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
The diagram factor is the ratio of the

Actual workdone per stroke to the theoretical workdone per stroke
Actual mean effective pressure to the theoretical mean effective pressure
Area of the actual indicator diagram to the area of theoretical indicator diagram
Any one of the above

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