Unleaded aviation gasoline

Details Unleaded aviation gasoline Unleaded aviation gasoline

1994-09-26

2001-02-13

Johnson, Jerry D. (Department: 1721)

Fuel and related compositions

Liquid fuels

Aluminum or heavy metal, other than lead, containing

C044S449000

Reexamination Certificate

active

06187064

ABSTRACT:

This invention relates to unleaded aviation gasoline compositions which satisfy the specification requirements of ASTM Specification D 910-90. More particularly, this invention provides unleaded high octane aviation gasoline compositions which will operate as well as, if not better than, present-day aviation gasolines. Additionally, this invention accomplishes this exceptionally important advantage on an economical basis, while at the same time conserving worldwide petroleum resources.
The specifications imposed upon aviation gasolines are necessarily extremely rigorous. Use of an off-specification motor gasoline in a passenger car or truck can, at worse, result in poor engine performance, stalling, or other operational problem which, while annoying, are normally not life-threatening. In contrast, if an aviation gasoline does not perform properly in a spark-ignition aviation engine, the consequences could be disastrous.
While leaded aviation gasolines have performed wonderfully well in actual service for many years*, many misguided persons have clamored for elimination of lead from gasoline. If their efforts succeed, the refining industry will be faced with the problem of trying to provide unleaded aviation gasoline that performs as well as leaded aviation gasoline and that does not exceed the economic constraints of the marketplace.
* It may well be remembered that leaded aviation gasoline was deemed at least partially responsible for the successful Battle of Britain.
Besides providing aviation fuels having the necessary octane quality, a particular problem which exists when attempts are made to eliminate use of alkyllead antiknock compounds in aviation gasoline base fuels otherwise satisfying the specification requirements of aviation gasoline, is valve seat recession, especially in aviation piston engines that were designed and manufactured to operate on leaded fuels.
As pointed out in U.S. Pat. No. 4,659,338, the problem of exhaust valve recession has been observed heretofore in connection with tractors, automobiles, and outboard motors. The problem in automotive engines was specifically addressed in U.S. Pat. No. 3,955,938 through incorporation in unleaded motor gasoline of a gasoline-dispersible sodium additive. The patent describes results of road tests with a 1970 Chrysler passenger car and a 1970 Ford motor car operated on such fuels. However, according to U.S. Pat. No. 4,659,338, sodium salts of organic acids have a tendency to emulsify water into gasoline, and with some sodium salts and undesirable extraction of the sodium into the water occurs. The approach suggested in this latter patent for overcoming the exhaust valve recession or wear problem is to include in the gasoline the combination of at least one hydrocarbon-soluble alkali or alkaline earth metal-containing composition and at least one hydrocarbon-soluble ashless dispersant. This suggestion may prove useful in connection with operation of land-based vehicles. However, in view of the careful control that must be imposed on aviation gasolines as regards fuel volatility, vapor pressure, potential gum content, dispersed particulates, etc., it is not likely that such additive combinations will comply with current specifications for aviation gasoline usage.
Thus a need exists for a way of economically achieving the dual objectives of meeting the octane quality needed for aviation gasoline and preventing or at least inhibiting exhaust valve recession or wear during the operation of aviation engines on unleaded aviation gasolines.
This invention is deemed to fulfill the above need and overcome the above problems most expeditiously.
In accordance with this invention, there is provided an unleaded aviation gasoline composition which comprises a blend of hydrocarbons and at least one cyclopentadienyl manganese tricarbonyl compound dissolved therein in an amount such that said gasoline composition has a minimum knock value lean rating octane number of 100 as determined by ASTM Test Method D 2700 and wherein Motor Method octane ratings are converted to aviation ratings in the manner described in ASTM Specification D 910-90, said composition being further characterized by having: a) a distillation temperature as determined by ASTM Test Method D 86 of 10% evaporated, 167° F. maximum temperature; 40% evaporated, 167° F. maximum temperature; 90% evaporated, 275° F. maximum temperature; and a final boiling point of 338° F. maximum temperature; the sum of the 10 and 50% evaporated temperatures being 307° F. minimum; the distillation recovery being 97% minimum; the distillation residue being 1.5% maximum; and the distillation loss being 1.5% maximum; b) a heat of combustion as determined by ASTM Test Method D 1405 and as calculated from Table 1 thereof of 18,720 btu per pound minimum, or a heat of combustion as determined by ASTM Test Method D 2382 of 18,700 btu per pound minimum, the latter method controlling in case of a discrepancy therebetween; c) a vapor pressure as determined by ASTM Test Method D 323 or D 2551 of 5.5 psi minimum and 7.0 psi maximum; d) a copper strip corrosion as determined by ASTM Test Method D 130 of number 1, maximum; e) a potential gum (5-hour aging gum) as determined by ASTM Test Method D 873 of 6 mg per 100 mL maximum, or a potential gum (16-hour aging gum as determined by ASTM Test Method D 873) of 10 mg per 100 mL; f) a sulfur content as determined by ASTM Test Method D 1266 or D 2622 of 0.05% by weight maximum; g) a freezing point as determined by ASTM Test Method D 2386 of −72° F. maximum; and h) a water reaction as determined by ASTM Test Method D 1094 wherein the volume change, if any, does not exceed ±2 mL.
Base fuels meeting the foregoing specifications are routinely produced by a number of petroleum refiners. Virtually any major U.S. petroleum refiner has the existing capability of supplying base fuels meeting these specifications. Indeed, at airports all around the country, well known brands of leaded aviation gasolines made from base gasolines meeting these requirements are used to fuel piston-engine aircraft that operate on aviation gasoline. Most aviation gasolines currently contain the tetraethyllead antiknock mixture. Petroleum refiners could of course, eliminate the use of such tetraethyllead antiknock mixture and thereby provide the corresponding unleaded base fuel. No new technology would be required to produce such base fuels. However, such unleaded base fuels could not be used to safely operate aircraft powered by gasoline-engines—the octane quality of the fuel would be too low and the risk of valve seat recession or wear, especially in older aircraft currently in widespread use, would be too high. Accordingly, in the absence of this invention, elimination of the tetraethyllead mixture from aviation gasoline would be expected to necessitate significant changes in the refining and blending of aviation gasolines in order to achieve high enough octane quality to satisfy the octane requirements of aviation engines to be operated on such fuels. This in turn would most likely necessitate more rapid depletion of worldwide petroleum resources and result in marked increases in the cost of aviation gasolines. So far as is known, the present invention is the only economical way of providing aviation gasolines having the requisite octane quality to satisfy aviation engine requirements plus the added protection of decreased exhaust valve recession. At the same time, none of the current specifications on aviation gasoline base fuels and none of the current manufacturing and blending procedures for producing aviation gasoline base fuels would need to be changed.
Preferred gasoline compositions are those in which the gasoline composition additionally has a minimum performance number reported to the nearest whole number and as determined by ASTM Test Method D 909 of 130. In this connection, a minimum performance number of 130 is equivalent to a knock value determined using isooctane plus 1.28 milliliters of tetraethyllead per gallon.
Another embodiment of this invention provid

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