Fuel compositions, methods and uses relating to quaternary ammonium salt additives for fuel used in spark ignition engines

1. A gasoline fuel composition comprising as an additive an ester compound which is the reaction product of a succinic acid or anhydride thereof having a polyisobutenyl substituent having a number average molecular weight of 700 to 1300 and an alcohol of formula H—(OR) n —OR 1 , wherein R is an optionally substituted alkylene group; R 1 is hydrogen or an optionally substituted hydrocarbyl group, and n is 0 or a positive integer; wherein n is not 0 when R 1 is hydrogen; wherein the polyisobutenyl substituted succinic acid or anhydride and alcohol of formula H—(OR) n —OR 1 are reacted in a molar ratio of from 1.5:1 to 1:1.5.

2. A method of combatting deposits in a direct injection spark ignition engine, the method comprising combusting in the engine a gasoline composition comprising as an additive the reaction product of an optionally substituted polycarboxylic acid or an anhydride thereof and a polyhydric alcohol of formula H—(OR) n OR 1 , wherein R is an optionally substituted alkylene group; R 1 is hydrogen or an optionally substituted hydrocarbyl group, and n is 0 or a positive integer, wherein n is not 0 when R 1 is hydrogen.

3. The composition according to claim 1 wherein the optionally substituted polycarboxylic acid or anhydride thereof is a hydrocarbyl substituted succinic acid or a hydrocarbyl substituted succinic anhydride.

4. The composition according to claim 1 wherein each R is ethylene or propylene.

5. The composition according to claim 1 wherein the polycarboxylic acid or anhydride thereof includes an optionally substituted alkyl or alkenyl group having 6 to 100 carbon atoms.

6. The composition according to claim 1 wherein the polycarboxylic acid or anhydride is a succinic acid or anhydride thereof having a polyisobutenyl substituent having a number average molecular weight of 100 to 5000.

7. The composition according to claim 1 wherein the polyisobutenyl substituted succinic acid or anhydride and alcohol of formula H—(OR) n —OR 1 are reacted in a ratio of from 2.5:1 to 1.5:1 and R 1 is hydrogen.

8. The composition according to claim 1 wherein n is 0 and R 1 is a C 6 to C 30 alkyl group.

9. The composition according to claim 1 wherein R 1 is hydrogen.

10. The composition according to claim 1 wherein n is 1 or more and R 1 is a C 4 to C 30 alkyl group.

11. The composition according to claim 1 wherein the additive is the reaction product of a succinic acid or anhydride of formula (A3) or (A4):

and an alcohol of formula H—(OR) n —OR 1 ; wherein R 2 is an alkyl or alkenyl group having 6 to 36 carbon atoms or a polyisobutenyl group having a number average molecular weight of from 200 to 1300; wherein the alcohol of formula H—(OR) n —OR 1 is selected from the group consisting of:

ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, trehalose, sorbitol, glycerol, pentaerythritol, trimethylol propane, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol and a polyethylene or polypropylene glycol having a number average molecular weight of 300 to 1200; or a C6 to C24 ether thereof; and

benzyl alcohol, tetradecanol, butanol, 2-butanol, isobutanol, octanol, 2-ethylhexanol, hexanol, cyclohexanol, cyclooctanol, 2-propylheptanol, 2-ethyl-1-butanol and isopropanol.

12. The composition according to claim 1 wherein the additive is the reaction product of a succinic acid or anhydride of formula (A3) or (A4) and an alcohol of formula H—(OR) n —OR 1 ; wherein R 2 is a polyisobutenyl group having a number average molecular weight of from 700 to 1300; wherein the alcohol of formula H-(OR) n —OR 1 is selected from the group consisting of:

butanediols, tripropylene glycol and polypropylene glycols having a number average molecular weight of from 300 to 600; and

tetradecanol, butanol and 2-ethylhexanol.

13. The method according to claim 2 which achieves “keep clean” performance.

14. The method according to claim 2 which achieves “clean up” performance.

15. The method according to claim 2 wherein the deposits are injector deposits.

16. The method according to claim 15 wherein the deposits are internal injector deposits.

17. The method according to claim 2 which combats intake valve deposits.

18. The composition according to claim 1 wherein the gasoline fuel composition comprises one or more further additives selected from the group consisting of:

a) carrier oils;

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

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

d) mannich base additives comprising nitrogen-containing condensates of a phenol, aldehyde and primary or secondary amine;

e) aromatic esters of a polyalkylphenoxyalkanol; and

f) quaternary ammonium salts.

19. The composition according to claim 1 wherein the gasoline composition comprises a mixture of two or more ester additives.

20. The method according to claim 2 which achieves an improvement in performance of one or more of:

improved fuel economy;

reduced maintenance;

less frequent overhaul or replacement of injectors;

improved driveability;

improved power; or

improved acceleration.