Exhaust Gas Recirculation Valve
An EGR or exhaust gas recirculation valve is used on gasoline and diesel engines to reduce the amount NOx or nitrous of oxides released into the atmosphere. When nitrogen and oxygen are combined with high cylinder temperatures this harmful NOx gas is formed. The x in NOx is a variable.
The EGR valve reduces the amount of NOx by recirculating a small amount of exhaust into the intake. It's a controlled opening between the intake and the exhaust. By mixing this inert gas into the air fuel charge, the cylinder’s temperature is reduced. Reducing the temperature reduces the amount of nitrous of oxides produced in the chamber. This prevents the engine's cylinders from reaching damaging temperatures and protects the environment from smog resulting from excessive NOx production.
There are different types of EGR systems used on different engines. The vacuum operated EGR valve used in the illustration above is a typical design. The valve is opened by vacuum supplied through a duty cycle solenoid and closed by a spring.