This report presents test results obtained during an investigation of the performance of a single-cylinder, high-speed, compression-ignition test engine when using multiple-orifice fuel-injection valve nozzles in which the number and the direction of the orifices were varied independently

Foster, H H

Spanogle, J A

English

NASA Technical Reports Server

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3Y J; A. .Spanogle and H. II, Ii’os%e;
Langley MemoriaI- Aeronautical. Laboratory
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https://ntrs.nasa.gov/search.jsp?R=19930081220 2020-03-17T04:00:17+00:00Z
NATICNAL ADVISORY COIMITTEE YOR AERONAUTICS
——
TECHNICAL NOTE NO. 382
——
BASIC REQUIREMENTS OY 17UEL-INJECTION NOZZLES
FOR QUIESCENT. COMBUSTIOI? CHAMBERS
.
By J. A.. Spanogle and Ii.”H..Foster.
Summary
This report presents test results obtained at the Langley
Memorial Aeronautical Laboratory of the Natiorial Advisory Com-
mittee for Aeronautics during an investigation of the performa-
nce of a single-cylinder’, high-speed, compression-ignition
test engine wheti using multiple-orifice fuel-injection valve
nozzles in which the nufiber and the direction of the orifices
were varied independently. The orifice sizes generally con-
formed to the principle that the orifice area should be pro-
portional to the volume of air served by the orifice.
The test results indicate that it is unnecessary to follow
the proportional principlq to’ extremes and that complication of
nozzle design does not give a commensurate increase in perform-
ance. The optimum angle between orifice axes was jtidged to be
25° for the conditions i.n this quiescent combustion chamber, but
this value “is not c“ritical.
.,
Introduction
In the course of the general program for the investigation
and development of the high-speed, compression-ignition, fuel-
injection engine as a power plant for aircrafts the staff ‘f . ~
the Langley Memorial Aeronautical Laboratory has been &eter-
mining the performance of a single-cylinder test engine with a
. vertiical disk-shaped combustion chamber in a cylinder head,
desi nated in the test series N.A.C.A. cylinder head Nom 4.
“c
The combustion chamber ‘in this cylinder head is considered
quiescent because there is no evidence that the movement of the
air in the combustion chamber has”’any effect on the distribution
of fuel. Various multiple-orifice injection-valve nozzles have
been use for introducing the fuel into the combustion chamber,
and former- tssts as repor”ted- in”N.A;C.A”. Technical Note No, 344
R (Reference 1) indicated that for this type of combustion-chamber
the area of each orifice in a nultiple-ori.fice nozzle should be
-proportional to the volume of air it served.#
–,-_=
7.
- f.
,.. —- - -+.. ..+.-.—-.. .— —... ----
2 N.A. C.A. Technical Note No. 382
The forced air flow in this quiescent combustion chamber
during injection of the fuel is of such a low velocity that it
has a negligible effect on the distribution of the fuel and
there is no evidence of residual air flow. Therefore, to ob-
tain as nearly a homogeneous mixture of fuel and air as possible,
it is necessary to meter the fuel to the air in the combustion
chamber by using the proper arrangement of the discharge orifice
or orifices. The assumptions necessary for a practical basis
for these tests are that in carefully manufactured nozzles with
round-holo orifices the coefficient of discharge will be the
same for all orifices, and that the same discharge pressure will
be acting on each orifice. These assumptions seem reasonable,
and therefore all factors in the formula for quantities dis-
charged becme identical, except for the areas, and it follows
that the amount of fuel discharged by each individual orifice
will he proportional to the area of the orifice. If, then, each
orifice area is in the same ratio to the total discharge area as
the volume of air it serves is to the total volume of air served,
the effectiveness of distribution will be dependent upon the
dispersion of the fuel in the spray and the shape of the volume
served.
To determine just how far it was advisable to follow this
principle comparative performance tests .were conducted with a
series of nozzles extending this idea beyond limits practicable
in the construction of nozzles for commercial engines. ‘
To determine the optimum angle between sprays another
series of comparative performance tests was run with nozzles in
which the orifice areas were held constant aad the angle varied.
Apparatus and Methods
The test equipment and general test methods used for the
tests hereii~ reported are the same as in Reference 1, except as
specifically noted.
The co’mlmstion chamber was made as nearly quiescent as
possible by using a new throat orifice (Fig. 1) that had a
larger opening than used in former te”sts and was so shaped as
to disturb the orderly forced flow of the air as little as
possible and to”prevent residual flow and formation of small
vortices. The larger opening increased the clearance volume so
that the compression ratio was 12.6:1 instead of 13!6:1, as in
former tests.
.-J
IT,A.C.A. Technical Note No. 382 3
< ..
.
Compression pressures and maximum-cylinder pressures were
indicated by means of the balanced diaphragm type of maximum- ,.
cylinder-pressure indicator (Reference 2) in place of the
trapped-pressure apparatus used in the former tests. Instead
of recording a double reading for maximum-cylinder pressures
as described in Reference 2, the operator recorded what he
considered a fair average. No attempt was made to operate the
engine at a particular “valu& of maximum-cylinder pressure;
instead, the pump was adjusted to give the desired fuel quantity
and then the timing was advanced until a faint knock was heara,i --
W1l-load fuel quantity 0.000325 pound per cycle is that”
quantity of fuel which w-ill be completely burned, “assuming ~ei-
fect comlnzstion, with the amount of air i“nducted per cycle at
82,5 per cen”t volumetric efficiency. The test results are not
corrected $or either .%arometric presstire or humidity. The in-
jection period as observed with an oscilloscope (Reference 3)
was about 35 to 37 crank degrees. The standard test speed was
1500 r.p.m,
S-cries E nozzles.- In the designing of nozzles for this .
.——--———-—
series of performance tests it was decided to abandon the &8
angular syacing used in the former tests and to standardize
pn an angl”e that would remain constant for all orifices. From
l data obtained from spray photographs by the Fuel Injection Sec-
tion (Reference 4) on comparable orifices tested untier condi-
tions comparable except for temperature, it was found that the
average value for spray-cone angle was 20°. Twenty degrees
was t~erefore adopted as a staridard spray-cone angle for the
1 Serie~ E nozzles, and al~ air,-volune calculations were based
on this value.
To continue with a design of nozzle” that could be compared
with those used in the former tests, the diameters of the 2
central’ ma”in orifices were maintained at 0.018 inch and the
volume of air in the mechanical clearance space between the
ptston crown and the cylin’der head was divided equally between
these :orifices for purposes of proportioning the other orifices.
A total of 16 orifices was used with 6 in one plane and 5 in
ea~h of 2 planes which were on either side of the first plane,
as. shown in Figure 2. The orifices “were drilled 2 at a time in
the order itidicated by the numbering in Figure 2. The designa-
tion of these nozzles is ,bj the use of the- letter E with a
nqmber derioting the number of orifices in the nozzle at ~h.e
time of test.
There is a slight deviation from the proportional-area
priaciple i.~ the E-series nozzles after E12, because it was
considered impracticable to use orifices smaller than 0.005-”
imch diameter. This aev$ation is not serious because the per-
.— ---
4#
.
. . . .
N.A. C,A. Technical Not& No. 382
centage of the total orifice area involved is smaller than the
experimental error.
T%e performance test results sho~n in Figures 3 and 4
indicate that no justifiable gain would be obtained by using
more than 6 orifices for this cylinder head. This conclusion
simplifies further work with this cylinder head.
Series F nozzlos.- Thore were a number of indications
——.——-—-—
during these tests that the 20° angle between sprays was not
the optimum, and the decision to continue with the 6-orifice
nozzles made it comparatively easy to invosti.gate the effect
OD engine performance of varying the augle between the axes
of the individual sprays.
About this time the results of the work on dispersion at
the Pennsylvania .State College were published (Reference ~),
and following the method outlined by Doctor Schweitzer the
boundaries of combustion wore laid out for the EG nozzle as
shown in Yigure 5. If the volume within this ~oundary is as-
.
sumed to be a minimum space requirement. for combustion, it may
be SOEIII that the boundaries overlap and that the spr~~s prob-
ably interfere with each other during combustion.
When the series 0$ nczzles for the investigation of the
effect of angular spacing was designed, it was again necessary
to deviate from the proportional-area principlo for the volume
of air to be served by each orifice chanced with the angle.
However, as the orifice sizes were maintained the same for all
angles, the departure from the proportional-area principle
averaged about 1 per cent, and this was neglected as it was
less than the error in the determination of performance values,
Accordingly, the different nozzles were made with corresponding
orifices of the same size.
The nozzles in this series are designated by the letter F
with a number denoting the angle in degrees between the axes of
the orifices. Thus , ~he EG ‘and the -1’~o arc identical nozzles.
The performance tests of these nozzles showed very little
difference between t“hem, so far as the curves in l?igure 6 are
concerned, but observation of the, exhaust gases and the sensi-
i
tiveness to controls led to the decision to standardize on an
angle of 25° for future work with this cylinder head.
As a further check, to indicate whether the 29° spacirig was ,
beyond the useful -limit, two 0.005-inch orifices were added,to
the l?~~ nozzle in the center to see if any unused air remained —
between the 2 main sprays. The resulting increase in perform-
l
N,A.C,A. Technical Note No. 382 5
ante, as shown in the curves of Figure 7, indicates that small
filler sprays are effective when the angle between the sprays
on either side is too great.
It is believed that a nozzle which would ‘be designated
F25 would give sufficiently good performance and that any in-
crease which could be secured by further refinements in nozzle
design would hardly be commensurate with the complication in-
volved in the construction of such a nozzle. However, the per-
formance data do not show that angular spacing is at all
critical within the range covered in these tests. The reason
for this lack of criticalness is suggested by the small per-
centages of fuel in the outer part of the spray as shown %y
the dispersion data in Reference 5.
These tests do not complete the work to be done in in-
vestigating the quiescent combustion chamber. In all tests
thus far the total discharge area has been disregarded and con-
sidered as a function of the injection system rather than of
. the combustion chamber. As it seems logical to investigate
variation in total discharge area along with variation in total “
air available, additional data concerning this variation will
l be obtained in forthcoming supercharging tests.
.
.
;
“ Conclusions
.’
.
Although the tests ‘reported herein and in Reference 1
were conducted on a particular cylinder head, they indicate
that there are de,finit.e basic. requirements which must be
satisfied in the design of multiple-orifice fuel-injection
valve nozzles for “u’se.in combustion with a quiescent combus-
tion chamber to insure the necessary mixture of fuel and air.
The fuel-injection system should be so designed that the
same pressure is effective in causing the discharge through
each orifice. The orifices themselves should be of the same
geometric shape so that they all have the same coefficient of
discharge. If these two conditions are satisfied, the nozzle
will be a%le to meter the fuel to the combustion air by having
the area of the individual orifices proportional to the volume
. of air served by each orifice.
These engine performance tests show that, in a multiple-
orifice fuel-injection valve nozzle for a quiescent combustion
.-
.
6 N.A.C.A. Technical Mote Ho. 382
chamber, there is no sharply defined optimun value for the
number or direction of the orifices.
Langley Memorial Aeronautical Laboratory,
National Advisory Committee for ACTOnaUti,CS,
Langley i?iold, Vs., Lfay x5, 1.931.
Reforoncos
1. Spanogle, J;”A,
and
??oster, E. H.
2. Sparioglo, J. A.
and
Collins, J. H.
3. Hicks, Chester ‘W.
and
liooro, Charles”S.
4. Gelalles, A. (1.
.
5, Schweitzer, P. H.
a Porformancc of a High-Speed.
Compr6ssi,on-Ignition Engin6”
Using Multiple-Orifice Tuel
Injection Nozzles. N,A,C.A.
Technical Note No, 344, June,
1930.
.
: A Balanced Diaphragm Typo of
.
Maximum Cylinder Pressure
Indicator. I?.A.C.A. Technical
lTote Ho, 359, Dec., 1930.
4
.-
: The Determination of Sovcral
Spray Characteristics of a
High-Speed oil Engino Injec-
tion Syst~m with an Oscillo-
scope. N,A,C.A. Technical
Note No. 298, Sept. , 1928.
: Effect of Orifico Longth-
Dianf3tcr Ratio on Spray
Characteristics. IT,A.C,A.
Technical lroto No. 352, Oct.,
1930.
: Factors in Hozzle Design in
the Light of Recent Oil Spray
Rosoarch. No. OGP-52-15.
page 121, Yransactionn of
A.S.M.E. , 1930.
l
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Fig. 2 Projected spray M.stributionusing nozzle E-16
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Basic requirements of fuel-injection nozzles for quiescent combustion chambers

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