US 3106194 A
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Oct. 1963 E. N. CANTWELL, JR., ETAL 3,106,194
METHOD FOR SUPPRESSING KNOCK IN SPARK-*IGNITION ENGINES Filed July 7, 1961 INVENTORS EDWARD N. CANTWELL,JR. CHARLES A. SANDY BY f /L ATTORNEY United States Patent 3,106,194 METHOD FOR SUPPRESSING KNOCK TN SPARK-IGNITIGN ENGINES Edward N. Cantweil, Jr., and Charles A. Sandy, Wilmington, DeL, assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware 4 Filed July 7, 1961, Ser. No. 122,594 5 Claims. (Cl. 123-1) This invention relates to an improved method for suppressing knock in spark-ignition, internal combustion engines, and particularly to a novel method of employing alkali metal antiknock compounds in a new and more effective form for such purpose.
Improvements in the resistance of fuels to knock are currently achieved through refining and blending of hydrocarbon fractions and the use of such additives as the tetraethyl lead antiknock compositions of: commerce. However, because of limitations inherent in these expedients, new means and materials are constantly being sought to obviate the rising costs of meeting the increasing demands for fuels for high compression engines.
Alkali metal compounds have been proposed for a variety of purposes associated with the combustion of hydrocarbon fuels, including the function of antiknock agents in spark-ignition engines. Heretofore, to introduce an alkali metal compound into the combustion zone, it has been proposed to employ it as a solution or a suspension in the hydrocarbon fuel, or to introduce it separately from the hydrocarbon fuel as a dust or a powder or as a solution in an auxiliary fuel such as water, alcohol, or mixtures thereof. Under these conditions, it has been found that only limited classes of alkali metal compounds, for example, the lithium salts of branched chain carboxylic acids as more particularly described by Sandy and Werntz in US. Patents 2,935,973, 2,935,974, and 2,935,975, are significantly effective to suppress knock in a wide variety of fuel types under a wide variety of engine conditions.
Alkali metal compounds suggested as antiknocks in the prior art, such as the alkali metal oleates and naphthenates and in particular Na and K salts and chelates of carboxylic acids and beta-dicarbonyl compounds, are either entirely ineffective when used conventionally or require specially constituted fuels (and/ or special engine conditions) to provide practical improvements in the knock-free power output of spark'ignition engines.
An object of this invention is to provide an improved ethod for obtaining knock-free operation of spark-ignition engines utilizing alkali metal antiknock compounds. Another object is to provide a method for providing alkali metal antiknock compounds in an improved form for the suppression of knock in spark-ignition engines. A further object is to provide a method for utilizing alkali metal compounds as antiknock agents whereby alkali metal compounds, that are normally ineffective or are only marginally effective by existing methods, produce significant increases in knock-free power output of sparkignition engines. Other objects are to advance the art. Still other objects will appear hereinafter.
The above and other objects of the invention are ac complished by the method for suppressing knock in a spark-ignition internal combustion engine containing a combustion chamber, which method comprises inducting into said combustion chamber a hydrocarbon fuel for said engine and air in the proportion required for burning said fuel, heating a vaporizable alkali metal antiknock compound which is an organic compound of the alkali metal and has a Vapor pressure ofat least about.
0.01 mm. of mercury below about 900 F. and vaporizing a knock-suppressing quantity of said alkali metal 3,19%,194 Patented Oct. 8, 1963 compound corresponding to at least 0.001 gram of alkali metal per gallon of hydrocarbon fuel, inducting the vaporized quantity of alkali metal compound into the combustion chamber simultaneously with the hydrocarbon fuel and air, and igniting and burning the fuel in the presence of the vaporized alkali metal compound.
This invention is based on the discovery that alkali metal antiknock compounds can be so constituted as to be vaporizable and that such compounds are-much more effective to suppress knock when vaporized into the combustion chamber than when introduced in accordance with prior methods. The superiority of the present method appears to lie in its ability to provide the alkali metal antiknock compound in an essentially vaporized (i.e. highly dispersed) state in quantities significantly greater than provided by the prior methods. In other words, the degree of dispersion of a given amount, rather than the total amount of the alkali metal compound, governs its effectiveness. Compared to the method of the present invention, introducing the alkali metal compound into the combustion zone as a solution in fuel components, whether by carburetion or injection techniques, furnishes the alkali metal compound in a relatively agglomerated, hence relatively ineffective, state between the time of initiation of the intake stroke and the ignition of the fuel charge. Even though, subsequent to the time of induction, the temperature attained in the combustion chamber during the compression stroke may in itself under ordinary conditions be sutlicient to volatize the alkali metal compound, there apparently is too little time before ignition for the alkali metal compound to become dispersed to the degree provided by the present method. Thus, even with highly volatile alkali metal compounds, the benefit of volatility (vaporizability) in the compound is largely lost, under the normal conditions of operating the engine, when the alkali metal compound is inducted into the engine in an essentially liquid or solid (i.e. agglomerated) physical state.
An important feature of the present invention is its ability to provide an alkali metal antiknock compound in a highly dispersed, e.g. vaporized, condition in the critical period between the intake and the combustion of the fuel charge. Conveniently, a suitable Li, Na or K compound as described hereinafter, is heated and volatilized in an auxiliary apparatus and the vapors inducted through an appropriate intake means into the combustion zone. Conveniently also, the volatilized metal compound is conveyed (i.e. entrained) into the combustion zone by a carrier gas at a temperature suflicient to prevent condensation of the alkali metal compound before it enters the combustion chamber for participation in the combustion process. The alkali metal compound may be sublimed (from the solid state) into the carrier stream or distilled into it evaporatively (from the molten state). For the purpose of the invention, it will be heated to a temperature, below its decomposition point, at which a significant knock-suppressing amount of the alkali metal compound enters into the carrier stream. The quantity of alkali metal compound introduced will normally correspond to at least about 0.001 gram of alkali metal per gallon of the hydrocarbon fuel admitted to the combustion zone. The temperature of vaporization to provide the alkali metal. in the proper form and amount will normally be in the range of about 300 F. to about 900 F., most usually from about 400 F. to about 800 F. Neither the carrier gas nor the fuel-air charge mixture to be ignited need be at the same temperature but should be at a temperature sufficient to maintain the alkali metal compound in the vaporized condition.
The alkali metal compound, in the vaporized condition, can be drawn into the combustion chamber during the intake stroke or pressurized into it during the compression stroke. The quantity of alkali metal compound entering the combustion chamber can be regulated by varying the temperature or rate of flow of carrier gas and/or the nature of the alkali metal compound. In general, the volatility, hence the relative proportion of the alkali metal compound in the vapor state, increases with temperature; the degree of volatility being a function of both the metallic part and the organic part of the molecule as discussed below. Preferably, the quantity of alkali metal compound employed and the conditions of vaporization and induction into the engine will be such as to provide from about 0.01 to about 1 gram of alkali metal per gallon of the fuel. Significant improvements however may be obtained with much smaller concentrations of the metal, while larger concentrations are usually unnecessary.
Suitable carriers are gases and mixtures of gases, such as air, nitrogen, methane, ethane, propane, hydrogen, the fuel-air mixture to be ignited, and their combustion products such as the carbon oxides. In general, any nonreactive volatile substance may serve as carrier, i.e. that does not react with or adversely affect the alkali metal compound or its antiknock effect. Only small proportions of carrier gas, based on the fuel-air charge, are required; for example, from about 0.1 to about vol. percent of the fuel-air mixture. The total air admitted to the combustion zone can be proportioned so that part of the normal total is introduced with the hydrocarbon fuel and part with the alkali metal compound. For example, if air is the carrier gas, it can be used at the same time to make up part or all of the air required for the fuel/air ratio, e.g. part can be added with the fuel and part with the alkali metal compound, or none added with the fuel and all with the alkali metal compound. If nitrogen is used as the carrier gas, the oxygen content of the normal fuel-air mixture can be increased corre spondingly to provide in the combustion chamber the normal 80/20 nitrogen/oxygen ratio. Also, when a hydrocarbon fuel or a combustible gas such as CO or H is employed as the carrier gas, the proportions thereof can be varied so that the total charge introduced into the combustion chamber contains the proportions of combustible and combustion-supporting substances needed for the operation of the engine.
The alkali metal compound functions primarily to suppress the tendency of the fuel charge to cause the engine to knock under the stress of the engine conditions, and its efiect is essentially independent of the fuel being com busted. The fuel may be a normally liquid or a normally gaseous hydrocarbon fuel suitable for use in sparkignition internal combustion engines, particularly fuels which are mixtures of hydrocarbons boiling in the gasoline range, or a refined gasoline as defined in ASTM D-28853. They may be clear fuels or fuels containing other antiknock agents such as tetraalkyl leads, e.g. containing up to 6 grams of lead per gallon of fuel as tetraethyl lead, tetramethyl lead, and mixtures thereof. They may be finished fuels which contain varying amounts of additives such as scavenging agents, dyes, antioxidants, anti-icing agents, rust inhibitors, inhibitors of haze and gum-formation, anti-preignition agents, and the like. Also, the fuel may be a normally gaseous hydrocarbon fuel, such as propane, butane, and mixtures thereof.
The invention is independent of the particular structure of the alkali metal compound provided that the compound is sufficiently vaporizable for the intended function. In general, organic alkali metal antiknock compounds, exerting a vapor pressure of at least about 0.01 mm. Hg below about 900 F. preferably below about 750 F., are suitable for induction into the combustion chamber of the engine by the method of the invention. Preferred are those compounds with vapor pressures of at least 0.1 mm. Hg at about 750 F. and below. Included are alkali metal compounds that are sublimable as Well as those distillable from the molten state at the indicated temperatures and pressures. The vapor pressures of solid and liquid alkali metal compounds are conveniently determined by the transpiration method, which measures the weight of substance required to saturate a known volume of a carrier gas at a given temperature. The carrier gas, preheated to the temperature of measurement, is passed at a known rate at essentially atmospheric pressure through a column containing the alkali metal compound which is heated to the temperatur of the gas. The amount of alkali metal compound vaporized at equilibruim is determined by contacting the gas stream with a cold surface and weighing the alkali metal condensate. The molar ratio of alkali metal compound to carrier gas at a pressure of 760 mm. is essentially equivalent to the vapor pressure in mm. of the alkali metal compound taken as the monomeric species.
However, in the method of the invention, it is not necessary that the carrier gas be saturated with respect to the alkali metal compound. Usually, a less-than-saturating amount of the alkali metal compound will be used, e.g. about 35% to about 70% saturation. Saturation of the carrier gas depends upon such factors as flow rate of carrier gas, rate of evaporation of the alkali metal compound, and the exposed surface area of the compound, which area in the case, for example, of a salt that is solid at the operating temperature will depend upon the size of the salt granules and the degree of packing. In any case, the amount of alkali metal compound introduced into the combustion chamber as vapor with the carrier gas should correspond to at least 0.001 gram, preferably about 0.-0ll gram, of metal per gallon of the hydrocarbon fuel.
As indicated above, the antiknock activity of an alkali metal compound is related to its vapor pressure. The more easily it canbe put into the highly dispersed state characterizing the vapor state and the greater the proportion of the alkali metal compound in the vapor state, the greater the antiknock effect. As illustrated in the examples given hereinafter, increasing the temperature used to vaporize a given alkali metal compound increases the quantity of the alkali metal compound in the vapor stream inducted into the combustion chamber and thereby increases markedly the resistance of the operating fuel to cause knock. It should be understood that the term vaporizability as used herein implies sufiicient thermal stability for vaporization to be accomplished and that not all alkali metal compounds are sufficiently thermally stable and vaporizable for the present purpose. Sufficiency of vapor pressure, as measured by the transpiration method for example, is also a sufiiciency of thermal stability for the alkali metal compound. Compounds of the alkali metals [that break down on being heated, even forming volatile products, without providing a compound of the alkali metal in the vaporized condition, are natural 1y unsuitable. The suitability of any alkali metal compound is simply and readily determined by known methods of measuring vaporizability as discussed above. The operating temperature should of course be below the decomposition temperature of the alkali metal compound and will vary depending on the volatility and thermal stability of the particular compound used and the effect desired. The optimum range for any compound is readily determined by trial. Raising the temperature above the optimum for a given compound may result in a decreased antiknock effect due to partial decomposition of (the alkali metal compound.
For use as antiknock agents in the method of the invention, alkali metal compounds, having the requisite volatility as determinedby the transpiration method, preferably are free of elements antagonistic to organometallic antiknock agents. In general, elements such as Cl, Br, I, P and S are avoided. However, such antagonistic elements can be tolerated, provided the overall effect is a positive enhancement of knock resistance. Preferably, the organic portion of the alkali metal compounds will be composed of elements of atomic numbers 1 to 9, most usually of C, H, and O, sometimes in combination with N and F. With lithium, the preferred alkali metal, the preferred antiknock compounds wfll be composed entirely of elements of atomic number 1 to 9.
Representative alkali metal antiknock compounds, having the requisite volatility and which may be used according to the present invention, include the lithium, sodium and potassium salts and chelates of branched chain organic oxyacids and alcohols, specifically carboxylic acids, beta-diketones and alcohols, wherein the metal is bonded to oxygen; preferably saturated aliphatic acids, beta-diketones and alcohols. It has been found that alkyl branches, within the first two carbon atoms of the oxygen bearing carbon atom, greatly enhance the volatility of the alkali metal derivative, and that, by such rather simple chemical architecture, alkali metal compounds can be devised that are sufficiently volatile for antiknock use according to the method of this invention.
Shitable branched chain saturated carboxylic acids are mono-, di-, and tri-substituted acetic acids wherein the substituent groups are saturated hydrocarbon radicals or their oxaand azo-analogs in which the heteroatom oxaand azo groups stand for ether oxygens and tertiary amino nitrogens. The substituted acetic acids are preferably acyclic, open chain structures, but may contain cyclic groups which for reasons of thermal stability are substantially strainless, i.e. 5, 6 and 7-membered rings, preferably carbocyclic. Usually, [they contain from 4 to 22 carbons, preferably 5 to 13. The trisubstituted acetic acids are particularly preferred because of the superior volatility characteristics of their alkali metal salts. Representative acids, which may be used as the lithium, sodium and potassium salts according to the invention, are:
Pivalic acid, i.e., 2,2-dimethylpropanoic acid 2,2-dimethylbutanoic acid 2,2-diethylhexanoic aicd a-Isopropoxyisobutyric acid Tris(methoxymethyl)acetic (tr-imethoxypivalic) acid 2-ethyl-2-butyldecanoic acid Methoxypivalic acid 1,2,2,3-tetramethylcyclopentane-l-carboxylic acid (carnpholic acid) 2-methyl-2-diethylaminobutanoic acid 2,2-dimethyl-3-dipropylaminopropanoic acid t-Butylacetic (3,3 dimethylbutanoic) acid t-Amylacetic acid t-Butylmethylacetic acid Ethyl isop-ropylacetic acid Z-ethylhexanoic acid Mixtures of the acids may be employed as the mixed salts of one or more alkali metals, as well as mixed Li, Na and K salts of the same branched acid.
Representative salts are lithium pivalate, potassium pivalate, lithium alpha-isopropoxyisobutyrate, lithium trimethoxypivalate, sodium alpha-isopropoxyisobutyrate, sodium tn'methylacetate, potassium alpha-isopropoXy-isobutyrate, lithium campllol ate, lithium 2-methyl-2-diethylaminobutanoate, sodium 2-rnethyI-Z-dibutylaminobutanoate, and potassium 2,2-dimethyl-3-dipropylamin opropanoate.
The acids for salt formation may also be the mixtures obtained by carboxylating olefins such as Z-methyl-pentene-l, 2,6-dimethylheptene-3, tripropylene, tetrapropylene (i.e. mixed tetr-amethylnonenes), and the like, with carbon monoxide and water in the presence of acid catalysts, as illustrated in US. Patent 2,831,877 and French Patent 1,130,080, and by H. Koch in Brennstoff Chemie, 36, 3211 (1955). Such treatment of the branched olefins yields tertiary carboxylic acids, that is, ltrialkylacetic acids.
The volatile antiknock compounds include the lithium, sodium and potassium chelates of branched chain saturated aliphatic beta-diketones wherein the branching is within the first two carbons of at least one of the carbonyl carbon atoms, for example diketones having the formula where R may be a branched alkyl group such as tert. alkyl, sec. alkyl, neoalkyl, 0r isoalkyl, having up to 8 carbon atoms, and R may be an alkyl group having up to 8 carbon atoms including R, or a lower polyfiuoroalkyl radical such as trifluoromethyl, omega-hydrotetrafluoroethyl, pentafluoroethyl, and octafluoroisobutyl radicals. Preferred beta-diketones are those in which both R and R represent a tertiary alkyl radical such as tert.-butyl. Specific representative alkali metal beta-diketonates are the lithium, sodium and potassium chelates of dipivalcyl methane, pivaloyl acetone, diisobutyryl methane, pivaloyl trifluoroacetone, 2-methy1-7ethyl-nonanedione-4,6, and 2,8,10,10 tetramethylundecandione 4,6; e.g. lithium dipivaloylmethane, potassium dipivaloylmethane, sodium dipivaloylmethane, and lithium pivaloyltrifluoroacetonate.
Also, the volatile alkali metal compounds include branched chain saturated aliphatic alcoholates, particularly tertiary and secondary alcoholates, which may be unsubstituted or substituted as discussed and. illustrated above in respect to the carboxylates and beta-diketonates. Thus, the alcoholates may contain alkoxy, dialkylamino and polyfiuoroalkyl groups. Examples of suitable alcohols are:
Bis (perfiuoroisopropyl) carbinol 2-methy1-3,3,4,4-tetrafluorobutanol 1, 3 -bis (N, N- dimethylamino) -2-methylprop an-2-ol Tertiary butanol 1,3-dimethoxy-2-methylpropan-2-ol, and the like.
Representative specific alcoholates are:
Lithium bis-(perfiuoroisopropyDcarbinolate Lithium tertiary-butoxide Sodium tertiary-butoxide Potassium tentiary-butoxide Lithium 2-methyl-3,3,4,4-tetrafiuorobut-2-oxide Lithium 1,3 bis(N,N-dirnethylamino) -2-methylprop-2- oxide Lithium 1,3-dimethoxy-Z-methylprop-2-oxide The discovery of volatility for alkali metal compounds is particularly surprising inasmuch as the salts and chelates of organic acids are generally regarded as ionic, i.e. salt-like substances, and hence (practically speaking) nonvolatile within the thermal stability limits of the organic portions of the structures. Thus, as gasoline additives, they do not carburete in the usual way with the vaporized, i.e. with the light end portions, of the hydrocarbon fuel charge, but when successfully carburetted appear to pass through the induction system as liquid phase, i.e. with the heavy ends of the gasoline. Also, attempts to distill an alkali metal derivative of an organic compound generally results in destruction of the molecule, and indeed, such destructive distillation of volatility, i.e. ability to carry the alkali metal into the vapor state in knock suppressing proportions.
While the lithium compounds are preferred for reasons of greater volatility, thermal stability and effectiveness as antiknock agents in the method of the invention, the sodium and potassium compounds are also useful by the present method, and it should be noted that sodium and potassium compounds in general are practically ineffective when used by the other methods of the art unless special conditions and fuels are employed.
The marked effectiveness of the vaporizable alkali metal antiknock compounds by the present method in both leaded and unleaded fuels permits the use of relatively low octane fuels in high compressions, i.e. high octane requirement engines. Such improvements are not ordinarily obtainable by the use of other antiknock agents alone or without first profoundly altering the structure. i.e. the octane rating, of the hydrocarbons comprising the gasoline.
Another important consequence of the present discovery is that significantly smaller concentrations of alkali metal antiknock compound can be used to provide a given antiknock response. The smaller concentrations offer the advantages of a smaller contribution of the alkali metal to combustion chamber deposits.
This invention may be best understood by reference to the accompanying drawings in which:
FIGURE 1 is a side view of a diagrammatical representation with parts in cross-section of one form ofapparatus which may be used in the process of this invention; and
FIGURE 2 is a view in longitudinal cross-section of the intake valve assembly employed in the apparatus of FIGURE 1.
Referring first to FIGURE 1, the alkali metal vapor induction unit consists essentially of a vaporization chamber 10, a carrier gas inlet tube 12, an intake tube 14, and an electromagnetically operated intake valve 16 for admitting vaporized alkali metal compound into the combustion chamber 18 of a spark-ignition engine 20. The engine 29 is provided with a conventional piston 22, an inlet line 24 and valve 26 for fuel and/ or air, and an exhaust line 28 and valve 3%. Provision is made as at 32 for direct fuel injection into the combustion chamber 13, as desired.
For ease of assembly, the bottom of the vaporization chamber is in the form of a removable cup 34 and has a grid 36 to support pellets of alkali metal compound. Tube 12 passes through grid 36 to open into the space between the grid and the floor of the cup 34, as shown. Intake tube 14 is fitted with a valved take ofi line 38, leading to a sampling and analyzing system (not shown). The exposed outer wall surfaces of the induction unit (i.e. the outer surfaces of the vaporization chamber 10, cup 34 tubes 12 and 14, and valve 16) are wrapped with electrical resistance heating wire 46 and covered with an outer ceramic asbestos coating 42. 7
Referring more specifically to FIGURE 2, the valve 16 consists essentially of a cylinder 44, having a longitudinal bore 46 to accommodate valve stem 48, machined to provide valve seat 51 for valve face 52, threaded on the end at 54 for attachment to the combustion chamber 18 of the engine, and machined to accommodate intake tube 14, as shown. The reduced diameter 4-9 of the valve stem 48 serves to provide a passageway for vaporized antiknock compound from intake tube 14 to the combustion chamber 18 when valve face 52 is away from its seat 50, i.e. when valve 16 is open as shown in FIGURE 2. Valve stem 48 is moved to open the intake valve by supplying electrical energy to the electromagnet 56. The intake valve 16 is closed by spring 58 when the magnetic field is relaxed, 52 closing on Si When the magnetic field is applied, the tension of the spring 58 is overcome and the valve stem is moved to open the valve.
To illustrate the operation of the apparatus of FIG- URES l and 2, and the effectiveness of vaporizable alkali metal antiknock compounds when inducted into an engine by the process of this invention, the alkali metal induction unit was employed in conjunction with a CPR-single cylinder engine, as specified in the ASTM supercharged method (ASTM D 90949T), the engine being coupled to a variable speed electric dynamometer, and having its cylinder head fitted with both a fuel injection system for injecting the operating fuel directly into the combustion chamber and a magnetostrictive-rate-of-change-of-pressure pickup for detecting knock visually on an oscilloscope.
In the operation of the unit, pellets of alkali metal compound are placed on the grid 36 of cup 34 and heated, by means of the electrical resistance heating wire 40 surrounding the vaporization chamber 19, to a temperature which vaporizes the alkali metal compound at the desired rate. Tubes 12 and 14 and valve 15 are heated similarly and are maintained at a temperature slightly higher, e.g. about 5 F. to about 50 F. above that of the vaporization chamber to prevent condensation of alkali metal compound in those parts of the unit. A carrier gas, e.g. air or N is admitted into the vaporization chamber It) by way of tube 12 at a controlled rate, and is heated to the temperature of the system. Entering cup 34 below grid 36, the heated carrier gas passes up through the eated alkali metal compound and carries vapors thereof into the combustion chamber 13 via tube 14 and valve 16 when the valve is open as in FIGURE 2. A set of contact points, driven by the engine, supplies electrical energy to open the valve 16 at 30 crankangle degrees after top center and to permit it to close at crankangle degrees after top center on the intake stroke. At the same time, the hydrocarbon fuel and air, in the proportion required for burning the fuel, are introduced into the combustion chamber of the engine.
The amount of alkali metal compound entering the combustion chamber was determined by diverting the carrier gas-alkali metal vapor stream composition (from its normal path into 18) into the sampling system via 38. The sampling system consisted of a series of chilled filters of pore size 0.3-0.4 micron (to completely remove the alkali metal compound). and a rotometer for measuring the carrier gas. Determining the amount of alkali metal compound removed from a given volume of carrier gas enables the calculation of the amount of alkali metal compound entering the combustion chamber with a given volume of carrier gas. The results described in Examples 1 to 4 given hereinafter were obtained with a carrier gas flow rate of 2 volume percent of the combustion air flow rate into the engine.
It should be noted that the preceding description of the apparatus and its operation are based on alkali metal compounds which are solid and which sublime into the carrier gas stream at the temperature of vaporization. When the alkali metal compound is molten at the operating temperature, grid 36 can be dispensed with and the inlet tube 12 may terminate close to the molten surface or may dip below it, with substantially equivalent results being obtained.
The process of the invention and the apparatus that may be employed therein has been illustrated above with standard test engines under standard conditions for evaluating fuels and additives. The apparatus and the process however are adaptable to commercial multicylinder sparkignition engines. For example, the vaporization chamber 10 can be fitted with a multiplicity of intake tubes 14 and valves 16, one for each cylinder of the engine. Alternatively, a complete separate vaporization unit may be provided for each cylinder. The vaporization and feed process can be electronically automated, in response to the rate of change of pressure in the cylinder, to supply antiknock compound on demand to any one o more of the cylinders, and in varying amounts according to the requirement of the particular cylinder.
Another procedure is to insert one or more cartridges of a solid sublimable alkali metal compound, such as lithium pivalate, in the intake manifold of the engine, arranged in series or parallel with the heated fuel-air mixture, or with the heated air supply of supercharged engines. Such cartridges can be heated by the hot feed gases or heated separately, as by a self-contained electrical heating unit. The parallel arrangement is more amenable to automatic control, using appropriate by-pass lines and valves, so that the alkali metal compound as vapor may be fed into the fuel-air intake system only when needed.
In order to more clearly illustrate this invention, preferred modes of practicing it, and the advantageous results to be obtained thereby, the following examples are given in which the amounts and proportions are by weight except where specifically indicated otherwise.
EXAMPLE 1 The apparatus shown in the drawings was used and was operated in the manner described hereinbefore in connection therewith, operating the CPR-single cylinder engine under the following conditions:
Engine Conditions The engine was calibrated by operating it under these conditions on a series of primary reference fuels (a mixture of isooctane and n-heptane or a mixture of isooctane and tetraethyl lead) and the compression ratio varied to produce trace knock with no alkali metal compound being introduced into the engine in any manner or form. From the data obtained, the knock-limited compression ratio for any other fuel or fuel additive combination could be converted to conventional performance number ratings (P.N.).
As a control, the engine was run on a blended automotive type gasoline containing various amounts of lithium pivalate solubilized therein by means of 5 volume percent ethanol, and the knock-limited compression ratio determined for each composition. Then, in accordance with the method of this invention, the engine was run on the same base gasoline not containing dissolved additive, but the additive, lithium pivalate (LiP), was introduced separately as vapor by means of the vapor induction apparatus of the drawings. The results of these experiments are tabulated below:
LiP as gasoline LiP as vapor solution Cone. Temp. of Cone. of LiP Increase in vaporiz., oi LiP Increase in g./gal. P. N. F. sisal. P. N.
fuel fuel EXAMPLE 2 The engine of Example 1 was modified by removing the fuel injection system and installing a standard carburetor and induction system as specified in ASTM motor method 10 (ASTM D-357). The engine and auxiliary equipment was operated in the manner described in Example 1, but under different engine conditions as noted below. Alkali metal compounds, as listed below, were inducted as vapor in a heated stream of nitrogen as in Example 1. The operating fuel was the gasoline of Example 1.
Engine Conditions Speed, -r.p.m 900. Inlet mixture temp, F 300. Spark advance, B.T.C 15 to 20. Jacket coolant temp, F 212. Manifold air pressure, Hg abs Atmospheric. Fuel-air ratio 0.080. Fuel induction Carbureton. Compression ratio Varied to produce trace knock.
Improving Knock Resistance With Vaporized Alkali Metal Antiknocks Spark advance, 15 BTCBase fuel rating, 66 P.N.
vaporiz. Cone. of In crease Antiknock compound chamber, compound in RN.
F. gjgal. fuel Lithium pivalate (pelletized) 665 1.0 (0. 07) 15.5 695 3. 2 (0. 224) 32. 6 v 710 10. 4 (0. 728) 40 Lithium alpha -isopropoxyisobuty- 535 1. 3 (0. O6) 5 4 rate. 625 4. 9 (0. 23) 31 690 7. 2 (0. 432) 46 Lithium dipivaloyl-methane 400 0. 4 (0 015) 2. 5
435 1. 2 5. 5 400 3.3 19. 5 475 5.1 30 Lithium pivaloyltritiuoroacet mate. 412 0.5 (0.017) 4 460 3. 8 10 485 9.7 15 Lithium eampholate 770 4.3 (0.17) 18. 5
790 10. 5 3s Lithium trimethoxypivalate 655 0.05 (0.0018) 1 740 0.1 2 790 0. 6 (0. 0216) 4 Potassium pivalate 750 0. 8 (0.22) 8.8 760 1. 3 9.5 782 2 16. 5 815 3.5 23 5 Potassium dipivaloylmethane 535 0. 4 (0. 07) 4. 0 640 0.6 9.7 Sodium dipivaloylmethane 425 O. 6 (0. 07) 4. 4 (0 055) Sodium a1 ha -iso r0 0x -is '-buty 6 0.4
rate. p p p y 655 1.2 18.7 700 2.1 31. 4
f'lhe number in parentheses under concentration is g. alkali metal/gal. of uel.
When lithium alpha-isopropoxyisobutyrate was dissolved in the fuel in the proportion of about 5 grams/gal- EXAMPLE 3 This example shows the antiknock activity of the vaporized alkali metal compounds with many different fuel types. The engine was operated as in Example 2, with a spark advance setting of 20 :B.T.C. Lithium pivalate (granulated) was used in the vaporizing chamber and the temperature varied to produce different concentrations of lithiumpivalate relative to the fuel. Fuels used, and the results, in terms of the increase in performance number of the fuel due to the presence of the vaporized lithium pivalate, are shown below.
Test Results Temp. of Increase Base fuel Base fuel vaporiz. Cone. of MP in RN.
I. chamber. gJgal. fuel due to f 1 I'Ihe numbers in parentheses are grams of alkali metal per gallon of The base fuels were:
(A) 115/145 aviation base stock. Greater than 90% aviation alkylate, 89% saturates, 11% aromatics, 0% olefins.
(B) 50 O.N. primary reference fuel (50% isooctane,
(C) 76 O.N. primary reference fuel (76% isooctane,
(D) 80 O.N. primary reference fuel (80% isooctane,
(F) Straight-run gasoline. 100% saturates, less than 1% aromatics, less than 1% olefins. Octane number 70 by research method (ASTM-D-908-51).
(G) Blended gasoline. motor alkylate, 90% catalytic cracked. Analysis: 60% saturates, 16% aromatics, 24% olefins. Octane number 86.9 by research method, 79.8 by motor method (D-357).
(H) Blended gasoline. 20% catalytic reformate, 34% light alkylate, 24% xylene, 12% toluene, 10% isopentane, 2% butane. Analysis: 54% saturates, 46 aromatics, less than 0.5% olefins. Octane number 100.9 by research method, 90.0 by motor method.
(1) Commercial premium gasoline containing 1.50 ml.
of TEL/gallon. Analysis: 36% saturates, 42% aromatics, 22% olefins. Octane number 100.2 by research method, 887 by motor method.
(J) Blended gasoline19% n-heptane, 5% cyclohexane, 5% methylcyclohexane, 5% methylcyclopentane, diisobutylene, 15% isoheptenes, 12% toluene, 12% xylene, 12% ethylbenzene. Analysis: 34% saturates, 36% aromatics, 30% olefins. Octane number 93.4 by research method, 81.1 by motor method.
(K) Gasoline 1+3 ml. tetraethyl lead (TEL)/gallon. Octane number 100.4 by research method, 88.0 by motor method.
The above results indicate that with paraffinic fuels, particularly the branched paraffins such as the alkylate fuel A and the primary reference fuels 0 through E, the antiknock effectiveness of lithium pivalate was greater than in fuels containing appreciable amounts of aromatics and olefins such as fuels G through K. However, the lithium pivalate was very effective with all fuels. The presence of tetraethyl lead (TEL) in the fuel had little or no effect on the antiknock activity of the alkali metal compound, as illustrated by the data with fuels I and K.
EXAMPLE 4 The data below show the antiknock activity of various alkali metal alkoxides. The engine was operated essentially as in Example 1. The operating fuel was a fullboiling range gasoline containing 39% aromatics, 10%
olefins, and 51% saturates having a research octane number of 92.
Temp. Vap. Cone. of Antiknoek compound for vapor temp, compound, Increase press F. g./gal. fuel in RN. 1 mm., F.
(1) Lithium bis-(perfluoro- 224 230 11.6 1 (.22) 6 isopropyl) earbinolate.
(2) Lithium tertiarybut- 284 300 1.15 (.10) 10 oxide. 360 3. 94 24) 37 (3) Sodium tertiarybut- 356 320 0.25 (.06) 0.5
oxide. 340 0. 73 (.18) 3. 5 365 1. 82 44) 19. 6 375 1. 98 (.48) 19 400 3.44 (.82) 31 420 4.59 (1.10) 38 (4) Potassium tertiarybut- 428 365 2. 08 (.72) 48 oxide. 385 4.20 (1.46) 53 (5) Lithium 2-metl1y1-3,3,4, 437 420 16.95 (.70) 8 4-tetrafluorobut-2- V oxide.
(6) Lithium 1,3-bis (N,N 460 400 1.40 (.06) 3 dimethylamo)-2- 420 5.74 (.24) 0 methylprop-2-oxide. 440 10.00 (.42) 10 (7) Lithium 1,3-dimeth0xy- 473 380 2.01 (.13) 18 2-methylprop-2-oxide. 400 3. 30 16) 31 1 Numbers in parentheses are grams of alkali metal/gal. fuel.
The second column of the above table gives the temperature at which the respective alkali metal compounds exert a vapor pressure of 1 mm. of Hg, obtained by independent measurement. The third column gives the operating temperature of the vaporization unit. The last column gives the increase in performance number obtained.
The fluorine and amino-substituted alkoxides appear less effective on an equal metal weight basis than the alkoxides composed only of C, H, O and metal. Howover, all are operable.
The following alkali metal compounds, in the above procedure, gave no significant ancrease in the performance number of the fuel; the compounds either decomposed in the vaporization unit or [failed to volatilize (i.e. sublime or distill) Li naphthenate,
Li oleate, and
Li acetyl acetonate.
For example, potassium naphthenate tested over the range 200 F. to 900 F showed no sign of sublimation, no alkali metal compound could be detected in the carrier gas stream and no improvement observed in the performance number of the operating fuel charge. Exactly the same results were obtained with Li oleate. Lithium naphthenate, when heated, showed signs of subliming at 850 F. At this temperature, the carrier gas momentarily contained alkali metal compound corresponding to 0.03 g. Li/igal. of the gasoline and provided an increase in performance number of 1; however, at this point also, the compound apparently decomposed for within a matter of minutes and antiknock effect disappeared altogether. Sodium naphthenate behaved similarly: on reaching 900 F. slight sublimation began and the vapor momentarily contained 0.13 g. Na/ gal. of the gasoline which provided an increase in performance number of 2, but very soon the antiknock effect disappeared and no further activity was observed on continued heating at 900 F. On heating lithium 'acetylacetonate, a momentary large antiknock effect was observed at 600 F. (0.12 g. Li/ gal. providing an increase in performance number of 22); at this point however the compound began to decompose and within 2-3 minutes the increase in performance number fell to zero and no further antiknock effect could be obtained at 600 F. or higher ternperature. In comparison, the compounds of this invention showed continued (no-t just momentary) volatiliza- 13 tion and the antiknock er'fect lasted indefinitely under the conditions of the test.
Use of a vaporiza'ble metal antiknock compound in the conventional intake manifold of a spark-ignition engine is illustrated in the following Example 5.
EXAMPLE The fuel-air mixture heater of a standard motor method (ASTM D357) engine was fitted with a thermocouple between the heater blades, and the unit enclosed with a stainless-steel wire mesh screen so that A pellets of test compounds could be contained inside the screen in close contact with the heater blades. With the thus modified heater in place and containing marble chips as a control, the engine was openated under the standard motor method conditions, except that temperature control over the heater (and hence over the fuel-air mixture at the intake port of the engine) was manually controlled. Using a blended automotive type leaded gasoline, an octane number rating of 88 (70 performance number) was obtained for the gasoline at a fuel-air mixture temperature of 300 R, which was the same value obtained by the standard motor method with the unmodified heating unit. Using the same fuel, the compression ratio for standard knock intensity was determined for various fuel-air mixture temperatures to establish control values.
The engine tests were then repeated with diameter pellets of alkali metal compound as described below in place of the marble chips in the enclosure surrounding the (fuel-air mixture heater blades.
(A) When pelletized lithium pivalate was used, the compression ratio for standard knock intensity was significantly greater than when marble chips were used at all fuel-air mixture temperatures above 150 F. At a mixture temperature of 227 F. (corresponding to a temperature of 575 F. for the lithium pivalate pellets at the heater blades, which was suflicient to produce substantial vaporization of the lithium pivalate into the fuelmixture), the knock intensity decreased rapidly to zero, both audibly and as measured by the standard knock meter. Standard knock intensity could not be established even though the compression ratio was increased to above to 1. Thus the quality of the gasoline had been increased by the lithium pivalate vapors to greater than 147 performance numbers.
(B) Repeating (A) with A pellets of the lithium chelate of dipivaloylmethane, the knock intensity of the gasoline was found to be significantly increased at all fuelair mixture temperatures above 125 F.; but, when the mixture temperature reached 190 F. corresponding to a Li compound temperature of 360 F., the knock intensity decreased to zero even at a compression ratio of 10 to 1. Thus, as in (A), the quality of the fuel has been appreciated to better than 147 performance numbers.
(C) Repeating the above procedure with pelletized lithium alpha-isopropoxyisobutyrate gave substantially identical results. With the lithium compound at a temperature of 400 F. and a tuel air mixture temperature at 190 F., no knock could be detected at a 1 0 to 1 compression ratio corresponding to a performance number requirement of at least 147 for the operating fuel. Thus, as in (A) and (B), the original 70 performance number fuel had been improved in quality by the presence of the vaporized alkali metal compound by at least 77 performance numbers.
In this Example 5, the pellets of the lithium compounds were prepared from powdered solid, without the use of a binder, in a conventional pelletizing machine.
Pelletized compounds can be also prepared by pouring a saturated methanolic solution of the compound over glass beads and allowing the solvent to evaporate. Substantially identical results are obtained with such preparations in the above engine procedure.
It will be understood that the preceding examples have been given for illustrative purposes solely and that this invention is not limited to the specific embodiments described therein. On the other hand, it will be readily apparent to those skilled in the art that, subject to the limitations set forth in the general description, the alkali meal antiknock compounds, the carrier gas, the proportions, the conditions, and the apparatus employed, may be widely varied without departing from the spirit or scope of this invention.
From the preceding disclosure, it will be apparent that this invention provides a novel method for suppressing knock in sp-ark ignition internal combustion engines and particularly for introducing the alkali metal antiknock compounds into the combustion chamber of the engine in a new (vaporized) form whereby greatly improved performance of the engines can be obtained. Therefore, it will be apparent that this invention constitutes a valuable advance in and contribution to the art.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as -follows:
1. The method for suppressing knock in a spark-ignition internal combustion engine containing a combustion chamber, which method comprises inducting into said combustion chamber a hydrocarbon fuel for said engine and air in the proportion required for burning said fuel, heating a vaporiz-able alkali metal an-tiknock compound which is an organic compound of the alkali metal and has a vapor pressure of at least about 0.01 mm. of mercury below about 900 F. and vaporizing a knock-suppressing quantity of said alkali metal compound corresponding to at least 0.001 gram of alkali metal per gallon of hydrocarbon fuel into a nonreactive carrier gas, induc-ting the carrier gas and the vaporized quantity of alkali metal compound into the combustion chamber simultaneously with the hydrocarbon fuel and air, and igniting and burning the fuel in the presence of the vaporized alkali metal compound.
2. The method for suppressing knock in a spark-ignition internal combustion engine containing a combustion chamber, which method comprises inductin-g into said combustion chamber a hydrocarbon fuel for said engine and air in the proportion required for burning said fuel, heating to a temperature of from about 300 F. to about 900 F. a vaporizable alkali metal antiknock compound which is an organic compound of the alkali metal and has a vapor pressure of at least about 0.01 mm. of mercury below about 900 F. and vaporizing a knock-suppressing quantity of said alkali metal compound corresponding to at least 0.001 gram of alkali metal per gallon of hydrocarbon fuel into a nonreactive carrier gas which is at a temperature sufficient to maintain the alkali metal compound in the vapor state, inducting the carrier gas and the vaporized quantity of alkali metal compound into the combustion chamber simultaneously with the hydrocarbon fuel and air, and igniting and burning the fuel in the presence of the vaporized alkali metal compound.
3. The method for suppressing knock in a spark-ignition internal combustion engine containing a combustion chamber, which method comprises inductin-g into said combustion chamber a hydrocarbon fuel for said engine and air in the proportion required for burning said fuel, heating to a temperature of from about 300 F. to about 900 F. a vaporizable alkali metal .antiknock compound which has a vapor pressure of at least about 0.01 mm. of mercury below about 900 F. and vaporizing a knock-suppressing quantity of said alkali metal compound oorresponding to at least 0.001 gram of alkali metal per gallon of hydrocarbon fuel into a minor proportion of a nonreactive carrier gas which is at a temperature sufficient to maintain the alkali metal compound in the vapor state, induct-mg the carrier gas and the vaporized quantity of alkali metal compound into the combustion chamber simultaneously with the hydrocarbon fuel and air, and igniting and burning the fuel in the presence of the vaporized alkali metal compound, said alkali metal antiknock compound being selected from the group consisting of the lithium, sodium and potassium salts and chelates of branched chain saturated ahiphatic carboxylic acids, branched chain saturated aliphatic betadiketones and branched chain saturated aliphatic alcohols which acids, beta-dtiketones and alcohols are composed of elements selected from the group consisting of carbon, hydrogen, oxygen, fluorine and nitrogen atoms including at least carbon, hydnogen and oxygen, and in which salts and chelates the alkali metal is bonded to the branched organic portion of the compound through oxygen.
4. The method for suppressing knock in a spark-ignition (internal combustion engine containing a combustion chamber, which method comprises inducting into said combustion chamber a hydrocarbon fuel for said engine and in the proportion required for burning said fuel, heating to a temperature of from about 300 F. to about 800 F. a vaporizable alkali metal antikrnock compound which has a vapor pressure of at least about 0.1 mm. of mercury below about 756- F. and vaporizing a knock-suppressing quantity of said alkali metal compound corresponding to from about 0.01 to about 1 gram of alkali metal per gallon of hydrocarbon fuel into from abut 0.1% to about 10% by volume based on the fuelair mixture of a nonreactive carrier gas which is at a temperature sufficient to maintain the alkali metal compound in the vapor state, inducting the canrier gas and the vaporized quantity of alkali metal compound into the combustion chamber simultaneously with the hydrocarbon fuel and air, and igniting and burning the fuel in the presence of the vaponized alkali metal compound, said alkali metal antikn ock compound being selected from the group consisting of the lithium, sodium and potassium salts and chelates of branched chain saturated aliphatic cerboxylic acids, branched chain saturated aliphatic beta-diketones and branched chain saturated aliphatic alcohols which acids, beta-diketones and alcohols are composed of elements selected from the group consistin of carbon, hydrogen, oxygen, fluorine and nitrogen 16 atoms including at least carbon, hydrogen and oxygen, and in which salts and che a es the alkali metal is bonded to "the branched organic portion of the compound through oxygen.
5. The method for suppressing knock in a spark-ignition internal combustion engine containing a combustion chamber, which method comprises inducting into said combustion chamber a hydrocarbon fuel for said engine and air in the proportion required for burning said fuel, heating to a temperature of from about 400 F. to about 809 F. a vaporizable alkali metal antiknock compound which has a vapor pressure of at least about 0.1 of mercury below about 750 F. and vaporizing a knocksuppressi-ng quantity of said alkali metal compound corresponding to from about 0.01 :to about 1 of alkali metal per gallon of hydrocarbon fuel into from about 0.1% to about 10% by volume based on the fuel-air mixture of a nonreactive carnier gas which is at a temperature sufficient to maintain the alkali metal compound in the vapor state, ind-noting the carrier gas and the vaporized quantity of alkali metal compound into the combustion chamber simultaneously with the hydrocarbon fuel and air, and igniting and burning the fuel in the presence of the vaporized alkali metal compound, s id alkali metal antilon-ock compound being an alkali metal salt of a branched chain saturated aliphatic carboxylic acid, which alkali metal has an atomic weight between 6 and 4t) and which acid is composed of carbon, hydrogen and oxygen.
References (Iited in the file of this patent UNITED STATES PATENTS 2,151,432 Lyons et a1 Mar. 21, 1939 2,935,973 Sandy et \al May 10, 1960 2,935,974 Sandy et al May 10, 1960 2,935,975 Sandy et el May 10, 1960 FOREIGN PATENTS 300,156 Great Britain Nov. 6, 1928 312,245 Great Britain May 17, 1929 658,959 France Jan. 22, 1929