Engine Fundamentals of an Automobile

Atoms:

Atoms are the basic "building blocks" of the world. They are extremely tiny. There are about 100 billion billion atoms in a single drop of water! There are about a hundred varieties of atoms. Each has a special name: Gold, silver, aluminium, oxygen, hydrogen so on. About 20% of air is a gas called oxygen. Any substance made up of  only one atom is called an element.

Chemical reactions:

Atoms of different elements can connect up with each other. The process is called chemical reaction. Chemical reactions go on all around us all the time. The burning of fuel in automobile engine is chemical reaction. We normally refer this chemical reaction as combustion.

Combustion:

Automotive fuels are made up mostly of two elements, hydrogen and carbon, which have the chemical symbols as H and C. It is therefore called as hydrocarbon (HC). During complete combustion of engine, these two elements unite with a third element, the gas oxygen (O). Oxygen forms about 20% of air we breathe. Each oxygen atom connects up with 2 hydrogen atoms. Each carbon atoms connects with 2 oxygen atoms. The combining of hydrogen and oxygen produces water. The combining of carbon and oxygen produces carbon dioxide.

During the combustion of gasoline in the engine, the burning gases get very hot. Their temperature can go as high as 6000°F  (3319°C). This high temperature produces the pressure that makes the engine run and produce power.

With ideal, or perfect, combustion, all of the hydrogen and all of the carbon in the gasoline would combine with oxygen to form harmless H2o and Co2. However in the engine we don't get ideal combustion. Instead some of the gasoline doesn't burn. Also, some only partly burn producing carbon monoxide  instead of co2. The Un burnt gasoline and partly burnt gasoline cause pollution of air as they exit through the tail pipe with the exhaust gases. This is the reason that modern cars are equipped with antipollution devices. The devices reduce the amount of HC and CO coming from the engine.

Expansion of solids with heat:

Any solid, such as the metal in the engine piston, expands and gets larger as the temperature increases. However the piston must be free to reciprocate in the cylinder even if it gets very hot. The piston is designed so that it does not expand too much. If it did, it would stick inside the cylinder and the engine would damage and cease.