Fuels and Combustion
Short/intense flame is produced during combustion of gaseous fuel by using

Preheated secondary air
Very little excess air
High amount/current of combustion air
Low amount/current of combustion air

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Fuels and Combustion
A coal having high ratio of volatile matter to fixed carbon as compared to a coal having low ratio of volatile matter to fixed carbon

Is more difficult to ignite and produces a shorter flame
None of these
Is less liable to spontaneous combustion on storage
Requires smaller combustion space and less secondary air

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