FAA Powerplant Written Practice Test

During engine operation, what is the result of applying carburetor heat?

1. It increases engine power significantly

2. It decreases air density to the carburetor

3. It improves fuel efficiency

4. It enhances the air-fuel mixture quality

The correct answer is: It decreases air density to the carburetor

Applying carburetor heat during engine operation primarily decreases the air density entering the carburetor. This occurs because carburetor heat takes warm air from around the engine, rather than the cooler, denser air that typically enters the carburetor. When warm air is introduced, it reduces the overall density of the air-fuel mixture. Although this can help prevent carburetor icing by keeping the temperature above freezing, it does lead to a decrease in engine power since the warmer air is less dense, resulting in the loss of the optimal air-fuel ratio. Therefore, while decreasing air density is a consequence of using carburetor heat, it is important to remember that this can have implications for engine performance under certain conditions. The other options do not accurately capture the primary effect of carburetor heat: increasing engine power significantly usually does not occur with carburetor heat, fuel efficiency is not necessarily improved, and while it may affect the quality of the air-fuel mixture, the dominant outcome is the alteration in air density affecting performance.