1. Field of the Invention
The present invention relates to diesel fuels, particularly low sulfur diesel fuels, containing additives which increase the lubricity while reducing the amount of smoke in the exhaust from diesel engines.
2. Description of the Related Art
The risk to human health and the environment because of diesel exhaust has been of increasing concern since the 1960's. These concerns came to a head in the late 1980's when Sweden took the first steps to address one of the major causes of automotive diesel exhaust emissions by imposing a tax on diesel fuel having a sulfur content of greater than 0.1%. Since 1993, environmental legislation in the U.S. has required that sulfur content of diesel fuel be less than 0.05%. The reduction in the sulfur content of diesel fuel has resulted in lubricity problems. It has become generally accepted that the reduction in sulfur is also accompanied by a reduction in polar oxygenated compounds and polycyclic aromatics including nitrogen-containing compounds which are responsible for the reduced boundary lubricating ability of severely refined (low sulfur) fuels. While low sulfur content is not in itself a lubricity problem, it has become the measure of the degree of refinement of the fuel and thus reflects the level of the removal of polar oxygenated compounds and polycyclic aromatics including nitrogen-containing compounds.
Low sulfur diesel fuels have been found to increase the sliding adhesive wear and fretting wear of pump components such as rollers, cam plate, coupling, lever joints and shaft drive journal bearings.
Thus, it would be desirable to increase the lubricity of diesel fuels by incorporating lubricity additives. It would also be advantageous if these additives would not increase and preferably decrease the amount of smoke and particulate content in the exhaust of diesel engines.