Internal Combustion Engines
The output of a diesel engine can be increased without increasing the engine revolution or size in following way

Supercharging
Feeding more fuel
Scavenging
Heating incoming air

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Internal Combustion Engines
Fuel consumption of diesel engines is not guaranteed at one quarter load because at such low loads

The small difference in cooling water temperature or in internal friction has a disproportionate effect
The friction is unpredictable
The engine is rarely operated
The friction is high

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