Internal Combustion Engine vs External Combustion Engine

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Chemistry ISU Report

In the car (Internal Combustion Engine)

Name: Chia Wei Qian

ID: 1101C12664

Period 4

Date: 14 May 2012

Lecturer: Mr. Jaroslaw Cebrowski


Car engine is amazing machine that convert the heat energy to mechanical energy to let the car move. As we know the modern car engine is works in the internal combustion so it is call internal combustion engines. But for the older technology, they used External Combustion Engines. It is far lower efficiency than internal combustion engines. The steam engine in old-style trains and steam boats are the best example of ECE (External Combustion Engines). The most of fuel that used in ECE is coal. The coal is burned to create the steam, and the high pressure of steam compressed and it create a motion in the engine. As we known gasoline and diesel are the basic fuel for Internal Combustion Engine. The gasoline and diesel are the type of gases that made from petroleum. The combustion of gasoline and diesel are mean that the gasoline or diesel react with the oxygen to create water and carbon dioxide gas. Gasoline/petrol is a mixture of few organic compounds, but the main compound of the Gasoline/petrol is the octane C8H18. So the simple chemical equation is 2C8H18 + 25O2 ( 16CO2 + 18H2O. Diesel is also a mixture of few hydrocarbon compounds. Diesel goes from C10H20 to C15H28 but the main compound of the diesel is C12H23. So the chemical equation is 4C12H23 + 71O2 ( 48CO2 + 46H2O. There are still possible for incomplete combustion of gasoline/petrol and diesel. Both incomplete reactions will produce the harmful carbon monoxide gas which can affect our wealth and oxygen gas. The incomplete combustion is performed because of not enough amount of oxygen gas. For the incomplete combustion of petrol, C8H18 + 17/2O2 ( 8CO + 9H2O. For the incomplete combustion of diesel, 2C12H23 + 27/2O2 ( 24CO + 23H2O. The coal is rather a mixture hydrocarbon compound, so there is no chemical formula for coal. Coal has few types, so the coal is contain 50%-100% of carbon and also other elements like hydrogen, nitrogen, oxygen and very small amount of sulphur by mass.

Description of Internal Combustion Engine

Steam engine in a train (External Combustion Engine)

Steam engine in a train is the 1st concept of ECE in car. In other words, steam engine is the 1st used of external combustion in the car engine. As the diagram above, the steam is created when the water or other fluids that turn into the higher pressure water vapour when it is heated by the combustion of coal. The water vapour is expanding 1600 times more than the volume of the water. So the expanding water vapour drives the pistons and crankshafts back and forth as the pistons and the crankshafts are connected together. So it causes the turning motion of the disc. Then the train is start moving forward.

Petrol or Diesel Engine (Internal Combustion Engine)


The four stroke cycle is the basic concept of the internal combustion of car engine convert heat into the motion. The four stroke which is intake stroke, compression stroke, ignition stroke and exhaust stroke.


Combustion of petrol or diesel oil in car engine

As the simple description of combustion of petrol or diesel oil in car engine, the mixture of oxygen gas and fuel (petrol or diesel oil) are fill in the cylinder when the piston go down and the intake valve open. So this is the intake stroke process. After that, the piston will going up to compress the mixture of oxygen gas and fuel. The compression of the mixture of oxygen gas and fuel increase the strength of explosion. Meanwhile it is the compression stroke process. In the ignition process, when the piston reaches the highest point in the cylinder, it is means that the gases also reach the maximum compression. At the same time, the spark plug emits a spark to lighting the fuel. The fuel react with oxygen gases perform combustion...
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