Fuels and Combustion
In general, the limit of inflammability/explosion limit of fuel gases is widened by the

Increase in temperature (i.e. preheating)
Increase in gas pressure
All of these
Use of pure oxygen for combustion instead of air

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Fuels and Combustion
Lignite is

A high rank coal
A black banded coal which burns with a non-smoky yellowish flame
Can be used for gasification and steam generation
A coking coal

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