Global Heavy Duty Diesel (HDD) engine emission legislation requires stepwise reductions in NOx and particulate emissions between 1989 and 2009. Many diesel engine manufacturers are now incorporating into HDD engines an Exhaust Gas Recirculation (EGR) system that is operated in a condensing mode for at least a portion of the time the engine is operated (e.g., at least 10% of the time the engine is operated), and retarding engine timing to reduce NOx and particulate emissions. In engines provided with a cooled EGR system, the EGR stream is cooled below the dew point of NOx and SOx and injected back into the engine under positive pressure. Under such conditions, water vapor condenses with the NOx and SOx to produce high levels of nitric and sulfuric acids in the recirculated exhaust gas stream. Under such conditions, unacceptable increases in the kinematic viscosity (kv) of lubricating oil compositions have been observed, even in the presence of relatively low levels of soot (e.g., 3 mass % soot).
Lubricating oil compositions comprise a major amount of base oil and additives that improve the performance and increase the useful life of the lubricant. Nitrogen-containing dispersants are commonly used lubricant additives. The function of a dispersant is to maintain in suspension within the oil, insoluble materials formed by oxidation and other mechanisms during use of the oil, to prevent sludge flocculation and precipitation of the insoluble materials. Another function of the dispersant is to reduce the agglomeration of soot particles, thus reducing increases in the viscosity of the lubricating oil upon use. In the severe environment of an engine provided with a cooled EGR system, it has been found that soot induced viscosity increase, as measured in a “Mack T-11” test cannot be controlled by conventional dispersants, even when the amount of such conventional dispersants are increased. Therefore, compounds providing potent soot dispersing properties and crankcase lubricants providing improved soot dispersing performance, have been continuously demanded.
U.S. Pat. No. 1,815,022 to Davis (1931) discloses condensates of naphthalene and essentially linear chlorinated waxes formed by Freidel Craft alkylation of the naphthalene. Such compounds are described as functioning as wax crystal modifiers or lube oil flow improver (LOFI) additives and were added to oil to improve the cold flow characteristics thereof. These compounds have not been used for a number of years and, due to the high chlorine content, these compounds would be considered unsuitable for use in a modern passenger car, or heavy duty diesel motor oil formulations. In modern formulations, these compounds have been supplanted by fumarate/vinyl acetate copolymers or polymethacrylate-based LOFIs.
U.S. Pat. No. 4,708,809 to Davis describes a lubricating oil composition containing a phenolic compound of the formula:(R)a—Ar—(OH)bwherein R is a saturated hydrocarbon group having 10 or more aliphatic carbon atoms; a and b are each independently 1 to 3 times the number of aromatic nuclei present in Ar; and Ar is a single, fused or linked polynuclear ring moiety that is optionally substituted. It is alleged that the addition of a minor amount of such a compound to a lubricant composition that is mixed with fuel will lead to a reduction in piston ring sticking in a two cycle engine.
U.S. Pat. No. 6,495,496 to Gutierrez et al. describes nitrogen-containing low molecular weight Mannich base condensates of hydroxy aromatic compounds, an aldehyde and an amine that are useful as soot dispersants in lubricating oils.
U.S. Pat. No. 6,750,183 to Gutierrez et al. discloses certain oligomers useful as soot dispersants, which oligomers are defined by the formula:
wherein each Ar independently represents an aromatic moiety optionally substituted by 1 to 6 substituents selected from H, —OR1, —N(R1)2, F, Cl, Br, I, —(L—(Ar)—T), —S(O)wR1, —(CZ)x—(Z)y—R1 and —(Z)y—(CZ)x—R1, wherein w is 0 to 3, each Z is independently O, —N(R1)2 or S, x and y are independently 0 or 1 and each R1 is independently H or a linear or branched, saturated or unsaturated, optionally substituted, hydrocarbyl group having from 1 to about 200 carbon atoms; each L is independently a linking moiety comprising a carbon-carbon single bond or a linking group; each T is independently H, OR1, N(R1)2, F, Cl, Br, I, S(O)wR1, (CZ)x—(Z)y—R1 or (Z)y—(CZ)x—R1, wherein R1, w, x, y and Z are as defined above; and n is 2 to about 1000.