US2933896A - Ignition devices for combustion chambers - Google Patents

Description

F. G. M. FERRIF:

IGNITION DEVICES FOR COMBUSTION CHAMBERS April 26, 1960 2 Sheets-Sheet 1 Filed June 4, 1956 INVENTDR Fnnucw GM. FERm fig,

nTTaeA/ Y8 1 April 1960 F. G. M. FERRIE 2,933,896

IGNITION DEVICES FOR COMBUSTION CHAMBERS Filed June 4, 1956 2 She ets-Sheet z l /g' I I. 0 4 J Q 27 mveu'ron 7 FRANCK G.M.FER'RI ATTORNEYS IGNITION DEVICES FOR COMBUSTION CHAMBERS Franck G. M. Ferri, Cachan, France, assignor to Societe Nationale dEtude et de Construction de Moteurs dAviation, Paris, France, a French company Application June, 4, 1956, Serial No. 589,146 Claims priority, application France JuneS, 1955 Claims. (31. 6039.82)

For the ignition of combustion chambers and particularly in the case-of turbo-machines and reaction jet propulplugs fed by systems of the so-called high energy type,

I the usual high-tension systems not being adequate to addition, the complexity" of the parts of the high energy system increases the possibilities of breakdown and this tion units. g

The present invention has for its object and improved ignition device whichis simple and reliable in operation, based on the action of a resistance which can be brought up to red heat under the effect of the passage of an electric current.

A device of this kind is particularly suitable for the ignition of combustion chambers of reaction propulsion effected withcertainty, whatever may be the conditions of altitude, speed, temperature, etc.

In a turbo-jet unit for example, the conditions of flow of the air and the fuel are very variable: for example the speed of the air at the delivery of the compressor may,

nited States ateiitff O sion units, there are used at the present time sparking especially necessitates their provision in duplicate on reacunits in which the ignition and the re-ignition must be I increase from 20 to 90 m./sec. at the moment of ignition. A normal type of resistance which would heat up sufficiently to ignite the fuel in a flow-of-air of 90 metres per sec. would be liable to disintegrate in a flow of 2 metres per'seci; conversely, a resistance suitable for. producing the ignition in a flow of 20 metres per sec.

would be likely to remain black at 90 metres per sec. and

would thus not achieve the desired result.

In-addition, the voltage generated by the source provided on board an aircraft may sometimes vary as much as two-fold, which would result, depending on the case,

in the resistance remaining black or, on the contrary, being heated to a prohibitive temperature.

The device in accordance with the present invention is intended to ensure a' satisfactory ignition and re-ignition, as independently as possible of the following factors:

(1) Speed of flow of the compressed air;

(2) The temperature of this air (which may ditfer from the temperature on the ground: for example upto a value of -56 C.);

(3) The quantity of fuel discharged on the resistance by the starting injectors;

(4) The temperature of this'fuel;

(5) The difference of potential at the terminals of the device (the difference of potential being capable of varying for example between 18 and 30 volts).

Finally, the device in accordance with the invention is adapted to produce ignition in a few seconds whatever the values of the variable factors referred to above may be.

In accordance with a preferred form of embodiment of the invention, the ignition device comprises a resistance which takes the form of a spindle or a small rod (this type of resistance will be simply called a rod in the description which follows) constituted by an appropriate sintered material, for example .with a base of a refractory carbide, having the required ohmic value and a satisfactory behaviour at high temperatures and in corrosive media. Sintered materials of this kind are commercially available, and the applicants have obtained particularly satisfactory results with silicon carbide.

The description which follows below with reference to the accompanying drawings (which are given by way of example only and not in any sense byway of limitation) Fig. 1.

Fig. 3 shows an-alternative form of construction.

Fig. 4 shows a further alternative form of embodiment.

Figs. 5 and 6 are cross-sections taken along the lines V-V and VI-VI of Fig. 4.

In accordance with the invention, the electric resistance is formed by a rod of sintered material, for example with a base of silicon carbide, the supply voltage being applied to the extremities of this rod. It should however be observed that other sintered metals would also be suitable for the construction of this rod. I

Figs. 1 and 2 show a form of embodiment in which two rods 11 and 12 of dilferentresistances are arranged side by side.

These rods comprise an end portion 11a-12a engaged against the pressure-of springs 13, 14, in housings 15, 16 formed in a metallic member 19 which is connected by a terminal 17 to a current-supply conductor 18. This metallic member 19 is enclosed in a casing 20 to which it is ,fixed by means of an insulating socket 21.

The rods 11 and 12 are housed-inside a metal skirt 22 'of cylindrical shape, two oppositely-facing windows 2323 being formed in the walls of this skirt, towards its lower extremity, so as to expose a certain length of the rods Hand 12. 'The cylindrical skirt 22 is ter- 'minated by a circular ba'se24, the internal surface of which is in contact with the extremities of the rods 11 and 12 which abut against this base due to the action of the springs 13, '14, even in the case of expansion or other deformation. i

The device which has just been described operates in the following way:

When it is desired to effect the ignition or the re-ignition of the combustion chamber in which the device is mounted, the current-supply conductor 18 is placed under tension, the return being effected through the skirt 22 to earth. The rods 11 and 12 of different resistance and connected in parallel, 'thushave current passed through them. The passage of this current normally heats up the rod 11 having the least resistance, to red heat, but leaves black or dark red only the rod 12 having a higher resistance, which is'simply heated.

The fuel, or the mixture of air and fuel which comes into contact with the rods by passing through the windows 23-23 is vaporised by the hot but not incandescent rod 12 and is then ignited by the rod 11 which is heated to bright red heat. By virtue of this arrangement, the ignition isensured in a very effective manner, whatever the external conditions may be. In addition, in case of a defect or damage to one of the rods, 11 for example, the ignition is then effected by the rod 12 which is finally be employed. Two or more rods with separate supply systems could also be utilised. I

Fig. 3 shows an alternative formof this kind comprising two rods 11 and 12 mounted in an insulating member 19' and connected to independent supply-current leads and 26, the return circuits being made through the skirt 22 to earth as in the previous case. In this case, the two rods can be put into operation either at the same time as in the case 'of Fig. l, or selectively for different ranges of supply voltage; the rod 11 being connected when the voltage is from 18 to 22 volts for example, and the rod 12 for a voltage of 22 to volts.

Figs. 4 to 6 show a further alternative form'ofconstruction which furthermore may be combined with those which have been described with reference to Figs. 1

and 3. e

The rod 27 is in this case mounted at one extremity on a metallic member 28 which serves as a contact and in which is formed a channel 29 for the intake of fuel'discharged through the jets 30 directed on to the surface of the rod 27. The jets 30 are inclined and have a direction roughly tangential to the cylindrical surface of the rod 27 inorder to produce on this surface a spreadingout effect of the jets of fuel and, in consequence, a better atomisation of these jets. I V

The opposite extremity of the rod 27 is gripped by a split ring 31 housed in the base 24 of the skirt 22, 'the gripping action being obtained by means of'the screws 33 and the fixing of the ring 31 being effected by ascrew, 34. The base 24 is in the form 'of a dish and may collect a certain quantity of liquid.

A small quantity of fuel is projected by the vjetsf30 on to the surface of the rod 27, the small drops, which may thus form, fiow along the cylindrical rod and are collected in the dish-shaped base 24; a part of these drops is however evaporated by contact with the rod before reaching the dish. The evaporation of the fuel collected in this dish ensures the cooling'of the members 31 and 24.

The ignition device just described is fitted on the wall 35 of the combustion chamber whose axis is shown at X-X, so that the rod 27 extends partly into and across the air-fuel mixture fiow through'the combustion chamber.

It is to be observed that silicon carbideywhich is employed in "accordance with the inventionfa's the material. for the rods, has particularly interesting properties amongst which are specially useful: a high electrical .resistance for a short length and a very good behaviour at high temperatures of the order of 2,000.

In addition, the electrical resistance of these rods'varies to a great extent with temperature and the law of this variation is not linear as in the case of metallic resistances. This particular feature maybe used to advantage in order to obtain shorter ignition times than with metallic resistance.

It will of course be understood that modifications may bemade to the forms of embodiment which have just been described, in particular by the substitution of equivalent technical means, without thereby departing from the spirit or from the scope of the present invention.

What I claim is:

1. In an aircraft carrying a source of electric current, having a voltage liable to vary within a substantial range, an engine ignition device operated by said source comprising at least. two separate electrical resistors in the form of rods made of a sintered material adapted to stand high temperatures and corrosive media, the resistances of said rods being substantially different and so determined that the higher resistance rod becomes operative to ignite fuel when the voltage applied thereto is relatively high and the lowerresistance rod becomes operative when the voltage applied thereto is relatively low.

2. Device as claimed in claim 1 wherein the rods are insulated from each other and selectively energized in accordance with the voltage level.

3. In a jet propulsion unit, the combination of a combustion chamber through which an air-fuelmixture flows and an electrically-operating ignition device comprising a resistance rod made of a sintered material adapted. to stand high temperatures and corrosive media, said rod extendingpartly into and across said flow to be bathed thereby and being of substantially cylindrical shape, and a plurality offuel injecting nozzles around said rod, at

r a distance therefrom, said nozzles pointing in directions substantially tangent to the cylindrical surface of the rod.

'4. Device as claimed in claim 3 further comprising a metal skirt'partly surrounding the rod and having a bottom, spring means acting on said rod to urge an end there- .of into contact with .said bottom, an earth connection on said skirt, and a lead connection between the source and the opposite end of said rod.

5. The combination of claim 3, wherein the rod extends substantially vertically and the nozzles have outlet orifices located in a substantially horizontal plane, in the vicinity-of the upper end of the rod, said orifices pointing in .a downwardly inclined .direction.

References Cited in the .file of this patent UNITED STATES PATENTS 1,359 514 1,525,624 Suter Feb. 10, 19 25 1,903,364 Grant et al. Apr. 4, 1933 2,178,659 White Nov. 7, 1939 Carington Mar. 27, 1951

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