When is an engine considered to be supercharged?

An engine is considered to be supercharged when the manifold pressure exceeds atmospheric pressure. This condition is achieved through the use of a supercharger, which is a device that increases the density of the air entering the engine's cylinders. By compressing the air, the supercharger allows more air molecules to enter the combustion chamber, which, in turn, enables the engine to burn more fuel and produce more power.

The fundamental principle behind supercharging is to force the engine to take in more air than it would under normal atmospheric conditions. When the pressure in the manifold (the pathway for air into the engine) exceeds that of the surrounding atmosphere, it indicates that the air has been sufficiently compressed. This increased air density leads to better combustion and enhanced performance characteristics in the engine.

In contrast, the other options do not accurately describe the conditions for supercharging. For instance, exhaust temperature being lower than normal can indicate other factors affecting combustion efficiency, but it does not directly relate to the supercharging process. Similarly, a doubling of horsepower output is not a definitive criterion for supercharging, as the performance of an engine depends on various factors, including design and tuning. The richness of the fuel-air mixture refers to the ratio of fuel to air but does not directly indicate