Q: Why does a diesel engine achieve better fuel economy over a gasoline engine in a similar vehicle?
A: Diesel fuel has more energy per gallon of fuel as compared to gasoline. The fuel delivery method is also more efficient. Diesels use direct injection. In direct injection, the fuel is sprayed directly into the engine’s cylinders. Since diesels also have higher compression ratios in the engine, the combustion process is also more efficient. In addition, diesels burn much less fuel at idle as compared to gasoline engines.