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Energy - Petrol and Diesel Engines for Vehicles.
What do Petrol and Diesel Engines do?
An engine burns a
(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.
What is the Efficiency of a Petrol or Diesel Engine?
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 %.
engine has a typical efficiency
of 20 to 30
A diesel engine has a typical efficiency of 30 to 40 %.
or diesel) is called "chemical
because energy is released during
chemical reactions with oxygen. The fuel is burned.
of chemical energy are electrical cells and food.
A cell (or battery)
transfers chemical energy into electrical energy.
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.
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