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, often used in large vehicles like trucks and buses. These engines are known for their durability and fuel efficiency, making them popular in industries that require heavy machinery, such as construction and shipping. However, they can produce more pollutants than gasoline engines, leading to ongoing discussions about environmental impact and cleaner alternatives.