FAA Powerplant Written Practice Test

What effect does high carburetor air temperature have on engine performance?

1. It increases volumetric efficiency

2. It has no effect on engine performance

3. It decreases volumetric efficiency

4. It improves fuel quality

The correct answer is: It decreases volumetric efficiency

High carburetor air temperature negatively impacts engine performance by decreasing volumetric efficiency. Volumetric efficiency refers to the engine's ability to draw in air and mix it with fuel for combustion. When the air temperature increases, the air becomes less dense, resulting in a lower mass of oxygen entering the combustion chamber. As the air is less dense at higher temperatures, there is a reduction in the amount of oxygen available for combustion. This can lead to a less efficient burning of fuel, which decreases the overall power output of the engine. In the context of carbureted engines, maintaining optimal air temperatures is crucial for achieving maximum efficiency and performance, as cooler air allows for better combustion and ultimately more power. The other options do not accurately reflect the relationship between high carburetor air temperature and engine performance. Increasing volumetric efficiency, having no effect on performance, or improving fuel quality would not occur in the presence of high air temperatures, as they would contradict the established principles of engine operation and thermodynamics.