US2863743A - Motor fuel - Google Patents

Description

United States Patent C) cc MOTOR FUEL John P. Pellegrini, Jr., Blawnox, and Helen I. Thayer,

Pittsburgh, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., aco'rporatiori of Delaware No Drawing. Application November 27, 1953 Serial No. 394,871

5 Claims. (Cl. 4469)' at high compression ratios, it has generally been necessary to employ a fuel having a high octane number. To obtain a high octane number most fuels require'the addi tion of an anti-knock agent such as tetraethyl lead. While the addition of tetraethyl lead to gasoline improves its octane number, the resulting fuel has" certain disadvantages arising from the presence of the lead. One of the chief objections to the use of leaded-fuels arises from the tendency of the fuel upon being burned to form lead deposits on the walls of the combustion chamber of-the engine and on the terminals of; the spark plugs, thus reducing the efficiency of the engine. The net effect of these deposits 'is that the octane number requirement of the engine gradually increases as the engine is operated until someequilibrium octane requirement is reached. The equilibriumoctane number requirement of some engines which have been in operation for 100 or more hours may be 50 to 60 percent higher than the octane number requirement of'the same engines at the start of their operation.

In an attempt to overcome the detrimental effect of the lead deposits in an engine, various scavenging agents have been added to the fuel to change the form of the lead deposit to-one which is'less-detrimentalr For example,-various volatile alkyl halides such as ethylene dibromide and/or ethylene dichloride have been used withthe' result that the lead deposits have :com'prised the bromides of lead is frequently evidenced by' engine knocking. The knocking thus encountered isthatre sulting from the initiation of a flame front at anypoint in the fuel-air mixture prior to the regularly-timed spark ignition. knocking due to explosive autoignition ofthe unburned portion of the fuel-air mixture to be traversed by the normal flame from the spark plug.

We have discovered that a motor fuel and particularly leaded-gasoline canbe improved with respect to its tendenc'y to preignite in anengine and that the octanenumber requirement of an engine in which his used can 'be lowered by incorporating in the fuel a small amount of an organo-phosphoramide having the following structural formula:

The adverse effect encountered asa result of the deposits of the chl'orides and This knocking should not be confused with 2,863,743 Patented Dec. 29, 1958 Ind where R is a substituent selected from the class consisting of an alkyl group and hydrogen. Specific examples of the alkyl radicals which we intend to include are methyl; ethyl; propyl; isopropyl; butyl; sec-butyl; amyl; hexyl; heptyl; octyl; nonyl; decyl; undecyl; dodecyl; tridecyl; tetradecyl; pentadecyl; hexadecyl; heptadecyl; octadecyl; and the like. I

While all the compounds designated by the above structural formula can be used to produce a motor fuel having improved preignition characteristics, it. will be understood, of course, that their effectiveness may vary.

The alkyl-phosphoramides are particularly advantageous for use in the motor fuels of our invention. While compounds wherein the R group is a long-chain alkyl radical such as octyl, nonyl, decyl, octadecyl, and the like can be employed, we prefer, for economic reasons, to use those alkyl-phosphoramides wherein the alkyl group contains from 1 to 4 carbon atoms; For example, we prefer to employ the methyl, ethyl, propyl and butyl phosphoramides. Hexamethylphosphoram'ide has been found to be particularly elfective'in reducing the preignition'characteristics of a gasoline normally tending to preignite in 'the combustion chamber of a spark-ignition engine.

Hexamethylpho-sphoramide hasalso been found to be effective in reducing the octane number requirement of an engine.

Specific examples of other compounds comingwithin the above structural formula and which can be used to produce an improved motor fuel are N,N,N"-trimethylphospho-ramide; N,N,N"-triethylphosphoramide; N,N,N'- triisopropylphosphoramide; and N,N',N"-trime'thyl-N,N', N"-tributylphosphoramide.

While any single organo-phosphoramide can be used in'c'onjunction with a motor fuel to produce the improved fuels of our invention; it should be understood that mixtures of two or more organo-phosphoramides'canbeused. For example, a mixture of trimethylphosphorarnideand hexamethylphosphor'amide can be used instead of either one of these compounds alone. Therefore, when the term organo-phosphoramide is us'edhereiii and 'in'the appended claims, it will be understood that'one or more organo-phosphoramides is intended. g,

The amount of the organo-pho'sphoramide 'which is incorporated in the fuel depends 'to" some extent upon the'particular fuel employed, aswell as the particular organo-phosphoramide selected. In general, the amount is based upon that amount theoretically required toconv ert the lead introduced-into the fuel in the form of tetraethyl lead to lead orthophosphate. While improved resnlts'can be obtained with very small'amounts, amounts corresponding to at least about 0.1 times that theoretically required are preferred. Especially good results are obtained by the use of at least about 0.2 times the theoretical amount required. In generaL'itis notnecessaryto employ more. than 1.5 times the amount theoretically required. Amounts greater than 1.5 times the theoretical amount can be employed, but for economic reasons, We prefer to use only the amount required to give the desired improvement. Therefore, we prefer to employ an amount equal to about 0.2 to about 1.5 times that theoretically required to convert the' lead to lead orthophosphate. In view of the fact that the amount of tetraethyl lead in the gasoline varies from one fuel to another, it is difficult to state on a weight basisthe amount of organo-phosphoramide based upon the Weight of gasoline. However, once knowing the amount of tetraethyl lead present in the gasoline, it is an easy matter to calculate the amount of the organo-phosphoramide required. Most gasolines on the market today contain up to about three cubic centimeters of tetraethyl lead per gallon of gasoline. Based upon fuels containing up to about three cubic centimeters of tetraethyl lead per gal- Ion of gasoline, we have determined that the amount of organo-phosphoramide required in accordance with our is that the molecular weight of one compound may be twice the molecular weight of another compound, so that to get an equivalent amount of phosphorus when using the compound having the greater molecular weight, one is required to use twicethe amount of compound on a weight basis. In any event, the amount of organo-phosphoramide used is sufficient to inhibit or substantially prevent preignitionof a gasoline normally tending to preignite in the combustion chamber of an engine.

The motor fuel to which the organo-phosphoramide is added can comprise a mixture of hydrocarbons boiling in the gasoline boiling range. For instance, the gasoline employed can be either a straight-run gasoline or a gasoline obtained from a conventional cracking process, or mixtures thereof. The gasoline to which the organophosphoramide is added in accordance with our invention can also contain components obtained from processes other than cracking, such as alkylation, isomerization, hydrogenation, polymerization, hydrodesulfurization, hydroforming, Platforming, or combinations of two or more of such processes, as well as synthetic gasoline obtained from the Fischer-Tropsch and related processes.

In addition to the organo-phosphoramide, the motor fuel can contain other additive agents including oxidation inhibitors, anti-rust, anti-knock and anti-freeze agents, metal deactivators, dyes, and the like. When the anti-knock agent is an organo-metallic composition such as tetraethyl lead, the motor fuel may also contain a lead scavenging agent such as a volatile alkyl halide or a mixture of volatile alkyl halides such as ethylene dichloride and/ or ethylene dibromide. When these halides are used they are ordinarily present in an amount corresponding to about one or two cubic centimeters per gallon of gasoline. As the amount of tetraethyl lead used goes down, however, the lead scavenging agent required also decreases. In accordance with our invention, the organo-phosphoramide can replace in whole or in part the volatile alkyl halide lead scavenging agent. However, the organo-phosphoramide can be used in conjunction with the usual amount of volatile alkyl halide without deleteriously affecting the beneficial effects of the organo-phosphoramide.

The organo-phosphoramides present no particular problem when it comes to adding them to the gasoline. While the organo-phosphoramide can be added directly to the gasoline, one convenient method of adding it to the fuel is by forming a concentrate thereof, thereafter adding the concentrate to the fuel. Thus, a gasoline-benefiting concentrate can be formed by admixing an organo-metallic anti-knock composition with an organo-phosphoramide. In some instances, it may be desirable to employ a mutual solvent. Any solvent which does not adversely affect the desirable properties of the fuel can be used. The concentrate can, of course, contain other additive agents such as an oxidation inhibitor, an anti-rust agent, an antiknock agent, an anti-freeze agent, a metal deactivator, a scavenging agent and a dye. When the anti-knock agent is an organo-metallic composition, such as tetraethyl lead, the scavenging agent can comprise a mixture of ethylene dibromide and ethylene dichloride. Since the amount of organo-phosphoramide required depends to some extent upon the amount of the organo-metallic anti-knock composition, this-method of adding the organo-phosphoramide to the gasoline serves as a convenient way of adding the correct amount. Thus, a

son for this is that the effectiveness of the compounds varies from one compound to another. Another reason gasoline-benefiting concentrate can be made by admixing tetraethyl lead with an alkyl-phosphoramide wherein the alkyl-phosphoramide is present in an amount between about 0.1 and 1.5 times the theoretical amount required to convert the lead to lead phosphate.

In order to illustrate the decrease in octane number requirement for an engine when operating with an improved gasoline in accordance with this invention, octane rating tests were made in a single-cylinder engine. The engine installation used was a modification of the standard ASTM assembly as described in the laboratory knockrating test procedure CRC designation F-1-545 and CRC designation F2545. These tests are described in the CRC Handbook, 1946 edition, compiled by the Coordinating Research Council, Incorporated. The engine assembly was modified to the extent that the Waukesha CFR engine was equipped with an L-head cylinder instead of an overhead valve.

The engine was operated on a cycling schedule alternating between the following conditions:

AirzFuel Ratio Ignition Timing Coolant Temperature, "F Oil Temperature, "F Carburetor, Intake Air, Humidity Control :1:5: Ice Tower... Ice Tower.

1 TDC=Top Dead Center.

In carrying out these tests, octane number requirements were recorded at the beginning of each test when the engine was clean and then periodically until the octane requirement had reached an equilibrium point. Table I sets forth the data obtained when the engine was operated with a reference gasoline containing about three cubic centimeters of tetraethyl lead per gallon of gasoline and the same leaded-gasoline containing 1.5 grams of hexamethylphosphoramide per gallon of gasoline. The amount of hexamethylphosphoramide employed corresponded to about 0.73 times that theoretically required to react with all of the lead present to form lead phosphate. In each case, the gasoline also contained a small amount of an antioxidant, a metal deactivator, a lead scavenging agent, and a dye.

Table I Engine Octane Requirement 1 Reference Gasoline 1 Research method.

The above data show that the equilibrium octane re- -quirement of a single cylinder CFR engine employed in the test was about 88 whenoperating with the reference gasoline and about 68 when operating with the reference gasoline containing 1.5 grams of hexamethylphosphoramide per gallon of gasoline. Thus, the equilibrium octane requirement of the engine operating with the improved gasoline was about 20 numbers below the requirement of the same engine operating with unimproved gasoline. Table II gives the inspection data on the gasolines used in the engine octane number requirement test.

In order toIillu'strate the improved results with respect to preignition,'.a;test-waswemployedin which the fuel was burned in a stationary Cadillacv engine having a 9:1 compression'ratio. The'en'gine conditions'at the time of the preignition evaluation'we're"as'follows:

, Speed 1,000 and 2,000 R..P. M.

"Spark advance 10.

AirzFuel ratio 111521 and 10.3:1 at 21,000 and 2,000-R. P.

M., respectively.

In this test the load and throttle position are varied, dependent upon when preignition is encountered. At the start of the test the engine is under no load. The throttle is gradually increased until preignition is observed. If full throttle is reached without preignition, the engine is operated at full throttle for 30 seconds or less if preignition occurs sooner. If preignition is not encountered after 120 hours (5 days), the test is usually discontinued. The data set forth in Table III was obtained when the Cadillac engine was operated under the above test pro cedure with a reference gasoline normally tending to preignite containing about 1.5 cubic centimeters of tetraethyl lead per gallon of gasoline and the same leadedgasoline containing 1.0 (1.1 times the theory) gram of hexamethylphosphoramide per gallon of gasoline. In each instance, the gasoline also contained a small amount of an antioxidant, a metal deactivator, and a lead scavenging agent.

It will be noted from the data in Table III that the engine operating on the reference gasoline showed mild preignition Within 48 hours and that violent preignition occurred within 72 hours. When the same engine was operated with the improved gasoline of the invention, there was no preignition even after 100 hours of operation. After 120 hours of operation with the improved fuel, only mild preignition was observed.

Table IV gives the inspection data on the gasolines employed in the preignition test.

Upon examination of the engine after operation with the reference gasoline and the reference gasoline containing hexamethylphosphoramide, it was observed that the engine deposits were dissimilar in many respects.

The engine deposits resulting from .using the reference igasoline wereIbrownish-bla ck in color,.had a tendency to adhere to metal surfaces and, when scrapedlfrom metal csurfaces were .inclinedto peel off in the form of flakes.

The engine deposits resultingffrom using the reference gasoline containing hexamethylphosphoramide, however, were light-colored, powdery, and were removed from the metal surfaces vupon which they hadbeen deposited with :llittle :difliculty.

In each of the preignition testsdescribedabove, when using thezreference,gasolineand the samegasoline con- .taininghexamethylphosphoramide, the combustion cham- .bers and .spark .plugs of thezCadillac engineat the st-art .ofrthetest were substantially free from deposits giving rise to preignition. In order to illustrate the effect of the improved motor fuel of the invention on an engine in which preignition has already commenced, the above test was repeated with the exception that when deposit-induced preignition was encountered when using the reference gasoline, the fuel was changed to the gasoline containing hexarnethylphosphoramide without shutting down the engine. Thus, when violent preignition was encountered with the reference gasoline at 72 hours, the fuel supply was switched to the same gasoline containing 1.0 gram of hexamethylphosphoramide. While the violent preignition did not subside immediately, probably because of the deleterious deposits laid down by the reference gasoline, there was a gradual improvement. For instance, at the end of 16 hours of operation with the fuel containing hexamethylphosphoramide, the engine was still violently preigniting. However, at the end of 39 hours only mild preignition was encountered and at the end of 77 hours no preignition was encountered. Even after 101 hours of operation no preignition was evidenced. However, when the engine was switched back to the reference gasoline, mild preignition was encountered within 22 hours and violent preignition occurred within The improved results obtained wtih a motor fuel of the invention are thus quite strikingeven'when starting with an engine in which preignition has already been encountered. While our invention is described above with reference to various specific examples and embodiments, it will be understood that the invention is not limited to such examples and embodiments and may be variously pracfrom 1 to 4 carbon atoms.

2. A motor fuel having improved preignition qualities comprising a major amount of gasoline containing about 1 to about 3 cubic centimeters of tetraethyl lead per gallon of gasoline, a lead scavenging amount of a halo-hydrocarbon and between about 0.001 and about hydrocarbon and between about 0.1 and 1.5 times the theoretical amount of hexamethylphosphoramide required to convert the lead to lead phosphate.

4. A gasoline preignition improving additive comprising a major amount of tetraethyl lea-d containing a lead scavenging amount of a halohydrocarbon and an alkyl-phosphoramide in an amount between about 0.1 and 1.5 times the theoreticalamount required to convert the I lead to lead phosphate, wherein the alkyl group in said 4.0 percent by weight based on the gasoline of hexa- 26 methylphosphoramide.

3. A motor fuel having improved preignition qualities comprising a major amount of gasoline containing about 1 to about 3 cubic centimeters of tetraethyl lead per gallon of gasoline, a lead scavenging amount of a haloalkyl-phosphoramide contains from 1 to 4 carbon atoms.

5. A gasoline preignition improving additive comprising a major amount oftetraethyl lead containing a lead scavenging amount of a halohydrocarbon and hexamethylphosphoramide in an amount between about 0.1 and 1.5 times the theoretical amount required to convert the lead to lead phosphate.

References Cited in the file of this patent UNITED STATES PATENTS Campbell Aug. 13, 1946 Yust et a1. Oct. 2, 1956 FOREIGN PATENTS Great Britain Nov. 26, 1952 OTHER REFERENCES Aviation Spark Plug Fouling, Its Cause and Control, by V. E. Yust and E. A. Broegemueller, published by the Society of Automotive Engineers, Inc., 29 West 39th St., N. Y. 18, N. Y.

Claims (1)

1. A MOTOR FUEL HAVING IMPROVED PREIGNITION QUALITIES COMPRISING A MAJOR AMOUNT OF GASOLINE CONTAINING ABOUT 1 TO ABOUT 3 CUBIC CENTIMETERS OF TETRAETHYL LEAD PER GALLON OF GASOLINE, A LEAD SCAVENGING AMOUNT OF A HALO-HYDROCARBON AND BETWEEN ABOUT 0.1 AND 1.5 TIMES THE THEORETICAL AMOUNT OF AN ALKYL-PHOSPHORAMIDE REQUIRED TO CONVERT THE LEAD TO LEAD PHOSPHATE, WHEREIN THE ALKYL GROUP IN SAID ALKYL-PHOSPHORAMIDE CONTAINS FROM 1 TO 4 CARBON ATOMS.