Question

What is thr difference between a combustible substance and a fuel??

Answer 1

The basic difference is that combustion is heating and no flames are produced whereas in burning most of the energy is converted to light energy and this results in less heat energy as compared to combustion.

Combustionis a chemical process in which a substance reacts rapidly with oxygen and gives off heat. The original substance is called the fuel, and the source of oxygen is called the oxidizer.
combustion refers to a process where a substance(termed--FUEL) reacts with oxygen to give out heat and light.
in this case it is not necessary that a substance will undergo combustion to produce a flame. substances that vapourize, only produce flame for E.G. charcoal undergo combustion but instead of forming a flame it glows( as dry charcoal do not form any vapour).
WHEREAS
when in a combustion process a flame is produced it is referred to burning. for E.G. a lighted candle.
here , it must be clear that only a fuel / combustible substance that vapourize form a flame implying all vapourizing substances do not produce a flame.
hope this helps .
regards Zareen.