Method for reducing piston deposits in a marine diesel engine

Abstract

A method of reducing the incidence of deposits on the pistons of a 4-stroke marine diesel engine during operation of the engine when it is fuelled with a marine residual fuel meeting the ISO 8217 2017 fuel standard for marine residual fuels and having a sulphur content of more than 0.1% and less than 0.5% by mass. The method includes the step of lubricating the engine using a lubricating oil composition comprising: a) at least 50% by mass, based on the mass of the composition, of an oil of lubricating viscosity; (b) 5 to 25% by mass, based on the mass of the composition, of an oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents; (c) 0.1 to 10% by mass, based on the mass of the composition of one or more oil-soluble or oil-dispersible ashless dispersants; and optionally, (d) 0.1 to 10% by mass, based on the mass of the composition of a polyalkylene-substituted succinic anhydride.

Claims

1. A method of reducing the incidence of deposits on the pistons of a 4-stroke marine diesel engine during operation of the engine when it is fuelled with a marine residual fuel meeting the ISO 8217 2017 fuel standard for marine residual fuels and having a sulphur content of more than 0.1% and less than 0.5% by mass, based on the mass of the fuel, the method comprising lubricating the engine using a lubricating oil composition comprising: (a) at least 50% by mass, based on the mass of the composition, of an oil of lubricating viscosity; (b) 5 to 25% by mass, based on the mass of the composition, of an oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, the or each oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent having a total base number of (TBN) as measured by ASTM D2896 of from 50 to 500 mg KOH/g; (c) 0.1 to 10% by mass, based on the mass of the composition of one or more oil-soluble or oil-dispersible ashless dispersants; and optionally, (d) 0.1 to 10% by mass, based on the mass of the composition of a polyalkylene-substituted succinic anhydride, wherein the lubricating oil composition provides the engine with reduced asphaltene agglomeration and/or reduced deposits on piston and ring assemblies, as compared with a lubricating oil composition lacking component (c) and/or component (d).

2. A method according to claim 1 wherein the marine residual fuel comprises one, or a mixture of two or more, residual refinery streams chosen from atmospheric tower bottoms, vacuum tower bottoms, light cycle oil, heavy cycle oil, fluid catalytic cracked cycle oil, fluid catalytic cracked slurry oil, thermally cracked residue, thermal tar, unfluxed tar, thermally cracked heavy distillate, Group I slack wax, deasphalted oil, thermally cracked kerosene gas-to-liquid wax, hydrotreated light cycle oil, hydrotreated heavy cycle oil, hydrotreated fluid catalytic cracked cycle oil, hydrotreated thermally cracked heavy distillates, hydrotreated bottoms, hydrocracker hydrowax and hydrotreated hydrocracker deasphalted oil.

3. A method according to claim 1 wherein the marine residual fuel consists essentially of one or a mixture of two or more residual refinery streams chosen from atmospheric tower bottoms, vacuum tower bottoms, light cycle oil, heavy cycle oil, fluid catalytic cracked cycle oil, fluid catalytic cracked slurry oil, thermally cracked residue, thermal tar, unfluxed tar, thermally cracked heavy distillate, Group I slack wax, deasphalted oil, thermally cracked kerosene gas-to-liquid wax, hydrotreated light cycle oil, hydrotreated heavy cycle oil, hydrotreated fluid catalytic cracked cycle oil, hydrotreated thermally cracked heavy distillates, hydrotreated bottoms, hydrocracker hydrowax and hydrotreated hydrocracker deasphalted oil.

4. A method according to claim 1 wherein the alkali metal or alkaline earth metal is calcium.

5. A method according to claim 1 wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents is present in an amount of from 6 to 20 mass %, based on the total mass of the composition.

6. A method according to claim 4 wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents is present in an amount of from 6 to 20 mass %, based on the total mass of the composition.

7. A method according to claim 1 wherein the one or more oil-soluble or oil-dispersible ashless dispersants comprises a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine.

8. A method according to claim 4 wherein the one or more oil-soluble or oil-dispersible ashless dispersants comprises a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine.

9. A method according to claim 5 wherein the one or more oil-soluble or oil-dispersible ashless dispersants comprises a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine.

10. A method according to claim 1 wherein the lubricating oil composition comprises (d) a polyisobutylene-substituted succinic anhydride.

11. A method according to claim 10 wherein the lubricating oil composition wherein said polyalkylene-substituted succinic anhydride is a polyisobutylene-substituted succinic anhydride.

12. A method according to claim 1 wherein the lubricating oil composition further comprises one or more anti-wear additives.

13. A method according to claim 12 wherein the one or more antiwear additives comprises a dihydrocarbyl dithiophosphate metal salt, preferably a zinc dihydrocarbyl dithiophosphate salt.

14. A method according to claim 1, wherein the asphaltene agglomeration is measured at ˜60° C. on compositions aged at ˜140° C. according to a Focused Beam Reflectance Method (FBRM) and reported as average counts per second over a ˜15-minute period, and wherein the piston and ring deposits are visually rated according to DIN 51349-3 on Top Land, 2.sup.nd Land, Groove 1, and Groove 2 after ˜60 hours in an engine running at full engine load and maximum rated speed under the conditions listed in Table 4.

Description

(1) The invention will now be described by way of example only.

(2) Lubricating oil compositions were prepared as shown in Table 1 below. Quantities given are in mass %, based on the total mass of the oil composition.

(3) TABLE-US-00003 TABLE 1 Component Oil 1 Oil 2 Oil 3 Disp 1 — 0.600 0.600 Disp 2 — 2.000 2.000 Det 1 3.755 3.755 3.755 Det 2 5.331 5.331 5.331 ZDDP 0.300 0.300 0.300 PIBSA — — 1.000 Gp II oil Balance Balance Balance

(4) The components used were are follows: Disp 1: a borated (1.3 mass % B) ashless dispersant being a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine, the polyisobutylene group having a number average molecular weight of 950. Disp 2: a non-borated ashless dispersant being a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine, the polyisobutylene group having a number average molecular weight of 2225. Det 1: a calcium salicylate detergent having a TBN as measured by ASTM D2896 of 350 mg KOH/g and a calcium content of 12.5 mass %. Det 2: a calcium salicylate detergent having a TBN as measured by ASTM D2896 of 225 mg KOH/g and a calcium content of 8 mass %. 1

(5) ZDDP: a zinc dialkyldithiophosphate where the 60% of the alkyl groups are 1° C.sub.4 groups and 40% are 1° C.sub.5 groups, and the zinc content is 8.8 mass %. PIBSA: a polyisobutylene-substituted succinic anhydride where the polyisobutylene group has a number average molecular weight of 950. Gp II oil: an API Group II mineral oil.

(6) The lubricating oil compositions were evaluated for asphaltene dispersancy using the Focused Beam Reflectance Method (FBRM). This technique provides a measurement of asphaltene agglomeration and so is indicative of the tendency of the lubricating oil to form piston deposits when used to lubricate an engine.

(7) The FBRM test method utilises a fibre optic probe. The tip of the probe contains an optic which focuses the laser light to a small spot. The optic is rotated so that the focussed beam scans a circular path over a window, past which the oil sample to be measured flows. As asphaltene particles in the oil flow past the window they intersect the scanning light path and backscattered light from the particles is collected. The scanning laser beam travels much faster than the particles which means that relative to the light, the particles are effectively stationary. As the focussed beam intersects one edge of a particle, the amount of backscattered light collected increases, decreasing again as the beam reaches the other edge of the particle. The instrument determines the time period over which increased backscattered light is detected. Multiplying this time period by the scan speed of the laser provides a distance. This distance is a chord length as it is the length of a straight line between two points on the edge of a particle. The FBRM technique measures tens of thousands of chord lengths per second so provides a chord length distribution, usually expressed in microns. An accurate measure of the particle size distribution of asphaltene particles in the sample is thus obtained.

(8) The FBRM equipment used was model Lasentec G400 supplied by Mettler Toledo, Leicester, UK. It was configured to give a particle size resolution of between 1 μm and 1 mm. data obtained can be presented in several ways but our studies have shown that the average counts per second can be used as a quantitative measure of asphaltene dispersancy. This value is a function of both the average particle size and the degree of agglomeration.

(9) Five different marine residual fuels were used. These are detailed in Table 2 below.

(10) TABLE-US-00004 TABLE 2 Sulphur content Asphaltene content (mass %) (mass %) Fuel 1 1.9 32.11 Fuel 2 2.5 24.70 Fuel 3 1.2 12.75 Fuel 4 0.47 15.25 Fuel 5 0.47 21.76

(11) Fuels 1-3 are examples of marine residual fuels which meet the current regulations for such fuels in that they have sulphur contents which are below 3.5 mass % and meet the ISO 8217 2017 fuel standard for marine residual fuels. These fuels will not be able to be used after 1 Jan. 2020 unless the ships in which they are used are fitted with appropriate exhaust gas cleaning systems.

(12) Fuels 4 and 5 are examples of marine residual fuels which will be able to be used after 1 Jan. 2020 as they have sulphur contents which are below 0.5 mass %. They also meet the requirements of the ISO 8217 2017 fuel standard for marine residual fuels.

(13) It is noteworthy that both higher sulphur-content fuels and low sulphur-content fuels have appreciable and similar asphaltene contents. Asphaltene content was determined by the ‘pentane in-solubles’ method set out in Appendix X1 of ASTM D2007-11.

(14) As a first step, individual samples (880 g) of each of the lubricating oil compositions detailed in Table 1 were artificially aged by heating to 140° C. with stirring in a multi-necked, flat-bottomed flask and passing air through the oil through sintered glass tubes at a flow rate of 45 litres/hour for 48 hours.

(15) Individual samples (49.5 g each) of the lubricating oil compositions aged as above were then heated to 60° C. and maintained at that temperature while being stirred. Weighed samples (9.90 g) of each of the fuels listed in Table 2 were added to each oil sample. The FBRM probe was inserted into each mixture and measurements collected for 15 minutes. The results obtained, expressed as average counts per second are detailed in Table 3 below. Each data point is the average of two individual measurements on each sample.

(16) TABLE-US-00005 TABLE 3 Fuel 1 Fuel 2 Fuel 3 Fuel 4 Fuel 5 Oil 1 18126 31370 1324 101.4 48280 Oil 2 34282 47583 2899 61.6 10854 Oil 3 31341 41651 1750 50.4 3801

(17) A distinct pattern of behaviour was evident for the fuels having a high sulphur-content (Fuels 1-3). Comparing results for Oil 1 and Oil 2, it is clear that the addition dispersant greatly reduced the ability of the oil to disperse asphaltenes, evidenced by the large increase in the average counts per second recorded. Some improvement was seen on the further addition of PIBSA (compare Oils 2 and 3) but the performance of Oil 3 was still significantly worse in each case than Oil 1.

(18) An equally distinct but contrasting trend was seen for the fuels with a low sulphur-content (Fuels 4 and 5). Here, the addition of dispersant (compare Oil 1 and Oil 2) led to a marked increase in the ability of the oil to disperse asphaltenes, behaviour which was further improved by the addition of PIBSA (compare Oils 2 and 3).

(19) These data illustrate that the method of the present invention enables a reduction in the incidence of piston deposits in a 4-stroke marine diesel engine when run on a residual fuel which is compliant with the upcoming IMO 2020 regulation.

(20) Oils 1, 2 and 3 as described in Table 1 above, were evaluated for cleanliness performance using a Ricardo Atlas II 4-stroke single cylinder medium speed engine. Each was 60 hours in duration, running at full engine load and maximum rated speed under the following conditions:

(21) TABLE-US-00006 TABLE 4 Feature Bore 159 mm Stroke 159 mm Power @ rated speed  71 kW @ 1500 rpm Torque @ speed 452 Nm @ 1500 rpm BMEP 18 bar Cylinder pressure 160 bar

(22) This test provides a measurement of the capability of lubricant to prevent deposition. A commercial very low sulphur heavy fuel oil (VLSFO) meeting the RMG380 specification was used for these tests (Fuel 6). It had a sulphur content below 0.5 mass % and met the requirements of the ISO 8217 2017 fuel standard for marine residual fuels.

(23) TABLE-US-00007 TABLE 5 Sulphur content Asphaltene content (mass %) (mass %) Fuel 6 0.49 15.65

(24) Upon test completion the upper areas of the piston and ring assembly were visually rated (via DIN 51349-3) for deposit that had formed during operation. Results are given in Table 6.

(25) TABLE-US-00008 TABLE 6 Top 2.sup.nd Groove Groove Total Deposits Land Land 1 2 (points) Oil 1 19.75 43.65 −3.70 8.00 67.70 Oil 2 24.90 41.65 −1.80 12.25 76.80 Oil 3 27.70 54.60 −4.50 14.45 92.25

(26) Comparing results for Oil 1 with Oil 2 and Oil 3, it is clear that the addition of dispersant reduced deposit levels in the engine when run using a marine residual fuel having a sulphur content below 0.5 mass % and meeting the requirements of the ISO 8217 2017 fuel standard for marine residual fuels.