Diesel fuels generally contain numerous deposit-forming substances. When such fuels are used, the degradation products build up on the metal surfaces of the engine, in particular the fuel injectors. When diesel fuel injectors become clogged or develop deposits, these deposits adhere to injector parts and cause injector sticking, injector tip fuel metering passage fouling, etc.

These problems result in the spray of the fuel into the combustion chamber not being uniform and/or atomised properly, resulting in poor combustion, increased engine noise, increased exhaust emissions and smoke, decreased power output and fuel economy.

The invention relates to diesel fuel additives, and in particular to additives which inhibit deposit formation in the fuel injectors of diesel fuelled engines.

The formation of deposits within the injectors of a diesel engine can be inhibited, as well as deposits removed, by incorporating an active detergent into the fuel.

Detergents based on polyisobutene (PIB) amines are well known intake valve deposit control detergents for use in gasoline fuelled engines. They are readily prepared in leading commercial processes by chlorinating the PIB and

then aminating the resultant PIB chloride. Conventional PIBs for use in making PIB amine derivatives have molecular weights (mol. wts.) >1000, the amines generally containing only one or two nitrogen atoms, i. e. ammonia, ethylene diamine, dimethylaminopropylamine and aminoethylethanolamine. They are of limited use as diesel detergents.

We have now discovered that greatly reduced fouling of diesel injectors is obtained using PIB amines having a nitrogen content higher than conventional PIB amines.

In addition, we have discovered that this effect is not limited to PIB amines; certain hydrocarbyl-substituted amines (hereinafter referred to as"hydrocarbyl amines") having a high nitrogen content have also been found to exhibit good diesel fuel injector detergency. Such effects can, for example, be achieved using Mannich bases derived from reacting hydrocarbyl-substituted phenols, especially polyisobutene-substituted phenols, with aldehydes and amines.

As will be appreciated by those skilled in the art, control of nitrogen content of a hydrocarbyl amine may be achieved by control of molecular weight of the hydrocarbyl moiety and/or appropriate amine selection.

For example, in the case of PIB amines, control of nitrogen content can be achieved by control of PIB molecular weight and/or amine selection.

One aspect of the invention thus provides a diesel fuel composition comprising a diesel fuel and a hydrocarbyl amine having a nitrogen content of 3t m/m or more.

Preferred amines for use in the invention include those of formula I: R1NR22 (I)

wherein Rl is an optionally substituted, saturated or unsaturated, straight-chained, branched or cyclic hydrocarbyl group, preferably containing from 1 to 80, more preferably 6 to 60, e. g. 15 to 45, carbon atoms; and each R2 is independently a hydrogen atom, an optionally substituted straight-chained or branched Cl-6 alkyl group, or the residue of an amine-containing moiety.

As used herein, the term"hydrocarbyl"may include straight-chained or branched alkyl, alkenyl, cycloalkyl, cycloalkenyl (including combinations such as alkylcycloalkyl, cycloalkylalkyl, etc.), aryl (including mono-and fused-ring structures, e. g. napthyl, and alkyl-substituted aryl, e. g. xylyl, tolyl, etc.) and aralkyl, e. g. benzyl (including alkyl-substituted aralkyl).

In the compounds herein described, R1 is preferably an alkenyl or poly (alkenyl) group, particularly preferably a C220 alkenyl or poly (C26alkenyl) group, for example a C812 alkenyl or poly (C24alkenyl) group. More preferably, Ru ils a poly (C24 alkenyl) group, for example a poly (propenyl), poly (butenyl) or poly (isobutenyl) group.

As used herein, the terms"poly (alkene)" and "poly (alkenyl)" are intended to cover products derived from the polymerisation of an olefin or mixture of olefins, in particular a-olefins, preferably C-io a-olefins, especially those products derived from the polymerisation of butenes or mixtures of ethene, propenes and butenes. Such compounds will comprise at least one olefinic bond, typically at least one vinylidene group.

Particularly preferred for use in the invention are

polyisobutene amines. These correspond to compounds of formula I in which R1 is derived from the polymerisation of isobutene, i. e. in which R1 is poly (isobutenyl).

Other hydrocarbyl amines suitable for use in the invention include hydrocarbyl-substituted Mannich bases, for example products which may be obtained by reaction of hydrocarbyl-substituted phenols, especially polyisobutene-substituted phenols, with aldehydes and amines.

In a further aspect the invention thus provides a diesel fuel composition comprising a diesel fuel and a Mannich base of formula II: wherein each R1 is as hereinbefore defined, preferably a poly (alkenyl) group, particularly preferably polyisobutenyl; each R3 independently represents a group of the formula -CH (R5) NR22 (in which Rs is hydrogen or an optionally substituted straight-chained or branched CI-5 alkyl group, preferably hydrogen, and each R2 is as hereinbefore defined); each Ru ils independently a straight-chained or branched C16 alkyl group, preferably a Cl-, alkyl group, e. g. methyl; n is 1 or 2, preferably 1; m is 0 or 1, preferably 0; and p is 1 or 2, preferably 1, wherein the Mannich base has a nitrogen content of 3% m/m or more.

In the compounds of formula II, where present, any R4 substituents are preferably at the 2-, 4-or 6- positions, most preferably at the 4-position of the phenol.

Preferred compositions in accordance with the invention include those comprising a compound of formula II in which n is 1, m is 0, p is 1, R1 is a polyisobutenyl group present at the 4-position, and R3 is a group of the formula-CH (R5) NR22 at the 2-position.

In cases where R4 is present, preferred compositions include those comprising a compound of formula II in which n is 1, m is 1, p is 1, R1 is a polyisobutenyl group present at either the 2-or 6-position, R3 is a group of the formula-CH (R5) NR22 at the other of the 2- or 6-position, and R4 is a methyl group at the 4- position.

In the compounds of formulae I and II, typical substituents which may be present in groups R2 and R 5 include alkyl groups, for example C16 alkyl groups, more preferably CI-4 alkyl groups, hydroxy and/or carboxy groups.

Increased nitrogen content may be achieved by increasing the relative number of nitrogen atoms in the compounds of the invention. Preferred compounds are generally those containing more than one nitrogen atom, e. g. up to 12 nitrogen atoms. As an amine-containing moiety, R may represent a group of the formula- (R-NH-) q-R-NH (where R is an alkylene radical of 1-5 carbon atoms and q is an integer whose value or average value is 1 to 10), for example, a group of formula- (CH2CH2NH), H (where x is typically 1 to 6).

Preferably the hydrocarbyl moiety, in particular the

poly (alkenyl) moiety, e. g. the polyisobutene moiety, in all compounds of the invention has a molecular weight of 200-5000, particularly <1000.

Especially preferred compounds for use in the invention are PIB amines and those Mannich bases of formula II in which Ri ils PIB.

Conventional PIBs and so-called"high-reactivity"PIBs (see for example EP-B-0 565 285) are suitable for use in the invention. High reactivity in this context is defined as a PIB wherein at least 50%, preferably 70% or more, of the terminal olefinic double bonds are of the vinylidene type.

Amines which may be employed in preparing the compounds herein described include any that have the ability to react with an a-olefin (e. g. a functionalised PIB) or with an aldehyde and an a-olefin substituted phenol (e. g. a PIB-substituted phenol).

Preferred amines are polyalkylene polyamines of the following general formula: H2N-(R-NH-) q-R-NH2 where R is an alkylene radical of 1-5 carbon atoms and q is an integer whose value or average value is 1 to 10.

The preferred polyalkylene polyamines are polyethylene polyamines conforming for most part of the structure: H2N (CH2CH2NH) H where x is generally 1 to 6.

Thus they include for example ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine and pentaethylene hexamine.

The most preferred polyethylene polyamines are tetraethylene pentamine and pentaethylene hexamine.

The compounds of the invention are blended into diesel fuels in amounts sufficient to provide from 10 to 2000 ppm (weight basis) of active detergent in the fuel.

Preferred amounts range from 30 to 800 ppm, most usually and preferably from 50 to 500 ppm.

The invention further provides a method of conferring detergency on a diesel fuel comprising the addition to said fuel of a hydrocarbyl amine as hereinbefore defined, in particular a polyisobutene amine or PIB- containing Mannich base, and a method of inhibiting deposit formation in a diesel engine, for example fuel injector deposit formation, comprising operating said engine on a diesel fuel composition as defined above.

Hydrocarbyl amines, e. g. polyisobutene amines, as defined above are either available commercially or can be manufactured by conventional means, for example chlorinating the corresponding a-olefin (e. g. a polyalkene) and then aminating the resultant chlorinated a-olefin (e. g. poly (alkenyl) chloride). For example, polyisobutene amines may be produced by chlorinating the PIB and then aminating the resultant chloride.

Alternative synthetic routes might include reaction of a an a-olefin (e. g. a polyalkene such as PIB) with CO/H2 followed by amination.

Mannich bases as defined above are either available commercially or can be manufactured by conventional means, for example by reacting an appropriately

substituted phenol, e. g. a PIB-substituted phenol, with an aldehyde and an amine. Preferably the aldehyde is an aldehyde having 1 to 6 carbon atoms which may optionally carry one or more susbtituents, e. g. hydroxy or carboxy groups. Especially preferably the aldehyde is formaldehyde (added to the reaction as paraformaldehyde). Preferably the amine used is one of those defined above.

Suitably substituted phenols, e. g. PIB-substituted phenols, are also available commercially or can be manufactured by conventional means, for example by reacting a phenol with an a-olefin, e. g. PIB, optionally in the presence of a catalyst. Preferably the catalyst is a Lewis acidic catalyst; especially preferably the catalyst is boron trifluoride, optionally stabilised with ether or other appropriate Lewis base. Typically, the resulting poly (alkenyl)-substituted phenol will be a 4-poly (alkenyl) phenol. However, 2-poly (alkenyl) and 2,4-di (poly (alkenyl)) phenols may also be produced. The main products, however, will generally be compounds of formula III: wherein R1, R4 and m are as hereinbefore defined.

The term"diesel fuel"as used herein means any distillate hydrocarbon fuel for compression ignition internal combustion engines, for example meeting the standards set in BS 2869 Parts 1 and 2.

The invention also contemplates diesel fuel compositions, and additive compositions therefor,

comprising combinations, preferably synergistic combinations, of a hydrocarbyl amine, e. g. a polyisobutene amine or PIB-containing Mannich base as defined above, and one or more of: other fuel detergents known per se, lubricity additives, cold flow improvers, antifoams, combustion improvers and cetane improvers.

The lubricity additives include those described in W097/45507, such as fatty acids, mono acids, dimer acids, fatty acid polyol esters such as glycerol esters, e. g. glycerol mono-oleate, alkenyl succinic acids or monoesters or diesters thereof such as alkenyl succinic acid polyol esters, e. g. polyisobutene succinic acid or esters thereof. Alkyl amines may also be used.

The combustion improvers may be alkyl nitrates or metallic additives such as fuel combustion improving alkali or alkaline earth metal salts of the general formula M (R) m. nL as described more fully in GB 2 285 451, alkali and alkaline earth metal carboxylate and succinate complexes acting as combustion improvers for diesel fuels and as diesel particulate filter (DPF) regeneration additives as set out in W096/34074; mixtures of alkali and alkaline earth metal salt complexes showing synergistic behaviour in regeneration of DPF traps as disclosed in W096/34074 and W097/40122; and compositions comprising complexes of iron and complexes of alkaline earth metals which provide synergy in regeneration of DPF traps as claimed in GB 9800869.

Cold flow improvers may be as disclosed in W095/33805, such as ethylene-unsaturated ester copolymers, e. g. comb polymers having one or more long chain hydrocarbyl branches pendant from a polymer backbone, polar nitrogen compounds, hydrocarbon polymers, e. g. ethylene a-olefin copolymers, and polyoxyalkylene compounds.

The invention will be better understood and illustrated from the following Examples which should not be regarded as limiting the invention in any way.

Example 1 A PIB amine detergent is obtained by reacting PIB chloride derived from 1000 mol. wt. polyisobutene with ethylene diamine. This is a typical gasoline detergent and is of limited use as a diesel detergent.

Example 2 A PIB amine detergent is obtained by reacting PIB chloride derived from 780 mol. wt. PIB (190g, 6.8% chlorine) with tetraethylene pentamine (138g) in toluene (116 ml). The mixture was refluxed for three hours and then heated to 170°C to remove toluene and further the reaction (4 hours).

After cooling hexane (100 ml), ethanol (100 ml), toluene (100 ml) and sodium carbonate (10E, 200 ml) were added.

The organic phase was separated and washed twice more with water. The final toluene solution was azeotroped dry.

Example 3-engine tests In order to show injector cleaning effectiveness of the detergent compositions of the invention, engine tests were performed on a base diesel fuel.

Tests were conducted using an XUD9 Peugeot IDI nozzle fouling test at 50 mg/kg active ingredient.

The engine was run 3000 rpm and 58 Nm load for 6 hours according to the CEC PF023 draft protocol.

Performance of each additive was assessed quantitatively by air flow measurement of fouling levels produced in the engine's injector nozzles. The build up of deposits

in the injector nozzles causes a reduction in the measured air flow and the degree of nozzle fouling can be quantified by air flows through clean injectors (before the test) and dirty injectors (after the test).

The flow measurements are recorded at certain needle lifts.

Additive Nozzle fouling/O. lmm lift Example 1 85 Example 2 64 The results clearly demonstrate that the additive of the invention is superior in diesel detergency performance to those currently manufactured and used for gasoline applications.

The performance of a PIB-substituted Mannich base, for example with a PIB moiety of 780 mol. wt. and tetraethylene pentamine as the amine moiety, would be expected to be similar to that of Example 2.

Example 4 A Mannich base detergent is obtained by reacting a C18 a-olefin substituted phenol with triethylene tetramine and glyoxylic acid in a suitable solvent (e. g. heptane, toluene, xylene or Shellsol ABTII) The resulting mixture is heated to reflux for three hours until all water is azeotropically removed.

Example 5 Analogously to Example 4, a Mannich base detergent is obtained by reacting a 780 mol. wt. polyisobutene substituted phenol with tetraethylene pentamine and paraformaldehyde.

Example 6 A Mannich base detergent is obtained by reacting a 550 mol. wt. polyisobutene with hydroxytoluene. This is followed by reaction with formaldehyde and triethylene tetramine in a suitable solvent (e. g. heptane, toluene, xylene or Shellsol Au).

Example 7 A hydrocarbyl amine is obtained by reacting a chlorinated C18 a-olefin with diethylene triamine.