The term "spark diesel" refers to a type of engine that is designed to operate on both gasoline and diesel fuels. This technology is becoming increasingly popular as it offers improved fuel efficiency and lower emissions compared to traditional gas or diesel engines. Some synonyms for "spark diesel" include dual-fuel engine, hybrid engine, and bi-fuel engine. These terms all describe the same type of technology where the engine can switch between two different fuel sources. Other related terms include flexible-fuel vehicles (FFVs) and alternative fuel vehicles (AFVs) which encompass a broader range of vehicles that can run on multiple types of fuel.