Organic nitrates as ignition enhancers

Abstract

A diesel fuel composition comprising an organic nitrate is described. The organic nitrate may be a terpene nitrate. Methods of using an organic nitrate for achieving a desired cetane number, and uses of organic nitrates for the purpose of reducing the ignition delay of the fuel and/or for increasing its cetane number to a defined level are also described, as are methods of operating a compression ignition engine.

1 . A diesel fuel composition for use in a compression ignition engine, said diesel fuel composition comprises an organic nitrate selected from the group consisting of:
 a cyclic nitrate of Formula (4):   
       
         
           
           
               
               
           
         
       
       and Formula (4A): 
       
         
           
           
               
               
           
         
       
       wherein each of R 1  to R 9  is independently selected from H or C 1 -C 6  alkyl, or nitrate(—ONO 2 ), wherein optionally one of R 4  and R 5  forms an optionally substituted alkylene bridge with one of R 8  and R 9 , which may be substituted by one or more C 1 -C 6  alkyl, and/or nitrate(—ONO 2 ); wherein at least one of R 1  to R 9  is not H, and provided that no more than one R 2  to R 9  comprises a nitrate group. 
     
     
         2 . The diesel fuel composition of  claim 1 , wherein at least one of R 1  to R 9  is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tert-butyl. 
     
     
         3 . The diesel fuel composition of  claim 1 , wherein one of R 4  and R 5  is methyl and one of R 8  and R 9  is isopropyl. 
     
     
         4 . The diesel fuel composition of  claim 1 , wherein one of R 4  and R 5  forms an optionally substituted alkylene bridge with one of R 8  and R 9 ; and wherein the alkylene bridge has the formula —(CR a R b ) n —, wherein R a  and R b  are independently selected from H, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl; and n is 1 or 2. 
     
     
         5 . The diesel fuel composition of  claim 4 , wherein the cetane number improver is defined by Formula (5): 
       
         
           
           
               
               
           
         
       
       or Formula (5A): 
       
         
           
           
               
               
           
         
       
       wherein (i) at least two of R a , R b , R 2 , R 3  and R 9  are methyl; (ii) R a  and R b  are methyl; (iii) R 2  and R 3  are methyl; (iv) R a , R b  and R 9  are methyl; or (iv) R 2 , R 3  and R 9  are methyl. 
     
     
         6 . The diesel fuel composition of  claim 1 , wherein the cetane number of the diesel fuel composition containing the organic nitrate is higher than the cetane number of the diesel fuel composition lacking the organic nitrate. 
     
     
         7 . The diesel fuel composition of  claim 1 , wherein said diesel fuel composition has a cetane number of between 52 and 58. 
     
     
         8 . The diesel fuel composition of  claim 1 , wherein the diesel fuel composition comprises one or more additional organic nitrate. 
     
     
         9 . A method for reducing the ignition delay and/or increasing the cetane number of a diesel fuel composition, said method comprises adding to the composition an amount of an organic nitrate, wherein the organic nitrate is selected from the group consisting of:
 a cyclic nitrate of Formula (4):   
       
         
           
           
               
               
           
         
       
       and Formula (4A): 
       
         
           
           
               
               
           
         
       
       wherein each of R 1  to R 9  is independently selected from H or C 1 -C 6  alkyl, or nitrate(—ONO 2 ), wherein optionally one of R 4  and R 5  forms an optionally substituted alkylene bridge with one of R 8  and R 9 , which may be substituted by one or more C 1 -C 6  alkyl, and/or nitrate(—ONO 2 ); wherein at least one of R 1  to R 9  is not H, and provided that no more than one R 2  to R 9  comprises a nitrate group. 
     
     
         10 . The method of  claim 9 , wherein at least one of R 1  to R 9  is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tert-butyl. 
     
     
         11 . The method of  claim 9 , wherein one of R 4  and R 5  is methyl and one of R 8  and R 9  is isopropyl. 
     
     
         12 . The method of  claim 9 , wherein the cetane number improver is defined by Formula (5): 
       
         
           
           
               
               
           
         
       
       or Formula (5A): 
       
         
           
           
               
               
           
         
         wherein (i) at least two of R a , R b , R 2 , R 3  and R 9  are methyl; (ii) R a  and R b  are methyl; (iii) R 2  and R 3  are methyl; (iv) R a , R b  and R 9  are methyl; (iii) R 2 , R 3  and R 9  are methyl. 
       
     
     
         13 . The method of  claim 9 , wherein said method is configured to increase the cetane number of the diesel fuel composition to achieve a target cetane number. 
     
     
         14 . The method of  claim 9  further comprising adding one or more additional organic nitrate to the fuel composition. 
     
     
         15 . The method of  claim 9 , wherein said method is configured to reduce the amount of 2-ethylhexyl nitrate (2-EHN) in the diesel fuel composition to achieve the target cetane number. 
     
     
         16 . The diesel fuel composition of  claim 1 , wherein the organic nitrate is present in the diesel fuel composition at a concentration of:
 (a) between 0.025% and 2.0% w/w;   (b) between 0.05% and 1.0% w/w; or   (c) 0.05% w/w, 0.1% w/w, 0.5% w/w or 1.0% w/w;   
       based on the total weight of the fuel composition. 
     
     
         17 . The diesel fuel composition of  claim 1 , wherein the organic nitrate is further defined as follows:
 (i) R 1 , R 6  and R 7  are H;   (ii) R 1 , R 6  and R 7  are H; R 2  and R 3  are methyl;   (iii) R 1 , R 6  and R 7  are H; R 5  is H and R 9  is methyl; or   (iv) R 1 , R 6  and R 7  are H; R 2  and R 3  are methyl; R 5  is H and R 9  is methyl.   
     
     
         18 . The diesel fuel composition of  claim 1 , wherein the organic nitrate is selected from the group consisting of: bornyl nitrate, fenchyl nitrate, and menthly nitrate.