuel by
the fuel pump in your car, and it is capable of opening and closing many times
per second.
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| Inside a fuel injector |
When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel -- to make as fine a mist as possible so that it can burn easily.
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| A fuel injector firing |
The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU. The injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurized fuel to all of the injectors. In order to provide the right amount of fuel, the engine control unit is equipped with a whole lot of sensors.
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| Three Fuel injectors. The fuel rail is the pipe on the left. |
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Air Intake System:
The function of the air intake system is to allow air to reach your car engine. Oxygen in the air is one of the necessary ingredients for the engine combustion process. A good air intake system allows for clean and continuous air into the engine, thereby achieving more power and better mileage for your car.
A modern automobile air intake system has three main parts: air filter, mass flow sensor and throttle body. Located directly behind the front grille, the air intake system draws air through a long plastic tube going into the air filter housing, which will be mixed with the car fuel. Only then will the air be sent to the intake manifold that supplies the fuel/air mixture to the engine cylinders.
An air filter is an important part of a car's intake system, because it is through the air filter that the engine "breathes". It is usually a plastic or metal box in which the air filter sits.
An engine requires an exact mixture of fuel and air in order to run, and all of the air enters the system first through the air filter. The air filter's job is to filter out dirt and other foreign particles in the air, preventing them from entering the system and possibly damaging the engine.
The air filter is usually located in the air stream to your throttle valve assembly and intake manifold. It is found in a compartment in an air duct to the throttle valve assembly under the hood of your car.
Oil or Lubrication System:
In the modern engine, the lubrication system is more vital than every due to the very low tolerances and higher temperatures that the engines must perform at.
The oil starts in the oil pan where it is drawn up through the pickup screen and tube, and forced through the oil pump. The pressure relief valve bleeds off any excess oil pressure and re-routes it back to the oil pan. The pump directs the oil to the oil filter where it is cleaned. If the oil filter is too dirty the pressure in the filter will build until a bypass valve, built in the filter, opens and allows the oil to go to the engine without cleaning. From the filter, the oil makes its way through oil galleries in the cylinder block to the crankshaft main bearings. It then flows through the hollow crankshaft to lubricate the connecting rod bearings. Other oil galleries in the block bring the oil to the top of the engine where the camshaft bearings, lobes and the valve lifters are lubricated. On some engines, push rods on top of the lifters deliver oil to rocker arms and valve stems.
The oil returns to the oil pan via gravity. Drain passages in the head allow the oil that has collected to flow through. Some of the oil returning to the pan hits the rotating crankshaft and is splashed around lubricating the piston, piston rings and cylinder walls.
oil filter
The function of the oil filter is to remove dirt, sludge and dust from the oil. Oil filters should be changed every time the engine oil is changed. Oil filters are designed to trap foreign particles suspended in the oil to prevent them from getting to engine bearings and other parts. Modern engines use the full flow filtering system. This means that all the oil goes through the filter before it goes to the engine parts.
The filter accomplishes the filtering task with the use of a filter element made from folded (pleated) paper. The folds provide a large filtering area within a small container. If the filter becomes clogged a special valve called the bypass valve will open and allow the oil to go to the engine parts without going through the filter. Another valve prevents the oil from draining out of the filter when the engine is stopped.
Filters come in different sizes and are rated in micron ratings. Micron rating refers to how small the dirt particles are that the filter will let through.
Specific Usage Oils:
Specific Usage Oils and Lubricants are of many types which used in various applications that are explained in greater details below:
Air Filter Cleaner: Air Filter Cleaners specially treated high quality detergent that provides quick, efficient and comfortable cleaning of air filters.
Air Filter Oil: Air filter Oil is a chemical or a fuel used for tuning and moistening the foam filter element of an air filter.
Compressor Oil: This type of oil is specifically used for lubricating the working parts such as bearings, pistons, rings, cylinders and valves along with the pressurized spaces in a compressor.
Engine Oil: This type of liquid oil acts as a protective lubricating barrier that carries the excessive heat away from moving engine parts. Engine Oil is used for cleaning, lubricating as well as cooling of an internal combustion engine.
Gear Oil: Gear Oil also called as motor oil, this type of oil is produced exclusively for lubricating transmissions, transfer cases, and differentials in automobiles. These oils have strong sulfur smell and can be used for enhancing the shifting performance of gearboxes.
Oil Additives: Oil additives are the liquids that are supposedly used for reducing engine wear and enhancing fuel efficiency.
Oil Stabilizer: Oil Stabilizer are the additional components added to the oil in order to enlarge and extend its life and reduces oil temperature in any type of engine be it gasoline or diesel. Moreover, oil stabilizers also discard noise, leaks as well as overheating in worn gearboxes.
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Ignition System:
With a four stroke gasoline engine, we use the motion of a piston to suck in air and fuel. Once the air/fuel mixture is trapped inside the cylinder we compress the mixture to raise its temperature close to what is required to start the air and fuel burning. As the piston nears the top of the compression stroke the spark plug fires.The heat of the spark provides enough extra energy to start the fuel burning.The burning air and fuel drastically raises the temperature and pressure inside the cylinder and the piston is forced back down for the Power stroke.
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Cooling System:
A car engine produces a lot of heat when it is running, and must be cooled continuously to avoid engine damage. Generally this is done by circulating coolant liquid usually water mixed with an antifreeze solution through special cooling passages. Some engines are cooled by air flowing over finned cylinder casings.
A water-cooled engine block and cylinder head have interconnected coolant channels running through them. At the top of the cylinder head all the channels converge to a single outlet. A pump, driven by a pulley and belt from the crankshaft, drives hot coolant out of the engine to the radiator, which is a form of heat exchanger. Unwanted heat is passed from the radiator into the air stream, and the cooled liquid then returns to an inlet at the bottom of the block and flows back into the channels again. Usually the pump sends coolant up through the engine and down through the radiator, taking advantage of the fact that hot water expands, becomes lighter and rises above cool water when heated. Its natural tendency is to flow upwards, and the pump assists circulation.
The radiator is linked to the engine by rubber hoses, and has a top and bottom tank connected by a core a bank of many fine tubes. The tubes pass through holes in a stack of thin sheet-metal fins, so that the core has a very large surface area and can lose heat rapidly to the cooler air passing through it. On older cars the tubes run vertically, but modern, low-fronted cars have cross flow radiators with tubes that run from side to side. In an engine at its ordinary working temperature, the coolant is only just below normal boiling point. The risk of boiling is avoided by increasing the pressure in the system, which raises the boiling point. The extra pressure is limited by the radiator cap, which has a pressure valve in it. Excessive pressure opens the valve, and coolant flows out through an overflow pipe. In a cooling system of this type there is a continual slight loss of coolant if the engine runs very hot. The system needs topping up from time to time.
Later cars have a sealed system in which any overflow goes into an expansion tank, from which it is sucked back into the engine when the remaining liquid cools.
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Exhaust System:
The exhaust manifold attaches to the cylinder head and takes each cylinders exhaust and combines it into one pipe. The manifold can be made of steel, aluminum, stainless steel, or more commonly cast iron.
All modern fuel injected cars utilize an oxygen sensor to measure how much oxygen is present in the exhaust. From this the computer can add or subtract fuel to obtain the correct mixture for maximum fuel economy. The oxygen sensor is mounted in the exhaust manifold or close to it in the exhaust pipe.
This muffler like part converts harmful carbon monoxide and hydrocarbons to water vapor and carbon dioxide. Some converters also reduce harmful nitrogen oxides. The converter is mounted between the exhaust manifold and the muffler.
Muffler:
The muffler serves to quiet the exhaust down to acceptable levels. Remember that the combustion process is a series of explosions that create allot of noise. Most mufflers use baffles to bounce the exhaust around dissipating the energy and quieting the noise. Some mufflers also use fiberglass packing which absorbs the sound energy as the gases flow through.
Exhaust pipe:
Between all of the above mention parts is the exhaust pipe which carries the gas through it's journey out your tail pipe. Exhaust tubing is usually made of steel but can be stainless steel (which lasts longer due to it's corrosion resistance) or aluminized steel tubing. Aluminized steel has better corrosion resistance than plain steel but not better than stainless steel. It is however cheaper than stainless steel.
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