.
GRAHAM EDGAR’ and H. A. BEATTY Ethyl Corp., Detroit, Mich.
Fuel Additives
- Problems and Progress
S O M E T H I N G has been added to petroleum fuels during the past 30 years, as Beard aptly put it in his review of the subject presented to the ASTM in 1954 (7). The use of additives has become a major factor in obtaining product quality in refinery operations, and their manufacture is an important segment of the chemical industry. “Without them our present mechanical output and service performance would be impossible,” Larson said in a recent survey (4). If fuel hydrocarbons having ideal physical and chemical properties could be manufactured economically, there would be no need to complicate them with additives. Despite major advances in refining methods, this goal is not yet within reach. Moreover, the problem becomes greater as the demands for product quality and quantity rise to new highs. As a result, the growth in use of additives shows no signs of leveling off. On the contrary, there has recently been a very considerable increase in both the scope and the complexity of additive technology. Developments in this field have now reached the point where even technical experts are not in agreement on some aspects. A confusing variety of results are widely published. The ultimate consumer who uses the fuels is understandably in a state of bewilderment over the new discoveries reported and benefits claimed. It is therefore timely to hold this symposium, to provide a better understanding of the present situation and to point toward future developments. As background for the papers to follow, this introduction indicates briefly the scope and size of the piesent market for additives and offers some general comments on their development and testing. I t is not intended here to go into textbook detail as to the chemical type, function, and economic value of individual additives. These points have often been described and are generally Deceased.
well appreciated. Instead, it seems preferable to cover an area that is not so well understood-the opportunities for further developments and the difficulties encountered in such work.
Scope of Commercial Additives The functional types of fuel additives which are in widespread or appreciable commercial use at the present time are listed in Table I. Since additives are, for the most part, tailor-made for the fuels in which they are to be used, the list is subdivided by fuel types. There are, of course, some particular additives, such as a given corrosion inhibitor, which may be used equally wel! in different types of fuel. Typical concentrations are all given in the same units to facilitate comparison of relative effectiveness. (For conversion to customary units, 4 p.p.m. by weight equals 1 lb./1000 bbl.) Also given (Table I) is the approximate dollar volume at the refinery in the present United States market; the sale of materials directly to the consumer is still quite small. Few of these numbers carry a pretense of high accuracy, but they do give a reasonable indication of the magnitudes involved. I n most cases, the dollar figures in Table I by no means represent the ultimate market potential, even at present levels of fuel consumption. Both increased needs for additives and developments leading to better costeffectiveness will tend to expand the present market. Nor do these figures represent the actual economic value of the additives, a subject which is outside the scope of this paper.
Borderline Additives The oil companies add the bulk of these additives directly to their fuels. They also market small amounts of certain ones as a separate package, to be added by the user of the fuel if needed. There remains another class of additives and another method of marketing which
should be mentioned. For a long time there have been on the public marketfrom sources other than oil companiesa large number and variety of concoctions offered directly to the consumer for addition to his fuel. At best these materials are of dubious value; at worst, they are outright fakes. Their existence is, in large part, a consequence of the problems to be discussed later in this paper-the lack of basic knowledge as to the action of additives and the inherent difficulties in determining their actual effects. Since early days, inventors-some without regard to thermodynamicshave sought for additives to achieve higher power or economy from fuels. Many materials, from mothballs to ether, have been added to gasoline. Apart from hydrocarbon blends, the only effective material used was water which has long been known as a means of increasing the density of the fuel-air charge to engines, thus raising maximum power output. Efforts in this direction had about died out when the discovery of antiknocks came along. This surprising development acted as a powerful stimulus to inventors and, more importantly, it conditioned the public to accept the possibility of an important benefit from a small amount of additive. A renewed flood of materia$ was offered on the market, with the usual extravagant claims as to performance. In England in 1924, the Empire Motor Fuels Committee reported that it had tested a large number of gasoline“dopes,” none of which showed any positive effect, except tetraethyllead ( 5 ) . At the U. S. Bureau of Standards in 1931, Dickinson said that of 150 compounds which had been submitted for tests, none showed any antiknock or other effect ( 2 ) . He pointed out that it was unreasonable to expect any gasoline additive to influence starting, vapor lock, fuel economy, or power (in the absence of knock) ; carbon removal might be possible but VOL. 48, NO. 10
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...
Metal deactivator Antirust Anti-icing 1IM Detergent 251
Lubd-t Deposit modifier AntiLnockEuid et fuel ndditives Anti ondmt Yew deactivator Corrosion inhibitor Iiescl fuel additives C a m s improver Stabilizer Comaion inhibitor deating OII additives
251
31 28
!
251 11 !
Combustion
improver Stabilizer Corrosion inhibitor
ii
’
Residual foe1 additives Ash modifier 51 Sludge disper-t 111 u n o
was difficult to determine, and he found no valid evidence of it. Newtheless, many of these additives we* actually sold, mme to a consider. able extent. Naphthalene, camphor, picrates, and nitrobenzene were particularly popular, and the solutions were invariably colored with dye. Lubricant-type fuel additives were common in the early thirties. They included mineral and natural oils, Halowax oil, graphite, etc. The U. S. Bureau of Standards could 6nd no significant effects of these materials, and the general opinion was that they “seem to do no harm.” The idea of metal catalysts for combustion-chamber surfaces and depQsits goes back to the twenties. A number of efforts haye been made to commerdalize different p r o p 4 along this line. The idea has undoubted fascination. When reduced to its ultimate simplicity, the method of application, which has not only been patented, but actually market&, consists in placing a mlid chunk of metal in the gasoline tank! Iron carbonyl as an antiknock has had only a very limited sale in this country. This is perhaps somewhat surprising, sine the antiknock effect is immediate and clearly evident, while the resulting engine wear and spark plug fouling take mme time to show u p The fake antiknockn have practically
1854
.
!
pounds used have been made in recent times, and there is still loom for further research. Ant+dauts. The& were intrcd u d in the late twenties to counteract the gum-forming tendency of cracked gamline. A great deal of researdl was done on the selection of compounds and thy establishment of test methods. I t took a long time, hyever, to obtain the several compounds in use d a y . M o m r it would appear that this development is by no meam concluded. The basic chemistry of gum f o r y t i o n and antioxidant action is evidently complicated. Many compounds which are powerful antioxidants in other circumstances are quite weak in gasoline. The relative effectiveness may vary for d i f f d n t fuels and different test or storage conditiofis. Mixtures may show an unexpected ‘ synexgkn. Simultaneous reactionshaving different temperature d c i e n t s apparently occur, so that tests accelerated by the use of high temperature are not alwap reliable as an index of behavior expected in normal storage. Table I1 gives some cxamplea of the reversals in relative eEectiveneSr of various antioxidants in diffvent gasolines at both high and moderate levels of gum formation (3). Since the particular materials involved are beside the point, they are designated by Iettera for simplicity. In e x ~ e p t i ~ n acasq l compounds may be very effective in mme gasolines and yet have no effect or even a pmoxidant action in others. The catalytic &ect of trace materials in gum formation may be considerable, but this bas sbrcely been explored except for copper. Just why this element should exhibit such an intense activity on oxidation reactions in gasoline is not clear. The fact is well rewgnized, however. Since adventitious traces of copper are unavoidable, it is common practice to add a metal deactivator whicb isolates available copper in the form of a strongly bonded chelate compound. Finally, it is evident that the gums which form in the treated gasolines am not always of the same composition and properties. Hence, mere measurement of the amount of dissolved gum is not a d a b l e index of h o d well a gasoline will behave in the induction system of an engine. The need for more basic research on
vanished, but other fuel doper continue to appear on the market from time to time. Altogether, literally hundreds of them have been &ted. This mrt of business adds up m no great dollar volume, but it does seem to provide a significant commentary on the technical knowledge and buying habits of the consumers. Their confusion is understandable. The true effects of additives are often difIicult or impoapible for the consumer to measure? h c e he usually haa no fa*lities for controlled teats. Imaginary effects-hether favorable or ad-m easy to obxrve, and the wish to believe readily becomes conviction. Indeed, the public has often been one step ahead of the oil companies in their arceptance of new additives, In due time, those additives of no merit disappear from the market; in the meantime, the Better Business Bureau and ,the Federal Trade Commisaidn have on d o n taken action to protect the consumer. Thus it would appear that in the long run the petroleum industry will gain by continuing its policy of providing fuel additivea of tested value, of seeking improved materia&, and of educating its customers as to the true technical merits and value of those products
Baric Knowledge , We have a good deal of information as to the results of using additives. However, we are not always certain just how these results are accomplished or why a particular compound is or is not a good additive. This is true even for materials like dyes, antioxidants, and a n t i k n d s , which have been in we for 20 to 30 yean and on which a great deal of research has been carried out. Basic knowledge of these additives is still incomplete, and new information is continually being added. Dyer. Consider, for example, the gawlineaoluble dyes. For such a simple problem, it might be expected that by now the technology would be pafected. Dyes were addqd to aviation gasoline as early as World War I. By the early thirties they were in general use in motor gasoline, to provide uniformity of color, to distinguish different brands or grades, and to indicate the prarnce of tetraethyllead. And yet with all this experiencl, improvements in the com-
Table 11.
Variations in Effectiveness of Antioxidants
DosdiM
N m
A
B
a
110
110 20
25 70 15
B
55
C
25
D E
1s 7
F
INDUSTRIAL AND ENOINIIRINO CIIEMISlRY
I
5
.... ..
.... ..
A*MdQnt D 25 5 C
50 5
.... ..
E
5
.... ..
.
Q
......
15 I 1
10 1
7
3
2
.. ..
70
F
..
..
A D D I T I V E S IN FUELS the whole subject is generally recognized. O n the basis of a recommendation from the CRC, the Office of the Chief of Ordnance has made contracts for a long range program of fundamental work along this line. Antiknock Mixtures. Of all fuel additives, antiknocks have been the most thoroughly studied because of their economic importance. Since the discovery of iodine in 1916, aniline in 1919, and tetraethyllead in 1921, there has been widespread exploration of different compounds and mixtures. At the same time, the fascination of the subject has stimulated much basic research on the chemistry involved in antiknock action. Considerable information has been accumulated, although the actual chemical reactions involved in the mechanism of antiknock action are not yet identified. Research is making progress toward an explanation of why the effectivenessof different elements and compounds varies as it does and why the effectiveness of a given compound depends so greatly on fuel and engine conditions. The mechanism of the destructive action of sulfur compounds on tetraethyllead has not been fully explained. In antiknock fluids, the chlorine and bromine compounds which accompany tetraethyllead are regarded as part of the antiknock mixture rather than as separate deposit modifiers. Again, a great deal of exploratory work on the halogen compounds has been carried out. The basic chemistry involved is known to be complex. It appears that the action of the two halogens differs in kind as well as in degree, that there is an optimum concentration of each for a given condition of use, and that different compounds containing the same elements are not equivalent. Deposit and Ash Modifiers. In the newer fields of deposit modifiers and combustion improvers, the knowledge at hand is largely empirical, despite some considerable background of experience. Combustion-chamber deposits in engines have long been troublesome and still are. This applies equally to deposits from leaded and unleaded fuels. There is a long history of unsuccessful effort to develop a carbon-remover additive which could be incorporated directly into the fuel. Since only limited success has resulted from massive injection of solvents into the engine and subsequent soaking, there does not appear to be much hope for the physical removal of deposits by any material in the fuel. There remains the possibility of a
chemical modification. Compounds of catalytically active metals have been applied directly to combustion-chamber surfaces or have been dissolved in the fuel. Claims of actual effectiveness have been advanced in some of the tests of mixtures of gasoline-soluble chromium and other metal chelates, and such material has had a limited amount of commercial use. Many other elements in various fuel-soluble forms have been tested for their effects on deposits. By and large, the results from such additives are difficult to measure and inconclusive, and not much is known about the chemistry involved. More definite effects are obtained when phosphorus compounds are added. Here fuel solubility and stability are readily attained, and hundreds of compounds have been tried. It has long been known that the chemical composition of combustion-chamber deposits (particularly those on the spark plugs) is modified by the presence of phosphorus. Again, different compounds of the element are by no means equivalent in additive action, and proper selection of compound type and concentration is required for optimum performance. Such additives are now in well-known commercial use, and further research along this line is in progress. An entirely different type of deposit modification is involved in the use of additives in residual fuels to reduce ash deposits and to prevent corrosion by vanadium. A number of elements are effective, including the alkaline earths, silicon, and phosphorus. These additives apparently achieve their effects by raising the fusion temperature of the ash. The result may be highly beneficial. Cost considerations, however, have restricted both research and industrial application in this field. Ignition and Combustion Improvers. The heavier fuels-for jet, Diesel, and heating uses-present ignition and combustion problems quite different from those of gasoline. T o get reliable spark ignition of jet fue! under unfavorable circumstances is a challenging problem. We can make kerosine spontaneously flammable in the open air by the addition of a small amount of aluminum borohydride, but no additive has yet been found which is useful in practice. For the compression ignition of Diesel fuel, the situation is quite different. Since the search started in the early thirties, hundreds of compounds and mixtures have been tested as cetane improvers, and many effective ones are known. The actual mechanism of ignition is complex, and it is noteworthy that different compounds vary greatly in effectiveness and that a material like metallic
sodium is many, many times as effective as the best peroxide or nitrate. Prevention of smoking and soot deposits from incomplete combustion is a problem of growing importance for all of the heavier fuels, since their aromatic content has been increasing steadily. Present knowledge on the subject appears to be more in the realm of empiricism than of science. Addition of fuelsoluble organic compounds of catalytic metals such as chromium, cobalt, nickel, and iron has a definite effect in some cases. In other cases, the addition of an alkyl nitrate may be beneficial. There are good possibilities for more research in this area. Surface-Active Additives. Lubricants, detergents, anti-icing agents, corrosion inhibitors, and stabilizers-these additive types include a wide variety of materials, but all seem to produce their effects primarily through a physical or surface action. Indeed, many of the materials in use serve more than one function. The need for such additives is increasing, and much interesting research and development is in progress. In particular, the distillate fuel oils are beginning to show some serious problems of sludge formation and agglomeration, and the use of stabilizers is becoming general. The details of the chemistry involved are under investigation. Both oxidation and thermal action seem to occur, and trace quantities of components may be important. Ordinary antioxidants are ineffective or even deleterious, and the stabilizers used are primarily peptizing agents or dispersants. Corrosion inhibitors are becoming widely used in all types of fuel, especially where storage conditions are severe. Since they are effective in small concentrations, their cost is quite small. An extraordinary variety of materials is known and used for this purpose. Some are water-soluble, others fuelsoluble; some concentrate a t the waterfuel interface, while others are volatile and carry their effectiveness into the vapor phase. Since early days, upper cylinder lubricants have often been added to fuel for reciprocating engines. Performance testing is difficult, and there is no general agreement as to the net benefits obtained. To some extent these oils may also act as solvents or carriers for removal of induction-system deposits. Detergent additives designed to meet this particular need are now coming into use. The whole problem of induction-system deposits is a complex one which warrants a more fundamental study. A related but much more specific deposit problem is that of ice formation in VOL. 48,
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the carburetor of passenger cars. Under suitable conditions, moisture from the air condenses as ice on the throttle plate, which has been chilled by evaporation of gasoline. Current trends in fuel volatility and carburetor settings tend somewhat to aggravate this. As a result, alcohols and other materials are coming into wider use as anti-icing additives. They are known to be effective to a degree, and it is generally assumed that they act in some way as antifreeze agents. Development and Testing The foregoing paragraphs have indicated the general problem posed by limitations in the basic knowledge of the chemistry involved in the action of additives. A correspondingly general problem is the difficulty of determining their actual effects. To a very real extent, each of these problems is intensified by the other: It is not easy to make good tests when one does not know what is happening, and it is not easy to discover what happens when there IS no good testing method. This impasse occurs, of course, in other fields. However, it is particularly acute in additives whose effects are preventive and whose action is obscure. For example, on adding an antiknock to a fuel, it is easy to see that knock no longer occurs, but what does occur remains hidden. In seeking to uncover this hidden action of additives, we encounter two fundamental difficulties-the complexity of the fuels themselves and the complexity of the environments in which they are stored and used. Fuel Composition. Liquid fuels are highly variable mixtures of many components. Trace quantities of unidentified sulfur, nitrogen, oxygen, and reactive hydrocarbon compounds can be of major importance. Certainly such compounds are responsible for gum, sludge, and part of the combustion-chamber deposits, and it appears that they may have considerable influence on the fuel’s sensitivity to knock and on the action of the antiknock agent. Moreover, any additive already placed in the fuel makes it that much more complicated a mixture when it comes to the testing of a different kind of additive. There would, therefore, appear to be a real need for more refined analytical methods and inspection tests to characterize the fuels used in additive-development work. Reactive components must be removed and identified before we can expect to know how the additives actually work. With the aid of modern tools, encouraging progress is already being made along this line in certain fundamental research programs. Once enough of this information has been obtained, it is recommended that synthetic, standard mixtures of known compounds be used as test fuels for research purposes.
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The data on antioxidants given in Table I1 illustrate the need for such standard test fuels. Another factor in testing which may be introduced by the fuel is the variation in additive effectiveness with concentration. In exceptional cases, this variation may be considerable. For example, in one gasoline an anti-icing additive had no observable effect at a low concentration but performed well at a high concentration; in another gasoline, it was effective at both levels (3) Similarly, in a burner test for soot formation, a particular additive showed no action whatever at 1% concentration but had a marked effect at a 27, level ( 3 ) . The response curves for antiknock agents vary widely among different hydrocarbons, as is well known. An even more striking example of abnormal results is an actual reversal of the effect of an additive with change in concentration. This appeared, for instance, in the course of some measurements of the durability of exhaust valves in engines operated under heavy duty conditions (3). At a low concentration, a particular gasoline additive decreased the durability to 50% of the base line value, but at a fourfold higher concentration, the durability was increased to 165y0’,. I n this case, other additives present in the fuel were probably a complicating factor. Storage a n d Handling Conditions. Testing fuels in the laboratory for gum formation, stability, and corrosion would not, at first sight, be expected to present much of a problem. Storage and handling conditions in the field would seem to be simple enough to permit good correlation with proper laboratory methods. Such, of course, is not the case. After more than 25 years’ work, we still do not have laboratory test methods which are fully reliable for predicting the results of actual storage and handling in the field. Moreover, such methods as we do have are mostly expensive and time consuming. This applies both to gum formation in gasoline and to sludge formation and corrosion in distillate fuels. Stabilizers often show a marked degree of specificity in performance for different fuels or storage conditions; corrosion inhibitors of high potency may become valueless in a severe test ( 3 ) . For prediction of gum formation and the effects of antioxidants in gasolines, the familiar induction-period test may be defective in some instances, and a very effective antioxidant can be overlooked for this reason ( 3 ) . An evident explanation is that we are deaIing here with phenomena which involve solubility, diffusion, and reactions at interfaces between phases. Such factors as temperature uniformity, turbulence, surface-volume ratio, presence of catalytic metals, and availability of water and oxygen are important. These may result
INDUSTRIAL AND ENGINEERING CHEMISTRY
in marked scale effects. Moreover, full scale storage conditions are as yet none too well characterized in these respects. For research and development purposes, there is an evident need to go to more sophisticated test methods, with all pertinent factors under adjustment and control. This does not necessarily mean greater time and expense, if better analytical tools can be used. For example, the measurement of sludge formation by means of light scattering and electron microscopy may develop as a rapid and accurate method. Combustion in Engines. The storage problem is difficult enough, but the situation is still worse when it comes to testing additives for effects which occur in an engine. This applies particularly to effects on combustion and its resulting deposits. The primary fact is that an engine, by and large, is an awkward piece of research equipment. Any engine is highly sensitive to slight changes in operating conditions, and this can result in a large variation in reaction conditions such as local temperatures, turbulence, surface activity, and the like. Small differences in component parts become magnified in their effects on durability and performance. Extreme care in test preparation and control is required to obtain satisfactory duplication of results. In the reciprocating engine, work on fuel additives is further complicated by the presence of lubricating oil with its many additives. h’evertheless, for work on additives aimed a t combustion control and engine deposits, it has proved impossible to find an adequate substitute for the engine itself. To be sure, there are many laboratory bench tests for such things as ease of ignition, smoking tendency, and deposit formation and character. These have merit in basic research, but they are generally not of much value in developing and testing additives for actual use. And so, of necessity, we come back to the engine itself and laboriously go through a series of test stages. First is the single-cylinder or single-combustor unit, then a full scale engine on a dynamometer stand, then a complete vehicle. and finally a fleet test on the road or in the air. The more closely the test approaches commercial practice, the more difficult it is to control and the more need there is for replicate tests to maintain a statistically satisfactory reliability. And the tests should cover a variety of conditions-combinations of engine type, fuel type, lubricant type, and type of operation-if the results are to have any generality. Surprising reversals can at times occur with some of these combinations. Results from a single test condition may not apply to other seemingly similar conditions and may lead the unwary to false conclusions. Experience and the ability to recognize
A D D I T I V E S IN FUEL meaningful results are essential when the amount of testing is limited. For example, in a certain engine durability test, the effect of a particular gasoline additive was completely reversed as the engine conditions were varied from severe to mild ( 3 ) . When two deposit modifiers were compared for their effect on spark plug fouling under two engine conditions (resulting from a difference in spark timing), one additive increased plug life to 120% of the base value in the first case and to 550y0in the second case; the other additive gave a higher value of 180% in the first case, but a negative result of only 70y0 in the second case ( 3 ) . Surface ignition in engines is particularly sensitive to operating conditions, and the relative effectiveness of two deposit modifiers may be quite different in one make of engine than in another. Instrumentation is a factor here: An additive may make surface ignition inaudible without eliminating it ( 3 ) . Although such reversals are the exception rather than the rule, the fact remains that many other similar examples could be cited, and the experimenter must be on the alert to detect their occurrence. As a more elaborate illustration of the difficulties in carrying out such tests and in drawing sound conclusions from them, the following results are pertinent ( 3 ) . The test in question was part of a program designed to measure the effect of a gasoline additive on the endurance of automobile engines in heavy duty service on the road. In this test, two distinctly different gasolines were used. In addition, there were small differences in both the composition and concentration of the additive. Only one make of automobile was involved here but with two slightly different engine models. The results, in abbreviated form, are shown in Table 111. We have here an extensive body of data representing well over a million miles of car testing and a very considerable expenditure. What conclusions can be reached from them? Taken at face value, it wouId appear that:
one is better at the lower concentration but inferior at the higher concentration 4. A small reduction in concentration of a n additive may increase the endurance twofold for one engine-fuel combination, while decreasing it for the other combination How representative are these data? Experience shows that they are a typical example of the degree of variation thatsometimes results from seemingly small changes in conditions. In such a case as this, many tests would be required to obtain a complete picture of the behavior of the additive. However, this may not be necessary. Adequate conclusions may be reached by interpretation of the results in relation to previous tests along similar lines. This is a matter of experience and judgment. Generally speaking, it would obviously be impossible to test every additive modification in every known engine, with every known gasoline, under every possible engine condition. No new additive would ever be marketed if that were necessary. Thus, there does not appear to be any easy solution to this problem of testing additives for use in engines. The best that can be done is to use a combination of different methods and equipment, as dictated by past experience, and to allow sufficient time and effort for reliable results. Better knowledge of the factors involved, improved instrumentation and control equipment, use of standard test fuels and oils, and refinements in chemical analyses of reaction products-all these, as time goes on, will help to improve the speed and accuracy of testing.
1. The base gasoline employed may influence the results substantially 2. Two nearly identical engines may vary greatly in endurance 3. Of two formulations of additive,
Future Improvements
One can see many opportunities for future progress from continued research and development on fuel additives. The existing lack of basic knowledge and the concomitant difficulties in testing may be a handicap and source of confusion at the moment, but their existence now also adds strength to the belief that further progress can and will be made as they are overcome. New needs for additives will arise. Some of these will come from developments in petroleum technology, such as changes in fuel volatility, hydrocarbon
type, crude source, and product distribution. Some will come from changes in engine and burner technology, such aa higher outputs from increases in compression ratio or gas temperature, changes to reduce smoking and air pollution, use of fuel for cooling purposes in aircraft, and other changes as yet unforeseen. In every instance, two basic requirements must be met. The additive must accomplish a useful purpose more economically than by another method, and it must not have a destructive effect on equipment or on other additives. I t will always be difficult to make an accurate evaluation of true cost-effectivenessversus economic need. In the long run, however, experience will indicate those improvements for which the need justifies the cost. Some of the many needs which are already evident are these : 1. A highly soluble or “liquid” dye for gasoline, to minimize the likelihood of induction-system deposits 2. A rapid test procedure to select the optimum antioxidant compound or mixture for each particular gasoline and special means for protection in the event of long-time storage under adverse conditions 3. Means of enhancing the action of anti-icing additives 4. More effective deposit modifiers or scavengers for combustion chamber deposits 5. Means of reducing the destruction of tetraethyllead by sulfur compounds in gasoline 6. An additive to promote complete combustion of hydrocarbons in gasoline engines 7. A combustion improver to reduce smoke from jet and Diesel fuels 8. A stabilizer for jet fuel exposed to high tempera tures 9. A low cost ash modifier for residual fuel These and other possibilities present a challenge to the petroleum industry and to those who supply additives. The problems are difficult but the potential rewards are great. Collectively, we have made much progress in past years. We look forward with confidence to further progress in the future. Literature Cited (1) . . Beard, L. C., Jr., ASTMBull. No. 198,
May 1954.
Table 111.
Gasoline
Engine Model
Fuel Additive
1953 1953 1953 1954
Formula 1 Formula 2 Formula 2 Formula 2
Relative Endurance, % At hioher At lower concn. of concn. of additive additive
85 100
.. 600
’
.
(2) Dickinson, H. C., IND.END.CHEM.23,
Effects of Small Changes in Test Conditions
180 135 250
530
517 (1931). (3) Ethyl ‘Corp: Research Laboratories, unpublished data. (4) Larson, C. M., Petroleum Engr. 28, C-44 (March 1955). (5) Proc. Znst. Automobile Engineers, Empire Motor Fuels Committee, 18, Part I (1924).
RECEIVED for review January 11, 1956 ACCEPTED March 5, 1956 VOL. 38, NO. 10
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