Device (10; 10'; 310; 410; 510; 610) for injecting a fluid into a mechanical system (1; 101; 201; 301; 401; 501; 601) liable to experience heating, the device comprising at least: - a body (20; 320; 420; 520; 620) containing a thermally initiable charge (40; 340; 440; 540; 640) that generates combustion gases, ignition of the charge being initiable under the action of an ignition command and/or under the effect of an application of heat, from a heated-up zone (Z24; Z324; Z424) of the body, to the charge, - a reservoir (60; 360; 460; 560; 660) containing the fluid, - means (30, 32, 34; 30'; 330, 332, 334; 430, 432, 434; 530, 590; 630, 690) for attaching the device (10; 10'; 310; 410; 510; 610) to the mechanical system (1; 101; 201; 301; 401; 501; 601), the attachment means being designed to place the reservoir (60; 360; 460; 560; 660) in fluidic communication with the mechanical system, and - means (36, 68; 336, 368; 436, 468; 568; 668) for delivering the pressurized fluid from the reservoir (60; 360; 460; 560; 660) by the direct action or the action via intermediate means (70, 72; 372; 472; 570, 572, 576, 579, 584; 670, 672, 676, 678, 679, 684) of the combustion gases, the means (36, 68; 336, 368; 436, 468; 568; 668) for delivering the pressurized fluid from the reservoir (60; 360; 460; 560; 660) comprising a non-fragmentable rupture seal (68; 368; 468; 568; 668), which initially closes the reservoir and ruptures when the pressure of the fluid in the reservoir (60; 360; 460; 560; 660) exceeds a predetermined pressure threshold, characterized in that the attachment means (30, 32, 34; 30'; 330, 332, 334; 430, 432, 434; 530, 590; 630, 690) comprise at least one injection fitting (30; 30'; 330; 430; 590; 690) equipped with an external screw thread (32; 332; 432) coated with an adhesive thread-locking film (34; 334; 434), in that the injection fitting (30; 30'; 330; 430; 530, 590; 630, 690) is made of a material which, on the one hand, has an elastic limit at 0.2% strain Re 0.2 comprised between 500 and 700 MPa and, on the other hand, a tensile strength Rmax comprised between 700 and 900 MPa, in that the rupture seal (68; 368; 468; 568; 668) is located in a volume delimited by the external screw thread (32; 332; 432) of the injection fitting (30; 30'; 330; 430; 590; 690), and in that the flow rate of pressurized fluid leaving the reservoir (60; 360; 460; 560; 660) is regulated with: - either the fluid being delivered evenly and continuously over a duration of several minutes; - or the fluid being delivered intermittently, in successive injections over several minutes. - a body (20; 320; 420; 520; 620) containing a thermally initiable charge (40; 340; 440; 540; 640) that generates combustion gases, ignition of the charge being initiable under the action of an ignition command and/or under the effect of an application of heat, from a heated-up zone (Z24; Z324; Z424) of the body, to the charge, - a reservoir (60; 360; 460; 560; 660) containing the fluid, - means (30, 32, 34; 30'; 330, 332, 334; 430, 432, 434; 530, 590; 630, 690) for attaching the device (10; 10'; 310; 410; 510; 610) to the mechanical system (1; 101; 201; 301; 401; 501; 601), the attachment means being designed to place the reservoir (60; 360; 460; 560; 660) in fluidic communication with the mechanical system, and - means (36, 68; 336, 368; 436, 468; 568; 668) for delivering the pressurized fluid from the reservoir (60; 360; 460; 560; 660) by the direct action or the action via intermediate means (70, 72; 372; 472; 570, 572, 576, 579, 584; 670, 672, 676, 678, 679, 684) of the combustion gases, the means (36, 68; 336, 368; 436, 468; 568; 668) for delivering the pressurized fluid from the reservoir (60; 360; 460; 560; 660) comprising a non-fragmentable rupture seal (68; 368; 468; 568; 668), which initially closes the reservoir and ruptures when the pressure of the fluid in the reservoir (60; 360; 460; 560; 660) exceeds a predetermined pressure threshold, - either the fluid being delivered evenly and continuously over a duration of several minutes; - or the fluid being delivered intermittently, in successive injections over several minutes.