Source: {"pile_set_name": "USPTO Backgrounds"}

The existing fleet of general aviation spark ignition piston engines, as well as new engines currently being delivered, and engines which are overhauled for use as replacements on existing aircraft, typically operate using leaded fuels, as allowed in the United States under an exemption provided by the 1990 Federal Clean Air Act Amendments. As that Act banned the use of leaded fuels for over-the-road vehicles in the Unites States, general aviation aircraft engines have become an increasingly visible source of atmospheric lead emissions. Environmental regulations and threatened regulations throughout the world have thus spurred investigations into the development and evaluation of possible alternative aviation fuels.
Most of the general aviation spark ignition piston engines in use today have been certified in the United States by the Federal Aviation Administration (FAA) for use with leaded aviation gasoline blends that meet the American National Standard No. ASTM D910 entitled Standard Specification for Aviation Gasolines. Under that standard, for Grade 100 fuel, 1.12 grams of lead per liter are provided in the fuel blend. In the most commonly used fuel, Grade 100LL, known as a “low lead” fuel, 0.56 grams of lead per liter are provided in the fuel blend. Both of those blends provide a minimum “knock value” lean mixture octane number of 99.6 per the ASTM D-2700 Test Method. Also, both of those blends provide a minimum “knock value” rich mixture octane number of 130, per the ASTM D 909 Test Method.
Given the regulatory environment, both in the U.S. and internationally, that seeks to require the minimization or elimination of the use of lead in general aviation aircraft reciprocating piston engines, the US FAA has been instrumental in conducting tests on various heretofore proposed formulations for low lead or no lead aviation gasolines. Their reports are publicly available through the US National Technical Information Service (NTIS), Springfield, Va. 22161. Such studies include the following reports:                (1) DOT/FAA/AR-04/25, entitled Full-Scale Engine Knock Tests of 30 Unleaded, High-Octane Blends, by David Atwood and Julian Canizales, issued by the Office of Aviation Research, Washington, D.C., in September 2004;        (2) DOT/FAA/AR-TN07/5, entitled High-Octane and Mid-Octane Detonation Performance of Leaded and Unleaded Fuels in Naturally Aspirated, Piston Spark Ignition Aircraft Engines, by David Atwood, issued by the U.S. Department of Transportation, Federal Aviation Administration, in March 2007;        (3) DOT/FAA/AR-08/40, entitled Full-Scale Engine Detonation Tests of 47 Unleaded High Octane Blends, by David Atwood, issued by the Office of Aviation Research, Washington, D.C., in September 2008; and        (4) DOT/FAA/AR-08/53, entitled Full-Scale Detonation and Power Performance Evaluation of Swift Enterprises 702 Fuel, by David Atwood, issued by the Office of Aviation Research, Washington, D.C., in January 2009.        
The September 2004 FAA report describes how over 200 blends of potential future aviation unleaded fuels were considered. Thirty of those blends, ranging in Motor Octane Number (MON) from 96.2 to 105.6 were sufficiently promising to be blended into batches and knock-tested (as determined by ASTM D-2700 standard) in a Lycoming IO-540-K aircraft engine at the FAA William J. Hughes Technical Center in Atlantic City, N.J. Components of such blends included ranges of some (or of all) of various ingredients, including super alkylate, toluene, ethyl tertiary butyl ether, meta-toluidine, ethanol, and methylcyclopentiadienyl manganese tricarbonyl (MMT), which were blended into a base fuel of either aviation alkylate or motor alkylate. Importantly, the FAA researcher reported that the performance of many of the tested blends deviated from that suggested by either their MON or by their performance number (PN).
The March 2007 FAA report compared detonation performance of mid and high octane leaded and unleaded fuels. The fuels were compared at the onset of light detonation. The fuels were tested in a naturally aspirated Lycoming IO-540-K engine and in a naturally aspirated Lycoming IO-320-B engine. For testing, the motor octane number (MON) of fuels was determined by ASTM International (ASTM) specification D2700. The supercharge rich rating was determined by the ASTM D-909 standard. In general, the testing showed that the Grade 100LL fuel (with values minimally meeting the MON and Supercharge Rating of ASTM D910) significantly outperformed the matrix of tested unleaded fuels of equivalent MON, including even those with much higher ASTM Standard D-909 supercharge rich ratings, particularly as seen when operated on full scale aircraft engines rather than the laboratory test engines used to establish the ASTM Standard D-2700 MON and the D-909 rich rating performance number (PN). The March 2007 report indicates that the supercharge rich ratings do not appear to have the same significance for the matrix of unleaded fuels that were tested as they do for leaded hydrocarbon fuels. Based on the blends tested, the report clearly suggests that development of a better detonation performance unleaded aviation fuel would be desirable.
The September 2008 FAA report was a continuation of the research described in the September 2004 report. Based on the results of the 30 potential future aviation unleaded fuel blends earlier tested, another matrix of 47 unleaded fuel blends was developed and detonation tested in a Lycoming IO-540-K aircraft engine at the FAA William J. Hughes Technical Center in Atlantic City, N.J. Components of such blends included varying ranges of “high octane components” such as aviation alkylate, super alkylate, toluene, ethyl tertiary butyl ether (ETBE), meta-toluidine, tert-butylbenzene. The blends contained iso-pentane for volatility control. Comprehensive blend formulations, by both volume fractions and mass fractions of those fuel blends were reported in Tables 2, 3, 4, and 5 of that report. The blends with a target range of 97.6 to 106.3 MON were tested against a baseline leaded reference fuel that met all specifications of ASTM D910 for Grade 100LL fuel with minimum MON and minimum performance number (PN) per ASTM D-909. The blends were also tested against a 100LL aircraft fuel purchased at the local airport. Here, the FAA researcher reported that none of the unleaded blends of equivalent or lower MON performed as well as the Grade 100LL fuel in the detonation tests, particularly as seen when operated on full scale engines rather than the laboratory test engines used to establish the ASTM D-2700 MON and the ASTM D-909 rich rating performance number. It was also demonstrated that increased fuel flow of the unleaded blends was required above the fuel flow required for 100LL in order to achieve equivalent detonation performance. In short, the tested blends provided less detonation protection than leaded formulations of equivalent MON, and appeared to potentially be less efficient. Importantly, the researcher again reported that using only motor octane number (MON) based on ASTM D-2700 (for knock rating, lean mixture) to predict full scale engine performance of unleaded fuels, is inadequate.
The January 2009 report provides results of tests on a high octane, bio-fuel (fermentation based) composition identified as Swift 702 fuel, from Swift Enterprises of Indiana. Swift 702 fuel was separately reported by Swift Enterprises, Inc., assignee of U.S. Patent Application Publication No. 2008/0244961 A1, published on Oct. 9, 2008, as being eighty three percent (83%) by weight of mesitylene (also known as, and hereinafter identified by the chemical name 1,3,5 trimethylbenzene), and seventeen percent (17%) by weight of iso-pentane. The FAA similarly reported that the Swift 702 fuel consisted of two pure chemical compounds. The Swift 702 fuel was reported by the FAA to have a motor octane number (MON) of 104.4, as determined by ASTM D-2700. The Swift 702 fuel was detonation tested in a Lycoming IO-540-K aircraft engine used in the tests noted in the two reports above. Also, the Swift 702 fuel was tested in a turbocharged non-intercooled Lycoming TIO-540-J2BD aircraft engine. These two engines were reported by the FAA as having been previously determined as having the highest octane requirements of engines in the active general aviation fleet. The Swift 702 fuel provided slightly better detonation performance than Grade 100LL fuel that was purchased from the local airport aviation gasoline fixed base operator. However, it did not meet the 50%, 90%, and end distillation points of the then current ASTM D910 specification. And, the energy content was noted as being only ninety three point six percent (93.6%) of Grade 100LL on a mass basis. Such a reduction in energy content, in conjunction with the higher fuel density, will reduce the available payload of the aircraft for a given trip of a given range. In some cases, such a reduction will be unacceptable to the operator, and may require expensive re-certification of the aircraft. Thus, it would be desirable that any replacement aviation fuel more closely meet the presently existing ASTM minimum specifications with respect to energy content per unit mass of fuel, in order to minimize any potential loss of range or payload for an aircraft using such fuels. And, it would be desirable to provide a replacement aviation fuel that minimizes the quantity of 1,3,5 tri-methylbenzene that must be produced to provide sufficient unleaded fuel to the aviation marketplace, since such compound