Engineering Thermodynamics
The air standard efficiency of an Otto cycle is given by (where r = Compression ratio, and γ = Ratio of specific heats)

1 - rγ - 1
1 - (1/ rγ - 1)
1 + rγ - 1
1 + (1/ rγ - 1)

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Engineering Thermodynamics
Carbonization of coal consists of

Drying and crushing the coal to a fine powder
Moulding the finely ground coal under pressure with or without a binding material
None of these
Heating the wood with a limited supply of air to temperature not less than 280°C

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