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

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

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Fuels and Combustion
Fuel gases containing hydrocarbons (ie.g. coke oven gas) are not preheated before burning, mainly because

It reduces its calorific value tremendously
There are chances of explosion during preheating
The hydrocarbons crack thereby choking and fouling the heat transfer surface by carbon soot
It reduces its flame temperature tremendously

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