Question 319Motor Plants - Assistant Engineer

The correct answer is C) scavenging air. In a large, low-speed, main propulsion diesel engine, the scavenging air is cooled by seawater. The scavenging air is the air that is used to purge the exhaust gases from the engine cylinders after combustion. Cooling this air helps to improve the engine's efficiency and performance. The other answer choices are incorrect because the cylinder heads, exhaust valves, and injectors are typically cooled by a separate freshwater cooling system, not directly by seawater. The seawater is primarily used to cool the scavenging air in this type of diesel engine configuration.