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It is unnecessary to say much with regard to the automobile of the future which is to take the place of the smart horse drawn carriage. In my opinion this will, without doubt, remain electrically driven.

It is probable that, in cases where only one carriage can be afforded, the gasoline care of the enclosed Limousine or of the Landaulette type will always be in demand; but I think it is now universally recognized that the type of gasoline care which is most advantageous for touring purposes-that is to say, fitted with an engine of high horse power and having a long wheel base and roomy bodyis least adapted for London streets and traffic conditions.

When two automobiles can be kept, it is more than probable that the electric carriage will be universally adopted for purely town use. The gasoline car, as it becomes more perfect, does not become simpler in construction, and I think it will be admitted that, however perfectly it runs when once started and clear of the town, it is not at present, or very likely to become, the carriage for shopping, calling, theatre or night use. It is very attractive to imagine the ideal car which can be used with comfort all the week in London and which provides the means of a country excursion from Friday to Monday; but is the gasoline car built especially to suit town conditions ever going to be at the same time a good touring car?

There remains to be considered one very important field of the future. What automobile is to take the place of the single horse brougham? The doctor's carriage may be taken as the typical private one horse carriage, the expenses of the running of which have to be kept as low as possible.

The average medical man cannot afford to pay more than £250 to £300 a year for the use of a carriage, including the driver. I do not think that any automobile of today which the smart doctor leaves standing outside the door of his fashionable patients could be let out to him at this figure.

I can foresee the electric brougham in a few years' time, when the cost of production is lowered by building in large quantities, and when standing costs are reduced by the number of carriages garaged, let out at about £250 pounds a year without driver. Assuming that an efficient driver may in time be procurable at £75 a year, we have a figure of £325 a year as the lowest inclusive cost which would be remunerative to the company supplying the carriages. Is this a prohibitive figure, considering the advantages which a business man would receive by the increased speed of his carriage, and, as a consequence, the larger amount of time he could give to his professional work?

White, Thomas L. "The Ultimate Internal Combustion Motor and Its Probable Fuel," The Iron Age (January 7, 1909), 16-17

By 1909 the internal combustion engine was the engine of choice for the automobile. Adequate sources of fuel were, however, a critical problem. White notes that development of the automobile had by this time proceeded to the point where the engine was set and the fuel had become the element to be experimented with. Observing that the engine had evolved "along the lines set by economic necessity," White contends that "from a business standpoint the introduction of a new fuel for use with the current equipment is a vastly better proposition than the introduction of a new type of motor to burn a new kind of fuel, no matter how good the latter may be."

THE ULTIMATE INTERNAL COMBUSTION MOTOR AND ITS PROBABLE FUEL

BY THOMAS L. WHITE

Perhaps the truest thing that can be said by way of a review of present practice in the design of automobile motors is that we are drawing to the close of a period of empirical construction and entering upon a period of systematic research. The principal need of the designer at the present time is for the kind

of information which the steam engineer derives from his steam tables, and, speaking of the well defined field covered by the power equipment of the selfpropelled vehicle, the indications are that in the present state of our knowledge no structural changes of a radical character are probable, or even possible, even in the event of a failure of the gasoline supply, and that further gains in thermal efficiency can only result from a more thorough study of the physical and chemical changes which occur in the working fluid from the moment that it enters the carburetor to the moment when it leaves the exhaust.

There is no intention in putting forward these propositions to claim finality of design for the existing type of motor nor to minimize the importance of the fuel issue. They simply represent the facts. It is significant, for instance, that although the high compression alcohol motor has a thermal efficiency of over 30 per cent, and alcohol is cheaper on the Continent than gasoline, there has been practically no attempt in France or in Germany to install this type of power plant in the automobile. It is equally significant that the Automobile Club of France is now offering a prize of 40,000 francs, not for a suitable equipment to burn alcohol, but for a "cheap fuel for general use and for a suitable device for its gasification, which must both be adaptable to all motor systems."

LIMITATIONS TO CHANGE IN ENGINE DESIGN

The fact of the matter is that the present type of automobile motor is the outcome of a number of determining conditions of which the necessity of using gasoline was only one, and the current impression that it is the low preignition temperature of gasoline and air mixtures that has prevented the use of high compressions is only partially correct. There are other reasons which are just as cogent. One of them is that the high pressure motor is not suited for lay use. In inexperienced hands the compression is apt to be lost, owing to the piston rings and valves giving out through want of attention. Another is that the high pressure motor is a violation of the accepted canon of automobile design that power must be sought in the direction of speed and not in the direction of weight. Still another objection, and, perhaps, the most important of all, is that it is difficult to the verge of impossibility to control the ignition of a high speed motor under conditions of varying load, unless the quality of the mixture can be depended on to be absolutely the same at all speeds. Where the fuel is vaporized by the ingoing air this condition is rarely attainable. The same trouble is experienced with the high compression suction producer engine. Here it is the percentage of free hydrogen in the producer gas which varies with the speed of the motor, and the opinion is held by many engineers that the presence of this hydrogen, in spite of its great fuel value, is a positive disadvantage.

Engineering progress is not as a rule along the lines which are technically the most desirable, but along the lines which have been set by economic necessity, and as a reason, though not a technical one, for the conservation of the present type of motor must be reckoned the natural inertia of the existing order. This is inimical to revolutionary policies. From a business standpoint the introduction of a new fuel for use with the current equipment is a vastly better proposition than the introduction of a new type of motor to burn a new kind of fuel, no matter how good the latter may be. Also it must be remembered that gasoline will for many years be an alternative fuel. In fact, in some localities it will continue to be the only fuel obtainable, and as the automobile in its capacity as a long distance vehicle has no fixed base of supplies, it will be necessary for it to be able to get along on gasoline on occasion, at any rate until the coming fuel is so widely used that a supply of it can always be depended on.

NEW LINES OF RESEARCH

If, as seems to be the case, the long supremacy of gasoline, and other causes of a less ephemeral character, have left a permanent stamp on the design of the automobile motor, then it is to the chemist that we must come not only for aid in the fuel question, but also for information about the phenomena of combustion, to enable us to use the type of heat engine which we have to the best advantage. The time has come when physical and chemical research must supplement a too narrow devotion to the purely mechanical side of motor engineering. To quote Prof. Vivian B. Lewes in this connection, "The engineer relies upon his indicator diagrams and tests of horsepower for information which could be much more easily obtained by analysis of the exhaust gases, and if

this method of investigation were employed important advances would very soon follow. Analyses of the exhaust gases from motor engines are remarkably scarce. Indeed, I do not know of any in this country. But Mr. Sorel, in 1903, published in France some results in which he showed that with a motor running at 1061 rev. per min. and using 382 g. of gasoline per brake-horsepower-hour, the products contained unburned compounds which represented 82 per cent of the hydrogen and 42 per cent of the carbon present in the original fuel, thus reducing the heat value of the gasoline used in the cylinder from 11,278 to 5085 calories."

Almost identically the same contention is urged by Dr. Warschauer in a recent address presented to the Association of German Chemists of Berlin. "Until now the design of vaporizers for different kinds of fuels has been determined entirely by empirical methods. Right here the assistance of the chemist is required by the automobile engineer. By systematic qualitative and quantitative gas analysis data of great value can be derived regarding the character of the combustion of fuels. To take an illustration from the field of illumination, I will quote one of the most important propositions from Stepenoff's "Theory of the Kerosene Lamp.' It is as follows: "The efficiency of the lamp is best determined by the analysis of the gases given off.' The same truth with a suitable change in the wording can also be applied to the explosion motor."

The analysis of the exhaust gases from the explosion motor, important though it may be, is, however, only a step. It reveals the last stage of the complicated reactions which have occurred during the expansion stroke, but it affords little information as to the actual nature of these reactions or of the heat changes which accompany them. If carbon be slowly oxydized in the open air, as in the decay of wood, or almost instantly consumed behind the piston of an engine, the amount of heat liberated and the final product are the same. The difference is not in the process, but in the conditions under which it is conducted, and the final goal of the work of the chemical engineer is the determination of the how, why and when of those factors, which in the case of the decaying wood and of the burning fuel are so widely divergent.

ACTION IN EXPLOSIVE MIXTURES

Some of the results which are coming to light in connection with the study of the energy transformations which occur in the motor are sufficiently starting. Thus it appears that carbon monoxide is absolutely inflammable in the absence of water, and, further, the velocity with which an explosion in a mixture of this gas with air is transmitted depends on the amount of aqueous vapor present. Again, there are reasons for believing that the propagation of the flame in the cylinder of a gas engine is not by direct inflammation, but by the compression to preignition point of successive layers of the mixture. It also seems that the old belief that carbon will burn to carbon dioxide in the presence of an excess of oxygen is not altogether well founded. Under certain conditions the lower oxide is just as likely to be formed as the higher.

The fact is that the idea that during the expansion stroke of an explosion motor the carbon and hydrogen of the fuel simply burn up more or less quickly must be abandoned. What really happens is infinitely more complex. Thus every reaction which can occur in the cylinder is reversible within the temperature, pressure and concentration limits of the cycle. Moreover, it is probable that the combustion of the mixture is far from being of a uniform character throughout its mass at any given moment. There is reason for believing that different reactions may occur simultaneously at different points of the working fluid. It is possible, for instance, that water is being formed and decomposed at the same moment during the same explosion.

Speaking of the investigations which are actually being made at the present, the determination of the rate of heat flow through the cylinder walls and the estimation of the specific heat of carbon dioxide at combustion temperatures are the subjects of recent monographs. The latter quantity is important in connection with the phenomenon of suppressed heat and in the determination of the proportion of a given quantity of hydrogen or carbon which can be oxydized under given conditions.

MIXED FUELS

As there seems to be little doubt that the fuel which will take the place of gasoline will be a blend with an alcohol base, it is becoming important to be able

to trace the effect of each individual ingredient in a mixed fuel. It may be pointed out that the properties of a blend are far from being a mere statistical average of the properties of its constituents, for each admixture has a functional as well as a quantitative effect on the behavior of the whole in the motor. Thus the addition of acetylene to alcohol by accelerating its combustion in the motor increases its efficiency. Lastly, it may be mentioned that the increase of the calorific value of a fuel by blending has no effect on the specific power of the motor in which it is burned. The maximum power of a given motor is independent of the calorific value of the fuel which is used in it, the popular belief to the contrary notwithstanding.

Midgley, Thomas, Jr. "Some Fundamental Relations Among the Elements and Compounds as Regards the Suppression of Gaseous Detonation," Industrial and Engineering Chemistry, April 1923: 421–423

The White article identified fuel as the critical element in further development and expansion of the automobile industry. Midgley's article reports on the most important step in solving the fuel problem, the development of anti-knock compounds. This article reveals the sophisticated understanding of the spark ignition engine which had been reached by the early 1920's, and described the development permitting achievement of improved power and performance of gasoline engines.

SOME FUNDAMENTAL RELATIONS AMONG THE ELEMENTS AND COMPOUNDS AS REGARDS THE SUPPRESSION OF GASEOUS DETONATION

Under certain conditions the combustion of gases is characterized by detonation. In the case of the combustion of a mixture of any given fuel in the internal-combustion engine the development of detonation is controlled primarily by the pressure to which the unburned portion of the mixture is subjected during combustion. In view of the fact that both the power output and the efficiency of the internal-combustion engine are functions of its compression, this factor has a large significance. Economical utilization shall be as high as is compatible with proper performance from a mechanical standpoint. Since the motor fuel available is practically of fixed composition, the factor that now limits the compression of automotive engines is the tendency of this fuel to detonate.

It has been found that the presence of very small amounts of certain materials in a fuel-air mixture influences its combustion in such a way that detonation is prevented. This detonation-influencing property is a function of certain compounds of a considerable number of the elements.

RECENT RESULTS OBTAINED IN THE STUDY OF GASEOUS DETONATION

Two things have recently been added to our knowledge of the mechanism of gaseous detonation. First, it has been demonstrated that even in nondetonating, or normal, combustion a higher pressure must exist ahead of the flame front than behind it. It has been shown, further, that the pressure immediately in advance of the flame front is controlled by the reaction velocity of combustion. If the reaction velocity is expressed by the equation W=KD"T", a mathematical expression can be derived for the pressure differences existing in the flame front at different total pressures. In this equation W is the reaction velocity expressed in pounds of gas entering the reaction per second, K is a constant whose value must be determined experimentally, T is the absolute temperature immediately in front of the flame, D is the density or concentration, and n and m are exponents whose values must be determined experimentally.

The expression derived on this basis predicts a critical pressure above which the combustion reaction proceeding through the gas must travel at the velocity

of sound. When the transmission of chemical activity reaches this velocity, a condition that we call "detonation" is produced.'

These developments may be considered as being based upon the physical chemistry involved in gaseous detonation. But they shed no light on the ultimate nature or mechanism of the chemical reactions involved. They merely apply the known laws of physics and chemistry to the analysis of the progressive combustion of a gaseous mixture.

WHAT ANTIKNOCK MATERIALS DO

Those compounds which, when present in combustible mixtures in very small amounts, have the effect of entirely removing the disturbances that characterize detonating combustion are called for convenience "antiknock" materials. Their effect appears to be that of increasing the critical pressure at which detonation occurs. Thus, if a mixture of acetylene and air of proper proportions contained in an open tube is ignited at one end a detonation wave is set up after the flame has traveled a short distance along the tube, as is shown by the high luminosity and by the loud and sharp "crack" that is produced. If the experiment is conducted in a strong glass tube, the intensity of the pressure wave resulting from the detonation is often such that a few inches of the tube at the end opposite the point of ignition are shattered into small pieces. But when a very small percentage of an antiknock material such as diethyl selenide is present in the acetylene-air mixture, the burn is very quiet and it lacks the high degree of luminosity that characterizes detonating combustion.'

The effect of antiknock materials upon internal combustion is even more striking. If, for example, an airplane engine, which has a compression ratio of about 5.3:1, is run on the commercial motor gasoline of to-day, a violent detonation or knock is produced. Even in the absence of instrumentation for detecting and measuring it, the detonation manifests itself by a loud hammering sound of a metallic quality and by a reduction in power from what should be the normal output of the engine. When a small amount of the vapor of diethyl selenide is admitted with the intake air, the detonation is entirely eliminated and a noticeable increase in the power of the engine is apparent. In a similar way, if a very small amount of tetraethyl lead, about 0.1 per cent by volume, is added to the fuel, the detonation entirely disappears, the engine runs with perfect smoothness, and its power rises to normal or to the value that it should have in the absence of detonation. Computation shows that quantitatively this result is produced by virtue of the presence of only 1 molecule of tetraethyl lead in over 80,000 molecules of fuel-air mixture.

In distinction from these materials whose effect is to eliminate detonation, there is another class of substances that induce detonation. This is in addition to those materials that are neutral as far as effect on detonation is concerned. The knock-inducing property characterizes to a small degree the ethyl compounds of bromine, oxygen, and sulfur. These elements also show this negative characteristic in the elemental form.

But the simple alkyl compounds of these elements exhibit a relatively small detonation-inducing effect. When oxygen is bonded into compounds such as alkyl nitrates or nitrites and phenyl nitro compounds, its effect for inducing detonation becomes very marked. Thus, if an engine is run on a fuel such as a benzenegasoline mixture that does not produce any knock, a violent detonation can be produced by the admission of a very small amount of some volatile organic nitrate or nitrite along with the fuel-air mixture. This detonation-inducing material is equally effective whether it is admitted as a vapor with the intake air or whether it is dissolved in the fuel. Quantitatively 1 gram molecule of isopropyl nitrite has a detonation-inducing effect that is equal to the inverse of about 0.1 gram molecule of tetraethyl lead. (The detonation-inducing elements are considered as possessing the negative of the antiknock property.)

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The mechanism by which these materials control the reaction velocity of combustion is not understood. It is inconceivable that their effect can be due to a simple thermal effect, such as an absorption of heat with a consequent cooling of the flame. The amount of the antiknock material present in the burning gas is too minute for such to be the case. As has previously been shown, the presence

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1 Midgley, J. Soc. Automotive Eng., 10 (1922), 357: Midgley and Janeway. “Laws Governing Gaseous Detonation," to be published in an early issue of J. Soc. Automotive Eng. 2 Midgler and Bovd. This Journal 14 (1922), 894.

3 Ibid., 14 (1922), 849.

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