EP4065671A1 - Use of alkyl phenol compounds as detergent additives for petrols - Google Patents

Abstract

The present invention relates to the use, for improving the detergency properties of a liquid fuel composition chosen from petrols comprising one or more detergent additives, of an additive consisting of one or more nitrogen-free compound(s) having an alkyl-phenol structure chosen from methyl-t-butyl phenols, dimethyl-t-butyl phenols, ethyl-t-butyl phenols, t-butyl phenols, di-t-butyl phenols, tri-t-butyl phenols, di-t-butyl-di-methyl phenols, and mixtures thereof. The present invention also relates to a method for improving the cleanliness of and/or for cleaning at least one inner portion of a spark-ignition internal combustion engine supplied with a liquid fuel chosen from petrols and comprising one or more detergent additives, the method consisting of adding to the fuel composition at least one such compound having an alkyl-phenol structure.

Description

DESCRIPTION

TITLE: Use of Alkyl Phenol Compounds as Detergency Additives for Gasoline The present invention relates to the use of particular alkyl phenol compounds as detergency additives in gasoline compositions.

The present invention also relates to a process or a method of improving the cleanliness and / or cleaning of at least an internal part of a spark-ignition internal combustion engine using these particular compounds.

STATE OF THE PRIOR ART Liquid fuels for internal combustion engines contain components which can be degraded during engine operation. The problem of deposits in the internal parts of combustion engines is well known to engine manufacturers. It has been shown that the formation of these deposits has consequences on engine performance and in particular has a negative impact on fuel consumption and particle emissions. Advances in fuel additive technology have made it possible to tackle this problem. So-called detergent additives used in fuels have already been proposed to maintain engine cleanliness by limiting deposits ("keep-clean" effect) or by reducing deposits already present in the internal parts of the combustion engine (effect “Clean-up” in English). Mention may be made, by way of example, of document US Pat. No. 4,171959 which describes a detergent additive for gasoline fuel containing a quaternary ammonium function. Document WO2006135881 describes a detergent additive containing a quaternary ammonium salt used to reduce or clean deposits, in particular on the intake valves. Nevertheless, engine technology is constantly evolving and fuel requirements must evolve to cope with these technological advances in combustion engines. In particular, the new direct injection systems gasoline expose the injectors to more severe conditions in terms of pressure and temperature, which favors the formation of deposits. In addition, these new injection systems have more complex geometries to optimize the spraying, in particular, more numerous holes having smaller diameters but which, on the other hand, induce greater sensitivity to deposits. The presence of deposits can alter combustion performance, and in particular increase pollutant emissions and particulate emissions. Other consequences of the excessive presence of deposits have been reported in the literature, such as increased fuel consumption or even vehicle handling problems.

There is also a problem of maintaining the detergency performance of fuels over time. Indeed, the Applicant has observed that when the fuel is stored for example in the vehicle tank or in an external storage tank before being consumed in the engine, its detergency performance deteriorates.

Conventional detergency additives make it possible to obtain good detergency performance during the few weeks following their incorporation into the fuel composition, but they do not make it possible to guarantee that these performances will be maintained for an extended storage period, typically several months .

The problem arises, among other things, for vehicles that run very little or very occasionally in which the fuel can be stored for quite long periods of time before it is completely consumed.

The problem also arises in particular in hybrid vehicles (or PHEV vehicles standing for “Plug-in Hybrid Electric Vehicle”) which are powered both by an electric battery and a conventional fuel composition such as in particular a composition of gasoline. In fact, in these vehicles, the gasoline composition is capable of being stored for particularly long periods of time in the tank of the vehicle, when the latter operates essentially by means of its electric battery. The prevention and reduction of engine deposits are essential for the optimal functioning of today's engines. There is therefore a need to provide detergent additives for gasolines promoting optimum operation of spark-ignition engines, including for new engine technologies and hybrid vehicle engines.

There also remains a need for universal detergency solutions which make it possible to prevent or reduce deposits on the internal parts of spark-ignition internal combustion engines, whatever the engine technology and / or the composition of the fuel.

OBJECT OF THE INVENTION The Applicant has discovered that particular compounds possessing an alkyl-phenol structure and not comprising a nitrogen atom exhibit unexpected properties, in that they improve the effectiveness of the detergent additives used in the compositions. of gasoline. These compounds exhibit an effect of the “booster” type of the detergent properties of conventional detergency additives, that is to say that their addition even in very small quantities (for example less than 50 ppm by weight) makes it possible to increase the performance detergency of said additives, and to maintain or even improve the detergency performance of said composition after storage for a period typically greater than 3 months, preferably greater than 6 months.

In other words, the addition of the compounds according to the invention in a fuel composition of the gasoline type and comprising at least one detergency additive has the effect of increasing the detergent properties of said composition and of allowing the maintenance or even improvement of these properties over time. These compounds thus make it possible to maintain the cleanliness of the engine, in particular by limiting or avoiding the formation of deposits (“keep-clean” effect in English) or by reducing the deposits already present in the internal parts of the combustion engine (“clean-up” effect in English).

The alkyl-phenol compounds used in the present invention are moreover known as antioxidants for fuel compositions, in particular of diesel type, that is to say with a function of improving oxidation stability. of these compositions. On the other hand, the discovery that these same additives can improve the detergency properties of a gasoline fuel composition is completely unexpected, and is at the origin of the present invention.

The additional advantages associated with the use as detergent additives of the compounds according to the invention are:

- optimal engine operation,

- reduced fuel consumption, - reduced pollutant emissions, and

- savings due to less engine maintenance.

A subject of the present invention is thus the use, to improve the detergency properties of a liquid fuel composition chosen from gasolines comprising one or more detergency additives, of an additive consisting of one or more compound (s) ) non-nitrogenous having an alkyl-phenol type structure chosen from methyl-t-butyl phenols, dimethyl-t-butyl phenols, ethyl-t-butyl phenols, t-butyl phenols, di-t-butyl phenols, tri-t-butyl phenols, di-t-butyl-di-methyl phenols, and mixtures thereof. The subject of the invention is also a process or method for improving the cleanliness and / or cleaning of at least one internal part of a controlled-ignition internal combustion engine supplied with a liquid fuel chosen from among gasolines and comprising one or more detergency additives. The method according to the invention consists in adding to said fuel composition an additive consisting of one or more non-nitrogenous compound (s) as defined above.

Preferably, said additive is incorporated into the fuel composition at a minimum content of 5 ppm by weight, and at a content up to 500 ppm by weight.

Preferably, the liquid fuel composition is chosen from hydrocarbon fuels, non-essentially hydrocarbon fuels, and mixtures thereof. According to a preferred embodiment, the additive according to the invention is used in liquid fuel to maintain cleanliness and / or clean at least one of the internal parts of said spark-ignition internal combustion engine.

In particular, the additive is used in liquid fuel to limit or prevent the formation of deposits in at least one of the internal parts of said engine and / or reduce the deposits existing in at least one of the internal parts of said engine.

Advantageously, the deposits are localized in at least one of the internal parts selected from the engine intake system, the combustion chamber and the fuel injection system, and preferably the fuel injection system.

In particular, the additive according to the invention is used to prevent and / or reduce the formation of deposits associated with the coking phenomenon and / or deposits of the soap and / or varnish type, preferably at the fuel injectors.

The additive according to the invention also makes it possible to reduce the fuel consumption of the spark-ignition internal combustion engine.

It also makes it possible to reduce pollutant emissions, in particular particulate emissions from the spark-ignition internal combustion engine.

The internal combustion engine is a spark ignition engine, also known as a gasoline engine. The invention is particularly suitable for gasoline engines with direct injection (DISI in English "Direct Injection Spark Ignition engine").

Other subjects, characteristics, aspects and advantages of the invention will emerge even more clearly on reading the description and the examples which follow. In what follows, and unless otherwise indicated, the limits of a domain of values are included in this domain, in particular in the expressions “between” and “ranging from ... to ...”. Moreover, the expressions “at least one” and “at least” used in the present description are respectively equivalent to the expressions “one or more” and “greater than or equal”.

Finally, in a manner known per se, the term “CN compound or group” denotes a compound or a group containing in its chemical structure N carbon atoms.

DETAILED DESCRIPTION

Alkyl phenol compounds:

The invention uses as an additive one or more non-nitrogenous compound (s) having an alkyl-phenol type structure.

By "non-nitrogenous" is meant that the compounds according to the invention do not include a nitrogen atom in their formula. The term “alkyl-phenol-type” structure is understood to mean that the compounds according to the invention have in their formula a phenolic nucleus (that is to say mono- or poly-hydroxybenzene) substituted by at least one alkyl group.

These compounds are chosen from methyl-t-butyl phenols, dimethyl-t-butyl phenols, ethyl-t-butyl phenols, t-butyl phenols, di-t-butyl phenols, tri-t-butyl phenols , di-t-butyl-di-methyl phenols, and mixtures thereof.

Preferred compounds are chosen from 2,6-di-t-butyl-4-methyl phenol (BHT), 4,6- di-tert-butyl-2-methylphenol, t-butyl hydroquinone (TBHQ), 2 , 6 and 2,4 di-t-butyl phenol, 2,4-dimethyl-6-t-butyl phenol, 2,4,6-tri-t-butyl phenol, 2,3,6-trimethyl phenol, 2,4,6-trimethyl phenol, 4,4'-methylene bis (2,6-di-t-butyl phenol) (CAS No. 1 18-82-1), alone or as a mixture. The particularly preferred compounds are chosen from tert-butyl phenols such as in particular 2,6-di-t-butyl-4-methyl phenol (BHT), 2,4-dimethyl-6-t-butyl phenol, methyl-tert-butylphenol, 2,6 and 2,4-di-t-butyl phenol, 2,4,6-tri-t-butyl phenol, and mixtures thereof.

Use

The alkyl-phenol additive according to the invention is used to improve the detergency performance of a liquid fuel composition selected from gasolines and which comprises one or more detergency additives. This is understood to mean that the incorporation, including in a very small amount (for example less than 50 ppm by weight relative to the total weight of the composition), of the compound according to the invention in such a fuel, produces an effect on cleanliness. spark ignition engines supplied with said fuel, compared with the same gasoline fuel comprising the same detergency additive (s) in the same proportions, but not comprising the additive of the alkyl-phenol type according to the invention. In other words, said additive is used to improve (or boost) the detergent performance of at least one detergency additive, in a gasoline composition.

According to a preferred embodiment, the additive according to the invention is used to improve the detergency performance of such a gasoline composition, which is stored for a period of at least 3 months, preferably a period of at least 6 months, before being consumed.

Advantageously, the use of said additive in the gasoline composition makes it possible, during the combustion of the latter, to limit or avoid the formation of at least one type of deposits as described below, and / or to reduce at least one type of existing deposits, compared to liquid fuel not comprising such a compound.

In particular, the use of the additives according to the invention in a gasoline type fuel makes it possible to maintain the cleanliness of at least one of the internal parts of the internal combustion engine and / or to clean at least one of the internal parts of the internal combustion engine.

The use of alkyl phenol compounds as additives in the fuel makes it possible in particular to limit or avoid the formation of deposits in at least one of the internal parts of said engine (“keep-clean” effect in English) and / or to reduce deposits. existing in at least one of the internal parts of said engine (“clean-up” effect). Advantageously, the use of said compound as an additive in the fuel makes it possible to observe both the two effects, limitation (or prevention) and reduction of deposits ("keep-clean" and "clean-up" effects).

Deposits are distinguished according to the type of internal combustion engine with spark ignition and the location of the deposits in the internal parts of said engine.

According to a preferred embodiment, the spark ignition internal combustion engine (or gasoline engine) is a direct injection engine (DISI in English “Direct Injection Spark Ignition engine”).

According to a preferred variant of this embodiment, the internal combustion engine is a spark ignition engine of a hybrid vehicle, preferably with direct injection.

The targeted deposits are those located in at least one of the internal parts of said spark ignition engine. The internal part of the spark-ignition engine kept clean (keep-clean) and / or cleaned (clean-up) is advantageously chosen from the engine's intake system, in particular the intake valves (IVD in English " Intake Valve Deposit ”), the combustion chamber (CCD in English“ Combustion Chamber Deposit ”or TCD in English“ Total Chamber Deposit ”) and the fuel injection system, in particular the injectors of an injection system indirect (PFI in English “Port Fuel Injector”) and / or the injectors of a direct injection system (DISI). Particularly preferably, the targeted deposits are located on the injectors of a direct injection system.

There are several well-known methods of evaluating the detergency performance of a fuel composition, among which one can cite the standard test methods CEC F-05-A-93 and CEC F-20-A-98 which are carried out on spark ignition engines. We can also cite the new CEC TDG-F-113 method on a direct injection gasoline engine (DISI), in particular the version dated 15.09.2015. According to a preferred embodiment, the improvement in the detergency properties obtained by the use according to the invention is evaluated by means of one of the following test methods: the CEC method F-05-A-93, the CEC F-20-A-98 method, and CEC TDG-Fl 13 method (version dated 15.09.2015), and preferably the above-mentioned CEC TDG-F-1 13 method.

According to an advantageous embodiment, the use of the additives according to the invention also makes it possible to reduce the fuel consumption of the spark-ignition internal combustion engine.

According to another advantageous embodiment, the use of the additives according to the invention also makes it possible to reduce the emissions of pollutants, in particular the emissions of particles from the internal combustion engine.

The additive according to the invention can be added to liquid fuel within a refinery and / or be incorporated downstream of the refinery, optionally mixed with other additives in the form of an additive package.

The compound (s) having an alkyl-phenol type structure according to the invention are advantageously used in the fuel composition at a total content of at least 5 ppm by weight, relative to the total weight of said composition.

Preferably, said compounds are used at a total content ranging from 5 to 500 ppm by weight, preferably from 10 to 200 ppm by weight, more preferably from 15 to 100 ppm by weight and better still from 20 to 50 ppm by weight, relative to the total weight of the composition of fuel.

The fuel composition The fuel composition, in which the compound (s) having an alkyl-phenol type structure are used as additives, typically comprises at least one liquid hydrocarbon cut obtained from one or more selected sources. from the group consisting of mineral sources, animal, vegetable and synthetic sources.

Oil will preferably be chosen as the mineral source.

The fuel composition is advantageously chosen from hydrocarbon fuels and non-essentially hydrocarbon fuels, and mixtures thereof. The term "hydrocarbon fuel" means a fuel consisting of one or more compounds consisting solely of carbon and hydrogen.

By non-essentially hydrocarbon fuel is meant a fuel consisting of one or more compounds consisting not essentially of carbon and hydrogen, that is to say which also contain other atoms, in particular oxygen atoms.

Hydrocarbon fuels include in particular light distillates having a boiling point in the range of gasolines. Gasolines include, in particular, any commercially available spark ignition engine fuel compositions. By way of representative example, mention may be made of gasolines meeting standard NF EN 228. Gasolines generally have sufficiently high octane numbers to avoid the knocking phenomenon. Typically, gasoline type fuels marketed in Europe, conforming to standard NF EN 228 have an engine octane number (MON in English "Motor Octane Number") greater than 85 and a research octane number (RON in English " Research Octane Number ”) of a minimum of 95. Petrol type fuels have, generally, a RON ranging from 90 to 100 and a MON ranging from 80 to 90, the RON and MON being measured according to the standard ASTM D 2699-86 or D 2700-86.

Non-essentially hydrocarbon-based fuels include in particular oxygenates, for example distillates resulting from the BTL (“biomass to liquid”) conversion of plant and / or animal biomass, taken alone or in combination; biofuels, for example oils and / or esters of vegetable and / or animal oils; bioethanols. The mixtures of hydrocarbon fuel and non-essentially hydrocarbon fuel are typically E _{x type gasolines.}

By gasoline of type E _x for a spark ignition engine is meant a gasoline fuel which contains x% (v / v) of oxygenates, generally ethanol, bioethanol and / or ethyl-tertio-butyl-ether. (ETBE), x denoting a number ranging from 0 to 100.

The sulfur content of the fuel composition is preferably less than or equal to 50 ppm, or even less than 10 ppm and advantageously sulfur free. Detergent additives

The fuel composition according to the invention further comprises one or more detergency additive (s), also called detergent additive (s), different from the alkyl phenol compounds according to the invention, and which can be chosen from additives detergency for fuels usually used. The latter are compounds well known to those skilled in the art.

The detergent additives can be in particular (but not limited to) chosen from the group consisting of amines, succinimides, alkenylsuccinimides, polyalkylamines, polyalkyl polyamines, polyetheramines, quaternary ammonium salts, triazole derivatives, and Mannich bases, and more preferably from Mannich bases, quaternary ammonium salts, and polyisobutylene mono- or poly-amines (or PIB- amines), more preferably still among quaternary ammonium salts and better still among polyisobutylene succinimides functionalized with a quaternary ammonium group, fatty acid amides functionalized with a quaternary ammonium group and their dimers such as di- (alkylamido compounds -propyl- quaternary ammonium) described for example in European patent application No. 18306589.5, and fatty-chain alkylamidoalkyl betaines.

Examples of detergent additives are given in the following documents: EP0938535, US2012 / 0010112, WO2012 / 004300, US4171959 and WO2006135881.

One can also advantageously use block copolymers formed of at least one polar unit and one non-polar unit, such as for example those described in patent application FR 1761700 in the name of the Applicant.

According to one embodiment, the fuel composition comprises at least one detergent additive consisting of a quaternary ammonium salt, obtained by reaction with a quaternization agent of a nitrogen compound comprising a tertiary amine function, this nitrogen compound being product of the reaction of an acylating agent substituted with a hydrocarbon group and of a compound comprising at least one tertiary amine group and at least one group chosen from primary amines, secondary amines and alcohols. Preferably, said nitrogen-containing compound is the reaction product of a succinic acid derivative substituted with a hydrocarbon group, preferably a polyisobutenyl-succinic anhydride, and of an alcohol or of a primary or secondary amine also comprising a group tertiary amine. Such detergent additives, as well as preferred combinations of detergent additives comprising them, are in particular described in patent application WO 2015/124584 in the name of the applicant.

The particularly preferred additives are chosen from Mannich bases bearing a polyisobutylene group; polyisobutylene mono- or poly-amines; polyisobutylene succinimides functionalized with an ammonium group quaternary; amides of fatty acids functionalized with a quaternary ammonium group and their dimers such as di- (alkylamido-propyl-quaternary ammonium) compounds; fatty chain alkylamidoalkyl betaines; and mixtures of these compounds.

Preferably, the total content of detergent additive (s) in the fuel composition (without including the compounds having an alkyl-phenol type structure according to the invention) ranges from 5 to 5000 ppm by weight, preferably from 10 to 1000 ppm by weight, and more preferably from 20 to 500 ppm by weight, relative to the total weight of the fuel composition.

Preferably, the ratio between the total weight content of compound (s) having an alkyl-phenol type structure according to the invention on the one hand and the total weight content of detergent additive (s) on the other hand ranges from 1: 60 at 1: 2, preferably from 1:20 to 1: 3.

Other additives

The fuel composition can also comprise other additives, in addition to the additive (s) consisting of compound (s) having an alkyl-phenol type structure according to the invention and of the detergent additive (s) described above.

This or these other additives will be chosen according to the type of gasoline fuel. They can be chosen, for example, in a nonlimiting manner, from anti-corrosion additives, antioxidant additives, dispersant additives, demulsifying additives, anti-foam agents, biocides, reodorants, procetane additives, friction modifiers. , lubricity additives or lubricity additives, combustion aid agents (catalytic combustion and soot promoters), cold resistance additives and in particular agents improving the cloud point and the pour point , TLF ("Limit Filterability Temperature"), anti-sedimentation agents, anti-wear agents, tracers, solvents / carrier oils and conductivity modifiers. Among these additives, mention may be made, for example and in a nonlimiting manner: a) lubricating additives or anti-wear agents, in particular (but not limitingly) chosen from the group consisting of fatty acids and their ester or amide derivatives, in particular glycerol monooleate, and mono- and polycyclic carboxylic acid derivatives. Examples of such additives are given in the following documents EP680506, EP860494, WO98 / 04656, EP915944, FR2772783,

FR2772784; b) anti-corrosion additives such as, for example, fatty acid ester dimers and aminotriazoles; c) demulsion additives.

It is especially preferred to use lubricity additives and anti-corrosion additives such as those mentioned in a) and b) above. These additional additives may be present in an amount ranging, for each, from 5 to 1000 ppm (each), preferably from 50 to 500 ppm by weight, relative to the total weight of the fuel composition. The process or method

The process or method for improving the cleanliness and / or cleaning at least one internal part of a spark-ignition internal combustion engine supplied with a liquid fuel chosen from among gasolines comprising one or more detergency additives, consists in adding to said fuel composition an additive consisting of at least one non-nitrogenous compound having an alkylphenol type structure as described above.

The combustion of this fuel composition thus additivated in an internal combustion engine produces an effect on the cleanliness of the engine, compared to a fuel composition containing the same ingredients except for said additive (s).

The combustion of this fuel composition makes it possible, in particular, to prevent and / or reduce the fouling of the parts. internal engine. These effects on engine cleanliness are as previously described in the context of reuse.

According to a preferred embodiment, a method of maintaining the cleanliness (“keep-clean”) and / or cleaning (“clean-up”) of at least one of the internal parts of an internal combustion engine with ignition ordered comprises: a) the addition, to a liquid fuel composition selected from gasolines and comprising one or more detergency additives, of an additive consisting of one or more non-nitrogenous compound (s) having a structure of the alkyl-phenol type as described above; then b) the combustion of the fuel composition resulting from step a) in the internal combustion engine.

According to a particularly preferred embodiment, the composition according to the invention is stored for a period of at least 3 months, and preferably at least 6 months, between steps a) and b) above.

This storage of the composition can be carried out in the tank of a vehicle, in particular of a hybrid vehicle (in particular of the PHEV type), or outside any vehicle. According to a preferred embodiment, the internal combustion engine is a direct injection controlled ignition (DISI) engine.

The internal part kept clean and / or cleaned of the spark ignition engine is preferably chosen from the engine's intake system, in particular the intake valves (IVD), the combustion chamber (CCD or TCD) and the fuel injection system, in particular the injectors of an indirect injection system (PFI) or the injectors of a direct injection system (DISI), and preferably the injectors of a fuel injection system direct injection.

According to a preferred variant, step (a) above is preceded by a preliminary step of determining the content of compound (s) of structure of alkyl-phenol type to be incorporated into said fuel composition in order to achieve a given specification. relating to the detergency properties of the fuel composition.

This preliminary step is common practice in the field of additivation of fuels and involves defining at least one characteristic representative of the detergency properties of the fuel composition as well as a target value.

The characteristic representative of the detergency properties of the fuel will depend on the type of spark-ignition internal combustion engine, the direct or indirect injection system and the location in the engine of the deposits targeted for cleaning and / or maintenance of the fuel. cleanliness.

Methods for evaluating the detergent properties of fuels have been widely described in the literature and are within the general knowledge of those skilled in the art. Mention will be made, by way of nonlimiting example, of the tests standardized or recognized by the profession or the methods described in the following literature:

For indirect injection spark ignition engines: - the Mercedes Benz M102E method, standardized test method

CEC F-05-A-93, and

- Mercedes Benz Ml 11 method, CEC F-20-A-98 standardized test method.

These methods make it possible to measure deposits on the intake valves (IVD), the tests generally being carried out on Eurosuper gasoline meeting the EN228 standard.

For direct injection positive-ignition engines:

- the method described by the applicant in the article "Evaluating Injector Fouling in Direct Injection Spark Ignition Engines", Mathieu Arondel, Philippe China, Julien Gueit; Conventional and future energy for automobiles; 10th international colloquium; January 20-22, 2015, p.375-386 (Technische Akademie Esslingen by Techn. Akad. Esslingen, Ostfildern), for the evaluation of coking type deposits on the injector, - the method described in document US20130104826, for the evaluation of coking type deposits on the injector,

-the CEC method of TDG-F-113 “DISI test” for the evaluation of coking type deposits on the injector, in particular the version dated 15.09.2015. The determination of the amount of compound (s) according to the invention to be added to the fuel composition to achieve a given specification is typically carried out by comparison with the fuel composition but without the compound (s) according to invention The method of maintaining cleanliness (keep-clean) and / or cleaning (clean-up) can also include an additional step c) after step b), of checking the target reached and / or adjustment of the additivation rate with the compound (s) according to the invention. The examples below are given by way of illustration of the invention, and should not be interpreted in such a way as to limit its scope. EXAMPLES

The performance in terms of detergency was evaluated using the Volkswagen EA111 CAVE engine test at SGS, in accordance with the CEC TDG-F-1 13 method (“DISI” engine test), version dated 15.09. 2015.

The procedure takes place in two stages. During a first step (fouling or "dirty-up" phase lasting 48 hours), a standard standard fouling fuel, without additives, is used (CEC fuel RF83-A-81). This phase results in an increase in injection time due to clogging of the injectors. We denote tinjO the injection time at the start of the test and ti nj 48 the injection time at the end of the dirty-up phase. The second step (called cleaning or "clean-up") consists in using a fuel with additives for 24 hours while continuing to measure the evolution of the injection time. We note tinj 72 the injection time at the end of the "clean-up" phase.

The percentage of restoration of the injection time after the clean-up step is calculated according to: (tinj 48 - tinj 72) x 100 / (ti nj 48 - tinj-0). The test was carried out by employing in the second step a fuel E consisting of unleaded petrol 98 meeting the EN228 standard, supplemented with a classic multifunctional additive package containing a classic commercial detergency additive consisting of a Mannich base. This detergency additive is present in the gasoline additive composition at a treatment rate of 258 ppm by weight (258 mg / kg).

The test was carried out with gasoline E on the one hand (comparative), then with gasoline E '(invention) which corresponds to gasoline E to which 30 ppm by weight of an additive A was added. consisting of a mixture of compounds having an alkyl-phenol type structure.

The composition of additive A is as follows:

- 55% by weight of 2,4-dimethyl-6-tert-butyl phenol;

- 15% by weight of 2,6-di-tert-butyl-4-methyl phenol (BHT),

- 30% by weight of a mixture of methyl- and di-methyl-tert-butylphenols.

The test was performed with gasoline E immediately after preparation. Then the essences E and E 'were stored for a period of 6 months outside, in a tank subjected to natural climatic variations with variable temperatures in the range going from 5 ° C to 25 ° C, and the test a was repeated with the species E and E 'at the end of this storage period.

The results obtained on the initial fuels E and E 'appear in Table 1 below: [Table lj

The addition of additive A made it possible to improve the detergent properties of the gasoline composition. The results obtained on fuels E and E 'after 6 months of storage are shown in Table 2 below:

[Table 2j

These results show that the detergent properties of composition E deteriorated after 6 months of storage. The presence of additive A according to the invention makes it possible not only to avoid a degradation of the detergency properties, but above all to improve these properties: in fact, after 6 months of storage, the detergent performance of composition E 'no only are greater than those of composition E, but in addition they are greater than that of the initial composition E before storage.

Claims

1. Use, to improve the detergency properties of a liquid fuel composition chosen from gasolines comprising one or more detergency additives, of an additive consisting of one or more non-nitrogenous compound (s) having an alkyl-phenol type structure chosen from methyl-t-butyl phenols, dimethyl-t-butyl phenols, ethyl-t-butyl phenols, t-butyl phenols, di-t-butyl phenols, tri-t-butyl phenols, di-t-butyl-di-methyl phenols, and mixtures thereof. 2. Use according to the preceding claim, characterized in that the compound (s) having an alkyl-phenol type structure are chosen from 2,6-di-t-butyl-4-methyl phenol (BHT), 4,6- di-tert-butyl-2-methylphenol, t-butyl hydroquinone (TBHQ), 2,6 and 2,4 di-t-butyl phenol, 2,4-dimethyl-6-t- butyl phenol, 2,4,6-tri-t-butyl phenol, 2,3,6-trimethyl phenol, 2,4,6-trimethyl phenol, 4,4'-methylene bis (2,6- di-t-butyl phenol), and mixtures thereof, and preferably from 2,6-di-t-butyl-4-methyl phenol (BHT), 2,4-dimethyl-6-t-butyl phenol, methyl-tert-butylphenol, 2,6 and 2,4 di-t-butyl phenol, 2,4,6-tri-t-butyl phenol, and mixtures thereof. 3. Use according to any one of the preceding claims, characterized in that the compound (s) having an alkyl-phenol type structure are used at a total content ranging from 5 to 500 ppm by weight, preferably from 10 at 200 ppm by weight, more preferably from 15 to 100 ppm by weight and better still from 20 to 50 ppm by weight, relative to the total weight of the fuel composition. 4. Use according to any one of the preceding claims, characterized in that the fuel composition is chosen from hydrocarbon fuels, non-essentially hydrocarbon fuels, and mixtures thereof. 5. Use according to any one of the preceding claims, characterized in that the detergency additive (s) are chosen from the group consisting of amines, succinimides, alkenylsuccinimides, polyalkylamines, polyalkyl polyamines, polyetheramines, quaternary ammonium salts, triazole derivatives, and Mannich bases, and more preferably among Mannich bases, quaternary ammonium salts, and polyisobutylene mono - Or poly-amines and more preferably still from: Mannich bases bearing a polyisobutylene group; polyisobutylene mono- or poly-amines; polyisobutylene succinimides functionalized with a quaternary ammonium group; amides of fatty acids functionalized with a quaternary ammonium group and their dimers such as di- (alkylamido-propyl-quaternary ammonium) compounds; fatty chain alkylamidoalkyl betaines; and mixtures of these compounds. 6. Use according to any one of the preceding claims, characterized in that the ratio between the total weight content of compound (s) having an alkyl-phenol type structure on the one hand and the total weight content of detergent additive (s) on the other hand is from 1:60 to 1: 2, preferably from 1:20 to 1: 3. 7. Use according to any one of the preceding claims, to limit or prevent the formation of deposits in at least one of the internal parts of a spark-ignition internal combustion engine and / or to reduce existing deposits in at least one of the internal parts of a positive-ignition internal combustion engine. 8. Use according to the preceding claim, characterized in that the internal combustion engine is a direct injection controlled ignition engine. 9. Use according to any one of claims 7 and 8, characterized in that the internal combustion engine is a hybrid vehicle spark ignition engine. 10. Use according to one of claims 7 to 9, characterized in that the internal part of the spark ignition engine kept clean and / or cleaned is chosen from the engine intake system, in particular the intake valves, the room of combustion, and the fuel injection system, in particular the injectors of an indirect injection system or the injectors of a direct injection system, and preferably among the injectors of a direct injection system . 11. Use according to any one of the preceding claims, characterized in that the fuel composition is stored for a period of at least 3 months, preferably a period of at least 6 months, before being consumed. 12. A method of maintaining the cleanliness and / or cleaning of at least one of the internal parts of a spark-ignition internal combustion engine comprising: a) adding to a liquid fuel composition chosen from gasolines comprising one or more detergency additives, of an additive consisting of one or more non-nitrogenous compound (s) having an alkyl-phenol type structure as defined in any one of claims 1 or 2; then b) the combustion of the fuel composition resulting from step a) in the internal combustion engine.