US3297914A

US3297914A - Glow plug igniters

Info

Publication number: US3297914A
Application number: US370992A
Authority: US
Inventors: John A Saintsbury
Original assignee: United Aircraft of Canada Ltd
Current assignee: Pratt and Whitney Canada Corp
Priority date: 1964-05-28
Filing date: 1964-05-28
Publication date: 1967-01-10
Anticipated expiration: 1984-01-10

Description

Jan. 10, 1967 J. A. SAINTSBURY GLOW PLUG IGNITERS Filed May 28, 1964 I m mm mm VIII N A S A n In 0 I.

ATTORNEY United States Patent 3,297,914 GLOW PLUG IGNITERS John A. Saintsbury, St. Bruno, Quebec, Canada, assignor to United Aircraft of Canada Limited, Longueuil, Quebec, Canada Filed May 28, 1964, Ser. No. 370,992 6 Claims. (Cl. 317-98) This invention relates to igniters, and more particularly to glow plug igniters for use in jet and turbine engines.

The classic igniter for internal combustion engines has been the spark plug which has been used for many years. This is still the major igniter used in gasoline engines. In fact, the large number of motor cars, busses and trucks which have been built and use gasoline engines has encouraged the continuing improvement of spark plugs. Thus, today spark plugs are reliable igniters of gasoline in internal combustion engines all over the world.

However, there are limitations to the abilities of spark plugs to function properly as desired in extreme conditions. At very low temperatures, and at high altitudes,

the use of spark plugs for igniting the heavier fuels is not all that is desired. For the newer engines such as jet engines, jet-turbine engines and turbine engines using liquid fuels, the spark plug has not functioned with the necessary reliability for use in aircraft.

Actually, there are several problems involved in igniting fuels in a combustion chamber for a jet or turbine engine. When the engine and the fuel are both cold, there is the problem of initial vaporization of the fuel. For ignition under these conditions, a long lasting, repetitive spark is required. High frequency oscillators for the generation of longer-lived sparks have been tried, but whether the spark is produced by high frequency oscillations or by high voltage AC. or DC, a large amount of auxiliary equipment is necessary to produce the spark.

Thus, in addition to not being sufficient reliable under adverse conditions, the use of spark plugs also requires the use of additional auxiliary equipment which occupies space and adds to the Weight and expense of the'equipment.

' Clearly, another form of igniter is needed for the ignition of fuels heavier than gasoline at low temperatures of engine, air and fuel.

Diesel engines use fuels which are heavier than gasoline, and use igniters for starting, particularly when cold. Generally, glow plugs are used in diesel engines to vaporize enough fuel at the start to initiate combustion. Thus, the natural substitute for spark plugs in the combustion chambers of other engines would appear to be the glow plug.

However, in the ignition of cold fuel in a cold com- 30 below Fahrenheit or lower. For example, it has been found that some glow plugs which operate suitably at higher ambient temperatures or with lighter weight fuels, would ignite only the small amount of fuel which came directly into contact with the heating element of the plug producing a torch of burning fuel emerging from the mouth of the glow plug, but not readily igniting the rest of the fuel in the combustion chamber. Of course, as the combustion chamber heats, combustion becomes general. But often, it is important to have virtually immediate ignition; or ignition in a matter of seconds.

It is the object of this invention to provide new and improved glow plugs adapted to promptly and reliably initiate combustion in a turbine engine combustion chamber.

Further objects and advantages will become apparent as the following description proceeds, which description should be considered together with the accompanying drawings in which:

FIG. 1 is a sectional view through a glow plug according to this invention;

FIG. 2 is a sectional view taken along line 22 of FIG. 1; and

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.

The prepared plug construction shown in FIGS. 1, 2 and 3 is illustrated as comprising a generally cylindrical metal houseing or shell 31 having a reduced portion adapted for mounting in an outer wall 32 such as the gas generator casing of a gas turbine engine. A heat insulating ceramic core 33 is contained in the shell 31 with a metal stop member 34 connected to the shell 31 at its outer ends to maintain the core 33 in position. A central bore in the core 33 has a larger diameter portion at its lower end. In the bore a metal conductor 36 is supported. The lower end of the conductor 36 fits within the larger diameter portion of the bore. A spiral heating element 42 is mounted on the shank portion of tthe conductor 36. A cross-shaped ceramic support 40 is supported in the shell 31 and, in turn, provides support for the heating element 42. This aids in preventing distortion of the heating element 42 at high temperatures. The support 40 has arms extending radially from a central core so as to provide regions between the arms where the igniting element is exposed to the interior of a cavity behind the support.

In use, the shell 31 is attached to the combustion chamber with the heating element 42 and extends in the combustion chamber itself with the lower end substantially flush with the combustion chamber wall 43 which is normally insulated by an air space from the wall 32. Being flush with the combustion chamber wall this allows collection of cold fuel in the cavity or fuel collection space behind the heating element 42. The free end of the conductor 36 is connected through an appropriate control system to one side of a source of electrical energy (not shown), the other side of the source being connected to the engine itself. When the circuit is closed, current passes'through the conductor 36, and the heating element 42 to the shell 31 and through the engine to the other side of the source. The heating element 42 then heats. Air passes through the small holes 44 in the shell 31 immediately behind the heating element 42 and through the heating element carrying with it some of the fuel which has been collected by the wall 43 and which has been vaporized by the heat from the element 42. The element 42 ignites the fuel-air mixture creating a torch-like flame that projects into the combustion chamber itself. The flame from the mouth of the glow plug quickly ignites the main body of fuel in the chamber and the flame is rapidly propagated. In addition, the heat radiating from the heating element 42 provides initial vaporization of some of the cold fuel in the combustion chamber and some of the vaporized fuel is mixed with air as it is drawn through the element 42. This, in turn, provides additional heat to vaporize additional cold fuel and more rapidly propagate the flame.

The presence of the holes 44 in the shell 31 immediately behind the heating element 42 provides a means for air to circulate through the heating element 42 drawing vaporized fuel with it. This enables the heating element 42 to be shielded from the direct action of the stream of fuel being admitted to the combustion chamber and serves to protect it from adverse reactions with the fuel and rapid quenching which would take place if the cold liquid fuel impinged directly onto the heating element Patented Jan. 10, 1967 42. Also, as the fuel-air mixture circulates through the holes 44 and the heating element 42 out into the combustion chamber, a flame is projected into the combustion chamber which promotes rapid ignition. The air flow provided by the 4 holes during combustion operation serves to keep heating element cool, which results in prolonged element life.

The heating element 42 itself is formed similarly to the heating elements of automobile cigarette lighters and may be made, for example, of an alloy of about 22% chromium, 5.4% aluminum, and the balance iron. Such an alloy has a melting point of about 2650 F. and can easily withstand operating temperatures in the neighbourhood of 23002400 F. A current of about 7.5 amperes through the heating element 42 will produce ignition in less than 18 seconds with fuel and ambient temperatures at about -20 F.

The actual connection of the heating element 42 to the central conductor 36 can be made as shown by slotting the end of the conductor and inserting the inner end of the coil or alternatively the inner end of the heating coil can be spot welded or brazed in position. Preferably a gap of from about .015 to .035 is left between the outer coil of the heater element and the inner wall of the housing 31.

The above specification has described and illustrated a new igniter for igniting the fuel in combustion chambers of jet engines, turbine engines, and the like. The

igniter described is particularly reliable when the temperature at which it is required to operate is below zero degrees Fahrenheit.- Since it is realized that the above description may indicate to others in the field further ways in which the principles of this invention may be used without departing from its spirit, it is intended that this invention be limited ony by the scope of the appended claims. A l

I claim:

1. An igniter for a gas turbine engine having a combustion chamber wall and a casing surrounding and spaced from said Wall and in which fuel is required to be ignited rapidly at low temperatures without preheating the fuel, said igniter comprising:

a hollow generally cylindrical housing having an open end adapted for mounting in said combustion chamber wall so that the interior of the housing is in communication with said combustion chamber, and mounting means rearwardly spaced from said open end and adapted for sealing engagement with said casing,

a core of thermal and electrical insulating material extending within said housing short of said open end so as to leave an exposed cavity within said housing and said open end,

an igniting element of high temperature, electrically conducting material mounted within said cavity adjacent the open end thereof,

said igniting element being disposed generally in a radial plane and having a front surface facing towards the interior of said combustion chamber and a parallel rear surface, and having one end electrically connected to said housing and its other end connected to an electric conductor extending through said core,

a support of heat resistant, electrically insulating material positioned Within said cavity adjacent the rear surface of said igniting element so as partly to cover and support said rear surface,

said support being spaced from the floor of said cavity so as to provide a fuel collection space behind said support, a peripheral wall on said housing surrounding said cavity, said wall having a plurality of apertures allowing radial communication of said space with the space between said combustion chamber wall and said casing,

said support being shaped so as to expose part of the rear surface of said igniting element to the interior of said fuel collection space.

2. An igniter as claimed in claim 1 wherein said apertures lie behind so as to be covered by part of said support.

3. An igniter as claimed in claim 1 wherein said support includes a central core and a plurality of arms extending radially from said core so as to leave circumferential spaces between the arms where said igniting element is exposed to the interior of said fuel collection space.

4. An igniter as claimed in claim 3 wherein said support is a generally cross-shaped piece of ceramic material.

5. An igniter as claimed in claim 1 wherein said heating element is made as a spiral coil with said conductor connected to the inner end of said spiral.

6. In a gas turbine engine having a combustion chamber in which fuel is required to be ignited rapidly at low temperatures without preheating the fuel, a combustion chamber Wall and a casing surrounding. and spaced from said wall, an igniter comprising:

a core .of thermal and electrical insulating material extending within said housing short of said open end so as to leave an exposed cavity within said housing and said open end,

said support, being shaped so as to expose part of the rear surface of said igniting element to the interior of said fuel collection space.

References Cited by the Examiner UNITED STATES PATENTS 1,362,227 12/1920 Clark Q. 219-270 1,763,343 6/1930 Cohen 317-98 1,945,597 2/ 1934 Cohen 219-270 2,484,544 10/1949 Bennett et al. 2l9270 2,966,941 1/ 1961 Breese et a1. 317-83 X 3,017,541 1/1962 Lawser 317-98 3,235,707 2/ 1966 Horwitt 219270 FOREIGN PATENTS 1,310,590 10/1962 France.

806,357 12/1958 Great Britain.

RICHARD M. WOOD, Primary Examiner.

V. Y. MAYEWSKY, Assistant Examiner.

Claims

1. AN IGNITER FOR A GAS TURBINE ENGINE HAVING A COMBUSTION CHAMBER WALL AND A CASING SURROUNDING AND SPACED FROM SAID WALL AND IN WHICH FUEL IS REQUIRED TO BE IGNITED RAPIDLY AT LOW TEMPERATURES WITHOUT PREHEATING THE FUEL, SAID IGNITER COMPRISING: A HOLLOW GENERALLY CYLINDRICAL HOUSING HAVING AN OPEN END ADAPTED FOR MOUNTING IN SAID COMBUSTION CHAMBER WALL SO THAT THE INTERIOR OF THE HOUSING IS IN COMMUNICATION WITH SAID COMBUSTION CHAMBER, AND MOUNTING MEANS REARWARDLY SPACED FROM SAID OPEN END AND ADAPTED FOR SEALING ENGAGEMENT WITH SAID CASING, A CORE OF THERMAL AND ELECTRICAL INSULATING MATERIAL EXTENDING WITHIN SAID HOUSING SHORT OF SAID OPEN END SO AS TO LEAVE AN EXPOSED CAVITY WITHIN SAID HOUSING AND SAID OPEN END, AN IGNITING ELEMENT OF HIGH TEMPERATURE, ELECTRICALLY CONDUCTING MATERIAL MOUNTED WITHIN SAID CAVITY ADJACENT THE OPEN END THEREOF, SAID IGNITING ELEMENT BEING DISPOSED GENERALLY IN A RADIAL PLANE AND HAVING A FRONT SURFACE FACING TOWARDS