System and method for reducing NOx emissions during transient conditions in a diesel fueled vehicle with EGR

Abstract

The present invention is a dual-stage fuel injection strategy for compression ignition engines in which 15-40% of the fuel is injected into the combustion chamber no later than about −20 to −30 CA ATDC and as early as IVC. The remaining fuel is then injected in one or more fuel pulses, none of which start before about −20 to −30 CA ATDC. The fuel injected early in the compression stroke forms a lean mixture that burns with low soot and low NOx emissions. The combustion of that fuel serves to increase in-cylinder temperature such that the ignition delay of subsequent fuel injection pulses is short. This mode is utilized when it is predicted that a NOx spike is imminent. Various other alternative methods for reducing NOx spikes are also disclosed such as specialized EGR systems that can provide EGR with low manifold vacuum.

1. A system for an engine having an intake manifold coupled to an intake conduit and an exhaust manifold coupled to an exhaust conduit, the system comprising:
 , the engine having a compression device coupled with a first portion to the engine, and comprising a compressor coupled to into to the intake conduit and a second portion turbine coupled to the exhaust manifold of the engine, the system comprising: into the exhaust conduit and configured to drive the compressor; 
 a combustion chamber communicating with the intake manifold and with the exhaust manifold; 
 a soot filter coupled into the exhaust conduit downstream of the turbine; 
 a fuel injector configured to inject a first pulse of fuel into the combustion chamber during a compression stroke and a second pulse of fuel during an expansion stroke, the compression stroke and the expansion stroke occurring during a first operating condition and in one engine cycle; 
 a first exhaust gas exhaust-gas recirculation system having a first end coupled to the exhaust manifold upstream of the second portion of the compression device turbine and a second end coupled to the intake manifold downstream of the first portion compression device compressor, said first the first exhaust-gas recirculation system also having a first valve that, which adjusts a first flow amount from the exhaust manifold to the intake manifold; and 
 a second exhaust gas exhaust-gas recirculation system having a first end coupled downstream of the second portion of the compression device turbine and the soot filter and a second end coupled to the intake manifold, said first the second exhaust-gas recirculation system also having a second valve that, which adjusts a second flow amount from the exhaust conduit to the intake manifold. 
 
     
     
       2. The system recited in  claim 1  further comprising a controller electrically coupled to said the first and second valve valves. 
     
     
       3. The system recited in  claim 2  wherein said controller determines engine operating conditions, and actuates both said first and second valve during a first mode, and only said second valve during a second mode based on said determined operating conditions. 
     
     
       4. The system recited in claim  3  1, wherein the engine is a diesel engine, and wherein said second end of said second exhaust gas recirculation system is coupled to the intake manifold downstream of the first portion of the compression device. 
     
     
       5. A system for an internal combustion engine having an intake manifold coupled to an intake conduit and an exhaust manifold coupled to an exhaust conduit, the system comprising:
 a first exhaust gas exhaust-gas recirculation path for introducing a first amount of burnt exhaust gas into an the intake manifold of the engine; 
 a first valve located in said coupled into the first exhaust-gas recirculation path; 
 a second exhaust gas exhaust-gas recirculation path for introducing a second amount of burnt exhaust gas into an the intake manifold of the engine; 
 a second valve located in said coupled into the second exhaust-gas recirculation path; 
 a compression device powered by exhaust flow that, which raises manifold pressure, the compression device comprising a compressor coupled into the intake conduit and a turbine coupled into the exhaust conduit and configured to drive the compressor; 
 a soot filter coupled into the exhaust conduit downstream of the turbine; 
 a fuel injector capable of delivering multiple injections per engine cycle to a combustion chamber; and 
 a controller for operatively coupled to the fuel injector and configured to:
 determiningdetermine an engine loadengine-load condition associated with decreased NOx emissions, and controllingcontrol both saidthe first and second valvevalves to be open during saidthe decreased NOx emissions; 
 estimate an interval where increased nitrogen-oxide emissions are predicted, a start of said interval responsive to fuel demand, an end of said interval responsive to manifold air pressure (MAP); and 
 during said interval, enact one or more of: injecting a first pulse of fuel into the combustion chamber during a compression stroke and a second pulse of fuel during an expansion stroke, the compression stroke and the expansion stroke occurring in one engine cycle; and drawing some exhaust through the second exhaust-gas recirculation path. 
 
 
     
     
       6. The system of  claim 5 , wherein said the controller further controls is further configured to open only one of said the first and second valve valves to be open during increased NOx conditions said interval. 
     
     
       7. A system for a diesel engine, comprising:
 a turbine coupled to an exhaust side of the engine; 
 a compressor coupled to into an intake manifold on an intake side of the engine; 
 a turbine coupled into an exhaust conduit on an exhaust side of the engine and configured to drive the compressor; 
 a soot filter coupled into the exhaust conduit downstream of the turbine; 
 a first exhaust gas exhaust-gas recirculation path from the exhaust side of the engine conduit to the an intake side of the engine manifold, the first exhaust gas exhaust-gas recirculation path having an exhaust portion and an intake portion, the exhaust portion coupled to the exhaust side of the engine conduit upstream of the turbine and the intake portion coupled to the intake side of the engine manifold downstream of the compressor; and 
 a second exhaust gas exhaust-gas recirculation path from the exhaust side of the engine conduit to the intake side of the engine conduit, the second exhaust gas exhaust-gas recirculation path having an exhaust portion and an intake portion, the exhaust portion coupled to the exhaust side of the engine conduit downstream of the turbine and the soot filter and the intake portion coupled to the intake side of the engine manifold; 
 a fuel injector capable of delivering multiple injections per engine cycle to a combustion chamber of the engine; and 
 a controller operatively coupled to the fuel injector and configured to:
 during a first operating mode, inject a first pulse of fuel into the combustion chamber during a compression stroke and a second pulse of fuel during an expansion stroke, the compression stroke and the expansion stroke occurring in one engine cycle; and 
 during a second operating mode, draw some exhaust through the second exhaust-gas recirculation path. 
 
 
     
     
       8. The system recited in  claim 7  wherein said first exhaust gas recirculation path includes a first control valve coupled between the exhaust portion and the intake portion of the first exhaust gas recirculation path. 
     
     
       9. The system recited in  claim 7  wherein said second exhaust gas recirculation path includes a second control valve coupled between the exhaust portion and the intake portion of the second exhaust gas recirculation path. 
     
     
       10. The system recited in  claim 7  further comprising a catalyst coupled to the exhaust side of the engine downstream of the turbine. 
     
     
       11. The system recited in  claim 7  further comprising a particulate filter coupled to the exhaust side of the engine downstream of the turbine. 
     
     
       12. The system recited in of  claim 7  wherein said the intake portion of the second exhaust gas exhaust-gas recirculation path is coupled to said intake side of the engine the intake conduit upstream of the compressor. 
     
     
       13. The system recited in of  claim 7  wherein said the intake portion of the second exhaust gas exhaust-gas recirculation path is coupled to said intake side of the engine the intake manifold, downstream of the compressor. 
     
     
       14. The system recited in  claim 13  further comprising a throttle on the intake side of the engine. 
     
     
       15. A system for a diesel engine, comprising:
 a turbine coupled to an exhaust side of the engine;   a compressor coupled to an intake side of the engine;   a first exhaust gas recirculation path from the exhaust side of the engine to the intake side of the engine, the first exhaust gas recirculation path having an exhaust portion and an intake portion, the exhaust portion coupled to the exhaust side of the engine upstream of the turbine and the intake portion coupled to the intake side of the engine downstream of the compressor; and   a second exhaust gas recirculation path from the exhaust side of the engine to the intake side of the engine, the second exhaust gas recirculation path having an exhaust portion and an intake portion, the exhaust portion coupled to the exhaust side of the engine downstream of the turbine and the intake portion coupled to the intake side of the engine downstream of the compressor.   
     
     
       16. The system recited in  claim 15  wherein said first exhaust gas recirculation path includes a first control valve coupled between the exhaust portion and the intake portion of the first exhaust gas recirculation path. 
     
     
       17. The system recited in  claim 15  wherein said second exhaust gas recirculation path includes a second control valve coupled between the exhaust portion and the intake portion of the second exhaust gas recirculation path. 
     
     
       18. The system recited in  claim 15  further comprising a catalyst coupled to the exhaust side of the engine downstream of the turbine. 
     
     
       19. The system recited in  claim 15  further comprising a particulate filter coupled to the exhaust side of the engine downstream of the turbine. 
     
     
       20. The system recited in  claim 15  further comprising an intercooler coupled to the intake side of the engine downstream of the compressor. 
     
     
       21. The system recited in  claim 20  further comprising a throttle coupled to the intake side of the engine downstream of the compressor and downstream of the intercooler. 
     
     
       22. The system of claim 1, wherein the second pulse of fuel is injected before +20 crank-angle degrees after top-dead-center (CA ATDC) of the engine cycle. 
     
     
       23. The system of claim 22, wherein the first pulse of fuel begins at or before −10 crank-angle degrees after top-dead-center (CA ATDC) of the engine cycle. 
     
     
       24. The system of claim 23, wherein the first pulse of fuel begins between −90 and −10 crank-angle degrees after top-dead-center (CA ATDC) of the engine cycle. 
     
     
       25. The system of claim 1, wherein the first pulse of fuel comprises between 5 and 25 percent of the fuel injected into the combustion chamber during the engine cycle. 
     
     
       26. The system of claim 1, further comprising a heat exchanger coupled into the second exhaust-gas recirculation system and configured to cool exhaust gas therein. 
     
     
       27. The system of claim 1, further comprising a heat exchanger coupled into the first exhaust-gas recirculation system and configured to cool exhaust gas therein via a coolant liquid. 
     
     
       28. The system of claim 1, further comprising a lean nitrogen-oxide catalyst coupled into the exhaust conduit downstream of the turbine. 
     
     
       29. The system of claim 1, wherein the first operating condition is predictive of increased nitrogen-oxide release from the combustion chamber, and wherein the fuel injector is further configured to inject fuel during a second operating condition predictive of less nitrogen-oxide release from the combustion chamber relative to the first operating condition. 
     
     
       30. The system of claim 29, wherein the increased nitrogen-oxide release comprises a spike in nitrogen-oxide release. 
     
     
       31. The system of claim 29, wherein the first valve is configured to close during the first operating condition, thereby restricting a flow of exhaust gas through the first exhaust-gas recirculation system. 
     
     
       32. The system of claim 29, wherein the second valve is configured to stay at least partly open during the first and second operating conditions, thereby admitting exhaust gas through the second exhaust-gas recirculation system. 
     
     
       33. The system of claim 1 wherein the second end of the second exhaust-gas recirculation system is coupled to the intake manifold upstream of the compressor. 
     
     
       34. The system of claim 5, wherein the controller is further configured to close the first valve during said interval. 
     
     
       35. The system of claim 7, wherein the controller is further configured to restrict exhaust flow through the first exhaust-gas recirculation path during the first or second operating modes. 
     
     
       36. The system of claim 7, wherein during the first operating mode, the first pulse of fuel is injected beginning at or before −10 crank-angle degrees after top-dead-center (CA ATDC) of the engine cycle, and the second pulse of fuel is injected before +20 crank-angle degrees after top-dead-center (CA ATDC) of the engine cycle. 
     
     
       37. The system of claim 7, wherein the first and second operating modes overlap. 
     
     
       38. The system of claim 7, wherein the first and second operating modes are entered upon in response to first and second conditions, respectively, the first and second conditions predictive of increased nitrogen-oxide release from the combustion chamber. 
     
     
       39. The system of claim 38, wherein the increased nitrogen-oxide release comprises a spike in nitrogen-oxide release. 
     
     
       40. The system of claim 38, further comprising injecting fuel into the combustion chamber during a third operating mode, wherein the third operating mode is entered upon in response to a third condition, the third condition predictive of reduced nitrogen-oxide release from the combustion chamber relative to the first and second conditions. 
     
     
       41. The system of claim 40, wherein the first or second condition comprises a fuel-injection demand exceeding a threshold value, and wherein the third condition comprises the fuel-injection demand being less than the threshold value. 
     
     
       42. The system of claim 40, wherein the first or second condition comprises one or more of an air-to-fuel ratio and an exhaust-gas recirculation flow rate falling below a threshold value, and wherein the third condition comprises the one or more of the air-to-fuel ratio and the exhaust-gas recirculation flow rate being above the threshold value. 
     
     
       43. The system of claim 40, wherein the first or second condition comprises one or more of a manifold air pressure exceeding a threshold rate of change and an engine load decreasing, and wherein the third condition comprises one or more of the manifold air pressure not exceeding the threshold rate of change and the engine load failing to decrease. 
     
     
       44. The system of claim 7, wherein the first pulse of fuel forms a homogeneous lean mixture, and the second pulse of fuel forms a stratified mixture.