US20230357656A1

US20230357656A1 - Use of diols as detergent additives

Info

Publication number: US20230357656A1
Application number: US17/780,707
Authority: US
Inventors: Hélène Rodeschini; Géraldine Delorme
Original assignee: TotalEnergies Onetech SAS
Current assignee: TotalEnergies Onetech SAS
Priority date: 2019-11-29
Filing date: 2020-11-27
Publication date: 2023-11-09
Also published as: FR3103815B1; FR3103815A1; CN115175975B; PL4065672T3; EP4065672B1; WO2021105321A1; EP4065672A1; CN115175975A

Abstract

The present invention relates to the use, for improving the detergency properties of a liquid fuel composition comprising one or more detergent additives, of an additive consisting of one or more hydrocarbon compound(s) comprising from 2 to 10 carbon atoms and two hydroxyl functions.The present invention also relates to a method for improving the cleanliness of and/or for cleaning at least one inner portion of an internal combustion engine supplied with a liquid fuel comprising one or more detergent additives, wherein such a hydrocarbon compound is added to the fuel composition.

Description

The present invention relates to the use of specific compounds of the diol family as detergent additives in fuel compositions.
The present invention also relates to a process or a method for improving the cleanliness of and/or for cleaning at least one inner portion of an internal combustion engine implementing these specific compounds.

PRIOR ART

The liquid fuels for internal combustion engines contain components that can degrade during the operation of the engine. The issue of the deposits in the inner portions of combustion engines is well known to engine manufacturers. It has been demonstrated that the formation of these deposits has consequences on the performance of the engine and in particular has a negative impact on the consumption and the emission of particles. The progress in the technology of fuel additives has allowed to confront this issue. “Detergent” additives used in fuels have already been proposed to maintain the cleanliness of the engine by limiting the deposits (“keep-clean” effect) or by reducing the deposits already present in the inner portions of the combustion engine (“clean-up” effect). Mention can be made for example of the document U.S. Pat. No. 4,171,959 which describes a detergent additive for a gasoline fuel containing a quaternary ammonium function. The document WO2006135881 describes a detergent additive containing a quaternary ammonium salt used to reduce or to clean the deposits in particular on the intake valves. Nevertheless, the technology of engines is constantly changing and the requirements for fuels must change to confront these technological advances of combustion engines. In particular, the new gasoline or diesel direct injection systems expose the injectors to harsher conditions in terms of pressure and temperature which favours the formation of deposits. Moreover, these new injection systems have more complex geometries to optimise the spraying, in particular, more numerous holes having smaller diameters but which, on the other hand, induce greater sensitivity to the deposits. The presence of deposits can alter the combustion performance, and in particular increase the polluting emissions and the emissions of particles. Other consequences of the excessive presence of deposits have been reported in the literature, such as an increase in fuel consumption and problems of driveability.
The prevention and the reduction of deposits in these new engines are essential for optimal operation of today's engines. There is therefore a need to propose detergent additives for fuels favouring optimal operation of combustion engines, in particular but not in a limiting way for the new engine technologies.
There also remains a need for universal detergency solutions, which allow to prevent or reduce the deposits on the inner portions of internal combustion engines, regardless of the engine technology and/or the nature of the fuel.

OBJECT OF THE INVENTION

The applicant has discovered that specific compounds of the diol type, as defined below, have remarkable and unexpected properties, in that they improve the effectiveness of the detergent additives used in fuel compositions.
These compounds have an effect of “booster” type on the detergency properties of the conventional detergent additives, that is to say that their addition even in a very small quantity (for example less than 50 ppm by weight) allows to increase in a remarkable manner the detergency performance of said additives.
In other words, the addition of the compounds according to the invention into a fuel composition, whether it is of the diesel or gasoline type, comprising at least one detergent additive, has the effect of increasing the detergent properties of said composition. They allow to maintain the cleanliness of the engine, in particular by limiting or by avoiding the formation deposits (“keep-clean” effect) or by reducing the deposits already present in the inner portions of the combustion engine (“clean-up” effect).
The additional advantages associated with the use as fuel additives of the compounds according to the invention are:

- optimal operation of the engine,
- a reduction in the fuel consumption,
- reduced polluting emissions, and
- savings due to less maintenance of the engine.

An object of the present invention is therefore the use, to improve the detergency properties of a liquid fuel composition comprising one or more detergent additives, of an additive consisting of one or more hydrocarbon compound(s) comprising from 2 to 10 carbon atoms and two hydroxyl functions.
An object of the invention is also a process or method for improving the cleanliness of and/or for cleaning at least one inner portion of an internal combustion engine supplied with a liquid fuel comprising one or more detergent additives, wherein an additive consisting of at least one hydrocarbon compound comprising from 2 to 10 carbon atoms and two hydroxyl functions is added to said fuel composition.
Preferably, the compound according to the invention is incorporated into the fuel composition in a minimum concentration of 5 ppm by weight, and in a concentration that can go up to 500 ppm by weight.
Preferably, the liquid fuel composition is chosen from the hydrocarbon fuels, the not substantially hydrocarbon fuels, and the mixtures thereof. Advantageously, the hydrocarbon fuel is chosen from gasoline and diesel fuels.
According to a preferred embodiment, the compound according to the invention is used in the liquid fuel to maintain the cleanliness of and/or clean at least one of the inner portions of said internal combustion engine.
In particular, said compound is used in the liquid fuel to limit or avoid the formation of deposits in at least one of the inner portions of said engine and/or to reduce the deposits existing in at least one of the inner portions of said engine.
Advantageously, the deposits are located in at least one of the inner portions chosen from the intake system of the engine, the combustion chamber and the fuel injection system.
In particular, the compound according to the invention is used to avoid and/or to reduce the formation of deposits related to the phenomenon of coking and/or the deposits of the soap and/or varnish type.
The compound according to the invention also allows to reduce the fuel consumption of the internal combustion engine.
It further allows to reduce the emissions of pollutants, in particular, the emissions of particles of the internal combustion engine.
According to a first embodiment, the internal combustion engine is a spark-ignition engine, also known as gasoline engine.
According to a second embodiment, the internal combustion engine is a compression-ignition engine, also known as diesel engine.
Other objects, features, aspects and advantages of the invention will appear even more clearly upon reading the following description and examples.
Hereinafter, and unless otherwise indicated, the limits of a range of values are comprised 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, C_Ncompound or group designates a compound or a group containing in its chemical structure N carbon atoms.

DETAILED DESCRIPTION

The Additive According to the Invention:
The invention implements as an additive a hydrocarbon compound comprising from 2 to 10 carbon atoms and two hydroxyl functions.
Preferably, this compound has the formula C_nH_2n+2O₂, with n an integer ranging from 2 to 10.
According to a preferred embodiment, n ranges from 3 to 8, more preferably from 4 to 8; even better n is 5 or 6, and even more preferably n is 6.
According to a particularly preferred embodiment, said compound is hexylene glycol.
The Use
The compound according to the invention is used as an additive to improve the detergency performance of a fuel composition. This means that the incorporation, including in a very small quantity, of the compound according to the invention into the liquid fuel comprising a detergent additive other than the compound according to the invention produces an effect on the cleanliness of the engines supplied with said fuel, in comparison to the same fuel not comprising the compound according to the invention.
Advantageously, the use of said compound in the fuel composition allows, in comparison to the liquid fuel not comprising such a compound, to limit or to avoid the formation of at least one type of deposits as described below, and/or to reduce at least one type of existing deposits.
In particular, the use of the compounds according to the invention in a liquid fuel allows to maintain the cleanliness of at least one of the inner portions of the internal combustion engine and/or to clean at least one of the inner portions of the internal combustion engine.
The use of said compound as an additive in the liquid fuel allows in particular to limit or to avoid the formation of deposits in at least one of the inner portions of said engine (“keep-clean” effect) and/or to reduce the existing deposits in at least one of the inner portions of said engine (“clean-up” effect).
Advantageously, the use of said compound as an additive in the liquid fuel allows to observe simultaneously both effects, of limiting (or of preventing) and of reducing deposits (“keep-clean” and “clean-up” effects).
The deposits are distinguished according to the type of internal combustion engine and the location of the deposits in the inner portions of said engine.
According to a first embodiment, the internal combustion engine is a spark-ignition or gasoline engine, preferably with direct injection (DISI “Direct Injection Spark Ignition engine”). The deposits targeted are located in at least one of the inner portions of said spark-ignition engine. The inner portion of the spark-ignition engine kept clean (keep-clean) and/or cleaned (clean-up) is, advantageously, chosen from the intake system of the engine, in particular the intake valves (IVD “Intake Valve Deposit”), the combustion chamber (CCD “Combustion Chamber Deposit” or TCD “Total Chamber Deposit”) and the fuel injection system, in particular the injectors of an indirect injection system (PFI “Port Fuel Injector”) or the injectors of a direct injection system (DISI).
According to a second embodiment, the internal combustion engine is a compression-ignition engine or diesel engine, preferably a direct injection diesel engine, in particular a diesel engine with a Common-Rail injection system (CRDI “Common Rail Direct Injection”). The deposits targeted are located in at least one of the inner portions of said diesel engine.
Advantageously, the deposits targeted are located in the injection system of the diesel engine, preferably, located on an outer portion of an injector of said injection system, for example the nose of the injector and/or on an inner portion of an injector of said injection system (IDID “Internal Diesel Injector Deposits”), for example on the surface of an injector needle.
The deposits can consist of deposits related to the phenomenon of coking and/or deposits of the soap and/or varnish type (lacquering).
The compounds according to the invention as described above can advantageously be used in the fuel to reduce and/or avoid the loss of power due to the formation of the deposits in the inner portions of a direct injection diesel engine, and said loss of power can be determined according to the engine test method of the standard CEC F-98-08.
Said compound(s) according to the invention can, advantageously, be used in the fuel to reduce and/or avoid the restriction of the flow of fuel emitted by the injector of a direct injection diesel engine during its operation, and said restriction of flow can be determined according to the engine test method of the standard CEC F-23-1-01.
More generally, there are several well-known methods for evaluating the detergency performance of a fuel composition, among which mention can be made, besides the aforementioned test methods of the standards CEC F-98-08 and CEC F-23-1-01 which are carried out on diesel engines, the test methods of the standards CEC F-05-A-93 and CEC F-20-A-98 which are carried out on spark-ignition engines.
According to an advantageous embodiment, the use of the compounds according to the invention also allows to reduce the fuel consumption of the internal combustion engine.
According to another advantageous embodiment, the use of the compounds according to the invention also allows to reduce the emissions of pollutants, in particular the emissions of particles of the internal combustion engine.
The compounds according to the invention can be added into the liquid fuel in a refinery and/or be incorporated downstream of the refinery, optionally in a mixture with other additives in the form of a package of additives.
The compound(s) according to the invention are advantageously used in the fuel composition in a total concentration of at least one 5 ppm by weight, relative to the total weight of said composition.
Preferably, the hydrocarbon compound(s) according to the invention are used in a total concentration ranging from 5 to 500 ppm by weight, preferably from 10 to 200 ppm by weight, preferably from 10 to 100 ppm by weight, more preferably from 10 to 50 ppm by weight, more preferably from 20 to 50 ppm by weight, and even better from 20 to 40 ppm by weight, relative to the total weight of the fuel composition.
The Fuel Composition
The fuel composition in which the compound(s) according to the invention are used as additives typically comprises at least one liquid hydrocarbon fraction coming from one or more sources chosen from the group consisting of the mineral sources, the animal, plant and synthetic sources.
Petroleum is preferably chosen as a mineral source.
The fuel composition is advantageously chosen from the hydrocarbon fuels and the not substantially hydrocarbon fuels, and the mixtures thereof.
Hydrocarbon fuel means a fuel consisting of one or more compounds consisting only of carbon and of hydrogen.
Not substantially hydrocarbon fuel means a fuel consisting of one or more compounds consisting not substantially of carbon and of hydrogen that is to say which also contain other atoms, in particular atoms of oxygen.
The hydrocarbon fuels comprise in particular middle distillates having a boiling temperature ranging from 100 to 500° C. or the lighter distillates having a boiling temperature in the gasoline range. These distillates can for example be chosen from distillates obtained by direct distillation of crude hydrocarbons, vacuum distillates, hydrotreated distillates, distillates coming from the catalytic cracking and/or the hydrocracking of distillates under vacuum, distillates resulting from conversion methods of the ARDS (atmospheric residue desulfuration) and/or viscoreduction type, distillates coming from the use of Fischer-Tropsch fractions. The hydrocarbon fuels are typically gasolines and diesel fuels.
Advantageously, the fuel composition is chosen from the gasolines and diesel fuels.
The gasolines comprise, in particular, all fuel compositions for a spark-ignition engine available on the market. As a representative example, mention can be made of the gasolines satisfying the standard NF EN 228. The gasolines generally have octane indices sufficiently high to avoid the phenomenon of knocking. Typically, the fuels of the gasoline type marketed in Europe, in compliance with the standard NF EN 228, have a motor octane number (MON) greater than 85 and a research octane number (RON) of at least 95. The fuels of the gasoline type generally have 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.
The diesel fuels comprise, in particular, all fuel compositions for a diesel engine available on the market. As a representative example, mention can be made of the diesel fuels satisfying the standard NF EN 590.
The not substantially hydrocarbon fuels comprise in particular oxygenates, for example the distillates resulting from the BTL (biomass to liquid) conversion of plant and/or animal biomass, taken alone or in combination; the biofuels, for example the oils and/or esters of vegetable and/or animal oils; the biodiesels of animal and/or plant origin and the bioethanols.
The mixtures of hydrocarbon fuel and of not substantially hydrocarbon fuel are typically diesel fuels of the B_xtype or gasolines of the Ex type.
Diesel fuel of the B_xtype for a diesel engine means a diesel fuel that contains x % (v/v) of esters of vegetable or animal oils (including used cooking oils) transformed by a chemical process called transesterification, obtained by reacting this oil with an alcohol in order to obtain fatty acid esters (FAE). With methanol and ethanol, fatty acid methyl esters (FAME) and fatty acid ethyl esters (FAEE) are obtained, respectively. The letter “B” followed by a number indicates the percentage of FAE contained in the diesel. Thus, a B99 contains 99% FAE and 1% middle distillates of fossil origin (mineral source), B20, 20% FAE and 80% middle distillates of fossil origin, etc. The diesels of the Bo type which do not contain oxygenated compounds are thus distinguished from the diesels of the B_xtype which contain x % (v/v) of fatty acid or vegetable oil esters, most often methyl esters (VOME or FAME), x designating a number ranging from 0 to 100. When the FAE is used alone in engines, the fuel is designated by the term B100.
Gasoline of the Ex type for a spark-ignition engine means a gasoline fuel that contains x % (v/v) oxygenates, generally ethanol, bioethanol and/or ethyl tertiary-butyl ether (ETBE), x designating a number ranging from 0 to 100.
The sulphur concentration of the fuel composition is, preferably, less than or equal to 1000 ppm, preferably less than or equal to 500 ppm, and more preferably less than or equal to 50 ppm, or even less than 10 ppm and advantageously without sulphur.
The Detergent Additives
The fuel composition according to the invention comprises one or more detergent additive(s), which can be chosen from the detergent additives for fuels usually used. The latter are compounds well known to a person skilled in the art.
The detergent additives can be in particular (but not in a limiting way) chosen from the group consisting of the amines, the succinimides, the alkenylsuccinimides, the polyalkylamines, the polyalkyl polyamines, the polyetheramines, the quaternary ammonium salts, the derivatives of triazole, and the Mannich bases, and more preferably from the Mannich bases, the quaternary ammonium salts, and the polyisobutylene mono- or poly-amines (or PIB-amines), even more preferably from the quaternary ammonium salts and even better from the polyisobutylene succinimides functionalised by a quaternary ammonium group, the fatty acid amides functionalised by a quaternary ammonium group and the dimers thereof such as the di-(alkylamido-propyl-quaternary ammonium) compounds described for example in the patent application WO2020/109568, and the fatty chain alkylamidoalkyl betaines.
Examples of detergent additives are given in the following documents: EP0938535, US2012/0010112, WO2012/004300, U.S. Pat. No. 4,171,959 and WO2006135881.
Block copolymers formed by at least a polar unit and an apolar unit, for example such as those described in the patent application FR 1761700 in the name of the applicant, can also advantageously be used.
According to a preferred embodiment, the fuel composition comprises at least one detergent additive consisting of a quaternary ammonium salt, obtained by reaction with a quaternisation agent of a nitrogen compound comprising a tertiary amine function, said nitrogen compound being the product of the reaction of an acylating agent substituted by a hydrocarbon group and a compound comprising at least one tertiary amine group and at least one group chosen from the primary amines, the secondary amines and the alcohols.
According to a particularly preferred embodiment, said nitrogen compound is the product of a reaction of a derivative of succinic acid substituted by a hydrocarbon group, preferably polyisobutenyl succinic anhydride, and an alcohol or a primary or secondary amine also including a tertiary amine group.
Such detergent additives, as well as preferred combinations of detergent additives comprising them, are in particular described in the patent application WO 2015/124584 in the name of the applicant.
Preferably, the total concentration of detergent additive(s) of the fuel composition (without including the hydrocarbon compounds according to the invention) ranges from 5 to 5000 ppm by weight, preferably from 10 to 1000 ppm by weight, and even better from 20 to 250 ppm by weight, relative to the total weight of the fuel composition.
Preferably, the ratio between the total weight concentration of hydrocarbon compound(s) according to the invention on the one hand and the total weight concentration of detergent additive(s) on the other hand ranges from 1:50 to 1:1, preferably from 1:20 to 1:1, more preferably from 1:20 to 1:2, and even better from 1:20 to 1:3.
The Other Additives
The fuel composition according to the invention can also comprise other additives, in addition to the detergent additive(s) and the hydrocarbon compound(s) according to the invention.
This or these other additives can be for example chosen, in a non-limiting manner, from the anti-corrosion/antioxidant additives, the dispersant additives, the demulsifying additives, the anti-foaming agents, the biocides, the reodorants, the cetane number improvers, the friction modifiers, the lubricity additives or smoothness additives, the combustion enhancer agents (combustion and soot catalytic promoters), the cold flow improvers and in particular the agents improving the cloud point, the pour point, the CFPP (cold filter plugging point), the anti-sedimentation agents, the anti-wear agents, the tracers, the solvents/carrier oils, and the agents modifying conductivity.
Among these additives, mention can be made in particular of:

- a) the cetane number improvers, in particular (but not in limiting way) chosen from the alkyl nitrates, preferably 2-ethyl hexyl nitrate, the aryl peroxides, preferably benzyl peroxide, and the alkyl peroxides, preferably tert-butyl peroxide;
- b) the anti-foaming additives, in particular (but not in limiting way) chosen from the polysiloxanes, the oxyalkylated polysiloxanes, and the fatty acid amides coming from vegetable or animal oils. Examples of such additives are given in EP861882, EP663000, EP736590;
- c) the cold flow improvers (CFI) chosen from the copolymers of ethylene and of unsaturated ester, such as ethylene/vinyl acetate (EVA), ethylene/vinyl propionate (EVP), ethylene/vinyl ethanoate (EVE), ethylene/methyl methacrylate (EMMA), and ethylene/alkyl fumarate copolymers described, for example, in the documents U.S. Pat. Nos. 3,048,479, 3,627,838, 3,790,359, 3,961,961 et EP261957;
- d) the lubricity additives or anti-wear agents, in particular (but not in a limiting way) chosen from the group consisting of the fatty acids and their ester or amide derivatives, in particular glycerol monooleate, and the derivatives of mono- and polycyclic carboxylic acids. Examples of such additives are given in the following documents: EP680506, EP860494, WO98/04656, EP915944, FR2772783, FR2772784;
- e) the cloud point additives, in particular (but not in limiting way) chosen from the group consisting of the long chain olefin/(meth)acrylic ester/maleimide terpolymers, and the polymers of esters of fumaric/maleic acids. Examples of such additives are given in FR2528051, FR2528051, FR2528423, EP112195, EP172758, EP271385, EP291367;
- f) the polyfunctional cold operability additives chosen from the group consisting of the polymers containing olefin and alkenyl nitrate as described in EP573490;
- g) the anti-corrosion additives for example such as the dimers of fatty acid esters and the aminotriazoles.

These additional additives can be present in a quantity ranging, for each, from 10 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 of and/or for cleaning at least one inner portion of an internal combustion engine supplied with a liquid fuel comprising one or more detergent additives involves adding to said fuel composition an additive consisting of at least one hydrocarbon compound as described above.
The combustion of this fuel composition to which additives have thus been added in an internal combustion engine produces an effect on the cleanliness of the engine, in comparison to a fuel composition containing the same ingredients except for said hydrocarbon compound(s).
The combustion of this fuel composition allows, in particular, to prevent and/or reduce the fouling of the inner portions of the engine. These effects on the cleanliness of the engine are as described above in the context of the use.
According to a preferred embodiment, a method for maintaining the cleanliness of (“keep-clean”) and/or for cleaning (“clean-up”) at least one of the inner portions of an internal combustion engine comprises:

- a) adding, to a fuel composition comprising at least one detergent additive, one or more hydrocarbon compounds as described above; then
- b) the combustion of the fuel composition resulting from step a) in the internal combustion engine.

According to a first embodiment, the internal combustion engine is a spark-ignition engine, preferably with direct injection (DISI).
The inner portion kept clean and/or cleaned of the spark-ignition engine is, preferably, chosen from the intake system of the engine, 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).
According to a second embodiment, the internal combustion engine is a diesel engine, preferably a direct injection diesel engine, in particular a diesel engine with a Common-Rail injection system (CRDI).
The inner portion kept clean (keep-clean) and/or cleaned (clean-up) of the diesel engine is, preferably, the injection system of the diesel engine, preferably an outer portion of an injector of said injection system, for example the nose of the injector and/or one of the inner portions of an injector of said injection system, for example the surface of an injector needle.
According to a preferred embodiment, the step (a) above is preceded by a previous step of determining the concentration of hydrocarbon compound(s) to be incorporated into said fuel composition to achieve a given specification relative to the detergency properties of the fuel composition.
This previous step is part of the routine practice in the field of adding additives to 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 depends on the type of internal combustion engine, for example diesel or spark-ignition, on the direct or indirect injection system and on the location in the engine of the deposits targeted for the cleaning and/or the maintaining of the cleanliness.
For diesel engines with direct injection, the characteristic representative of the detergency properties of the fuel can, for example, correspond to the loss of power due to the formation of the deposits in the injectors or the restriction of the flow of fuel emitted by the injector during the operation of said engine.
The characteristic representative of the detergency properties can also correspond to the appearance of deposits of the lacquering type at the needle of the injector (IDID).
Methods for evaluating the detergency properties of fuels have been widely described in the literature and are part of the general knowledge of a person skilled in the art. As a non-limiting example, mention is made of the trials standardised or recognised by the profession or the methods described in the following literature:
For Direct Injection Diesel Engines:

- the DW10 method, an engine testing method of the standard CEC F-98-08, for measuring the loss of power of direct injection diesel engines
- the XUD9 method, an engine testing method of the standard CEC F-23-1-01 Issue 5, for measuring the restriction of flow of fuel emitted by the injector
- the method described by the applicant in the application WO2014/029770 pages 17 to 20, for evaluating the lacquering deposits (IDID).

For Indirect Injection Spark-Ignition Engines:

- the method Mercedes Benz M102E, a testing method of the standard CEC F-05-A-93, and
- the method Mercedes Benz M111, a testing method of the standard CEC F-20-A-98.

These methods allow to measure the deposits on the intake valves (IVD), the tests generally being carried out on a Eurosuper gasoline satisfying the standard EN228.
For Direct Injection Spark-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; Jan. 20-22, 2015, p. 375-386 (Technische Akademie Esslingen par Techn. Akad. Esslingen, Ostfildern), for evaluating the deposits of the coking type on the injector,
- the method described in the document US20130104826, for evaluating the deposits of the coking type on the injector.

The determination of the quantity 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 to the fuel composition but without the compound(s) according to the invention.
The method for maintaining the cleanliness (keep-clean) and/or for cleaning (clean-up) can also comprise an additional step c) after step b), of verifying the target reached and/or of adjusting the rate of addition of the compound(s) according to the invention.
The hydrocarbon compounds according to the invention have remarkable properties as boosters of effectiveness of the detergent additives in a liquid fuel, in particular in a diesel fuel or in a gasoline fuel. These compounds are particularly remarkable in particular because they are effective for a wide range of liquid fuels, for several types of engine specifications and against various types of deposits that form in the inner portions of internal combustion engines.
The examples below are given as an illustration of the invention, and should not be interpreted in such a way as to limit the scope thereof.

EXAMPLES

Example 1: Detergency Tests of the “Keep-Clean” Type in a Diesel Fuel

The performance in terms of detergency has been evaluated by using the XUD9 engine test, involving determining the loss of flow rate defined as corresponding to the restriction of the flow of a diesel emitted by the injector of a diesel engine with a prechamber during its operation, according to the engine testing method of the standard CEC F-23-1-01.
The goal of the XUD9 test is to evaluate the aptitude of the additive and/or of the composition of additives tested to maintain the cleanliness, an effect called “keep-clean”, of the injectors of a Peugeot XUD9 A/L diesel engine with four cylinders and with prechamber injection, in particular to evaluate its aptitude to limit the formation of deposits on the injectors.
The test was carried out on a virgin diesel of the B7 type satisfying the standard EN590, to which a known detergent additive consisting of a quaternary ammonium salt obtained by reaction of propylene oxide with the product of the reaction of a polyisobutenyl succinic anhydride, the polyisobutenyl group (PIB) of which has a number average molecular weight (Mn) of 1000 g/mol, and dimethylaminopropylamine has been added, at a treatment concentration of 37.5 ppm by weight (37.5 mg/kg). The diesel to which an additive has thus been added is labelled diesel G.
The test was carried out with the diesel G on the one hand, and with the diesel G to which 20 ppm by weight of hexylene glycol has been added on the other hand.
The test starts with a Peugeot XUD9 A/L diesel engine with four cylinders and with prechamber injection equipped with clean injectors, the flow rate of which has been previously determined. The engine follows a determined test cycle for 10 hours and 3 minutes (repetition of the same cycle 134 times). At the end of the test, the flow rate of the injectors is once again evaluated. The quantity of fuel necessary for the test is 60 L. The loss of flow rate is measured on the four injectors. The results are expressed in percentage of loss of flow rate for various needle lifts. Usually, the fouling values at 0.1 mm of needle lift are compared since they are more discriminating and more precise and repeatable (repeatability <5%). The change in the loss of flow rate before/after test allows to deduce the loss of flow rate as a percentage. Given the repeatability of the test, a significant detergent effect can be affirmed for a reduction in loss of flow rate or a gain in flow rate greater than 10 points (>10%).
The results obtained are gathered in Table 1 below:

	TABLE 1

		Loss of flow
	Diesel fuel	rate (%)

	G (comparative)	10.7%
	G + 20 ppm of hexylene glycol (invention)	0.5%

The above results show that the addition of the hexylene glycol leads to significantly better detergency performance in terms of prevention of the fouling of the injectors of the engine (“keep-clean” effect).

Example 2: Detergency Tests of the “Clean-Up” Type in a Diesel Fuel

The following two consecutive phases were carried out, by reproducing for each phase the test method described in example 1 above:

- Phase 1 of fouling (or “dirty up”) with a conventional diesel fuel of the B7 type, compliant with the standard EN 590 and not containing any detergent additive. The loss of flow rate evaluated after this first phase is 80%.
- Phase 2 of cleaning (or “clean up”) with the candidate fuel.

The test was carried out by using as the candidate fuel in phase 2 the diesel G on the one hand, and the diesel G to which 20 ppm by weight of hexylene glycol has been added on the other hand, as described in example 1 above.
The results obtained are gathered in Table 2 below:

	TABLE 2

		Loss of flow
	Diesel	rate (%)

	G (comparative)	51.6%
	G + 20 ppm of hexylene glycol (invention)	21.9%

The above results show that the addition of the hexylene glycol leads to very markedly better detergency performance in terms of reduction of the fouling of the injectors of the engine (“clean up” effect).

Claims

1. A method for improving the detergency properties of a liquid fuel composition comprising one or more detergent additives, the method comprising:

adding to the liquid fuel composition an additive consisting of one or more hydrocarbon compound(s) comprising from 2 to 10 carbon atoms and two hydroxyl functions.

2. The method according to the preceding claim, characterised in that said hydrocarbon compound has the formula C_nH_2n+2O₂, with n being an integer ranging from 2 to 10.

3. The method according to the preceding claim, characterised in that n ranges from 3 to 8.

4. The method according to the preceding claim, characterised in that said hydrocarbon compound is hexylene glycol.

5. The method according to claim 1, characterised in that the hydrocarbon compound(s) are added to the liquid fuel composition in a total concentration ranging from 5 to 500 ppm by weight to the total weight of the fuel composition.

6. The method according to claim 1, characterised in that the fuel composition is chosen from hydrocarbon fuels, fuels not substantially hydrocarbon fuels, and the mixtures thereof.

7. The method according to claim 1, characterised in that the fuel composition is chosen from gasoline fuels and diesel fuels.

8. The method according to claim 1, characterised in that the detergent additive(s) are chosen from a group consisting of amines, succinimides, alkenylsuccinimides, polyalkylamines, polyalkyl polyamines, polyetheramines, quaternary ammonium salts, derivatives of triazole, and Mannich bases.

9. The method according to claim 1, characterised in that the total concentration of detergent additive(s) different from said hydrocarbon compounds in the fuel composition ranges from 5 to 5000 ppm by weight relative to the total weight of the fuel composition.

10. The method according to claim 1, characterised in that the ratio between the total weight concentration of hydrocarbon compound(s) on the one hand and the total weight concentration of detergent additive(s) on the other hand ranges from 1:50 to 1:11.

11. The method according to claim 1, to limit or avoid the formation of deposits in at least one of the inner portions of an internal combustion engine and/or to reduce the deposits existing in at least one of the inner portions of an internal combustion engine.

12. The method according to the preceding claim, characterised in that the internal combustion engine is a spark-ignition engine or gasoline engine.

13. The method according to claim 11, characterised in that the internal combustion engine is a compression-ignition engine or diesel engine.

14. A method for improving the cleanliness of and/or for cleaning at least one inner portion of an internal combustion engine supplied with a liquid fuel comprising one or more detergent additives, wherein an additive consisting of at least one hydrocarbon compound as defined in claim 1 is added to said fuel composition.

15. The method according to claim 2, characterised in that n is 5 or 6.

16. The method according to claim 1, further characterised in that the detergent additive(s) are Mannich bases.

17. The method according to claim 1, further characterised in that the detergent additive(s) are quaternary ammonium salts.

18. The method according to claim 1, further characterised in that the detergent additive(s) are polyisobutylene succinimides functionalised by a quaternary ammonium group.

19. The method according to claim 1, characterised in that the total concentration of detergent additive(s) different from said hydrocarbon compounds in the fuel composition ranges from 20 to 250 ppm by weight relative to the total weight of the fuel composition.

20. The method according to claim 1, characterised in that the ratio between the total weight concentration of hydrocarbon compound(s) on the one hand and the total weight concentration of detergent additive(s) on the other hand ranges from 1:20 to 1:3.