Method for using partial homogeneous charge compression ignition in a diesel internal combustion engine for NOx trap regeneration

Abstract

A method for operating a diesel IC-engine being able to run in a conventional mode and in a partial Homogeneous Charge Compression Ignition (pHCCI) mode. The method comprises the features of switching the pHCCI mode from lean pHCCI to rich pHCCI as a response to a control signal indicating that the NO x -absorbent shall be regenerated. In the rich pHCCI mode, the ratio of recirculated exhaust gases is from 20 to 55%. The rich pHCCI mode further comprises the feature of injecting at least 70% of the fuel to be injected in each working cycle in the main injection whereby the central axis of the fuel spray is directed towards the piston bowl cavity. The method will increase the operation window for rich pHCCI which in turn will have the benefits of less oil dilution and better fuel economy while regenerating the NO x -absorbent.

1 . A method for regenerating a NOx-adsorbing catalyst coupled downstream of a diesel internal combustion engine, the engine having at least one cylinder, the method comprising: 
 operating the engine in a lean partial homogeneous charge compression ignition (PHCCI) mode;    providing an indication that the catalyst needs to be regenerated; and    in response to said indication, switching engine operation to rich PHCCI mode, said rich PHCCI mode characterised in that a ratio of recirculated exhaust gases of 20 to 55% in the gas being admitted to an engine cylinder, said rich pHCCI mode being further characterised in that the central axis of a fuel spray in a main injection for each working cycle is directed towards a piston bowl cavity, said main injection comprising at least 70% of the fuel to be injected in each working cycle.    
   
   
       2 . The method according to  claim 1 , characterized in that said main injection of fuel in said rich pHCCI mode is injected in the interval of 30 degrees Before Top Dead Center (BTDC) to 15 degrees After Top Dead Centre (ATDC), preferably in the interval of 30 degrees BTDC to 9 degrees ATDC.  
   
   
       3 . The method according to  claim 2 , characterized in that the temperature of said gas being admitted to the cylinder during said rich pHCCI mode is in the interval of 60 to 200 degrees Celsius, preferably in the interval of 60 to 130 degrees Celsius.  
   
   
       4 . The method according to  claim 3 , characterized in that said rich PHCCI mode further comprises a pilot and/or a post injection in a working cycle wherein said fuel injected in the pilot and/or post injection vaporises before it reaches a liner of a cylinder wall, if the fuel spray is directed towards the liner.  
   
   
       5 . The method according to  claim 4 , characterized in that all fuel injected in a working cycle in said rich PHCCI mode is injected in the main injection.