A tank's engine determines the tank's power, including its ability to accelerate, climb hills, and generally maneuver over terrain. The power-to-weight radio determines the ability to accelerate to the maximum speed. A destroyed engine has a chance of starting a fire inside of your tank. This in turn can lead to the destruction of other modules, and eventually the entire tank. In addition, a ruptured fuel tank will increase the chance of a fire. A damaged engine will cut the power in half, drastically reducing acceleration and maximum speed. An inoperable engine will reduce engine power to zero and disable the turning controls until it is repaired.
This is lesser-known amongst players, but the engine does affect traverse speed.
Power - The engine power affecting how quickly the tank accelerates. Measured in horsepower (hp).
Chance of Fire - The chance the engine will start a fire inside the tank if destroyed.
Type - The engine type. Some consumables are only available for specific engine types.