EP2759588B1 - Fuel for self-ignition engines based on monooxymethylene dimethyl ether - Google Patents

Description

The invention relates to a fuel for compression ignition engines, i. H. a diesel fuel.

Out SAE TECHNICAL PAPER SERIES, 1999-01-1508, pp. 1-13 Mixtures of monooxymethylene dimethyl ether (dimethoxymethane) and diesel are known as fuels for diesel engines. The addition of diesel fuel serves to increase the cetane number of the monooxymethylene dimethyl ether from 29 to values above 40. However, the addition of diesel fuel leads to an undesirable soot emission. On the other hand, the operation of a diesel engine with pure monooxymethylene dimethyl ether is not possible because the cetane number of 29 is too low. As a result, a cold start is not possible and misfires occur during part-load operation.

From the Motortechnische Zeitschrift MTZ, 72nd year, page 198-202 (2011 ) the use of dioxymethylene dimethyl ether and trioxymethylene dimethyl ether / tetraoxymethylene dimethyl ether mixtures as an additive to diesel fuel is known. Although the use of these ethers leads to a significant reduction in soot emissions, a particle filter is still required to meet the existing legal requirements. In addition, these polyoxymethylene dimethyl ether mixtures can be prepared only with great effort.

The invention has for its object to overcome the above disadvantages. In particular, the invention is based on the object of fulfilling the existing legal requirements for reducing the CO ₂ emission and the emission of air pollutants, using residual biomass and carbon dioxide as the starting material for producing a fuel for compression-ignition engines, and using as little as possible a soot-free combustion of the fuel in the engine in order to create the basis for very low exhaust emissions (local zero emissions based on the model of electric vehicles), to provide a non-toxic substitute for methanol, to achieve high exhaust gas recirculation compatibility for internal engine NO _x reduction and the cost, volume and weight of To reduce exhaust gas aftertreatment systems, for example by avoiding particle filters.

According to the invention, this object is achieved with a fuel for compression ignition engines, i. H. a diesel fuel, as claimed in claim 1, which contains at least 80% by weight of monooxymethylene dimethyl ether and up to 20% by weight of at least one oxygenate of the n-polyoxaalkane type, which consists of the group consisting of polyoxymethylene dialkyl ethers of the formula RO (-CH2O-) nR with n = 4 to 10 and R = alkyl radical, polyethylene glycol dialkyl ethers and / or polyethylene glycol monoalkyl ether formals, and that the fuel has a cetane number (CZ) of ≥ 48.6, preferably ≥ 51.

The term "contains" also includes the term "consists of".

The fuel according to the invention for compression ignition engines therefore includes monooxymethylene dimethyl ether as the base fuel. Monooxymethylene dimethyl ether (dimethoxymethane) has the structural formula CH ₃ OCH ₂ OCH ₃ .

The use of monooxymethylene dimethyl ether initially has the advantage that, in contrast to all higher polyoxymethylene dimethyl ethers, such as a trioxymethylene dimethyl ether / tetraoxymethylene dimethyl ether mixture, it is already produced on an industrial scale.

The fuel for compression ignition engines according to the invention contains at least about 80% by weight, preferably at least about 90% by weight, and particularly preferably at least about 95% by weight, of monooxymethylene dimethyl ether.

As mentioned, it is crucial for the solution of the above-mentioned tasks that the fuel according to the invention for compression ignition engines has a cetane number of 48 48.6, preferably 51 51.

In a preferred embodiment, the fuel according to the invention for compression ignition engines does not contain any proportions of conventional hydrocarbon-based diesel fuels. This ensures an even more advantageous soot-free fuel combustion.

In the fuel for compression ignition engines according to the invention, a cetane number of Kraftstoff 48.6, preferably 51 51, is achieved in that it contains at least one oxygenate of the n-polyoxaalkane type, which consists of the group consisting of polyoxymethylene dialkyl ether of the formula RO (-CH ₂ O-) _n R with n = 4 to 10 and R = alkyl radical, polyethylene glycol dialkyl ethers and / or polyethylene glycol monoalkyl ether formals is selected.

The fuel for compression ignition engines according to the invention contains up to about 20% by weight, preferably up to about 5% by weight, particularly preferably up to about 3% by weight, of the at least one aforementioned n-polyoxyalkane type oxygenate.

The cetane number increases almost linearly with the concentration of the at least one n-polyoxaalkane type oxygenate. The increase in the cetane number also correlates with the molecular weight MG of the n-polyoxaalkane type oxygenate used. This means that the higher the molecular weight, the less oxygenate of the n-polyoxaalkane type has to be used. Oxygenates of the type n-polyoxaalkanes with a molecular weight MW> 1000 daltons are, however, less suitable, since they dissolve more poorly in monooxymethylene dimethyl ether, especially in the cold.

The alkyl radical of the at least one n-polyoxaalkane type oxygenate is an end-closing alkyl group, for example a methyl or ethyl group. It is preferably methyl groups. It is therefore preferred that the polyoxymethylene dialkyl ether of the formula RO (-CH ₂ O-) _n R with n = 4 to 10 and R = alkyl radical is polyoxymethylene dimethyl ether of the formula CH ₃ O (-CH ₂ O-) _n CH ₃ with n = 4 to 10. N is particularly preferably 5 to 9 and very particularly preferably 6 to 7.

The polyethylene glycol dialkyl ethers are preferably polyethylene glycol dimethyl ethers.

The polyethylene glycol monoalkyl ether formals are preferably polyethylene glycol monomethyl ether formals.

It is preferred that the polyoxymethylene dimethyl ethers have a molecular weight MW of 100 to 400 daltons, preferably 166 to 346 daltons.

The polyoxymethylene dimethyl ethers are preferably used in an amount of up to about 20% by weight, particularly preferably up to about 5% by weight and very particularly preferably up to about 3% by weight.

A particularly preferred polyoxymethylene dimethyl ether is tetraoxymethylene dimethyl ether, since this leads to a significant increase in viscosity.

In a particularly preferred embodiment, the polyethylene glycol dimethyl ethers have a molecular weight MW of 400 to 1000 daltons, preferably of 500 to 1000 daltons.

The polyethylene glycol dimethyl ethers are preferably used in an amount of up to about 20% by weight and particularly preferably up to about 5% by weight.

Suitable polyethylene glycol dimethyl ethers are, for example, polyglycol DME 500, polyglycol DME 750 and polyglycol DME 1000, all available from Clariant. Polyethylene glycol DME 500 is preferably used in an amount of up to approximately 20% by weight, particularly preferably up to approximately 10% by weight and very particularly preferably up to approximately 5% by weight. Polyglycol DME 750 is preferably used in an amount of up to about 10% by weight and particularly preferably up to about 5% by weight. Polyglycol DME 1000 is preferably used in an amount of up to about 6% by weight and particularly preferably up to 3% by weight.

Polyethylene glycol dialkyl ethers, in particular polyethylene glycol dimethyl ether, are already being produced on an industrial scale, which facilitates the introduction of the fuel according to the invention for compression ignition engines.

The polyethylene glycol monomethyl ether formals preferably have a molecular weight of 400 to 1100 daltons.

Polyethylene glycol monomethyl ether formals are preferably used in an amount of up to about 20% by weight, particularly preferably up to about 10% by weight and very particularly preferably up to about 5% by weight. Polyethylene glycol monomethyl ether formals with a molecular weight of less than 400 daltons, for example 2,5,7,10-tetraoxaundecane with a molecular weight of 192 daltons, is less effective. Higher molecular weight polyethylene glycol monomethyl ether formals, i.e. H. Polyethylene glycol monomethyl ether formals with a molecular weight of 400 to 1100 daltons are particularly suitable. For example, tetraethylene glycol monomethyl ether formal with a MW of 428 daltons can be used. This is available, for example, from two moles of tetraethylene glycol monomethyl ether and one mole of methanal. For example, polyethylene glycol monomethyl ether formal with a MW of 950 to 1070 daltons can also be used. This is obtainable, for example, from two moles of polyethylene glycol monomethyl ether with a molecular weight of 470 to 530 Daltons (for example Polyglycol M from Clariant) and one mole of methanal.

Polyethylene glycol monoalkyl ether formals, in particular polyethylene glycol monomethyl ether formals, can be prepared by known processes from the industrially produced polyethylene glycol monoalkyl ethers by reaction with methanal, e.g. B. as paraformaldehyde.

The use of polyethylene glycol monoalkyl ether formals, in particular polyethylene glycol monomethyl ether formals, leads to results similar to the use of polyoxymethylene dialkyl ethers, in particular polyoxymethylene dimethyl ether.

The use of at least one oxygenate of the n-polyoxaalkane type not only leads to the cetane number of the fuel according to the invention for compression ignition engines being increased to 48 48.6, preferably 51 51, but also to the physical properties of the fuel according to the invention for compression ignition engines, for example the viscosity, the surface tension, the vapor pressure and the compressibility (modulus of elasticity) are approximated to those of a diesel fuel.

The kinematic viscosity of monooxymethylene dimethyl ether is 0.40 mm ² / s at 20 ° C and thus by a factor of 5 below the minimum requirements of the standard EN 590 (standard for diesel fuel DIN EN 590, May 2010 edition) of 2 mm ² / s. The difference can cause problems when using standard diesel injection systems. This can increase the amount of leaks in gap seals. The use of at least one oxygenate of the n-polyoxaalkane type also remedies this by increasing the viscosity of the fuel according to the invention for compression-ignition engines. In this way, the injection characteristic can be influenced positively. For example, increasing the viscosity increases the mean drop diameter and the depth of penetration of the fuel jet.

Due to its polar properties, the lubricity of monooxymethylene dimethyl ether is already in the range of a diesel fuel. However, the use of at least one oxygenate of the n-polyoxaalkane type leads to a further improvement, i. H. to increase lubricity (HFRR reduction).

Monooxymethylene dimethyl ether has a surface tension of 21.2 mN / m at 25 ° C. The use of at least one oxygenate of the n-polyoxaalkane type in the fuel according to the invention for compression ignition engines increases this value to up to 26 mN / m (in comparison, diesel fuel has a surface tension of 27 to 28 mN / m). The surface tension has a significant influence on the droplet size distribution resulting from the atomization process and thus also on the penetration depth of the fuel jet. When designing the fuel injection, the penetration depth of the jet can be influenced, for example, by using a suitable amount of the at least one oxygenate of the n-polyoxaalkane type.

Monooxymethylene dimethyl ether has a vapor pressure of 45 kPa at 20 ° C. By using at least one n-polyoxaalkane type oxygenate, it is possible to lower the vapor pressure by up to 10%.

$$2{\mathrm{CH}}_3\mathrm{OH}+4{\mathrm{CH}}_2\mathrm{O}\to {\mathrm{C}}_6{\mathrm{H}}_{14}{\mathrm{O}}_5\left(\mathrm{OME}4\right)$$

The energy balance chain for the production of monooxymethylene dimethyl ether (OME 1) compared to, for example, tetraoxymethylene dimethyl ether (OME 4) from methanol and methanal also offers clear advantages: $$2{\mathrm{CH}}_3\mathrm{OH}+{\mathrm{CH}}_2\mathrm{O}\to {\mathrm{C}}_3{\mathrm{H}}_{\mathrm{8th}}{\mathrm{O}}_2\left(\mathrm{OME}1\right)$$

$$2{\mathrm{CH}}_3\mathrm{OH}+4{\mathrm{CH}}_2\mathrm{O}\to {\mathrm{C}}_6{\mathrm{H}}_{14}{\mathrm{O}}_5\left(\mathrm{OME}4\right)$$

$$\mathrm{\Delta }\mathrm{H}=-\mathrm{318}\mathrm{kJ}/\mathrm{mol}$$

CH ₂ O is produced by partial, exothermic oxidation of the methanol: $$2{\mathrm{CH}}_3\mathrm{OH}+{\mathrm{O}}_2\to 2{\mathrm{CH}}_2\mathrm{O}+{\mathrm{H}}_2\mathrm{O}$$

$$\mathrm{\Delta }\mathrm{H}=-\mathrm{318}\mathrm{kJ}/\mathrm{mol}$$

$$6{\mathrm{CH}}_3\mathrm{OH}+2{\mathrm{O}}_2\to {\mathrm{C}}_6{\mathrm{H}}_{14}{\mathrm{O}}_5\left(\mathrm{OME}4\right)+5{\mathrm{H}}_2\mathrm{O}$$

By combining Equations 1 and 2 with Equation 3 we get: $$6{\mathrm{CH}}_3\mathrm{OH}+{\mathrm{O}}_2\to 2{\mathrm{C}}_3{\mathrm{H}}_{\mathrm{8th}}{\mathrm{O}}_2\left(\mathrm{OME}1\right)+2{\mathrm{H}}_2\mathrm{O}$$

$$6{\mathrm{CH}}_3\mathrm{OH}+2{\mathrm{O}}_2\to {\mathrm{C}}_6{\mathrm{H}}_{14}{\mathrm{O}}_5\left(\mathrm{OME}4\right)+5{\mathrm{H}}_2\mathrm{O}$$

It can be seen that the oxygen consumption and thus the energy loss in the production of OME4 from methanol according to equation 5 is twice as high as in the production of OME1 according to equation 4.

In a preferred embodiment, the fuel according to the invention for compression ignition engines contains di-tert-butyl peroxide (DTBP). Di-tert-butyl peroxide also leads to the desired increase in the cetane number.

Di-tert-butyl peroxide is preferably added in an amount of 0.01 to 0.3% by weight and particularly preferably in an amount of 0.1 to 0.2% by weight. A too low amount does not lead to the desired increase in cetane number, while an excessive amount should be avoided for cost reasons.

The use of di-tert-butyl peroxide also has the advantage that, unlike nitrate-based cetane number improvers, such as 2-ethylhexyl nitrate, it burns without the formation of fuel NO _x .

Di-tert-butyl peroxide is particularly suitable as a cetane number improver for fuels for compression ignition engines with monooxymethylene dimethyl ether as the base fuel. The addition of 0.1% by weight of di-tert-butyl peroxide leads to this in connection with monooxymethylene dimethyl ether as the base fuel for an increase in the cetane number by 8 units, whereas for diesel fuel the average increase is only between 2 and 4 units (SAE 952368, 1995).

In a particularly preferred embodiment, the fuel according to the invention for compression ignition engines contains monooxymethylene dimethyl ether, at least one oxygenate of the n-polyoxaalkane type and di-tert-butyl peroxide, the latter preferably in an amount of 0.01 to 0.3% by weight. The addition of di-tert-butyl peroxide makes it possible, if desired, to reduce the amount of the at least one n-polyoxaalkane type oxygenate with respect to the increase in cetane number.

In a particularly preferred embodiment, the fuel according to the invention for compression ignition engines contains at least 80% by weight of monooxymethylene dimethyl ether, 1 to 20% by weight, preferably 5 to 20% by weight, particularly preferably 5 to 19.7% by weight of at least one oxygenate of the n-polyoxaalkane type, selected from the group consisting of polyoxymethylene dimethyl ether, polyethylene glycol dimethyl ether and / or polyethylene glycol monomethyl ether formals, and 0.01 to 0.3% by weight of di-tert-butyl peroxide.

In a particularly preferred embodiment, up to about 20% by weight, preferably up to 11.5% by weight and particularly preferably up to about 10% by weight, of the monooxymethylene dimethyl ether can be replaced by dimethyl ether. This leads to an increase in the vapor pressure to 60 kPa (summer fuel) or 90 kPa (generation of a "fat vapor bell") and a reduction in costs. Dimethyl ether serves as a substitute for monooxymethylene dimethyl ether. Dimethyl ether has a vapor pressure of 504 kPa at 20 ° C and dissolves well in monooxymethylene dimethyl ether. The use of dimethyl ether makes it possible to adapt the vapor pressure of the fuel according to the invention for compression ignition engines to the European standard EN 228 (standard for petrol fuels DIN EN 228 edition 2007) and the cetane number and filterability to the standard EN 590. The viscosity of the fuel according to the invention for compression ignition engines is approximated as far as possible to the requirements of the EN 590 standard.

The amounts of the components containing monooxymethylene dimethyl ether, oxygenates of the n-polyoxalkane type, if appropriate dimethyl ether and di-tert-butyl peroxide preferably give 100% by weight in terms of their% by weight.

The fuel for compression ignition engines according to the invention has a higher viscosity than monooxymethylene dimethyl ether, the cold filterability (CFPP) is retained, the density is increased and the cetane number is brought to a value of 48 48.6, preferably 51 51.

As already mentioned above, the fuel according to the invention for compression ignition engines in a preferred embodiment contains no hydrocarbons, i.e. no hydrocarbon-based diesel fuel.

Furthermore, the fuel according to the invention for compression ignition engines has the following advantages:
The fuel for compression ignition engines according to the invention enables the indirect use of methanol as a fuel for engines. The approval of the supply of methanol as fuel at public petrol stations in the European Union and the USA appears to be excluded in the future due to its pronounced toxic properties. On the other hand, methanol can be converted to monooxymethylene dimethyl ether on an industrial scale. The fuel according to the invention for compression ignition engines thus enables the indirect use of methanol as fuel for compression ignition engines, since methanol is only suitable for the operation of spark ignition engines.

The fuel according to the invention for compression ignition engines thus enables the indirect use of methanol and dimethyl ether as liquid fuel for diesel engines. Dimethyl ether is an excellent diesel fuel which, like monooxymethylene dimethyl ether, burns without soot. The main disadvantage of dimethyl ether is its low boiling point of -25 ° C. It must therefore be handled as liquefied petroleum gas and therefore has the disadvantage that the existing infrastructure for liquid fuels cannot be used.

In contrast to methanol, monooxymethylene dimethyl ether is largely non-toxic. It is also used in cosmetics and pharmacy and has water hazard class 1.

The raw material methanol can be produced directly by hydrogenation of carbon dioxide. This makes it possible to recycle carbon dioxide from power plants, cement plants and steelworks and thus to achieve a theoretical reduction of up to 50% in carbon dioxide.

The combustion of the fuel according to the invention for compression-ignition engines in lean-burn compression-ignition engines is carried out analogously to the combustion of the gaseous dimethyl ether, even at high EGR rates, soot-free and particle-free. This allows very low NO _x and particle number emissions to be achieved with internal engine measures. The exhaust gas aftertreatment does not require a particle filter, but only an oxidation catalytic converter which prevents the emission of unburned and partially burned fuel according to the invention for compression ignition engines. The advantages are the reduction in the calorific value-related fuel consumption due to the low exhaust gas back pressure of the exhaust system and a significant reduction in the costs, the space requirement and the weight of the exhaust gas aftertreatment system.

The fuel according to the invention for compression ignition engines can be produced largely free of sulfur compounds without any special additional cleaning. This enables the use of inexpensive non-precious metal catalysts for the post-oxidation of unburned oxygenates and carbon monoxide.

The fuel according to the invention for compression ignition engines can be used in engines which are lubricated with the chemically related engine oils based on polyalkylene glycol. The usual entry of small amounts of fuel in the engine oil and smaller amounts of engine oil in the fuel remains without negative effects because of the chemical relationship of the two substances.

The invention is illustrated further below with the aid of examples. However, the examples are not intended to be limiting or limiting of the present invention in any way.

Example 1:

Monooxymethylene dimethyl ether is mixed with 20, 10 or 7.5 polyethylene glycol DME 500 (Clariant). The cetane number of the mixtures increases from 40 (monooxymethylene dimethyl ether) to 75, 55 and 51. The viscosity of the mixtures increases from 0.45 to 0.72, 0.53 and 0.50 mm ² / s. The CFPP drops from <-80 ° C to -17 ° C, -25 ° C or <-30 ° C ° C.

Example 2:

5 or 3% by weight of polyethylene glycol DME 1000 (Clariant) are dissolved in monooxymethylene dimethyl ether. The mixture has a CZ of 53 or 50 and a viscosity of 0.49 or 0.44 mm ² / s. The CFPP increases to -3 ° C or - 10 ° C.

Example 3:

5% by weight of polyethylene glycol DME 1000 (Clariant) is dissolved in monooxymethylene dimethyl ether. By adding the mixture with 0.05% by weight or 0.1% by weight of DTBP, the CZ increases to 54.4 and 55.2, respectively.

Example 4:

3% by weight of polyethylene glycol DME 1000 (Clariant) is dissolved in monooxymethylene dimethyl ether. By adding the mixture with 0.05% by weight of DTBP, the CZ increases to 52.

Example 5:

Monooxymethylene dimethyl ether is mixed with 10% by weight of polyethylene glycol DME 500 and 10% by weight of tetraoxymethylene dimethyl ether. The CZ increases to 65. The kinematic viscosity increases to 0.59 mm ² / s. The increase in lubricity is noteworthy (drop in the HFRR wear value to 240 µm). The CFPP is -28 ° C.

Example 6:

Monooxymethylene dimethyl ether is mixed with 10% by weight of polyethylene glycol DME 500 and 5% by weight of tetraoxymethylene dimethyl ether. The CZ rises to 55.

Embodiment 7:

5% by weight of OME6-10 (OME6-10 = polyoxymethylene dimethyl ether) is dissolved in monooxymethylene dimethyl ether (average MW 290). The CZ increases to 55 and the viscosity to 0.7 mm ² / s.

Example 8:

The fuels for compression ignition engines described in Examples 1 to 7 can absorb up to 11.5% by weight of dimethyl ether by pressing on gaseous dimethyl ether. The dissolved amount of monooxymethylene dimethyl ether depends on the respective vapor pressure requirements of the seasons. The properties of the fuels contained are comparable to those of Examples 1 to 7.

Comparative Example 1:

Pure monooxymethylene dimethyl ether (Ineos, Mainz 99.7%) has a CZ of 40, a viscosity of 0.45 mm ² / s (20 ° C), a surface tension of 21.2 mN / m, and a vapor pressure of 20 ° C 42.6 kP and a CFPP below -60 ° C

Comparative Example 2:

5% by weight of polyethylene glycol monomethyl ether 350 (Clariant) are dissolved in monooxymethylene dimethyl ether and 0.1% by weight of DTPB is added. The cetane number increases to 51. The solution is frozen at -18 ° C. When thawed, flakes form which only fully dissolve at 9.2 ° C.

Comparative Example 3:

• Die Messung der Cetanzahl wurde mit dem Messgerät "AFIDA" der Firma ASG . Analytik Service Gesellschaft, Trentiner Ring 30, 86356 Neusäss bestimmt:
  Das Funktionsprinzip von AFIDA (Advanced Fuel Injection Delay Analyzer) ist wie folgt:
  Eine Hochdruckpumpe befüllt über eine Hochdruckleitung einen Hochdruckspeicher (Rail) mit dem zu prüfenden Kraftstoff. Das nachgeschaltete Piezoeinspritzventil (Bosch Piezoinjektor) spritzt eine definierte Kraftstoffmenge in die vorgeheizte, mit Druckluft beaufschlagte Brennkammer.

3% by weight of polyethylene glycol monomethyl ether 1000 (Clariant) are dissolved in monooxymethylene dimethyl ether and 0.1% by weight of DTBP is added. The Cetane number rises to 52. The solution is frozen at -18 ° C. When thawed, flakes form which only fully dissolve at 4 ° C.

• The cetane number was measured using the "AFIDA" measuring device from ASG. Analytik Service Gesellschaft, Trentiner Ring 30, 86356 Neusäss determines:
  The functional principle of AFIDA (Advanced Fuel Injection Delay Analyzer) is as follows:
  A high-pressure pump fills a high-pressure accumulator (rail) with the fuel to be tested via a high-pressure line. The downstream piezo injector (Bosch piezo injector) injects a defined amount of fuel into the preheated, pressurized combustion chamber.

The finely atomized fuel ignites and the resulting combustion gases lead to an increase in pressure in the combustion chamber. The temporal pressure curve is recorded in high resolution and ignition delay and the cetane number are calculated. AFIDA can be coupled with devices for determining the exhaust gas composition.

With the help of a gas mixer, the composition of the combustion air can be specifically changed (setting a lambda value). The device is calibrated like the CFR or BASF cetane number engine with primary standards.

A scheme of the experimental procedure is in the Figure 1 shown.

The following test conditions were used: - combustion chamber temperature: 650 ° C - combustion chamber pressure: 10 bar - injection pressure: 1000 bar - injection quantity: 50 mg - Fuel thermostatting: 25 ° C

• Die kinematische Viskosität ist in mm²/s bei 20°C angegeben und wurde nach DIN ISO 3104 bestimmt.
• Der CFFP (Cold Filter Plugging Point), d. h. die Temperatur bei der der Prüffilter unter definierten Bedingungen durch einen Kraftstoff nicht mehr durchfließen wird, erfolgte nach DIN EN 116.
• Die Bestimmung des Durchmessers einer Verschleißkalotte (in µm) als Maß für die Schmierfähigkeit (HFRR (High Frequency Reciprocating Rig)) erfolgte bei 25°C gemäß DIN EN ISO 12156-1. Je größer der Durchmesser, umso geringer ist die Schmierfähigkeit des Kraftstoffs. Nach DIN EN 590 beträgt der Grenzwert ≤ 460 µm.

The sample was fed fully automatically using an autosampler (capacity: 36 samples of 40 ml each). The fuel is injected via a high-pressure pump and a standard Bosch piezo injector. This corresponds to the current state of the art and is currently installed in the Audi A6, for example. After the measurement, the entire fuel system is automatically flushed to prevent sample mixing. The actual combustion takes place in a high pressure cylinder with approx. 0.6 l combustion chamber volume.

• The kinematic viscosity is given in mm ² / s at 20 ° C and was determined according to DIN ISO 3104.
• The CFFP (Cold Filter Plugging Point), i.e. the temperature at which the test filter will no longer flow through under certain conditions due to a fuel, was carried out in accordance with DIN EN 116.
• The diameter of a wear cap (in µm) was determined as a measure of the lubricity (HFRR (High Frequency Reciprocating Rig)) at 25 ° C according to DIN EN ISO 12156-1. The larger the diameter, the lower the lubricity of the fuel. According to DIN EN 590, the limit is ≤ 460 µm.

Claims (9)

1. A fuel for compression-ignition engines, containing monooxymethylene dimethylether, characterised in that the fuel contains at least 80 % by weight monooxymethylene dimethylether and up to 20 % by weight of at least one oxygenate of the n-polyoxaalkane type, which is selected from the group consisting of polyoxymethylene dialkylethers of the formula RO(-CH₂O-)_nR, wherein n = 4 to 10 and R = an alkyl group, polyethylene glycol dialkylethers and/or polyethylene glycol monoalkylether formals, and in that the fuel has a cetane number of ≥ 48.6.
2. A fuel according to claim 1, characterised in that the fuel has a cetane number of ≥ 51.
3. A fuel according to claim 1 or claim 2, characterised in that the polyoxymethylene dialkylethers are polyoxymethylene dimethylethers, the polyethylene glycol dialkylethers are polyethylene glycol dimethylethers and the polyethylene glycol monoalkylether formals are polyethylene glycol monomethyl ether formals.
4. A fuel according to claim 3, characterised in that the polyoxymethylene dimethylether has a molecular weight MG of 100 to 400 daltons.
5. A fuel according to claim 3, characterised in that the polyethylene glycol dimethylether has a molecular weight MG of 400 to 1000 daltons.
6. A fuel according to claim 3, characterised in that the polyethylene glycol monomethylether formal has a molecular weight MG of 400 to 1000 daltons.
7. A fuel according to at least any one of the preceding claims, characterised in that the fuel contains di-tert-butyl peroxide.
8. A fuel according to claim 7, characterised in that the fuel contains up to 0.3 % by weight di-tert-butyl peroxide.
9. A fuel according to any one of the preceding claims, characterised in that it does not contain any hydrocarbons.

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