Gas generator and turbojet fitted with such a generator for starting

1. A gas generator comprising a casing forming at least a portion of a ring and housing a pyrotechnic charge;

the casing having at least a semi-annular shape with respect to a longitudinal axis for integration with a rotary machine and comprising:

coaxially inner and outer curved wall portions radially disposed with respect to the longitudinal axis,

forward and rearward wall portions spaced axially from each other with respect to the longitudinal axis and connecting the inner and outer curved wall portions,

the inner and outer curved wall portions and the forward and rearward wall portions defining a chamber therein, the chamber spaced radially from the longitudinal axis and extending circumferentially with respect to the longitudinal axis, the forward and rearward wall portions defining an axial width of the chamber, and

at least one opening for ejecting the gas produced during combustion of the charge; and

the pyrotechnic charge comprises a plurality of discrete unit charge elements, wherein:

the discrete unit charge elements are disposed in serial succession circumferentially along the circumferential extent of the chamber,

serially adjacent ones of the discrete elements are separate from each other at discrete locations spaced circumferentially along the circumferential extent of the chamber, and

each of the discrete unit charge elements has a width that fits substantially within the axial width of the chamber to hold the elements in position axially between the forward and rearward wall portions.

2. A gas generator according to claim 1 , wherein the pyrotechnic charge is made up of a plurality of unit charge segments spaced apart from one another by means of resilient spacer elements.

3. A gas generator according to claim 1 , wherein the pyrotechnic charge is constituted by a chain made up of a succession of unit charge elements.

4. A gas generator according to claim 1 , wherein the unit charge elements are disposed in a chain on at least one connection cable and are held spaced apart from one another on the cable by spacers.

5. A gas generator according to claim 1 , including at least one ignitor fixed to the casing to control ignition of the pyrotechnic charge.

6. A gas generator according to claim 1 , wherein the casing presents an opening enabling the pyrotechnic charge to be introduced into the casing, the opening being provided with a shutter element.

7. A gas generator according to claim 1 , wherein the casing is made of a metal material or a thermostructural composite material.

8. A turbojet comprising a compressor and a turbine constrained to rotate together, the turbojet including a gas generator comprising:

a casing forming at least a portion of a ring and housing a pyrotechnic charge, the casing having at least one opening for ejecting the gas produced during combustion of the charge, and wherein the pyrotechnic charge is made up of a plurality of unit charge elements disposed one behind the other inside the casing;

the generator being disposed in the vicinity of the compressor or the turbine so as to entrain them in rotation with the gas produced during combustion of the propellant charge.

9. A turbojet according to claim 8 , wherein the gas generator is placed in the vicinity of the turbine.

10. A turbojet according to claim 9 , wherein the casing of the generator is fixed on the converging portion of the nozzle shroud and the generator further including means for conveying the gas produced in the casing to the blades of the turbine.

11. A turbojet according to claim 8 , wherein the gas generator is placed in the vicinity of the compressor.

12. A turbojet according to claim 11 , wherein the casing of the generator is constituted by a compressed air feed torous of said turbojet.