US2406544A - Motor fuel and process of using same - Google Patents

Description

ug 27, 1946 E. R. .JOHNSON MOTOR FUEL AND PROCESS 0F USING SAME Filed July 4, 1942 FUEL AIR

RATIO ELMER R, JOHNSON NVENTOR BY 'AJM/M HIS A TTORNE Y Patented Aug. 27, 1946 MOTOR FUEL AND PROCESS or USING SAME Elmer R. Johnson, Beacon, N. Y., assignor to Texaco Development Corporation, Jersey City N. J., a corporation of Delaware Application July 4, 1942, Serial No. 449,751

13 Claims.

My invention relates to improved fuels for internal combustion engines, and to methods for producing and utilizing such fuels.

In the past, motor fuels have generally been rated on the basis of their performance under relatively lean mixture operating conditions. This has resulted from considerations of fuel economy in the operation of automotive engines, andl test methods such as the CFR octane number determinations have been devised accordingly. Moreover, most fuels have somewhat better anti-knock characteristics under rich mixture operating conditions, i. e., air-fuel ratios of about 12/1, than under lean mixture operating conditions, i. e., air-fuel ratios of about 15/1. In the usual automotive engine, air-fuel ratios of less than 12/1 have been of no interest, since the use of such mixtures has resulted in both loss of power and loss of economy.

In the operation of supercharged engines, on the other hand, and especially those of high speed, high heat load types, the performance of fuels in mixtures richer than 12/1 becomes important. With Such engines, the maximum power output at full throttle without detonation is obtainable only with super-rich mixtures, i. e., with air-fuel ratios less than 11/1, and usually considerably below 10/ 1. In order to obtain maximum power output from an aircraft engine for take-off under heavy load, it is desirable to employ a fuel having anti-knock characteristics especially suited for operation at such super-rich mixtures.

It has been found that various fuels differ markedly in their performance in super-rich mixture, even though their anti-knock characteristics at leaner mixtures may be substantially identical. Certain of the aromatic hydrocarbons such as benzene and toluene, when incorporated in a motor fuel, have been found to have the character istie of considerably improving'the fuel in its performance in super-rich mixtures, without affecting the lean mixture performance to a similar extent. However, the improvement which can be effected in this manner has usually been insuflicient to satisfy the desired requirements for maximum permissible power output from aviation fuels. As a result, the practice has been to incorporate in the fuels relatively large amounts of tetraethyl lead to increase the antiknock qualities of the fuel at both lean mixtures and super-rich mixtures. This procedure is undesirable, however, in view of the high concentrations of the toxic lead compound required, and is uneconomical in view of the unnecessary increase in the lean mixture anti-knockcharacters 2 istics of the fuel. There has thus been a demand for an anti-knock additive which is capable of preferentially improving the performance of m0- tor fuels in super-rich mixtures.

I have now discovered that metal carbonyl antiknock agents unexpectedly have this desired characteristic. Thus, I have found that iron pentacarbonyl, which is inferior to tetra-ethyl lead as an anti-knock agent for automotive fuels in lean mixtures, and has not been successful as a commercial anti-knock agent for this reason, has Surprisingly better anti-knock effects than tetraethyl lead when employed in fuels supplied to supercharged engines at super-rich mixtures.

Iy have further found that iron pentacarbonyl is superior to tetra-ethyl lead in its effect on base fuels of high anti-knock ratings. It is generally recognized that tetra-ethyl lead is of most value in base fuels of poor quality, and that even with suchfuels, the improvement effected by tetraethyl lead diminishes rapidly with increasing amounts added. Similarly, tetra-ethyl lead often produces very much less than additive effects, when employed in conjunction with other fuel components of anti-knock value, such as aromatic hydrocarbons, aromatic amines, and the like. Iron pentacarbonyl, on the other hand, is capable of improving the anti-knock properties of Very high quality base fuels, and does not exhibit the degree of diminishing returns for added increments encountered with tetra-ethyl lead.

One aspect of the present invention, therefore, is the production of super fuels by the incorporation of metal carbonyls in base fuels of high anti-knock value, and especially in base fuels containing aromatic hydrocarbons or combinations of aromatic hydrocarbons and other antiknock components.

The metal carbonyls which may be employed in accordance with the present invention are the carbonyls of the metals of the eighth group of the periodic table, and especially the variouscarbonyls of the metals of atomic numbers 26 to 28, i. e., iron, nickel, and cobalt. Of these compounds, 1 prefer to use iron pentacarbonyl, and my inventionwill be specifically illustrated with reference to this compound,

Iron pentacarbonyl may be employed in aocordance with the present invention either in blended .super fuels, or as an auxiliary agent (either alone or in an auxiliary fuel) to be employed for increasing the power output of supercharged engines. In the latter type of application, the iron pentacarbonyl, or an auxiliary fuel containing the iron pentacarbonyl, may be in- 3 jected into the main fuel supply or directly into the engine at times of increased power demand, as in take-off operation of supercharged aircraft engines. The supply of the auxiliary material may be controlled manually, but is preferably controlled automatically, as by a valve such as that described in U. S. Patent 2,002,482 of Leo B. Kimball. In any event, for maximum power output, the air-fuel ratio should be manually or automatically reduced below 11 1 when supplying the auxiliary iron carbonyl.

A blended fuel containing iron pentacarbonyl may be used as a separate fuel for operation of supercharged engines during periods of maximum power demand, or may be used as the sole fuel for such engines. In the former case, the blend containing the iron pentacarbonyl is preferably of the super-fuel type, being formulated for maximum power output in super-rich mixtures. Such a fuel is useful, for example, as a take-off fuel for supercharged aircraft engines, in which case a fuel formulated for optimum lean mixture performance may then be employed as the cruising fuel.

If the fuel blend containing the iron pentacarbonyl is to be employed as the sole fuel, for operating at both lean mixtures and super-rich mixtures, the base fuel stock is preferably chosen on the basis of its power output in lean mixtures, and the performance at super-rich mixtures is then increased by the incorporation of iron pentacarbonyl, with or without additional anti-knock components such as aromatic hydrocarbons and tetra-ethyl lead. Base fuel stocks containing relatively large amounts of 2,2,4- trimethylpentane are particularly valuable for this purpose. Examples of such stocks are the alkylate from the hydrogen fluoride alkylation of isobutane with isobutylene, as described in copending application Ser. No. 429,471 of Louis A. Clarke, and the hydrogenated co-dimer from the cold acid co-polymerization of butylenes.

Except for particular formulations, as noted above, the base fuel stocks for use in the present invention may be any of the known types of motor fuels for' internal combustion engines. Straight run gasolines, thermally or catalytically cracked gasolines, polymer gasolines, alkylation gasolines, thermally or catalytically reformed or hydroformed gasolines, and various blends of such products are suitable for the present purpose. Other common fuel constituents such as light hydrocarbons to meet volatility requirements, gum inhibitors, stabilizing agents, and agents for scavenging metallic anti-knock residues, may be incorporated in the fuels in accordance with prior practices in the art.

The aromatic hydrocarbons to be employed in conjunction with iron pentacarbonyl in the formulation of super fuels are preferably the lower molecular weight mono-cyclic compounds such as benzene, toluene, xylenes, ethylbenzene, and isopropylbenzene. These materials may be used in the form of pure compounds, or as commercial hydrocarbon fractions, such as coal tar distillates, benzene alkylates, or hydro-formed naphtha fractions, which contain considerable amounts of these compounds. As little as per cent by volume of an aromatic hydrocarbon will usually have a beneficial effect on the performance of a fuel in super-rich mixtures, and amounts up to 40 per cent by volume, or even more, may be used in fuel blends to which iron pentacorbonyl is to be added. I generally prefer, however, to

4 use amounts ranging from about 5 per cent to about 20 per cent by volume.

I have found that the stability of the metal carbonyls in fuel blends containing aromatic hydrocarbons may be materially improved if the aromatic hydrocarbon is subjected to treatment with strong sulfuric acid, or an equivalent oxidizing agent, prior to incorporation in a mixture containing the metal carbonyl. For example,

, iron pentacarbonyl, when incorporated in a fuel containing commercial ethylbenzene prepared by the alkylation benzene, may be found to be so unstable as to form a dark precipitate almost immediately. However, if the ethyl benzene is first subjected to treatment with 93 per cent sulfurie acid, neutralized, and dried, this precipitate formation is avoided, and the blended fuels have stability equal to fuels which contain iron pentacarbonyl, butl no aromatic hydrocarbons. For the formulation of super fuels, therefore, I prefer to use aromatic hydrocarbons which have been subjected to such acid washing, or equivalent oxidizing treatment, and which will be referred to herein as acid treated aromatic hydrocarbons.

Although the instability due to aromatic hydrocarbons may be minimized in accordance with the above treatment, it should be recognized that the metal carbonyls of the present class have an inherent tendency to instability in the presence of light or oxygen. The carbonyls, or fuels containing them, should therefore be protected against these elements as adequately as possible. stabilizing agents or inhibitors may be used to minimize the instability of fuels during shipping and storage, but the safest method to insure against instability is to incorporate the metal carbonyls inthe fuel blends only a short time before the intended use of the fuels.

The amount of metal carbonyl to be employed in any fuel blend will depend on the anti-knock characteristics of the base fuel and the desired characteristics of the final blend. Any measurable amount of carbonyl compound will effect an improvement in the performance of a fuel in super-rich mixtures, and the upper limit of concentration is apparently fixed only by economic considerations. Generally, amounts ranging from 0.1 to 10.0 ml. of a liquid metal carbonyl per gallon of fuel, or amounts corresponding to 0.05 to 5.0 g. of metal per gallon of fuel, will be satisfactory. I generally prefer to Vuse amounts of iron pentacarbonyl in super fuel blends ranging from about 2 ml. to about 6 ml. per gallon of fuel, or to supply iron carbonyl from an auxiliary source in aboutJ these ratios when using the material in conjunction with a main fuel supply for operating supercharged engines at air-fuel ratios below 11/ 1.

My invention will be further illustrated by the following specific examples:

Example I A 300 F. end-point alkylation gasoline obtained by the sulfuric acid alkylation of isobutane with butylenes was tested in a supercharged engine in accordance with the AFD-3C test method, and the values of the permissible indicated mean eifective pressure (IMEP without detonation) were determined for fuel-air ratios ranging from excessively lean to excessively rich. The maximum permissible IMEP was found to be approximately 134 lbs./sq. in. at a fuel-air ratio of 0.111 (an air-fuel ratio of 9/1). The same alkylation gasoline, containing 2.1 ml. of

iron pentacarbonyl per gallon (0.87 g. of Fe per gallon), was tested in the same engine, and the corresponding values of permissible IMEP were determined. The maximum permissible IMEP in this case was approximately 192 lbs/sq. in. at an air-fuel ratio of 9.4/1. The values of permissible IMEP for the same alkylation gasoline containing 0.87 g. of Pb per gallon, in the form of tetra-ethyl lead, were determined by similar tests in the same engine. In this case, the maximum permissible IMEP was found to be only approximately 164 lbs. sq. in. The values of permissible IMEP for different fuel-air ratios for these three fuels are shown graphically in the accompanying drawing.

As may be seen from the above example, the substitution of an equivalent amount of iron pentacarbonyl for tetra-ethyl lead in this alkylation gasoline results in an increase in maximum power output from the supercharged engine of nearly 12 per cent, even though tetra-ethyl lead is a better anti-knock agent than iron pentacarbonyl in this base fuel at the usual automotive air-fuel ratios ranging from 12.5/1 to 15.0/1.

Ewmple II A fuel consisting of 60 per cent by Volume of 300 F. end-point alkylation gasoline of the type described above and 40 per cent by volume of acid treated ethylbenzene was tested in a supercharged engine by the AFD-3C test method. The maximum permissible IMEP was found to be approximately 207 lbs/sq. in. at an air-fuel ratio of 7/1. This fuel with the addition of 2.1 m1. of iron pentacarbonyl per gallon (0.87 g. Fe per gallon) was tested in the same engine, and at an air-fuel ratio of 8.4/ 1 the permissible IMEP was approximately 228 lbs/sq. in. In this test the available fuel was utilized before the maximum IMEP was reached. However, the permissible IMEP was increasing rapidly with decreasing air-fuel ratios, indicating that a maximum value considerably in excess of 228 lbs/sq. in. would be reached at an air-fuel ratio lower than 8.4/1. In an accompanying test, 228 lbs/sq. in. was the maximum permissible IMEP obtainable with a fuel consisting of commercial iso-octane and tetra-ethyl lead in an amount corresponding to approximately 4.24 g. of Pb per gallon.

Eample III A fuel consisting of 80 per cent by volume of 300 F. end-point alkylation gasoline and 20 per cent by volume of acid treated ethylbenzene was tested in a supercharged engine in accordance with the AFD-3C test method. The maximum permissible IMEP was found to be approximately 175 lbs/sq. in. at an air-fuel ratio of 7.2/1. The same base fuel plus 2.0 m1. of iron pentacarbonyl per gallon (0.83 g. Fe per gallon) produced a maximum permissible IMEP of approximately 212y lbs/sq. in. This base fuel plus 4.0 ml. of iron pentacarbonyl per gallon (1.66 g. Fe per gallon) produced a permissible IMEP of approximately 250 lbs/sq. in. at an air-fuel ratio of 8/1. The maximum permissible IMEP could not be determined with this fuel at lower air-fuel ratios, since the power output was greater than could be measured by the test engine dynamometer. However, it may be seen that even at a value less than the maximum, the permissible power output of this base fuel was increased at least 43 per cent by the addition of 1.66 g. of .Fe per gallon, in the form of iron pentacarbonyl.

Eample IV The CFRM octane ratings were determined for the base fuel utiilzed in Example II and for this base fuel plus various amounts of iron pentacarbonyl and tetra-ethyl lead, as shown in the table below:

Concentra- Equivalent CFRM l tion, ml. of TEL Additive metal/gal one in isofuel octane" None 91. 7 Fe(CO)5 0.83 97.3 Do- 4.15 101.1 0.09 D0- 0. 83 101. 5 0.12 Pb(C2H5)4 3. 18 Fe(CO 4. 15 103. 2 0.26 Pb(C2H5)4 3.18

It is to be understood, of course, that the above examples are merely illustrative, and do not limit the scope of my invention. As has previously been pointed out, other metal carbonyls of the present class may be substituted for the iron pentacarbonyl employed in these examples, and the particular fuels of the examples may be modied in other respects in accordance with' prior practices in the art. In general, it may be said that the use of any equivalents, or modifications of procedure which would naturally occur to one skilled in the art, is included in the scope of this invention. Only such limitations should be imposed on the scope of my invention as are indicated in the appended claims.

I claim:

1. An aviation motor fuel blend adapted for use in supercharged engines and having a preferentially improved maximum power output at full throttle, without detonation, at super-rich air-fuel ratios richer than 11:1, as compared with lean air-fuel ratios leaner than 11:1 comprising a high antiknock rating base fuel containing a major proportion of isoparalinic hydrocarbon gasoline, and a carbonyl of a metal of atomic number 26 to 28 in an amount sucient to convert the base fuel into the aforesaid aviation motor fuel blend.

2. An aviation motor fuel blend adapted for use in supercharged engines and having a preferentially improved maximum power output at full throttle, without detonation, at super-rich air-fuel ratios richer than 11:1, as compared with lean air-fuel ratios leaner than 11:1 comprising a high anti-knock rating base fuel containing a major proportion of alkylate gasoline, and a carbonyl of a metal of atomic number 26 to 28 in an amount sufficient to convert th'e base fuel into the aforesaid aviation motor fuel blend.

3. The motor fuel of claim 1, in which the metal is iron.

4. The motor fuel of claim 1, in which the metal is nickel.

5. The motor fuel of claim 1, in which the metal is cobalt.

-6. The motor fuel of claim 1, in which' the metal carbonyl is iron Pentacarbonyl.

7. An aviation motor fuel blend adapted for use in supercharged engines and having a preferentially improved maximum power output at full throttle, without detonation, at super-rich air-fuel ratios richer than 11:1, as compared with lean air-fue1 ratios leaner than 11:1 comprising a high anti-knock rating base fuel comprising ai major proportion of an isoparafiinic hydrocarbon constituent and a minor proportion of an aromatic hydrocarbon constituent, and a carbonyl of a metal of atomic number 26 to 28 in an amount sufficient to convert the base fuel into the aforesaid aviation motor fuel blend.

8. The motor fuel of claim 7, in which the metal carbonyl is iron pentacarbonyl.

9. An aviation motor fuel blend adapted for use in supercharged engines and having a preferentially improved maximum power output at full throttle, without detonation, at super-rich air-fuel ratios richer than 11:1, as compared with lean air-fuel ratios leaner than 11:1 comprising a high anti-knock rating base fuel containing a major proportion of an isoparanic hydrocarbon constituent, a minor proportion of an aromatic hydrocarbon constituent and a small amount of tetra-ethyl lead, and a carbonyl of a metal of atomic number 26 to 28 in an amount sufficient to convert the base fuel into the aforesaid aviation motor fuel blend.

10. The motor fuel of yclaim 9, in which the metal carbonyl is iron pentacarbonyl.

11. The method of making an aviation motor fuel blend having a preferentially improved maximum power output in supercharged engines at full throttle, Without detonation, at super-rich air-fuel ratios richer than 11:1, as compared with lean air-fuel ratios leaner than 11:1, comprising incorporating in a high anti-knock rating base fuel containing a major proportion of isoparafnic hydrocarbon gasoline a carbonyl of a. metal of atomic number 26 to 28 in an amount sufficient to convert the base fuel into the aforesaid aviation motor fuel blend.

l2. The method of claim 11, in which the metal carbonyl is iron pentacarbonyl.

13. The method of making an aviation motor fuel blend having a preferentially improved maximum power output in supercharged engines at full throttle, without detonation, at super-rich air-fuel ratios below 11:1, as compared with lean air-fuel ratios leaner than 11:1, comprising incorporating in a high anti-knock rating base fuel containing a major proportion of alkylate `gasoline a carbonyl of a metal of atomic number 26 to 2'8 in an amount suflicient to convert the base fuel into the aforesaid motor fuel blend.

ELMER R. JOHNSON.

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