Gasoline, the fuel now used, is an extremely volatile and inflammable liquid capable of forming explosive mixtures, the cause of many catastrophes in aviation. It is therefore of special interest to investigate the possibility of using fuels which, while being less volatile than gasoline, would nevertheless enable this engine to function satisfactorily

Dumanois, P

English

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d-dad ‘“
/’ TECHNICAL MEMORANDUMS
NATIOITALADVISORY COMMITTEE FOI%AXRONAUTIGS
No. 451
AVIATION FUELS
(With Especial Refereflceto “White Spirit”)
By P. “Dumanois
Frgm llW Technique Adronautique”
April 15, 192’7
Wshington
February, 1928
..
https://ntrs.nasa.gov/search.jsp?R=19930090812 2020-06-17T03:54:23+00:00Z
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31176014410964——
NATIONAL ADVISORY COMMITTEE
TECHNICAL MEMOFMDUM
,.. ,—..
AVIATIONF
(With Especial Reference to
FOR AERONAUTICS.
No. 451. ,
UELS*
“White Spirit I’).
By P. Duyamois.
Among the questions which concern aviation, the various
problems presented by the fuels are of prime importance. Gaso-
line, t’nefuel now used, is an extremely volatile and inflamma-
ble liquid capable of forming explosive mixtures, the cause of
many catastrophes in aviation.
It would obviously be very advantageous to employ less vol-
atile fuels, so as to diminish the fire hazard, but it seems prob-
able that, for a long time to come, only the explosion engine
will be capable of keeping its weight per horsepower low enough
for aviation purposes.
It is therefo~e of special interest to investigate the pos-
sibility of using fuels which, while being less volatile than
gasoline, would nevertheless enable this engine to function sat+
isfactorily.
Let us first consider the various dangers resulting from
the use of gasoline.
. ,..,,
‘1. From the storage viewpoint, gasoline presents an trndeni-
able danger. The handling of the fuel in filling the tanks and
the keeping of aizplanes in flying order in the same locality
* “Au sujet des coiibustibles dlaviation” from “La Technique Adro-
nautique,“ April 15, 1927, pp. 105-109.
.—
N.A. C.A. Techni~dl Memorandum No. 451 2
favor the formation of dangerous mixtures susceptible of produc-
ing fires which almost instantly become conflagrations. The
evaporation resulting from its volati~it~ is therefore not only
the cause of a useless waste but also a constant source of dtmger.
2. From the viewpoint of functioning in flight, in the case
of backfiriitgto the carburetor, there is danger of the gasoline
taking fire and starting a conflagration. However, when the
backfiring is not due to any organic defect of the engine or to
a leak in the intake pipe, this danger is much less serious than
might be supposed, The risk from this source is very slight,
when the engine is well cared for and no gasoline is allowed to
collect inside the hood, when the air intake is outside and when
pipes opening outside the fuselage are provided to carry off any
gasoline which may collect.
3* In the case of a large leak in the pipe conducting the
gasoline to the carburetor and in the vicinity of the latter,
the danger is considerable, because this fuel evaporates and
fills the hood with an explosive mixture, which is liable to ig-
nite in case of backfiring or even from
pipe. What is then to be feared is not
which can be localized by the judicious
,.
., -,.
ers, ‘out the damage to the hood and the
contact with the exhaust
so much the fire itself,
use of fire extinguish-
extinguisher pipes caused
by the explosion. For the results of this explo~ion to be seri-
ous, however, the carbureted mixture must evidently have the
right composition at the precise instant that a source of igni–
,—-—. ,, .,,.! !! !.. I 1. . ..-!—! —-,. -— . . ,.-—. —.——.
-1
N.A.C.A. Technical Memorandum No. 451 3
tion is produced. This danger cannot be disregarded, however;
as accidents are generally caused by unfortunate coincidences.
Moreoverj a lar~e leak in the carburetor Or in the fuel Pipe
may result in the production of too poor a mixture and thus
cause backfiring.
4. Iil case of a capsize, the tanks are geneTally broken
~open and the gasoline scattered in all directions. It is liable
to come ii~contact with hot objects, such as the exhaust pipe
is of the same or-
fli~ht, as, for ex-
generally sets fire
or valves, whose temperature may exceed 700°C (1292°F.). The
fire hazard is therefore great. The danger
der when the engine is seriously damaged in
ample, by the “~reaking of the piston, which
to the oil in the crailkcase, a fire which is then communicated
to the fuel, if t’necarburetor or fuel pipe is damaged.
From the above considerations it follows that the great
volatility of gasoline is a priine cause of accidents in cases
1 and 2. In case 3 the volatility of the gasoline is liable to
cause a catastrophe by an explosion damaging the engine itself.
Lastly, in case 4, it seems probable that, whatever fuel is
used, there is always a fire hazard when parts of the engine or
the exhaust pipe reach a temperature above the miniimm ignition
temperature of the fuel. In this connection, let us bear in
.
mind that the heavy petroleum oils iewite at a lower temperature
than gasoline and that benzol ignites at a higher temperature.
.N.A. C.A. Technical Memorandum No. 451 4
,..
In fact, it may be considered that all tHe fuels’are liable to
ignite.on conta,ct with”an object ”above-6500C”’(12020F.-). “ It--is
obvious, therefore, that the volatility of @soline is a cause of
danger and we are ilaturallyled to investigate the possibility
of using a less volatile ftiel i-naviation engines. ‘ -
The specifications for aviation fuels ~tieremade after a
large number of endurailce tests on engines of all powers=- The
experiments demonstrated that two qualities were essential f~r
satisfactory functioning, namely, homogeneity and volatility.
When less volatile fuels were tested on the ground, it was found
t ha.t, after.a.longer or shorter time, carbon deposits were formed,
premature ignitions, and sometimes explosions occurred due to
the fact that the more or less oily carbon deposit~ formed a sort
of insulati-nglayer on the inside of the combustion chamber.
This seemed to demonstrate the necessity of using very volatile
fuels. After awhile our attention was called to the fact that,
when one exafilinest-nebarogra-ms of climbs, made by test pilots
having the technical knowledge necessary for making a climb un-
der the best conditions and sufficient professional skill to
handle their airplanes to the best advantage, it is found that,
in nearly all the barograms, above a certain altitude, .generally
comprised between 9500 and 10,000 meters (31,167 and 32,808 feet),
the curve of ascent presents a sharp curve corresponding to a
limitation of the ceilin~ much below the one which would. result
from the consistent prolongation of the barometric curve.
N.A. C.A. Technical Memorandum No. 451 5
In order to explain this peculiar phenomenon, it would aP-
pear. necessary to introduce an imPortant variation in the phys–
ical properties which affect the functioning of the airplane.
Now, neither the air, nor the cell, nor the engine, nor the pro–
peller, nor the barograph seems, a priori, to depend on any,
discontinuous parameter for a certain value of the altitude.
There refflainsnothing but the fuel, which seems capable of ac-
counting for this phe-nomenon. In fact, at the abovementioned
altitudes, the atmospheric pressure is only about 200 mm (7.87
in. ) of inercury. Moreover, as a result of the warming of the
carburetor due to the fact that the fuel is contained in a tank
protected by the fuselage, the fuel has ~ considerably higher
temperature than that of the surrounding air. In a climb to
9500 m (31,167 ft.), Adjutant Moutonnier found that the tempera–
ture of the tank was still 15°C (59°F.), while the outside temp-
erature was below –40°C (–40°F.). It is obvious therefore that
the atmospheric pressure is of the order of magnitude of the
vapor tension of aviation gasoline. If we take into account,
moreover, the natural enrichment of the carbureted mixture with .
increase in altitude, it is reasonable to suppose that, with
the usual fuels, there is a certain limit at which, by r@son
of the excessive relative value of the vapor tension of the gas-
.
oline with respect to the external pressure, the carburetor no
longer furnishes a mixture with the requisite qualities for ob-
taining a good carburetion.
—
N.A. C.A.
We
Given a
ground,
Technical Memorandum No. 451 6
have therefore been led to make the following hypothesis.
1,
fuel having a vapor, tension
.h which produces on the
at the atmospheric pressure H, a satisfactory function-
ing in an aviation engine,”other things being equal, a fuel hav-
ing the same qualities of homogeneity but a vapor tension equal
to a h will produce a functioning equivalent to an altitude at
.
which the atmospheric pressure is a H. It i,s’veryevident that
a law conceived in such ‘anabsolute folm cannot be strictly veri–
fied, because the vapor tension is not the only physical charac–
teristic which affects the formation of the ca?!btiretedmixture:
The nature of the fuel, its composition and viscosity, the mech–
anism of the carbtiretorand th~ degree of atomization have a
bearing fihich is not ilegligible, It is nevertheless ttie that,
with the automatic carburetor devices used.; the ilfiportanceof
the vapor tension is primordial from tileviewpoints of the atom–
ization of the fuel a-ridof the homogeneity of the mixture. This
hypothesis seems, moreover, to accord very well with the results
dbtained some 15 years ago by Bellem and Grageras in the carbure~
tion of kerosene in explosion engines.
matic carburetor, they employed a pump
cycle the requisite quantity of fuel.
Instead of using an auto–
which delivered at each
This fuel was drawn in at
the beginning of the intake period, the intake valve remaining
.,..,., ,, ...... .
closed during a certain portion of the stroke. The partial va.c--
uum thus obtained was,favorable to the vaporization of the fuel.
We believe, moreover, that the device, employed had some effect
--- ., ,-.,----- .. . .. . ......— .-—
N.A. C.A. Technical Memorandum No. 451 7
on the results obtained.
Since it follows from
volat ility of the aviation
the condition of obtaining
the foregoing considerations that the
gasoline was accurately determined by
on the ground a satisfactory function-
ing of the engine, it is very evidei~tthat fuels with a lower
vapor tension would give poorer results on the.ground and would
be lia,ble to produce incrustations or fouling. This point is
important, for it is obvioukly desirable to have, at the alti-
tude of utilization, a not very volatile fuel, in order to in-
sure proper functioning, but it is also necessary to be able to
reach this altitude without the engine becomin~ foul. It is, in
fact, of no avail to eliminate the fire hazami at the expense of
infinitely ;floreproba’cle engine failure in taking off or while
climbing. This disadvantage can be overcome by using @,soline
to start with, which we ‘havedone, Qut we deem this solution
unsatisfactory and one to be regarded only as a makeshift.
On the other hand, we have had the opportunity to demon- .
strate the possibility of using, in automobile engines, fuels
heavier than gasoline, provided they contain a sufficient propor-
tion of volatile substances capable of playing the part of sol-
vents and vaporizers of the heavier components. By preventiilg -
detonation, it i~ thus possible to obtain very satisfactory func-
tioning. We have successfully used ethyl alcohol carbureted
N.A.C.A. Technical Memorandum No. 451 8
with 30$ kerosene, is also mixtures bf gasoline and kerosene.*
We have thus been led to infer that, reciprocally, if we can take
a certain ~soline and remove the heavy constituents, it should
also be possible to remove from it the light constituents without
disturbing the functioning? We were thUs led to experiment with
11a Detroleum product distilling entirely between‘lwhite spirit, .
130° and 180°. The first tests made on a vehicle having a 10 HP.
engine of 68 mim (3.68 in.) bore and 10CImm (3.94 in.) stroke,
produced a very satisfactory functiofiing without altering the
en~ine ai~dwithout other modification than the adjustment of the
spraying nozzles and a slight heating obtained by simply leading
the fuel pipe over the exhaust manifold, which gave the fuel a
tempeiiature of about 25°C (77°F.). The start was made by in-
jecting a few cubic centimeters of gasoline into the fuel pipe,
or by heating the float chamber by electricity. With this fuel
we traveled over 3000 km (1864 miles), mostly in Paris, without
any ki-ndof accident. In comparison with gasoline the maximum
speed diminishedfrom 80 to 75 km (49.7 to 46.6 miles) per hour,
the fuel consumption increased about 10~ and the fouling was a
little more pronounced. Otherwise the functioning was excellent.
These results led us to experiment with an airplane engine.
October 29, 1926, we obtained authorization from the General Di–
* The results were exhibited to the ‘lSocie’te’de Navigation At?ri-
enne.,”May 20, 1’325,at a session where Mr. Painlev6, Minister
of Wa:, wished to have them presented. Since then different
S*T.Ae. vehicles have functioned satisfactorily with a fuel con-
taining 50% kerosene.
JT.A. C.A. Technical Memorandum No. 451 9
rector of Aeronautics, on putting the results of our experiments
at his disposal..- The engine employed was a 180 HP. Hispano, cho-
.
sen because of the shortness of the intake pipe, a favorable con-
~Lition for preventing condensation.
The first tests, made ofithe
necessary, on the grotind,-to l&ve
for gasoline, in order to make up
bench, demonstrated that it was
a little richer adjustment than
for the greater viscosity of
the fuel, that the flow velocity had to be Slightly diminished
and that the fuel in the float clximbethad to be kept at a tem-
perature of about 25°C (77°Fh). ~ndef these conditions the max-
imum number of revolutions pe? mihute dbtained on the bench was
1770, in ‘glaceof 1800, with .gasdline~
The engine was mourlted cm an ai~pla,neand, on December 16,
1926, the first test was made by the engineef Ceccaldi. The take-
off was made with gasoline, IIwhite”spirit’fbeing substituted at
9 an altitude of 500 m (1640 ft.). The climb was continued to.
3000 m (9842 ft.), at which altitude a horizontal stretch was
flown. The total time of functioning .with the IIwhitespirit!’
was 28 minutes. The functioning was satisfactory at both high
and low speed, but the pick-ups were very troublesome.
It was demonstrated during this flight test that the engine
which lost, on the ground, about 80 R.P.M., as compared with
gasoline, made 1700 R.P.M. in horizontal flight at 3000 m (9842
ft.), as a~ainst a maximum of 1630 R.P.M. with @soline under the
same conditions.
—
N.A. C.A. Technical Memorandum No. 451 10
The results have no other value than to demonstrate the pos–
sibilitieso These seem to confirm the hypotheses which led to the
experiments and which should not be considered final. They were
obtained with an ordinary engine and an ordinary carburetor.
Doubtless the carburetor, which was designed especially for gaso-
line, is not equally well adapted for “white spirit” and should
be altered, in order to effect a better evaporation. It is also
probable that the intake pipes should be modified in certain en-
gines, where their length tends to cause condensation. It never-
theless seems, in view of the results obtained, that the inves-
tigation should be continued.
Lastly, fire hazards cannot be entirely eliminated by the
use of fuels having properties similar to those of “white spirit.”
It must not be forgotten that all fuels are made to burn. What-
ever its flashing point, if a fuel is brought in contact with ob-
jects above its ignition temperature, it is liable to take fire.
It is none the less true that, from the viewpoint of the safety of
handling and storing and especially of the danger of explosion in
case of a leak in the carburetor or fuel pipe, the fire hazards
would be greatly reduced. It would therefore constitute a decid–
ed improvement from the standpoint of safety.
In concluding, let us note that the idea of employing safety
fuels is not a new one. The first ~esearches were made in 1917
on the initiative of Mr. Breton, with reference
Mr. Ferri6, a naval engineer of hydraulics made
.
to “tank” engines.
bench tests in
N.A. C.A. Technical I[emora,ndumNo. 451 11
1921–1922, which led him to consider the use of non-volatile
fuels ia explosion engines. Unfortunately, the experiments of’
Mr. Ferri& remained unknown until recently. We first learned
of them through a letter receitiedfdom him; after we had begtin
our investigation.
Mr. Ferrid considers that the limit of the volatility of
the fuels is determined by the condition that they must exist
only in the state of vapoi at the end of the comp~bssion peridd,
takin Z into account the elevation in tempefattirk!produced by
the compression, He also thinks that the chances of condensa–
t~on on the tills are inversely proportional to the final vol-
ume and directly proportional to the duration of contact with
the walls, i.e., higher compression and lower engine speed. We
agree with Mr. Ferri6 in this view. We think, however, that
the abovementioned conditions, while being necessary, are not
sufficient. Thus , with kerosene, a compression ratio of 6 suf-
fices to obtain a temperature of over 300°0 (572°F.), at which
the kerosene is converted into vapor. .
Under these conditions, functioning is not possible, how–
ever, due to detonation and premature ignition. In the last
analysis, these phenonena limit both the proportion of heavy
constituents and the admissible maximum compression pressure.
Finally, the experiments with “white spirit” seem to indi-
cate that, due to its viscosity being greater than that of gas-
oline, it will be necessary to improve the atomization. It is
.
.
N..A.C.A. Technical Memorandw No. 451 12
probable, moreover, that the improvement of the atomization, in
producing a more homogeneous mixture, would, at t’hesame time,
make it possible to function at a higher compression pressure
without danger of detonation~
Translation by Dwight M. Minerj
National Advisory Committee
for Aeronautics.
—.


Aviation fuels : with especial reference to "white spirit."

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