During cruising, which type of mixture is generally preferred?

During cruising, a weak mixture is generally preferred because it enhances fuel efficiency and optimizes engine performance. In the context of reciprocating engines, having a lean or weak mixture—where there is a higher ratio of air to fuel—leads to more complete combustion. This is vital for maintaining engine temperature, reducing the likelihood of fouling spark plugs, and ensuring cleaner emissions.

In cruising conditions, the engine operates at a steady state rather than going through cycles of acceleration or deceleration, which makes a weak mixture ideal. The engine can utilize the surplus air to burn fuel more completely while producing sufficient power. This balance helps in achieving better fuel economy over long durations of operation, which is a significant consideration for cruise phases.

In contrast, a rich mixture is beneficial primarily during full power situations, such as takeoff or climbing, where maximum power output is required. Stoichiometric mixtures are typically used to achieve a balance between power and efficiency but are less efficient than a weak mixture during cruising. Thus, a weak mixture aligns with the need for efficiency and sustained performance during cruising.