progress in petroleum technology - ACS Publications - American

Tetraethyllead GRAHAM EDGAR

Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: January 1, 1951 | doi: 10.1021/ba-1951-0005.ch019

Ethyl Corp., New York,Ν.Y.

This paper discusses the properties which make tetraethyllead practical as an antiknock agent, and treats briefly the problems involved in its use and the progress that has been made in methods for its manufacture. The importance and interrelationship of high antiknock gasoline and efficient automotive engines are outlined, and probable future progress in several phases of the broad problems of fuels and engines is forecast. The part that tetraethyllead has played in the improvement of gasoline quality is discussed, and some suggestions are made as to possible future improvements in its utilization.

Twenty-five years ago, tetraethyllead was just being reintroduced to the petroleum industry after having been withdrawn from the market for a year while the United States Public Health Service was carrying out the extensive investigation which led to the con clusion that the material, i n concentrations not exceeding 3 m l . per gallon of gasoline, was safe when used i n motor fuel. The 25 years following have seen a steady growth i n the use of tetraethyllead, until today practically all United States motor and aviation gaso lines contain i t , and many foreign gasolines as well. This progress has not been without opposition and difficulties. A t one time, few motor manufacturers approved its use, de spite its potential advantages, because of its real or fancied effects upon engine parts, and i t is a tribute to the real value of the product that intensive work to correct such problems as actually existed has been done and is being done by the automotive and air craft industries, the petroleum industry, and the producers of tetraethyllead. Likewise, exactly 25 years ago, at the fall meeting of the AMERICAN CHEMICAL SOCIETY, there was announced the synthesis and high antiknock value of a paraffin h y drocarbon, 2,2,4-trimethylpentane, which was later to become commonly known as isooctane. The importance of the discovery of iso-octane l a y i n its pointing the way for the petroleum industry to improve the antiknock quality of gasoline without the use of a n t i knock agents, but by altering hydrocarbon structure. Experience has shown that the two methods are supplements rather than substitutions. Tetraethyllead and iso-octane a p peared together i n 100 octane aviation gasoline of W o r l d W a r I I , and were credited with playing a substantial part i n winning the Battle of B r i t a i n . Today, through a research program, sponsored by the American Petroleum Institute, nearly 300 different pure hydrocarbons of a l l types i n the gasoline range have been synthesized and their antiknock effectiveness has been measured with and without tetra ethyllead under many different engine conditions. A n d today, the petroleum refiner carries out operations which are deliberately designed to produce hydrocarbons of the specific types that have high antiknock quality and add tetraethyllead to the result ing gasoline. Our present high quality gasolines, the best i n the world, are made b y us ing both of the above Unes of approach. 221

In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

222

ADVANCES IN CHEMISTRY SERIES


Selection of Tetraethyllead as Antiknock Agent When the decision was made more than 25 years ago that tetraethyllead was the most promising antiknock to commercialize, the data were very scanty i n comparison with our knowledge today, yet even if we were beginning a l l over again we would still select tetraethyllead. The choice would be made from three broad classes of compounds: the hydrocarbons, the amines, and the organometallics. A n indication of the relative effectiveness of compounds i n these classes is given i n Figure 1. The hydrocarbons should be regarded as fuels rather than as antiknocks, and although the petroleum industry has made tremendous strides i n manufacturing either individual hydrocarbons (such as iso-octane or cumene) or petroleum fractions high i n blending value, their antiknock effectiveness is not comparable with that of the amines and metals. The amines as a class have been thoroughly explored, and although some have been discovered (unpublished work) which are substantially higher i n antiknock value than the simple amines such as aniline, there appears no prospect that they can compete economically with tetraethyllead. Their usefulness would appear to be confined to special cases, such as the use of xylidine or monomethylaniline to supplement tetraethyllead i n aviation fuels.

Figure 1.

Relative Effectiveness of Antiknock Compounds

Representative single-cylinder engine test data (I, 2)

Of the organometallic compounds, there are many which exhibit antiknock value; however, lack of one or more of the essential qualities of solubility, volatility, stability, and low cost has so far ruled out a l l but two—the lead alkyls and iron carbonyl. T h e latter is probably the cheapest known source of antiknock increase. I t was marketed for a time i n Germany and to a limited extent i n this country, until i t became generally recognized that the great increase i n engine wear which its abrasive combustion products produce makes its use impractical. O n l y limited success has attended the tremendous amount of effort to reduce this wear, and there appear to be no prospects of the commercial use of iron carbonyl as an antiknock agent. This leaves only the lead alkyls, of which there are many, varying i n intrinsic antiknock effectiveness, volatility, stability, and cost. The original selection of tetraethyllead from this group may be regarded as a stroke of genius, good fortune, or both, for i t has about the maximum antiknock effectiveness of the group; i t possesses good stability; In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

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EDGAR—TETRAETHYLLEAD

1925

1930

1935

1940

1945

1950

YEAR

Figure 2 . Comparison of Tetraethyllead Price with Commodity Price Index for Chemicals and Allied Products Yearly average

its volatility is a happy compromise between the high value desirable for use i n the fuel and the low value desirable for safety i n manufacturing and handling; its cost is also about the minimum. Although research i n the field will continue, as fuels and engines change, there appears i n the light of our present knowledge no prospect of an antiknock that will be better than tetraethyllead on the basis of three criteria: low cost of manufacture, effectiveness under different conditions of use, and relative freedom from disadvantages i n use. These three criteria deserve more detailed consideration.

Manufacture and Cost of Tetraethyllead Fluids Tetraethyllead was originally manufactured b y the reaction of disodium-lead alloy with ethyl bromide, but for about the past 25 years i t has been manufactured b y the reaction of monosodium-lead alloy and ethyl chloride. During this time, continued research and development have improved manufacturing methods to an extent which has permitted the sales price to be reduced remarkably. Figure 2 illustrates this well. This reduction has been made possible b y : (1) the shift from the ethyl bromide reaction to the ethyl chloride reaction; (2) substantial improvements i n yield i n the alkylation reaction, now around 9 0 % of the theoretical; (3) increases i n size of the charge to the reaction vessel and reduction of the time required for the operations of alkylation and distillation (in the past 13 years alone, the time cycle has been more than halved, thus more than doubling the plant throughput) ; (4) the general economics usually inherent i n large scale In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

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manufacture; and (5) most important of a l l , reduction i n the cost of intermediates, sodium-lead alloy and ethyl chloride (which today constitute about 8 0 % of the total cost), and of the cost of the added constituents of the fluid, ethylene dichloride and ethylene dibromide. The manufacture of ethyl chloride from petroleum ethylene rather than from alcohol and the manufacture of ethylene dibromide from bromine separated from sea water were important milestones i n cost reduction. Plans for a continuous process for tetraethyllead manufacture have been announced i n the press, but i n the absence of technical details no evaluation of this process is possible.

Figure 3. Effect of Tetraethyllead Content of Fuel and Test Mileage on Octane Number Requirement Fleet of 66 1946 Ford, Chevrolet, and Plymouth cars operated in normal city and country service. Fuel catalytically cracked naphtha. Oil 100% Pennsylvania regular, changed at 5000-mile intervals

Meanwhile, extensive investigation of other of the many reactions b y which tetraethyllead can be synthesized, such as the substitution of magnesium and other alkylating metals for sodium and of other ethyl esters for ethyl chloride, has led to the conclusion that none of these is likely to replace the lead-sodium-ethyl chloride method i n the foreseeable future. Further reduction i n cost would appear most likely to come from refinements i n the existing process, and further reduction i n operating hazards. One important factor i n the cost is not susceptible to improvement b y research—the cost of pig lead, which today represents about 1 8 % of the selling price of tetraethyllead as motor fluid. The present price of pig lead is about three times that during most of the past 25 years.

Properties Concerned with Use Although no more practical antiknock is now known than tetraethyllead, i t cannot be said that a l l of its properties are ideal for its purposes. Its less desirable properties can well be discussed. Toxicity. Tetraethyllead itself is a h i g h l y toxic material, and safe methods for its manufacture and handling have required extensive study. T h e problem is now under excellent control, but eternal vigilance is necessary to keep i t so. A t one time, many doubts existed over the safety even of gasoline containing it, but 25 years of i n tensive study and experience have proved that gasoline containing not over 3 m l . of In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.



Figure 4.

225

Improvement in Exhaust-Valve Life b y Use of Valve Rotators

tetraethyllead per gallon is safe as normally used. Research now i n progress may some time determine just what the safety factor i s — i n other words, how much more than 3 m l . could be safely used. Experience with aviation gasoline containing up to 6 m l . per gallon does not answer the question, because of differences i n the manner of use and the volatility of the gasoline. Storage Stability. Tetraethyllead is entirely stable at ordinary temperatures in the absence of light or oxygen. A t one time there were some problems involving instability in gasoline, but at present small amounts of the usual antioxidants, plus the present practice of well-nigh complete removal of bismuth i n the manufacture of the tetraethyllead itself, have practically eliminated the formation of solid deposits i n gasoline in storage. Volatility. T h e low v o l a t i l i t y of tetraethyllead (2 m m . of mercury at 50° C ) , while a great advantage i n reducing manufacturing and handling hazards, may result i n some maldistribution relative to fuel i n individual cylinders of multicylinder engines. Research i n progress shows that this is a most complicated problem, but i n general the practical effects are not serious. The use of mixed lead alkyls of higher volatility than tetraethyllead would fail to provide a practical solution, as their intrinsic antiknock value is lower than that of tetraethyllead and their manufacturing cost would be higher. Sensitivity to Sulfur. T h e effectiveness of tetraethyllead as a n antiknock is markedly reduced by one of the normal constituents of gasoline—sulfur. T h e different types of sulfur compounds show varying degrees of tetraethyllead destruction, but all have a deleterious effect, and as much as two thirds of the effectiveness of tetraethyllead may be lost i n a gasoline high i n sulfur. E n g i n e Deposits. Tetraethyllead when burned alone with gasoline i n the engine leaves a n " a s h " composed largely of lead oxide, which has certain deleterious effects on the engine. This fact was early recognized, and numerous agents were designed to eliminate the ash or otherwise minimize its effects. Organic bromides and chlorides were found to be the most effective scavenging agents, and today we know of nothing better. However, later research has shown that the proper kinds and proportions of,these halides vary with the nature of the engines and the conditions of operation. The actual mixtures In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

226


Γ

ANTIKNOCK RATING OF A SENSITIVE FUEL RELATIVE TO ISOOCTANE » 100

140

0 ML TEL 3 ML TEL 120


100

80

60

40

NONTURBULENT TYPE

FLAT-TOP PISTON STANDARD INTAKE VALVE

TURBULENT TYPE "SQUISH" PISTON SHROUDED INTAKE VALVE

Figure 5. Effect of Combustion Chamber Design on Relative Antiknock Rating of Sensitive Fuel -COMPRESSION RATIO

1955

Figure 6. Average Compression Ratio of Passenger Car Engines 1942-45 no production


227


now used are designed to give over-all optimum results for the use to which they are to be put; thus, aircraft and automotive engines require different mixtures. D u r i n g 25 years, several changes i n composition of the antiknock mixtures have been made, reflecting changes i n average conditions of use with different engines, fuels, and lubricants. Recent research work indicates that i n heavy-duty service the use of bromine and chlorine com ponents of volatility close to that of tetraethyllead may offer promise of some further improvement.


OCTANE

NUMBER

(RESEARCH

METHOD)

ψ PREMIl

Γ

.A

r

/ R E G ULAR

7925

1930

1935

1940

1945

1950

1955

YEAR

Figure 7.

Average Antiknock Quality of Regular and Premium Grade Motor Gasolines

Winter and summer averages. Data prior to 1941 Motor method ratings

estimated from

Oxidation or combustion of any fuel and oil i n an engine tends to form troublesome deposits on a l l exposed parts: intake and exhaust valves and manifolds, combustion chamber, spark plug, piston, cylinder wall, and crankcase. The presence of tetraethyllead fluids may aggravate these troubles, may have no effect, or may even lessen them. D u r ing the past 25 years, tetraethyllead has frequently appeared to be the "whipping b o y " for almost a l l deposit troubles, and i t has required extensive and continuing research to develop the true facts, the problem being complicated b y the interrelationship of tetra ethyllead, fuel, oil, engine design, and operating conditions. Today, the broad problem of all engine deposits is well recognized b y both the petroleum and automotive industries, as well as b y the suppliers of antiknocks. Cooperative work is i n progress to find prac ticable means of solving the various problems, one b y one. Studies of the formation, chemical composition, and properties of deposits have shown that they consist of partially oxidized organic material, including more or less nitrogen, sulfur, and phosphorus. Compounds of iron, silicon, calcium, and other metals are present i n small quantity, together with substantial amounts of lead oxides, sulfates, and halides from combustion of the antiknock fluid. The effects of these deposits are both physical and chemical i n nature; they may physically interfere with lubrication, heat transfer, gas flow, operation of valves and spark plugs; chemically, they may bring about corrosion and oxidation. Probably the most serious effect brought about b y deposits is the increase i n octane In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

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ADVANCES IN CHEMISTRY SERIES MILLIONS OF

BARRELS

1200

1000

800


600

400

200

O L -

1925

1930

1935

1940

1945

I95C

Y E A R

Figure 8. Total Yearly Volume of U. S. Gasoline Data for motor and aviation (1949-50) from (4). Data for aviation (1928-40) estimated by Standard Oil Co. (N. J.). Data for premium and regular grades from Ethyl Corp.

number requirement of the engine. This increase averages about 10, but may be as great as 25 or 30 octane numbers in extreme cases. The effect is practically independent of the presence or amount of tetraethyllead i n the fuel, as shown i n Figure 3. Other problems which appear to involve lead are exhaust valve burning, exhaust valve guide corrosion i n heavy-duty engines, and spark plug fouling. M a j o r steps toward solving the general problems of deposits have been made: (1) by engine manufacturers through selection of engine designs, materials of construction, and maintenance procedures which make engines less sensitive to fuels, lubricants, and additives; and (2) by petroleum refiners through selection of fuels, lubricants, and additives which are compatible. F o r example, i n heavy-duty automotive engines the use of sodium-cooled valves and/or valve rotators has increased valve life 300 to 4 0 0 % (Figure 4), making i t approximately equal to piston ring life; i n aircraft engines improved design and operating technique have doubled spark plug life. I n general, i t would appear that some degree of trouble must always be expected from deposits—trouble which i n some part, though by no means wholly, is due to the antiknock compound. However, progress has been made to the point where the present problems cannot be regarded as critical. Moreover, present research indicates that there is hope for substantial further improvement. In any case, the extent to which tetraethyllead contributes to these problems is a small price to pay for its value as a fuel constituent.

High-Antiknock Gasoline The selection of the power plant and fuel combination for a specific job with any given performance is, i n the long run, based on initial cost and operating convenience. In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.



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For vehicular use, many and various combinations have been tried, which include steam, electricity, gas, gasoline, and fuel oil engines of widely different types. There have been much more research and invention along this line than is generally appreciated, and out of it all has come the modern reciprocating internal combustion engine burning gasoline. It appears improbable that fundamentally new discoveries will be made i n this field; future improvements are likely to be refinements of what we have today. I t also appears probable that for a very long time to come all passenger cars and the majority of trucks, busses, tractors, and light aircraft will be powered by the conventional gasoline engine. The high output and excellent economy of the high-compression engine have been long known, and the average compression ratio of automotive engines has increased steadily during the past 25 years. However, as a result of developments i n the production of high antiknock fuels within the last few years, new engines have been designed which are really high-compression engines, built to permit operation at compression ratios well above those permitted b y present gasolines. Perhaps the most important single factor i n the design of these engines has been the increased stiffness of the crankshaft and other parts, which has been shown to remove the "roughness" that was characteristic of earlier high-compression engines. Already four new postwar engines embodying this principle have appeared, and others are expected i n the not too distant future. The trend appears definitely to be i n the direction of Vee engines of short stroke, with well cooled overhead valves, and with combustion chambers designed as far as possible to minimize the antiknock requirement of the engine at a given compression ratio.

The principal limitation on increases in compression ratio is the requirement for high antiknock fuel. Engine designers are well aware of this, and large amounts of research are i n progress on so-called "mechanical octane numbers"—i.e., any means of lowering the fuel antiknock requirement for a given engine performance or, preferably, of increasing the performance for a given antiknock level. Methods which have been studied include : (1) better cooling and elimination of hot spots, down-draft carburetion, and straightthrough type mufflers; (2) more accurate ignition timing; and (3) pistons and combustion In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.


230 CONSUMPTION

INDEX,

1930 - 100


3 0 0 0 r

chambers designed to obtain turbulence i n the charge. A n illustration of the advantages of turbulence, particularly i n fuels of high "sensitivity," and these particularly when treated with tetraethyllead, is shown i n Figure 5. Other methods of minimizing the need for fuels of high antiknock value are based on the fact that i n a given engine the maximum antiknock requirement is needed only part of the time, usually although not always at full throttle and low speed. I n present engines, automatic change i n ignition timing and mixture enrichment at full throttle take advantage of this. Suggested dual-fuel systems or supplemental fuel injection are also effective but inconvenient and frequently costly. The low price of gasoline even of high antiknock level tends to discourage these means of obtaining the desired performance. It may be concluded that much progress will be made i n reducing the fuel antiknock quality required at a given engine compression ratio. However, i t seems likely that such progress will be utilized b y engine manufacturers to increase compression ratios, because of the fuel economy and engine performance to be gained thereby. The end result will be a demand for fuel of still higher antiknock quality rather than a reduction from present levels. Figures 6 and 7 illustrate the trends to high-compression engines and high gasoline antiknock quality for the past 25 years. These trends may be expected to continue, except as modified temporarily by restrictions imposed by national defense needs, shortages of materials, etc.

Tetraethyllead as a Component of Gasoline During the past 25 years, while the total gasoline volume has increased greatly, the use of tetraethyllead has increased even more rapidly. I n Figures 8, 9, and 10 are shown, plotted against the years: the barrels of leaded and nonleaded regular grade, premium grade, aviation, and total U , S. gasoline; the average tetraethyllead content of these In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

231



gasolines; and a comparison of the rates of increase i n gasoline consumption and tetra ethyllead use. N o w an interesting question may be asked—namely, what value does this added tetraethyllead have, and what would have been the cost of obtaining the same end result without its use?

0

1

i

Ο

20

1

1

40 60 OCTANE NUMBER

1

80

1

I

100 0

1

1

»o

2 4 6 ML TEL IN ISOOCTANE

Figure 11. Performance Number Equivalents for Octane Numbers and Tetraethyllead in Iso-octane T o discuss this question intelligently, i t is necessary to comment briefly on the octane number scale, and to examine some substitution for i t . The octane number scale is an invaluable deyice for measuring i n the laboratory the antiknock quality of fuels, but the numbers so determined are b y no means a linear yardstick of the value of a fuel i n terms of its performance i n an actual engine. Here the maximum allowable compression ratio and degree of supercharge i n a supercharged engine are the important characteristics of the fuel, and these are best expressed i n terms of performance numbers. The performance number is essentially a linear measure of the maximum—i.e., knock limited—power developed i n an "average" variable compression or supercharged engine on a given fuel compared with the power developed on pure iso-octane, the latter being taken at 100. Hence performance numbers may be taken as a linear measure of a fuel's potential value. (Inasmuch as performance numbers have a defined relation to octane numbers below 100 and to iso-octane plus tetraethyllead above 100, the conventional laboratory octane n u m ber data can be directly translated into performance numbers, as shown i n Figure 11.) Using this performance number scale as the measure of quality, an appraisal of the average regular and premium grades of motor gasoline of 1950 is shown i n Figure 12. I t In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

232


is apparent that, in both grades, a substantial portion of the total performance number is contributed by the addition of tetraethyllead. The effectiveness per milliliter of tetra-* ethyllead is the same in the two grades, despite the fact that the premium grade has a higher level base stock and a higher tetraethyllead concentration than the regular grade. The cost of obtaining incremental performance numbers by refining processes is difficult to determine because of variations in refinery practices and equipment, i n product demand from refinery to refinery, and i n crude sources. The cost of obtaining a similar incremental increase in performance number b y use of tetraethyllead can be accurately obtained. PERFORMANCE NUMBER


80

Figure 12.

REGULAR PREMIUM GRADE GRADE Increase in Antiknock Quality Due to Tetraethyllead Typical 1950 motor gasolines

If we consider the typical 1950 gasolines mentioned above, with and without tetraethyllead, any reasonable method of estimation shows that the cost of the increased antiknock quality obtained b y tetraethyllead is substantially less than the cost would have been for the same increase by refining operations. The almost universal use of tetraethyllead i n gasoline is i n itself a demonstration of its economy. Furthermore, its use permits flexibility i n day-to-day refinery operations required to make gasoline of a given specification. I n aviation gasoline, the value of tetraethyllead is still greater, as i t would be practically impossible to manufacture aviation gasoline of the desired quality i n quantity great enough to meet the demand, were i t not for the use of an antiknock agent. I n general, the trend toward increasing costs of producing crude oil and of processing i t to high antiknock gasoline, which has been emphasized b y Holaday (5), increases the economic value of tetraethyllead, while a t the same time the higher retail prices of gasoline (including taxes) emphasize the importance of the fuel economy which higher quality gasoline makes possible.

Future Possibilities Accomplishments to date i n the utilization of antiknock agents have been largely made b y cut and try methods, rather than by the application of theory. I t is logical to expect that continuing basic research will provide a better understanding of knock and antiknock action, and of the tetraethyllead-fuel relationship, and this should lead to deIn PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

233



velopments of practical value. Despite the increases which have occurred i n base fuel quality, we are nowhere near the point of diminishing returns i n the antiknock effective ness of tetraethyllead. If we analyze the data of A P I Project 45 and other research work in terms of performance numbers, we find that the percentage increase i n perform ance number due to tetraethyllead is generally the same in high antiknock hydrocarbons as in low antiknock hydrocarbons of the same chemical type; hence the actual increase in value of tetraethyllead is greater at high antiknock levels, as a greater actual rise i n per formance number is obtained. This may be seen i n Figure 13, where the performance numbers of an assortment of paraffin and naphthene hydrocarbons are plotted with and without 3 m l . per gallon of tetraethyllead. A similar, but less consistent effect is observed for aromatics and olefins. Among the possibilities for further improvement i n the utility of tetraethyllead i n motor gasolines at high antiknock levels are at least three: (1) development of still " m i l d e r " engines for best use of sensitive fuels with tetraethyllead; (2) discovery of economic means of reducing the sulfur i n gasoline to very low levels or of otherwise m i n i mizing its deleterious effect on tetraethyllead; (3) production of base gasolines which, blended with tetraethyllead, will give higher road antiknock values than indicated b y conventional laboratory test methods. A striking example of this last possibility is given in Figure 14, which shows the road ratings of a conventional gasoline base and a special blend, each having the same ratings by the laboratory methods. W i t h or without tetra ethyllead added, the special blend is far superior to the present-day gasoline. PERFORMANCE NUMBER, 3.0 ML TEL PER GAL 160

140

/ 120

100

o ο» 80

60

40 Ο PARAFFINS Δ NAPHTHENES 20' 20

80

100

120

140

PERFORMANCE NUMBER, CLEAR

Figure

13.

Effect of Tetraethyllead in Paraffin and Naphthene Hydrocarbons Research method ratings



234 |>

PERFORMANCE


'20,

.

NUMBER

1

T E L ,

M L PER GAL

Figure 14. Road Antiknock Ratings of Conventional Fuel and Specially Blended Fuel Identical laboratory antiknock ratings

Conclusions The trends of the past 25 years toward increasingly better quality gasolines and concurrent improvement i n engine performance are expected to continue. Improvements take time and no radical overnight developments are anticipated. M u c h further research, design, and investment will be needed, but the end of the road is not i n sight and the petroleum and automotive industries are not apt to stand still so long as progress is possible. In the progress which has occurred, tetraethyllead has played an important part, and its utility as a component of gasoline may reasonably be expected to increase still further i n the future.

Literature Cited (1) Dunstan, A .E.,Nash,A.W.,Tizard, Henry, and Brooks, B . T., "Science of Petroleum," London, Oxford University Press, 1938. (2) Ethyl Corp., unpublished data. (3) Holaday, W . M . , SAE Journal, 56, No. 5, 30 (1948). (4) U . S. Bur. Mines, "Domestic Demand," 1951. R E C E I V E D M a y 31, 1951.


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