Why are diesel engines often heavier and more expensive than gasoline engines of equal horsepower?

Diesel engines are typically heavier and more expensive than gasoline engines of equal horsepower primarily due to their structural requirements for handling high-pressure combustion.12

Unlike gasoline engines, which use spark plugs to ignite a fuel-air mixture, diesel engines rely on compression-ignition. They operate with much higher compression ratios—typically ranging from 14:1 to 22:1—to heat the air inside the cylinder sufficiently to ignite the fuel upon injection. To withstand these significantly higher internal pressures and temperatures, diesel engines must be built with more robust, heavier components.132

Additionally, the fuel-injection systems required for diesel engines are complex and must be engineered to deliver fuel at very high pressures, often ranging from 7 to 70 megapascals, to ensure efficient combustion. While these factors contribute to a higher initial cost and increased weight, diesel engines are often preferred for their durability and superior fuel efficiency, which results in lower operating costs over time.12