Both the turbocharged engine and naturally aspirated engine are both internal combustion engines. But there is a difference in how they work.
Let’s start with a naturally aspirated engine. A naturally aspirated engine is an internal combustion engine that works with normal atmospheric air pressure without an air compressor such as a turbo or supercharger.
The naturally aspirated engine sucks in air from the atmosphere, and the air goes into the engine, before the air gets to the cylinder, the pressure is not increased. When the air gets to the cylinder, the piston moves upwards to reduce the volume of the cylinder and thereby increase the air pressure before combustion takes place.
Meanwhile, a turbocharged engine sucks in air from the atmosphere to a component known as turbo, and the air pressure is increased before it is sent to the cylinder for combustion.
So the major difference between the two is that the naturally aspirated engine uses the air from the atmosphere without the air pressure being increased or compressed. While the turbocharged engine tampers with the air pressure, by increasing the pressure by compressing it. So before the air gets to the cylinder it has already been compressed.
No wonder an engine with a Turbocharger is more powerful than a naturally aspirated engine. Because the turbo helps the engine suck more air and therefore be able to burn more fuel which results in more power. A turbocharged engine can also use a supercharger in place of a turbocharger depending on the engine design. Whether turbocharger or supercharger, it serves the same purpose, the only difference is what the manufacturer decides to use.
It is statistically believed that the turbo increases the volume of air that goes into the engine by 50% more than a naturally aspirated engine.
For example, a 4-cylinder diesel generator without a turbo is rated at 45 kVA. Yet, another similar 4-cylinder engine with a turbo is rated 75 kVA.
Then you can ask yourself, what is the difference? The difference is the turbo. The turbo makes the engine more powerful because the engine sucks in more air and burns more fuel, than a naturally aspirated engine.
Looking at the same series of engines, you will also notice that the Turbocharger engine’s piston and cylinder is bigger than the one of the naturally aspirated engine of the same series.
So if you see an engine without a turbo as a supercharger it is referred to as a naturally aspirated engine. But when you see an engine with a turbocharger or supercharger that compresses the air before going to the engine, it is referred to as a turbocharged engine.
Note: A 2-stroke Detroit diesel with a blower is still a naturally aspirated engine, not a turbocharged engine because a blower does not compress the air as much as a supercharger or a turbo.