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Energy Transfer

Energy - Devices - Engine.

Links in pink will take you to the GCSE Chemistry site.

An engine burns a hydrocarbon  (petrol or diesel)
which has come from a fossil fuel.
The engine uses the released energy to rotate a steel shaft.
The rotational energy is used to move the vehicle
and to generate electricity for the vehicle's needs.

The fossil fuel is called "chemical energy"
because energy is released during chemical reactions with oxygen.
The fuel is burned.

Other examples of chemical energy are electrical cells and food.

A cell (or battery) transfers chemical energy into electrical energy.

Living organisms eat food and food is also called "chemical energy"
because energy is released during respiration.
Respiration is the reaction of oxygen with glucose
and is the reverse of photosynthesis.

An engine will transfer some of the available chemical energy
into rotational energy and some into heat.
We can calculate the efficiency of the engine using the equation

efficiency (%) = (useful energy out ÷ total energy in) x 100.

If the available chemical energy is 270,000J
and the rotational energy produced is 70,000J, then

efficiency = (70,000 ÷ 270,000) x 100
= 25·9 %.

A petrol engine has a typical efficiency of 20 to 30 %.
A diesel engine has a typical efficiency of 30 to 40 %.

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