Combustion exhaust purification system and method

A combustion exhaust purification system comprising:

• an exhaust passageway having one end connected to a combustion exhaust source:
• a deNOx catalyst positioned in said exhaust passageway;
• an injector mounted on said exhaust passageway upstream from said deNOx catalyst and being capable of injecting an amount of a NOx reducing fluid into said exhaust passageway;
• a tank capable of holding the NOx reducing fluid;
• a pipe connected between said injector and said tank and being capable of carrying the NOx reducing fluid from said tank to said injector;
• means for determining the operating condition of the combustion exhaust source:
• means for measuring the temperature of the exhaust in said exhaust passageway;
• a computer in communication with said determining means, said measuring means and said injector, and being capable of controlling said injector;
• means, attached to said pipe, for pressurizing the NOx reducing fluid in said pipe:
• wherein said injector has only two operating states, an open operating state and a closed operating state;
• said computer controls the amount of time said injector is in said open operating state and in said closed operating state during each injector cycle;
• means for maintaining said injector at a substantially fixed mass flow rate when in said open operating state;
• wherein said injector includes an injector block;
• and
• the system further comprises means for circulating a coolant fluid into contact with said injector block.

A method of reducing NOx content of combustion exhaust from an engine flowing through an exhaust passageway using an exhaust purification system, comprising the steps of:

• predetermining optimal amounts for the injection of a NOx reducing fluid over a portion of the operating range of the engine and over a range of exhaust temperatures;
• positioning a deNOx catalyst in the exhaust passageway;
• measuring the temperature of the exhaust;
• determining the operating condition of the engine;
• determining whether the engine is warm;
• computing an injection amount for a subsequent injector cycle time period based upon the predetermined optimal amounts, the measured temperature of the exhaust, and the determined operating condition of the engine;
• and
• determining whether a portion of said exhaust purification system has malfunctioned;
• injecting the injection amount of the NOx reducing fluid into the exhaust passageway upstream from the deNOx catalyst if the engine is warm and the injection system is not malfunctioning;
• and
• cooling a portion of said exhaust purification system.