METHOD FOR REDUCING AND/OR CONTROLLING ABNORMAL GAS COMBUSTION IN A MARINE ENGINE OR A CONTROLLED-IGNITION ENGINE

Abstract

The present invention relates to the use of a copolymer (C) comprising repeat units corresponding to alkyl methacrylate monomers, said monomers comprising at least one or more monomer(s) (A), the same or different, selected from among (C6-C10) alkyl methacrylate monomers; one or more monomer(s) (B), the same or different, selected from among (C10-C18) alkyl methacrylate monomers, in a lubricant composition comprising at least one base oil for reducing and/or controlling abnormal gas combustion in an engine, preferably a marine engine or a controlled-ignition engine.

Claims

1. A method for reducing and/or controlling abnormal gas combustion in an engine comprising the addition in a lubricating composition comprising at least one base oil of a copolymer (C) comprising repeat units corresponding to alkyl methacrylate monomers, said monomers comprising at least: one or more monomer(s) (A), the same or different, selected from among (C6-C10) alkyl methacrylate monomers; one or more monomer(s) (B), the same or different, selected from among (C10-C18) alkyl methacrylate monomers, said monomers (B) differing from said monomers (A).

2. The method according to claim 1, wherein the copolymer (C) comprises repeat units corresponding to: monomers (A), the same or different, selected from among (C6-C10) alkyl methacrylate monomers; monomers (B), the same or different, selected from among (C10-C18) alkyl methacrylate monomers, said monomers (B) comprising at least one (C12) alkyl methacrylate monomer and/or at least one (C14) alkyl methacrylate monomer.

3. The method according to claim 1, wherein monomers (A) and monomers (B) represent at least 75 weight % of the total of monomers used to prepared copolymer (C), preferably they represent at least 90%, more preferably at least 95%, further preferably at least 97%, better still at least 99%, preferably at least 99.5 weight %.

4. The method according to claim 1, wherein the weight ratio of monomers (B) to monomers (A) is between about 99:1 and about 10:90.

5. The method according to claim 1, wherein monomers (A) are branched and are preferably 2-ethyl-hexyl methacrylate and/or monomers (B) are linear, preferably monomers (B) are a mixture of C10 alkyl methacrylate, C12 alkyl methacrylate, C14 alkyl methacrylate, C16 alkyl methacrylate, and C18 alkyl methacrylate.

6. The method according to claim 1, wherein copolymer (C) comprises units corresponding to C10 alkyl methacrylate, C12 alkyl methacrylate, C14 alkyl methacrylate, C16 alkyl methacrylate, C18 alkyl methacrylate, and C8 alkyl methacrylate monomers.

7. The method according to claim 1, wherein the lubricant composition comprises from 50 to 10000 ppm by weight of active material of copolymer (C) relative to the total weight of the composition.

8. The method according to claim 1, wherein the engine is a marine engine, preferably a pure gas or dual-fuel marine engine, two-stroke or four-stroke.

9. The method according to claim 1, for reducing the quantity of lubricant composition in the combustion chamber of the engine, preferably of the marine engine.

10. A method to reduce and/or control abnormal gas combustion in an engine, comprising the lubrication of the engine with a lubricating oil comprising: at least one base oil; at least one copolymer (C) such as defined in claim 1.

11. Method to reduce the quantity of lubricant composition in the combustion chamber of an engine comprising the lubrication of the engine with a lubricating oil comprising: at least one base oil; at least one copolymer (C) such as defined in claim 1.

12. Method to reduce and/or control abnormal gas combustion resulting from auto-ignition of the lubricant composition in an engine comprising the lubrication of the engine with a lubricating oil comprising: at least one base oil; at least one copolymer (C) such as defined in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0165] The invention is illustrated by the following examples that are nonlimiting.

[0166] FIG. 1 translates percentage pre-ignition by the lubricant as a function of intake temperature.

[0167] FIG. 2 translates the frequency of abnormal combustion as a function of intake temperature.

DETAILED DESCRIPTION OF AN EXAMPLE

[0168] The test for measuring the frequency of pre-ignitions of the gas mixture when using different lubricant compositions was conducted on a single-cylinder gas-powered engine comprising a combustion chamber with a bore size of 108 mm and stroke of 115 mm with a compression rate of 11.4, corresponding to a displacement of 1054 cm.sup.3 of the single cylinder.

[0169] The rotation speed of the single-cylinder engine was 1000 rpm. The chosen operating point was equivalent to an Indicated Mean Effective Pressure IMEP of 23 bar, corresponding to an application representing a heavy engine load.

[0170] The ignition system of the single cylinder gas engine used “open-chamber” spark plug technology so that it was possible to repeat the ignition command with precision on each engine combustion cycle. The single-cylinder gas engine was also fitted with a cylinder pressure sensor to measure the trend in pressure in the cylinder, to determine the maximum cylinder pressure values at each engine cycle and to calculate released energy during a combustion cycle.

[0171] Prior to the test for measuring abnormal gas combustion in the combustion chamber, a mixture was prepared composed of gas having a methane number equivalent to 70% and of air comprising nitrogen and oxygen with an excess air ratio (air/gas) of 1.6 compared with the stoichiometric ratio used for combustion of the gas.

[0172] To observe the effect of the lubricant on the phenomenon of abnormal combustion, the air/gas mixture was heated to a temperature of about 55° C. then gradually increased up to a maximum temperature of 110° C., and compressed to 3.6 bar when entering the single-cylinder gas engine.

[0173] The following compositions in Table 2 were tested.

TABLE-US-00002 TABLE 2 Comparative example Example of the invention Base oil (weight %) 89.08 87.08 Composition of — 2 weight % of a base oil copolymer (C) composition comprising 0.1 weight % of dry matter of copolymer (C) Additives 10.92 10.92

[0174] Copolymer (C) was obtained with the following protocol:

[0175] A four-necked flask, fitted with a stirrer, a condenser, a thermocouple and nitrogen purge, was charged with 645.5 g of water and 8.7 g of Aerosol®OT. Stirring was set at 200 rpm and the nitrogen purge set in operation. To the reaction mixture were added 240 g of C10-C18 alkyl methacrylate, 60 g of 2-ethylhexyl methacrylate and 129.9 g of acetone. The reaction medium was heated to 43° C. via a water bath adjusted at 45° C. When the reaction medium reached 43° C., 0.04 g of t-butyl hydroperoxide in 7.5 g of water were added. After 5 minutes, 0.29 g of sodium ascorbate dissolved in 7.5 g of water and 0.60 g of 0.25% solution of iron sulfate hexahydrate were added. Nitrogen purging was replaced by nitrogen inerting. The reaction was left to continue for 5 hours after which the reaction mixture was left to cool to room temperature and isolated.

[0176] Example 1. Experimental protocol for measuring the frequency of pre-ignitions by the lubricant before the ignition command of the single-cylinder gas engine, and the frequency of abnormal combustion generated by pre-ignition of the lubricant.

[0177] The effect of the lubricant on the phenomenon of abnormal combustion was determined on the single-cylinder gas engine by measuring the frequency of pre-ignitions due to the lubricant before the main ignition command of the engine, and the frequency of pre-ignitions by the lubricant generating a rise in cylinder pressure corresponding to abnormal combustion.

[0178] To determine the frequency of pre-ignitions due to the lubricant, the heat release rate was measured for each combustion cycle. The ignition command was repeatedly set at −4° crank angle (CA) before the top dead center. Therefore, for each cycle, each rise in heat release starting before −6° crank angle was counted as abnormal pre-ignition generated by the lubricant before the main ignition command of the engine. The test was started at an intake temperature of the air-gas premixture set at about 55° C. Throughout the test, the temperature was gradually increased until a pre-ignition event was observed. The total of these abnormal events, when related to the 15 000 combustion events recorded during the 30 minutes of each test, gave the frequency of abnormal pre-ignition generated by the lubricant before the main ignition command of the engine.

[0179] To determine the frequency of pre-ignition by the lubricant generating a rise in cylinder pressure corresponding to abnormal combustion, for each cycle the maximum pressure reached in the cylinder was measured. The test was started at an intake temperature of the air-gas premixture set at about 55° C. Throughout the test, the temperature was gradually increased until a pre-ignition event was observed. The operating point of the single-cylinder gas engine was determined and generated a normal maximum cylinder pressure of 80 bar. In the event of abnormal combustion, it was considered that the maximum cylinder pressure in the combustion chamber should exceed the limit of 120 bar so that the cycle could be counted as abnormal pre-ignition generated by the lubricant. The total of these abnormal events related to all 15 000 combustion events recorded during the 30 minutes of each test gave the frequency of abnormal pre-ignition generated by the lubricant.

[0180] This test allowed the evidencing inter alia of the effect of the lubricant on resistance to the phenomenon of pre-ignition of the air/gas mixture due to auto-ignition of the lubricant before the normal ignition command, and the effect of the lubricant on the intensity of the peaks of maximum cylinder pressure in the event of abnormal combustion, representing the energy released by abnormal combustion.

[0181] The lubricant compositions in Table 2 were tested.

[0182] The results given in FIG. 1 were generated from temperature conditions under which a phenomenon of abnormal combustion was initiated, and translate the intensity of the phenomenon of abnormal combustion.

[0183] The results given in FIG. 2 translate the temperature conditions on and after which there is onset of the phenomenon of abnormal combustion, and the frequency of onsets of this phenomenon over a given cycle.

[0184] In FIG. 1 the frequency of pre-ignition by the lubricant composition is measured. It can be seen that this percentage is decreased for the composition of the invention. In addition, it is observed that pre-ignition by the lubricant starts at higher temperatures for the lubricant compositions of the invention.

[0185] In FIG. 2, the frequency of abnormal combustion is measured as a function of the intake temperature of the air-gas premixture. It can be seen that the frequency is decreased for the composition of the invention i.e. the frequency of pre-ignitions, also called abnormal combustion, starts at a higher temperature contrary to the comparative composition.

[0186] Consequently, from the results in FIGS. 1 and 2, it is seen that the compositions of the invention allow both limitation of the onset of the phenomenon of abnormal combustion and limitation of the intensity thereof, contrary to the comparative composition.