Method and system for operating two-and four-stroke engines using low sulfur fuels

Abstract

A method for operating a two-stroke engine using low sulfur fuels. Blended cylinder oil is produced by blending base oil and at least one additive where the total base number (“TBN”) of the blended cylinder oil ranges from 1 TBN to 20 TBN. The engine is operated by supplying the blended cylinder oil and a fuel having less than 1.0% sulfur to the engine cylinders. The additive includes a low TBN calcium salts at a weight ratio ranging from 90:10 to 10:90; or any combination thereof. A method for operating a 4-stroke engine using low and high sulfur fuels. Blended oil, having a TBN that is greater than 20 TBN, is produced by blending base oil and at least one additive. The engine is operated by exchanging a low sulfur fuel having less than 1.0% sulfur with a high sulfur fuel. The engine lubricating system is switched to the blended cylinder oil in accordance with switching the fuel from a low sulfur fuel to a high sulfur fuel.

Description

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/874,105, filed Dec. 11, 2006.

FIELD OF THE INVENTION

The invention relates to a method of creating blended cylinder oils for use with low sulfur fuels.

BACKGROUND OF THE INVENTION

Two-stroke crosshead engines used in marine or stationary applications are equipped with two separate lubricating oil systems. One lubricating system includes so-called system oil that is used in the engine crank case for lubrication and cooling of the engine's bearings and oil-cooled pistons as well as for activation and/or control of various valves or the like. Typical system oils usually have an SAE viscosity of about 30 with a relatively low TBN content, typically below 10. These exemplary values may vary dependent on the actual application and the specific design of the systems that the oils are used in.

The other lubricating system, of a two-stroke crosshead engine, includes an all-loss lubricant (cylinder oil) that normally is used for lubrication of the engine's cylinders, piston rings and piston skirt. Typically cylinder oil is spent continuously by each turn of the engine whereas the system oil in principle is not spent (except by smaller unintentional leakages). The lubrication system comprising the cylinder oil is also often referred to as an “all-loss” lubrication system as the oil is spent. Cylinder oil typically contains certain additives that function to reduce, minimize or neutralise the acid level of the cylinder system. Generally, cylinder oils have an SAE (Society of Automotive Engineering) viscosity equivalent to about 50 and normally have a total base number (“TBN”) of about 40 to 70 for the neutralisation of acid products produced during the combustion process.

Four-stroke, trunk piston diesel engines, however, use only a single oil type for lubrication and cooling. Such engines are used as secondary/auxiliary or propulsion engines on ships, or in stationary power generation or liquid/gas transmission applications. Such used oils typically have a SAE viscosity of about 30 or 40.

The performance properties of lubricants, in both four-stroke and two-stoke engines, is typically measured periodically. The properties may not go beyond certain limits without jeopardizing the condition of the oiled engine component. Ultimately, the useful properties of both trunk piston engine and system oil degenerate over time and resulting in either replenished or a complete replacement of the oil. Similarly, other lubricants used on-board vessels or at stationary sites, such as hydraulic fluids, gear oils, turbine oils, heavy duty diesel oils, compressor oils and the like, do deteriorate over time, due to e.g. contamination, oxidation, hydrolysis etc. and therefore have are replenished or changed at certain intervals.

It is desirable to operate diesel engines using low sulfur fuels to reduce sulfur emissions. In particular, it is desirable to use straight vegetable oils (“SVO”), or SVO derivatives, and other low and very low sulfur fuels in combination with lubricants having low total base number. To operate diesel engines with low sulfur fuels and retain performance at temperatures exceeding 200° C., low TBN lubricants are needed. The present invention provides a novel approach to produce lubricants having suitable TBN values for the sulfur level of the fuel used to power the diesel engine.

SUMMARY OF THE INVENTION

The present invention provides for a method for operating a two-stroke engine using low sulfur fuels. Blended cylinder oil is produced by blending base oil and at least one additive. The TBN of the blended cylinder oil falls within the range 1 TBN to 20 TBN. The engine is operated by supplying the blended cylinder oil and a fuel having less than 1.0% sulfur to the engine cylinders. The blended cylinder oil has a composition containing a base fluid of lubricating viscosity and a mixture of at least two of the following metal detergent additives: a low (or non-overbased) TBN calcium phenate; a low (or non-overbased) TBN calcium sulphonate; a low (or non-overbased) TBN calcium salicylate, or any combination thereof, wherein the at least two additives have a weight ratio ranging from 90:10 to 10:90.

The present invention further provides for a method for operating a 4-stroke engine using low and high sulfur fuels. Blended oil is produced by blending base oil and at least one additive. The blended oil has a TBN that is greater than 20 TBN. The engine is operated by exchanging a low sulfur fuel having less than 1.0% sulfur with a high sulfur fuel. The engine lubricating system is switched to the blended oil in accordance with switching the fuel from a low sulfur fuel to a high sulfur fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the illustrative embodiments shown in the drawing, in which:

FIG. 1 shows a schematic block diagram of a two-stroke engine of one embodiment according to the present invention; and

FIG. 2 shows a schematic block diagram of a four-stroke engine of one embodiment according to the present invention

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a schematic representation of a system 100 including at least one two-stroke cross-head diesel engine 101. The engine 101 includes a first lubricating system containing system oil 102 and a second lubricating system includes an all-loss lubricant or cylinder oil 107. The system further includes used system oil conduit 103 and 109, system oil recycle loop 108a and 108b, waste tank 106, a fresh system oil tank 105, separator 107, transfer line 112, blending apparatus 104, additive tank 115, fluid storage tank 116, low sulfur-fuel tank 118, high sulfur fuel tank 119 and fuel line 120, for carrying out the method of the present invention. Fluid storage tank 116 may be used to store base oil, trunk piston engine oil, or used trunk piston engine oil.

According to an embodiment of the present invention, a two-stroke engine may be operated by supplying the blended cylinder oil and a fuel having sulfur content ranging from 1.0 wt. % sulfur to 0.001 wt. % sulfur to the engine cylinders. In one embodiment, the fuel contains sulfur content ranging from 0.5 wt. % sulfur to 0.001 wt. % sulfur. In another embodiment, the fuel corresponds to straight vegetable oil. Blended cylinder oil having a TBN ranging from 1 TBN to 20 TBN is suitable for use with a low sulfur fuel. Blended cylinder oil having a TBN ranging from 1 TBN to 20 TBN may be produced by blending base oil and at least one additive. The additives include bases, detergents, anti-oxidants, dispersants and fiction modifiers.

Blended cylinder oil may be produced by mixing one or more additives with base fluid including base oil, fresh system oil, used system oil, trunk piston engine oil, or used trunk piston engine oil. In one such embodiment, fresh system oil may be obtained from fresh system oil tank 105 and transferred to blending apparatus 104 via fresh system oil conduit 110, system oil recycle loop 108a, separator 107, and transfer conduit 112. In another embodiment, base oil, trunk piston engine oil or used trunk piston engine oil may be obtained from fluid storage tank 116 and transferred to the blending apparatus 104.

In yet another such embodiment, used system oil may be used to produce blended cylinder oil. The used system oil may be obtained from the crank case section of the two-stroke engine 101, transferred to blending apparatus 104 via used system oil conduits 103 and 108 and transfer line 112. The two-stroke engine, from which the used system oil is obtained, may be tapped continuously, near-continuously or intermittently for used system oil and the used system oil is replenished with fresh system oil.

The blending process produces blended cylinder oil suitable for use in two-stroke engines operating with low sulfur fuels. In one embodiment, the base fluid has a viscosity in the range of 9 cSt to 30 cSt at 100° C. The blended cylinder oil has a composition containing a base fluid of lubricating viscosity and a mixture of at least two of the following metal-organic detergent additives: a low (or non-overbased) TBN calcium phenate; a low (or non-overbased) TBN calcium sulphonate; a low (or non-overbased) TBN calcium salicylate, or any combination thereof, wherein the at least two additives have a weight ratio ranging from 90:10 to 10:90. The TBN of the blended cylinder oil falls within the range 1 TBN to 20 TBN. In another embodiment, the blended cylinder oil further includes a metal source including metals other than calcium and transition metals.

A metal-organic detergent additive typically has a metal to organic anion mole ratio of 1:1 for Group IA metals and 0.5:1 for Group IIA metals. In one embodiment of the present invention, a non-overbased metal-organic detergent additive has a metal to organic anion mole ratio ranging from 0.2:1 to 1:1 for Group IA metals and a metal to organic anion mole ratio ranging from 0.1:1 to 0.5:1 for Group IIA metals. In another embodiment of the present invention, a non-overbased metal-organic detergent additive has a metal to organic anion mole ratio ranging from 0.3:1 to 0.8:1 for Group IA metals and a metal to organic anion mole ratio ranging from 0.2:1 to 0.3:1 for Group IIA metals. In one embodiment of the present invention, an overbased metal-organic detergent additive has a metal to organic anion mole ratio ranging from 1:1 to 8:1 for Group IA metals and a metal to organic anion mole ratio ranging from 0.5:1 to 4:1 for Group IIA metals. In another embodiment of the present invention, an overbased metal-organic detergent additive has a metal to organic anion mole ratio ranging from 2:1 to 6:1 for Group IA metals and a metal to organic anion mole ratio ranging from 1:1 to 3:1 for Group IIA metals.

The amount of additive mixed with the lubricating oil, to create the cylinder oil, may be determined from the amount of sulfur in the fuel and the TBN of the additive.

In one embodiment, the additives include detergents such as phenate, sulphonate or salicylate salts. For an embodiment where the detergent includes calcium phenate as an additive, the calcium phenate has a TBN ranging from 20 TBN to 250 TBN. In another embodiment, the calcium phenate has a mole ratio of metal to phenate ranging from 0.2:1 to 1.5:1 for a Group IA metal and ranging from 0.1:1 to 0.5:1 for a Group IIA metal. In yet another embodiment, the calcium phenate has a mole ratio of metal to phenate ranging from 0.5:1 to 1:1 for a Group IA metal and ranging from 0.3:1 to 0.5:1 for a Group IIA metal.

For an embodiment where the detergent includes calcium sulphonate as an additive, the calcium sulphonate has a TBN ranging from 10 TBN to 300 TBN. In another embodiment, the calcium sulphonate has a mole ratio of metal to sulphonate ranging from 0.2:1 to 2:1 for a Group IA metal and ranging from 0.1:1 to 0.5:1 for a Group IIA metal. In yet another embodiment, the calcium sulphonate has a mole ratio of metal to sulphonate ranging from 0.5:1 to 1.5:1 for a Group IA metal and ranging from 0.3:1 to 0.5:1 for a Group IIA metal.

For an embodiment where the detergent includes calcium salicylate, the calcium salicylate has a TBN ranging from 10 TBN to 200 TBN. In another embodiment, the calcium salicylate has a mole ratio of metal to salicylate ranging from 0.2:1 to 2:1 for a Group IA metal and ranging from 0.1:1 to 0.5:1 for a Group IIA metal. In yet another embodiment, the calcium salicylate has a mole ratio of metal to salicylate ranging from 0.5:1 to 1.5:1 for a Group IA metal and ranging from 0.3:1 to 0.5:1 for a Group IIA metal.

In another embodiment, the base additives include basic salts of alkaline or earth alkaline elements. The alkaline/earth alkaline elements may be e.g. K, Na, Ca, Ba, Mg or the like. The basic salts may belong to the inorganic chemical families of e.g. oxides, hydroxides, carbonates, sulfates or the like.

The dispersants may belong to the organic chemical families of succinimides or the like.

As discussed above, the blended cylinder oil may be used in two-stroke crosshead engines combustion engines. The creation of blended cylinder oil results from the availability of the required initial fluid and the additives and makes this method very suitable for offshore or on-site applications. In one embodiment, the production of blended cylinder oil according to the present invention may take place on-site such as a marine vessel. In another embodiment, the production of blended cylinder oil according to the present invention may take place using off-shore equipment or stationary plants.

Alternatively, the blended cylinder oil is based on a mixture of oils that continuously, near-continuously or intermittently are tapped from an existing system and where the used oils are replenished with fresh oil.

As discussed above, it is desirable to operate marine vessels with fuels having different sulfur content. In one embodiment, the vessel operates with a 4-stroke engine using blended trunk piston engine oil.

FIG. 2 shows schematic representation of system 200 including a 4-stroke diesel engine 201 wherein the sulfur content of the fuel may be varied. System 200 further includes filters 202, 204, and 205, oil loop 203, oil container 204, three way valve 206, additive tank 207, trunk piston engine oil (“TPEO”) conduit, mixer 209, transfer line 210, optionally holding tank 211, blended TPEO transfer line 212, low sulfur fuel tank 214, high sulfur fuel tank 215 and fuel transfer line 213.

During routine operation of marine vessels, the fuels used to power the engines may be switched from low sulfur fuels to high sulfur fuels. In one embodiment, blended trunk piston engine oil (“TPEO”) is produced that is suitable for use in 4-stroke engines where the TBN of the TPEO depends upon the sulfur content of the fuel. While the engine is operated using a low sulfur fuel, TPEO having TPN values ranging from 5 TBN to 20 TBN may be used as the engine lubricant. In another embodiment, the low sulfur fuel contains sulfur content ranging from 1.0 wt. % sulfur to 0.001 wt. % sulfur. In yet another embodiment, the low sulfur fuel contains sulfur content ranging from 0.5 wt. % sulfur to 0.001 wt. % sulfur. In still yet another embodiment, the low sulfur fuel corresponds to a Straight Vegetable Oil (SVO). When a high sulfur fuel is used, the engine is operated using TPEO having TPN values ranging from 20 TBN to 70 TBN as the engine lubricant. In one embodiment, the high sulfur fuel contains sulfur content ranging from 1.1 wt. % to 4.5 wt. %. In another embodiment, the high sulfur fuel contains sulfur content ranging from 1.1 wt. % to 2.0 wt. %.

When low sulfur fuel is switched to a high sulfur fuel, the engine lubricating system is then switched to the blended TPEO. The blended TPEO has a composition containing a base fluid of lubricating viscosity and a mixture of at least two of the following metal-organic detergent additives: non-overbased or overbased TBN calcium phenate; a non-overbased or overbased TBN calcium sulphonate; non-overbased or overbased TBN calcium salicylate, or any combination thereof, wherein the at least two additives have a weight ratio ranging from 90:10 to 10:90. In one embodiment, the TBN of the blended TPEO has TPN within the range 1 TBN to 20 TBN. In another embodiment, the TBN of the blended TPEO has a TBN greater than 20 TBN. In yet another embodiment, the TBN of the blended TPEO has TPN within the range 20 TBN to 70 TBN.

The present disclosure may be embodied in other specific forms without departing from the spirit or essential attributes of the disclosure. Accordingly, reference should be made to the appended claims, rather than the foregoing specification, as indicating the scope of the disclosure. Although the foregoing description is directed to the preferred embodiments of the disclosure, it is noted that other variations and modification will be apparent to those skilled in the art, and may be made without departing from the spirit or scope of the disclosure.

In the claims, any reference signs placed between parentheses shall not be constructed as limiting the claim. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

Claims

1. A method for operating a two-stroke engine, comprising:

(a) producing a blended cylinder oil having a total base number (TBN) ranging from 20 TBN to 1 TBN by blending a base oil and at least one additive; and

(b) operating the engine by supplying the blended cylinder oil and a fuel contains a sulfur content ranging from 1.0 wt. % sulfur to 0.001 wt. % sulfur to the engine cylinders.

2. The method of claim 1, wherein the base oil is selected from the group consisting of system oil, used system oil, trunk piston engine oil, or used trunk piston engine oil.

3. The method of claim 2, wherein the at least one additive is selected from the group consisting of detergents, anti-oxidants, and friction modifiers.

4. The method of claim 1, wherein the fuel contains a sulfur content ranging from 0.5 wt. % sulfur to 0.001 wt. % sulfur.

5. The method of claim 1, wherein the fuel corresponds to a Straight Vegetable Oil (SVO).

6. The method of claim 1, wherein the two-stroke engine is operated on a marine vessel.

7. The method of claim 6, wherein said blending is performed on the marine vessel.

8. The method of claim 6, wherein said blending is not performed on the marine vessel.

9. The method of claim 1, wherein the blended cylinder oil has a composition containing a base fluid of lubricating viscosity and a mixture of at least two of the following: a low (or non-overbased) TBN calcium phenate; a low (or non-overbased) TBN calcium sulphonate; a low (or non-overbased) TBN calcium salicylate, or any combination thereof, wherein the at least two additives have a weight ratio ranging from 90:10 to 10:90.

10. The method of claim 9, wherein the blended cylinder oil composition has a TBN in the range of 1 TBN-15 TBN.

11. The method of claim 9, wherein calcium phenate has a TBN from 20 TBN to 250 TBN.

12. The method of claim 9, wherein the calcium phenate has a mole ratio of metal to phenate ranging from 0.2:1 to 1.5:1 for a Group IIA metal and ranging from 0.1:1 to 0.5:1 for a Group IIA metal.

13. The method of claim 9, wherein the calcium sulphonate has a TBN from 10 TBN to 300 TBN.

14. The method of claim 9, wherein the calcium sulphonate has a mole ratio of metal to phenate ranging from 0.1:1 to 2:1 for a Group IIA metal and ranging from 0.1:1 to 0.5:1 for a Group IIA metal.

15. The method of claim 9, wherein the calcium salicylate has a TBN from 10 TBN to 200 TBN.

16. The method of claim 9, wherein the calcium salicylate has a mole ratio of metal to phenate ranging from 0.1:1 to 2:1 for a Group IA metal and ranging from 0.1:1 to 0.5:1 for a Group IIA metal.

17. A method for operating a 4-stroke engine, comprising:

(a) producing a blended TPEO having a total base number (TBN) that is greater than 20 TBN by blending a base oil and at least one additive;

(b) operating the engine by exchanging a low sulfur fuel having a sulfur content ranging from 1.0 wt. % sulfur to 0.001 wt. % sulfur with a high sulfur fuel having a sulfur content ranging from 1.1 wt. % sulfur to 4.5 wt. % sulfur; and

(c) switching the engine lubricating system to the blended TPEO in accordance with the exchanging.

18. The method of claim 17, wherein the base oil is selected from the group consisting of system oil, used system oil, trunk piston engine oil, or used trunk piston engine oil.

19. The method of claim 18, wherein the at least one additive comprises at least one base.

20. The method of claim 19, wherein the at least one base comprises basic salts of alkaline or earth alkaline elements, and/or detergents and/or dispersants.

21. The method of claim 17, wherein the blended TPEO composition has a TBN in the range of 20-70 TBN.

22. The method of claim 17, wherein the low sulfur fuel corresponds to a Straight Vegetable Oil (SVO).

23. The method of claim 17, wherein the 4-stroke engine is operated on a marine vessel.

24. The method of claim 23, wherein said blending is performed on the marine vessel.

25. The method of claim 23, wherein said blending is not performed on the marine vessel.

26. The method of claim 17, wherein blended TPEO has a composition containing a base fluid of lubricating viscosity and a mixture of at least two of the following metal-organic detergent additives: non-overbased or overbased TBN calcium phenate; a non-overbased or overbased TBN calcium sulphonate; non-overbased or overbased TBN calcium salicylate, or any combination thereof.