Polyalkylene glycol base oils for reducing NOx in gaseous fuel combustion engines

Abstract

The invention relates to the use of a lubricant based on polyalkylene glycol in a gaseous fuel combustion engine for reducing NOx emissions of the gaseous fuel combustion engine. The present invention relates to a method for reducing NOx emissions of a gaseous fuel combustion engine, the method comprising the step of lubricating the gaseous fuel combustion engine with a polyalkylene glycol-based lubricant.

Description

[0001] The present invention relates to the use of a polyalkylene glycol based lubricant in a gaseous fuel combustion engine for reducing the NOx emissions of the gaseous fuel combustion engine. The present invention relates to a method for reducing the NOx emissions of a gaseous fuel combustion engine, the method comprising the step of lubricating the gaseous fuel combustion engine with a polyalkylene glycol based lubricant.

[0002] More and more gasses, such as hydrogen, are also being discussed as potential fuels for future combustion engines. As soon as battery-electric engines reach their limits, gasses, such as hydrogen, are being discussed as energy carriers. In public, hydrogen is often discussed together with fuel cells for the conversion of energy into electricity. However, gaseous fuel engines are generally a better alternative in terms of cost, dynamics and durability.

[0003] A disadvantage of gaseous fuel engines can be high emissions, such as NOx.

[0004] WO 2008 / 048909 discloses a hydrogen fuel combustion engine with a special exhaust gas recirculation, EGR, to address NOx emissions.

[0005] It is an object of the present invention to find a way to reduce NOx emissions in a gaseous fuel combustion engine.

[0006] This object is solved by using a polyalkylene glycol based lubricant in a gaseous fuel combustion engine for reducing the NOx emissions of the gaseous fuel combustion engine.

[0007] This object is also solved by a method for reducing the NOx emissions of a gaseous fuel combustion engine, the method comprising the step of lubricating the gaseous fuel combustion engine with a polyalkylene glycol based lubricant.

[0008] NOx emissions are typically produced in the combustion chamber of a gaseous fuel combustion engine by the chemical interaction between nitrogen (N2) and oxygen (O2) in the atmosphere. Nitric oxide (NO) is usually formed in the highest concentration, but other NOx compounds such as NO2 are also formed in lower amounts. NOx emissions preferably refer to the sum of the emissions of NO and NO2.

[0009] NOx emissions can be analyzed by Fourier transform infrared spectroscopy (FTIR).

[0010] Various FTIR analyzers for NOx analysis are commercially available. FTIR typically measures the entire infrared spectrum to identify the unique chemical fingerprint of various gases. NOx can be analyzed directly from the source without the need for sample preparation. Preferably, NOx is analyzed by FTIR of the sum of NO and NO2.

[0011] NOx emissions are typically analyzed in the exhaust gas of a gaseous fuel burning engine.

[0012] NOx emissions are typically analyzed in the exhaust gas of a gaseous fuel burning engine.

[0013] Typically, the NOx emissions of the gaseous fuel burning engine are reduced compared to a mineral oil based lubricant in the gaseous fuel burning engine.

[0014] Typically, the NOx emissions of the gaseous fuel burning engine are reduced compared to a mineral oil based lubricant in the gaseous fuel burning engine, wherein the polyalkylene glycol based lubricant and the mineral oil based lubricant have the same kinematic viscosity at 100 °C, like 11 mm 2 / s.

[0015] The mineral oil based lubricant typically has an SAE (Society of Automotive Engineers) engine oil grade of W 30, preferably 10 W 30.

[0016] The mineral oil based lubricant typically has a kinematic viscosity at 100 °C of about 11 mm 2 / s.

[0017] The NOx emissions are typically reduced by at least 100 ppm, preferably at least 200 ppm, and in particular at least 300 ppm compared to a mineral oil based lubricant.

[0018] The NOx emissions are typically reduced by at least 20%, preferably at least 30%, and in particular at least 40% compared to a mineral oil based lubricant.

[0019] Gaseous fuel burning engines and in particular hydrogen fuel burning engines are commercially available in various sizes from various companies. The gaseous fuel burning engine can be stationary (e.g. in a thermal power plant) or mobile (e.g. in a ship, an airplane, a tractor, a harvester-thresher or a truck). The gaseous fuel burning engine can have port fuel injection or direct injection.

[0020] The gaseous fuel burning engine is typically fueled with a gas comprising methane, natural gas, hydrogen or mixtures thereof. The gaseous fuel burning engine is preferably fueled with a gas comprising methane or hydrogen or mixtures thereof.

[0021] In a preferred form, the gaseous fuelled combustion engine is fuelled with hydrogen gas, which can contain at least 90 wt%, preferably at least 95 wt%, and in particular at least 97 wt% hydrogen gas.

[0022] In another preferred form, the gaseous fuelled combustion engine is fuelled with a hydrogen gas mixture, such as a mixture of hydrogen gas and a hydrocarbon. In another preferred form, the gaseous fuelled combustion engine is fuelled with a mixture of hydrogen gas and a hydrocarbon. Suitable mixtures of hydrogen gas and a hydrocarbon are mixtures of hydrogen gas and diesel, or mixtures of hydrogen gas and natural gas, with the latter being preferred. The hydrogen gas mixture can contain at least 2 wt%, preferably at least 5 wt%, and in particular at least 8 wt% hydrogen gas.

[0023] In another preferred form, the gaseous fuelled combustion engine is fuelled with natural gas, which can contain at least 50 wt%, preferably at least 70 wt%, and in particular at least 80 wt% methane.

[0024] In another preferred form, the gaseous fuelled combustion engine is fuelled with methane, which can contain at least 90 wt%, preferably at least 95 wt%, and in particular at least 98 wt% methane.

[0025] The polyalkylene glycol-based lubricant can comprise one or more polyalkylene glycols. Preferably, the polyalkylene glycol-based lubricant comprises at least two polyalkylene glycols, which optionally differ in kinematic viscosity at 100°C.

[0026] The polyalkylene glycol-based lubricant typically comprises at least 50 wt%, preferably at least 70 wt%, and in particular at least 85 wt% polyalkylene glycol. In the case that the polyalkylene glycol-based lubricant comprises at least two polyalkylene glycols, then these amounts relate to the sum of these at least two polyalkylene glycols.

[0027] The polyalkylene glycol-based lubricant typically comprises less than 3 wt%, preferably less than 1 wt%, and in particular less than 0.1 wt% mineral oil, such as an API Group I, II, or III base oil. In another form, the polyalkylene glycol-based lubricant is free of mineral oil, such as an API Group I, II, or III base oil.

[0028] The polyalkylene glycol in the polyalkylene glycol-based lubricant is typically an alkoxylated alcohol, preferably a C1-C8alkanol, more preferably a C1-C4alkanol, and in particular a C1-C2alkanol, which is ethoxylated and / or propoxylated. 20 alkanol, or a C2-C4alkanol, and in particular a C1-C8alkanol, which is ethoxylated and / or propoxylated. 20 alkanol, or a C2-C4alkanol, and in particular a C1-C8alkanol, which is ethoxylated and / or propoxylated.

[0029] Suitable alkoxylated alcohols are ethoxylated, ethoxylated and propoxylated, or ethoxylated and butoxylated. Preferably, the alkoxylated alcohol is ethoxylated and propoxylated.

[0030] The alkoxylated alcohol can have a number average molecular weight Mn in the range of 400 to 10 000 Da, preferably 700 to 3000 Da, and in particular 1000 to 1500 Da. Mn can be calculated based on the hydroxyl value.

[0031] The alkoxylated alcohol can contain at least 20 wt%, preferably at least 30 wt% and in particular at least 40 wt% ethyleneoxy units.

[0032] The alkoxylated alcohol can contain 20 wt% to 80 wt% ethyleneoxy units and 80 wt% to 20 wt% propyleneoxy units. The alkoxylated alcohol preferably contains 30 wt% to 70 wt% ethyleneoxy units and 70 wt% to 30 wt% propyleneoxy units. In particular, the alkoxylated alcohol contains 40 wt% to 60 wt% ethyleneoxy units and 60 wt% to 40 wt% propyleneoxy units. The wt% of ethyleneoxy and propyleneoxy typically add up to at most 100 wt%.

[0033] The alkoxyl groups in the alkoxylated alcohol can be random or in block sequence. Preferably, the alkoxyl groups (e.g. ethoxyl and propoxyl) in the alkoxylated alcohol are in random sequence.

[0034] The polyalkoxylated chain of the alkoxylated (e.g. ethoxylated and propoxylated) alcohol can be terminated by a hydroxyl group or a Ci to C4 alkyl group, with hydroxyl being preferred.

[0035] Suitable alcohol units in the alkoxylated alcohol are linear or branched Ci-C 20 alkanol or C2-C 20 alkanol or C2-C8 alkanediol, and in particular Ci-C6 alkanol or C2-C6 alkanediol.

[0036] In another preferred form, the alcohol units in the alkoxylated (e.g. ethoxylated and propoxylated) alcohol are linear or branched Ci-C 12 alkanol, preferably Ci-C6 alkanol, and in particular Ci-C4 alkanol.

[0037] The alcohol units in the alkoxylated alcohol can be a technical mixture of various chain lengths and isomers.

[0038] The polyalkylene glycol based lubricant can have a kinematic viscosity at 40 °C in the range of 10-300 mm 2 / s, preferably 20-150 mm 2 / s, and in particular 35-80 mm 2 / s.

[0039] The polyalkylene glycol based lubricant can have a kinematic viscosity at 100°C of at least 3 mm 2 / s, preferably 5-40 mm 2 / s, and in particular 8-20 mm 2 / s.

[0040] The polyalkylene glycol based lubricant can have a kinematic viscosity at 100°C of at least 3 mm 2 / s, preferably less than 15 mm 2 / s, and in particular less than 13 mm 2 / s.

[0041] The polyalkylene glycol based lubricant can have a viscosity index at 100°C of at least 150, preferably at least 180, and in particular at least 200.

[0042] The kinematic viscosity can be determined according to ASTM D445.

[0043] The polyalkylene glycol based lubricant can have a pour point of less than -30°C, preferably less than -40°C, and in particular less than -45°C. The pour point can be determined according to ASTM D 97.

[0044] The polyalkylene glycol based lubricant can be soluble in water (e.g. at 20°C) such as at least 10 g / l, preferably at least 100 g / l.

[0045] Lubricant generally refers to a composition capable of reducing friction between surfaces, preferably metal surfaces, such as the surfaces of a mechanical device.

[0046] The polyalkylene glycol based lubricant can comprise lubricant additives such as polymeric thickening agents, corrosion inhibitors, detergents, dispersants, anti-foaming agents, dyes, wear protection additives, extreme pressure agents, anti-wear additives, friction modifiers, metal deactivators, pour point depressants, demulsifiers.

[0047] The polyalkylene glycol based lubricant can comprise up to 20 wt%, preferably up to 15 wt% and in particular up to 10 wt% of lubricant additives.

[0048] The polyalkylene glycol based lubricant preferably does not contain viscosity improvers.

[0049] The polyalkylene glycol based lubricant preferably does not contain silicon anti-foaming agents.

[0050] Suitable (polymeric) thickening agents include, but are not limited to, polyisobutylene (PIB), oligomer copolymer (OCP), polymethacrylate (PMA), copolymers of styrene and butadiene, or high viscosity esters (complex esters).

[0051] Corrosion inhibitors can include various oxygen-, nitrogen-, sulfur-, and phosphorus-containing materials, and can include metal-containing compounds (salts, organometallic compounds, etc.) and non-metal-containing materials or ashless materials. Corrosion inhibitors can include, but are not limited to, additive types such as, for example, the following hydrocarbyl-, aryl-, alkyl-, arylalkyl-, and alkylaryl-forms of: detergents (neutral, overbased), sulfonates, phenates, salicylates, alcoholates, carboxylates, salixarates, phosphites, phosphates, thiophosphates, amines, amine salts, amine phosphates, amine sulfonates, alkoxylated amines, ether amines, polyether amines, amides, imides, oxazoles, oxadiazoles, triazoles, benzotriazoles, benzothiazoles, mercaptobenzothiazoles, tolyltriazoles (TTZ-types), heterocyclic amines, heterocyclic thioethers, thiazoles, thiadiazoles, mercaptotiadiazoles, dimercaptotiadiazoles (DMTD-types), imidazoles, benzimidazoles, dithiobenzimidazoles, imidazolines, oxazolines, Mannich reaction products, glycidyl ethers, acid anhydrides, carbamates, thiocarbamates, dithiocarbamates, polyglycols, etc., or mixtures thereof.

[0052] Detergents include cleaning agents that adhere to soil particles, thereby preventing the soil particles from adhering to critical surfaces. Detergents can also adhere to metal surfaces themselves to keep the metal surfaces clean and prevent corrosion from occurring. Detergents include calcium alkylsalicylate, calcium alkylphenate, and calcium alkylarylsulfonate, with alternative metal ions such as magnesium, barium, or sodium being used. Examples of cleaning agents and dispersants that can be used include metal-based detergents such as neutral and overbased alkaline earth metal sulfonates, alkaline earth metal phenates, and alkaline earth metal salicylates, alkenyl succinimides and alkenyl succinimide esters and borohydrides thereof, phenates, salienius complex detergents, and ashless dispersants that have been modified with sulfur compounds. These agents can be conveniently added and used individually or in mixtures in amounts ranging from > 0.01% to < 1.0% by weight relative to the weight of the base stock; these can also be in high total base number (TBN), low TBN, or mixed high / low TBN forms.

[0053] Dispersants are lubricant additives that help prevent the formation of sludge, varnish, and other deposits on critical surfaces. Dispersants can be succinimide dispersants (e.g., N-substituted long chain alkenyl succinimides), Mannich dispersants, ester-containing dispersants, condensation products of fatty hydrocarbyl monocarboxylic acid acylating agents with amines or ammonia, alkyl aminophenol dispersants, hydrocarbyl-amine dispersants, polyether dispersants, or polyether amine dispersants. In one embodiment, the succinimide dispersant includes a polyisobutylene-substituted succinimide, where the polyisobutylene from which the dispersant is derived can have a number average molecular weight of about 400 to about 5,000, or about 950 to about 1,600. In one embodiment, the dispersant includes a borated dispersant. Typically, the borated dispersant includes a succinimide dispersant (including polyisobutylene succinimides), where the polyisobutylene from which the dispersant is derived can have a number average molecular weight of about 400 to about 5,000. The borated dispersants are described in more detail above in the extreme pressure agent description.

[0054] Suitable extreme pressure agents are sulfur-containing compounds. In one embodiment, the sulfur-containing compound can be a sulfurized olefin, a polymeric sulfide, or mixtures thereof. Examples of sulfurized olefins include sulfurized olefins derived from propylene, isobutylene, pentene; organic sulfides and / or polymeric sulfides (including benzyl disulfide); bis-(chlorobenzyl) disulfide; dibutyl tetrasulfide; di-tert-butyl poly sulfide; and sulfurized methyl oleate, sulfurized alkyl phenol, sulfurized dipentene, sulfurized terpenes, sulfurized Diels-Alder adducts, N'N dialkyldithiocarbamic acid alkylsulfonate phenyl esters; or mixtures thereof. In one embodiment, the sulfurized olefin includes sulfurized olefins derived from propylene, isobutylene, pentene, or mixtures thereof. In one embodiment, the extreme pressure additive sulfur-containing compound includes a dithiophthalazine or derivative, or mixture thereof. Examples of dithiophthalazines include compounds such as 2,5-dimercapto-l,3,4-thiadi azole or hydrocarbyl-substituted 2,5-dimercapto-l,3,4-thiadiazo le, or oligomers thereof. Oligomers of hydrocarbyl-substituted 2,5-dimercapto-l,3,4-thiadiazo le are typically formed by forming a sulfur-sulfur bond between 2,5-dimercapto-l,3,4-thiadiazo le units to form a derivative or oligomer of two or more of the thiadiazo le units. Suitable 2,5-dimercapto-l,3,4-thiadiazo le-derived compounds include, for example, 2,5-bis(tert-nonyldithio)-l,3,4-thiadiazo le or 2-tert-nonyldithio-5-mercapto-l,3,4-thiadiazo le. The number of carbon atoms on the hydrocarbyl substituents of the hydrocarbyl-substituted 2,5-dimercapto-l,3,4-thiadiazo le typically includes 1 to 30, or 2 to 20, or 3 to 16. The extreme pressure additive includes a compound containing boron and / or sulfur and / or phosphorus. The extreme pressure agent can be present in the lubricant composition from 0 wt.-% to about 20 wt.-%, or from about 0.05 wt.-% to about 10.0 wt.-%, or from about 0.1 wt.-% to about 8 wt.-% of the lubricant composition.

[0055] Examples of anti-wear additives include organic borates, organic phosphites such as didodecyl phosphite, organic sulfur-containing compounds such as sulfurized sperm oil or sulfurized terpenes, zinc dialkyldithiophosphates, zinc diaryldithiophosphates, phosphosulfurized hydrocarbons, and any combination thereof.

[0056] The friction modifiers can include metal-containing compounds or materials as well as ashless compounds or materials, or mixtures thereof. Metal-containing friction modifiers include metal salts or metal ligand complexes, where the metal can include an alkali metal, an alkaline earth metal, or a transition metal. Such metal-containing friction modifiers can also have a low ash characteristic. The transition metal can include Mo, Sb, Sn, Fe, Cu, Zn, and others. The ligand can include hydrocarbyl derivatives of alcohols, polyols, glycerol, partial glycerol, mercaptans, carboxylic acid esters, carbamates, thiocarbamates, dithiocarbamates, phosphates, thiophosphates, dithiophosphates, amides, imides, amines, thiazoles, thiadiazoles, dithiazoles, diazoles, triazoles, and other polar molecular functional groups containing an effective amount of O, N, S, or P, either individually or in combination. In particular, Mo-containing compounds can be particularly effective, such as, for example, Mo-dithiocarbamates (Mo(DTC)), Mo-dithiophosphates (Mo(DTP)), Mo- amines (Mo(Am)), Mo-alkoxides, Mo alcohol-amine, and the like.

[0057] Ashless friction modifiers can also include lubricant materials containing an effective amount of a polar group, such as hydroxyl-containing hydrocarbyl base oils, glycerol esters, partial glycerol esters, glycerol ester derivatives, and the like. The polar group in the friction modifier can include hydrocarbyl groups containing an effective amount of O, N, S, or P, either individually or in combination. Other friction modifiers that can be particularly effective include, for example, salts (both ash-containing and ashless derivatives) of fatty acids, fatty alcohols, fatty amides, fatty esters, hydroxyl-containing carboxylic acid esters, and similar synthetic long chain hydrocarbyl acids, alcohols, amides, esters, hydroxyl carboxylic acid esters, and the like. In some cases, fatty organic acids, fatty amines, and sulfurized fatty acids can be used as suitable friction modifiers. Examples of friction modifiers include fatty acid esters and amides, organomolybdenum compounds, molybdenum dialkyl thiocarbamates, and molybdenum dialkyl dithiophosphates.

[0058] Suitable metal deactivators include benzotriazoles and derivatives thereof, such as 4- or 5-alkylbenzotriazoles (e.g., Tinuvin® 292), and derivatives thereof, 4,5,6,7-tetrahydrobenzotriazole, and 5,5'-methylenebisbenzotriazole; Mannich bases of benzotriazole or triazole, such as 1 -[bis(2- ethyl-hexyl)aminomethyl)triazole and 1 -[bis(2-ethylhexyl)aminomethyl)benzotriazole; and alkoxyalkylbenzotriazoles, such as 1 -(nonyloxymethyl)benzotriazole, 1 -(1 -butoxyethyl)benzotriazole, and 1 -(1 -cyclohexyloxybutyl)triazole, and combinations thereof. Additional non-limiting examples of one or more metal deactivators include 1,2,4-triazoles and derivatives thereof, such as 3-alkyl (or aryl)-1,2,4-triazoles, and Mannich bases of 1,2,4-triazoles, such as 1 -[bis(2-ethylhexyl)aminomethyl-1,2,4-triazole; alkoxyalkyl-1,2,4-triazoles such as 1 -(1 -butoxyethyl)-1,2,4-triazole; and acylated 3-amino-1,2,4-triazoles, imidazole derivatives, such as 4,4'-methylenebis(2-undecyl-5-methylimidazole) and bis[(N-methyl)imidazol-2-yl]methanol octyl ether, and combinations thereof. Still additional non-limiting examples of one or more metal deactivators include sulfur-containing heterocyclic compounds, such as 2-mercapto-benzothiazole, 2,5-dimercapto-1,3,4-thiadiazole, and derivatives thereof; and 3,5-bis[di(2- ethylhexyl)aminomethyl]-1,3,4-thiazolidin-2-one, and combinations thereof. Yet still additional non-limiting examples of one or more metal deactivators include amino compounds, such as salicylidene propylenediamine, salicylaminoguanidine, and salts thereof, and combinations thereof. The amount of one or more metal deactivators in the composition is not particularly limited, but is typically present in an amount of about 0.01 to about 0.1, about 0.05 to about 0.01, or about 0.07 to about 0.1 wt.-%, based on the weight of the composition. Alternatively, one or more metal deactivators can be present in an amount of less than about 0.1, less than about 0.7, or less than about 0.5 wt.-%, based on the weight of the composition.

[0059] Pour point depressants (PPD) include polymethacrylates, alkylated naphthalene derivatives, and combinations thereof. Additives commonly used such as alkyl aromatic polymers and polymethacrylates can also be used for this purpose. Typically, the treatment rate is in the range of > 0.001 wt.-% to < 1.0 wt.-%, relative to the weight of the base stock.

[0060] Demulsifiers include trialkyl phosphates, and various polymers and copolymers of ethylene glycol, ethylene oxide, propylene oxide, or mixtures thereof.

[0061] Example

[0062] The following polyalkylene glycol based lubricant ("PAG oil A") was tested:

[0063] 44.6 wt% alkoxylated alcohol (statistically ethoxylated and propoxylated butanol, 50 / 50 wt%), KV40 135-155 mm 2 / s (ASTM D445).

[0064] 44.5 wt% alkoxylated alcohol (statistically ethoxylated and propoxylated butanol, 50 / 50 wt%), KV40 18-22 mm 2 / s (ASTM D445).

[0065] 0.5 wt% silicone-free defoamer (polyethylene oxide-polypropylene oxide-polyethylene oxide (EO-PO-EO) triblock polymer, molar mass about 2500-2800, molar mass of PO block about 2200-2500 g / mol, amount of PE block in the triblock polymer about 10%.

[0066] 10.4 w% additive package with solubilizer, antioxidant and corrosion inhibitor.

[0067] This polyalkylene glycol based lubricant has KV40 = 52 mm 2 / s, KV100 = 11 mm 2 / s, VI = 215, pour point -54°C. It is classified as a 10 W 30 engine oil. It does not contain a silicone defoamer and does not contain a viscosity index improver.

[0068] As a comparative mineral oil based lubricant, a commercially available Group III mineral oil based engine oil from Motorex® in Switzerland was tested. This mineral oil based lubricant has KV40 = 76 mm 2 / s, KV100 = 11 mm 2 / s, VI = 139, pour point -27°C. It is classified as a 15 W 30 engine oil.

[0069] Example 1

[0070] The emission test was performed on a commercially available combined heat and power plant Vitobloc® 200 type EM 9 / 20 (Viessmann, Germany) having a 3-cylinder gas combustion engine (Toyota, 952 cm3 displacement), without turbocharging, lambda = 1, stationary at 1500 rpm, with an electrical power of 8.5 kW, a thermal power of 20.1 kW, a torque of 54.2 Nm, a series engine control (ecu), and an indicated mean effective pressure (pme) of 6.8 bar.

[0071] The engine has port fuel injection, is water-cooled and lubricated by circulating lubrication. The exhaust system has a controlled 3-way catalytic converter. After the catalytic converter, the CO and NOx emissions in the exhaust gas are determined by FTIR (about 500°C - 550°C).

[0072] The combustion engine is operated at constant load and is fueled with a mixture of hydrogen and methane in a ratio of 1 : 9.

[0073] The combustion engine is lubricated with the above polyalkylene glycol-based lubricant PAG oil A, or, for comparison, with a mineral oil-based lubricant.

[0074] In both cases, the emissions of CO and NOx are determined over a period of 240 seconds after an operating time of 85 hours of the combustion engine, and the average values are determined.

[0075] The CO emissions of the polyalkylene glycol-based lubricant and the comparative mineral oil-based lubricant are at similar levels of about 100 ppm.

[0076] The NOx emissions of the polyalkylene glycol-based lubricant are about 395 ppm, while the comparative mineral oil-based lubricant leads to NOx emissions of about 850 ppm.

[0077] After an operating time of 300 h with the polyalkylene glycol-based lubricant, a visual analysis of the engine block is carried out. Now significant wear is found.

[0078] Example 2

[0079] The combustion engine described in Example 1 is used. The combustion engine is lubricated with the above polyalkylene glycol-based lubricant PAG oil A, or, for comparison, with the mineral oil-based lubricant of Example 1.

[0080] In test run 2A, the combustion engine is fueled with CH4 for 100 hours.

[0081] In test run 2B, the combustion engine was first fueled with CH4 / H2 (ratio 9 / 1) for 28 hours and then with CH4 / H2 (ratio 8 / 2) for 100 hours.

[0082] Various parameters of the polyalkylene glycol-based lubricant were analyzed before and after test runs 2A and 2B. The results are shown in Table 1.

[0083] The data show that the polyalkylene glycol-based lubricant has excellent stability in a gas-fueled combustion engine: no wear was observed as determined by the concentration of abrasive metals in the lubricant; the water concentration did not increase; the kinematic viscosity, VI, and acid number remained unchanged.

[0084] Table 1: Analysis data of the polyalkylene glycol-based lubricant

[0085]

[0086] Example 3

[0087] The test scuffing performance was performed to evaluate the piston ring-cylinder liner-oil tribosystem with temperature-dependent scuffing limits.

[0088] The test procedure was based on Obert et al., Tribology International 94 (2016) 306 - 314: The scuffing limit is very sensitive to the oil quantity and the oil temperature (viscosity). The scuffing limit is usually only valid for one oil temperature. The load range was 50 - 400 N with 4 mm stroke at 20 Hz and the oil lubrication was 0.1 pl / min. The test was performed according to the step method: in case of scuffing, the load was decreased, in case of no scuffing, the load was increased. If the load exceeded 400 N, the temperature was increased by 10 K. If the load was below 50 N, the temperature was decreased by 10 K. Thus, an average load value at one temperature level was obtained.

[0089] The samples used were:

[0090] Cylinder liner: Daimler OM471, Stratum (Ø 132)

[0091] Piston ring variant: Volvo HDE13, MIP 230 (PVD)

[0092] The polyalkylene glycol-based lubricant PAG oil A was used as described above. For comparison, a commercial oil 0W-20 diesel with a kinematic viscosity at 40 °C of about 40 mm2 / s and a kinematic viscosity at 100 °C of about 8 mm2 / s was used.

[0093] The results are summarized in Tables 2 and 3: Table 2 shows that the PAG oil is better than the diesel engine oil in terms of scuffing limit. Table 3 shows that the PAG oil is better than the diesel engine oil in terms of friction coefficient, which indicates better fuel economy.

[0094] Table 2:

[0095]

[0096] Table 3: Friction coefficient at 200 °C

[0097]

Claims

1. Use of a polyalkylene glycol based lubricant for reducing NOx emissions of a gaseous fuel combustion engine.

2. Use according to claim 1, wherein, The polyalkylene glycol based lubricant comprises at least two polyalkylene glycols.

3. Use according to claim 1 or 2, wherein, The polyalkylene glycol based lubricant comprises at least 50 wt% of the polyalkylene glycols.

4. Use according to any one of claims 1 to 3, wherein, The polyalkylene glycol is an alkoxylated alcohol.

5. Use according to claim 4, wherein, The alkoxylated alcohol comprises at least 20 wt% of ethylene oxide units.

6. Use according to claim 4 or 5, wherein, The alkoxylated alcohol is an ethoxylated and propoxylated Ci-C 20 alkanol or an ethoxylated and propoxylated C2-C 20 alkanediol.

7. Use according to any one of claims 1 to 6, wherein, The polyalkylene glycol based lubricant is soluble in water.

8. Use according to any one of claims 1 to 7, wherein, The polyalkylene glycol based lubricant has a viscosity index of at least 180 at 100 °C.

9. Use according to any one of claims 1 to 8, wherein, The polyalkylene glycol based lubricant has a pour point of below -30 °C.

10. Use according to any one of claims 1 to 9, wherein, The NOx concentration is analyzed by Fourier transform infrared spectroscopy.

11. Use according to any one of claims 1 to 10, wherein, The NOx emissions are reduced compared to a mineral oil based lubricant in the gaseous fuel combustion engine.

12. The use according to any one of claims 1 to 11, wherein, The NOx emissions are reduced by at least 20% compared to a mineral oil based lubricant.

13. Use according to any one of claims 1 to 12, wherein, The NOx emissions are reduced by at least 100 ppm compared to the mineral oil based lubricant.

14. The use according to any one of claims 1 to 13, wherein, The gaseous fuel combustion engine is fueled by a gas comprising methane, natural gas, hydrogen or mixtures thereof.

15. A method for reducing NOx emissions of a gaseous fuel combustion engine, the method comprising the step of lubricating the gaseous fuel combustion engine with a polyalkylene glycol based lubricant.

16. The method of claim 15, wherein, The alkoxylated alcohol is an ethoxylated and propoxylated Ci-C 20 alkanols or ethoxylated and propoxylated C2-C 20 alkanediols.

17. The method of claim 15 or 16, wherein, The polyalkylene glycol based lubricant is soluble in water.

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