US2720869A - Method of operating a compression ignition engine - Google Patents

Description

United rates METHQD F OPERATING A COMPRESSION IGNITION ENGINE No Drawing. Application August 5, 1954, Serial No. 448,160

13 Claims. (Cl. 123l) to Ethyl of Dela- This invention pertains to a method of operating a compression ignition engine and is particularly concerned with a method of inducting alkali metals into the fuel of such engines which enhances cetane number and improves combustion characteristics.

It has long been known that certain metals can be added to diesel fuels for the purpose of enhancing their cetane number and improving their combustion characteristics. One method of incorporating the metal into the fuel is to prepare a dispersion of the metal in a liquid dispersion medium and then dilute this dispersion with the diesel fuel. Objectional features of this technique are that upon storage, the alkali metal settles and due to atmospheric conditions and water in the fuel, it reacts to destroy its efiectiveness and to produce contaminants. Mixing the liquid dispersions with the fuel in the fuel system of the engine is likewise undesirable. In some instances, the reaction of the metal with water from the atmosphere can be a fire hazard. In order to alleviate the reaction problem, it has also been proposed to coat the metal particles with polyethylene, thereby preventing contact between the metal and the water. The latter technique still suffers the disadvantage that upon prolonged storage, the coated particles tend to settle and must be re-dispersed prior to induction in the combustion chamber. Further, because of the coating of the ethylene polymer on the alkali metal particles, the effectiveness of the alkali metal in improving cetane number is considerably reduced. Therefore, the advantage achieved with respect to nonreactivity with water is at the expense of the effectiveness of the alkali metal. Thus, it is desirable to provide a method for incorporating the alkali metals in the fuels of compression ignition engines in a manner which will eliminate the settling problems and also eliminate the deterioration and hazards involved due to the exposure of the alkali metal to water or atmospheric conditions upon prolonged storage. As a result of my work in this field, I have disatent 0 covered a method of operating a compression ignition engine which takes advantage of the full effectiveness of the alkali metals and overcomes the above and other disadvantages of the prior art methods.

It is, therefore, an object of this invention to provide a new and novel method of operating compression ignition engines. A more specific object is to provide a method of operating compression ignition engines wherein finely divided alkali metal is introduced to the fuel just prior to combustion in an efiicient and practical manner without encountering settling of the metal in the fuel. The above and other objects of this invention will be apparent hereinafter.

In a method of operating a compression ignition engine wherein a fuel is injected into the combustion chamber and compressed therein to attain ignition temperature and the products of combustion act upon a piston thereby producing a driving force, the improvement has now been found which comprises contacting the fuel with a solid dispersion of finely divided alkali metal whereby the metal is released and suspended in the fuel prior to injection of the fuel into the combustion chamber so as to increase the cetane number and improve the combustion characteristics of the fuel. In general, the fuel is contacted with the solid dispersion of finely divided alkali metal at some point in the fuel system between the fuel tank and the discharge port or ports of the injectors. The fuel is contacted with the alkali metal dispersion at a convenient point between the fuel pump and the discharge ports of the injectors or between the fuel tank and the pump. It is preferable to contact the fuel with the solid dispersion between the fuel tank and the pump to avoid compression of the fuel in the dispersion container which would thereby decrease the efficiency of injection into the combustion chamber. By my technique, the lapse of time between the contact and injection is a matter of a few seconds generally not more than about one minute and preferably less than 30 seconds. Thus, my method provides an eflicient and practical means for introducing finely divided alkali metals into a diesel fuel for the purpose of improving the combustion characteristics and the cetane number of that fuel. In practicing my invention the fuel is passed over the solid dispersion essentially immediately prior to injection into the combustion chamber, and in this manner by means of erosion and solubility of the dispersion medium, the finely divided alkali metal particles are released and suspended into the fuel. The solid dispersion which I employ comprises a mixture of finely divided alkali metal uniformly dispersed in a solid dispersion medium. In another embodiment, the solid dispersion comprises a mixture of finely divided alkali metal, a dispersion medium, and a modifying agent which alters the dispersion in order to meet particular physical characteristics.

As noted above, the alkali metal dispersions which I employ are solid dispersions comprising a mixture of finely divided alkali metal uniformly distributed in a solid dispersion medium. The concentration of the finely divided metal can be varied over wide limits. That is, the concentration of the metal in the solid dispersion can be between about 10 and 85% by weight. Best results are achieved, however, when the concentration is between about 40 to by weight. Likewise, the particle size of the alkali metal can be varied over wide limits from very minute particles up to about 1000 microns in size. I especially prefer that the particle size of the alkali metals be not greater than about 20 microns since these small particle sizes have been shown to be most effective.

The dispersion media which I employ are solids at atmospheric conditions. In general, they can be any solid organic compound or mixture which is essentially inert or non-reactive with an alkali metal is substantially soluble in diesel fuel and has a melting point above atmospheric temperature. I especially prefer those dispersion media which have a melting point above about C. since the solid metal dispersions containing as the dispersion medium a material having this physical characteristic are most practical for the use of induction of the metal into diesel fuel by erosion and solution. In some instances, the solid dispersion medium can have a lower melting point, as for example about 60 C., depending upon the climatic conditions under which the solid dispersion is to be employed. Another criterion of choice of the dispersion medium is that it be substantially soluble in diesel fuel over a temperature range from 50 to +70 C. Thus, the dispersion media which I employ are solid materials preferably selected from the group consisting of hydrocarbons and ethers. The solid hydrocarbons employed are either non-aromatic or aromatic. The solid non-aromatic hydrocarbons are intended to include the solid alkanes, alkenes,

cyclanes, cyclenes, polycyclanes, and polycyclenes. When the solid dispersion medium is a solid alkane, it can be, for example, nonadecane, eicosane, heneicosane, tetracosane,

hexacosane, dotriacos'aiie, triacontane, hentriacontane, and the like. The solid alkanes having melting points above about 70 C. are, for example, dotriacontane, tritriacontane, tetratriacontane, tetracontane, tetratetracontan'e, pent'acontane, and the like. The solid 'alkenes can be, 'for example, 'decosenel; Z methyltri'cOSene-Z; hexacosene-l; heptacos'ene-l; "hentriacontene-l; and the like. Those solid alkenes having melting points above about 70 C. include, fore'xample, 'heptatriacontene-l; octatriac'ontene l; tetracohtene-l; pe'nta'conterre-l; hexaco'ntene- 1; and the like. The solid cyclanes which can be employed as dispersion rnedia according to my invention are, for example, octadecylcy'clohe'xane; cyclohexyldocosane; -cyclohexylhexac'osane; cyclote'tradecan'e; cyclopentade'c'an'e; cyclod'ocosane; and the like. Cyclooctadec'aiie, hexaethylcyclohexane, 'cycloheptatriacontane, cyclopentacontane, and the like, are examples of the cyclanes havin'g melting'poi'rit's abov'e about 70 C. Among the solid cyclenes which can be employed are, for example, eyclopentadecene; cycloheptade'cene; cyclotriacontadi'e'n'e-Llb; andthe likejand particularly thosehaving melting points above about 70 C. as, for example, d-bo'rnylen'e; l-bornyl'ene'; dl-3 ,7,7-t'rimethyl-( 1,2,2) -bicycloheptene-l; and the like. The polycyclanes and polycyclenes include,"-for example, 3 ihethyl-1-'(3 methylcyclopentyl)-cyclopentane; dihydrodicyclopentadiene; cyclopentadecylcycl'opentadecane; ca'rnphene; perhydronaphthacene; androstane; and the like. Those polycyclanes and polycyclenes having melting points above about 70 C. include, fo'r'example, bis-( 1 methyl 4 isopropyl)-cyclohexane; 1,3-dicyclohexylcyclohexane; l,1,l,2'-tetracyclohexylethane; (l,2,2)-bicycloheptane; perhydropyrene; pregnane; norcholane; cholan'e'; cholestane; camphane', 3,4 cyclohexano (0,4,4) bicycl'odec'adiene 3 (1,6); sciadopitene; and the like.

When the solid dispersion=mediurnisa solid aromatic material, it can be a solid mononuclear material, polynuclear material in which the r-ings are notffused, or polynuclear material i'n WhiCh the ringsare fused. Typical examples'of the solid mononuclear-aromatic materials include pentamethylbenzene; 1 ,2-di-t'ert-butyl-4-methylbenzene; octadecylbenze'ne; l'-phen'yleico'sane, and the like. Examples of 'mononuclear solid aromatic hydrocarbons having a melting point above about 70 C. include -durene; 1,2,4 or l,3,'5-triethylbe'nzene; 1,4-'di t'er't-butylbenzene; l,3,5 triisopropylbenzene; -l,2'- dioctadecylbenzene; hexaethylbenzene; 1,4;dicyelohexylbehzene; and the like. Among the solid polyniielear aromatic hydrocarbons wherein the rings aren'ot 'fused are included, for example, l-methyl-'4'-phenylben2'ene; -l-tert-butyl-4-phenylbenzene; l,2-diphenylethane; andth'e like. These solid'polynuclear hydrocarbons in which the'rings are not fused which I employ and have melting points above about 70 C. include, for example, biphenyl; 4,4-dimethylbiphenyl; 4,4'-diethylbiphenyl; 2,2-diisopropyl-phenylbiphenyl; 1,2- di-p-tolylethane; 1,4-diphenylhexane: m-diphenylbenzene; 4 cyclohexylbiphenyl; 1,4 diphe'nylbenzene; triphenyldimethylcyclopentane; 3,3'-dipheriylbiphenyl; stilbene; and the like. Among the solid polynuclear aromatic hydrocarbons in which the rings are fused 'are'included, for example, Z-methylnaphthalene; cyclohexylnaphthalene; 3-methylnaphthene; 1-phenyl-2-methylindene; 9-methylfluorene; and the like. Examples of 'polynu'clear hydrocarbons having melting points above about 70 C. includenaphthalene; 2,3-dimethylnaphthalen'e; 1,4-'dicyclohexylnaphthalene; acenaphthene; fiuorene; 2 methylfiuorene; acenaphthylene; phenylnaphthalene; 'ethylpyrene;-retene; fluor-anthene; and the like. Itis to be understood that mixtures of hydrocarbons which 'are solid can be employed as the dispersion medium. For example, amongsuch materials are the various waxes, especially those'waxes obtained in petroleum refining.

When the dispersion media are the ethers, they can be any ether which is solid and 'gener'ally'has the criteria described-previously. Such ethers'include both thenonaromatic and aromatic ethers. Typical examples of nonaromatic ethers include didodecyl ether; ditetradecyl ether; dihexadecyl ether; dioctadecyl ether; and the like, including mixing ethers as, for example, octadecyleicosyl ether, and other straight chain or branched chain ethers which are derived from mono or poly alcohols of the alkane, alkene, cyclane, and cyclene series. Examples of solid non-aromatic ethers having melting points above 70 C. include ditetracosyl ether; dihexacosyl ether; ditriacontyl; dihentriacontyl; or ditetracontyl ethers; and the like. Among the solid aromatic ethers are included, for example, ethyLB-naphthyl ether; o-diethoxyben'zene; 1,2,3 trimethoxybenzene; trimethyleneglycoldiphenyl ether; and the like. Those solid aromatic ethers which have melting points above about 70 C. include, for example, methyl-fl-naphthyl ether; p-diethoxybenzene; biphenylene oxide; benzyl-u-naphthalene ether; 4-methoxybiphenyl; 1,2-diphenoxyethane; and the like. It is to be understood that the foregoing is merely a representative list of the hydrocarbon and ether type materials which I employ as dispersion media. Otherexamples will be evident to those skilledin the art. Primarily because of greater availability, and superior physical characteristics, the solid hydrocarbons, particularly naphthalene, biphenyl, and a'cenaphthene are preferred dispersion media.

In many instances because of varying climatic conditions and handling of the solid dispersion, it is desirable that it meet particular physical characteristics. Among such characteristics are that it be a solid which is dimensionally stable. That is, it will not flow when subjected to a wide temperature rangeof about to C., nor will it lose its shape by applying a slight pressure thereto. It should also be stable to mechanical fracture and not lose its shape when dropped a distance of about 3 feet toa solid surface. Likewise, when exposed to rapid thermal change of the temperature range mentioned above thermal fracture should 'not occur. The solid dispersions should have a substantially equivalent rate of solubility or erosion into the fuel over the aforementioned temperature range and the particles which-are eroded should not be greater than about 0.04 inch in order to prevent plugging of the fuel lines and injectors. In order to meet these particular physical characteristics, the solid dispersions described previously are modified by incorporating an additional material which is termed a modifying agent.

The modifying agents which I employ are liquids, semisolids, and greases. Solids which are different from the dispersion medium are also employed as modifying agents. By modifying agent, I intend a material which alters the physical characteristics of the solid dispersions. In general, the criteria of choice of the modifying agents are that they be substantially soluble or dispersible in the dispersion medium, essentially inert to the metal, non-brittle, and substantially soluble in the fuel by which the solid dispersion is to be subsequently dissolved or eroded. I particularly prefer those materials which, when incorporated in the dispersion medium, modify the dispersion such that they reduce the brittleness thereof and modify the erosion and solution characteristics of the dispersion into the fuel so that the latter characteristics will be substantially equivalent'over a temperature range from about 50 to +70 'C. It is also preferable that the modifying agent have a melting point below the temperature at which the dispersion is to beprepared, although this is not required if the modifying agent is of small particle size, preferably less than about microns and dispersible within the medium. Likewise, it is'preferable to employ as a modifying agentthose materials having a boiling point above the melting point of the alkali-metal in order to avoid the use of pressure when preparing the dispersion.

As noted'above, the modifying agents can be'liquids, semi-solids, greases, or solids. When the modifying agents are -liquids, they can be selected from the group consisting of liquid hydrocarbons and ethers. The liquid hydrocarbons can be liquid non-aromatic or aromatic materials. The liquid non-aromatic hydrocarbons include liquid alkanes, alkenes, cyclanes, or cyclenes. Typical examples of the liquid alkanes are heptane, octane, nonane, and the like up to and including about octadecane and their various branched chain isomers. Among the liquid alkenes are included, for example, heptylene, octylene, and the like up to and including about octadecylene and the corresponding branched chain isomers thereof. When the modifying agent is a liquid non-aromatic cyclane, it can be, for example, cycloheptane, cyclooctane, methylcyclohexane, and the like. When the modifying agent is a cyclene, it can be, for example, cycloheptene, cyclooctene, methyl-A -cyclohexene; methyl-A -cyclohexene, and the like. When the modifying agent is a liquid aromatic material, it can be selected from the group consisting of the mononuclear, polynuclear, nonfused ring and polynuclear fused ring materials. Typical examples of the liquid mononuclear aromatic materials include toluene; ethylbenzene and the like monoaliphatic substituted derivatives of benzene up to and including about n-hexadecylbenzene; the xylenes; 1-methyl-4-ethylbenzene; 1,2- diethylbenzene; 1-methyl-4-n-hexadecylbenzene; 1,2,3-trimethylbenzene; 1,2,3,4,5-tetraethylbenzene; butene-Z-ylbenzene; 3-phenyloctene-4; l-methyl-Z-(propane-2-yl)- benzene; cyclopropylbenzene; cyclohexylbenzene; l-cyclopentyl-3-phenylpropane; methylcyclohexyltoluene; cyclopentene-l-ylbenzene; and the like. When the modifying agent is a liquid polynuclear non-fused material, I employ, for example, 1-methyl-2-phenylbenzene; 1,2-diphenylbutane; 1-phenyl 2-o-tolylpropane; l-phenyl-Z-benzylbutane; 1,5,9-triphenylnonane; 1,2,4-triphenylcyclopentane; and the like. When the liquid aromatic modifying agent is a polynuclear fused ring material, it can be, for

example, indane; S-methylindane; tetralin; 6-n-hexadecyl- 1,2,3,4-tetrahydronaphthalene; 1-ethyl-6-methyl-1,2,3,4- tetrahydronaphthalene; indene; 1,4-dihydronaphthalene; 1,4,6-trimethyl-1,2-dihydronaphthalene; 1,2-cyclopentano- 1,2,3,4-tetrahydronaphthalene; octanthrene; 1,2-benzoeycloheptane-3; l-methylnaphthalene; 2-isopropylnaphthalene; l,3,G-trimethylnaphthalene; 4cyclohexyl-1,2-dihydronaphthalene; l-cyclohexylnaphthalene; l-phenylindane; and the like.

When the modifying agent is a liquid ether, they are selected from the group consisting of the non-aromatic, aromatic, and poly ethers. The non-aromatic ethers include the monoaliphatie and mixed ethers. Typical examples of the monoaliphatic ethers which I employ are di-nbutyl ether; di-sec-butyl ether; diisobutyl ether; di-n-amyl ether; di-n-heptyl ether; and the like. mixed ethers which I employ are n-amylmethyl ether; tert-arnylethyl ether; n-butylisopropyl ether; ethylisoamyl ether; n-butyl-n-propyl ether; and the like. The aromatic ethers include the mono ethers, alkyl aryl ethers, and the alkaryl alkyl ethers. Typical examples of the mono aromatic ethers include dibenzyl ether; diphenyl ether; and the like. When the aromatic ether is an alkyl aryl ether, I employ, for example, methylphenyl ether; methyl-o,m, orp-tolyl ether; methyl-a-naphthyl ether; ethylphenyl ether; ethyl-o,m, or p-tolyl ether; ethyl-a-naphthyl ether; phenyl-n-propyl ether; isopropylphenyl ether; n-butylphenyl ether; n-butyl-o-tolyl ether; isoamyl-n-naphthyl ether; and the like. The alkaryl alkyl ethers which I employ are, for example, benzylmethyl ether; benzylethyl ether; benzyl-n-butyl ether; and the like. Examples of the poly ethers which I employ include ethylene glycol ethylmethyl ether; ethylene glycol methyl-n-propyl ether; 1,4-dioxane; pyrocatechol dimethyl ether; resorcinol dimethyl ether; 1,2,4-trimethoxybenzene; and the like.

It is not necessary thatthe liquid modifying agents be pur materials. I can employ mixtures of the hereinbefore mentioned modifying agents as, for example, petroleum distillates, kerosenes including diesel fuels, gasoline, mixtures of the ethers, and the like. When the modifying agent is a semi-solid, it can be petrolatum,

Examples of the petroleum waxes, natural and synthetic greases, preferably of a hydrocarbon base, and the like. When the modifying agent is a solid, I employ those materials described previously as dispersion media so long as it is different than the dispersion medium employed and alters the dispersions physical characteristics as defined above. In some instances, particularly when only a minor proportion, that is less than about 2% by weight is employed, certain inorganic modifying agents are suitable. For example, the bentones, especially the activated bentones, have been employed with good results. Likewise, combinations of modifying agents can be employed. For example, a mixture of petrolatum and a petroleum distillate having an end point maximum of 550 F., a freezing point maximum of 76 F., and a specific gravity of about 0.825 will alter the erosion and solubility characteristics to more uniformly produce substantially equivalent solubility and erosion of the dispersion within the temperature range of about 50 to C. It has been found that petrolatum enhances solubility and erosion at the lower temperature and the above mentioned petroleum distillate does likewise at the higher temperature. The liquid hydrocarbons or mixtures thereof are preferred modifying agents since they are superior in modifying the physical characteristics of the dispersion. Other modifying agents or combinations thereof will be apparent to those skilled in the art.

By employing the technique of my invention, the problem of settling of the metal in the fuel is obviated since the metal is suspended essentially immediately prior to combustion in the engine. A further particular advantage of my method of operating a compression ignition engine is that the dispersion is not contaminated by atmospheric action as is obtained during storage, nor is it necessary to re-disperse the alkali metal because of settling which is obtained during storage when employing the liquid dispersions. Another additional advantage to the method of my invention is that the dispersion is easily handled and is not subject to stratification, settling, or the like even under extreme atmospheric conditions as is frequently required when operating these engines at various locations.

To further demonstrate the method of this invention, the following examples are presented wherein all parts are by weight unless otherwise specified.

Example I To a vessel equipped with a means for agitation, heating means, and inlet and outlet ports, was added 200 parts of naphthalene and 200 parts of sodium pieces about A; inch in size. The mixture was heated to a temperature of and maintained under an atmosphere of pre-purified nitrogen. It was then agitated for a period of about 20 minutes with a cruciform head agitator rotating at about 20,000 R. P. M. At the end of this period, the mixture was then poured into a cylindrical mold and cooled to room temperature under a pre-purified nitrogen atmosphere. A sample of this solid dispersion was dissolved in kerosene in order to determine the particle size of the sodium. This was found to be an average of 9 microns with a range between about 1 to 20 microns.

A cylindrical container adapted for retaining a portion of the above solid dispersion and having an inlet and outlet tube such that a liquid could pass over the solid dispersion is attached to the fuel line of a CFR diesel engine between the fuel tank and pump becoming a part of the fuel system. A portion of the solid dispersion prepared above is placed in the container. A diesel fuel, straight run from Gulf Coastal petroleum, having a cetane number of 33 is charged to the fuel tank and passed over the dispersion at a rate such that the fuel by erosion and solution of the dispersion medium contains about 0.05% by weight of sodium. The cetane number by the ASTM method (D613) is raised to 75.

Example 11 To a reaction vessel equipped with a means for agitation, heating means, and inlet and outlet ports, was added 2001parts of naphthalene and 20 parts of mineral oil having a flash point of 385 F. and a viscosity of 310-320 cen'ti'stokes'at 70 C. This mixture was heated to a temperature of about 120 C., and 200 parts of sodium were added thereto which melted "upon addition. The mixture'was maintained under an atmosphere of prepurified nitrogen and vigorously agitated with a cruciform head agitator rotating at about 20,000 R. P. M. for a period of about 20 minutes. The mixture was then poured into a cylindrical mold and cooled to room temperature under apre-purified nitrogen atmosphere.

The solidified sodium dispersion was then removed rom'the mold and dropped 3 feet to 'a'solid surface. Such mechanical shock did not fracture the dispersion. The dispersion was then cut in 'two in order to observe the uniformity of the metal particles in the dispersion. No Stratification was noted. A 'portionof the dispersion was heated to 70 C., then immediately immersed in oil maintained at -50 C. for two minutes, and upon removal was examined to note any fractures and these were not evident, and then immediately dropped 18 inches where, again, no fracturing took place. Another small portion was dissolved in kerosene and the particle size of the sodium was determined by microscopic examination to average about 9 microns with a range of between about 1 to 30 microns. A portion of the solid dispersion, 2 parts, was placed into a container and covered with kerosene, about 42 parts, while maintained at a temperature of 70 C. A second equal portion was simultaneously covered with kerosene as described above in a separate container and maintained at atemperature of about '50 C. Upon standing for a period of about 15 minutes, by visual observance, the erosion and solubility of the two samples were found to be substantially identical and substantially equal quantities of the sodium particles were released and suspended in the kerosene. Third and fourth portions, substantially'equal tothe above mentioned portions, were also placed in separate containers and covered by equivalent portions of kerosene while being maintained at -50 C. and +70 C. respectively. In this instance in order to simulate the flow of the fuel over the solid dispersion, the kerosene was agitated. Again by visual observation, the sodium particles were released by erosion and solubility into the kerosene at substantially the same rate. The latter tests, i. e., mechanical and thermal fracture, solubility, etc. indicate that the dispersion is satisfactory for induction in diesel engine fuels and handling under extreme climatic conditions.

Another sample of this solid dispersion was placed into the cylindrical container as described in Example I, and the same diesel fuel was passed over the solid dispersion at a steady rate of about 1 foot per second. The fuel was found-to contain about 0.1% by weight of sodium and had a cetane number of 87 as determined by the ASTM method.

Example III A solid dispersion comprising 200 parts sodium, 200 parts naphthalene, 40 parts petrolatum, and 1 part oleic acid was prepared asdescribed in Example I. The average particle size of sodium of this dispersion was 8 micronsand the range was from 1 to 19. Upon subjecting it tothe tests described in Example II, these were found to be satisfactory. When this dispersion is placed into the container as mentioned above and the fuel is "passed thereover at about lfoot per second,'the cetane number, as 'determined'by the ASTM 'm'eth'od, increases from 33 to 89 andthe concentration ofthe sodium in thefuel is again'about Il by weight.

Example IV Similar results are achieved when a dispersion comprising 200 parts sodium of average particle size 8 microns and ranging from l-20 microns, 196 parts biphenyl, 2 parts oleic acid, and 10 parts kerosene is employed. The cetane number increases from 33 to 79 with the concentration of the sodium in the fuel about 0.05% by weight.

Example V This run was repeated essentially the same as above using as the solid dispersion 200 parts sodium of average particle size of 6 microns ranging from 1-l2 microns, 198 parts naphthalene, 2 parts oleic acid, and 10 parts of a petroleum distillate having an end point maximum of 550 F. and a freezing point maximum of -76 F. .In this instance, the increase in cetane number is 35 with the concentration of the sodium in the fuel at about 0.025% by weight.

Example VI When the dispersion employed comprises 198 parts of sodium of average particle size of 10 microns ranging from l-25 microns, 198 parts naphthalene, 2 parts oleic acid, and 4 parts Ofparafiin wax, the increase in cetane is 66 with the concentration of the sodium in the fuel at about 0.25% by weight.

Example VII A dispersion comprising 200 parts of sodium, particle average 11 micronsrange 1 to 30 microns, and 200 parts of p-diethoxybenzene is eroded in the manner described above with the fuel flowing at a rate of about 0.5 foot per second. In this instance, with a concentration of the sodium in the fuel of about 0.15% by weight, the cetane number is 93 in contrast to 33 of the starting fuel,

Example VIII When a dispersion comprising 200 parts of sodium, average particle size 13 microns, range 1-32 microns, 198 parts of durene, 2 parts of oleic acid, and 15 parts of n-butyl-n-propyl ether is eroded by the fuel so that the concentration of the sodium in the fuel during combustion is about 0.2% by weight, the increase in cetane number is 65.

Similar results are obtained when other alkali metals are substituted for sodium in the above and other examples as, for example, potassium, lithium, rubidium, and cesium. Likewise, equally good results are obtained when other dispersion mediums are employed than those presented in the examples, such as, acenaphthene, 2- phenylnaphthalene, and the like hydrocarbons and ethers mentioned previously. Thus, the dispersion compositions which will produce similar results are, for example, a solid dispersion of finely divided potassium in acenaphthene and mineral oil; a solid dispersion of finely divided lithium in l-phenylnaphthalene and kerosene; a solid dispersion of finely divided sodium in biphenylene oxide and mineral'oil; and the like. Many other combinations of the metals, dispersion media, and modifying agents will be evident to those skilled in the art.

As noted above, in certain instances dispersing agents are employed in the dispersion since these dispersing agents prevent agglomeration of the metal particles when subsequently eroded by the fuel and also aid in the preparation of the more finely divided particle size of the metal in the dispersion. Although not always required, it is preferred to use the dispersing agents. These agents are well known and adequately set forth in the literature. Among those employed are the fatty acids and their salts, carbon black, high molecular weight alcohols and ethers, certain polymers and copolymers, and the like.

The proportions of the various constituents in these solid dispersions can be varied over a wide'ra'nge. In

general, the preferred dispersions comprise between about 0.8'to 1.2 parts of dispersion medium per part by weight of alkali metal. When employed, the proportion of modifying agent should be between about 0.005 to 0.6 part by weight of alkali metal and the proportion of dispersing agent should be between about 0.0 to 0.25 part by weight per part by weight of alkali metal. ferred composition which is employed about 0.9 to 1.05 parts of dispersion about 0.01 to 0.5 part of modifying agent and between about 0.0 and 0.01 part of dispersing agent per part by weight of alkali metal.

It is to be understood that the shape of the dispersion can be modified greatly by employing various casts into which the dispersion is molded. That is, it can be cubical, cylindrical, circular, or a solid having an irregular surface which will impart greater surface area per unit mass. Likewise, alternate means for eroding the dispersion into the fuel will be evident to those skilled in the art. Further, although these dispersions are not too reactive under atmospheric conditions, they can be coated by various plastics which can be readily peeled from the solid dispersion before use or coated by fuel soluble materials as, for example, the solid hydrocarbons which will protect the dispersion from contamination and dissolves when in use. Such coatings are applied by dipping or spraying.

As described previously, the fuel is contacted with the solid dispersion at a convenient point between the fuel tank and the injectors. Such contact can be made between the fuel pump and the injectors or preferably between the fuel tank and the pump. In either event, the time between the contact and combustion is a matter of seconds, generally not more than about 1 minute, and usually less than 30 seconds. Thus, there is insufficient opportunity for settling of the alkali metal or maldistribution to be achieved. A further criterion of choice of the location of contact of the solid dispersion in the fuel system is that the lines subsequent to the dispersion container do not have constrictions smaller than about 0.04 inch. Constrictions smaller than this size should be avoided in order to eliminate plugging which may occur. It will be evident that only minor modifications need be made to the fuel systems of commercial diesel engines in order to practice my invention. For example, in those engines wherein an excess of the fuel is employed for cooling the injector, and this excess is recycled to the fuel tank, the recycle line can have a take-off line to the dispersion container with its discharge side connecting to the fuel line between between the fuel tank and the pump. By means on a T-valve or the like at the connection of the recycle and take-off lines, recycle to the fuel tank can be stopped when the metal is to be eroded into the fuel, thus avoiding unnecessary build-up in metal concentration. In those engines where there is no recycle, the dispersion container is connected to the fuel line as described in the examples and forms a part of the fuel system. These and various other modifications of the fuel system will be evident to those skilled in the art.

Suitable means can also be provided for by-passing the dispersion in those instances when the added advantage of the alkali metal is not required. This is conveniently accomplished by having a by-pass fuel line over the solid dispersion area which can be cut in by mechanical means. F or example, when the engine is to be first started, while cold, the fuel can be passed over the solid dispersion thereby improving ignition of the cold temperature starting due to the presence of the alkali metal. After running the engine for a short period, the improved benefits of the alkali metal may not be required and, therefore, the fuel system can be cut out in order to by-pass the dispersion. Advantage of this technique can be taken also during acceleration after an idling period and the like instances wherein the added cetane characteristic of the fuel is required. It is to be understood that when a by-pass A particularly pre-' comprises between medium, between system is employed, it can be a partial by-pass. That is, by a valve or other suitable means part of the fuel is caused to pass over the solid dispersion and the remainder does not. The two streams are then brought together subsequently and mix before pumping or injection into the combustion chamber. Other modifications will be evident.

Having thus described the method of my invention, it is not intended that it be limited except as noted in the appended claims.

I claim:

1. In a method of operating a compression ignition engine wherein a fuel is injected into a combustion chamber and compressed therein to attain ignition temperature and the products of combustion act upon a piston thereby producing a driving force, the improvement comprising contacting said fuel at a point between the fuel tank and the injectors with a solid dispersion of finely divided alkali metal whereby the metal is released and suspended in said fuel prior to injection into said combustion chamber so as to increase the cetane number of said fuel.

2. In a method of operating a compression ignition engine wherein a fuel is injected into a combustion chamber and compressed therein to attain ignition temperature and the products of combustion act upon a piston thereby producing a driving force, the improvement comprising contacting said fuel at a point between the fuel tank and the injectors with a solid dispersion of finely divided alkali metal in a solid, fuel soluble dispersion medium whereby the metal is released and suspended in said fuel.

3. The method of claim 1 wherein said solid dispersion comprises finely divided sodium metal dispersed in naphthalene.

4. The method of claim 1 wherein said solid dispersion comprises a mixture of finely divided sodium, naphthalene, and mineral oil.

5. In a method of operating a compression ignition engine wherein a fuel is injected into a combustion chamber and compressed therein to attain ignition temperature and the products of combustion act upon a piston thereby producing a driving force, the improvement comprising contacting said fuel at a point between the fuel tank and the injectors with a solid dispersion of finely divided alkali metal consisting of between about 0.8 to 1.2 parts by weight of a dispersion medium per part by weight of said alkali metal whereby the metal is released and suspended in said fuel prior to injection into said combustion chamber so as to increase the cetane number of said fuel.

6. In a method of operating a compression ignition engine wherein a fuel is injected into a combustion chamber and compressed therein to attain ignition temperature and the products of combustion act upon a piston thereby producing a driving force, the improvement comprising contacting said fuel at a point between the fuel tank and the injectors with a solid dispersion of finely divided alkali metal consisting of between about 0.8 to 1.2 parts of naphthalene, between about 0.005 to 0.6 parts by weight of a modifying agent, and between about 0.0 to 0.25 parts by weight of a dispersing agent per part by weight of said alkali metal whereby the metal is released and suspended in said fuel prior to injection into said combustion chamber so as to increase the cetane number of said fuel.

7. In a method of operating a diesel engine wherein a diselfuel is injected into a combustion chamber and compressed therein to attain ignition temperature, and the products of combustion act upon a piston, thereby producing a driving force, the improvement comprising contacting said diesel fuel at a point between the fuel tank and the injectors with a solid dispersion of finely divided alkali metal in concentration between about 10 to per cent by weight in a solid fuel-soluble dispersion medium whereby said metal is released and suspended in said fuel prior to injection so as to increase the cetane number of said fuel.

8. The method of claim 7 wherein said dispersion medium is selected from the group consisting of solid organic compounds and mixtures thereof having a melting point above atmospheric temperature.

9. The method of claim 7 wherein said. dispersion medium is a solidhydrocarbon.

10. The method of claim 7 wherein saiddispersion medium is petroleum wax.

11. Method of claim 7 wherein said alkali metal is sodium.

12. The method of claim 7 wherein said alakli metal is a sodium of particle size less than about .1000 microns, said dispersion medium is petroleum Wax, and said: sodium is in concentration of between about 40. to 65 per cent by Weight in said petroleum: wax.

13. In a method of. operating a diesel engine wherein a diesel fuel is injected into a combustion chamber and compressed therein to attain ignition temperature, and the products of combustion act upon a piston, thereby producing adriving force, the improvement comprising contacting said diesel fuel at a point between the fuel tank and the injectors with a solid dispersion of sodium of particle size less than about 20 microns in concentration between about 40 to 65 per cent by weight in petroleum wax whereby said metal is released and suspended in said fuel prior to injection so as to increase the cetane number of said fuel.

No references cited.