DE69101966T2 - Gasoline composition. - Google Patents

Description

The present invention relates to a gasoline composition comprising a major amount of a gasoline suitable for use in carburetor engines and a minor amount of at least one additive.

U.S. Patent No. 3,632,510 discloses lubricating oil and fuel compositions containing a major amount of a lubricating oil and a minor amount of an ester derivative (containing mixed ester metal salts) of a hydrocarbon-substituted succinic acid, wherein the hydrocarbon substituent contains at least about 50 aliphatic carbon atoms and no more than about 5% olefinic bonds based on the total number of covalent carbon-carbon bonds in the substituent. Sources for the hydrocarbon substituent include essentially saturated olefin polymers, especially polymers of monoolefins having from 2 to 30 carbon atoms. Polyisobutylene is believed to be the most preferred source of the hydrocarbon substituent. Alcohols believed to be suitable for preparing the ester derivatives include compounds of the general formula

HO(R₁-O)R₂-OR₃

in which R₃ is hydrogen, aryl, a lower alkyl such as ethyl, propyl, tert-butyl, pentyl, etc.; or aralkyl; n has a value of 0 to about 150 and R₁ and R₂ are lower alkylenes with up to 8 carbon atoms. When added to fuels, the ester derivatives are said to promote the cleanliness of the fuel system by preventing the formation of deposits in fuel tanks, fuel lines, carburettors, fuel injection systems and are said to reduce, in many cases, deposits in combustion chambers, spark plug fouling and exhaust valve deposits. They are also effective as a filter blockage agent.

U.S. Patent No. 4,846,848 discloses compositions containing a minor amount of a polyalphaolefin having a viscosity at 100°C of 2 to 20 centistokes (2 x 10-6 to 2 x 10-5 m2/s) and optionally also an aliphatic polyamine, an alkali or alkaline earth metal salt of a succinic acid derivative as a flame speed improver and/or a polyolefin. The succinic acid derivative either has as a substituent on at least one of its alpha carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group having 20 to 200 carbon atoms, or it has as a substituent on one of its alpha carbon atoms an unsubstituted or substituted hydrocarbon group having 20 to 200 carbon atoms, which is bonded to the other alpha carbon atom by means of a hydrocarbon group having 1 to 6 carbon atoms to form a ring structure. The salts of the succinic acid derivative can be monobasic salts, with the remaining carboxyl group being aminated or esterified. However, no amines or alcohols suitable for use in amination or esterification are mentioned. The preferred salts are referred to as dibasic salts.

Published patent application UK 2 177 416 A (registered by the applicant as K 6240 GBR) discloses a petrol composition comprising a major amount of a petrol suitable for use in carburettor engines and, as an ignition rate enhancing agent, a minor amount of an alkali metal or alkaline earth metal salt of a succinic acid derivative.

with an unsubstituted or substituted aliphatic hydrocarbon group having 20 to 200 carbon atoms as a substituent on at least one of its alpha carbon atoms, or a succinic acid derivative having a unsubstituted or substituted aliphatic hydrocarbon group having 20 to 200 carbon atoms as a substituent on one of its alpha carbon atoms, which is bonded to the other alpha carbon atom by means of a hydrocarbon group having 1 to 6 carbon atoms to form a ring structure. Salts of the succinic acid derivative may be monobasic, with the remaining carboxyl group being aminated or esterified. However, no amines or alcohols suitable for use in amination or esterification are mentioned. The preferred salts are referred to as dibasic salts.

British Patent Specification No. 1,306,233 discloses compositions for use in fuels comprising an oil-soluble, carboxyl-containing dispersant and a thermally stable, relatively low volatile petroleum fraction. The carboxyl-containing dispersant is a carboxylic acid or anhydride, an ester, a metal salt or acylated derivative thereof. Substantially saturated aliphatic hydrocarbon-substituted succinic acids and anhydrides are particularly preferred as dispersants.

It has now been found that alkali metal salts of certain succinic acid derivatives are suitable as ignition aids (agents for improving the ignition speed) and, compared to ignition aids already known from the prior art, these have the advantage that they are less viscous and less prone to agglomeration, the latter being a particularly serious problem since it can cause valve sticking.

According to the present invention, therefore, there is provided a gasoline composition comprising a major amount of a gasoline suitable for use in carburetor engines and a minor amount of an alkali metal salt of a partial ester of an alkyl polyether alcohol of the general formula

HO(CH₂- -O)R (I)

in which n is an integer from 4 to 25, R represents a C6-C20 alkyl group and each R1 is independently a hydrogen atom or a C1-C10 alkyl group, with a succinic acid derivative having as a substituent on at least one of its alpha carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group having 15 to 200 carbon atoms optionally bonded to the other alpha carbon atom by means of a hydrocarbon group having 1 to 6 carbon atoms to form a ring structure.

The present invention further provides a method of operating a carburetor engine which comprises introducing a gasoline composition as defined above into said engine.

The alkali metal salt of the partial ester is preferably the sodium or, above all, the potassium salt.

An alkyl or aliphatic hydrocarbon substituent group may be linear or branched.

Preferably, n is an integer from 4 to 20, more preferably from 4 to 15 and most preferably n has the value 5 or 6.

Preferably, each R contains at least 6 carbon atoms, more preferably at least 7 carbon atoms. Advantageously, R represents a C9-C15 or more preferably a C12-C15 alkyl group.

Preferably, each R¹ independently represents a hydrogen atom or a C₁-C₅ alkyl, preferably a methyl or ethyl group.

The compounds of general formula (I) are known compounds or can be prepared by processes analogous to known processes.

The nature of the substituent(s) on at least one of the alpha carbon atoms of the succinic acid derivative is very important since it largely determines the solubility of the alkali metal salt of the partial ester in gasoline.

The aliphatic hydrocarbon group may suitably be derived from a polyolefin whose monomers comprise 2 to 6 carbon atoms, e.g. from a polyethylene, polypropylene, polybutylene, polypentene, polyhexene or a mixed polymer. Particularly preferred is an aliphatic hydrocarbon group derived from polyisobutylene.

Preferably, the aliphatic hydrocarbon group has 15 to 150, more preferably 15 to 100, and advantageously 15 to 45 carbon atoms. Aliphatic hydrocarbon groups having 20 to 30 carbon atoms have been found to be very effective.

The aliphatic hydrocarbon group may contain substituents, e.g. one or more hydrogen atoms may be replaced by another atom, e.g. a halogen atom, or by a non-aliphatic organic group, e.g. a substituted or unsubstituted phenyl group, or a hydroxy, ether, ketone, aldehyde or ester group.

The succinic acid derivative may have more than one C₁₅-C₂₀₀₀ aliphatic hydrocarbon group attached to one or both of its alpha carbon atoms. Preferably, the succinic acid comprises a C₁₅-C₂₀₀₀ aliphatic hydrocarbon group on one of its alpha carbon atoms. On the other alpha carbon atom there is suitably no substituent or only a fairly short hydrocarbon residue, e.g. a C₁-C₆ group. The latter group may be linked to the aliphatic C₁₅-C₂₀₀₀ hydrocarbon group to form a ring structure.

The preparation of substituted succinic acid derivatives is known in the art. If a polyolefin is used as a substituent, the substituted succinic acid derivative may be suitably prepared by mixing the polyolefin, e.g. polyisobutylene, with maleic acid or maleic anhydride and passing chlorine through the mixture to form hydrochloric acid and a polyolefin-substituted succinic acid as described in British Patent Application No. 949,981.

For example, British Patent Specification No. 1 483 729 discloses the production of hydrocarbon-substituted succinic anhydride by thermally reacting a polyolefin with maleic anhydride.

The partial ester of polyolefin-substituted succinic acid may conveniently be prepared by reacting, in known manner, the polyolefin-substituted succinic acid with an alkyl polyether alcohol of the general formula (I), e.g. with such an alcohol in which n is 5, R is a mixture of C₁₂-C₁₅ alkyl groups and R₁ is a methyl group, which is available under the trade mark "Oxilube-500" from subsidiaries of the Royal Dutch/Shell group. The corresponding alkali metal salt can conveniently be prepared from the partial ester by reaction with an alkali metal hydroxide, such as potassium hydroxide.

The gasoline composition according to the present invention may suitably contain 1 to 1000 parts by weight, preferably 100 to 400 parts by weight, of the alkali metal salt of the partial ester, which preferably results in an alkali metal concentration, preferably potassium concentration, in the range of 4 to 16 parts by weight pM.

Those skilled in the art will appreciate that the presence of the alkali metal in gasoline compositions according to the present invention can be expected to provide protection against valve seat depression in engines.

The gasoline composition of the present invention may also contain other additives. For example, it may contain a lead compound as an antiknock agent and accordingly the gasoline composition of the present invention includes both leaded and unleaded gasoline. The gasoline composition may also contain antioxidants such as phenols, e.g. 2,6-di-tert-butylphenol, or phenylenediamines, e.g. N,N'-di-sec-butyl-p-phenylenediamine, or antiknock additives which are not lead compounds, or polyetheramino additives, e.g. as described in U.S. Patent No. 4,477,261 and European Published Patent Application No. 151,621.

A particularly suitable additive which can be used in addition to the alkali metal salt of the partial ester in the gasoline composition according to the present invention is a polyolefin derived from C2-C6 monomers. Preferably, the polyolefin is polyisobutylene having 20 to 175 carbon atoms, and especially having 35 to 150 carbon atoms. The amount of polyolefin in the gasoline composition according to the invention is preferably 100 to 1200 parts by weight p.m.

Alternatively, part or all of the polyolefin derived from C₂-C₆ monomers may be replaced by a polyoxyalkylene glycol hemiether of the general formula (II)

R²O - [(EO)m(PO)t)]-H (II)

in which EO is ethyleneoxy, PO is propyleneoxy, R² is a C₁-C₂₀ alkyl group and m and t are average numbers of ethyleneoxy and propyleneoxy groups in each half-ether molecule such that m/(m+t) is in the range of 0 to 0.5 and t/(m+t) is in the range of 0.5 to 1, the average molecular weight (Mn) (number average) of the half-ether being in the range of 500 to 3000.

Preferably, R² in formula II is a mixture of C₁₂-C₁₅-alkyl groups and the kinematic viscosity of the half-ether is about 80 mm²/s at 20°C determined according to ASTM D445 and such a half-ether is available under the trademark "Oxilube-949" from subsidiaries of the Royal Dutch/Shell group. The amount of half-ether in the gasoline composition according to the present invention is preferably in the range of 100 to 1200 parts by weight p.m.

Another particularly suitable additive, in addition to the alkali metal salt of the partial ester, for the gasoline composition of the present invention is a polyamine containing a C20-C150 alkyl or alkenyl group. Preferably, the polyamine is N-polyisobutylene-N',N'-dimethyl-1,3-diaminopropane. The amount of polyamine present in the gasoline composition of the present invention is preferably from 5 to 200 parts by weight.

A particularly suitable additive combination which can be present in addition to the alkali metal salt of the partial ester in the gasoline composition according to the invention is described in US Patent No. 4,357,148. This additive combination comprises an oil-soluble aliphatic polyamine and a hydrocarbon polymer This additive combination reduces the increase in the octane requirement increase (ORI). The ORI reduction also prevents or removes deposits in the combustion chamber and on adjacent surfaces in carburetor engines. Although various types of polyamines and various types of polymers can be used, it is preferred to use a polyolefin whose monomers comprise 2 to 6 carbon atoms together with a polyamine containing a C₂₀₋₁₅₀ alkyl group or alkenyl group. Therefore, the gasoline composition according to the present invention preferably comprises such a combination. A very advantageous type of the polyolefin mentioned is polyisobutylene having 20 to 175 carbon atoms, especially polyisobutylene having 35 to 150 carbon atoms. The polyamine used is preferably N-polyisobutylene-N',N'-dimethyl-1,3-diaminopropane. The content of polyolefin and of alkyl or alkenyl group-containing polyamine present in the gasoline composition according to the invention is preferably in the range of 100 to 1200 parts by weight pM and in the range of 5 to 200 parts by weight pM, respectively. The composition may suitably further contain a nonionic surfactant such as an alkylphenol or an alkyl alkoxylate. Suitable examples of such surfactants include C4-C18 alkylphenol and C2-6 alkyl ethoxylate or C2-6 alkyl propoxylate or mixtures thereof. The amount of surfactant is advantageously in the range of 10 to 1000 parts by weight pM. The composition may suitably further contain a detergent such as a polyolefin-substituted succinimide. Suitable examples of such detergents include the polyolefin-substituted succinimides described in EP-A-271937. The amount of detergent is advantageously in the range of 10 to 1000 parts by weight pM

The gasoline composition according to the invention comprises a larger amount of a gasoline (base fuel) suitable for use in carburetor engines. These include hydrocarbon base fuels, which boil substantially in the gasoline boiling range of 30 to 230ºC. These base fuels may comprise mixtures of saturated, olefinic and aromatic hydrocarbons. They may be derived from distillation gasoline, synthetically produced aromatic hydrocarbon mixtures, from thermally or catalytically cracked hydrocarbon feedstocks, from hydrocracked petroleum fractions or from catalytically reformed hydrocarbons. The octane number of the base fuel is not critical and is generally above 65. In the gasoline, substantial amounts of hydrocarbons may be replaced by alcohols, ethers, ketones or esters. Of course, the base fuels are suitably substantially free of water since water could impair proper combustion.

The alkali metal salts of the partial esters may be added separately to the gasoline or they may be mixed with other additives and added to the gasoline together with them. A preferred method of adding these salts to gasoline is to first prepare a concentrate of these salts followed by adding this concentrate in a calculated desired amount to the gasoline.

The present invention therefore further provides a concentrate suitable for addition to gasoline, which comprises a diluent compatible with the gasoline containing 20 to 50% by weight, based on the diluent, of an alkali metal salt of a partial ester of an alkyl polyether alcohol of the general formula

HO(CH2- -O) (I)

in which n is an integer of 4 to 25, R represents a C6-C20 alkyl group and each R¹ independently represents a hydrogen atom or a C1-C10 alkyl group, with a succinic acid derivative having an unsubstituted or substituted aliphatic hydrocarbon group having 15 to 200 carbon atoms on at least one of its alpha carbon atoms as a substituent, which may optionally be bonded to the other alpha carbon atom via a hydrocarbon group having 1 to 6 carbon atoms to form a ring structure.

Suitable diluents compatible with gasoline are hydrocarbons such as heptane, alcohols or ethers such as methanol, ethanol, propanol, 2-butoxyethanol or methyl tert-butyl ether. The diluent is preferably an aromatic hydrocarbon solvent such as toluene, xylene, mixtures thereof or mixtures of toluene or xylene with an alcohol. If desired, the concentrate may contain an anti-hazer, especially an ethoxylated alkylphenol formaldehyde resin of the polyether type. The anti-hazer, if used, is preferably contained in the concentrate in an amount of 0.01 to 1% by weight, based on the diluent.

The invention further provides for the use of an alkali metal salt of a partial ester of an alkyl polyether alcohol of the general formula (I)

HO(CH₂- -O) R (I)

in which n is an integer from 4 to 25, R is a C6-C20 alkyl group and each R1 is independently a hydrogen atom or a C1-C10 alkyl group, with a succinic acid derivative having as a substituent on at least one of its alpha carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group having 15 to 200 carbon atoms which may optionally be bonded to the other alpha carbon atom by means of a hydrocarbon group having 1 to 6 carbon atoms to form a ring structure, as an ignition aid and as an anti-sticking agent in a gasoline composition comprising a major portion of a gasoline suitable for carburetor engines.

The invention will now be explained in more detail using the following examples.

example 1

Polyisobutylene having a number average molecular weight (Mn) of 280 as determined by gel permeation chromatography and maleic anhydride are stirred while heating to 180°C in a nitrogen atmosphere. Chlorine is then added to the reaction mixture over a period of 5 hours and the reaction mixture is kept at 180°C for an additional 4 hours. The molar ratio of polyisobutylene/maleic anhydride/chlorine in the reaction mixture is 1.0/1.5/1.12. Excess maleic anhydride is then removed by distillation, leaving polyisobutenylsuccinic anhydride with an acid value of 5.9 mmol/g.

A mixture of the polyisobutenylsuccinic anhydride obtained above (100 g) with 148 g of an alkyl polyether alcohol of the general formula (I) in which n has the value 5, R is a mixture of C₁₂-C₁₅ alkyl groups and R¹ is a methyl group (available under the trademark "Oxilube-500" from subsidiaries of the Royal Dutch/Shell group) is then heated to 200ºC for 5 hours at atmospheric pressure and for 1 hour at a pressure of 20 mmHg to give a partial ester with an acid value of 2.1 mmol/g. After cooling, the partial ester obtained (100g) is dissolved in xylene (50g) and the resulting mixture is mixed with a solution of potassium hydroxide in methanol (8.5g of 83% by weight potassium hydroxide dissolved in 21.2g of methanol). The reaction mixture is heated to 65ºC for a period of 3 hours, at the end of which the reaction mixture is filtered and the filtrate is retained.

After cleaning the filtrate, the desired salt is obtained. (Potassium content: 4.4 mole percent).

Example 2

A mixture of polyisobutylene with an average molecular weight (Mn) of 340 (number average) determined by gel permeation chromatography (280 g) and maleic anhydride (196 g) is heated to 200 °C for 16 hours, at the end of which excess maleic anhydride is distilled off and polyisobutenyl succinic anhydride with an acid value of 5.3 mmol/g is obtained.

A mixture of the polyisobutenyl succinic anhydride obtained above (303.9 g) with 405.5 g of an alkyl polyether alcohol of the general formula (I) as mentioned in Example 1 is heated to 200°C for 3 1/2 hours at atmospheric pressure and for 1 hour at a pressure of 20 mmHg. The product obtained, a partial ester, is found to have an acid value of 1.04 mmol/g. The reaction of the partial ester (681 g) obtained above and dissolved in xylene (500 ml) with a solution of potassium hydroxide in methanol (8.5 g of 83% by weight potassium hydroxide dissolved in 21.2 g of methanol) at 65°C over a period of 3 hours, followed by filtration and subsequent purification, yields the desired salt with a potassium content of 4.0 mole percent.

Example 3

By a procedure analogous to that described in Example 2, a potassium salt of a partial ester of an alkyl polyether alcohol of the general formula (I) in which n is 5, R is a mixture of C9-C11 alkyl groups and R1 is a hydrogen atom, having an average molecular weight (Mn) of 380 (number average) as determined by gel permeation chromatography (available under the trade mark "Dobanol 91-5" from subsidiaries of the Royal Dutch/Shell group) and polyisobutenyl succinic acid is prepared using the above-mentioned alkyl polyether alcohol instead of the alkyl polyether alcohol mentioned in Example 2.

Example 4

By a process analogous to that described in Example 2, a potassium salt of a partial ester of a condensate of a mixture of C12-C15 alkanols, propylene oxide and ethylene oxide at a molar ratio of alkanol:propylene oxide:ethylene oxide of 1:4.2:5.6 (density at 20°C determined according to ASTM D 1298 of 0.98; viscosity index determined according to ASTM D 2270 of 186; number average molecular weight (Mn) of 700; available under the trademark "Oxilube-501" from subsidiaries of the Royal Dutch/Shell group) and polyisobutenyl succinic acid is prepared using the above condensate instead of the alkyl polyether alcohol mentioned in Example 2.

Example 5

A mixture of polyisobutylene with an average molecular weight (Mn) (number average) of 353, determined by gel permeation chromatography (45 kg) and maleic anhydride (25 kg) is heated to 200 °C for 16 hours, after which excess maleic anhydride is distilled off and polyisobutenyl succinic anhydride with an acid value of 4.04 mmol/g is obtained (residual amount of maleic anhydride < 0.1 % by weight and of polyisobutenyl 21.7 % by weight).

A mixture of polyisobutenyl succinic anhydride (35 kg) as obtained above and 35.2 kg of the alkyl polyether alcohol of the general formula (I) as mentioned in Example 1 are heated at 200°C at atmospheric pressure for 4 1/2 hours. The product obtained, a partial ester, has an acid value of 1.04 mmol/g. Reaction of the partial ester obtained (69 kg) dissolved in xylene (30 kg) with a solution of potassium hydroxide in methanol (17 kg of a 25% by weight solution) at 65°C for 3 hours, followed by filtration and subsequent purification leads to the desired salt with a potassium content of 2.10% by weight. The concentration of non-volatiles is 61.1% by weight.

Example 6

In order to be able to predict what might happen in a vehicle engine under certain driving conditions, it is possible to study the external appearance and viscosity characteristics of an additive package (mixture) after removing all light components (i.e. those components with a boiling point below 350ºC). Thus, additive packages A to H, as shown in Table 1, are distilled to remove the light components using a rotary evaporator operated for one hour at 140ºC and 1.3 Pa, and the viscosities of the remaining residues are according to ASTM D 445. The results are summarized in Table I. The additives used were: Additive I: N-polyisobutylene-N',N'-dimethyl-1,3-diaminopropane, the polybutylene having an average molecular weight of 1350, determined by vapor phase osmometry. Additive II: potassium polyisobutenyl succinate, the polyisobutenyl having an average molecular weight of 950, determined by vapor phase osmometry; Additive III: polyisobutylene having an average molecular weight of 650, determined by gel permeation chromatography; and Additive IV: a polyoxyalkylene glycol hemiether of formula (II) in which R² is a mixture of C₁₂-C₁₅ alkyl groups, said hemiether having a kinematic viscosity of about 80 mm²/s at 20ºC, determined according to ASTM D 445, which is available under the trademark "Oxilube- 949" from subsidiaries of the Royal Dutch/Shell group.

It is well known that the viscosity of an additive package residue and the tendency of the additive package to cause valve sticking are directly related to one another. That is, the higher the viscosity of an additive package residue, the more it tends to cause valve sticking. It is clear from Table I that the residues of additive packages C to H, which contain the products of Examples 1, 2 and 4, have lower viscosities compared to the viscosities of the residues of the prior art additive packages A and B. It can be concluded from this that the additive packages C to H also have a lesser tendency to cause valve sticking compared to the additive packages A and B.

Example 7

Additive packages A, B and C are tested for intake valve sticking in a Volkswagen Transporter using the following procedure.

The vehicle is first driven on a base fuel over a distance of 50 km to flush the fuel system. The vehicle is then driven on a test run of 112 km with a mixture of the base fuel and one of the additive packs A, B and C. During this distance, the vehicle is subjected to hot soak periods, idling periods and maximum speeds of 24, 40 and 56 km/h in second, third and fourth gear. During the hot soak periods, the vehicle is left to stand for 10 minutes with the engine switched off. Conversely, during the idling periods, the vehicle is left to stand for 30 minutes with the engine switched on.

At the end of the test run, the vehicle is parked overnight in a refrigerated trailer at a temperature of -16ºC. The valve sticking is evaluated the next morning by measuring the maximum compression pressure in each cylinder.

In a similar manner, additive packages A, B and C are tested in a Vauxhall Cavalier vehicle.

The results are shown in Table II, from which it can be seen that the average maximum compression pressure for additive package C is higher than that for the prior art additive package A on the Volkswagen Transporter and on the Vauxhall Cavalier, and also higher than that for the prior art additive package B on the Volkswagen Transporter.

Example 8

To evaluate the performance of ignition aids, test runs are carried out using a 1.3-litre Astra engine which has been modified to allow the combustion chamber one of the cylinders has optical access. The compression ratio for the cylinder considered in the test runs is 5.8:1. In each test, the engine is operated at 200 rpm for 2 hours, and measurements are taken continuously during this time. From the data collected, the reduction in the cyclic change of the indicated mean effective pressures (IMEP) can be determined for each ignition aid tested. The tests are carried out with unleaded petrol with 2.4 and 8 parts by weight of pM potassium. The potassium is added as a salt of the partial ester of polyisobutylene substituted succinic acid (the polyisobutylene having an average molecular weight of 280 as determined by gel permeation chromatography) with the alkyl polyether alcohol of formula (I) in which n is 5, R is a mixture of C₁₂-C₁₅ alkyl groups and R¹ is a methyl group (available under the trademark "Oxilube-500" from subsidiaries of the Royal Dutch/Shell group).

The results of the experiments are shown in Table III. Table I Components Additive package Parts by weight pM Treatment amount Additive Example Residue Appearance Cloud point Pour point C = Clear, h = Haze p = Phase separation Table II Compression pressure (bar) Additive Packing Overnight temp. (ºC) Vehicle type medium Table III Amount of potassium (wt. pM) Reduction of the cyclic change of IMEP (%)

Claims (10)

1. A gasoline composition comprising a major part of a gasoline suitable for use in carburettor engines and a minor part of an alkali metal salt of a partial ester of an alkyl polyether alcohol of the general formula (I) HO(CH₂- -O) R (I) in which n is an integer from 4 to 25, R is a C6-C20 alkyl group, and each R¹ is independently a hydrogen atom or a C1-C10 alkyl group, with a succinic acid derivative having as a substituent on at least one of the alpha carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group having 15 to 200 carbon atoms, optionally bonded to the other alpha carbon atom by means of a hydrocarbon group having 1 to 6 carbon atoms to form a ring structure. 2. A gasoline composition according to claim 1, in which the alkali metal is potassium. 3. A gasoline composition according to claim 1 or 2, in which the aliphatic hydrocarbon group is derived from a polyolefin whose monomers have 2 to 6 carbon atoms. 4. A gasoline composition according to any preceding claim, in which the aliphatic hydrocarbon group has 15 to 45 carbon atoms. 5. A gasoline composition according to any preceding claim, in which R is a C�9-C₁₅ alkyl group. 6. A gasoline composition according to any one of the preceding claims, which additionally contains small amounts of a polyolefin derived from a C₂-C₆ monomer and/or a polyoxyalkylene glycol half-ether of the general formula (II) R²O-[(EO)m(PO)t)]-H (II) in which EO is ethyleneoxy, PO is propyleneoxy, R² is C₁-C₂₀ alkyl, and m and t are average numbers of ethyleneoxy and propyleneoxy groups in each half-ether molecule such that m/(m+t) is in the range of 0 to 0.5 and t/(m+t) is in the range of 0.5 to 1, the average molecular weight (Mn) (number average) of the half-ether being 500 to 3000, and a polyamine containing a C₂₀-C₁₅₀ alkyl or alkenyl group. 7. A gasoline composition according to claim 6, which contains 100 to 1200 parts by weight of the polyolefin and/or polyoxyalkylene glycol half ether and 5 to 200 parts by weight of the polyamine containing the alkyl or alkenyl group. 8. A concentrate suitable for addition to a gasoline, comprising a diluent compatible with the gasoline containing 20 to 50% by weight, based on the diluent, of an alkali metal salt of a partial ester of an alkyl polyether alcohol of the general formula HO(CH₂- -O) R (I) in which n is an integer from 4 to 25, R represents a C6-C20 alkyl group and each R1 is independently a hydrogen atom or a C1-C10 alkyl group, with a succinic acid derivative having as a substituent on at least one of the alpha carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group having 15 to 200 carbon atoms, optionally bonded to the other alpha carbon atom by means of a hydrocarbon group having 1 to 6 carbon atoms to form a ring structure. 9. A method of operating a carbureted internal combustion engine comprising introducing into said engine a gasoline composition according to any of claims 1 to 7. 10. Use of an alkali metal salt of a partial ester of an alkyl polyether alcohol of the general formula HO(CH₂- -O) R (I) in which n is an integer from 4 to 25, R is a C₆-C₂₀-alkyl group and each R¹ is independently a hydrogen atom or a C₁-C₁₀-alkyl group, with a succinic acid derivative having as substituents on at least one of the alpha carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group having 15 to 200 carbon atoms, which may optionally be substituted by means of a hydrocarbon group having 1 to 6 carbon atoms to form of a ring structure may be bonded to the other alpha carbon atom, as an ignition aid and valve stick-preventing agent in a gasoline composition comprising a major portion of a gasoline suitable for use in carbureted engines.