The present invention relates to a diesel fuel composition comprising a hydrocarbon diesel fuel and additives which keep the injection system of a diesel engine clean.

In diesel engines efficient operation of the fuel injection system is of extreme importance. However, such injection systems are subject to build-up of deposits therein, resulting in reduced engine performance, e.g. in noisy running of the engine, the excessive emission of smoke, hydrocarbons and carbon monoxide, and poor starting performance. Engine manufacturers design injectors to accommodate some deposit levels. Amounts beyond the expected levels lead to the above problems. Therefore diesel fuels which do not form excessive deposits and/or which can remove deposits from the injectors would be very advantageous.

From United States patent specification No. 3,502,451 polymers from low molecular weight olefins are known which can be used in gasoline for spark-ignited internal combustion engines. Said polymers are effective for preventing the formation of or removing deposits on the intake valves in an internal combustion engine. However, it is known from United States patent specification No. 3,849,085 that the polymers referred to are sensitive to high temperatures in the intake manifold of the engine and that a portion of the polymer can decompose when subjected to high temperatures, tending to form deposits. Since in diesel engines the temperature of the injection system is substantially higher than the intake system temperature in internal combustion engines, it would be expected that this type of polymer would be unsuitable for preventing deposit formation in diesel engines.

This is the more so, as diesel fuel is- heavier than gasoline. The tendency to soot and other deposits during the combustion of diesel fuel is therefore greater than in the case of gasoline.

It has now surprisingly been found that this type of polymer can be used for keeping the injection system of diesel engines clean if it is employed in combination with another additive. The present invention therefore relates to a diesel fuel composition comprising a hydrocarbon diesel fuel having a cetane number in the range from 25 to 60, a polyolefin and a polyamine wherein at least one hydrocarbon chain having at least 25 carbon atoms is bound directly to a nitrogen atom.

The hydrocarbon diesel fuel can be any fuel suitable for operating diesel engines, e.g. in road vehicles or ships. Usually, the initial boiling point of such a fuel is at least 140 °C (at atmospheric pressure). The end boiling point generally is below 400 °C. The invention is of particular advantage in hydrocarbon fuels boiling in the range from 150 to 390 °C, especially from 175 to 370 °C. Such fuels can be obtained directly from a crude oil

(straight-run), but also from a catalytically or thermally cracked product or a hydrotreated product. Mixtures of such products are also possible. If desired, the diesel fuel may comprise quality improvers. It is apparent that the fuel composition according to the present invention does not include gasoline. Gasoline and diesel fuel do not only differ in distillation characteristics as will be appreciated by the person skilled in the art but also in cetane number ranges. A typical cetane number range for gasoline is 10 to 20.

The polyamines used in the composition according to the invention may be primary, secondary or tertiary. They can be aromatic or aliphatic. Suitable polyamines are ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, propylene- or butylene diamine, or o,ω-diamines of alkylene groups containing 3 to 18 carbon atoms. Preferably, as polyamine a diamine is used. In particular a polyamine is preferred which contains in addition to the hydrocarbon chain(s) at least one organic group having from 1 to 10 carbon atoms bound to nitrogen.

Such an organic group can be bound to the same nitrogen atom as the one to which a hydrocarbon chain having at least 25 carbon atoms is bound. By organic group should be understood any ono- valent radical, built up substantially from carbon and hydrogen, in which however dependent on the chosen method of preparation of the substituted polyamine, minor amounts of one or more other elements, e.g. halogen or oxygen, may be present. Examples of suitable organic groups are straight or branched alkyl groups which may carry aromatic or cycloaliphatic hydrocarbon substituents. The organic groups having up to 10 carbon atoms are advantageously selected from alkyl groups with an unbranched carbon chain. Prefe¬ rence is given to substituted polyamines in which the organic grou (s) has (have) less than 5 carbon atoms, methyl groups being particularly preferred. Examples of such suitable substituted polyamines are compounds having a hydrocarbon chain with over 25 carbon atoms, attached to an N-methyl-ethylene diamino or N-propyl ethylene diamin group. Advantageously the polyamine moiety applied is an N'-substituted N,N-dimethyl-l,3-diamino propane moiety. The hydrocarbon chain having at least 25 'carbon atoms present in the polyamine, preferably has at most 500 carbon atoms. The chain is advantageously a polymer constituted of recurrent olefinic units, such as ethylene, propylene, butylene, butadiene and the like. Generally such olefinic units contain 2 to 8 carbon atoms. It is understood that instead of ethylene or propylene a diolefin may be used which after polymerization and hydrogenation yield a saturated polymer or copolymer of ethylene and/or propylene units. So, it is possible to hydrogenate the product of the 1,4-polymerization of butadiene and to obtain polyethylene. Hydrogenation of the product of the 1,4-polymerization of isoprene yields a copolymer of ethylene and propylene. Preferably, the hydrocarbon chain consists of C,- and/or C;-monoolefinic units. Especially preferred are polymers concisting of isobutylene units. The polymer bound directly to a nitrogen atom of the polyamine has advantageously a number average molecular weight ranging from

500 to 1500, corresponding with 35 to 105 carbon atoms in the chain. The most preferred polyamine is N-polyisobutylene-N* ,N'- dimethyl diamino propane, in which the polyisobutylene moiety has a number average molecular weight ranging from 500 to 1500. The polyolefin component of the composition according to the present invention can be a polymer as described in United States patent specification No. 3,502,451, e.g. polymers prepared from monoolefins or diolefins or copolymers thereof. Polymers from diolefins are preferably subsequently hydrogenated. The number average molecular weight is generally in the range from 500 to

3500, preferably from 550 to 1500, determined by osmometry. In the composition according to the present invention the polyolefin polymers are preferably based on <_„- and/or C,-monoolefins, especially isobutylene. The amount of the additives should be such that only accep¬ table amounts of deposit are built-up on the injection system of a diesel engine. Preferably, the amount of the polyamine is from 5 to 200 ppmw and the amount of the polyolefin is from 100 to 1200 ppfflw, based on the total composition. The relative amounts of the poly- amine and the polyolefin is preferably such that the weight ratio of the polyamine to the polyolefin ranges from 1:10 to 1:40.

The diesel fuel composition according to the invention is advantageously prepared by mixing a suitable amount of the poly¬ amine and an amount of the polyolefin to the hydrocarbon diesel fuel. Conveniently this is obtained by mixing a concentrate con¬ taining the polyamine and the polyolefin in suitable relative amounts in a carrier liquid, with the diesel fuel. To such a concentrate other compounds may have been added, such as a dehazer. Thereto the concentrate may contain from 0.01 to 0.2 %w of a polyether type ethoxylated alk lphenol-formaldehyde resin. It is apparent that the carrier liquid must be compatible with diesel fuel. A suitable carrier liquid is xylene.

The diesel fuel composition according to the invention may further contain known additives such as nitrates or nitrites as

cetane improver or a pour point depressant such as copolymers of ethylene and vinylesters, e.g. vinylacetate.

The invention will now be illustrated with reference to the following Examples. EXAMPLE I

A 1.6 1 turbocharged VW Golf diesel engine having four pintle- type injectors was subjected to 33 test cycles per experiment, each cycle comprising 20 s idle running, 5 min running at 1500 rpm and 30 min running at 3000 rpm. Subsequently each injector was checked for deposit formation. This was attained by drawing air which was previously dried through the injector by a vacuum pump. A constant pressure drop across the injector of 0.6 bar was maintained. The needle in the injector was lifted 0.1 mm and the air-flow through the injector was determined. For these experiments a diesel fuel having a cetane number of 43 was used. In these experiments three additives were used. Additives I and II were N-polyisobutylene-N' ,N'-dimethy1-1,3- diamino propane, the polyisobutylene chain in additive I having a number average molecular weight of 1350 and that in additive II a number average molecular weight of 900. Additive III was polyiso¬ butylene with a number average molecular weight of 700. Conditions and results are presented in Table I.

- 6 -

TABLE I

Experiment Additive amount Mean air flow through No. (ppmw) injectors cm ³ /min 1 - 38 2 100 42 3 II + III .8 + 400 65

The mean air flow through the injectors before the test amounted to 265 cm ³ /min. According to the engine manufacturer the presence of some deposit on the injectors is acceptable, since optimum perfor¬ mance at a needle-lift of 0.1 mm is achieved with air flows in the range from 50 to 120 cm ³ /min.

From the above results it is apparent that such an optimum performance was only attained by using the fuel composition accor¬ ding,to the invention. EXAMPLE II

At the end of the test cycles, described in Example I, the noise of the engine, running at 1500 rpm, was determined at 0.7 m from the engine front.

* Results are indicated in Table II.

TABLE II

Experiment No. Additive amount (ppmw) noise (dBA) 1 89.5 2 100 90.0 3 II + III 18 + 400 85.8

From the above results of the fuel compositions tested the fuel composition according to the invention yielded the greatest reduction in engine noise.