Use of Detergent Additives For Reducing a Particle Amount in the Exhaust Gas of Direct Injection Diesel Engines

Abstract

The present invention relates to the use of detergent additives for reducing or preventing the formation of deposits in the injection systems of direct-injection diesel engines and in particular in common rail injection systems.

Description

The present invention relates to the use of detergent additives for reducing the amount of particles in the exhaust gas emissions of direct-injection diesel engines and in particular of diesel engines with common rail injection systems.

In direct-injection diesel engines, the fuel is injected through a multihole engine injection nozzle which reaches directly into the combustion chamber and distributes it in an ultrafine manner (nebulizes it), instead of being introduced into a pre-chamber or swirl chamber in the classical (chamber) diesel engine. The advantage of the direct-injection diesel engines lies in their performance, which is high for diesel engines, and a nevertheless low consumption. In addition, these engines achieve a very high torque even at low speeds.

Currently, essentially three methods are used to inject the fuel directly into the combustion chamber: the conventional distributor injection pump, the unit-injector or unit-pump system and the common rail system.

In the common rail system, the diesel fuel is conveyed by a pump with pressures up to 2000 bar into a high-pressure line, the common rail. Starting from the common rail, branch lines run to the different injectors which inject the fuel directly into the combustion chamber. The full pressure is always applied to the common rail, which enables multiple injection or a special injection form. In the other injection systems, in contrast, only one injection is possible. The injection in the case of the common rail is divided essentially into three groups: (1.) preinjection, by which essentially softer combustion is achieved, so that hard combustion noises (“knocking”) are reduced and the engine seems to run quietly; (2.) main injection which is responsible in particular for a good torque profile; and (3.) post-injection which in particular ensures a low NO_x value. In this post-injection, the fuel is generally not combusted, but rather evaporated by residual heat in the cylinder. The thus formed exhaust gas/fuel mixture is transported to the exhaust gas system, where the fuel acts as a reducing agent for the nitrogen oxides NO_x in the presence of suitable catalysts.

The variable, cylinder-individual injection in common rail injection systems allows a positive influence on the harmful substance emission of the engine, for example the emission of nitrogen oxides (NO_x), carbon monoxide (CO) and in particular of particles (soot). This makes it possible, for example, that engines equipped with common rail injection systems can satisfy the Euro 4 standard theoretically even without additional particle filters.

The exhaust gas regulations of the Euro 4 standard (EU 4) which are intended to lead to improved air cleanliness in Europe require compliance with certain limiting values which have to be complied with not only at the factory adjustment but also after 100 000 km kilometrage of the engine, and are measured under particular test conditions. For instance, the limiting value for particle emission from diesel engines is 0.025 g/km.

In-house investigations have found that, in the course of engine operation of direct-injection diesel engines and in particular of those having a common rail injection system, there is an increase in the particle emission. This is attributed, inter alia, to the formation of deposits in the injection system. For example, carbonization deposits can form at the injection nozzle, but there are also deposits at other parts of the injection system. In particular, there is formation of deposits in the injectors, which has the effect that they exhibit altered response behavior, as a result of which the fuel is no longer injected in the correct dosage, i.e. the amount injected deviates upward or downward from the original setting. The deposits may also have the effect that the fuel is no longer nebulized to a sufficiently fine degree, i.e. no longer with a sufficiently small droplet size, and/or no longer with the correct geometry. Overall, the formation of deposits leads, with increasing kilometrage, to the combustion proceeding in an ever more suboptimal manner, in particular in an ever more incomplete manner, and thus with carbonization/soot formation, which contributes to an increase in the amount of particles in the exhaust gas emissions of the engine and ultimate failure to comply with limiting values of the Euro 4 standard over prolonged periods or compliance only with the aid of costly and inconvenient particle filters.

It is therefore an object of the present invention to provide additives which reduce the particle emission which increases in the course of engine operation by, for example, inter alia, reducing or preventing the formation of deposits in the injection systems of direct-injection diesel engines, especially in common rail injection systems.

The object is achieved by the use of an additive composition consisting of at least one detergent additive and optionally at least one carrier oil for reducing the amount of particles in exhaust gas emissions of direct-injection diesel engines.

In particular, the direct-injection diesel engines are those with common-rail injection systems. In these, the reduction in the particle emission is attributed, inter alia, to reduction or prevention of the formation of deposits especially in the injectors.

In the context of the present invention, the term “particles” has the same definition as in the Euro 4 standard.

Detergent Additives

The detergent additives are preferably amphiphilic substances which have at least one hydrophobic hydrocarbyl radical having a number-average molecular weight (M_n) of from 85 to 20 000 and at least one polar moiety which is selected from:

• (a) mono- or polyamino groups having up to 6 nitrogen atoms, of which at least one nitrogen atom has basic properties,
• (b) nitro groups, if appropriate in combination with hydroxyl groups,
• (c) hydroxyl groups in combination with mono- or polyamino groups, in which at least one nitrogen atom has basic properties,
• (d) carboxyl groups or their alkali metal or alkaline earth metal salts,
• (e) sulfonic acid groups or their alkali metal or alkaline earth metal salts,
• (f) polyoxy-C₂- to -C₄-alkylene groups which are terminated by hydroxyl groups, mono- or polyamino groups, in which at least one nitrogen atom has basic properties, or by carbamate groups,
• (g) carboxylic ester groups,
• (h) moieties which are derived from succinic anhydride and have hydroxyl and/or amino and/or amido and/or imido groups and/or
• (i) moieties obtained by Mannich reaction of substituted phenols with aldehydes and mono- or polyamines.

The hydrophobic hydrocarbyl radical in the above detergent additives, which ensures sufficient solubility in the fuel, has a number-average molecular weight (Mn) of from 85 to 20 000, especially from 113 to 10 000, in particular from 300 to 5000. Typical hydrophobic hydrocarbyl radicals which can be used, in particular in conjunction with the polar moieties (a), (c), (h) and (i), are longer-chain alkyl or alkenyl groups, in particular the polypropenyl, polybutenyl and polyisobutenyl radical each having Mn=from 300 to 5000, especially from 500 to 2500, in particular from 700 to 2300.

Examples of the above groups of detergent additives include the following:

Additives comprising mono- or polyamino groups (a) are preferably polyalkenemono- or polyalkenepolyamines based on polypropene or on conventional (i.e. having predominantly internal double bonds) polybutene or polyisobutene having Mn=from 300 to 5000. When polybutene or polyisobutene having predominantly internal double bonds (usually in the beta and gamma position) are used as starting materials in the preparation of the additives, a possible preparative route is by chlorination and subsequent amination or by oxidation of the double bond with air or ozone to give the carbonyl or carboxyl compound and subsequent amination under reductive (hydrogenating) conditions. The amines used here for the amination may, for example, be ammonia, monoamines or polyamines, such as dimethylaminopropylamine, ethylenediamine, diethylenetriamine, triethylenetetramine or tetraethylenepentamine. Corresponding additives based on polypropene are described in particular in WO-A 94/24231.

Further preferred additives comprising monoamino groups (a) are the hydrogenation products of the reaction products of polyisobutenes having an average degree of polymerization P=from 5 to 100 with nitrogen oxides or mixtures of nitrogen oxides and oxygen, as described in particular in WO-A 97/03946.

Further preferred additives comprising monoamino groups (a) are the compounds obtainable from polyisobutene epoxides by reaction with amines and subsequent dehydration and reduction of the amino alcohols, as described in particular in DE-A 196 20 262.

Additives comprising nitro groups (b), if appropriate in combination with hydroxyl groups, are preferably reaction products of polyisobutenes having an average degree of polymerization P=from 5 to 100 or from 10 to 100 with nitrogen oxides or mixtures of nitrogen oxides and oxygen, as described in particular in WO-A 96/03367 and WO-A 96/03479. These reaction products are generally mixtures of pure nitropoly-isobutenes (e.g. α,β-dinitropolyisobutene) and mixed hydroxynitropoly-isobutenes (e.g. α-nitro-β-hydroxypolyisobutene).

Additives comprising hydroxyl groups in combination with mono- or polyamino groups (c) are in particular reaction products of polyisobutene epoxides, obtainable from polyisobutene having preferably predominantly terminal double bonds and Mn from 300 to 5000, with ammonia or mono- or polyamines, as described in particular in EP-A 476 485.

Additives comprising carboxyl groups or their alkali metal or alkaline earth metal salts (d) are preferably copolymers of C₂-C₄₀-olefins with maleic anhydride which have a total molar mass of from 500 to 20 000 and whose carboxyl groups have been converted fully or partly to the alkali metal or alkaline earth metal salts and any remainder of the carboxyl groups has been reacted with alcohols or amines. Such additives are disclosed in particular by EP-A 307 815. Such additives serve mainly to prevent valve seat wear and can, as described in WO-A 87/01126, advantageously be used in combination with customary fuel detergents such as poly(iso)buteneamines or polyetheramines.

Additives comprising sulfonic acid groups or their alkali metal or alkaline earth metal salts (e) are preferably alkali metal or alkaline earth metal salts of an alkyl sulfosuccinate, as described in particular in EP-A 639 632. Such additives serve mainly to prevent valve seat wear and can be used advantageously in combination with customary fuel detergents such as poly(iso)butenamines or polyetheramines.

Additives comprising polyoxy-C₂- to C₄-alkylene moieties (f) are preferably polyethers or polyetheramines which are obtainable by reaction of C₂-C₆₀-alkanols, C₆-C₃₀-alkanediols, mono- or di-C₂-C₃₀-alkylamines, C₁-C₃₀-alkylcyclohexanols or C₁-C₃₀-alkylphenols with from 1 to 30 mol of ethylene oxide and/or propylene oxide and/or butylene oxide per hydroxyl group or amino group and, in the case of the polyetheramines, by subsequent reductive amination with ammonia, monoamines or polyamines. Such products are described in particular in EP-A 310 875, EP-A 356 725, EP-A 700 985 and U.S. Pat. No. 4,877,416. In the case of polyethers, such products also have carrier oil properties. Typical examples of these are tridecanol butoxylates, isotridecanol butoxylates, isononylphenol butoxylates and polyisobutenol butoxylates and propoxylates and also the corresponding reaction products with ammonia.

Additives comprising carboxylic ester groups (g) are preferably esters of mono-, di- or tricarboxylic acids with long-chain alkanols or polyols, in particular those having a minimum viscosity of 2 mm²/s at 100° C., as described in particular in DE-A 38 38 918. The mono-, di- or tricarboxylic acids used may be aliphatic or aromatic acids, and particularly suitable ester alcohols or ester polyols are long-chain representatives having, for example, from 6 to 24 carbon atoms. Typical representatives of the esters are adipates, phthalates, isophthalates, terephthalates and trimellitates of isooctanol, of isononanol, of isodecanol and of isotridecanol. Such products also have carrier oil properties.

Additives which comprise moieties derived from succinic anhydride and have hydroxyl and/or amino and/or amido and/or imido groups (h) are preferably corresponding derivatives of alkyl- or alkenyl-substituted succinic anhydride and in particular the corresponding derivatives of polyisobutenylsuccinic anhydride which are obtainable by reacting conventional or highly reactive polyisobutene having Mn=from 300 to 5000 with maleic anhydride by a thermal route or via the chlorinated polyisobutene. Particular interest attaches to derivatives with aliphatic polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine or tetraethylenepentamine. The moieties having hydroxyl and/or amino and/or amido and/or imido groups are, for example, carboxylic acid groups, acid amides of monoamines, acid amides of di- or polyamines which, in addition to the amide function, also have free amine groups, succinic acid derivatives having an acid and an amide function, carboximides with monoamines, carboximides with di- or polyamines which, in addition to the imide function, also have free amine groups, or diimides which are formed by reaction of di- or polyamines with two succinic acid derivatives. Such fuel additives are described in particular in U.S. Pat. No. 4,849,572.

Additives (i) comprising moieties obtained by Mannich reaction of substituted phenols with aldehydes and mono- or polyamines are preferably reaction products of polyisobutene-substituted phenols with formaldehyde and mono- or polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine or dimethylaminopropylamine. The polyisobutenyl-substituted phenols may stem from conventional or highly reactive polyisobutene having Mn=from 300 to 5000. Such “polyisobutene-Mannich bases” are described in particular in EP-A 831 141.

For a more precise definition of the individual fuel additives detailed, reference is explicitly made here to the disclosures of the abovementioned prior art documents.

Particular preference is given to detergent additives from group (h). They are preferably the reaction products of alkyl- or alkenyl-substituted succinic anhydrides, in particular of polyisobutenylsuccinic anhydrides, with amines. It is self-evident that these reaction products are obtainable not only when substituted succinic anhydride is used, but also when substituted succinic acid or suitable acid derivatives such as succinyl halides or succinic esters are used.

Particularly preferred detergent additives are polyisobutenyl-substituted succinimides, especially the imides with aliphatic polyamines. Particularly preferred polyamines are d iethylenetriamine, tetraethylenepentamine and pentaethylenehexamine, particular preference being given to tetraethylenepentamine. The polyisobutenyl radical has a number-average molecular weight Mn of preferably from 500 to 5000, more preferably from 500 to 2000 and in particular of about 1000.

It is self-evident that the detergent additives may be used alone or in combination with at least one of the aforementioned detergent additives.

In a preferred embodiment, the detergent additive is used in combination with at least one carrier oil.

Carrier Oils

Suitable mineral carrier oils are the fractions obtained in crude oil processing, such as brightstock or base oils having viscosities, for example, from the SN 500-2000 class; but also aromatic hydrocarbons, paraffinic hydrocarbons and alkoxyalkanols. Likewise useful is a fraction which is obtained in the refining of mineral oil and is known as “hydrocrack oil” (vacuum distillate cut having a boiling range of from about 360 to 500° C., obtainable from natural mineral oil which has been catalytically hydrogenated under high pressure and isomerized and also deparaffinized). Likewise suitable are mixtures of abovementioned mineral carrier oils.

Examples of synthetic carrier oils which are useful in accordance with the invention are selected from: polyolefins (poly-alpha-olefins or poly(internal olefin)s), (poly)esters, (poly)alkoxylates, polyethers, aliphatic polyether amines, alkylphenol-started polyethers, alkylphenol-started polyether amines and carboxylic esters of long-chain alkanols.

Examples of suitable polyolefins are olefin polymers having Mn=from 400 to 1800, in particular based on polybutene or polyisobutene (hydrogenated or nonhydrogenated).

Examples of suitable polyethers or polyether amines are preferably compounds comprising polyoxy-C₂-C₄-alkylene moieties which are obtainable by reacting C₂-C₆₀-alkanols, C₆-C₃₀-alkanediols, mono- or di-C₂-C₃₀-alkylamines, C₁-C₃₀-alkylcyclo-hexanols or C₁-C₃₀-alkylphenols with from 1 to 30 mol of ethylene oxide and/or propylene oxide and/or butylene oxide per hydroxyl group or amino group, and, in the case of the polyether amines, by subsequent reductive amination with ammonia, monoamines or polyamines. Such products are described in particular in EP-A-310 875, EP-A-356 725, EP-A-700 985 and U.S. Pat. No. 4,877,416. For example, the polyether amines used may be poly-C₂-C₆-alkylene oxide amines or functional derivatives thereof. Typical examples thereof are tridecanol butoxylates or isotridecanol butoxylates, isononylphenol butoxylates and also polyisobutenol butoxylates and propoxylates, and also the corresponding reaction products with ammonia.

Examples of carboxylic esters of long-chain alkanols are in particular esters of mono-, di- or tricarboxylic acids with long-chain alkanols or polyols, as described in particular in DE-A-38 38 918. The mono-, di- or tricarboxylic acids used may be aliphatic or aromatic acids; suitable ester alcohols or polyols are in particular long-chain representatives having, for example, from 6 to 24 carbon atoms. Typical representatives of the esters are adipates, phthalates, isophthalates, terephthalates and trimellitates of isooctanol, isononanol, isodecanol and isotridecanol, for example di-(n- or isotridecyl) phthalate.

Further suitable carrier oil systems are described, for example, in DE-A-38 26 608, DE-A-41 42 241, DE-A-43 09 074, EP-A-0 452 328 and EP-A-0 548 617, which are explicitly incorporated herein by way of reference.

Examples of particularly suitable synthetic carrier oils are alcohol-started polyethers having from about 5 to 35, for example from about 5 to 30, C₃-C₆-alkylene oxide units, for example selected from propylene oxide, n-butylene oxide and isobutylene oxide units, or mixtures thereof. Nonlimiting examples of suitable starter alcohols are long-chain alkanols or phenols substituted by long-chain alkyl in which the long-chain alkyl radical is in particular a straight-chain or branched C₆-C₁₈-alkyl radical. Preferred examples include tridecanol and nonylphenol.

Further suitable synthetic carrier oils are alkoxylated alkylphenols, as described in DE-A-10 102 913.6.

Preferred carrier oils are synthetic carrier oils, particular preference being given to polyethers.

The detergent additive, if appropriate in combination with a carrier oil, is fed to the injection system preferably with the diesel fuel.

The detergent additive or the mixture of different detergent additives is added to the diesel fuel in an amount of preferably from 10 to 2000 ppm by weight, more preferably from 20 to 1000 ppm by weight, even more preferably from 50 to 500 ppm by weight and in particular from 50 to 200 ppm by weight, for example from 70 to 150 ppm by weight.

When a carrier oil is used, it is added to the diesel fuel in an amount of preferably from 1 to 1000 ppm by weight, more preferably from 10 to 500 ppm by weight and in particular from 20 to 100 ppm by weight.

In addition, the diesel fuel may comprise further customary coadditives such as cold flow improvers, corrosion inhibitors, demulsifiers, dehazers, antifoams, cetane number improvers, combustion improvers, antioxidants or stabilizers, antistats, metallocenes, metal deactivators, dyes, solvents and the like. It is assumed that the use of these additives has essentially no influence on the reduction of the particle emission.

Suitable cold flow improvers are, for example, copolymers of ethylene with at least one further ethylenically unsaturated monomer, e.g. ethylene/vinyl acetate copolymers.

Suitable corrosion inhibitors are, for example, succinic esters, in particular with polyols, fatty acid derivatives, for example oleic esters, oligomerized fatty acids, substituted ethanolamines and products which are sold under the trade name RC 4801 (Rhein Chemie Mannheim, Germany) or HiTEC 536 (Ethyl Corporation).

Suitable demulsifiers are, for example, the alkali metal or alkaline earth metal salts of alkyl-substituted phenol- and naphthalenesulfonates and the alkali metal or alkaline earth metal salts of fatty acids, and also neutral compounds such as alcohol alkoxylates, e.g. alcohol ethoxylates, phenol alkoxylates, e.g. tert-butylphenol ethoxylate or tert-pentylphenol ethoxylate, fatty acids, alkylphenols, condensation products of ethylene oxide (EO) and propylene oxide (PO), for example also in the form of EO/PO block copolymers, polyethyleneimines or else polysiloxanes.

Suitable dehazers are, for example, alkoxylated phenol-formaldehyde condensates, for example the products available under the trade name NALCO 7D07 (Nalco) and TOLAD 2683 (Petrolite).

Suitable antifoams are, for example, polyether-modified polysiloxanes, for example the products obtainable under the trade name TEGOPREN 5851 (Goldschmidt), Q 25907 (Dow Corning) and RHODOSIL (Rhone Poulenc).

Suitable cetane number improvers are, for example, aliphatic nitrates such as 2-ethylhexyl nitrate and cyclohexyl nitrate, and peroxides such as di-tert-butyl peroxide.

Suitable antioxidants are, for example, substituted phenols such as 2,6-di-tert-butyl-phenol and 2,6-di-tert-butyl-3-methylphenol, and phenylenediamines such as N,N′-di-sec-butyl-p-phenylenediamine.

Suitable metal deactivators are, for example, salicylic acid derivatives such as N,N′-disalicylidene-1,2-propanediamine.

Suitable solvents are, for example, nonpolar organic solvents such as aromatic and aliphatic hydrocarbons, for example toluene, the xylenes, “white spirit” and products which are sold under the trade name SHELLSOL (Royal Dutch/Shell Group) and EXXSOL (ExxonMobil), and polar organic solvents, for example alcohols, such as 2-ethylhexanol, decanol and isotridecanol.

Preferred coadditives are demulsifiers, dehazers, antifoams, cetane number improvers, antioxidants, metal deactivators, corrosion inhibitors and solvents.

These customary coadditives are, if desired, added in amounts customary for the purpose.

Diesel Fuels

The diesel fuels are, for example, crude oil raffinates which typically have a boiling range of from 100 to 400° C. These are usually distillates having a 95% point of up to 360° C. or even higher. However, they may also be “ultra low-sulfur diesel” or “city diesel”, characterized by a maximum 95% point of, for example, 345° C. and a maximum sulfur content of 0.005% by weight, or by a 95% point of, for example, 285° C. and a maximum sulfur content of 0.001% by weight. Also suitable in addition to the diesel fuels obtainable by refining are those obtainable by coal gasification or gas liquefaction (“gas-to-liquid” (GTL) fuels). Also suitable are mixtures of the aforementioned diesel fuels with renewable fuels, such as biodiesel or bioethanol.

The diesel fuels are more preferably those having a low sulfur content, i.e. having a sulfur content of less than 0.05% by weight, preferably of less than 0.02% by weight, in particular of less than 0.005% by weight and especially of less than 0.001% by weight, of sulfur.

The inventive use of detergent additives achieves the effect that, in the exhaust gas emissions of direct-injection diesel engines, especially of diesel engines with a common rail injection system, the increase in the amount of particles is significantly smaller than in the exhaust gas emissions of direct-injection diesel engines which are operated without the use of detergent additives. In particular, the effect is achieved that, after 100 000 km of engine operation, preferably at most 2.5 times, more preferably at most 2.2 times and in particular at most 2 times, the amount of particles is present in comparison to the factory adjustment. In particular, the amounts of particles present in the emission remain distinctly below the limiting value of the Euro 4 standard. The values reported relate to the exhaust gas emissions withdrawn directly downstream of the engine (“engine out”), i.e. upstream of any particle filter installed which would of course reduce the amount of particles in the emission. Factory adjustment means that state of the direct-injection diesel engine or of the injection system as it is adjusted in the factory, i.e. before the delivery to the dealer or end user (at kilometer 0 as it were). The inventive use of detergent additives not only ensures compliance with the limiting values for particle emissions according to Euro 4 standard even without additional particle filters over an engine kilometrage of 100 000 km, but also for an operating time going well above this.

EXAMPLE

An engine having a common rail injection system was operated for 70 000 km with a diesel fuel according to EN 590 which had been additized with 90 ppm by weight of Kerocom PIBSI (a detergent additive from BASF AG which comprised a polyisobutylenesuccinimide). For comparison, an engine of identical design was likewise operated for 70 000 km under identical conditions with a diesel fuel according to EN 590 which did not comprise any detergent additive. The amounts of particles present in the emission were measured directly downstream of the engine (“engine out”). The results are listed in the table which follows.

TABLE
	Amount of particles	Amount of particles
Diesel fuel	at 0 km [g/km]	after 70 000 km [g/km]
without detergent	0.008	0.019
additive
with detergent	0.008	0.011
additive

As the results show, the use of detergent additives leads to a reduced amount of particles in the exhaust gases.

Claims

1-6. (canceled)

7. A fuel additive composition for reducing the amount of particles in exhaust gas emissions of direct-injection diesel engines consisting of at least one detergent additive and optionally at least one carrier oil.

8. The fuel additive composition of claim 7 wherein the detergent additive comprises the reaction product of alkyl- or alkenyl-substituted succinic acid or a derivative thereof with an amine.

9. The fuel additive composition of claim 8 wherein the detergent additive comprises polyisobutenyl-substituted succinimide.

10. The fuel additive composition of claim 7 wherein the detergent additive is in combination with at least one carrier oil.

11. A method for reducing the amount of particles in exhaust gas emissions of direct-injection diesel engines comprising the addition to the fuel of an additive composition consisting of at least one detergent additive and optionally at least one carrier oil.

12. The method according to claim 11 wherein the diesel engine is one equipped with a common rail injection system.

13. The method according to claim 11 wherein the detergent additive comprises the reaction products of alkyl- or alkenyl-substituted succinic acids or derivatives thereof with amines.

14. The method according to claim 11 wherein the detergent additive comprises polyisobutenyl-substituted succinimides.

15. The method according to claim 11 wherein the detergent additive is in combination with at least one carrier oil.

16. The method according to claim 11 wherein the amount of particles present in the exhaust gas emissions of the diesel engine, measured directly downstream of the engine after 100,000 km of engine operation, is higher by a factor of at most 2.5 than at the factory adjustment, and the limiting value for the amount of particles of the Euro 4 standard is simultaneously not exceeded.