JP2019048910A - Lubricant composition for diesel engine, and method for improving base number holding performance or method for improving long-drain performance - Google Patents

Abstract

To provide a lubricant composition for diesel engine that can hold a base number for a long time and improve long-drain performance.SOLUTION: A lubricant composition for diesel engine contains a lubricant base oil, an epoxy compound, a phosphorus-containing antiwear agent, and a metal cleaner.SELECTED DRAWING: None

Description

  The present invention relates to a lubricating oil composition for a diesel engine, and a method for improving base number maintenance performance or a method for improving long drain performance.

  In recent years, a diesel engine vehicle such as a large truck, a bus, etc. is equipped with a post-processing device from the viewpoint of emission control. A DPF (diesel particulate filter) is used as one of the aftertreatment devices.

  From the viewpoint of improving the long drain property (oxidation stability) of the lubricating oil composition for diesel engines, metal additives such as metal detergents are often used. However, since these metal additives are discharged as they are without being burned, they cause the deterioration of the purification performance of the DPF due to clogging and the like. Moreover, the regulation of the amount of sulfated ash exists in JASO DH-2 specification of the lubricating oil composition for diesel engines.

  From the viewpoint of maintaining the purification performance of the DPF, it is required to use an ashless additive for lubricating oil instead of the metal-based additive. For example, as a lubricating oil composition for diesel engines, one in which an amine compound is blended with a lubricating base oil is disclosed (see, for example, Patent Documents 1 and 2). However, even in the conventional lubricating oil composition, there is room for further improvement in the long drain property.

JP, 2011-094144, A JP, 2013-508529, A

  The present invention has been made in view of the above circumstances, and it is a main object of the present invention to provide a lubricating oil composition for a diesel engine capable of maintaining a base number for a long period and improving long drain performance. .

  In order to solve the above problems, the present invention provides a lubricating oil composition shown in the following [1] and [2], a method for improving base number maintenance performance or a method for improving long drain performance shown in the following [3], The use (application) of the composition shown to 4] and the use (application) for manufacture of the composition shown to following [5] are provided.

[1] A lubricating oil composition for a diesel engine, comprising a lubricating oil base oil, an epoxy compound, a phosphorus-containing antiwear agent, and a metallic detergent.
[2] The lubricating oil composition for a diesel engine according to [1], wherein the content of the epoxy compound is 0.5 to 1.5% by mass based on the total amount of the composition.
The lubricating oil composition for diesel engines as described in [3] [1] or [2] which lubricates, The improvement method of base number maintenance performance, or the improvement method of long drain performance.
[4] Use of the composition as a lubricating oil for a diesel engine, wherein the composition contains a lubricating base oil, an epoxy compound, a phosphorus-containing antiwear agent, and a metallic detergent. use.
[5] A use of the composition for producing a lubricating oil for a diesel engine, the composition comprising a lubricating base oil, an epoxy compound, a phosphorus-containing antiwear agent, and a metallic detergent. Contain, use.

  ADVANTAGE OF THE INVENTION According to this invention, the lubricating oil composition for diesel engines which can maintain a base number over a long period and can improve long drain property is provided. The lubricating oil composition for diesel engines of the present invention is particularly useful for diesel engines for heavy vehicles such as buses and trucks. Further, according to the present invention, there are provided a method for improving base number maintenance performance or a method for improving long drain performance using a lubricating oil composition for a diesel engine.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

  The lubricating oil composition for a diesel engine according to one embodiment contains a lubricating base oil, an epoxy compound, a phosphorus-containing antiwear agent, and a metal detergent.

[Lubricant base oil]
The lubricant base oil can be applied to a lubricant base oil used in the general lubricant field. Here, specific examples of the lubricating base oil include mineral base oils, synthetic base oils, or a mixture of both.

  Examples of mineral base oils include kerosene fractions obtained by distillation of paraffinic, naphthenic, or aromatic crude oils; normal paraffins obtained by extraction from kerosene fractions; and paraffinic, naphthenic, Or a lubricating oil fraction obtained by distillation of an aromatic crude oil, or a Fischer-Tropsch wax obtained by a wax such as slack wax and / or a gas-to-liquid (GTL) process obtained by a lubricating oil dewaxing step, A synthetic wax such as GTL wax is used as a raw material, solvent deasphalting, solvent extraction, hydrocracking, hydroisomerization, solvent dewaxing, catalytic dewaxing, hydrorefining, hydrorefining, sulfuric acid washing, white clay, etc. Or paraffinic mineral oil, naphthenic mineral oil, normal paraffinic base oil, isopa purified by appropriately combining two or more Fin-based base oils, aromatic base oils and the like. One of these mineral base oils may be used alone, or two or more thereof may be used in combination in any ratio.

  Examples of synthetic base oils include poly α-olefins or their hydrides; propylene oligomers, isobutylene oligomers, polybutenes, 1-octene oligomers, 1-decene oligomers, olefin oligomers such as ethylene-propylene oligomers or their hydrides; Alkyl naphthalene; diester (ditridecyl glutarate, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc.); polyol ester (trimethylol propane capri , Trimethylolpropane pelargonate, trimethylolpropane oleate, pentaerythritol 2-ethylhexanoate, pentaerythritol pera Goneto etc.); polyoxyalkylene glycols, dialkyl ethers, polyphenyl ether, and the like. One of these synthetic base oils may be used alone, or two or more thereof may be used in combination in an optional ratio.

The kinematic viscosity at 40 ° C. of the lubricating base oil comprising a single base oil or a combination of two or more base oils is not particularly limited, but is preferably 15 mm ² / s or more, more preferably 19 mm ² / s or more More preferably, it is 30 mm ² / s or more. The kinematic viscosity of the lubricating base oil at 40 ° C. is preferably 100 mm ² / s or less, more preferably 50 mm ² / s or less, and still more preferably 36 mm ² / s or less. When the kinematic viscosity of the lubricating base oil at 40 ° C. is within the above range, the proper viscosity of the lubricating base oil can be secured, and a good oil film tends to be obtained in the practical use temperature range.

The kinematic viscosity at 100 ° C. of the lubricating base oil comprising a single base oil or a combination of two or more base oils is not particularly limited, but is preferably 2 mm ² / s or more, more preferably 3.5 mm ² / s. or more, and more preferably 5 mm ² / s or more. The kinematic viscosity of the lubricating base oil at 100 ° C. is preferably 20 mm ² / s or less, more preferably 15 mm ² / s or less, and still more preferably 12 mm ² / s or less. If the kinematic viscosity of the lubricating base oil at 100 ° C. is within the above range, the proper viscosity of the lubricating base oil can be ensured, and a good oil film tends to be obtained in the practical use temperature range.

  The viscosity index of the lubricating base oil comprising a single base oil or a combination of two or more base oils is not particularly limited, but is preferably 80 or more, more preferably 90 or more, and still more preferably 100 or more. When the viscosity index is in the above range, stability of the viscosity with respect to the external temperature is secured, so that the oil film tends to be stably formed even against the external temperature change during use.

  The kinematic viscosity and viscosity index at 40 ° C. and 100 ° C. in the present specification mean values measured in accordance with JIS K 2283 “Crude oil and petroleum products—Kinematic viscosity test method and viscosity index calculation method”, respectively.

[Epoxy compound]
The lubricating oil composition contains an epoxy compound. By including the epoxy compound in the lubricating oil composition, the base number of the lubricating oil composition is maintained for a long time, and the long drain property is improved.

  The epoxy compound is not particularly limited as long as it is a compound having an epoxy group in the molecule, but is preferably an epoxy compound having an alicyclic epoxy group.

  The epoxy compound having an alicyclic epoxy group is not particularly limited as long as it is a compound having an alicyclic epoxy group in the molecule. As a cycloaliphatic epoxy group, for example, a compound formed by bonding an oxygen atom to two adjacent carbon atoms constituting a cyclic aliphatic skeleton, or an oxygen atom bonded to two non-adjacent carbon atoms And the like. The alicyclic epoxy group is preferably a compound formed by bonding an oxygen atom to two adjacent carbon atoms constituting a cyclic aliphatic skeleton. The cyclic aliphatic skeleton is preferably a 5- to 8-membered ring, more preferably a 5- or 6-membered ring, more preferably a 6-membered ring.

  The alicyclic epoxy group may be a group represented by the following formula (A), that is, a 3,4-epoxycyclohexyl group.

  Although the number in particular of the alicyclic epoxy group in the epoxy compound which has an alicyclic epoxy group is not restrict | limited, Preferably it is 1-6, More preferably, it is 2-6, More preferably, it is 2-4.

  When the number of alicyclic epoxy groups in the epoxy compound having an alicyclic epoxy group is two or more, the alicyclic epoxy groups may be bonded by a single bond, and they are bonded via a linking group. It may be There are no particular restrictions on the type of linking group that links the alicyclic epoxy groups, and examples of linking groups include divalent hydrocarbon groups, carbonyl groups (-CO-), ether bonds (-O-), An ester bond (-COO-), a carbonate bond (-OCOO-), and the group that combined these, etc. are mentioned. As a bivalent hydrocarbon group, a C1-C6 linear or branched alkylene group, a bivalent alicyclic hydrocarbon group etc. are mentioned, for example.

  Among these, the epoxy compound having an alicyclic epoxy group is a compound represented by the following formula (B), that is, 3 ', 4'-epoxycyclohexylmethyl (3,4-epoxy) cyclohexane carboxylate Is preferred. By including such a compound in the lubricating oil composition, the long drain property can be further improved.

  As the compound represented by the above formula (B), for example, commercially available products such as “Ceroxide 2021P” (Daicel Corporation) can be used.

  The content of the epoxy compound is preferably 0.5 to 1.5% by mass, more preferably 0.5 to 1.0% by mass, based on the total amount of the composition. When the content of the epoxy compound is in the above range, the long drain property can be further improved.

[Phosphorus-containing antiwear agent]
The lubricating oil composition contains a phosphorus-containing antiwear agent. Here, a phosphorus containing antiwear agent means the antiwear agent which contains a zinc atom as a constitutent element. The phosphorus-containing antiwear agent is not particularly limited, and antiwear agents used in the general lubricating oil field can be used.

  The phosphorus-containing antiwear agent includes, for example, phosphites (phosphites), phosphates (phosphates), thiophosphites, dithiophosphites, trithiophosphites, thiophosphorus Acid esters (thiophosphates), dithiophosphates (dithiophosphates), trithiophosphates (trithiophosphates), etc .: These metal salts (zinc salts etc.) and the like can be mentioned. Among these, the phosphorus-containing antiwear agent is preferably zinc dialkyldithiophosphate (ZDTP), which is preferably a zinc salt of dithiophosphates, or zinc dialkylphosphate (ZP), which is a zinc salt of phosphates, Is a zinc dialkyl dithiophosphate (ZDTP).

  Examples of zinc dialkyl dithiophosphate (ZDTP) include compounds represented by the following general formula (C), and the like.

Wherein ^{(C), R} 11 ~R ¹⁴ independently represents a linear or branched alkyl group having 1 to 24 carbon atoms.

  As a zinc dialkyl phosphate (ZP), the compound etc. which are represented by the following general formula (D) are mentioned, for example.

Wherein ^{(D), R} 21 ~R ²⁴ independently represents a linear or branched alkyl group having 1 to 24 carbon atoms.

  The content of the phosphorus-containing antiwear agent is preferably 0.02% by mass or more, more preferably 0.04% by mass or more, in terms of phosphorus element based on the total amount of the composition, from the viewpoint of antiwearing property. In addition, the content of the phosphorus-containing antiwear agent is preferably 0.12% by mass or less, more preferably 0.08% by mass or less, in terms of phosphorus element based on the total amount of the composition from the viewpoint of catalyst poisoning reduction. Furthermore, it is 0.06 mass% or less.

[Metal detergent]
The lubricating oil composition contains a metallic detergent. The metal-based detergent is not particularly limited, and metal-based detergents used in the general lubricating oil field can be used.

  Examples of metal detergents include alkali metal or alkaline earth metal sulfonates, normal salts such as phenates and salicylates, basic salts, and overbased salts. Examples of alkali metals include sodium and potassium, and examples of alkaline earth metals include magnesium, calcium and barium. Among these, the metal of the metal detergent is preferably an alkaline earth metal, more preferably magnesium or calcium, more preferably calcium.

  The content of the metal-based detergent is preferably 0.15% by mass or more, more preferably 0.18% by mass or more, in terms of metal element, based on the total amount of the composition, from the viewpoint of preventing clogging of the post-treatment device Furthermore, it is 0.20 mass% or more. Further, the content of the metal-based detergent is preferably 0.30% by mass or less, more preferably 0.28% by mass or less, in terms of metal element, based on the total amount of the composition, from the viewpoint of base number persistence. is there.

[Ash-free dispersant]
The lubricating oil composition may contain an ashless dispersant. The ashless dispersant is not particularly limited, and ashless dispersants used in the general lubricating oil field can be used.

  As the ashless dispersant, for example, a mono- or bis-succinimide having at least one linear or branched alkyl group or alkenyl group having 40 to 400 carbon atoms in the molecule, an alkyl group having 40 to 400 carbon atoms Or benzylamine having at least one alkenyl group in the molecule, polyamine having at least one alkyl group having 40 to 400 carbon atoms or alkenyl group in the molecule, modified products thereof such as boron compounds, carboxylic acid, phosphoric acid and the like Etc.

  When an ashless dispersant is used, its content may be 2.0 to 10.0 mass% based on the total amount of the composition.

[Viscosity Index Improver]
The lubricating oil composition may contain a viscosity index improver. The viscosity index improver is not particularly limited, and viscosity index improvers used in the general lubricating oil field can be used.

  As a viscosity index improver, for example, non-dispersed or dispersed ethylene-α-olefin copolymer or its hydride, polyisobutylene or its hydride, styrene-diene hydrogenated copolymer, polyalkylstyrene etc. may be mentioned. Be Among these, the viscosity index improver is preferably an ethylene-α-olefin copolymer or a hydride thereof.

  Other examples of the viscosity index improver include non-dispersed or dispersed poly (meth) acrylate viscosity modifiers, non-dispersed or dispersed olefin- (meth) acrylate copolymer viscosity index improvers, styrene-maleic anhydride maleic acid Examples thereof include acid ester copolymer-based viscosity index improvers and mixtures thereof.

  When using a viscosity index improver, the content may be 3.0 to 10.0 mass% based on the total amount of the composition.

Pour point depressant
The lubricating oil composition may contain a pour point depressant. The pour point depressant is not particularly limited, and it is possible to use a pour point depressant which is used in the general lubricating oil field.

  Examples of pour point depressants include polymethacrylate polymers compatible with the lubricating base oil used.

  When the pour point depressant is used, its content may be 0.1 to 1.0% by mass based on the total amount of the composition.

[Other additives]
The lubricating oil composition may further contain any commonly used lubricating oil additive, depending on the purpose. As such additives, for example, friction modifiers, antiwear agents other than phosphorus-containing antiwear agents (extreme pressure agents), antioxidants, corrosion inhibitors, antirust agents, antiemulsifiers, metal deactivators And antifoam agents.

  Examples of the friction modifier include ashless friction modifiers such as fatty acid ester type, aliphatic amine type and fatty acid amide type, and metal type friction modifiers such as molybdenum dithiocarbamate and molybdenum dithiophosphate. For example, an amine compound, an imide compound, a fatty acid ester, a fatty acid amide having in the molecule at least one alkyl group or alkenyl group having 6 to 30 carbon atoms, particularly a linear alkyl group or linear alkenyl group having 6 to 30 carbon atoms And fatty acid metal salts can be preferably used.

  Examples of the antiwear agent (extreme pressure agent) other than the phosphorus-containing antiwear agent include, for example, disulfides, polysulfides, sulfurized olefins, sulfurized oils and fats and the like.

  Examples of the antioxidant include phenol-based and amine-based ashless antioxidants, copper-based and molybdenum-based metal-based antioxidants, and the like. Specifically, for example, as a phenolic ashless antioxidant, 4,4′-methylenebis (2,6-di-tert-butylphenol), 4,4′-bis (2,6-di-tert- Examples of amine-based ashless antioxidants include phenyl-α-naphthylamine, alkylphenyl-α-naphthylamine, dialkyl diphenylamine, diphenylamine and the like.

  As a corrosion inhibitor, a benzotriazole type, a tolyltriazole type, a thiadiazole type, an imidazole type compound etc. are mentioned, for example.

  Examples of the rust inhibitor include petroleum sulfonate, alkyl benzene sulfonate, dinonyl naphthalene sulfonate, alkenyl succinic acid ester, polyhydric alcohol ester and the like.

  Examples of the demulsifier include polyalkylene glycol nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl naphthyl ether and the like.

  Examples of the metal deactivator include imidazoline, pyrimidine, azole derivative and the like.

As the antifoaming agent, for example, silicone oil which may have a halogenated alkyl group having a kinematic viscosity of 100 to 100000 mm ² / s at 25 ° C., alkenyl succinic acid derivative, polyhydroxy aliphatic alcohol and long chain fatty acid And esters of methyl salicylate and o-hydroxybenzyl alcohol, and the like.

  When these other additives for lubricating oil are used, their contents may be 0.01 to 20% by mass based on the total amount of the composition.

  The lubricating oil composition of the present embodiment is preferably classified into SAE (Society of Automotive Engineers) viscosity grade 5W-30 or 10W-30.

Kinematic viscosity at 100 ° C. of the lubricating oil composition is not particularly limited, it is preferably 6.9 mm ² / s or more, more preferably 9.3 mm ² / s or more. The kinematic viscosity at 100 ° C. of the lubricating oil composition is preferably 16.3 mm ² / s or less, and more preferably not more than 12.5 mm ² / s. If the kinematic viscosity of the lubricating oil composition at 100 ° C. is within the above range, an appropriate viscosity can be secured, and the oil film retention tends to be more excellent.

The kinematic viscosity at 40 ° C. of the lubricating oil composition is not particularly limited, but is preferably 40 mm ² / s or more, more preferably 50 mm ² / s or more, still more preferably 60 mm ² / s or more. The kinematic viscosity of the lubricating oil composition at 40 ° C. is preferably 120 mm ² / s or less, more preferably 100 mm ² / s or less, and still more preferably 80 mm ² / s or less. When the kinematic viscosity of the lubricating oil composition at 40 ° C. is within the above range, an appropriate viscosity can be secured, and the oil film retention tends to be more excellent.

  The viscosity index of the lubricating oil composition is not particularly limited, but is preferably 120 or more, more preferably 130 or more, and still more preferably 135 or more. When the viscosity index is in the above range, stability of the viscosity with respect to the external temperature is secured, so that the oil film tends to be stably formed even against the external temperature change during use.

  According to the JASO DH-2 standard for lubricating oil compositions for diesel engines, it is determined that the amount of sulfated ash is in the range of 1.0 ± 0.1 mass% (0.9 mass% or more and 1.1 mass% or less) It is done. Therefore, the sulfated ash content of the lubricating oil composition of the present embodiment is preferably 1.0 ± 0.1 mass% (0.9 mass% or more and 1.1 mass% or less). The amount of sulfated ash in the present specification means a value measured in accordance with JIS K 2272.

  In the JASO DH-2 standard of lubricating oil compositions for diesel engines, the base number by the hydrochloric acid method is required to be in the range of 5.5 mg KOH / g or more. Therefore, it is preferable that the base value by the hydrochloric acid method of the lubricating oil composition of this embodiment is 5.5 mgKOH / g or more. In addition, the base number by the hydrochloric acid method in this specification means the value measured based on JISK2501.

  According to the lubricating oil composition for a diesel engine of the present embodiment, the base number can be maintained for a long time, and the long drain property can be improved. Therefore, it is possible to provide a method for improving base number maintenance performance or a method for improving long drain performance, which performs lubrication using such a lubricating oil composition.

  Hereinafter, the present invention will be more specifically described by way of examples. However, the present invention is not limited to these examples.

[Preparation of lubricating oil composition]
(Examples 1 to 3 and Comparative Examples 1 and 2)
As shown in Table 1, lubricating oil compositions of Examples 1 to 3 and Comparative Examples 1 and 2 were prepared. In the preparation of the lubricating oil composition, the content of the viscosity index improver was mainly adjusted so that the kinematic viscosity at 100 ° C. was in the range of 10.6 to 10.8 mm ² / s. . The obtained lubricating oil composition was subjected to an internal combustion engine lubrication oxidation stability test to examine the long drain property (oxidation stability).

  The details of each component shown in Table 1 are as follows.

<Lubricant base oil>
Base oil A-1: hydrogenated refined mineral oil (GpI) (40 ° C. kinematic viscosity: 22 mm ² / s, 100 ° C. kinematic viscosity: 4.4 mm ² / s, viscosity index 103, JXTG Energy Co., Ltd., “Super oil N22” )
Base oil A-2: hydrogenated refined mineral oil (GpI) (40 ° C. kinematic viscosity: 87 mm ² / s, 100 ° C. kinematic viscosity: 10.4 mm ² / s, viscosity index 101, JXTG Energy Co., Ltd., “Super oil N 100 S” )

<Additives for lubricating oil>
Epoxy compound B-1: 3 ', 4'-epoxycyclohexylmethyl (3,4-epoxy) cyclohexanecarboxylate, Daicel Co., Ltd., "Ceroxide 2021 P"
Metal detergent C-1: Calcium sulfonate (calcium content: 12.5% by mass, base number: 320 mg KOH / g)
Performance additive D-1: additive package (phosphorus-containing antiwear agent (dialkyldithiophosphate zinc (content based on the total amount of package additives: 7.5% by mass, based on the total amount of package additives) Phosphorus content: 0.51% by mass, metal detergent (calcium sulfonate (content based on the total amount of package additives): 26.4% by mass, calcium based on the total amount of package additives Content: 3.4% by mass), ashless dispersant, antioxidant (including diphenylamine))
Viscosity index improver E-1: Olefin copolymer (weight-average molecular weight (Mw): 119000, shear stability index (SSI): 24)
Pour point depressant F-1: polymethacrylate (weight average molecular weight (Mw): 169000)

(Measurement of kinematic viscosity)
The kinematic viscosity and the viscosity index at 40 ° C. and 100 ° C. of the lubricating oil compositions of Examples 1 to 3 and Comparative Examples 1 and 2 were measured in accordance with JIS K 2283. The results are shown in Table 1.

(Measurement of sulfated ash content)
The sulfated ash content of the lubricating oil compositions of Examples 1 to 3 and Comparative Examples 1 and 2 was measured in accordance with JIS K 2272. The results are shown in Table 1.

(Measurement of base number)
Based on JIS K 2501, the base number of the lubricating oil compositions of Examples 1 to 3 and Comparative Examples 1 and 2 according to the hydrochloric acid method was determined as “base number before ISOT”. The results are shown in Table 1.

(Internal combustion engine lubrication oxidation stability test (ISOT))
According to JIS K 2514, internal combustion engine lubrication oxidation stability test (ISOT) was conducted on the lubricating oil compositions of Examples 1 to 3 and Comparative Examples 1 and 2. Although ISOT is usually performed under the conditions of 165.5 ° C. for 24 hours, in order to increase the severity, the test was performed under the conditions of 175 ° C. for 48 hours. After ISOT, based on JIS K 2501, the base number by the hydrochloric acid method was determined as “base number after ISOT”. The results are shown in Table 1. In addition, the ratio of “base number after ISOT” to “base number before ISOT” (“base number after ISOT” / “base number before ISOT”) was calculated as “base number ratio”.

  The lubricating oil compositions of Examples 1 to 3 using an epoxy compound had improved base number retention performance and improved long drain performance. On the other hand, the lubricating oil composition of Comparative Example 1 in which the epoxy compound was not used had a lower base number ratio than the lubricating oil compositions of Examples 1 to 3. In addition, the lubricating oil composition of Comparative Example 2 to which a metal-based detergent is added can not satisfy the JASO DH-2 standard (sulfated ash content: 1.0 ± 0.1 mass%), and the base number ratio is also It was low. From these results, it was confirmed that the lubricating oil composition for a diesel engine of the present invention can maintain the base number for a long time and improve long drain property.

Claims (3)

Lubricant base oil,
Epoxy compound,
Phosphorus-containing antiwear agent,
Metal detergents,
A lubricating oil composition for a diesel engine, comprising:   The lubricating oil composition for a diesel engine according to claim 1, wherein the content of the epoxy compound is 0.5 to 1.5% by mass based on the total amount of the composition.   A method of improving base number maintenance performance or a method of improving long drain performance, comprising performing lubrication using the lubricating oil composition for a diesel engine according to claim 1 or 2.