System for purging a device

A system for purging orifice clogging due to coking of a device for injecting fuel into an exhaust system of an engine comprising:

• a device having an input and an output coupled to an exhaust system;
• at least one air valve having an input coupled to an air supply and an output coupled to the device through a check valve;
• at least one fuel valve having an input coupled to a fuel supply and an output coupled to the device through a check valve;
• wherein when the least one air valve is open and the at least one fuel valve is closed, air flows from the air supply to the device and is injected into the exhaust system of the engine;
• wherein when the at least one air valve is closed and the at least one fuel valve is open, fuel flows from the fuel supply to the device and is injected into the exhaust system of the engine.