Steam Boilers, Engines, Nozzles and Turbines
Spontaneous combustion is a phenomenon in which

Coal bursts into flame without any external ignition source but by itself due to gradual increase in temperature as a result of heat released by combination of oxygen with coal
All the fuel burns instantaneously producing high energy release
Fuel burns with less air
Explosion in furnace

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Steam Boilers, Engines, Nozzles and Turbines
Coke is produced by

Heating wood in a limited supply of air at temperatures below 300°C
Enriching carbon in the coal
Strongly heating coal continuously for about 48 hours in the absence of air in a closed vessel
Pulverizing coal in inert atmosphere

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Steam Boilers, Engines, Nozzles and Turbines
The function of a piston rod is

To guide motion of the piston rod and to prevent it from bending
To convert heat energy of the steam into mechanical work
To exhaust steam from the cylinder at proper moment
To transfer motion from the piston to the cross head

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