Method and Use for the Prevention of Fuel Injector Deposits

Abstract

A method of substantially removing, or reducing the occurrence of, injector deposits in a diesel engine operated using a diesel fuel containing a minor amount of a metal-containing species is disclosed. The method includes adding to a diesel fuel the reaction product between a hydrocarbyl-substituted succinic acid or anhydride and hydrazine. The diesel engine is equipped with fuel injectors having a plurality of spray-holes, each spray-hole having an inlet and an outlet, and the fuel injectors have one or more of the following characteristics: (i) spray-holes which are tapered such that the inlet diameter of the spray-holes is greater than the outlet diameter; (ii) spray-holes having an outlet diameter of 0.10 mm or less; (iii) spray-holes where an inner edge of the inlet is rounded; (iv) 6 or more spray-holes; (v) an operating tip temperature in excess of 250° C.

1 . A diesel fuel composition comprising a major amount of a diesel fuel and a minor amount of the reaction product between a hydrocarbyl-substituted succinic acid or anhydride and hydrazine, wherein at least 25% by weight of the reaction product has a molecular weight which is more than 2 times the average molecular weight of the hydrocarbyl group of the hydrocarbyl-substituted succinic acid or anhydride. 
   
   
       2 . A diesel fuel composition according to  claim 1  wherein the reaction product between the hydrocarbyl-substituted succinic acid or anhydride is predominantly an oligomeric species of the structure: 
     
       
         
         
             
             
         
       
     
     where R′ represents the hydrocarbyl substituent and where n is an integer and greater than 1, preferably between 2 and 10, more preferably between 2 and 7, for example 3, 4 or 5. 
   
   
       3 . A diesel fuel composition according to  claim 1  wherein the hydrocarbyl group of the hydrocarbyl-substituted succinic acid or anhydride comprises a C 8 -C 36  group or a polyisobutylene group with a number average molecular weight of between 200 and 2500. 
   
   
       4 . A diesel fuel composition according to  claim 1  wherein the hydrocarbyl-substituted succinic acid or anhydride and hydrazine are reacted in a molar ratio of 2:1-1:4, preferably, 1:1-1:3. 
   
   
       5 . A diesel fuel composition according to  claim 1  wherein the reaction product between the hydrocarbyl-substituted succinic acid or anhydride and hydrazine is present in the diesel fuel in an amount between 10 and 500 ppm by weight based on the weight of the fuel.