Fuel modifiers for natural gas reciprocating engines

Abstract

Described herein are fuel modifiers for natural gas reciprocating engines, while recognizing the application of the inventions herein may be applied more broadly, to other natural gas-based engine systems. The fuel modifiers are primarily free-radical initiators, and the presence of this fuel modifier allows the engine operator to operate the engine under leaner conditions because, while employing the same ignition energy, more free-radicals are formed, thus overcoming the problems associated with dilution of the pool of free-radicals in the flame.

What is claimed: 
     
         1 . A method for reducing the ignition energy required for ignition of a natural gas fuel in a natural gas engine, comprising providing a natural gas fuel comprising a natural gas base fuel and a fuel modifier to a natural gas engine, wherein the fuel modifier is selected from azo compounds, dialkylsulfides, alkyl sulfones, nitroalkyls, peroxygens, hydrocarbons which contain symmetrically substituted carbon-carbon bonds where that bond is relatively weak, or a mixture thereof. 
     
     
         2 . The method of  claim 1 , wherein the base fuel and the fuel modifier are pre-blended or are blended proximal to the engine prior to introduction into the engine, or are separately introduced into the engine. 
     
     
         3 . The method of  claim 1 , wherein the base fuel and the fuel modifier are pre-blended prior to introduction into the engine. 
     
     
         4 . The method of  claim 3 , wherein the base fuel and the fuel modifier are blended proximal to the engine prior to introduction into the engine. 
     
     
         5 . The method of  claim 1 , wherein the base fuel and the fuel modifier are separately introduced into the engine. 
     
     
         6 . The method of  claim 1 , wherein the fuel modifier is selected from the group consisting of azobisisoalkyls represented by structures (1) and (2): 
       
         
           
           
               
               
           
         
         wherein R 1  through R 4  are each independently selected from the group consisting of hydrogen; hydroxyl; methyl; 2-cyanoprop-2-yl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 15  aminoalkyl groups, C 1 -C 15  carboxyalkyl groups, C 1 -C 15  aminocarboxyalkyl groups and C 1 -C 15  hydroxycarboxyalkyl groups; 
         the fuel modifier is selected from the group consisting of dialkylsulfides represented by structure (3): 
       
       
         
           
           
               
               
           
         
         wherein R 5  and R 6  are each independently selected from the group consisting of hydrogen; hydroxyl; methyl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 15  aminoalkyl groups, C 1 -C 15  carboxyalkyl groups, C 1 -C 15  aminocarboxyalkyl groups, C 1 -C 15  hydroxycarboxyalkyl groups, C 1 -C 15  aryl groups, and C 1 -C 15  alkylaryl groups; 
         the fuel modifier is selected from the group consisting of sulfones represented by structure (4): 
       
       
         
           
           
               
               
           
         
         wherein R 7  and R 8  are each independently selected from the group consisting of hydrogen; hydroxyl; methyl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 15  aminoalkyl groups, C 1 -C 15  carboxyalkyl groups, C 1 -C 15  aminocarboxyalkyl groups and C 1 -C 15  hydroxycarboxyalkyl groups; 
         the fuel modifier is selected from the group consisting of nitro compounds represented by structure (5): 
       
       
         
           
           
               
               
           
         
         wherein R 9  is selected from the group consisting of hydrogen; hydroxyl; methyl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 15  aminoalkyl groups, C 1 -C 15  carboxyalkyl groups, C 1 -C 15  aminocarboxyalkyl groups, C 1 -C 15  hydroxycarboxyalkyl groups, C 1 -C 15  aryl groups, and C 1 -C 15  alkylaryl groups; 
         the fuel modifier is selected from the group consisting of peroxygens compounds represented by structure (6): 
       
       
         
           
           
               
               
           
         
         wherein R 10  and R 11  are independently selected from the group consisting of hydrogen; 
         methyl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 30  carboxyalkyl groups, C 1 -C 30  hydroxycarboxyalkyl groups, C 1 -C 15  aryl, and C 1 -C 15  alkylaryl groups; or 
         the fuel modifier is selected from the group represented by the formula below:
   R 13 —C(R 14 ,R 12 )—C(R 14 ,R 12 ,R 13 )
 
 
         wherein R 12 , R 13 , and R 14  are independently selected from the group consisting of hydrogen; methyl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 30  carboxyalkyl groups, C 1 -C 30  hydroxycarboxyalkyl groups, C 1 -C 15  aryl, and C 1 -C 15  alkylaryl groups. 
       
     
     
         7 . The method of  claim 6 , wherein the fuel modifier comprises azobisisobutylnitrile, dimethylsulfide, dimethylsulfone, nitromethane, di-tert-butyl peroxide, dimethoxymethane, or 2,3-dimethyl-2,3-diphenylbutane. 
     
     
         8 . The method of  claim 1 , wherein the spark or laser ignition energy required for fuel ignition is reduced compared with the corresponding spark or laser ignition energy required for a natural gas engine operating on a natural gas fuel that does not include the fuel modifier. 
     
     
         9 . The method of  claim 1 , wherein the lean limit at a combustion efficiency of 80% is extended by over 14% for a natural gas engine operating on a natural gas fuel comprising the natural gas base fuel and the fuel modifier compared with a natural gas engine operating on a natural gas fuel that does not include the fuel modifier. 
     
     
         10 . The method of  claim 1 , wherein the minimum ignition energy MIE 90  for laser ignition of a natural gas fuel comprising the natural gas base fuel and the fuel modifier is reduced by at least about 36% compared with a natural gas fuel that does not include the fuel modifier. 
     
     
         11 . The method of  claim 1 , wherein the fuel modifier is selected from the group consisting of azo compounds having a molecular weight of between 80 and 500 g/mol, and a decomposition temperature between 80 and 300° C. 
     
     
         12 . The method of  claim 1 , wherein the fuel modifier is selected from the group consisting of azobisisoalkyls represented by structures (1) and (2): 
       
         
           
           
               
               
           
         
         wherein R 1  through R 4  are each independently selected from the group consisting of hydrogen; hydroxyl; methyl; 2-cyanoprop-2-yl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 15  aminoalkyl groups, C 1 -C 15  carboxyalkyl groups, C 1 -C 15  aminocarboxyalkyl groups and C 1 -C 15  hydroxycarboxyalkyl groups. 
       
     
     
         13 . The method of  claim 1 , wherein the fuel modifier is selected from the group consisting of dialkylsulfides represented by structure (3): 
       
         
           
           
               
               
           
         
         wherein R 5  and R 6  are each independently selected from the group consisting of hydrogen; hydroxyl; methyl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 15  aminoalkyl groups, C 1 -C 15  carboxyalkyl groups, C 1 -C 15  aminocarboxyalkyl groups, C 1 -C 15  hydroxycarboxyalkyl groups, C 1 -C 15  aryl groups, and C 1 -C 15  alkylaryl groups. 
       
     
     
         14 . The method of  claim 1 , wherein the fuel modifier is selected from the group consisting of sulfones represented by structure (4): 
       
         
           
           
               
               
           
         
         wherein R 7  and R 8  are each independently selected from the group consisting of hydrogen; hydroxyl; methyl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 15  aminoalkyl groups, C 1 -C 15  carboxyalkyl groups, C 1 -C 15  aminocarboxyalkyl groups and C 1 -C 15  hydroxycarboxyalkyl groups. 
       
     
     
         15 . The method of  claim 1 , wherein the fuel modifier is selected from the group consisting of nitro compounds represented by structure (5): 
       
         
           
           
               
               
           
         
         wherein R 9  is selected from the group consisting of hydrogen; hydroxyl; methyl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 15  aminoalkyl groups, C 1 -C 15  carboxyalkyl groups, C 1 -C 15  aminocarboxyalkyl groups, C 1 -C 15  hydroxycarboxyalkyl groups, C 1 -C 15  aryl groups, and C 1 -C 15  alkylaryl groups. 
       
     
     
         16 . The method of  claim 1 , wherein the fuel modifier is selected from the group consisting of peroxygens compounds represented by structure (6): 
       
         
           
           
               
               
           
         
         wherein R 10  and R 11  are independently selected from the group consisting of hydrogen; methyl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 30  carboxyalkyl groups, C 1 -C 30  hydroxycarboxyalkyl groups, C 1 -C 15  aryl, and C 1 -C 15  alkylaryl groups. 
       
     
     
         17 . The method of  claim 16 , wherein the fuel modifier is selected from the group consisting of linear and branched C 1 -C 15  alkyl peroxides. 
     
     
         18 . The method of  claim 1 , wherein the fuel modifier is selected from the group represented by the formula below:
   R 13 —C(R 14 ,R 12 )C(R 14 ,R 12 ,R 13 )
   wherein R 12 , R 13 , and R 14  are independently selected from the group consisting of hydrogen;   methyl; and linear or branched, substituted or unsubstituted C 1 -C 15  alkyl groups, C 1 -C 15  alkenyl groups, C 1 -C 15  hydroxyalkyl groups, C 1 -C 15  alkoxyalkyl groups, C 1 -C 30  carboxyalkyl groups, C 1 -C 30  hydroxycarboxyalkyl groups, C 1 -C 15  aryl, and C 1 -C 15  alkylaryl groups.