Strategy for quenching incipient combustion of residual homogeneous charges during compession strokes in a diesel engine

Abstract

During regeneration of a DPF ( 22 ), cylinders of a diesel engine ( 12 ) are fueled by main injections and post-injections. This creates exhaust having sufficiently high temperature and suitable constituent content to cause particulates trapped in the DPF to burn off. However, residual unburnt fuel will create an air-fuel mixture that is sufficiently homogeneous to begin combusting during a subsequent compression stroke. The invention quenches incipient combustion of the mixture during the compression stroke by injecting fuel into the respective cylinder before the next main injection of fuel.

1 . A method of operating a compression ignition engine having an exhaust system comprising a diesel particulate filter (DPF) that traps combustible particulates in exhaust resulting from combustion of fuel in cylinders of the engine and that at times is regenerated by in-cylinder combustion that creates exhaust having sufficiently high temperature and suitable constituent content to cause particulates trapped in the DPF to burn off, the method comprising, during regeneration of the DPF: 
 fueling the cylinders with main injections of fuel at or near top dead center (TDC) that demarcates a compression stroke and a power stroke for a respective cylinder to cause a main combustion event in a respective cylinder;    after completion of a main injection of fuel for a respective cylinder, injecting additional fuel into the respective cylinder during the power stroke to create exhaust having sufficiently high temperature and suitable constituent content to cause particulates trapped in the DPF to burn off when exhaust from the respective cylinder passes through the DPF after the respective cylinder has been opened to the exhaust system while leaving in the respective cylinder after it has been once again been closed to the exhaust system, a residuum of unburnt fuel that, after introduction of charge air during an ensuing intake stroke, will create an air-fuel mixture that is sufficiently homogeneous to begin combusting during a subsequent compression stroke; and    quenching any incipient combustion of the mixture during the compression stroke by injecting fuel into the respective cylinder before the next main injection of fuel.    
   
   
       2 . A method as set forth in  claim 1  wherein the fueling of cylinders with main injections of fuel at or near top dead center (TDC) is timed to commence in advance of TDC for a respective cylinder.  
   
   
       3 . A method as set forth in  claim 1  wherein the injecting of additional fuel during the power stroke is timed to commence no earlier than about 60° after TDC for a respective cylinder.  
   
   
       4 . A method as set forth in  claim 1  wherein the injecting of fuel into the respective cylinder during the compression stroke is timed to commence substantially when the mixture being compressed would otherwise begin to combust.  
   
   
       5 . A method as set forth in  claim 4  wherein the injecting of fuel into the respective cylinder during the compression stroke is timed to commence at about 20° in advance of TDC.  
   
   
       6 . A compression ignition engine comprising: 
 cylinders within which combustion occurs;    an intake system for introducing air into the cylinders;    a fueling system for injecting fuel into the cylinders;    an exhaust system comprising a diesel particulate filter (DPF) that traps combustible particulates in exhaust resulting from combustion of fuel in the cylinders and that at times is regenerated by in-cylinder combustion that creates exhaust having sufficiently high temperature and suitable constituent content to cause particulates trapped in the DPF to burn off; and    a control system for controlling various aspects of engine operation including the injection of fuel into the cylinders by the fueling system during regeneration of the DPF by a) causing the fueling system to inject main injections of fuel at or near top dead center (TDC) that demarcates a compression stroke and a power stroke for a respective cylinder to cause a main combustion event in a respective cylinder, b) causing the fueling system, during the power stroke for a respective cylinder, to inject additional fuel into the respective cylinder to create exhaust having sufficiently high temperature and suitable constituent content to cause particulates trapped in the DPF to burn off when exhaust from the respective cylinder passes through the DPF after the respective cylinder has been opened to the exhaust system while leaving in the respective cylinder after it has been once again been closed to the exhaust system, a residuum of unburnt fuel that, after introduction of air through the intake system during an ensuing intake stroke, creates an air-fuel mixture that is sufficiently homogeneous to begin combusting during a subsequent compression stroke, c) and quenching any incipient combustion of the mixture during the compression stroke by causing the fueling system to inject fuel into the respective cylinder before the next main injection of fuel.    
   
   
       7 . An engine as set forth in  claim 6  wherein the control system causes the main injections of fuel at or near top dead center (TDC) to commence in advance of TDC for a respective cylinder.  
   
   
       8 . An engine as set forth in  claim 6  wherein the control system causes injection of additional fuel during the power stroke to commence no earlier than about 60° after TDC for a respective cylinder.  
   
   
       9 . An engine as set forth in  claim 6  wherein the control system causes the injecting of fuel into the respective cylinder during the compression stroke to commence substantially when the mixture being compressed would otherwise begin to combust.  
   
   
       10 . An engine as set forth in  claim 9  wherein the control system causes the injecting of fuel into the respective cylinder to commence at about 20° in advance of TDC.  
   
   
       11 . A method of operating a compression ignition engine to avoid, in cylinders of the engine during compression strokes, uncontrolled combustion of homogeneous air-fuel charges created by residual unburnt fuel from fueling that occurred prior to the compression strokes, the method comprising: 
 injecting fuel into the cylinders prior to compression strokes for operating the engine while at times leaving residual unburnt fuel capable of mixing with new fresh air charges to form homogeneous air-fuel mixtures that would begin combusting during the compression strokes; and    injecting some quantity of fuel into the respective cylinders during the compression strokes in advance of top dead center (TDC) to quench any incipient combustion of such homogeneous mixtures.    
   
   
       12 . A method as set forth in  claim 11  wherein the injecting of fuel into the cylinders prior to compression strokes comprises fueling the cylinders with main injections of fuel at or near top dead center (TDC) followed by post-injections of fuel during power strokes.  
   
   
       13 . A method as set forth in  claim 12  wherein post-injections of fuel are timed to commence no earlier than about 60° after TDC.  
   
   
       14 . A method as set forth in  claim 11  wherein the step of injecting some quantity of fuel into the respective cylinders is timed to commence substantially when the mixtures being compressed would otherwise begin to combust.  
   
   
       15 . A method as set forth in  claim 14  wherein the step of injecting some quantity of fuel into the respective cylinders is timed to commence at about 20° in advance of TDC.  
   
   
       16 . A compression ignition engine comprising: 
 cylinders within which combustion occurs;    an intake system through which air for combustion is delivered to the cylinders;    a fueling system for injecting fuel into the cylinders; and    a control system for controlling various aspects of engine operation including the injection of fuel into the cylinders by the fueling system by a) injecting fuel into the cylinders prior to compression strokes for operating the engine while at times leaving residual unburnt fuel capable of mixing with new fresh air charges delivered through the intake system to form homogeneous air-fuel mixtures that would begin combusting during the compression strokes, and b) injecting some quantity of fuel into the cylinders during the compression strokes in advance of top dead center (TDC) to quench any incipient combustion of such homogeneous mixtures.    
   
   
       17 . An engine as set forth in  claim 16  wherein the control system causes the injecting of fuel into the cylinders prior to compression strokes by fueling the cylinders with main injections of fuel at or near top dead center (TDC) followed by post-injections of fuel during power strokes.  
   
   
       18 . An engine as set forth in  claim 17  wherein the control system causes post-injections of fuel to commence no earlier than about 60° after TDC.  
   
   
       19 . An engine as set forth in  claim 16  wherein the control system causes the injecting of some quantity of fuel into the respective cylinders to commence substantially when the mixtures being compressed would otherwise begin to combust.  
   
   
       20 . An engine as set forth in  claim 19  wherein the control system causes the injecting some quantity of fuel into the respective cylinders to commence at about 20° in advance of TDC.