An 11-liter engine refers to an internal combustion engine with a displacement of 11 liters, which measures the total volume of all the cylinders in the engine. This large engine size is typically found in heavy-duty vehicles, such as trucks, buses, and construction equipment, where significant power and torque are required for demanding tasks. Engines of this size are designed to produce high levels of horsepower and torque, making them suitable for towing and carrying heavy loads. They often use diesel fuel for better fuel efficiency and durability, contributing to their popularity in commercial applications.