US2720448A - Motor fuels - Google Patents

Description

MOTOR FUELS Fred S. Arimoto, New Castle, Del., assignor to E. Lndu Pont de Nemours and Company, Wilmington, Del., a

. corporation of Delaware No Drawing. Application October 27, 1952, Serial No. 317,145

12 Claims. (Cl. 44-69) This invention relates to motor fuels for spark ignition engines and to anti-knock compositions for use in such motor fuels.

In operating internal combustion engines, particularly the modern engines with high compression ratios, it has been found that the tendency for the fuel mixture topreignite increases as the engine is operated. Also, the octane 1 value of the fuel required to prevent knock must bejincreased after the engines have been in operation for some time and this socalled octane demand. increases until a fairly constant value is reached. It is believed that both these effects are closely related to the formation of solid deposits in the engine, although the present invention does not depend on any theory for the cause of the increased octane demand and increased pre-ignition tendency.

It has been reported by Hughes et al. in Industrial and Engineering Chemistry, 43, 2841-2844 (1951), that alkyl borates of the formula B(OR)3, such as triethyl and triisobutyl borates, and alkyl borines of the formula RaB, such as normal and tertiary butyl borines, incorporated inthe gasoline used, reduce the increase in octane requirement. Compounds of these types, however, cannot be used under actual practical conditions because of their reactivity. Thus, the borines are very readily oxidized, even at the dilution at which they would be used in gasoline, and some are even spontaneously inflammable in pure form. The borate esters show an equally serious sensitivity to bydrolysis and are rapidly attacked by the small amount of water always present in commercial gasoline. Even when they are used in dried gasoline in experimental engine tests, they are hydrolyzed by atmospheric moisture in the carburetor and in a fairly short time clog its passages with solid hydrolysis products.

It is an object of the present invention to provide improved motor fuels for spark ignitionengines. Another object is to provide motor fuels for spark ignition engines which minimize the tendency of deposits to promote preignition during continued engine operation. A further object is to provide new and improved anti-knock compositions for addition to motor fuels for spark ignition engines. A still further object is to provide anti-knock compositions which, when added to motor fuels for spark ignition engines, causes the motor fuels to minimize the tendency of deposits to promote pre-ignition during continued engine operation. Other objects are to provide new compositions of matter and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished by my invention which comprises hydrocarbon motor fuels for spark ignition engines which contain tetraethyl lead and, for each gallon of motor fuel, from 0.1 to about 3 ml. of a borinate ester of the formula R2BOR which contains 9 to 18 carbon atoms and wherein each R is a hydro- 2,720,448 Patented Oct. 11, 1 955 carbon radical of 1 to 7 carbon atoms, and anti-knock mixtures comprising tetraethyl lead and between 2 and 0.02 volumes of such borinate esters for each volume of tetraethyl lead.

The borinate esters of my invention are very effective in reducing the tendency of deposits to promote pre ignition of motor fuels, containing tetraethyl lead, in spark ignition engines during continued engine operation. By pre-ignition is meant ignition of the fuel-air mixture in the engine cylinder by hot deposit surfaces. My borinate esters have the unpredictable and unobvious advantage, over other boron compounds previously proposed for this purpose, of being very stable toward oxygen and moisture so that they are quite satisfactory for use under the conditions encountered in practice; that is, they are highly resistant to oxidation and to hydrolysis at atmospheric temperatures over long periods and under the conditions prevailing in the carburetors and intake manifolds of spark ignition engines. Also, they are soluble in the hydrocarbon motor fuels and in the anti-knock mixtures, at least to the extent required for the purposes of my invention. While the borinate esters decrease slightly the octane number of the motor fuel, such decrease was less than 2 numbers when used in a concentration of 3 ml. per gallon, and usually was very much less.

The motor fuels will, preferably, be gasoline, but may be any other combustible liquids of suitable volatility commonly employed as fuels for spark ignition engines, including parafiinic, naphthenic and aromatic hydrocarbons, isooctane, and mixtures of isooctane with other suitable liquid hydrocarbons. Such motor fuels may also contain antioxidants, stabilizers, dyes, or other compounds which are commonly employed in motor fuels.

The motor fuel will contain tetraethyl lead in a proportion of from about 0.5 ml. to about 5 ml. per gallon of the motor fuel. The concentration of tetraethyl lead in the motor fuel will be varied as is usual with the engine and its use. In automotive engines, the concentration of tetra ethyl lead is usually in the range of from about 1.5 ml. to about 3.0 ml. per gallon of motor fuel. In light airplane engines, the concentration of tetraethyl lead is usually in the range of from about 1 ml. to about 2 ml. per gallon of motor fuel. However, larger high output aircraft engines usually require from about 2.5 ml. to about 5 ml. of tetraethyl lead per gallon of motor fuel.

The motor fuel may contain a halo-hydrocarbon lead scavenging agent in an amount of up to about 5 theories, usually from about 1 to about 5 theories, and preferably from about 1 to about 2 theories, based on the tetraethyl lead. One theory of a scavenging agent is that quantity which provides 2 atoms of active halogen per atom of lead in the tetraethyl lead. The class of halo-hydrocarbon scavenging agents is well known and a great many of them have been disclosed in prior patents and in the literature. Generally, they are hydrocarbons in which at least one hydrogen has been replaced by chlorine or bromine or both. The most commonly employed scavenging agents are ethylene dichloride and ethylene dibromide, and they are the preferred scavenging agents in the compositions of my invention. Lead halides, such as PbCl2 and PbBrz, formed by the reaction of lead with the scavenging agent, are more active to cause pre-ignition than other lead compounds found in the engine deposits. Hence reduction in the amount of scavenging agent fur: ther reduces the tendency toward pre-ignition.

The borinate esters of my invention have the formula RzBOR wherein each R is a hydrocarbon radical of 1 to 7 carbon atoms and contains a total of from 9 to 18 carbon atoms. The total number of carbon atoms in the borinate esters is that required to provide compounds having a volatility roughly approximating that of tetraethyl lead. Preferably, the borinate esters will contain from 9 to 15 carbon atoms. The Rs in the formula may be the same or different and may be alkyl, aryl, aralkyl, alkaryl or cycloaliphatic radicals. The allryl radicals may be primary, secondary or tertiary, and straight or branched chain radicals. Ordinarily, each R is a monovalent radical, but two Rs may together represent a divalentradical such as a polymethene radical. Preferably, one R will be an alkyl radical of 1 to carbon atoms and each of the other Rs will be a hydrocarbon radical of the class of alkyl radicals of 3 to 5 carbon atoms, phenyl radicals and tolyl radicals. More particularly, I prefer the borinate esters which contain 9 to carbon atoms and in which eachRis an alkyl radical of 3'to 5 carbon atoms, such as propyl dipropylborinates, n-butyl di-n-butyl borinate, t-bu tyl dit-butylborinate, isobutyl di-n-butylborinate, nb'utyl" di-tertiarybutylborinate, and the amyl diamylborinates. The most preferred borinate ester is n-butyl di-nbutylborinate. Other borinate esters, within the scope of my invention, are: Methyl diphfinylborinate Ethyl diphenylborinate Ilsobutyl diphenylborinate n' -Butyl di-p-tolylborinate Methyl di-n-butylborinate Phenyl dipropylborinate Methyldi t-butylborinate Some of the borinate esters and the method of preparing them are disclosed by Meerwein et al. in J. Prakt. Chem. 147, p. 226250 (1936), and by Johnson et al. in I; Am- Chem. Soc., 60, p. 119 (1938). The n-butyl din-butylborinate, methyl di-n-butylborinate, isobutyl di-nbutylborinate, methyl di-t-butylborinate, n-butyl di-tbutylborinate, ethyl diphenylborinate and isobutyl diphenylborinate were prepared either by the method of Johnson et al., starting with the trisubstituted borine, or by the reaction of the borate ester with a limited quantity of theappropriate Grignard reagent.

v The borinate esters of my invention will be employed in a concentration of from 0.1 ml. to about 3 ml. per gallon. of motor fuel, and preferably in a concentration of from about 0.1 ml. to about 1 ml. per gallon. As little as 0,1 ml. of n-butyl di-n-butylborinate per gallon of motor fuel has produced a definite reduction of the normal increase in pre-ignition tendency of combustion chamber deposlts over a considerable period of engine operation.

Ordinarily, tetraethyl lead is sold in the form of an antirknock mixture for addition to motor fuels. Such anti-knock mixtures usually consist essentially of tetraethyl lead, the desired proportion of halo-hydrocarbon I lead. scavenging agent, a dye for identifying the composition and, the motor fuel containing it, and a small amount of a liquid hydrocarbon as a diluent. While the borinate esters of my invention may be added to the motor fuel identifying thernixture and the motor fuel containing it, and the usual liquid hydrocarbon diluent. The resulting compositions are stable, homogeneous liquidcompositions which are particularly suitable for addition to motor fuels for the purpose of preventing knocking and of reducing the tendency of the motor fuel to create combustion chamber deposits prone to cause pre-ignition during continued operation of the engine with such motor fuel.

In order to more clearly illustrate my invention, preferred modes of carrying the same into effect and the advantageous results to bev obtained thereby, the follow ing examples are given:

Example I A General Motorsv research engine (compression ratio 10:1) was operated under low duty cyclicconditions (spark advance 9 before top dead center, one minute operation at idle speed (500 R. P. M.), followed by three minutes at 1750 R. P. M. and 20 brakehorsepower) and its pre-ignition level determined as combustion chamber deposits accumulated. The pre-ignition tendency or requirement is expressed in terms of minimum Performance Number of fuel required to eliminate pro-ignition in the engine. This engine was operated as above with catalytically cracked gasoline containing per gallon 3 ml. of tetraethyl lead and one theory ofethylene dichloride plus 0.5 theory of ethylene dibromide. The pre-ignition level of the engine rose from a performance number of 78 (clean engine), to an equilibrium value of 156 after 70 hours of operation and continued at this level for at least 60 hours more. This is an effective increase of 78 performance numbers.

Using the same fuel containing in addition 0.5 mi. n-butyl di-n-butylborinate per gallon, the pre-ignition requirement increased from 73 to 92 performance number in 20 hours, at which equilibrium value it remained for at least 110 hours, an effective increase of only 19 performance numbers. The marked advantages of the borinate in reducing pre-ignition is evident.

Example 2 A 1951 Oldsmobile Rocket engine was operated under low dutycyclic condition (spark advance 9- before top dead center, one minute operation at idle separately from the tetraethyl lead, it is desirable to add them to the anti-knock mixture in a proportion to provide the desired amount in the motor fuel when the mixture is added to the motor fuel.

Thus, an important feature of my invention is an antiknock mixture consisting essentially of tetraethyl lead and between 2 and 0.02 volumes of a borinate ester of my invention per volume of tetraethyl lead. Usually, such mixtures will also contain the desired scavenging agents The borinate esters are miscible in all proportions with the tetraethyl lead and with mixtures thereof with the scavenging agents. Preferably, the borinate ester will be in the proportion of from about 0.5 to about 0.03 volume per volume of tetraethyl lead. Also, preferably, the scavenging agent will be in aproportion of from about 1 to about 2 theories. Usually, it will be desirable to incl de in the anti-knock mi r a ye for the purpose f speed (500 R. P. M.), followed by three minutes at 1750 R. P. M.) with a catalytically cracked gasoline containing 3 ml. of tetraethyl lead per gallon together with 1.0 theory of ethylene dichloride and 0.5 theory of ethylene dibromide as in Exampde 1. The pre-ignition requirement was determined at intervals with wide-open throttle operation maintained for 20 minutes. The engine was operated for 130 hours to build up deposits, at whichtime the pro-ignition requirement was 83. The engine was then operated with the same fuel to which had been added. 0.5 ml. of n-butyl di-n-butylborinate per gallon. The pre-ignition requirement decreased to 75 during- 120 hours.

During the entire 110 hours of operation with the borinate, the carburetor and intake manifold showed no evidence of plugging nor any deposition whatever from the borinate. On the other hand, when an attempt was made to test a fuel containing tributyl borate, the carburetor passages became clogged with hylrolysis products and a clean carburetor had to be installed after 12 hours of operation.

Example 3 Using the same type of engine and testing conditions as in Example 2, and the same leaded fuel containing in addition 05 ml. of n-butyl di-n-butylborinate per gallon, the equilibrium pre-ignition requirement was 83 after operating for 152 hours. This rose to 85 when the borinate was omitted from the fuel for the next 104 hours. On again, adding the same amount of borinate tothe fuel, the requirement decreased to 80.

In addition to. their effect upon pre-ignition, the borinate esters of the present invention have, also been observed to have a desirable efliect upon the increase in the octane demand which takes place as an engine is operated. In other words, it has been observed that the octane number of the fuel, required to operate an engine without knocking after it has been in operation for some time, is less if the engine has been operated over this period with a fuel containing a borinate ester. However, the effect of the borinate esters on preignition, as shown in the examples, is of greater practical significance, particularly in the types of high compression engines now being deveoped.

The borinate esters of my invention have the formula RzBOR and hence structurally are somewhat similar to the borines, which have the formula RsB. Since the borines are extremely suscpetible to oxidation at atmospheric temperatures, it would be expected that the borinate esters would also be quite susceptible to oxidation, particularly at the elevated temperatures present in the carburetors and the intake manifolds of spark ignition engines, and over long periods of storage. However, a gasoline solution of n-butyl di-n-butylborinate showed no change at all when stored in the presence of air for at least six weeks. Also, when motor fuels, containing the borinate esters, were used in the operation of automobile engines over long periods of time as in the examples, there was no evidence of any oxidation of any of the borinate esters, such as the deposition of non-volatile oxidation products in the carburetors and other parts of the intake systems of the engines.

Since the borinate esters of my invention contain an ester group, and since the the borate esters, having the formula B(OR)3, are very susceptible to hydrolysis in the presence of moisture at atmospheric temperatures, it would be expected that the borinate esters of my invention would also be somewhat susceptible to hydrolysis in the presence of Water or water vapor at atmospheric temperatures and particularly at the elevated temperatures present in the carburetors and the intake manifolds of spark ignition engines, and over long periods of storage. However, as shown in the examples, motor fuels containing the borinate esters could be used over long periods of time without difiiculty, whereas a motor fuel containing a borate ester (tributyl borate) could not.

The stability of n-butyl di-n-butylborinate toward hydrolysis by water (and therefore its suitability for use in gasoline under practical conditions) is further shown by the fact that it showed no signs of hydrolysis when kept in contact with twice its volume of water at room temperature for 7 days. Tributyl borate, on the other hand, showed a visible amount of solid hydrolysis product in 1 minute under these conditions. Similarly, a 2.5% by volume solution of n-butyl di-n-butylborinate in gasoline (much more concentrated, about 95 ml. per gallon, than would be used in practice) showed no signs of hydrolysis in contact with water for at least 35 days, while the same concentration of tributyl borate in gasoline formed a precipitate in contact with water in 20 minutes.

It will be understood that the preceding examples are given for illustrative purposes solely, and that my invention is not limited to the specific embodiments disclosed therein. On the other hand, it will be apparent to those skilled in the art that, within the scope of the general description, variations can be made in the borinate esters, in the proportions thereof employed in the motor fuels and in the anti-knock mixtures, in the composition of the motor fuels, in the composition of the anti-knock mixtures, in the engines, and in the techniques employed, without departing from the spirit or scope of my invention.

It will be apparent that, by my invention, I have provided novel motor fuels for spark ignition engines and novel anti-knock mixtures useful for making such motor fuels, whereby the tendency for pre-ignition during continued operation of the engines therewith is materially'reduced by means which are practical. Therefore, it is obvious that my invention constitutes a valuable advance in and contribution to the art. i

I claim:

1. A hydrocarbon motor fuel for spark ignition engines containing, for each gallon thereof, from about 0.5 to about 5 ml. of tetraethyl lead, and from 0.1 to about 3 ml. of a borinate ester of the formula RzBOR which contains 9 to 18 carbon atoms and wherein each R is a hydrocarbon radical of 1 to 7 carbon atoms and at least one R is an alkyl radical.

2. A hydrocarbon motor fuel for spark ignition engines containing, for each gallon thereof, from about 0.5 to about 5 ml. of tetraethyl lead, and from 0.1 to about 3 ml. of a borinate ester of the formula RzBOR which contains 9 to 18 carbon atoms and wherein one R is an alkyl radical of l to 5 carbon atoms and each of the other Rs is a hydrocarbon radical of the class consisting of alkyl radicals of 3 to 5 carbon atoms, phenyl radicals and tolyl radicals.

3. A hydrocarbon motor fuel for spark ignition engines containing, for each gallon thereof, from about 0.5 to about 5 ml. of tetraethyl lead, and from 0.1 to about 3 ml. of a borinate ester of the formula RzlBOR which contains 9 to 15 carbon atoms and wherein each R is an alkyl radical of 3 to 5 carbon atoms.

4. A hydrocarbon motor fuel for spark ignition engines containing, for each gallon thereof, from about 0.5 to about 5 ml. of tetraethyl lead, and from 0.1 to about 3 ml. of n-butyl di-n-butylborinate.

5. An anti-knock mixture consisting essentially of tetraethyl lead, and between 2 and 0.02 volumes per volume of tetraethyl lead of a borinate ester of the formula RzBOR which contains 9 to 18 carbon atoms and wherein each R is a hydrocarbon'radical of 1 to 7 carbon atoms and at least one R is an alkyl radical.

6. An anti-knock mixture consisting essentially of tetraethyl lead, and between 2 and 0.02 volume per volume of tetraethyl lead of a borinate ester of the formula RzBOR which contains 9 to 18 carbon atoms and wherein one R is an alkyl radical of 1 to 5 carbon atoms and each of the other Rs is a hydrocarbon radical of the class consisting of alkyl radicals of 3 to 5 carbon atoms, phenyl radicals and tolyl radicals.

7. An anti-knock mixture consisting essentially of tetraethyl lead, and between 2 and 0.02 volumes per volume of tetraethyl lead of a borinate ester of the formula RzBOR which contains 9 to 15 carbon atoms and wherein each R is an alkyl radical of 3 to 5 carbon atoms.

8. An anti-knock mixture consisting essentially of tetraethyl lead, and between 2 and 0.02 volumes per volume of tetraethyl lead of n-butyl di-n-butylborinate.

9. An anti-knock mixture consisting essentially of tetraethyl lead, from about 1 to about 5 theories of a halohydrocarbon scavenging agent, and from about 0.5 to about 0.03 volumes per volume of tetraethyl lead of a borinate ester of the formula RzBOR which contains 9 to 18 carbon atoms and wherein each R is a hydrocarbon radical of 1 to 7 carbon atoms and at least one R is an alkyl radical.

10. An anti-knock mixture consisting essentially of tetraethyl lead, from about 1 to about 5 theories of a halohydrocarbon scavenging agent, and from about 0.5 to about 0.03 volumes per volume of tetraethyl lead of a borinate ester of the formula RzBOR which contains 9 to 18 carbon atoms and wherein one R is an alkyl radical of l to 5 carbon atoms and each of the other Rs is a hydrocarbon radical of the class consisting of alkyl radicals of 3 to 5 carbon atoms, phenyl radicals and tolyl radicals.

11. An anti-knock mixture consisting essentially of tetraethyl lead, from about 1 to about 5 theories of a halohydrocarbon scavenging agent, and from about 0.5 to about 0.03 volumes per volume of tetraethyl lead of a borinate ester of the formula RzBOR which contains 9 References Cited in the file of this patent to :15 :earbon atoms and wherein each R :is an .alkyl mibl:ofBiatol5 carbonfatoms. N E STATES Sv :12. An'antiwkn'o'ck mixture consisting-essentially ofte't- 1 1 :Lyons et "f" p 193.9

frae thyl lead, lfromaaboutil Eto =about.5 theories of 1a zhalo- 5 2257194 Rosen -i 1941 hydrocarbon scavenging agent, and from about 0.5 to

about 0.03 volumes per volume of tetraethyl lead of nzbunyl 1 di=.n-Ibutylboninate.

Claims (1)

1. A HYDROCARBON MOTOR FUEL FOR SPARK IGNITION ENGINES CONTAINING, FOR EACH GALLON THEREOF, FROM ABOUT 0.5 TO ABOUT 5 ML. OF TETRAETHYL LEAD, AND FROM 0.1 TO ABOUT 3 ML. OF A BORINATE ESTER OF THE FORMULA R2BOR WHICH CONTAINS 9 TO 18 CARBON ATOMS AND WHEREIN EACH R IS HYDROCARBON RADICAL OF 1 TO 7 CARBON ATOMS AND AT LEAST ONE R IS AN ALKYL RADICAL.