Engineering Thermodynamics
The condition for the reversibility of a cycle is

The pressure and temperature of the working substance must not differ, appreciably, from those of the surroundings at any stage in the process
All of these
All the processes, taking place in the cycle of operation, must be extremely slow
The working parts of the engine must be friction free

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Engineering Thermodynamics
Producer gas is obtained by

Passing steam over incandescent coke
Partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast
Carbonization of bituminous coal
Passing air and a large amount of steam over waste coal at about 650°C

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