FAA Powerplant Written Practice Test

What is a major consequence of high carburetor air temperatures in a reciprocating engine?

1. Improved engine performance

2. Increased volumetric efficiency

3. Decrease in volumetric efficiency

4. Enhanced fuel combustion

The correct answer is: Decrease in volumetric efficiency

High carburetor air temperatures in a reciprocating engine negatively impact the engine's performance due to a decrease in volumetric efficiency. Volumetric efficiency refers to the ratio of the amount of air-fuel mixture actually drawn into the engine cylinders compared to the theoretical maximum amount that could be drawn in. When the air temperature is high, the air becomes less dense, resulting in a lower mass of air being drawn into the engine. This loss of density means that there is less oxygen available for combustion, which subsequently reduces the amount of fuel that can be effectively burned. Consequently, the engine cannot produce the optimal power output, leading to a drop in overall performance. Maintaining appropriate air temperatures is crucial for ensuring that the engine operates efficiently and produces the necessary power.