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

All the fuel burns instantaneously producing high energy release
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
Fuel burns with less air
Explosion in furnace

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Steam Boilers, Engines, Nozzles and Turbines
For a Parson's reaction turbine, if α₁ and α₂ are fixed blade angles at inlet and exit respectively and β₁ and β₂ are the moving blade angles at entrance and exit respectively, then

α₁ = β₁ and α₂= β₂
α₁ = α₂ and β₁ = β₂
α₁ < β₁ and α₂ > β₂
α₁ = β₂ and β₁ = α₂

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