Summary The two main components of the 4-stroke intake system are the air cleaner and the intake manifold. But in a diesel engine, fuel is delivered separately and the intake system carries air only. Also, since the diesel engine doesn’t have a carburetor, it has no throttle. Some diesels use a pneumatic governor with a butterfly valve at the entrance to the inlet manifold Diesel engines often have more than one air cleaner. Let’s look at the intake system for a 2-stroke diesel engine. There is only a very short time at the end of its power stroke to scavenge the exhaust gases and refill the cylinder with air. To achieve this in the time available, 2-stroke diesels use an engine-driven air pump, usually called a blower. It pressurizes the air so that when the inlet ports open, air from the blower enters the cylinder and helps scavenge the exhaust gases. Some 2-stroke diesel engines use a turbocharger which feeds air under pressure to the blower. The intake system of the diesel engine can be used to increase engine output. This can be done by increasing volumetric efficiency, that is, by increasing the amount of air-fuel mixture burned in the cylinders. In diesel injection systems, this partly occurs automatically because of the increased efficiency of fuel injection. Output can also be improved by using large, free-flowing intake manifolds, and by increasing the number, or the size, of inlet valves per cylinder to admit more charge into the combustion chamber. Another method is to use forced induction or supercharging.