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What is a car?

Inside a classic car engine

Photo: The restored (and nicely polished!) engine in a classic car from the early 1970s.

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.

Nodding donkey oil pump

Photo: Petroleum can be extracted from the ground by "nodding donkey" pumps like this one. Picture courtesy of US Department of Energy.

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!

Chart comparing typical fuel consumption in barrels per year of various cars.

Photo: Why does the world use so much oil? There are now about a billion petroleum-powered cars on the planet and, as this chart shows, even the most energy-efficient models burn through at least 10 barrels (420 gallons) of petroleum in a year. Drawn using energy impact scores for 2016 models shown on the US Department of Energy's Fuel Economy website.

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.

Types of Engine:


1. External combustion (E.C.) Engine


It is an engine in which combustion of fuel take place outside of the engine. In this type of engine heat, which is generated by burning of fuel is use to convert the water or other low boiling temperature fluid into steam. This high pressure steam used to rotate a turbine. In this engine we can use all solid, liquid and gases fuel. These engines are generally used in driving locomotive, ships, generation of electric power etc.


Advantages of E.C. engine-

  • In these engines starting torque is generally high.
  • Because of external combustion we can use cheaper fuels as well as solid fuel.
  • They are more flexible compare to internal combustion engines.



2. Internal Combustion (I.C.) Engine


It is an engine in which combustion of fuel take place inside the engine. When the fuel burns inside the engine cylinder, it generates a high temperature and pressure. This high pressure force is exerted on the piston (A device which free to moves inside the cylinder and transmit the pressure force to crank by use of connecting rod), which used to rotate the wheels of vehicle. In these engines we can use only gases and high volatile fuel like petrol, diesel. These engines are generally used in automobile industries, generation of electric power etc.


Advantages of I.C. engine-

  • It has overall high efficiency over E.C. engine.
  • These engines are compact and required less space.
  • Initial cost of I.C. engine is lower than E.C. engine.
  • This engine easily starts in cold because of it uses high volatile fuel.


Types of I.C. Engine

I.C. engine is widely used in automobile industries so it is also known as automobile engine. An automobile engine may be classified in many manners. Today I am going to tell you some important classification of an automobile engine.


According to number of stroke:


1.Two stroke engine


In a two stroke engine a piston moves one time up and down inside the cylinder and complete one crankshaft revolution during single time of fuel burn. This type of engine has high torque compare to four stroke engine. These are generally used in scooters, pumping sets etc.


2.Four stroke engine


In a four stroke engine piston moves two times up and down inside the cylinder and complete two crankshaft revolutions during single time of fuel burn. This type of engines has high average compare to two stroke engine. These are generally used in bikes, cars, truck etc.

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.

How does a four-stroke engine make power?

How the cylinder in a car engine makes power

Watch this animation and you'll see that a car engine makes its power by endlessly repeating a series of four steps (called strokes):

  1. Intake: The piston (green) is pulled down inside the cylinder (gray) by the momentum of the crankshaft (grey wheel at the bottom). Most of the time the car is moving along, so the crankshaft is always turning. The inlet valve (left) opens, letting a mixture of fuel and air (blue cloud) into the cylinder through the purple pipe.
  2. Compression: The inlet valve closes. The piston moves back up the cylinder and compresses (squeezes) the fuel-air mixture, which makes it much more flammable. When the piston reaches the top of the cylinder, the sparking plug (yellow) fires.
  3. Power: The spark ignites the fuel-air mixture causing a mini explosion. The fuel burns immediately, giving off hot gas that pushes the piston back down. The energy released by the fuel is now powering the crankshaft.
  4. Exhaust: The outlet valve (right) opens. As the crankshaft continues to turn, the piston is forced back up the cylinder for a second time. It forces the exhaust gases (produced when the fuel burned) out through the exhaust outlet (blue pipe).

The whole cycle then repeats itself.

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.