AMP - Aviation Maintenance Technician Powerplant Practice Exam

What defines a "lean mixture" in engine operation?

1. A fuel-air mixture with a higher proportion of fuel compared to air

2. A fuel-air mixture with equal proportions of fuel and air

3. A fuel-air mixture with a higher proportion of air compared to fuel

4. A mixture that leads to increased engine temperature

The correct answer is: A fuel-air mixture with a higher proportion of air compared to fuel

A "lean mixture" in engine operation is defined as a fuel-air mixture that has a higher proportion of air compared to fuel. In this scenario, the engine receives more air than is typically necessary for the combustion of the available fuel. This condition can enhance engine efficiency and improve fuel economy, as the excess air allows for more thorough combustion of the fuel, potentially resulting in lower emissions. When an engine runs on a lean mixture, it tends to operate at lower fuel flow rates, which can also lead to higher combustion temperatures. However, the primary defining characteristic is the relative proportion of the air versus fuel in the mixture. Thus, understanding the proper balance of air and fuel is crucial in achieving optimal engine performance and efficiency.