Rocket engine injector orifice to accommodate changes in density, velocity, and pressure, thereby maintaining constant mass flow rate of propellant into rocket combustion chambe

Stein, S.

English

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REPLY TO 
ATTNOF: GP 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 
TO 9 USI/Scientific Sr Technical Information Division 
Attention: Miss Winnie M e  Morgan 
FROM 3 GP/Office of Assistant General 
Counsel for Patent Matters 
SUBJECT: Announcement of NASA-Owned 
U,S. Patents in STAR 
In accordance with the procedures contained in the Code GP 
to Code US1 memorandum on this subject, dated June 8, 1970, 
the attached NASA-owned U.S, patent is being forwarded €or 
abstracting and announcement in NASA STAR. 
The following information is provided:: 
U,S. Patent No, 
Corporate Source s Aiesea 
Supplementary 
Corporate Source 
NASA Patent Case No,: E- 
Enclosure z 
M 
0 (THRU) 
00 
(CODE) 
(CATEGORY) 
LL 
j 
2 (NASA CR OR TMX OR AD NUMBER) 
u- 
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https://ntrs.nasa.gov/search.jsp?R=19710015260 2020-03-17T02:58:29+00:00Z
S. STEIN 
ROCKET ENGINE INJECTOR 
Filed O c t .  31, 1966 2 Sheets-Sheet 1 
30 36 \32 
FIG. I 
BY 
ova 
F i l e d  Oct. 31, 1966 
S. STEIN 
R O C K E T  E N G I N E  I N J E C T O R  
2 Sheets-Sheet 2 
FIG. 2 
INVENTORS 
SAMUEL STEIN 
BY 
velocity and pressure of the propellant and is self-actuated 
in adjusting for a predetermined flow rate. 
A further object of the invention is to provide a rocket 
States of as represented by Adrnin~stsatos engine injector in which sensing and actuation functions 
of the ~ ~ t i ~ ~ ~ l  Aeronautics and Space ~ d ~ i & t ~ ~ f i ~ ~  5 take Place at  the plane of propellant entry into the engine 
combustion chamber at each point of entry for uniformity 
of flow across the injector face. 
A still further object of the invention is to provide 
a rocket engine injector which acts to introduce a phase 
lag to dampen combustion chamber pressure oscillations. 
These and other objects of the invention will be ap- 
parent from the specification which follows and from the 
drawings wherein like numerals are used throughout to 
identify like parts. 
the drawings: 
3,408,816 
ENGENE ~~~E~~~~ 
Ohio, assignor acp united Samuel Stei 
Piled Oct. 31, 1966, Ser. No. 591,014 
5 Claims. (el. 60-240) 
A 
Maintaining the mass flow rate of Propellant into a 
rocket combustion chamber substantially Constant as Pro- 
pellant temperature changes by automatically varying the 
cross-sectional area of the injector orifice to accommodate 15 
changes in density, velocity, and pressure. FIG. 1 is an enlarged sectional view of a rocket engine 
injector element constructed in accordance with the pres- 
ent invention; and 
The invention described herein was made by an em- FIG. 2 is an enlarged sectional view similar to FIG. 1 
ployee of the United States Government and may be 20 showing the relative positions of injector element parts 
manufactured and used by or for the Government for 
governmental purposes without the payment of any 
royalties thereon or therefor. 
This invention relates to the injection of propellants 
into a rocket engine combustion chamber. More partic- 
ularly, the invention is concerned with the control or reg- 
ulation of the Row of a liquid rocket propellant to com- 
pensate for changes in density. 
An injector for a rocket engine usually has one or 
more elements with fked area orifices through which 
the propellants flow into the combustion chamber. Cer- 
tain problems have been encountered with the use of such 
orifices because of changes in the temperature of the 
propellants. It bas been found that the temperature of a 
liquid propellant is significantly higher during the starting 
portion of a rocket engine run due to the initial cooling 
of various engine components by the propellant. This tem- 
perature increase in the propellant produces a density 
decrease. 
In general, for the flow of fluids through a fixed area 
orifice in which the pressure differential causing the flow 
remains constant, a decrease in density will cause a de- 
crease in the mass flow rate in pounds per second. How- 
ever, in the case where the fluids are propellants and their 
reaction affects the pressure differential causing flow 
through the fixed area orifice, a decrease in density will 
initially cause a decrease in the mass Row rate. This, in 
turn, creates a greater pressure difEerentia1 which will 
then produce a higher flow rate. Such an increase in 
as a rocket engine is started. 
Referring now to the drawings, there is shown in FIG. 
1 an injector element 10 constructed in accordance with 
the present invention. The injector element 10 has a 
28 tubular member 12 which extends between a back wall 
14 and a face plate 16 of an injector located at one end 
of a rocket engine combustion chamber. The tube 12 
is rigidly mounted on the back wall 14 by a nut 18. A 
plenum chamber 20 is formed between the back wall 14 
30 and the face plate 16 for containing a propellant, such 
as liquid hydrogen. 
Another propellant, such as liquid oxygen, is stored 
on the opposite side of the back wall 14 from the plenum 
chamber 20. The liquid oxygen passes through the bore 
35 22 of the tube 12 to a reduced diameter passage 24 which 
terminates in the plane of the surface of the face plate 
16. Seals 26 and 28 prevent entry of the liquid oxygen 
into the plenum chamber 18. 
The liquid oxygen is injected as a cylindrical stream 
40 through the bore 22 and the passage 24 into the combus- 
tion chamber. The liquid hydrogen is injected through an 
annular orifice 30 to form a tubular stream around the 
liquid oxygen in a coaxial manner as described in U.S. 
Patent No. 3,136,123. 
The annular orifice 30 is formed by an opening in an 
orifice plate 32. An end portion of the tubular member 
12 extends into this opening and has a tapered surface 34 
which forms a generally truncated conical configuration. 
A centrally disposed opening in the orifice plate 32 has 
50 a contoured surface 36 which mates with the tapered sur- 
45 
propellant flow will create a smaller pressure differential 
which will again reduce the flow rate. This alternating face 34 on the end of the tubular member P2.'The post- 
phenomena continues and sustains itself on a self-exciting tioning of the contoured surface 36 with respect to the 
basis. tapered surface 34 determines the area of the aimular 
Another problem arising with the use of conventional opening 30. Thus, the conical annular passage 30 con- 
injectors is that certain of these have a sensing device 55 stitutes a variable area orifice, and the longitudinal posi- 
tioning of the orifice d a t e  32 with resoect to the tube 112 located at or near the injector but not at the plane of 
injection. Such devices do not reflect actual flow condi- 
tions at the plane of injection, and they are unable to de- 
tect any variations of flow conditions at each point of 
injection. 
These problems have been solved by the injector of the 
present invention which utilizes elements having variable 
area orifices. The area of each orifice is altered auto- 
matically to accommodate changes in density, velocity 
and pressure. 
It is, therefore, an object of the present invention to 
provide a rocket engine injector element which automat- 
ically regulates the flow of propellant at each point of 
injection to reduce excitation sources of combustion cham- 
ber pressure oscillations. 
Another object of the invention is to provide a rocket 
engine injector which is self-sensing to changes in density, 
determines the area of opening. 
The orifice plate 32 is mounted for reciprocable move- 
ment along the axis of the injector element 10 in a suit- 
60 able opening which extends through the injector face 
plate 16. The orifice plate has a sleeve 38 which re- 
ceives the tubular member . The sleeve 38 is free to 
slide along the tubular member 12. A retaining ring 40 
is mounted on the end of the sleeve 38 remote from the 
er. The retaining ring 40 is held 
A coil spring 44 encircles the sleeve 38 and is enclosed 
by a retaining housing 46 that is rigidly mounted on the 
tubular member 12. One end of the spring 44 engages 
70 an inwardly turned flange 48 on the housing 46 while 
the opposite end of the spring engages the retaining 
ring 40. 
3,408,816 
4 
The spring 44 is selected SO as to enable the orifice 
plate 32 to move from an extended position shown in 
FIG. 2 at the start of the engine firing to a retracted posi- 
tion shown in FIG. 1. More particularly, as the orifice 
plate 32 moves to the extended position shown in FIG. 2 5 
occur because the injection pressure is more readily con- 
trolled. Also, the pressure differential versus flow rate re- 
lationship remains relatively constant over the entire 
densityrange. 
An injector element constructed in accordance with the 
invention can also dampen combustion chamber pressure the spring 44 is compressed between the retaining ring 40 
and the flange 48. The spring 44 exerts a restoring force 
against the retaining ring 48 which moves the sleeve 38 
and orifice plate 32 to the retracted position shown in 
FIG. 1. In this manner the compression spring 44 op- 
poses an increase in the area of the annular orifice 30. 
The annular opening 30 is placed in communication 
with the plenum chamber 20 by suitable ports 50 which 
extend through the orifice plate 32. Fuel from this cham- 
ber passes through the ports 90 and flows into the com- 
bustion chamber through the annular orifice 38 thereby 
providing a cooling film for the exposed surface of the 
orifice plate 32 when it projects from the injector face as 
shown in FIG. 2. 
oscillations when such oscillations result from the acoustic 
property of the chamber and are not induced by or de- 
pendent on a pulsating flow. 
In a conventional injector element, the chamber os- ' cillation causes a corresponding propellant flow variation. 
By way of illustration, assume the propellant flow is 
phased so that in the vibration cycle as the chamber 
pressure increases the burning rate also increases due 
5 to flow changes and burning rate changes which can drive 
or sustain the oscillation. If the spring 44 and orifice plate 
32 have a lower natural frequency than that of the ex- 
citing chamber pressure force, the direction of motion of 
the orifice plate will be 180" out of phase with the excit- 
Referring to the present invention the extended position 20 ing force. Thus, during a vibration cicle the orifice plate 
of the orifice plate 32 shown in FIG. 2 presents a suitable will open further as the chamber pressure increases. This 
area of the annular orifice 26 for low density fuel at the will cause a pulsating flow of propellant to oppose the 
start of the rocket engine. After the rocket engine has exciting force in a manner analogous to a damped vibra- 
been started the fuel reaches the injector at a lower tem- tion absorber. 
perature and a higher density. These changes are sensed 25 To illustrate the beneficial technical effect of the inven- 
by the orifice plate 32 which positions itself accordingly. tion injection parameters for a variable area orifice are 
When the fuel has reached its maximum density, the set forth in Table I. The fuel is considered to  be at 190" 
orifice plate 32 is a t  the position shown in FIG. 1 thereby R. when the rocket engine is started and at a final 
affording a small orifice area. temFerature of 60" R. This corresponds to a density in- 
When a pressure differential exists between the injec- 30 crease of about ten times. By providing a small ramp 
tion pressure in the plenum 20 and the combustion cham- in chamber pressure from 270 p.s.i.a. for fuel at 190" R. 
TABLE I 
Combustion Mass 
Injection Chamber Pressure Flow Flow Denqity Tempera- 
Pressure, Pressure, Change, Rate Area, Lb&it.i ture, ' R. 
35n 270 80 n. 496 n. i m  n. 347 isn 
p.s.i.a. p.s.1.a. AP Lb./S&. I n . 2  
.~. . _... . ._ 
350 275 75 0.506 0.1355 0.417 is0 
350 280 70 0.516 0.1209 0.590 120 
350 285 65 0.526 0.1056 0.858 93 
350 290 60 0.535 0.0912 1.289 77 
350 295 55 0.544 0.0'772 2.029 69 
350 300 50 0.553 0.064 3.630 60 
ber pressure through an injector element 10 constructed to 300 p.s.i.a. for fuel at 60" R., a constant injector pres- 
in accordance with the present invention, the orifice plate 45 sure of 350 p.s.i.a. can be employed. The tabulated valves 
32 is positioned proportional to this differential pressure. in Table I indicate the relationship of density being the 
The restoring force of the spring 44 is also proportional determinant for flow area to provide the mass flow rate 
to the differential pressure. The mass flow rate com- for developing the communsurate chamber pressure. 
mensurate with the differential pressure determines the While a preferred embodiment of the invention has 
chamber pressure. The mass flow rate is equal to the 50 been described, it will be appreciated that various struc- 
product of orifice area, propellant density and flow ve- tural modifications can be made to the disclosed injector 
locity. The pressure differential and the spring force are without departing from the spirit of the invention or the 
proportional to the propellant density x flow velocity.z scope of the subjoined claims. 
The mass flow rate is proportional to the spring force, 
and the difference between the differential pressure at the 55 
beginning and the end of the firing is reflected in the corn- 
bustion chamber pressure. Depending on the specific ap- 
plication, this difference can be made small as desired; 
on the order of 25 p.s.i., for example. In such an example, 
the chamber pressure could be 575 p.s.i. initially and 6o 
finalize at 600 p s i .  It will be appreciated that the opera- 
tional characteristics can be varied to meet specific fuels, 
What is claimed is: 
I. In combination with a rocket engine having a com- 
bustion chamber. 
installations and the like. 
In a conventional injector the fuel may be metered to 
the rocket engine at a uniform mass flow rate with the 65 
injection pressure slightly higher than that required for 
this mass flow rate through the injector. When this oc- 
curs the chamber pressure is increased beyond that com- 
mensurate with the mass flow rate at the metering point. 
Because this higher chamber pressure cannot be main- 
tained for the metered flow rate, the chamber pressure 
must necessarily drop beyond the normal value. This pro- 
vides an excessive pressure differential, and the oscilla- 
tion continues on a self-excited basis. 
with the present invention these oscillations cannot readily 
With an injector element constructed in accordance 75 
a source of propellant at a substantially constant pres- 
sure, 
an injector element in communication with said source 
having an orifice at one end of the combustion cham- 
ber for directing pressurized propellant, said injector 
element comprising 
a fixed tubular member having a peripheral sur- 
face extending about a centrally disposed bore 
for conveying propellant and injecting the same 
as a cylindrical stream into the combustion 
chamber, 
a movable member having a mating surface facing 
said peripheral surface for forming said orifice 
so that propellant is injected in the form of a tu- 
bular stream about said cylindrical stream, said 
movable member being slidably mounted on 
said fixed tubular member for reciprocable 
movement toward and away from the combus- 
tion chamber to  change the spacing between 
said surfaces, and 
3,408,816 
means responsive to cha s in propellant density for 
sliding said movable member along said k e d  tubular 
member thereby varying the cross-sectional area of 
said orifice so that the mass flow rate of propellant 
remains substantially constant as the propellant tem- 6 
perature changes. 
2. Apparatus as claimed in claim 
an orifice plate adjacent an end of the combustion 
a sleeve rigidly secured to said orifice plate, said sleeve 
being slidably mounted on the fixed tubular member. 
3. Apparatus as claimed in claim 2 wherein the fixed 
tubular member has a tapered peripheral surface ad- 
jacent the end thereof at the combustion chamber and 15 
the orifice plate has a centrally disposed opening for 
receiving said end of the tubular member thereby forming 
an annular orifice, said opening having a contoured sur- 
face for mating with said tapered surface. 
"- 4: Apparatus as claimed in claim 3 wherein the injector 20 
element includes biasing means for moving the sleeve 
along the k e d  tubular member away from the combus- 
tion chamber thereby moving the orifice plate toward 
able member comprises: 
chamber, and 10 
the tubular member to m the contoured surface to- 
ward the tapered surface to decrease the size of the 
orifice. 
5. Apparatus as claimed in claim 4 wherein the biasing 
means comprises a compression having one end operably 
connected to a sleeve and the other end operably con- 
nected to the tubular member so that said spring is com- 
pressed when the orifice plate moves away from the tubu- 
lar member to increse the cross-sectional area of the 
orifice. 
eferences Cited 
UNITED STATES PATENTS 
2,513,720 711950 Hallinan _ _ _ _ _ _ _ _ _ _ _ _  239-75 
2,775,484 12/1956 Fox _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  239-75 
2,995,008 811961 Fox _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  60-240 
3,150,485 9/1964 Hickerson _ _ _ _ _ _ _ _ _ _ _  60-258 
3,232,049 2/1966 Rhodes _ _ _ _ _ _ _ _ _ _ _ _  60-39.27 
3,323,308 611967 Greco _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  60-240 
3,344,605 1011967 Mageean _ _ _ _ _ _ _ _ _ _ _ _  60-258 
MARTIN P. SCHWADRON, Primary Examiner. 
DOUGLAS HART, Assistant Examiner. 


Rocket engine injector Patent

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