What are the two primary functions of fuel in the engine?

The primary functions of fuel in an engine revolve around its roles in the combustion process and temperature regulation. Fuel acts as a combustion agent, which means it is the substance that, when combined with air and ignited, produces the energy necessary to power the engine. This energy is essential for generating the thrust required for the aircraft to operate.

Additionally, fuel also serves as a cooling agent. During combustion, the fuel absorbs heat, helping to regulate the temperature within the engine. This is crucial for preventing engine overheating, which could lead to failure or damage.

The other choices do not fully encompass the primary roles of fuel. While some options mention lubrication and temperature maintenance, these are more relevant to oil and coolant systems rather than fuel. Fuel's key contributions are focused specifically on facilitating combustion and managing engine temperature through its inherent properties. Thus, the option that identifies fuel's role as both a combustion agent and a cooling agent accurately captures the dual purpose of fuel in the engine.