After-Treatment System and Method for Six-Stroke Combustion Cycle

Abstract

A method and system of operating an internal combustion engine on a six-stroke cycle utilizes an after-treatment system to reduce emissions such as nitrogen oxides. The method and system introduce a first fuel charge to a combustion chamber and combusts the first fuel charge to produce a first stoichiometric lean condition. The method and system next introduce a second fuel charge and combust the second fuel charge to produce a second stoichiometric lean conditions. The exhaust gasses are then directed to a selective catalytic reduction catalyst with a reductant agent to reduce the nitrogen oxides to nitrogen and water.

We claim: 
     
         1 . A method of reducing emissions from an internal combustion engine operating a six-stroke cycle, the method comprising:
 introducing a first fuel charge to a combustion chamber of the internal combustion engine to produce a first stoichiometric lean condition in the combustion chamber and combusting the first fuel charge to produce initial combustion products including hydrocarbons and nitrogen oxides;   introducing a second fuel charge to the combustion chamber to produce a second stoichiometric lean condition and combusting the second fuel charge and the initial combustion products to produce exhaust gasses and increase the nitrogen oxides relative to the hydrocarbons;   directing the exhaust gasses to a selective catalytic reduction (SCR) catalyst;   introducing a reductant agent to the SCR catalyst; and   converting nitrogen oxides in the exhaust gasses to nitrogen and water.   
     
     
         2 . The method of  claim 1 , wherein the second stoichiometric lean condition is closer to stoichiometric than the first stoichiometric lean condition. 
     
     
         3 . The method of  claim 1 , wherein the fuel is diesel having a stoichiometric air/fuel ratio of about 14.5:1 to about 14.7:1. 
     
     
         4 . The method of  claim 3 , wherein the first stoichiometric lean condition has an air/fuel ratio of approximately 30:1 and the second stoichiometric lean condition has an air/fuel ratio of between about 14.7:1 to about 20:1. 
     
     
         5 . The method of  claim 1 , wherein combusting of the second fuel charge occurs at an engine operating temperate of about 380° to about 450° C. 
     
     
         6 . The method of  claim 1 , wherein the SCR catalyst is a vanadium-based SCR catalyst. 
     
     
         7 . The method of  claim 6 , wherein the reductant agent is selected from the group consisting of ammonia and urea. 
     
     
         8 . The method of  claim 1 , wherein the exhaust gasses include particulate matter in an amount less that 0.04 grams/kilowatt-hour so as to not require a diesel particulate filter. 
     
     
         9 . The method of  claim 1 , further comprising oxidizing hydrocarbons remaining in the exhaust gasses with a diesel oxidation catalyst. 
     
     
         10 . An internal combustion engine system operating on a six-stroke cycle comprising:
 an internal combustion engine including a cylinder, a piston reciprocally disposed in the cylinder to move between a top dead center position and a bottom dead center position, an injector communicating with the cylinder to introduce fuel, and an exhaust system communicating with the engine to direct exhaust gasses from the cylinder;   a selective reduction catalyst for selective catalytic reduction (SCR) of nitrogen oxides disposed in the exhaust system;   a reductant agent storage reservoir accommodating a reductant agent and communicating with the exhaust system to introduce the reductant agent to the SCR catalyst; and   a controller controlling the injector to introduce fuel during a first compression stroke and/or a first power stroke of the piston at a quantity to produce a first stoichiometric lean condition in the cylinder, and to introduce fuel during a second compression stroke and/or a second power stroke of the piston to produce a second stoichiometric lean condition in the cylinder.   
     
     
         11 . The system of  claim 10 , wherein the second stoichiometric lean condition is closer to stoichiometric than the first stoichiometric lean condition. 
     
     
         12 . The system of  claim 11 , wherein the fuel is diesel having a stoichiometric point of between about 14.5:1 to about 14.7:1. 
     
     
         13 . The system of  claim 12 , wherein the first stoichiometric lean condition has an air/fuel ratio of approximately 30:1 and the second stoichiometric lean condition has an air/fuel ratio of a about 14.7:1 to about 22:1. 
     
     
         14 . The system of  claim 10 , wherein the SCR catalyst is a vanadium-based SCR catalyst. 
     
     
         15 . The system of  claim 10 , wherein the system lacks a diesel particulate filter. 
     
     
         16 . A method of reducing emissions from an internal combustion engine comprising introducing a first fuel charge and air to a combustion chamber of the internal combustion engine to produce a first stoichiometric lean condition and combusting the first fuel charge and air to produce initial combustion products;
 introducing a second fuel charge to the combustion chamber with the initial combustion products to produce a second stoichiometric lean condition and combusting the second fuel charge and initial combustion products to produce exhaust gasses;   directing the exhaust gasses from the combustion chamber to a selective catalytic reduction catalyst (SCR) for selective catalytic reduction of nitrogen oxides;   introducing a reductant agent to the SCR catalyst;   converting nitrogen oxides in the exhaust gasses and the reductant agent to nitrogen and water by selective catalytic reduction.   
     
     
         17 . The method of  claim 16 , wherein the second stoichiometric lean condition is closer to stoichiometric than the first stoichiometric lean condition. 
     
     
         18 . The method of  claim 16 , wherein combusting of the second fuel charge and the initial combustion products occurs at temperature between about 380° C. to about 450° C. 
     
     
         19 . The method of  claim 16 , wherein nitrogen oxides are present in the exhaust gasses in a greater relative amount than hydrocarbons. 
     
     
         20 . The method of  claim 16 , wherein the exhaust gasses have less than 0.04 grams/kilowatt-hour of particulate matter.