How does increased ambient air temperature affect engine knock?

Increased ambient air temperature affects engine knock by increasing the possibility of engine knock. Engine knock, also known as detonation, occurs when fuel in the engine's combustion chamber ignites prematurely. Higher ambient temperatures can lead to a rise in the temperature of the intake air as it enters the engine. Warmer air is less dense and may not provide the necessary cooling effect during the compression stroke, allowing for more energy and heat retention within the combustion chamber.

As the cylinder temperature rises, there is a greater chance that the fuel-air mixture will reach a temperature sufficient for spontaneous ignition before the spark plug fires. This premature ignition can create a knocking or pinging sound and can cause damage to the engine over time. Therefore, with the increase in ambient air temperature, the likelihood of engine knock occurring also increases, making it essential for engine performance management and tuning, especially in hotter climates or during summer months.

The other options can be ruled out since a reduction in engine knock or no effect from ambient temperature changes would not align with the known thermodynamic principles governing combustion in engines. Additionally, the idea that increased temperatures make engine knock impossible contradicts the fundamental mechanics of how combustion works in relation to temperature.