High temperature spark plug for igniting liquid rocket propellant

Watson, J. E.

English

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REPLY ro 
ATTN OF: GP 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 
October 12, 1970 
TO : USI/Scientific & Technical Information Division 
Attention:: Miss Winnie M. Morgan 
FROM : 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 U S 1  memorandum on this subject, dated June 8, 1970, 
the attached NASA-owned U.S. patent is being forwarded for 
abstracting and announcement i n  NASA STAR. 
The following information is provided: 
U , S ,  Patent No, :: 3,229,139 
Corporate Source : Lewis Research Center 
Supplementary 
Corporate Source I 
NASA Patent Case NO,: XLE-00660 
I 
Gayle Parker 
Enclosure: 
Copy of Patent 
NASA-HQ 
https://ntrs.nasa.gov/search.jsp?R=19700030609 2020-03-17T02:10:00+00:00Z
an. 11, 1966 J. E. WATSON 
HIGH TEMPERATZRE SPARK PLUG 
Filed Oct.  18, 1962 
BY 
3 , 2 ~ 9 ~ 1  
INVENTOR 
JOHN E. WATSON 
A ? !  P a  
ATORNEY S 
3,229,139 states patent Office Patented Jan. 11, 1966 
1 
3,229,139 
HIGH TEMPERATURE SPARK PLUG 
John E. Watson, Cleveland Heights, Ohio, asskuor to the 
United States of America as represented by the Admin- 
istrator of the National Aeronautics and Space Ad- 
ministration 
Filed Oct. 18, 1962, Ser. No. 231,604 
1 Claim. (CI. 313-11.5) 
(Granted under Title 35, U.S. Code (1952), sec. 266) 
The invention described herein may be manufactured 
and used by or for the Government of the United States 
of America for governmental purposes without the pay- 
ment of any royalties thereon or therefor. 
This invention relates to an improved ignitor plug and, 
more particularly, to an ignitor plug that is capable of 
operating in an extremely hot environment. 
Present day devices, such as Liquid fueled ,rockets, op- 
erate at very high temperatures, such as 4500" F. or even 
higher, and utilize ignitor plugs for ignition. For  reli- 
ability in rocket firing these ignitor plugs should have a 
reasonable life expectancy even when exposed to such 
high temperatures. 
I t  has been found that the conventional spark plugs 
that are customarily used to ignite the rocket propellants 
have an expected life that is measured in seconds at these 
high temperatures. This necessitates frequent replace- 
ment and may even result in ignition failure. 
In order to solve the ignition problems inherent with 
the conventional spark plugs, the present invention utilizes 
an ignitor plug having an electrically conductive annular 
electrode of a temperature resistant material, and this 
electrode encloses the base of the plug casing to shield 
the center electrode. The annular electrode forms a 
chamber adjacent the innermost end of the center elec- 
trode, and an aperture in the annular electrode that is 
aligned with the center electrode provides gaseous com- 
munication between the plug exterior and the center elec- 
trode. 
2 
tween the nut 21 and insulator 12 in a conventional man- 
ner. 
Threads 23 formed on the exterior surface of the casing 
12 at  the base thereof adjacent the annular electrode 13 
6 enable the ignitor plug 10 to be mounted in an aperture 
in an electrically conducting wall of a combustion cham- 
ber. When the ignitor plug 10 is so installed it is in 
physical and electrical contact with the combustion cham- 
ber wall, and the annular electrode 13 is the only part ex- 
tending from the inner surface of this wall into the com- 
bustion chamber where the surface 19 is exposed to flame 
impingement from the burning gases. 
According to the present invention the annular electrode 
13 is made of graphite in the form of a disc that is rigidly 
15 mounted at the base of the plug 10 by crimping the bottom 
surface of the casing 11 adjacent the threads 23. The an- 
mlar  electrode 13 is able to withstand a temperature in 
excess of 7000" F. and serves to shield the exposed por- 
tion 17 of the center electrode 16 together with the ceramic 
20 insulator 12 from the high temperatures of the burning 
gases while enabling the ignitor plug 10 to produce the 
required spark for igniting the propellant in the cornbus- 
tion chamber. This spark arcs across the gap between 
the cylindrical exposed portion 17 adjacent the bottom 
25 surface 18 and the annular shoulder formed by the 
intersection of the conical surface. 14 and the cylindrical 
aperture 15. 
As is shown in the drawing, the bottom surface 18 of 
the center electrode 16 is generaily coplanar with this an- 
30 nular shoulder, and for optimum spark propagation a 
clearance of about 0.025 inch to about 0.050 inch between 
the exposed portion 17 and the surface of the aperture 15 
is required although a satisfactory spark will be produced 
when this gap is in the range of between about 0.01 inch 
35 and about 0.15 inch. The exposed portion 17 of the elec- 
trode 16 is in gaseous communication with the outer sur- 
face of the ignitor plug 10 through the cylindrical aperture 
15, and this enables the spark to ignite the propellant 
in the combustion chamber. 
It is. therefor, an obiect of the present invention to pro- 40 Although the preferred embodiment of the invention 
vide an improved igd;ttor plug f i r  high temperature-op- 
eration that has a life expectancy that is measured in hours 
or days rather than seconds. 
Another 'object of the invention is to provide an im- 
proved ignitor plug structure having no metallic parts 
exposed to direct flame impingement. 
Other objects and advantages of the invention will be 
apparent from the drawing and specification which fol- 
lows. 
The drawing is a vertical section through an ignitor plug 
constructed in accordance with the present invention. 
An ignitor plug 10 shown in the drawing has a tubular 
metal shell or casing 11 that is electrically conducting. An 
elongated ceramic insulator 12 i s  positioned within the 
longitudinal bore of the casing 11. 
An annular electrode 13 is positioned at the base end 
of the casing 11 and a conical surface 14 thereof faces 
toward the insulator 12. AR aperture 15 at the center of 
the annular electrode 13 is generally coaxial with the bore 
of the casing and an elongated center electrode 16 extends 
through the insulator 12 along the axis thereof in coaxial 
relationship with the aperture 15. 
The inner end of the center electrode 16 extends beyond 
the insulator 12 to provide an exposed portion 17 adjacent 
the annular electrode 13, and this portion has a bottom 
surface 18 immediately adjacent the aperture 15. 'The 
bottom surface 18 of the center electrode 16 is recessed 
from the exterior surface 19 of the electrode 13 that is 
exposed to the extremely hot temperatures of the com- 
bustion flame. The upper end of the center electrode 16 
opposite the exposed portion 17 is threaded at 20 to re- 
ceive a terminal nut 21. A washer 22 is interposed be- 
has been disclosed and described, it will be apparent that 
various structural modifications and changes may be made 
to the ignitor plug 10 without departing from the spirit 
of the invention or from the scope of the subjoined claim. 
45 For example, the inwardly directed surface 14 of the an- 
nular electrode 13 may be planer instead of conical as 
shown in the drawing. Likewise, the exterior surface 18 
may be tapered to provide a thinner cross-sectioil which 
would store less heat. 
Additionally, the exterior surface 19 may be coated with 
50 a ceramic oxide, such as zirconium oxide. With such a 
coating the. annular electrode 13 can be either graphite 
or a refractory metal such as tungsten. 
While the center electrode 16 is preferably steel, a high 
55 temperature refractory metal, such as molybdenum or 
tungsten may be used. In some applications this electrode 
may also be made from graphite. 
What is claimed is: 
An ignitor for use in a high temperature environment 
60 in excess of 4500" F. in the combustion chamber of a 
liquid fueled rocket comprising 
a tubular metal shell having means for mounting the 
same in the wall of the rocket combustion chamber, 
an insulator at least partially disposed within said shell, 
a graphite annular electrode disposed at one end of 
said tubular shell and extending therebeyond into 
the rocket combustion chamber, said annular eiec- 
trode being provided with a recessed portion on the 
inner side thereof facing said tubular shell a d  hav- 
ing a cylindrical aperture in axial alignment wirh said 
insulator for placing the recessed portion in corn. 
65 
70 
3,229,139 
3 
munication with the outer surface of said annular 
electrode in the rocket combustion chamber, said 
cylindrical aperture b&g provided with an annular 
shoulder adjacent said recessed portion, and 
a graphite rod having a diameter smaller than that of 
said cylindrical aperture forming a center electrode 
extending coaxially through said insulator and beyond 
the end thereof to provide an exposed portion ad- 
jacent said recessed portion, the end of said exposed 
portion remote from said insulator being coplanar 
with said shoulder on said annular electrode and 
spaced therefrom for providing a spark gap, said 
annular electrode serving to shield said exposed por- 
tion of said centef electrode from high temperature 
burning gases in the rocket combustion chamber. 
4 
References Cited by the Examiner 
UNITED STATES PATENTS 
1,568,62 1 1 1 1926 Rabezzana. 
1,987,612 111935 Fernandez _ _ _ _ _ _ _ _  313-139 X ' 2,088,945 811937 Xardell _ _ _ _ _ _ _ _ _ _  313-138 X 
2,391,458 1211945 Hensel _ _ _ _ _ _ _ _ _ _  313-311 X 
2,406,172 8/1946 Smithells. 
2,871,389 111959 Skunda _ _ _ _ _ _ _ _ _ _  313-141 X 
3,061,756 1011962 Henderson _ _ _ _ _ _ _ _ _ _  313-311 
10 
GEORGE N. WESTBY, Primary Examiner. 
JOHN W. HUCKERT, Exunziner. 
P. C. DEMEO, Assistant Exumfner. 
15 


High temperature spark plug Patent

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