Quaternary ammonium compounds and their use as fuel or lubricant additives

1. A fuel composition comprising as an additive one or more quaternary ammonium compounds of formula:

wherein each of R 1 , R 2 , R 3 and R 4 is independently selected from an optionally substituted alkyl, alkenyl or aryl group having 1 to 6 carbon atoms and R 5 is hydrogen or an optionally substituted hydrocarbyl group and a diluent or carrier.

2. A fuel composition according to claim 1 wherein the fuel is diesel fuel.

3. A fuel composition according to claim 2 further comprising one or more detergents selected from the group consisting of:

(i) an additional quaternary ammonium salt additive which is not a quaternary ammonium salt of formula:

wherein each of R 1 , R 2 , R 3 and R 4 is independently selected from an optionally substituted alkyl, alkenyl or aryl group having less than 8 carbon atoms and R 5 is hydrogen or an optionally substituted hydrocarbyl group;

(ii) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol;

(iii) the reaction product of a carboxylic acid-derived acylating agent and an amine;

(iv) the reaction product of a carboxylic acid-derived acylating agent and hydrazine;

(v) a salt formed by the reaction of a carboxylic acid with di-n-butylamine or tri-n-butylamine;

(vi) the reaction product of a hydrocarbyl-substituted dicarboxylic acid or anhydride and an amine compound or salt which product comprises at least one amino triazole group; and

(vii) a substituted polyaromatic detergent additive.

4. A fuel composition according to claim 1 wherein the fuel is gasoline fuel.

5. A fuel composition according to claim 1 further comprising one or more gasoline detergents selected from the group consisting of:

(p) hydrocarbyl-substituted polyoxyalkylene amines or polyetheramines;

(q) acylated nitrogen compounds which are the reaction product of a carboxylic acid-derived acylating agent and an amine;

(r) hydrocarbyl-substituted amines wherein the hydrocarbyl substituent is substantially aliphatic and contains at least 8 carbon atoms;

(s) Mannich base additives comprising nitrogen-containing condensates of a phenol, aldehyde and primary or secondary amine;

(t) aromatic esters of a polyalkylphenoxyalkanol;

(u) an additional quaternary ammonium salt additive which is not a quaternary ammonium salt of formula:

wherein each of R 1 , R 2 , R 3 and R 4 is independently selected from an optionally substituted alkyl, alkenyl or aryl group having less than 8 carbon atoms and R 5 is hydrogen or an optionally substituted hydrocarbyl group; and

(v) tertiary hydrocarbyl amines having a maximum of 30 carbon atoms.

6. A method of improving the performance of an engine, the method comprising combusting in said engine a fuel composition comprising as an additive one or more quaternary ammonium compounds as claimed in claim 1 .

7. A method according to claim 6 wherein the engine is a gasoline engine and the fuel is a gasoline fuel.

8. A method according to claim 6 wherein the engine is a diesel engine having a fuel injection system which comprises a high pressure fuel injection (HPFI) system with fuel pressures greater than 1350 bar.

9. A method according to claim 6 , wherein improvement in performance is achieved by combating deposits in the engine.

10. A method according to claim 9 , which combats internal diesel injector deposits.

11. A method according to claim 10 combats external diesel injector deposits, including injector nozzle deposits and injector tip deposits.

12. A method according to claim 8 which combats fuel filter deposits.

13. A method according to claim 6 wherein the improvement in performance is a power gain compared to when combusting an unadditised base fuel and with clean injectors.

14. A method of preparing a fuel composition as claimed in claim 1 , the method comprising adding the quaternary ammonium salt additive to the fuel after the fuel has left the distribution terminal.