DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SUKVEY

GEOKGE OTIS SMITH, DIRECTOR

BULLETIN 392

COMMERCIAL DEDUCTIONS

FROM COMPARISONS OF

GASOLINE AND ALCOHOL TESTS ON 

INTERNAL-COMBUSTION ENGINES

BY

ROBERT M. STRONG

WASHINGTON

GOVERNMENT PRI N TI NG= OFFICE 

1909

CONTENTS.

Page.

Introduction......................!............................,.......... 5

Differences in engines...................................................... 6

. General statement....................................................... 6

. Gasoline engines run with alcohol...................................... 6

Special engines for alcohol............................................. 6

Alteration of gasoline engines........................................... 7

Effects of fuel quality.1 .................................................... 8

Mixtures of gasoline and alcohol........................................ 8

Gasoline with a spray or jet of water..................................... 8

Alcohol of different strengths........................................... 9

Relative adaptability of gasoline and alcohol............................. 10

Effects of principal operating conditions.................................... 13

Effect of different loads.................................................... 13

Effect of mixture quality............................................... 13

Effect of time of ignition............................................... 15

Tests with variable load............................................... 15

Tests with change in time of ignition................................... 16

Tests with variable fuel supply......................................... 17

Incidental material.................................................... 18

.Limits of fuel-consumption rates............................................. 18

Limits set by operating conditions..... ................................. 18

Limits set by engine design............................................... 21

Other factors affecting fuel consumption.................................... 21

Speed of engine........................................................ 21

Size of engine.......................................................... 22

Carburation.......................................................... 23

Throttling............................................................. 23

Valve timing........................................................... 24

Jacket temperature..................................................... 25

Preheating the air..................................................... 27

Size and intensity of ignition spark..................................... 29

Degree of compression................................................. 29

Synopsis of results and general conclusions ............;.................... 31

Survey publications on fuel testing ........................................ 37

3

COMMERCIAL DEDUCTIONS FROM COMPARISONS OF 

GASOLINE AND ALCOHOL TESTS ON INTERNALCOMBUSTION ENGINES.

By ROBEKT M. STRONG.

INTRODUCTION.

The following report is a summary of the commercial results which 

were obtained from 2,000 tests conducted by the United States Geological Survey at St. Louis, Mo., and Norfolk, Va., in 1907 and 1908, 

under the technical supervision of E. H. Fernald, engineer in charge of 

the producer-gas section of the technologic branch. The tests dealt 

primarily with gasoline, forming part of the investigation of mineral 

fuels provided for by acts of Congress. To determine the relative 

economy and efficiency of gasoline it was compared with denatured 

alcohol. The tests, many of which were undertaken in connection 

with work for the Navy Department, supplemented, to a certain 

extent, the work of previous investigations, but only so far as was 

necessary to emphasize some of the more important points and to lead 

up to the defining of conditions required for the economical use of 

gasoline and alcohol.

In order to determine and eliminate the affecting engine conditions 

as far as possible, the investigation was commenced by making comparative gasoline and alcohol tests on the same engines. These tests 

were repeated on other engines of approximately the same size and 

speed, having different degrees of compression, different methods of 

governing, and different carburetors. The final report will include 

much material that may be of use in engine design, but that side 

of the investigation was not pursued any further than was necessary 

to obtain the best possible results for alcohol and for gasoline with the 

engines at hand, and to prove that the minimum fuel-consumption 

rate for each could be obtained in approximately the same manner. 

The effects of engine and of operating conditions both have a bearing 

on the commercial deductions but will be discussed only in a general 

way at this time.
6 GASOLINE AND ALCOHOL TESTS.

DIFFERENCES IN ENGINES.

GENERAL STATEMENT.

Gasoline and alcohol engines' are built and operated on exactly 

the same principles, and the action of the two fuels is relatively the 

same. Explosive mixtures of the vapors of gasoline and of alcohol 

with air are formed in the same manner, and the subsequent burning 

of these explosive mixtures in the engine cylinder takes place in a 

similar way and with similar results.

GASOLINE ENGINES RUN WITH ALCOHOL.

Almost any gasoline engine with a well-designed carburetor will 

run as well with alcohol as with gasoline, from the standpoint of 

operation, except for a difference in ease of starting and in certainty 

of operation at low speeds. Under conditions requiring widely 

varying speeds the engine.is less certain to operate satisfactorily at 

very low speed when alcohol is used, unless some special adjustment 

is made. The only change required for the use of alcohol in a gasoline engine, if any, is in the size of the fuel passageways. The fuel 

needle valve must be capable of being opened twice as wide for alcohol 

as is required for gasoline, and the spray nozzle must not be restricted 

to just the size that is required to supply the needed quantity of 

gasoline. The fuel passageways in a carburetor can usually be easily 

drilled out, and so far as producing-power at constant speed is concerned the engine will be just as serviceable with either fuel. This 

change need not be such as to affect the consumption of gasoline, 

but with this change alone the consumption of alcohol will be from 

one and a half times to twice as much as the consumption of gasoline 

for the same power.

SPECIAL ENGINES FOR ALCOHOL.

By using alcohol in an alcohol engine with a high degree of compression (about 180 pounds per square inch above atmospheric 

pressure much higher than can be used for gasoline on account 

of preignition from the high temperatures produced by compression), 

the fuel-consumption rate in gallons per horsepower per hour can be 

reduced to practically the same as the rate of consumption of gasoline for a gasoline engine of the same size and speed. The indications 

are that this possible 1 to 1 fuel-consumption ratio by volume for 

gasoline and alcohol engines will hold true for any size or speed, 

if the cylinder dimensions and revolutions per minute of the two 

engines are the same.

An alcohol engine is as adaptable to commercial requirements as a 

gasoline engine, except that with the present types of carburetors 

the same increased difficulty in starting and in operating at very
DIFFEKENCES IN ENGINES. 7

low speeds is experienced as for a gasoline engine when alcohol fuel 

is used. The adaptability of alcohol is such, however, that this difference, which is due to ineffective vaporization, is not necessarily 

permanent.

When alcohol is used in a gasoline engine with the maximum 

degree of compression for gasoline, the available horsepower of the 

engine is increased about 10 per cent. An alcohol engine with the 

maximum degree of compression for alcohol will have an available 

horsepower 30 per cent greater than a gasoline engine of the same 

cylinder size, stroke, and speed. Owing to the higher explosion 

pressures, however, an alcohol engine should be built heavier than 

a gasoline engine, but the weight per horsepower nray be less.

ALTERATION OF GASOLINE ENGINES.

Some gasoline engines may be so changed that a sufficiently high 

compression pressure is secured to make it possible to reduce the 

consumption of alcohol in gallons per horsepower per hour to'an 

equality with that for gasoline before the engine was changed; the 

change, however, precludes the further use of gasoline, as it can not 

be used satisfactorily with compression pressures much in excess 

of 70 to 75 pounds per square inch above atmospheric.

The degree of compression may be most easily changed by lengthening the connecting rod, which changes the position of the piston at 

the extreme end of the compression stroke. This can only be done, 

however, in an engine which is not counterbored and in which the 

shape of the clearance space is such that the piston will not strike 

the cylinder head or valves. The type of connecting rod usually 

used for stationary engines can be lengthened very easily by putting 

liners between the crank-pin end of the connecting rod and the crank 

brasses. This makes it possible to adjust the degree of compression 

to whatever fuel it is desired to use with but little trouble.

If the cylinder is counterbored, or if there is not sufficient room at 

the head of the cylinder to allow the piston to travel back far enough 

to increase the compression pressure to the amount desired, a new 

cylinder head should be cast with smaller clearance space. Attaching 

plates to the piston or cylinder head is seldom, if ever, satisfactory. 

The arrangement of the valve-actuating mechanism often determines 

the position of the valves, which may be such that a small enough 

clearance space can not be secured without almost an entire redesign 

of the engine. Furthermore, with the increased compression pressure 

required for the economical use of alcohol, the maximum pressure 

from explosions or combustion will increase and will be as high as 

600 or 700 pounds per square inch for maximum load when the 

compression is raised to 180 or 200 pounds per square inch above 

atmospheric pressure. The ordinary stationary engine, especially the
& GASOLINE AND ALCOHOL TESTS.

horizontal type, is not usually built heavy enough to withstand such 

pressures continuously; hence, while it may be quite possible to raise 

the compression of a gasoline engine sufficiently to convert it into 

an economical alcohol engine, it is not always advisable to do so. 

This is especially true if the difference in cost of fuel is a comparatively 

small consideration, as is often the case.

EFFECTS OF FUEL QUALITY.

MIXTURES OF GASOLINE AND ALCOHOL.

The increased difficulty of starting an engine with alcohol and. the 

increased uncertainty of operation under variable speed conditions 

has suggested the use of gasoline and alcohol in a double carburetor, 

which mixes the vapors or sprays of the two fuels with air in the 

usual manner. Tests on two similar engines having different degrees 

of compression were made with such mixtures. For the two engines 

26 and 21 tests were required to obtain the best time of ignition and 

best mixture quality (as regulated by the fuel needle valve and 

auxiliary air valve) for 7 different proportions of gasoline and alcohol. 

The results obtained are not as conclusive for the tests with the 

higher degree of compression as might be wished on account of 

affecting engine conditions which were known and recorded but not 

eliminated. The results of these tests, which will be given in full in 

the final report, indicate, if rightly interpreted, that the maximum 

thermal efficiency for mixtures of gasoline and alcohol will vary from 

that for alcohol alone to that for gasoline alone, when the best 

degree of compression is used in each case; and that the total fuel 

consumption will not be less than the minimum for either fuel alone

and will depend on the limiting degree of compression for each different proportion. If this be true, there is no advantage in using gasoline and alcohol together -except for starting and operating under 

conditions of variable speed;, and these advantages should be obtainable through some other means, such as more suitable design of 

induction passageways and carburetor. Moreover, the use of gasoline 

in any appreciable quantity does away with many of the advantages 

that are obtained from the use of alcohol alone, such as safety and 

absence of disagreeable odors.

GASOLINE WITH A SPRAY OR JET OF WATER.

The fact that the limiting compression pressure for gasoline and 

alcohol used together was always greater than for gasoline alone suggested that possibly by substituting water for alcohol and so increasing the limit of compression a corresponding increase in thermal 

efficiency for gasoline could be obtained. Following this suggestion, 

tests were first made on a gasoline engine with various proportions
EFFECTS OF FUEL QUALITY. 9

of gasoline and water. So far as possible the best results were obtained for each given proportion, from all gasoline to as much water 

as gasoline, but no change in the thermal efficiency or rate of consumption of gasoline could be made; this result showing that the 

effect of the water, if any, was balanced. Since higher compressions 

could be used, depending on the proportion of water, a similar set of 

experiments was made with one of the alcohol engines in which the 

compression pressure was about 130 pounds per square inch. Again 

the thermal efficiency could not be increased or the consumption rate 

decreased to values better than the best obtained for gasoline alone 

in a gasoline engine. For the two engines 28 and 23 tests were 

required to determine the best possible results for each percentage 

of water used; but the results are not conclusive, for there is a question whether the particular engine used for the latter tests, with the 

higher degree of compression, was free from conditions of construction that affected the best results obtainable. Details of these tests, 

which have been worked up in full, are to be given in the final 

report and will afford much information to anyone interested in 

carrying the investigation further.

In general, the introduction of a small quantity of water with the 

fuel will prevent preignition from too high compression or overheated parts in the clearance space. The heavy explosion pound 

often obtained in a gasoline engine operating under maximum load 

may be entirely eliminated and the running of the engine made much 

quieter and smoother by using a small quantity of water. The shock 

and wear of moving parts is thus obviously reduced. If the water 

contains any grit, however, the cylinder and piston will soon become 

scored; hence ordinarily it is not advisable to use a spray of water 

continuously with the air or fuel. The amount of cooling water required to keep the cylinder walls at a given temperature is diminished 

very noticeably when as much water as gasoline is taken into the 

cylinder, and the effect of smaller quantities of water is proportional.

ALCOHOL OF DIFFERENT STRENGTHS.

We are not limited to the use of denatured alcohol, which is about 

90 per cent ethyl alcohol, so far as the engine is concerned. Even 

50 per cent alcohol can be used, though not very satisfactorily. With 

this grade an engine is hard to start and is uncertain in operation; 

that is, the operating conditions are limited. The thermal efficiency 

decreases rapidly with increased dilution. The rate of decrease of the 

thermal efficiency with decrease in percentage of alcohol, however, is 

not constant^ but is more and more rapid as the alcohol becomes more 

dilute. From 94 per cent to 80 per cent alcohol, however, the consumption of pure alcohol is about the same, and the total consumption is 

almost directly proportional to the increase in percentage of water. ' 

86818 Bull. 392 09 2
10 GASOLINE AND ALCOHOL TESTS.

The maximum power of the engine also decreases as the alcohol is 

diluted, but, as is the case with the thermal efficiency, the percentage 

of decrease with dilutions between 94 and 80 per cent is negligible. 

When 50 per cent alcohol is used, however, the maximum horsepower of the engine is only 72 per cent of that for 94 per cent alcohol. 

Less cooling water is required for the engine cylinders with alcohol 

than with gasoline, and when the alcohol is diluted with water a 

further reduction is made in the required quantity of cooling water, 

the effect being similar to that produced when water spray is taken 

into the cylinder with the mixture of gasoline vapors and air. When 

50 per cent alcohol is used, scarcely any cooling water is required.

Full details of the tests from which the above results were obtained 

are to be given in the final report. Some of the data are very interesting, including indicator diagrams from two sets.of experiments 

with different carburetors. One set of 15 tests was made with a 

double carburetor, with which the sprays of water and alcohol were 

mixed. For the other set of 31 tests previously diluted alcohol was 

used in a special carburetor. The best results for 5 and 6 different 

percentages of dilution, respectively, were determined. These tests 

were made on a gasoline engine with a considerably lower degree of 

compression than, that found best for 94 per cent alcohol. No 

attempts to use higher degrees of compression for the more dilute 

alcohol were made. The results are conclusive as far as they go. 

They probably would not be different had a higher degree of compression been used; but, be that as it may, the commercial significance 

of the results as obtained lies in the fact that if 80 per cent alcohol 

can be manufactured for 15 per cent less per gallon than 90 per cent 

alcohol it becomes a commercial advantage to use the lower grade, 

provided the difference in cost of handling the greater bulk does not

offset the gain in cost of manufacture. It is even possible that the 

use of .70 per cent alcohol or lower grades will prove to be cheaper; 

but the use of these more dilute alcohols is limited to a certain extent 

by the difficulty of starting an engine using them and by the increased 

uncertainty of operation, especially under conditions of variable 

speed. Adaptability must be taken into account when comparing 

fuels.

RELATIVE ADAPTABILITY OF GASOLINE AND ALCOHOL.

Different properties limit the availability or determine the adaptability of liquid gasoline and alcohol and their combinations for use 

in internal-combustion engines of existing types. Gasoline is more 

volatile than alcohol, and the heat of combustion of a pound of gasoline 

is considerably greater than that of a pound of alcohol. The weight 'of 

air theoretically necessary for complete combustion of a pound of gasoline is different from that for alcohol, but the theoretical heating
EFFECTS OF FUEL QUALITY. 11

values of a cubic foot of gasoline vapor and air and a cubic foot of 

alcohol vapor and air, with just sufficient air for complete combustion in each case is very nearly the same about 80 British thermal 

units. Further than this but little is positively known about the 

properties of the working mixtures of alcohol or gasoline vapors and 

air, except that the pressure to which differently proportioned explosive mixtures of air and vapors of either fuel can be compressed 

without preigniting in the engine varies, and that an explosive mixture 

of alcohol vapor and air can be compressed to over twice as high a 

pressure as an explosive mixture of gasoline and air before self-igniting 

(preigniting in the engine).

Mixtures of air and fuel vapors, or sprayed fuel, are delivered to 

the cylinder of an engine, mixed with the remaining hot products of 

combustion, and subsequently burned.' Differences in the homogeneity and intimacy of this ultimate mixture, in the limit of excess of 

air that can be used without the mixture becoming too dilute to fire 

and in the rate of flame propagation, may each affect the completeness of combustion, and though the mixture quality be relatively the 

same alcohol may burn more completely than gasoline, or vice versa. 

The specific heat of the burned or burning charge may also be different for alcohol and for gasoline mixtures, thus changing the theoretical basis of comparison, and may also affect the rate of heat loss to 

the cylinder walls. But be all these things as they may, the ultimate 

effect is such that alcohol can be used a little more efficiently than 

gasoline, even in the same engine with the same degree of compression that is, more efficiently with respect to the percentage of 

available heat that is transformed into useful work, but with equal 

efficiency with respect to the quantity of fuel consumed when the 

best degree of compression for each is used.

Considering only the heating values of gasoline and alcohol, it is 

obvious that, if other factors are equal, the relative consumption of 

alcohol and gasoline will be inversely proportional to their respective 

heating values. The low heating value of denatured alcohol, which 

corresponds very closely to 94 per cent by volume ethyl alcohol, will 

average about 10,500 British thermal units per pound, while the 

low heating value of 0.71 to 0.73 specific gravity gasoline will average 

about 19,100 British thermal units per pound. The comparison 

gives a consumption-rate ratio of 1.8 to 1 by weight for a thermal 

efficiency ratio of 1 to 1. In actual operation, however, where gasoline and alcohol were each used in the same medium-sized (10 to 15 

horsepower) stationary gasoline engines without change of compression or speed, and the operating conditions, including load, were 

limited to the best possible for each fuel, a ratio of alcohol consumption to gasoline consumption in pounds per brake horsepower per 

hour was obtained as low as 0.98 to 0.59, equivalent to 1.66 to 1 by
12 GASOLINE AND ALCOHOL TESTS.

weight, or 1.45 to 1 by volume, with a thermal efficiency ratio of 28 

to 26 per cent (based on the low heating value and indicated horsepower), or 1.1 to 1. By raising the degree of compression from that 

best for gasoline (about 70 pounds per square inch above atmospheric) 

to that best for alcohol (about 180 pounds per square inch above 

atmospheric) the consumption-rate ratio was further reduced and a 

ratio of 0.7 to 0.59 pound per brake horsepower per hour, equivalent 

to 1.2 to 1 by weight, or 1 to 1 by volume, was obtained with a 

thermal efficiency ratio of 39 to 26 per cent, or 1.5 to 1.

These figures are not the results of single tests, but are the average 

values obtained for a number of tests under identical conditions; furthermore, these values were duplicated on different engines and at 

different times on the same engine. They represent the best practical values that were obtained for each fuel and stated degree of 

compression with the equipment at hand. They were obtained under 

special test conditions, however, and are not commercial values; nor 

were they obtained offhand, even by skilled operators.

Likewise, a consumption rate was obtained as low as 0.58 pound 

per brake horsepower per hour for gasoline with a corresponding thermal efficiency of 28 per cent, but the compression pressure used was 

90 pounds per square inch above atmospheric. With this degree 

of compression, it is necessary to use the weakest mixtures that will 

explode, in order to prevent preignition, and the load had to be 

reduced accordingly. Heavy loads could not be carried without 

excessive preigniting. Similarly, a fuel-consumption rate of 0.68 

pound per brake horsepower per hour, with a corresponding thermal 

efficiency of 40 per cent, was obtained for alcohol, with a compression 

pressure of 200 pounds per square inch above atmospheric, but preignitions were prevented only with difficulty and by a method similar 

to that used with gasoline, so that the conditions under which these 

results were obtained were not considered practical and the values 

have not been used in the discussion. They do not, however, change 

the ratios given.

The thermal efficiencies given in this discussion were calculated 

from the indicated horsepower and the lower heating value of the fuel. 

The method employed in determining the average indicated horsepower for each load was carefully worked out and the results were very 

satisfactory. They are consistent throughout with the brake horsepower determinations. It is not at all impossible to obtain the 

average indicated horsepower with sufficient accuracy for all practical 

purposes, if the load is kept reasonably constant; but the indicator 

diagrams must be taken in a careful, systematic, and understanding 

manner to be of any value at all.

The difference between the brake and the indicated horsepower, 

or the friction loss of the engines used, was practically the same and
EFFECTS OF OPERATING CONDITIONS. 13

constant. For 484 tests on the five engines the average difference 

was 2.3. A full description of the methods used in determining the 

average indicated horsepower from the indicator diagrams, with 

tables giving details of the tests from which the mechanical efficiency 

of each engine at various loads was obtained, will be given in the final 

report. These tables substantiate the above statements.

EFFECTS OF PRINCIPAL OPERATING CONDITIONS.

EFFECT OF DIFFERENT LOADS.

The fuel-consumption ratios given above for alcohol and gasoline 

(1.45 to 1 and 1 to 1 by volume) are little affected by the load when 

the other operating conditions are limited to the best for each load. 

This limitation requires continual change in the time of ignition and 

in the quantity of fuel supplied, as regulated by the igniter and the 

fuel needle valve, with a correspondingly wide difference in the 

numerical values obtained for the minimum fuel-consumption rates 

for the different loads. Thus the minimum consumption rate of 

gasoline and alcohol for the maximum load is about 10 per cent 

greater than that for the- best load, which is usually about 80 to 85 

per cent of the maximum load; while the minimum fuel-consumption 

.rate for light load; say about one-third load, may be anything greater 

than that for best load, depending on the disturbing effect of the 

governor. With the engines used for this investigation, the minimum 

fuel-consumption rate for one-third load was approximately 50 per 

cent greater than that for best load.

EFFECT OF MIXTURE QUALITY.

For gasoline and alcohol alike, the ratio of air to fuel for the condition of minimum fuel consumption at maximum load was found to 

be approximately that for a chemical mixture, that is, theoretically 

just sufficient air for complete combustion in each case. This ratio 

for gasoline is approximately 15 parts of air to 1 of fuel by weight, and 

for denatured alcohol (90 per cent ethyl alcohol), approximately 8 

parts of air to 1 of fuel. The minimum fuel-consumption rate at best 

load (about 80 per cent of maximum load) was obtained with a 

mixture of between 19 and 23 parts of air to 1 of gasoline by weight, 

and of between 9| and 11£ parts of air to 1 of alcohol by weight, 

when used at the same compression pressures; that is, for the most 

economical use of gasoline and alcohol at the same compression the 

calculations show that from 25 to 50 per cent excess air was used, 

depending on the estimated mixture temperature.

From a series of observations of the temperatures of the fuel and 

air mixtures as they enter the cylinder of the engine, and from 

measurements of exhaust temperatures for various conditions of
14 GASOLINE AND ALCOHOL TESTS.

operation, a careful estimate was made of the temperature of the 

ultimate mixture in the cylinder at the beginning of the compression 

stroke. For the condition of minimum fuel consumption for loads 

from maximum load to somewhat below best load (about 75 per cent 

of the maximum load) these estimates show a range of ultimate 

mixture temperatures from not to exceed about 160° F., if no vaporization of fuel takes place in the cylinder, to not less than 60° F. ; if 

all the fuel is vaporized in the cylinder.

The average weight of fuel per charge was obtained from the fuelconsumption rate and the average number of fuel admissions per 

minute, from which the corresponding volume of fuel per stroke was 

calculated. The volume of fuel and air mixture per stroke was 

calculated from the piston displacement, multiplied by a factor 

obtained from the light spring indicator diagram of the suction and 

compression stroke. These diagrams, if taken carefully, show 

accurately the volumetric efficiency of the pump action of the engine. 

Such, in brief, were the data used in determining the air-to-fuel ratios 

stated above, and a careful study of all the conditions affecting them 

indicate that the actual values lie about midway between the limits 

given.0

The accuracy of the foregoing method of determining the mixture 

quality may be questioned, but, be that as it may, for every load there 

is some best mixture quality and for.every mixture quality there is 

some best time of ignition. But the mixture quality may not be 

constant for any given load, because there is a disturbing effect if a 

hit-or-miss governor attachment is used, and the throttling method of 

governing complicates matters by affecting the compression. From 

maximum load to about 80 per cent of the maximum, with the best 

time of ignition, the best mixture is the weakest that will make the 

engine carry the load. Using such a mixture automatically eliminates 

the disturbing effect of the governor; or at least the effect is minimized 

and made constant when the mixture is such that only sufficient 

governor action is obtained to carry the load satisfactorily under 

reasonably constant conditions. At about 80 per cent of the maximum load the weakest mixture that will carry the load approaches 

the limit of dilution with air, beyond which it becomes nonexplosive 

for the conditions under which it is used in the engine; hence for the 

light loads the disturbing effect of the governor makes the mixture 

quality irregular, and may be such that the best results will be obtained with the fuel needle valve much wider open than for the heavier 

loads.

The extent of the irregularity of the mixing can readily be seen by 

inspection of series of indicator diagrams taken on the same card. If 

the hit-or-miss method of governing is used, the irregularities caused

« A more detailed discussion of this feature of the investigation has been prepared in the final report.
EFFECTS OF OPERATING CONDITIONS. 15

by the governor action will be seen clearly in a series of diagrams 

taken from cut-out to cut-out, or for about the first ten explosions 

after cut-outs. Such a series also illustrates the fact that when the 

mixture is irregular the time of ignition, though regulated to give the 

best ultimate results, is by no means the best for each individual 

charge of explosive mixture. This may account in part for the fact 

that the minimum fuel-consumption rate is increased when irregular 

conditions are caused by the governor action with light loads.

EFFECT OF TIME OF IGNITION.

Ignition at or near dead center will give the best results in some 

cases, as for maximum load, while in others ignition as early as 

35° before dead center will be found best. No general rule can be 

given. The best time of ignition can be judged to a certain extent

by inspection of the indicator diagrams, and seems to be relatively

earlier for alcohol than for gasoline.

The rate of flame propagation is different for different ratios of air 

to fuel vapor. A very rich explosive mixture or a very lean one 

burns slowly as compared with those of intermediate ratio. The 

rate may depend somewhat on the pressure at the time of ignition 

and may be different for alcohol and gasoline mixtures. The indications are that the rate of flame propagation for alcohol mixtures is 

slower than that for gasoline mixtures of the same relative quality 

compressed to the same pressure, but may be practically the same 

when the best compression pressure for each fuel is used. x

Providing an ignition device such that the time of ignition can be 

varied from about zero, or dead center, to about 35° advance, is 

almost as important for obtaining the best results as providing a fuel 

needle valve so constructed that a wide range of mixture quality can 

be obtained; for, as previously stated, it is the best mixture quality 

with the best time of ignition that must be determined for different 

loads; and this mixture is considerably richer for maximum load than 

for rated or best load when the governor action is constant.

If the construction of the engine is such that the time of ignition 

can not readily be varied for each load to suit the best mixture quality, 

the point to be considered is not that for every mixture quality there 

is some best time of ignition, but rather that for a given time of 

ignition there is some best mixture quality. The fixed time of ignition affects the fuel-consumption rate of the engine by limiting the 

quality of mixture that can be used.

TESTS WITH VARIABLE LOAD.

The load, then, may affect the fuel-consumption rate of an engine 

by limiting the mixture quality that can be used and by determining 

the irregularity caused by the method of governing. The relation
16 GASOLINE AND ALCOHOL TESTS.

between load, mixture quality, and time of ignition is very complex. 

The best combination could be determined only by series of systematic tests. Such, tests were made to determine the minimum consumption for each engine with each fuel, with each carburetor used, 

etc., and for each imposed independent condition of operation, such 

as speed or compression.

Thus, in obtaining the foregoing consumption rates and ratios, 14 

series of tests were made to determine the minimum fuel-consumption 

rate for each of an average of about five loads, from maximum load 

to approximately one-third maximum load, on five different engines, 

with different carburetors, methods of governing, and degrees of 

compression.

Four of the 14 series of tests were made with gasoline on three 

different engines. Two of these were 15-horsepower Otto gasoline 

engines of identical size, construction, and equipment. The third, 

a 10-horsepower Nash gasoline engine, was totally different in method 

of governing and detail of carburetor construction. Two series of 

tests with gasoline were made on this 10-horsepower engine, but 

with different carburetors.

Five engines were used for the ten series of alcohol tests, of which 

two were made on the 15-horsepower Otto gasoline engines and a 

third on one of these engines after the degree of compression had 

been raised as much as possible by lengthening the connecting rod. 

The fourth, fifth, and sixth series of tests were made on a 15-horsepower Otto alcohol engine of identical size with the Otto gasoline 

engine, but with a different valve arrangement and method of governing. A different degree of compression was obtained for each of 

these series of tests by lengthening the connecting rod. The seventh 

and eighth series of tests were made on a 10-horsepower Nash gasoline 

engine with two different carburetors. The ninth and tenth series 

of tests were made on a 10-horsepower Nash alcohol engine, which was 

identical in size, construction, and equipment with the 10-horsepower 

Nash gasoline engine, the only difference being that a higher degree 

of compression was obtained by diminishing the clearance space in 

the cylinder head. Different carburetors were used for the two 

series of tests on this engine.

TESTS WITH CHANGE IN TIME OF IGNITION.

Two series of tests, consisting of nine individual tests with alcohol 

and nine with gasoline, were made*on the 15-horsepower Otto gasoline 

engine to determine the effect of change in time of ignition on the 

fuel-consumption rate when the load and fuel needle-valve setting 

were kept constant. The load and needle-valve setting selected were 

such that a wide range of ignition timing could be used.
EFFECTS OF OPERATING CONDITIONS. 17

For the gasoline tests the load was 85 per cent of the maximum. 

The best results, a consumption of 0.66 pound per brake horsepower 

per hour-, were obtained for an ignition timing of 13° before dead 

center. For an ignition timing of 21° before dead center the fuelconsumption rate .was increased 9 per cent, and 36 per cent for an 

ignition timing of 15 Q after dead center.

For the alcohol tests the .load was 79 per cent of the maximum..

 The best results, a consumption of 1.1 pounds per brake horsepower 

per hour, were obtained for an ignition timing of 25° before dead 

center. For an ignition timing of 30° before dead center the fuelconsumption rate was increased 4 per cent, and 64- per cent for an 

ignition timing of 5° after dead center.

The time of ignition was carried to the limit both ways for each 

fuel, the limit being the earliest or latest ignition with which the engine would cany the load satisfactorily. The disturbing effect of

-the governor was thus not constant, but it was comparatively slight 

throughout and the irregularity was probably not appreciable.

TESTS WITH VARIABLE FUEL SUPPLY.

Four series of tests with gasoline and alcohol were made on the 

two 15-horsepower Otto gasoline engines. The conditions for two of 

these series with gasoline and alcohol respectively, were as follows;

For the tests with gasoline a brake load of 85 per cent of the maxi^ 

mum was applied, and the time of ignition selected (21° before dead 

center) was such that the widest possible range of fuel needle-valve 

settings for this load could be used. Starting with the minimum 

opening of the fuel needle valve and a corresponding rate of fuel 

consumption of 0.62 pound per brake horsepower per hour, the fuelneedle-valve opening was increased until the engine could scarcely 

carry the load, as indicated by the governor action. This fuel 

needle-valve setting gave'a consumption rate of 1.31 pounds per brake 

horsepower per hour, or an increase of 110 per cent.

For the tests with alcohol a brake load of 79 per cent of the maximum was applied and the time of ignition selected (17° before dead 

center) was such that the widest possible range of fuel needle-valve 

settings for this load could be used. Starting with the minimum 

opening of the fuel needle valve and a corresponding rate of fuel 

consumption of 1.1 pounds per brake horsepower per hour, the 

fuel needle-valve opening was increased until the maximum opening 

was reached. This fuel needle-valve setting gave a consumption 

rate of 1.6 pounds per brake horsepower per hour, or an increase of 

45 per cent.

When the results of these tests were platted, showing the relation 

between the brake horsepower and the rate of fuel consumption, 

86818 Bull. 392 09 3
18 GASOLINE AND ALCOHOL TESTS.

the results obtained for six intermediate fuel needle-valve settings 

were found to lie on a straight line between the values given above 

in each case. As the load was kept constant the disturbing effect 

of the governor was not eliminated, but probably was slight, as shown 

by the indicator diagrams.

The other two series of tests were made in a similar way, but with 

a light load, so that the disturbing effect of the governor was relatively 

great. In these tests, 11 each for gasoline and alcohol, the needlevalve settings were not carried to the limit either way, but only so 

far as was necessary to show that for light loads the minimum fuelconsumption rate is not obtained with the smallest possible fuel 

needle7valve setting, the best setting being rather that which gave 

the most nearly uniform mixtures, as shown by the regularity of the 

shape of the successive indicator diagrams. This was also found to 

be true when the best ultimate settings were determined for the light 

loads.

INCIDENTAL MATERIAL.

In all, 1,300 tests, including trial tests, were made to determine 

the foregoing deductions and figures. The detailed results of these 

tests afford an opportunity to study the effect of -degree of compression, mixture quality, and time of ignition on the fuel-consumption 

rate, and include a great deal of incidental material, such as indicator cards, maximum-pressure measurements, temperature records 

for fuel and air mixtures entering the cylinder, and the like. The 

fuel-consumption rates are given in pounds, gallons, and British 

thermal units per brake and indicated horsepower per hour. Mechanical efficiency, indicated thermal efficiency, and thermal efficiency of the brake are also given. But these tables are too bulky

and involved to present at this time. The trial tests have been prepared in condensed form for the final report, and thus present some 

interesting and important information, showing what difficulty was 

experienced in determining the best ultimate results in some cases.

LIMITS OF FUEL-CONSUMPTION RATES.

LIMITS SET BY OPERATING CONDITIONS.

So wide is the range of adaptability of alcohol and gasoline, to the 

 operating conditions governing or limiting the performance and fuel 

consumption of internal-combustion engines, that for engines operating under different conditions the ratio of the rates of consumption 

of the two fuels per unit of power may be almost anything, even the 

reverse of their heating values; that is, even though the two engines are 

in good running condition and operating perfectly to all outward 

appearances, are of the same size, with compression regulated to that
LIMITS OF FUEL-CONSUMPTION KATES. . 19

best for their respective fuels^and carry the same percentage of maximum load, the operating conditions may be made such that the engine 

run with gasoline will use twice as much fuel in pounds per brake horsepower per hour as the alcohol engine. Such a ratio is quite likely to be 

obtained in practice from off-hand comparison of the performance of 

two engines; but obviously such a comparison would be meaningless. 

When an engine is running at maximum load and governing for 

constant speed, only about 50 per cent excess alcohol can be supplied 

without causing the engine to slow down and stop; while at half load 

about two arid a half times the amount needed can be supplied before 

the engine will show any outward change in operation, except that 

possibly an odor of alcohol or formalin in the exhaust will indicate 

to the operator that an excess of fuel is being supplied. An oversupply of alcohol does not produce an exhaust of black smoke, as 

does-an excessive supply, of gasoline; yet the percentage of excess of

alcohol and gasoline that can be used without being detected outwardly is approximately the same. .The maximum percentage of 

excess of gasoline that can be used at maximum loads is a little 

greater than that for alcohol. With light loads alcohol is likely to be 

used in greater excess, because the smoke is absent that with gasoline 

indicates any great oversupply.

With the stationary engines which govern for constant speed the 

following general rule of adjustment for minimum fuel consumption 

will hold in almost every case for loads from about half load to maximum load, if the engine is in good mechanical condition: Adjust the 

time of ignition and fuel needle valve so that the least possible amount 

of fuel is admitted per stroke without reducing -the speed of the 

engine. In order to obtain the minimum fuel consumption for the 

gradation of loads from maximum down to about half load, a continuous reduction of fuel supply with earlier time of ignition will be 

necessary; that is, the smallest quantity of fuel supplied per stroke 

that will carry the load will give the minimum fuel consumption when 

the best time of ignition, which changes with the quality of the 

mixture, is used.

When the above rule is applied to obtain the minimum fuel-consumption rate for the maximum load that the engine is called on to 

carry, the fuel needle valve and igniter settings found to be the best 

will, in most cases, be nearly the best possible settings for all other 

loads down to about half load; at least the best constant setting 

condition that can be obtained for a varying load between those 

limits.

With the hit-or-miss method of governing, even though the number 

of fuel admissions per minute be a maximum, that is, though the 

number of cut-outs be only sufficient to insure certainty of operation, 

depending on the fluctuation of load, and though nearly every first
20 GASOLINE AND ALCOHOL TESTS.

fuel admission after cut-outs misfire on o account of too weak mixture, 

the adjustment stated may be the most economical.

With the throttling method of governing, when the disturbing 

effect of the governor is minimized, the above rules will hold for all 

loads down to about one-quarter load and. lower in some cases.

The foregoing deductions in reference to the maximum and minimum rates of fuel consumption are made from the results of 4 series 

of tests with gasoline and alcohol on the same engine (15-horsepower 

Otto gasoline engine) and subsequent incidental observations on the 

other engines using alcohol with the higher degrees of compression. 

Two previously determined series of tests on the same Otto gasoline 

engine, consisting of 158 and 220 single tests, respectively, were taken 

to obtain the minimum consumption rate of gasoline and of alcohol 

for seven and ten loads, respectively, between maximum load and 

about one-third maximum load, and two additional series, of 13 and 

24 tests, respectively, were made to determine the maximum rate of 

gasoline and of alcohol consumption for seven loads covering the 

same range. Later, when tests were made with alcohol on the Otto 

alcohol engine and the degree of compression greatly increased, it 

was found that the maximum amount of alcohol that could be used 

with the higher degree of compression was very much less for the 

same percentage of maximum load; but the percentage in excess of 

the minimum quantity that could be used was practically the same.

Deductions relating to constant engine settings were made from 

12 series of tests with an average of about four different loads for each 

set. of fixed conditions. Four of these experiments were made with 

gasoline and eight with alcohol. Some of them were made with the 

fuel needle valve and igniter settings which gave the minimum fuelconsumption rate for the maximum load which the engine would

carry, while others were made with the settings which gave the 

minimum fuel-consumption rate for the load with which the best 

results were obtained (about 85 per cent maximum load). These 

settings were kept constant for each experiment or series of tests.

The results of the tests with constant engine settings were used in 

conjunction with the results of the tests which were made to determine the minimum fuel-consumption rate for each different load, and 

in which the fuel needle-valve setting and time of ignition were 

varied accordingly. This comparison was made in order to show the 

relation between the constant settings and best settings for the various loads, as indicated by the ultimate results expressed in pounds 

of fuel consumed per brake horsepower per hour. Tables giving 

details of the tests, and curves illustrating the wide range of results 

that may be obtained between the limits of operating conditions, 

have been prepared for the final report.
FACTORS AFFECTING FUEL CONSUMPTION. 21 

LIMITS SET BY ENGINE DESIGN.

The limiting effect of engine conditions on the relative adaptability 

. of gasoline and alcohol that is, the limiting effect of the fundamental principles of engine and carburetor design and construction which 

are not under the control of the operator may be eliminated to a 

great extent in the consideration of the comparative consumption of 

the two fuels. Some engines operating under varying loads may be 

a great deal less economical than others, owing to different methods 

of governing or the like, though all other conditions be equal. But 

the best practical engine conditions have been thoroughly worked out 

by many of the builders of high-grade gasoline engines, and though 

the average rate of consumption of either fuel may be almost anything greater than some one minimum figure which depends on 

both engine and operating conditions, the same approach to the

minimum consumption figure for each fuel can be obtained with the.

same degree of skill in operating and the same care in design and 

construction, alike for gasoline and alcohol engines, regardless of 

many of the little details of design, construction, and equipment, 

which distinguish them and may otherwise affect the average rates 

of fuel consumption.

At present the skill in operating, designing, and constructing 

engines for the use of alcohol may not be so great as for gasoline 

engines. The average operator and0 engine builder in this country 

has had less experience with alcohol than with gasoline. Since this 

is a difference that will, however, vary with the relative use of alcohol 

and gasoline, and since one pint of gasoline per brake horsepower 

per hour may be given as a fair average consumption for an engine 

when operated at about rated load and under favorable conditions, 

a like figure can reasonably be expected for alcohol when a like understanding of its use is attained and engines as well adapted to its economical use are constructed. This conclusion is based on the results 

of tests on stationary engines of medium speed and size. The indications are, however, that the ratios given would remain the same, 

or possibly change a little in favor of alcohol, were all the engine 

conditions worked out to their most .advantageous limit and the 

exact effect on the fuel consumption determined.

OTHER FACTORS AFFECTING FUEL CONSUMPTION.

SPEED OF ENGINE.

The speed, or a combination of piston speed and revolutions per 

minute, will affect the fuel economy and thermal efficiency, and for 

a limited range, at least, increased speed will decrease the fuel consumption and increase the thermal efficiency, nearly alike for both
22 GASOLINE AND ALCOHOL TESTS.

fuels if the best operating conditions are obtained for both. This is 

likely to hold true up to the limiting practical combination of piston 

speed and revolution per minute, which is governed by mechanical 

conditions, but the tests from which the above inference was drawn 

covered only a range of speeds of 200 to 290 revolutions per minute, 

with corresponding average piston speeds of 500 to 750 feet per 

minute.

Series of tests with gasoline and with alcohol, consisting of 16 and 

27 tests, respectively, were made on the same engine (15-horsepower 

Otto gasoline engine) with the same compression. These tests were 

required to determined the best load, fuel needle-valve setting, and 

time of ignition, for each of the speeds mentioned and an intermediate one. With speeds of 200 to 300 revolutions per minute, the 

rate of fuel consumption, in pounds per brake horsepower per hour, 

.varied with increasing speed from 0.68 to 0.64 for gasoline (a decrease of 6 per cent) and from 1.11 to 1.05 for alcohol (a decrease 

of 5.5 per cent). A change in the speed of the engine is likely to 

change many conditions affecting the rate of fuel consumption, such 

as throttling from too-high air velocity through the carburetor, air 

passageways, and valves, as well as'by affecting the mixture quality 

and best time of ignition. Hence it is very difficult to eliminate all 

the independent variables and determine the exact effect of change 

in speed alone. The detailed ^report of these tests may, however, 

assist in so extending this phase of the investigation as to determine 

the most advantageous limits of the possible combinations of speed 

and cylinder dimensions.

SIZE OF ENGINE.

Similarly, the size of the engine that'is, of the engine cylinderhas a certain influence on the fuel economy and thermal efficiency. 

A large-cylinder engine can be operated with a higher efficiency than 

a small one, probably because of the difference in heat loss due to 

the lesser ratio of cooling surface to volume of charge or heat liberated. But the difference from this cause, which has been fairly well 

determined by experiment, is negligible for the difference in the size 

of the engines used for this work. It is small as compared to the 

difference caused by mechanical conditions, such as leakage and friction, which are likely to be much greater in proportion for a small 

engine than for a large one. For similar reasons it is also harder to 

maintain compression with a small engine than with a large one, 

and this difficulty increases with the degree of compression. Hence 

a small alcohol engine is likely to be less satisfactory than a small 

gasoline engine, this depending entirely, however, on the perfection 

of construction and the skill of the operator.
FACTORS AFFECTING FUEL CONSUMPTION. 23 

CARBURATION.

The construction of carburetors and induction passageways suitable to the economical use of gasoline and alcohol are details of engine 

design and the conditions governing carburation are, to a great 

extent, predetermined. In most cases but little is left for the 

operator to adjust aside from the quantity of the fuel or the quality 

and quantity of air and fuel mixture. '

The principle of the ordinary carburetor is that of the simple 

atomizer, and any effective atomizing device will make a good carburetor if the other influencing conditions are properly taken care 

of. Since alcohol is less volatile than gasoline, and hence harder to 

vaporize, a higher velocity of air through the carburetor and a 

greater excess of fuel is required to obtain an explosive mixture on 

starting an engine with alcohol than with gasoline. This higher air 

velocity may be obtained by giving the engine a higher rotative

speed (which will also tend to assist the vaporization of the spray 

carried by the air, by giving less time for the dissipation of the heat 

of compression to the cylinder walls), or by throttling the carburetor 

in such a way as further to increase the velocity of the air at the 

spray nozzle and reduce the pressure at which vaporization takes 

place. With a combination of these conditions it is not difficult 

to start a small alcohol engine "cold." To start a large alcohol engine, however, which can not readily be revolved rapidly by hand, 

some mechanical means of bringing it up to speed will be required, 

or if the engine is not too large this may be accomplished by priming 

with gasoline and starting in the usual manner. Hot passageways 

and cylinder'walls assist in vaporizing the fuel at the start, at least, 

but are not necessary if the previously mentioned conditions are maintained. :

Under similar operating conditions with equal air velocities more 

alcohol than gasoline will pass into the cylinder of the engine in the 

form of a spray, but unless too great an excess of fuel is used it 

is probably completely vaporized by the heat from the cylinder walls 

and hot gases left in the clearance space from the preceding explosion or by the heat developed during compression. With the ordinary piston speeds used in stationary engine practice, a velocity of 

the air through the carburetor at the spray nozzle sufficiently high 

to produce as effective vaporization or atomization of alcohol as 

of gasoline can be obtained without throttling the engine to any 

appreciable degree.

THROTTLING.

Some very interesting and instructive information on the effect 

of throttling as an operating condition has been'obtained. It appears that for any given compression the more the charge is-diluted
24 GASOLINE AlsID ALCOHOL TESTS.

the better will be the fuel economy and thermal efficiency of the engine, if the smallest quantity of fuel possible per charge and the best 

time of ignition are used. The details of the tests that show, and 

possibly explain, this condition of affairs are too many and complicated to take up at this time; but it is evident that if the rule is true 

equal volumetric efficiency of the pump action (suction and compression strokes) is one of the conditions that must be imposed on 

comparative tests with gasoline and alcohol, when used either in 

the same or in different engines. Irregularities of pump action can 

be eliminated only by obtaining the maximum possible compression, 

and consequently the minimum possible amount of throttling for 

the engines used. The entire amount of throttling is not, however, 

always under the control of the operator, for it depends on the conditions under which the engine is running, the size of the passageways and valves, and the timing of the valves.

VALVE TIMING.

The effect of the timing of the exhaust valve is comparatively 

small and for any reasonably well-designed and adjusted engine 

can be neglected. The timing of the inlet valve, however, is of considerable importance. If an automatic inlet valve is used, the spring 

tension and the distance the valve opens will determine the timing 

and the amount the charge is throttled in passing the valve. The 

best spring tension and lift for automatic valves differ under different 

conditions and no general rule for adjustment can be given. The 

best adjustment can usually be determined by trial, if the best 

combination of the spring tension and lift is that with which the engine will carry the greatest load, when the needle-valve and igniter 

settings are adjusted accordingly. If the engine is equipped with 

an indicator so that light spring diagrams of the suction and the beginning of the compression stroke can be taken, the best combination 

of spring tension and valve lift can readily be determined by so 

adjusting them that the maximum volumetric efficiency of the pump 

stroke is obtained, as shown by the point at which the compression 

line crosses the atmospheric line.

When the inlet valve is mechanically operated, its maximum lift is 

predetermined by the design; but where a considerable lost motion 

is provided for, the lift and timing of the valve can usually be changed 

considerably. In some engines the timing can also be changed by 

shifting the gears that drive the two-to-one shaft. In general, the 

timing of a mechanically operated inlet valve should be such that it 

does not completely close until about 20° to 30° after the piston has 

passed the dead center at the beginning of the compression stroke. 

No set rule, however, can be given, and the same methods should be 

employed as in determining the best spring tension and lift of the
FACTORS AFFECTING FUEL CONSUMPTION. 25

automatic valve. Light spring diagrams illustrating the application 

of this method of determining the best valve settings have been prepared for the final report.

The throttling effect of restricted induction passageways may often 

be greatly reduced by proper timing of the inlet valve. The air passageway through carburetors, however, is often so small as to throttle 

the charge beyond the possibility of recovery by timing of the inlet 

valve. This is not necessary and should be avoided.

JACKET TEMPERATURE.

A question asked by almost every operator is: "What effect has 

the temperature of the jacket or cooling water on the fuel economy 

and thermal efficiency of an alcohol or gasoline engine, and what is 

the best jacket temperature?" The only safe answer to this question 

is: "The best jacket'temperature is that which gives the best results." 

Many tests tend to show that the temperature of the cooling water 

has little if any appreciable effect, by controlling to a greater or less 

extent the temperature of the cylinder walls, on the fuel economy and 

thermal efficiency of the engine. Jacket temperature may, however, 

have a great effect on the performance of the engine from its influence 

on other conditions than cylinder-wall temperature. It has been 

pretty well established that when jacket temperature affects the fuel 

consumption of an alcohol or gasoline engine it is more by effect on 

cylinder lubrication, fit of piston and valves, and carburation than 

by change in heat loss to the cylinder walls. A hot jacket may stop 

leakage by way of the piston and valves by making them tight from 

expansion, or it may make a tight piston stick and bind and warp 

valves or valve seats that are tight when the cylinder walls are kept 

cold. If the cylinder oil used is thick and heavy, it will flow better 

when the cylinder is kept hot, but thin oil is more likely to run out 

and leave the piston dry. If the design of the carburetor is such that 

efficient carburation and uniform mixtures depend on hot passageways, a hot jacket will help counteract the effect of such poor or 

limited design; and the ultimate effect of a hot jacket on the fuel 

consumption is, for this reason, likely to be greater for alcohol than 

for gasoline.

The temperature to which the jacket water can be raised is limited 

in some engines by a design such that for a high temperature of jacket 

water the cooling system is not effective in keeping all the parts below 

the temperature that will cause preignition. It is not necessary to 

keep the temperature of the jacket water high if the design and construction of the engine is right to begin with and suitable cylinder oil 

is used. A "hot jacket" may, however, be a good remedy for many 

ills that result from poor or limited design and construction.
26 GASOLINE AND ALCOHOL TESTS.

*

When a constant load is applied to a gasoline or alcohol engine and 

the governor action is reasonably steady, or the disturbing effect of the 

governor is constant, a change in temperature of the jacket water, if 

it causes any increase or decrease of mechanical or thermal efficiency, will so change the action of the governor as to compensate for 

the more or the less economical use of the fuel. This change in the 

action of the governor alters its disturbing effect on the quality or the 

uniformity of the mixture, and the operating conditions are almost 

hopelessly altered so far as determining the isolated effect of change 

in jacket temperature is concerned. The ultimate effect of the change 

in jacket temperature may, however, be determined if the best combination of fuel needle-valve settings and time of ignition are used in 

each case and if the load is above about 50 per cent of the maximum 

the engine will carry,. so that the disturbing effect of the governor 

action will be automatically reduced to a minimum.

If the hit-or-miss method of governing is used, the minimum action 

of the governor that is, the minimum practical number of cut-outs 

per minute will be the same, regardless of the effect of jacket temperature on the efficiency of carburation.

If the throttle method of governing is used, however, the efficiency 

of carburization may be affected by the position of the governor-controlled throttle valve; that is, by the amount of throttling and consequent change in the suction and the compression pressures, so that 

the best combination of fuel needle-valve settings and time of ignition 

may be different for different jacket temperatures and may complicate 

the effect on the rate of fuel consumption through a change in both 

mixture quality and compression. This is true for both gasoline and 

alcohol, but where the jacket temperature affects the efficiency of 

carburation, the resultant effect on the rate of fuel consumption will 

be greater for alcohol than for gasoline.

The results of the tests that were made with different jacket temperatures for each of the engines used for this work indicate that the 

effect of jacket temperature on the efficiency of carburation of gasoline and of alcohol can be eliminated in both cases by proper care in 

designing the carburetor and induction passageways. These experiments consisted of eight series of tests, three with gasoline and five 

with alcohol. First, the minimum gasoline consumption rate at best 

load for the 15-horsepower Otto gasoline engine (hit-or-miss method 

of governing) was determined when a low jacket temperature (about 

80° F. at the outlet) was used, and the effect of raising the temperature 

of the jacket water to the boiling point (212° F. at the outlet) was noted. 

There was no apparent change in the action of the governor to indicate 

any change in the efficiency with which the fuel was being used, but 

to make certain the consumption rate was determined for nine 

different outlet jacket-water temperatures between 80° and 212° F.
FACTORS AFFECTING FUEL CONSUMPTION. 27

The results of these tests show that whatever change there may have 

been in the temperature of the cylinder walls, as measured by the 

outlet temperature of the jacket water for a range of over 100° F., 

the change in the rate of fuel consumption was slight a decrease of 

less than 0.01 pound of fuel per brake horsepower per hour, or 1.7 

per cent. A similar series of nine tests was made for alcohol, with 

identical results.

These tests were carried a little further with the second 15-horsepower Otto gasoline engine, and the engine settings were systematically sought that would give the best results for each of five different 

outlet temperatures of the jacket water. Two series of tests were 

made, 49 with gasoline and 19 with alcohol, but with the same ultimate 

effect as before. After the compression pressure of this engine had 

been raised to about 85 pounds per square inch above atmosphere, 

another systematic series of search tests, 12 in all,- was made with

alcohol to determine the minimum fuel consumption for four different 

jacket temperatures (as measured by the outlet temperature of the 

jacket water) from 80° to 212° F., but the amount of decrease in the 

rate of fuel consumption was the same as that previously noted. 

Similar experiments on the 10-horsepower Nash gasoline engine (hitor-miss method of governing), consisting of 5 tests with gasoline and 

9 with alcohol, gave the same results, though the details of the 

method of governing and carburetor construction were different.

The 15-horsepower Otto alcohol engine, which was equipped with 

a still different carburetor, and on which the throttle method of 

governing was used, could not be operated satisfactorily with alcohol 

when the outlet temperature of the jacket water was below 100° F., 

except under a partially throttled condition, with a corresponding 

increase in the rate of fuel consumption. For outlet temperatures of 

the jacket water between 100° and 200° F., the best fuel needle-valve 

setting and corresponding best time of ignition were coincident with 

the minimum amount of throttling and corresponding maximum 

compression. There was but little gain in fuel economy about 0.01 

pound per brake horsepower per hour.

Though the results of these tests are almost entirely negative, they 

were necessary for establishing the best operating conditions; and the 

tables which give all the data that were taken in them are of vital 

importance to the study of the whys and wherefores. These tables 

will appear in the final report.

PREHEATING THE AIR.

Preheated air may be of great benefit when the carburation is 

ineffective, or the mixture not uniform in quality; but preheating the 

air is not necessary to obtain the best results with alcohol/ and if
28 GASOLINE AND ALCOHOL TESTS.

carried to any great degree will materially diminish the capacity of 

the engine and decrease the maximum practical degree of compression.

Preheating the air to 250° F. reduced the maximum horsepower of 

the engine about 15 per cent for alcohol and about 14 per cent for 

gasoline. With an air temperature of 75° to 85° F., the temperature of the gasoline vapor or spray and air mixture, taken as it 

entered the cylinder through the inlet valve housing, was from 80° 

to 100° F. It was usually approximately the same as the air temperature. When the air was preheated to 450° F., the mixture temperature was raised only to 172° F.

With an air temperature of 72° F., the temperature of the air and 

alcohol mixture at the inlet valve was found to be 61° F. This mixture temperature was increased only to 96° F. when the air was preheated to 250° F., and the condition of minimum fuel consumption 

for maximum load was maintained in both cases, as for the tests with 

gasoline.

By platting the minimum fuel-consumption rates in pounds of fuel 

per brake horsepower per hour, and the brake load in per cent of 

maximum brake horsepower for the normal and preheated-air temperature tests, the results show a slight increase in the fuel-consumption rate with increased air temperature. An increase of about 0.05 

pound per brake horsepower per hour, alike for gasoline and alcohol 

and the same for all loads, was obtained for air preheated to 250° F.

With air preheated to approximately 250° F., a series of 48 tests 

with alcohol was made on the 15-horsepower Otto gasoline engine, as 

required to determine the minimum rate of alcohol consumption for 

each of-4 different loads from maximum load to about one-third load, 

so that comparison could be made with results previously determined 

by a series of tests for 4 different loads when the air was not preheated. 

A similar experiment with gasoline consisted of 35 tests on the same 

15-horsepower Otto engine for maximum load and half load when the 

air was preheated. A previously taken set of tests for 7 loads from 

maximum load to one-third load when the air was not preheated 

was used for comparison.

Twenty-seven additional tests with gasoline and 48 with alcohol 

were made in order to determine the minimum fuel consumption and 

mixture temperatures corresponding to intermediate temperatures 

of the preheated air for various loads.' No beneficial effect could be 

obtained directly or indirectly by the use of preheated air. It 

should be stated, however, that in the engine used for these tests the 

passageway between the carburetor and inlet valve was very short, 

and the mixture temperatures given are the temperatures of the air 

mixed with atomized and partially vaporized fuel as it passed into 

the cylinder.
FACTORS AFFECTING FUEL CONSUMPTION. 29 

SIZE AND INTENSITY OF IGNITION SPARK.

Misfiring from ineffective ignition is, of course, detrimental to the 

fuel economy of an engine for either fuel alike, but the ordinary ignition appliances are apparently as effective for igniting alcohol mixtures as gasoline mixtures. No attempt was made to obtain information as to the comparative efficiency of different methods of ignition, but the question was gone into far enough to demonstrate that 

under operating conditions approximately best for gasoline, increasing the size or intensity of the spark (as measured by the voltage 

and current supplied to a make-and-break ignitor) from 4.5 watts 

(4.5 volts and 1 ampere, the amount necessary to ignite every 

charge) to 48 watts (19 volts and 4.4 amperes) had no effect on the 

thermal efficiency or fuel economy of the engine. The details of 

these tests, four in all, will be given in the final report for reference 

if further study is desired.

In* view of the fact that this is a much disputed point, it should be 

saidcthat if the method of ignition used is the jump spark in the hightension secondary circuit of an induction coil, there will be a certain 

amount of building up in the coils and lag of the vibrator, causing 

the spark to lag. This lag may or may not be appreciable, but if 

changing the current or the voltage of the ignitor circuit affects this 

lag to any appreciable degree its effect on the fuel economy and thermal efficiency will be that of changing the time of ignition, and will 

coincide with any effect produced by change in the intensity and size 

of spark ; or it may account for the entire change which is apparently 

due to the change in the intensity and size of spark. If the mechanically operated low-tension make-and-break method of ignition is 

used, as was the case in the experiments referred to, there will be no 

building-up effect or lag, as the spark occurs after the circuit has been 

closed for some little time, and is not affected by change in voltage or 

current.

DEGREE OF COMPRESSION.

As previously stated, the minimum fuel-consumption rates and 

maximum thermal efficiencies for gasoline and alcohol were obtained 

with the maximum degree of compression that could be used for each. 

Furthermore, when alcohol Was used, it was found that the maximum thermal efficiencies obtained, for six different degrees of com-

(

P "Y19 

^ } ; where E equals "

the thermal efficiency, calculated from the indicated horsepower 

and lower heating value of the fuel, Pa equals atmospheric pressure 

in pounds per square inch absolute, and Pb equals the pressure at 

the end of compression stroke in pounds per square inch absolute.
30 GASOLINE AND ALCOHOL TESTS.

Each of the above degrees of compression was the maximum for 

the respective clearance ratio of the engine used; they ranged from 

70 to 200 pounds per square inch above atmosphere (85 to 215 

pounds absolute). The maximum thermal efficiency values referred 

to above range from 28 per cent to 40 per cent for the range of compression pressures given, and were obtained from a preceding series 

of tests made to determine the variation of best fuel economy and 

maximum thermal efficiency with load. These series of tests were 

made on different engines with different clearance ratios and corresponding degrees of compression, as follows: Four series of tests 

on four engines, each with a different clearance ratio; three series 

of tests on the same engine with three different clearance ratios; 

and two series of tests on two different engines with the same clearance ratio.

Similarly, when gasoline was used, the best thermal efficiencies 

obtained for compressions of 70 pounds per square inch above atmosphere (85 pounds absolute) and 92 pounds per square inch above

(

P V17 

P^ ) '

These results were obtained from a series of tests on two gasoline 

engines having the same clearance ratio and compression pressure 

and a third engine having a smaller clearance ratio and a correspondingly higher compression pressure.

The above equations are similar to the theoretical equation for 

thermal efficiency when expressed in terms of pressure from the air 

card, or standard reference diagram, and differ only in the numerical 

value of the exponent. The exponent for the theoretical air card, 

or standard reference diagram efficiency, is 0.29.

It must be clearly understood, however, that the thermal efficiencies obtained for the different clearance ratios and corresponding 

degrees of compression fulfilled the equations only when the maximum 

thermal efficiency of the engine was obtained, which required that 

the engines be put in the best possible running condition and operated 

to the best advantage. This required that the best combination of 

time of ignition and fuel needle-valve setting for the best load be 

obtained. When the engines were in the best possible running condition, and were operated for minimum fuel consumption, the best 

load was coincident with the minimum disturbing effect of the 

method of governing and the maximum compression pressure for 

the clearance ratio of the engine. This latter condition is of vital 

importance for the comparison of thermal efficiency for different 

compressions; for if, for any reason at all, the engines are operated 

under different conditions with respect to throttling of the charge, 

the maximum thermal efficiencies obtainable will not fulfill the same 

equation. The extent of the effect of throttling on the maximum
GENERAL CONCLUSIONS. 31

thermal efficiency obtainable for any corresponding compression 

pressure will be seen from the following illustration.: When alcohol 

was used in an engine whose clearance ratio was such that the 

maximum compression pressure, with the minimum throttling (94 per 

cent of piston displacement), was 70 pounds per square inch above 

atmosphere (85 pounds absolute), a maximum thermal efficiency 

of 28 per cent was obtained. Similarly, a maximum thermal efficiency of 35.8 per cent was obtained for an engine whose clearance 

ratio was such that the maximum compression pressure, with minimum throttling (approximately the same as given above), was 140 

pounds per square inch above atmosphere (155 pounds absolute).

(

P \'19 

~ } . But when ¥\>J

the latter engine was throttled to such'an extent that the compression

pressure Was reduced to 70 pounds per square inch above atmosphere 

(85 pounds absolute) the maximum thermal efficiency for the correspondingly reduced load was 35 per cent, or an increase of 7 in percentage over the value obtained for the engine whose maximum compression was 70 pounds per square inch above atmosphere, and does 

not fulfill the equation given above. The horsepower of the engine 

was, of course, greatly reduced (to approximately one-third maximum load). Maximum thermal efficiencies for intermediate conditions of throttling and corresponding compression pressures gave 

similar results, and the same was found to hold true for other engines. 

No attempt to explain these results or to discuss their significance 

will be made at this time, as the details of the tests are necessary 

for a clear understanding of the deductions.

SYNOPSIS OF RESULTS AND GENERAL CONCLUSIONS.

Some of the more important results and conclusions stated in this 

bulletin are summarized below:

1. The low heating value of completely denatured alcohol will 

average 10,500 British thermal units per pound, or 71,900 British 

thermal units per gallon.

The low heating value of 0.71 to 0.73 specific gravity gasoline will 

average 19,200 British thermal units per pound, or 115,800 British 

thermal units per gallon.

The low heating value of a pound of alcohol is approximately sixtenths of the low heating value of a pound of gasoline.

A pound of gasoline requires approximately twice the weight of 

air for complete combustion as a pound of alcohol.

The heating value of a cubic foot of an explosive mixture of alcohol 

vapor and air having theoretically just sufficient air for complete 

combustion is approximately equal to that of a cubic foot of a similar
32 GASOLINE AND ALCOHOL TESTS.

explosive mixture of gasoline vapor and air about 80 British thermal 

units per cubic foot.

2. Explosive mixtures of alcohol vapor and air can be compressed 

to much higher pressures in an engine cylinder without preigniting 

than can explosive mixtures of gasoline vapors and air. The maximum pressure of compression that can be used without causing preignition will in each case depend partly on the quality of the explosive mixture, on the design of the engine, and the speed at which it 

is operated.

For 10 to 15 horsepower four-cycle stationary engines of the usual 

type a compression pressure of about 70 pounds per square inch 

above atmospheric was found to be the maximum that could be 

used for gasoline mixtures, and about 180 pounds the maximum that 

could be used for alcohol mixtures without causing preignition.

The maximum compression pressure that could be used without 

causing preignition was in each case found to be the most advantageous from the standpoint of fuel economy.

3. When the degree of compression is in each case that best suited 

to the economical use of the fuel designated, some types of gasoline 

engines are better adapted to the service for which they are designed 

than similar alcohol engines and vice versa. The relative amount of 

fuel consumed being disregarded, this is also true when the degree of 

compression is that ordinarily used for gasoline mixtures, as when 

denatured alcohol is used in gasoline engines; but in general the alcohol engine is or can be so designed and constructed as to be equal to 

the gasoline engine in adaptability to service.

A gasoline engine having a compression pressure of 70 pounds but 

otherwise as well suited to the economical use of denatured alcohol 

as gasoline will, when using alcohol, have an available horsepower 

about 10 per cent greater than when using gasoline.

When the fuels for which they are designed are used to an equal 

advantage, the maximum available horsepower of an alcohol engine 

having a compression pressure of 180 pounds is about 30 per cent 

greater than that of a gasoline engine having a compression pressure 

of 70 pounds, but of the same size in respect to cylinder diameter, 

stroke, and speed.

When denatured alcohol is used in 10 to 15 horsepower four-cycle 

stationary engines having a compression pressure of approximately 

180 pounds and the engines are operated at their maximum loads, 

the pressures during explosion or combustion reach 600 to 700 

pounds. Stationary gasoline engines, in which the compression pressure in some cases can be raised to 180 pounds, are not usually built 

heavy enough to withstand such explosion pressures for any length 

of time.
GENEKAL CONCLUSIONS. 33

4. A gasoline engine having the degree of compression ordinarily 

used for gasoline mixtures will in general require 50 per cent more 

denatured alcohol than gasoline per brake horsepower per hour.

Gasoline and alcohol engines of similar construction having 

degrees of compression best suited to the fuel supplied will in general 

require equal volumes of gasoline and denatured alcohol, respectively, 

per brake horsepower per hour.

Gasoline engines of the usual four-cycle stationary type will 

ordinarily consume about a pint of gasoline per brake horsepower per 

hour when operated at about rated load and with a reasonably 

favorable adjustment of the mixture quality and time of ignition.

When carrying light loads or carrying their maximum loads, gasoline and alcohol engines governed for constant speed require a greater 

quantity of fuel per brake horsepower per hour than when carrying 

their rated loads, if rated at about 75 to 80 per cent of their maximum 

loads; but unless the mixture quality and time of ignition are adjusted 

to suit each change of load, the rate of consumption per brake horsepower per hour will in general be least at maximum load and will 

increase with decrease in load.

When any of the usual methods of governing are used to control 

the speed of gasoline or alcohol engines, the rate of fuel consumption 

per brake horsepower per hour will ordinarily be about twice as great 

at one-third load as at maximum load. At the same time an excessive 

rate of consumption of gasoline or denatured alcohol at any given 

load, if due to the incorrect adjustment of the mixture quality and 

time of ignition only, may be as great as but not greater than 

approximately twice the minimum required before it will be noticeable from outward indications.

5. The thermal efficiency of alcohol and gasoline engines will in 

general increase with the pressure to which the charge is compressed 

when ignited.

The maximum thermal efficiency of 10 to 15 horsepower four-cycle 

stationary engines of the usual type when operated with a minimum 

amount of throttling was found to increase with the compression

/14.7"\." 

pressure according to the formulas E = 1 ( -p ) for gasoline and

/14.7\*9 

E = 1 ( -tr- ) for alcohol, where E = the thermal efficiency based

on the indicated horsepower and low heating value of the fuel and 

P = the indicated pressure of the charge at the end of the compression 

stroke in pounds per square inch absolute.

6. .A high thermal efficiency and a rate of consumption of less 

than a pint per brake horsepower per hour, both for gasoline and for 

denatured alcohol, can often be obtained when the degree of com-
34 GASOLINE AND ALCOHOL TESTS.

pression, the load, the quality of the explosive mixture, and the time 

of ignition are carefully adjusted. A fair representation of the best 

economy values obtained, taken from the results of tests on 10 to 15 

horsepower Nash and Otto stationary engines, and the corresponding 

thermal efficiencies are given in the following table:.

Results from tests made on 10 to 15 horsepower Nash and Otto stationary engines.

Fuel.

Compression 

pressure 

(pounds), o

f 70 

\ 90 

70 

\ 180 

I 200

Fuel consumed per 

brake horsepower 

per hour.

Pound.

0.60 

.58 

.96 

.71 

.68

Gallon.

0.100 

.097 

.140 

.104 

.099

Thermal 

efficiency 

(per cent).6

26 

28 

28 

39 

40

a Per square inch above atmosphere.

6 Based on the Indicated horsepower and the lower heating value of the fuel.

7. When by means of a double carburetor gasoline and alcohol are 

used simultaneously in varying proportions from practically all gasoline to practically all alcohol, the most advantageous degree of compression will vary from that found to be the best for gasoline mixtures 

to that found to be the best for alcohol mixtures.

Tests that were made with such an adjustment of compression 

indicate that the total amount of fuel (gallons of gasoline + gallons of 

denatured alcohol) required for any given load is practically constant 

for the entire range of proportions from all gasoline to all denatured 

alcohol.

8. When water is sprayed into an explosive mixture of gasoline 

vapor and air as it is being taken into the cylinder of an engine and

is introduced at the most advantageous location, it may in many 

cases be supplied in amounts up to as much water as gasoline by 

weight without affecting the performance of the engine, except as 

noted below.

The capacity or maximum available horsepower of an engine 

decreases with an increase in the percentage of water, by weight, 

present in the explosive mixture of gasoline vapor and air.

When used in an engine having a constant degree of compression, 

the presence of water in an explosive mixture of gasoline vapors and 

air in quantities equal to or less than the weight of gasoline does not 

increase or decrease the amount of gasoline required to carry any 

given percentage of the corresponding maximum available load.

The pressure to which an explosive mixture of gasoline vapor, 

water, and air can be compressed in an engine cylinder without preigniting increases with an increase in the percentage of water in the 

mixture, and can be raised to about 140 pounds when the weights of 

water and gasoline are equal.
GENEBAL CONCLUSIONS. 35

That the amount of gasoline required is not affected by an increase 

in the compression pressure when preignition is prevented only by 

the introduction of water as above stated is indicated by the results 

of tests made on an engine having a compression pressure of 130 

pounds. These tests are limited, however, and the results are not 

conclusive.

9. Alcohol diluted with water in any proportion from denatured 

alcohol, which contains about 10 per cent .of water, to mixtures containing about as much water as denatured alcohol can be used in 

gasoline and alcohol engines if they are properly equipped and 

adjusted.

When used in an engine having a constant degree of compression, 

the amount of pure alcohol required for -any given load increases and 

the maximum available horsepower of the engine decreases with a 

diminution in the percentage of pure alcohol in the diluted alcohol 

supplied. The rate of increase and decrease respectively is such, 

however, that the use of 80 per cent alcohol instead of 90 per cent, 

or denatured alcohol, has but little effect on the performance of the 

engine; so that if 80 per cent alcohol can be had for 15 per cent less 

cost than 90 per cent alcohol and could be sold without tax when 

denatured, it would be more economical to use the 80 per .cent 

alcohol.

When an engine is supplied with diluted alcohol, the compression 

pressure that can be used without causing preignition increases with 

an increase in the percentage of water by weight in the mixture, 

but no tests were made to determine the effect of increased compression pressure on the economy with which diluted denatured alcohol 

could be used.

10. The relative hazard involved in the storage and handling of 

gasoline and denatured alcohol is of particular importance in considering their use as fuels for marine and factory engines and engines to 

be placed in the basements of office buildings, in coast-defense fortifications, or in like places where a general fire would be likely to result 

from the accidental burning of the fuel stored or carried for immediate supply, or where the forming of explosive or inflammable mixtures of the fuel vapors and air in the immediate vicinity would be 

hazardous.

It is indicated by statistics and is also the general consensus of 

opinion of those experienced in handling gasoline, kerosene, and 

alcohol that the hazard involved in the use of denatured alcohol is 

very much less than in the use of gasoline and possibly less than in 

the use of kerosene, but as yet the relative fire risk has not been 

definitely established. Considerable work has been done on this 

phase of the investigation and a series of tests that will be of assistance in determining the relative hazard involved in the use of these
36 GASOLINE AND ALCOHOL TESTS.

fuels is in progress at the testing station of the United States Geological 

Survey in Pittsburg, Pa.

11. In regard to general cleanliness, such as absence of smoke and 

disagreeable odors, alcohol has many advantages over gasoline or 

kerosene as a fuel. The exhaust from an alcohol engine is never 

clouded with a black or grayish smoke, as is the exhaust of a gasoline 

or kerosene engine when "the combustion of the fuel is incomplete, and 

it is seldom, if ever, clouded with a bluish smoke when a cylinder oil 

of too low a fire test is used or an excessive amount supplied, as is 

so often the case with a gasoline engine. The odors of denatured 

alcohol and the exhaust gases from an alcohol engine are also not 

likely to be as obnoxious as the odor of gasoline and its products of 

combustion.

12. Very few alcohol engines are being used in the United States 

at the present time, and but little has been done toward making them 

as -adaptable as gasoline engines to the requirements of the various 

classes of service. Engines for stationary, marine, and traction 

service, automobiles, motor trucks, and motor railway cars designed 

especially to use denatured alcohol have, however, been tried with 

considerable success.

The price of denatured alcohol is greater than the price of gasoline, 

and the quantity of denatured alcohol consumed by an alcohol 

engine as ordinarily constructed and operated is in general relatively 

greater than the quantity of gasoline consumed by a gasoline engine 

of the same type. Considerable attention is being given to the 

development of processes for the manufacture of alcohol from cheap 

raw materials which are generally available, and it seems reasonable 

to expect that the price of denatured alcohol will eventually become 

as low as or lower than the price of gasoline, especially if the price of

gasoline advances. It also seems reasonable to expect a greater 

general improvement in alcohol engines than in gasoline engines. . When used as a fuel, denatured alcohol is not always so classed as 

to be exempt from restrictions placed on the use of gasoline by the 

rules of insurance and transportation companies or city ordinances. 

The restrictions that are placed on the use of denatured alcohol are, 

however, never greater than those placed on the use of gasoline. In 

some places they are such that the use of an alcohol engine is permitted where the use of a gasoline engine is prohibited. For instance, 

alcohol motor trucks and automobiles are admitted to many of the 

steamer piers in New York that are not open to gasoline machines.

Where the restrictions placed on the use of denatured alcohol 

are less than those placed on the use of gasoline or where safety and 

cleanliness are important requisites, the advantages to be gained by 

the use of alcohol engines in place of gasoline engines may be such 

as to overbalance a considerable increase in the fuel expense, especi-
SURVEY PUBLICATIONS ON FUEL TESTING. 37

ally if the cost of fuel is but a small portion of the total expense 

involved, as is often the case. Denatured alcohol, will, however, 

probably not be used for power purposes to any great extent until 

its price and the price of gasoline become equal and the equality 

of gasoline and alcohol engines in respect to adaptability to service 

required and quantity of fuel consumed per brake horsepower, which 

has been demonstrated to be possible, becomes more generally realized. 

A further general development in the design and construction of 

engines that use kerosene, or cheaper distillates, and the crude 

petroleums may be reasonably expected and may delay the extensive 

use of denatured alcohol for some time to come, but as yet comparatively 

few data pertaining .to this phase of the general, investigation are 

available. Some investigations relating specifically to the extent and 

economy with which these cheaper oils can be used as fuels for internalcombustion engines of the types suited to various classes of service 

are, however, in progress at the testing station of the United States 

Geological Survey, where a Hornsby-Akroyd and a Mietz & Weiss 

oil engine have been installed. These engines are being used for 

tests with the various grades of kerosene.

SURVEY PUBLICATIONS ON FUEL TESTING.

A classified list of Survey papers dealing with coal is given in Bulletin 316 and in an extract from that bulletin, pp. 439 to 532, published separately. 

The following publications on fuel testing, except those to which a 

price is affixed, can be obtained free by applying to the Director, 

Geological Survey, Washington, D. C. The priced publications can 

be purchased from the Superintendent of Documents, Government 

Printing Office, Washington, D. C.

BULLETIN 261. Preliminary report on the operations of the coal-testing plant of the 

United States Geological Survey at the Louisiana Purchase Exposition, in St. Louis, 

Mo., 1904; E. W. Parker, J. A. Holmes, M. R. Campbell, committee in charge. 1905. 

172pp. 10 cents.

PROFESSIONAL PAPER 48. Report on the operations of the coal-testing plant of the 

United States Geological Survey at the Louisiana Purchase Exposition, St. Louis, 

Mo., 1904; E. W. Parker, J. A. Holmes, M. R. Campbell, committee in charge. 1906. 

In three parts. 1492 pp., 13 pis. $1.50.

BULLETIN 290. Preliminary report on the operations of the fuel-testing plant of the 

United States Geological Survey at St. Louis, Mo., 1905, by J. A. Holmes. 1906. 

240 pp. 20 cents.

BULLETIN 323. Experimental work -conducted in the chemical laboratory of the 

United States fuel-testing plant at St. Louis, Mo., January 1, 1905, to July 31, 1906, 

by N. W. Lord. 1907. 49 pp. 10 cents.

BULLETIN 325. A study of four hundred steaming tests, made at the fuel-testing 

.plant, St. Louis, Mo., 1904, 1905, and 1906, by L. P. Breckenridge. 1907. 196pp.

BULLETIN 332. Report of the United States fuel-testing plant at St. Louis, Mo., 

January 1, 1906, to June 30, 1907; J. A. Holmes, in charge. 1908. 299 pp. '
38 GASOLINE AND ALCOHOL TESTS.

BULLETIN 334. The burning of coal without smoke in boiler plants; a preliminary 

report, by D. T. Randall. 1908. 26 pp. 5 cents.

BULLETIN 336. Washing and coking tests of coal and cupola tests of coke, by Richard Moldenke, A. W. Belden, and G. R. Delamater. 1908. 76 pp. 10 cents.

BULLETIN 339. The purchase of coal under government and commercial specifications on the basis of its heating value, with analyses of coal delivered under government contracts, by D. T. Randall. 1908. 27 pp. 5 cents.

BULLETIN 343. Binders for coal briquets, by J. E. Mills. 1908. 56 pp.

BULLETIN 362. Mine sampling and chemical analyses of coals tested at the United 

States fuel-testing plant, Norfolk, Va., in 1907, by J. S. Burrows. 1908. 23 pp. 

5 cents.

BULLETIN 363. Comparative tests of run-of-mine and briquetted coal on locomotives, by W. F. M. Goss. 1908. 57 pp.

BULLETIN 366. Tests of coal and briquets as fuel for house-heating boilers, by D. T. 

Randall. 1908. 44pp.

BULLETIN 367. Significance of drafts in steam-boiler practice, by W. T. Ray and 

Henry Kreisinger. 1909. 61 pp.

BULLETIN 368. Washing and coking tests of coal at Denver, Colo., by A. W. Belden, 

G. R. Delamater, and J. W. Groves. 1909. 54 pp., 2 pis.

BULLETIN 373. The smokeless combustion of coal in boiler plants, by D. T. Randall 

and H. W. Weeks. 1909. 188 pp.

BULLETIN 378. Results of purchasing coal under government specifications, by 

J. S. Burrows; Burning the small sizes of anthracite for heat and power purposes, by 

D. T. Randall. 1909. 44 pp.

BULLETIN 385. Briquetting tests at Norfolk, Va., by C. L. Wright. 1909".. 41 pp., 

9 pis.

BULLETIN 393. Incidental problems in producer-gas tests, by R. H. Fernald and 

others. 1909. 29 pp.

BULLETIN 402. The utilization of fuel in locomotive practice, by W. F. M. Goss. 

1909. 28pp.

BULLETIN 403. Comparative tests of run-of-mine and briquetted coal on torpedo 

boat Biddle, by W. T. Ray and Henry Kreisinger. 1909. 49 pp.

0