Gasoline Fuel Composition

This invention relates to fuel compositions, and more particularly to gasoline fuel compositions, and more particularly still, to unleaded gasoline fuel compositions containing an additive to reduce the wear on non-hardened, automotive exhaust valve seats, such as exhaust valve seats composed of cast iron.

Valve recession is the process whereby the exhaust valve seats in an internal combustion, four-stroke engine are worn away by metal-to-metal contact with the valves during high speed, heavy-load conditions. As the valve seat is worn away, the valve becomes recessed in the engine head which results in loss in valve lash to the point of poor seating, valve burning and substantial power losses. If the conditions continue, severe engine damage will result which can eventually cause engine failure.

Cars subject to valve seat recession are generally limited to cars built prior to 1971. After 1971, valve and valve seats in automotive engines were hardened by a heat-treating process which eliminated the problem. Pre-1971 and many post-1971 trucks also have non-hardened seats and are subject to valve seat recession with unleaded gasolines.

For years the automotive industry has recognized that alkyl lead antiknock compounds are effective additives for preventing exhaust valve seat wear. Apparently, lead oxide coats the valve seats, lubricating and protecting these surfaces. The protection offered by lead additives is sufficient even at concentrations as low as 0.1 grams (as Pb) per gallon of fuel. However, somewhere between about 0.075 and 0.1 grams per gallon, lead additives lose their effectiveness in preventing valve recession. Thus, for operation with "unleaded" fuels (i.e., those containing no more than about 0.05 grams of lead per gallon), it can be seen that the wear on the valve seat is greater than that for leaded fuels containing 0.1 grams per gallon or more of lead. In fact, the rate of valve recession can be as much as 25 to 50 times as great, and it has been reported (in U.S. Pat. No. 3,898,055 issued to Bray) that the exhaust valves in an engine operating at full load on unleaded fuel can "sink" or recess as much as 1 to 5 mm. in only 10 hours. Obviously, such excessive wear rates cannot be tolerated, and with leaded fuels being phased out due to governmental regulations, the need for a non-leaded gasoline additive to prevent valve recession is vital.

It is, of course, known that tricresyl phosphate is somewhat effective for this purpose, as reported, for example, in U.S. Pat. No. 3,807,794 issued to Kerley et al. and in SAE Paper No. 710673 by Kent and Finnegan entitled "The Effect of Some Fuel and Operating Parameters on Exhaust Valve Seat Wear" published in 1971. However, tricresyl phosphate has one major detrimental property which has prevented its use on a commercial scale, namely, that it is extremely toxic.

It is, therefore, an object of the present invention to provide an unleaded gasoline composition containing sufficient of a relatively non-toxic additive to prevent or reduce the wear associated with unhardened exhaust valve seats of internal combustion engines.

In the present invention, it has been found that excessive wear of exhaust valve seats in an internal combustion engine, such as an automotive engine, can be prevented when operating on low lead or unleaded gasoline fuels by introducing into the fuel an additive containing a gasoline-soluble amine salt of an acid of phosphorus or an ester thereof. Such additives are introduced into the fuel in an amount at least sufficient to reduce the wear rate of the exhaust valve seats as compared to the same fuel without the additive.

In the drawing are two graphs depicting data obtained from the experiments described in the Example hereinafter.

In FIG. 1 are shown the data relating to the amount of valve recession after 40 hours of engine operation with gasolines containing varying concentrations of an amine salt of an alkylacid ester of orthophosphoric acid.

FIG. 2 is a similar graph, but depicting the results obtained after 60 hours operation with the same additive.

The present invention is directed to overcoming or substantially reducing the valve recession phenomenon associated with the operation of an internal combustion engine running on unleaded gasoline fuel. In the invention, an additive containing one or more gasoline-soluble phosphorus compounds, typically and preferably having a relatively high boiling point, i.e., at or above 300.degree. C., is combined with the unleaded fuel prior to introduction into the combustion chambers of the engine. Preferably, the additive contains phosphorus only in compounds having a boiling point at or above 300.degree. C., said additive being introduced into the fuel so as to provide a concentration therein effective to reduce the rate of wear of the engine exhaust valve seats.

Among the phosphorus compounds useful in the invention are the gasoline-soluble amine salts of a phosphoric acid or ester thereof. Thus, the compound may, for example, be a partially or fully neutralized product between one or more organic amines and an acid of phosphorus, e.g., hydrophosphoric acid, metaphosphoric acid, pyrophosphoric acid, but preferably orthophosphoric acid. By "partially or fully neutralized," it is meant that the compound may have one or more, or, indeed, all, of the acidic hydrogen atoms associated with the phosphoric acid replaced with an organic ammonium cation. Hence in the usual case, wherein orthophosphoric acid or an organic orthophosphoric acid is the chosen acid, the resulting salt may have between one and three of the acidic hydrogen atoms of the orthophosphoric acid replaced with an organic amine or one or two in the case of the organic phosphoric acid.

The preferred phosphorus compounds for use in the invention are the gasoline-soluble amine salts of esters of orthophosphoric acid. Such compounds include salts which may be represented by one of the following two formulae: ##STR1## wherein R.sub.2, R.sub.3, and R'.sub.3 are the same or different organic radicals and R.sub.1, R.sub.4, R'.sub.4, R.sub.5, and R'.sub.5 are independently selected from the group consisting of hydrogen and organic radicals. (By "organic radicals," it is herein meant to include all radicals containing at least one carbon atom.) The organic radicals in the above two formulae may be either aliphatic or aromatic and may be either substituted or unsubstituted and may contain heteroatoms (i.e., oxygen, sulfur, or nitrogen), as desired. Additionally, the aliphatic radical may be acyclic or alicyclic or straight or branched chained, and may, for example, be a substituted or unsubstituted alkyl, alkenyl, or alkynyl group. Typically, when any of R.sub.1, R.sub.2, R.sub.3, R'.sub.3, R.sub.4, R'.sub.4, R.sub.5, and R'.sub.5 are organic radicals, said radicals independently contain between 1 and 50 carbon atoms, usually at least 3 carbon atoms and no more than 40 carbon atoms.

In the most preferred embodiment of the invention, the phosphorus compound is an amine salt of an alkylacid ester of orthophosphoric acid, with it being understood that such esters have one or two of the three acidic hydrogen atoms replaced by an alkyl group. Such compounds have a formula as set forth above in (I) or (II) wherein R.sub.1 is either hydrogen or an alkyl group, R.sub.2 is an alkyl group, and R.sub.3 and R'.sub.3 are organic radicals, but most preferably aliphatic radicals, and R.sub.4, R'.sub.4, R.sub.5, and R'.sub.5 are either hydrogen or an organic radical, with aliphatic radicals given preference over aromatic radicals and with hydrogen given preference over any organic radical. When R.sub.3, R'.sub.3, R.sub.4, R'.sub.4, R.sub.5, and R'.sub.5 are aliphatic radicals, they may be the same or different, acyclic or alicyclic, but usually contain at least 3 carbon atoms, preferably from 6 to 24 carbon atoms, and most preferably from 8 to 18 carbon atoms. Normally, when R.sub.3, R'.sub.3, R.sub.4, R'.sub.4, R.sub.5, and R'.sub.5 are aliphatic radicals, all carbon atoms bonded to the nitrogen atom will be saturated, with preference being given for R.sub.3, R'.sub.3, R.sub.4, R'.sub.4, R.sub.5, and R'.sub.5 being independently either an unsubstituted alkyl or alkenyl radical, although hydrogen is more preferred than either as to R.sub.4, R'.sub.4, R.sub.5, and R'.sub.5. It is also highly preferable, in this embodiment of the invention, that R.sub.2 be a branched chain alkyl group, preferably an unsubstituted branched chain alkyl group of at least 13 carbon atoms, usually from 13 to 16 carbon atoms; the same is true for R.sub.1, when R.sub.1 is selected to be an alkyl group. The branching in R.sub.1 and R.sub.2, in accordance with this embodiment of the invention, is most preferred to occur at a location other than on the carbon atom directly bonded to the oxygen atom of the above formula. In that case, the resulting compound may be termed an amine salt of a branched chain primary alkyl acid ester of orthophosphoric acid (or a primary alkyl phosphate neutralized with an amine), which compounds are more fully described in U.S. Pat. No. 3,228,758 issued to Bauer, herein incorporated by reference in its entirety. The compounds therein described fall within the most preferred for use in the present invention, with the best mode of the present invention being practiced when a primary amine is employed and the ester is a diester, i.e., when R.sub.4 and R.sub.5 of the above formula (I) are both hydrogen and both R.sub.1 and R.sub.2 are the described branched chain alkyl radicals.

The presently preferred additive for commercial application is sold under the designation DMA-4 by E. I. duPont de Nemours and Company. Although the exact composition of DMA-4 is believed to be proprietary, it is known that DMA-4 does conform to the above formula (I) wherein R.sub.1 and R.sub.2 each contain 16 to 33 carbon atoms, believed to be branched chain alkyl groups, R.sub.3 is an ethylhexyl group, believed to be 2-ethylhexyl, and R.sub.4 and R.sub.5 are both hydrogen.

Suitable amine salts for use in the invention may be prepared as the gasoline-soluble product of the reaction between an acid of phosphorus with one or more amines. However, in the preferred embodiment, wherein an amine salt of an organic phosphate (i.e., an amine salt of a phosphoric acid ester) is desired, such salts usually require a reaction between a phosphorus oxide, such as phosphorus pentoxide (P.sub.2 O.sub.5), with one or more alcohols to form a mono- or diester thereof, followed by neutralization with one or more amines, such as a primary, secondary, or tertiary amine. In preparing such salts, one may employ the stoichiometric amounts. In the case of a reaction involving P.sub.2 O.sub.5 with the alcohol followed by reaction with the amine, the stoichiometric molar ratio is 2:1:4, alcohol to P.sub.2 O.sub.5 to amine, when the monoester is desired, and 4:1:2 when the diester is desired. For reactions involving orthophosphoric acid, the stoichiometric molar ratio is 1:1:2, alcohol to acid to amine, for the monoester and 2:1:1 for the diester. Obviously, however, the use of stoichiometric amounts is not critical; one could use more or less than the stoichiometric amounts, with excess reactant remaining, which may or may not be desirable, depending upon individual circumstances. Methods of producing salts by the foregoing procedures are taught in greater detail in U.S. Pat. No. 3,228,758 issued to Bauer, U.S. Pat. No. 3,384,466 issued to Popkin, U.S. Pat. No. 2,863,742 issued to Cantrell et al., and U.S. Pat. No. 2,863,904 issued to Cantrell et al., all of which are herein incorporated by reference in their entireties. The preparation methods for the amine salts useful in the most preferred embodiment are taught in the Bauer patent, wherein it is disclosed that a primary alcohol containing a branched chain alkyl group of at least 13 carbon atoms is reacted with phosphorus pentoxide, using 2 to 4 moles of the alcohol to react with the phosphorus pentoxide, and with 3 moles providing roughly a 50--50 mixture of the di- and monoesters. The reaction may be effectuated over a 12-hour time period at 65.degree. C., following which the product is reacted at a temperature below 65.degree. C. with 2 moles of an amine, preferably a primary amine such as 2-ethylhexylamine, to produce a salt useful in the invention.

The fuels into which the phosphorus additive are introduced comprise low lead or unleaded gasoline and usually consist essentially of low lead or unleaded gasolines. Low lead and unleaded gasolines, by definition herein, contain less than 0.1 and no more than 0.05 gram lead (Pb) per gallon, respectively. The typical gasoline for use in the present invention finds use in any gasoline-powdered, spark-ignition, internal combustion engine, but particularly in automotive internal combustion engines. Such engines usually operate on gasolines having a boiling range between about 80.degree. F. and about 430.degree. F., preferably between about 90.degree. and 430.degree. F., and typically have motor (MON) and research (RON) octane numbers of at least 80 and 90, respectively, with such high octane numbers, of course, being provided herein without the use of lead compounds, such as tetraethylead.

The source of the gasoline is not critical; it may be derived from straight-run naphtha, alkylate gasoline, polymer gasoline, isomerized stocks, thermally or catalytically cracked hydrocarbon stocks, and hydrocracked and catalytically reformed stocks. In addition, the gasoline may be derived from a petroleum crude oil or from synthetically prepared oils, such as shale oil and oils derived from coal. The typical gasoline used in the invention contains olefins, generally in a proportion above about 5 percent by volume, oftentimes in a proportion above about 7 percent by volume.

In addition to the phosphorus additive described above, the gasoline may further contain any of a number of known non-leaded additives. Typical of such additives are anti-icing agents, detergents, demulsifiers, corrosion inhibitors, dyes, deposit modifiers, octane improvers, and dispersants.

The amount of the phosphorus additive introduced into the gasoline is that amount necessary to cause at least some reduction in valve recession for those engines employing unhardened exhaust valve seats, such as cast iron exhaust valve seats. It has been found, however, for the amine salt of an organic acid phosphate known as DMA-4, that at least 100 pounds of additive per thousand barrels of gasoline are needed to reduce the valve recession characteristics to levels similar to that achieved with leaded fuels. Preferably, however, at least about 160, and more preferably at least about 200 pounds of additive are utilized, with concentrations above about 750 pounds per thousand barrels not usually offering any increased benefit for increased amounts of additive. At present, the most preferred range is from about 200 to about 550 pounds per thousand barrels, with 275 pounds per thousand barrels being the presently contemplated commercial optimum.

For amine salt additives other than DMA-4, the amounts required will depend on their phosphorus content. That is to say, other amine salts of an acid or ester of phosphorus should be used in concentrations so as to provide the same amount of phosphorus as DMA-4. The equivalent phosphorus concentration (in grams phosphorus as P per gallon) for other additives to provide the same phosphorus content as for DMA-4 can be obtained by multiplying the values given above for DMA-4 by 5.454.times.10.sup.-4. For these other additives, the preferred levels, more preferred, etc., will be the equivalent as stated for DMA-4. Thus, for example, the commercial optimum for DMA-4 being 275 pounds of additive per thousand barrels of gasoline, the commerical optimum for other additives will be that amount which provides 0.15 grams of phosphorus (as P) per gallon.

The effectiveness of the described amine salts of organic phosphates for reducing exhaust valve seat wear when an automotive engine is operated on unleaded fuel is demonstrated in the following Example. The Example is provided to illustrate the invention, not to limit the invention as defined in the claims.

A Chevrolet automotive engine having a 350-cubic-inch displacement and also having new heads with unhardened exhaust valve seats was placed on a dynamometer test stand. Two carburetors were used with the engine, one feeding fuel to four cylinders and the other to the other four. This allows the engine to be run, with both the test fuel and a reference unleaded fuel, so that the wear on the exhaust valve seats could be measured and compared against that of the reference. The reference gasoline differs from the test feed only in that it contains no additive for reducing exhaust valve recession.

The test procedure is as follows. The engine is operated on an alternating two-step cycle taking 4 minutes to complete. The engine first idles for 36 seconds at 1,000 rpm and then runs at 3,000 rpm for 204 seconds with a load of 160 pounds (120 horsepower). This cycle is equivalent to operating an automobile at a speed of 80 miles per hour while pulling a trailer uphill. The test is stopped at 20, 40, and 60 hours of operation, and the valve recession of each exhaust valve is measured and the average is determined for the valves associated with the four cylinders running on the test fuel, and also for the reference. After each test to determine the effectiveness of a given additive, a new head with new exhaust valve seats was installed in the engine.

The foregoing test procedure was employed to test the following fuels:

(1) Unleaded fuels containing varying concentrations of DMA-4 additive, i.e., 69, 138, 275, and 550 pounds per thousand barrels, with the test at 275 pounds per thousand barrels being run twice;

(2) Leaded fuel containing 0.1 gram lead (Pb) per gallon; and

(3) Unleaded fuel containing tricresyl phosphate in a concentration so as to provide 0.3 gram phosphorus (P) per gallon of gasoline.

The data obtained from the experiment are shown in the following Table, with the data obtained at 40 and 60 hours being also shown graphically in FIGS. 1 and 2, respectively.

As the data in the table and the drawing clearly show, the DMA-4 additive is remarkably effective for reducting exhaust valve seat recession. Specifically, when the additive is used in concentrations above about 100 pounds per thousand barrels (0.05 gram of phosphorus per gallon), it is highly effective for reducing valve recession to levels equal to or better than that provided by 0.1 gram per gallon of lead. Similarly, the data show, at 550 pounds per thousand barrels of DMA-4 additive (0.3 gram phosphorus (P) per gallon), that DMA-4 clearly provides better protection than that offered by the equivalent dosage of phosphorus added as tricresyl phosphate.

In view of the foregoing, it is evident that the invention is capable of many alternatives, modifications, variations, and embodiments. It is intended to encompass within the invention all such alternatives, modifications, variations, and embodiments as fall within the spirit and scope of the following claims.