Lesson 1/Learning Event 1
said to explode. The pressure created by the burning gunpowder forces the bullet out of the barrel at a very
fast speed. The energy created by the burning gunpowder is heat energy which does the useful work of
speeding the bullet on its journey.
In an automotive internal combustion engine, pressure is exerted on a piston in a cylinder in the same way
pressure is exerted on the bullet, forcing it-to move. However, instead of using gunpowder to create heat
energy, we use a mixture of fuel and air.
COMBUSTION
Any fuel such as gasoline, wood, or paper will not burn by itself. A gas, called oxygen, must be present to mix
and burn with the fuel. (Oxygen is a colorless and odorless gas that is contained in the air around us.)
This can be proven with a small jar, an airtight lid, and a wooden match. Strike the match, place it inside the
jar, and close the lid tightly. The match will burn fast at first and then begin to die down. The flame will
probably go completely out before the match is all burned.
The reason for the fire going out before the match was burned is that all the oxygen sealed in the jar was
burned or used up. For complete combustion of the fuel, an engine must also have an ample supply of air to
mix with the fuel. Since the engine gets the oxygen from the air, we generally refer to it as air instead of
oxygen.
TYPES OF ENGINES
Automotive engines may be grouped or classified according to the types of fuel burned, cooling system used, or
the arrangement of the valves or cylinders. The most common way of grouping them is by the type of fuel
they burn; for example, gasoline, diesel, and multifuel engines. Multifuel engines are designed to burn many
different fuels.
Types of Cooling Systems
Engines are classified by type of cooling system as being air- or liquid-cooled. Actually, all engines are cooled
by air to some extent. However, they are only classed as air-cooled when air is the only external means of
carrying heat away from the cylinders.
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