A diesel engine is a type of internal combustion engine that uses diesel fuel to operate. Unlike gasoline engines, which ignite fuel with a spark, diesel engines compress air to a high temperature, causing the diesel fuel to ignite when injected. This process makes diesel engines more efficient and powerful, especially for heavy-duty vehicles. Diesel engines are commonly found in trucks, buses, and ships due to their durability and fuel efficiency. They tend to produce more torque, making them suitable for transporting heavy loads. However, they also emit higher levels of certain pollutants, which has led to increased scrutiny and regulations.