Synthetic fuel with reduced particulate matter emissions and a method of operating a compression ignition engine using said fuel in conjunction with oxidation catalysts

Abstract

The invention provides a compression ignition engine fuel derived from a Fischer-Tropsch process, which fuel has a generally increasing iso:n paraffins ratio with increasing paraffin carbon number at least between C 9 to C 18 , less than 0.05% m/m sulphur, and less than 10% by mass aromatics. The fuel may have on average more than 0.9 alkyl branches per paraffinic molecule as measured by H + NMR analysis. The invention also provides a method for operating a compression ignition engine to produce low particulates emissions, which method comprises combusting the fuel with oxygen or an oxygen containing gas in the engine. Yet further the invention provides a method of improving the conversion efficiency of oxidation catalysts used in conjunction with compression ignition engines, said method including combusting the fuel in the compression ignition engine in the presence of said oxidation catalysts and in oxygen or an oxygen containing gas.

1 . A compression ignition engine fuel derived from a Fischer-Tropsch process, wherein an iso-paraffin to n-paraffin mass ratio of the fuel generally increases as paraffin carbon number increases from C 9  to C 18 , wherein the fuel has less than 0.05% m/m sulphur and less than 10% by mass aromatics, and wherein the fuel has an average of more than 0.9 alkyl branches per paraffinic molecule as measured by H+ NMR analysis.  
     
     
         2 . A compression ignition engine fuel as claimed in  claim 1 , wherein the fuel has an average of more than 1 alkyl branch per paraffinic molecule.  
     
     
         3 . A compression ignition engine fuel as claimed in any  claim 1 , wherein the iso-paraffin to n-paraffin mass ratio of the fuel generally increases as paraffin carbon number increases from C 9  to C 24 .  
     
     
         4 . A compression ignition engine fuel as claimed in  claim 1 , wherein the fuel comprises at least 50 mass % iso-paraffins.  
     
     
         5 . A compression ignition engine fuel as claimed in  claim 3 , wherein the fuel comprises at least 60 mass % iso-paraffins.  
     
     
         6 . A compression ignition engine fuel as claimed in  claim 1 , wherein the iso-paraffin to n-paraffin mass ratio is from 1:1 to 4:1.  
     
     
         7 . A compression ignition engine fuel as claimed in  claim 1 , wherein the fuel predominantly comprises C 8  to C 24  paraffins.  
     
     
         8 . A compression ignition engine fuel as claimed in  claim 1 , wherein the fuel predominantly comprises C 9  to C 22  paraffins.  
     
     
         9 . A compression ignition engine fuel as claimed in  claim 1 , wherein the fuel comprises more than 70 mass % of C 12  and higher paraffins.  
     
     
         10 . A compression ignition engine fuel as claimed in  claim 9 , wherein the fuel comprises paraffins having an average carbon number of from 13 to 19.  
     
     
         11 . A compression ignition engine fuel as claimed in  claim 10 , wherein the fuel comprises paraffins having an average carbon number of about 15.  
     
     
         12 . A compression ignition engine fuel as claimed in  claim 1 , wherein the fuel is substantially oxygenate free and comprises less than 0.1% oxygen.  
     
     
         13 . A compression ignition engine fuel as claimed in  claim 1 , wherein the fuel has a cetane number of at least 55.  
     
     
         14 . A method of improving the conversion efficiency of an oxidation catalyst used in conjunction with a compression ignition engine, the method comprising: 
 combusting a compression ignition engine fuel derived from a Fischer-Tropsch process, wherein an iso-paraffin to n-paraffin mass ratio of the fuel generally increases as paraffin carbon number increases from C 9  to C 18 , wherein the fuel has less than 0.05% m/m sulphur and less than 10% by mass aromatics, and wherein the fuel has an average of more than 0.9 alkyl branches per paraffinic molecule as measured by H+ NMR analysis, in a compression ignition engine in the presence of an oxidation catalyst and an oxygen containing gas, such that a conversion efficiency of the oxidation catalyst is improved.    
     
     
         15 . A method as claimed in  claim 14 , further comprising: 
 operating the compression ignition engine at idling or low engine loads.    
     
     
         16 . A method as claimed in  claim 14 , wherein the compression ignition engine fuel is a gas-to-liquids diesel fuel.  
     
     
         17 . A method for operating a compression ignition engine to produce low particulates emissions, the method comprising: 
 combusting a compression ignition engine fuel derived from a Fischer-Tropsch process, wherein an iso-paraffin to n-paraffin mass ratio of the fuel generally increases as paraffin carbon number increases from C 9  to C 18 , wherein the fuel has less than 0.05% m/m sulphur and less than 10% by mass aromatics, and wherein the fuel has an average of more than 0.9 alkyl branches per paraffinic molecule as measured by H+ NMR analysis, with an oxygen containing gas in a compression ignition engine, whereby low particulate emissions are produced.    
     
     
         18 . A method as claimed in  claim 17 , wherein the low particulate emissions comprise particulates having a maximum number weighted particle size distribution of less than 1×10 8  particles per cm 3  and an average particle size of from 10 nm to 20 nm.  
     
     
         19 . A method as claimed in  claim 17 , wherein the low particulate emissions comprise fewer nanoparticles than particulate emissions produced by a compression ignition engine combusting a diesel fuel derived from a crude oil.  
     
     
         20 . A method as claimed in  claim 17 , wherein the low particulate emissions comprise more than 70% fewer particulates of a size less than or equal to 50 nm when compared to particulate emissions produced by combusting, under similar combustion conditions, a low sulphur crude oil-derived diesel fuel.