Injectors with a solenoid: Used in gasoline engines, they are controlled by a solenoid that uses electrical current. Injectors for the Common Rail System: Diesel engines often use high-pressure common-rail fuel systems, which store fuel under pressure and pump it directly into the combustion chamber as required.  Direct Fuel Injectors: These may be found in both gas and diesel engines and work to increase economy and performance by injecting fuel directly into the combustion chamber.