Problems associated with fuel lubricity arose in the mid- 1960's when a number of aviation fuel pump failures occurred. After considerable research, it was realized that advances in the refining of aviation turbine fuel had resulted in the almost complete removal of the naturally occurring lubricating components from the fuel. The removal of these natural lubricants resulted in the seizure of fuel pump parts. By the mid-1980's, it seemed likely that a similar problem was imminent in diesel fuel pumps. Fuel injection pump pressures had been steadily increasing while there was also a growing concern to reduce the sulfur content of the diesel fuel. The desire to reduce the sulfur content of the diesel fuel, in an effort to reduce pollution, required the use of more rigorous fuel refining processes. It was determined that as refining processes became more stringent, the naturally occurring oxygen containing compounds and polyaromatics which contribute to diesel fuel's inherent lubricity were eliminated.
Environmental concerns have led to a need for fuels with reduced sulfur content, especially diesel fuels. However, the refining processes that are used to produce fuels with low sulfur contents also result in a product of lower viscosity and a lower content of other components in the fuel that contribute to its lubricity, for example, polycyclic aromatics and polar compounds. Furthermore, sulfur containing compounds in general are regarded as providing anti-wear properties and a result of the reduction in their proportions, together with a reduction in proportions of other components providing lubricity, has been an increase in reported failures of fuel pumps in diesel engines using low sulfur fuels.
This problem may be expected to become worse in the future because in order to meet stricter requirements on exhaust emissions, high-pressure fuel pumps are being introduced and are expected to have more stringent lubricity requirements than present equipment.
In certain types of in-line diesel injection pumps, engine oil contacts diesel fuel. Engine oil may also come into contact with the diesel fuel through direct addition of used engine oil to the fuel. Certain types of lubricity additives used in low sulfur diesel fuel have been found to contribute to fuel filter blockage and to pump plunger sticking. Lubricity additives having poor compatibility with engine oil have been shown to cause these problems. Compatibility is defined as the tendency for the diesel fuel containing the lubricity additive not to form fuel insoluble deposits, gels or heavy sticky residues when in contact with engine oil. These deposits, gels or residues have been shown to cause fuel filter blockage and injection pump sticking. The additives of the present invention are compatible with engine oil.
Mannich reaction products have been taught for use as detergent/dispersants in fuels, primarily gasoline, for years. The prior art Mannich reaction products typically contain high molecular weight alkyl groups on the hydroxyaromatic compounds. In contrast, the Mannich reaction products of the present invention are obtained from alkyl-substituted hydroxyaromatic compounds wherein the alkyl group contains from 9 to 30 carbon atoms.
U.S. Pat. No. 3,877,889 discloses Mannich bases useful as additives for liquid fuels to impart dispersancy, anti-icing and rust inhibiting properties. The reference fails to teach the use of said Mannich reaction products as lubricity additives in low sulfur compression ignition fuels.
U.S. Pat. No. 4,231,759 teaches reaction products obtained from the Mannich condensation of high molecular weight alkyl-substituted hydroxy aromatic compounds, amines and aldehydes for improving the detergency of liquid hydrocarbon fuels.
U.S. Pat. No. 5,853,436 discloses diesel fuel compositions containing a lubricity enhancing amount of a salt of an alkyl hydroxyaromatic compound and an aliphatic amine. These salts are different than the reaction products of the present invention.
While the prior art is replete with numerous treatments for fuels, it does not disclose the addition of the present additives to low sulfur compression ignition fuels or teach their use for providing enhanced lubricity to said fuels.