1. Field of the Invention
The present invention relates to fuels, particularly gasoline fuels which are substantially free of oxygenates. More specifically, the present invention relates to a low-emission gasoline fuel which, upon combustion in a spark-ignited engine, provides surprisingly low emissions, particularly of nitrogen oxide emissions, and is also substantially free of oxygen-containing compounds.
2. Description of the Prior Art
One of the major environmental problems confronting the United States and other countries is atmospheric pollution caused by the emission of pollutants in the exhaust gases and gasoline vapor emissions from gasoline fueled automobiles. This problem is especially acute in major metropolitan areas where atmospheric conditions and the great number of automobiles result in aggravated conditions. While vehicle emissions have been reduced substantially, air quality still needs improvement. The result has been that regulations have been passed to further reduce such emissions by controlling the composition of gasoline fuels. These specially formulated, low emission gasolines are often referred to as reformulated gasolines. In California, low emissions gasoline is often referred to as California Phase 2 gasoline. One of the requirements of these gasoline regulations is that, in certain geographic areas, oxygen-containing hydrocarbons, or oxygenates, be blended into the fuel.
Congress and regulatory authorities, such as CARB (the California Air Resources Board), have focused on setting specifications for low emissions, reformulated gasoline. The specifications, however, require the presence of oxygenates in gasoline sold in areas that are not in compliance with federal ambient air quality standards for ozone, and the degree of non-attainment is classified as severe, or extreme. Among the emissions which the reformulated gasoline is designed to reduce, are nitrogen oxides (NO.sub.x), hydrocarbons (HC), and toxics (benzene, 1,3-butadiene, formaldehyde and acetaldehyde). A reduction in these emissions has been targeted due to their obvious impact upon the air we breathe and the environment in general.
There is increasing attention from environmental agencies regarding the need for a reduction in emissions of nitrogen oxides. NO.sub.x emissions are known precursors for smog created in metropolitan areas. Most of the NO.sub.x emissions are man-made, with gasoline fueled engines generating about 24% of the man-made NO.sub.x emissions. NO is the major constituent of NO.sub.x emissions from combustion processes. NO is a precursor of NO.sub.2 in the atmosphere and a critical constituent in the formation of ozone. NO.sub.2 can irritate the lungs and reduce respiratory function. NO.sub.x can be an important precursor to secondary formation of particulates, according to the "National Air Quality and Emission Trends Report," 1992, Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, EPA 454/R-93-031, October 1993. A reduction of nitrogen oxides, particularly in large metropolitan areas such as Los Angeles and Sacramento, Calif., and many eastern U.S. states, would be most valuable. As a consequence of all these harmful effects, the reformulated gasolines have been designed to reduce NO.sub.x emissions.
Oxygenated gasoline is a mixture of conventional hydrocarbon-based gasoline and one or more oxygenates. Oxygenates are combustible liquids which are made up of carbon, hydrogen and oxygen. All the current oxygenates used in reformulated gasolines belong to one of two classes of organic molecules: alcohols and ethers. The Environmental Protection Agency regulates which oxygenates can be added to gasoline and in what amounts.
The primary oxygen-containing compound employed in gasoline fuels today is methyl tertiary butyl ether (MTBE). While oxygen is in most cases required in reformulated gasolines to help effect low emissions, the presence of oxygenates in gasoline fuels has begun to raise legitimate environmental concerns. For example, the oxygenate methyl tertiary butyl ether has been observed in drinking water reservoirs, and in a few instances, ground water in certain areas of California. As a result, the public is beginning to question the benefits and/or importance of having cleaner burning gasolines, if they simply pollute the environment in other ways. Furthermore, oxygenates also have a lower thermal energy content than non-oxygenated hydrocarbons, and therefore reduce the fuel economy of gasoline fueled motor vehicles.
Thus, while some of the concerns with regard to gasoline fuels containing oxygenates, such as methyl tertiary butyl ether, could be overcome by further safe handling procedures and the assessment of present facilities to reduce the risk of any spills and leaks, there remains a growing public concern with regard to the use of oxygenates in gasoline fuels. In an effort to balance the need for lower emission gasolines and concerns about the use of oxygenates it, therefore, would be of great benefit to the industry if a cleaner burning gasoline without oxygenates could be made. A cleaner burning gasoline resulting in low NO.sub.x emissions would be of particular benefit to the environment in light of the increased attention to reducing nitrogen oxide emissions. The availability of such a gasoline, which contained substantially no oxygenates, would allow the public to realize the environmental benefits of low emissions, yet ease the concern of potential contamination of ground waters, and the environment in general, with oxygenates. Of benefit to the industry would also be such a low emission, gasoline which contained substantially no oxygenates and also offered more flexibility to refiners in blending the gasoline.
Accordingly, it is an object of the present invention to provide a gasoline fuel which can truly benefit the environment and offer good performance.
It is another object of the present invention to provide a gasoline fuel which provides good emissions, yet is substantially free of oxygenates.
Yet another object of the present invention is to provide a low-emission, substantially oxygenate-free gasoline fuel which exhibits surprisingly low NO.sub.x emissions when combusted in an automobile internal combustion engine.
Still another object of the present invention is to provide a gasoline fuel which provides good emissions and also permits more flexibility to refiners in blending the gasoline.
These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.