US-20260126014-A1 - METHOD AND SYSTEM FOR STARTING AN AERONAUTICAL TURBINE ENGINE HAVING A FREE TURBINE AND A SINGLE-SPOOL GAS GENERATOR

US20260126014A1US 20260126014 A1US20260126014 A1US 20260126014A1US-20260126014-A1

Abstract

Method for starting an aeronautical free turbine and single-spool gas generator turbomachine, in which to ensure, under the control of a turbomachine regulation computer, the startup of the turbomachine solely from a battery delivering a nominal direct voltage of 28V, two electric machines attached to the same accessory gearbox mechanically linked to the gas generator of the turbomachine and mounted in parallel on the battery are actuated sequentially, the first electric machine being started under a starting torque allowing an increase in the speed of the gas generator with a determined minimum acceleration, and the second electric machine being started only after detection of the ignition of the combustion chamber of the gas generator.

Inventors

Vincent POUMAREDE
Sylvain Pierre Votie
Lucie Stéphanie APOSTIN

Assignees

SAFRAN HELICOPTER ENGINES

Dates

Publication Date: 20260507
Application Date: 20240214
Priority Date: 20230214

Claims (10)

1 . A method for starting an aeronautical free turbine and single-spool gas generator turbomachine, wherein to ensure, under the control of a turbomachine regulation computer, the startup of the turbomachine solely from a battery delivering a nominal direct voltage of 28V, two electric machines attached to the same accessory gearbox mechanically linked to the gas generator of the turbomachine and mounted in parallel on the battery are actuated sequentially, the first electric machine being started under a starting torque allowing an increase in the speed of the gas generator with a determined minimum acceleration, and the second electric machine being started only after detection of the ignition of the combustion chamber of the gas generator and before reaching a critical speed corresponding to the maximum resisting torque of the gas generator, the sum of the starting torques developed by the two electric machines being sufficient to guarantee in all circumstances that the torque margin at the maximum drag point corresponding to the maximum resisting torque of the gas generator is positive.
2 . The starting method according to claim 1 , wherein, once the ignition of the gas generator combustion chamber is detected, to start the second electric machine before reaching the critical speed, it is further verified that the rotation speed of the gas generator is greater than a predetermined minimum speed N1 or that the acceleration of the gas generator is smaller than a predefined acceleration threshold DN2.
3 . The starting method according to claim 2 , wherein the predetermined minimum speed N1 is defined so as to ensure moderate acceleration of the gas generator in a preferred combustion chamber ignition window, and the predefined acceleration threshold DN2 is calculated so as to avoid a phenomenon of stagnation of the gas generator in a speed area corresponding to the maximum drag torque.
4 . The starting method according to claim 1 , wherein the turbomachine regulation computer stops the first and second electric machines when, the maximum drag point having been exceeded, the speed of the gas generator of the turbomachine has reached a threshold from which the gas generator is capable of accelerating on its own to idle speed.
5 . A system for starting an aeronautical free turbine and single-spool gas generator turbomachine, a turbomachine regulation computer controlling the startup of the turbomachine solely from a battery-delivering a nominal direct voltage of 28V, wherein it comprises two electric machines attached to the same accessory gearbox mechanically linked to the gas generator of the turbomachine and mounted in parallel on the battery, the turbomachine regulation computer being configured to sequentially actuate the two electric machines, the first electric machine being started under a starting torque allowing an increase in the speed of the gas generator with a determined minimum acceleration, and the second electric machine being started only after detection of the ignition of the combustion chamber of the gas generator and before reaching a critical speed corresponding to the maximum resisting torque of the gas generator, the sum of the starting torques developed by the two electric machines being sufficient to guarantee in all circumstances that the torque margin at the maximum drag point corresponding to the maximum resisting torque of the gas generator is positive.
6 . The starting system according to claim 5 , wherein the first and second electric machines are two identical 28V brushed starter-generators each equipped with their regulation gearbox.
7 . The starting system according to claim 5 , wherein the first electric machine is a 28V series starter and the second electric machine is a 28V brushed starter-generator equipped with its regulation gearbox.
8 . The starting system according to claim 5 , wherein each of the two electric machines is respectively connected to the battery by an associated starting contactor.
9 . A rotary-wing or fixed-wing aircraft turbomachine comprising a starting system according to claim 5 .
10 . A rotary-wing or fixed-wing aircraft comprising at least one turbomachine according to claim 9 .

Description

TECHNICAL FIELD The present invention relates to the field of the control of the startup of the aircraft turbomachines and more particularly concerns a method and a system for starting an aeronautical free turbine and single-spool gas generator turbomachine. PRIOR ART Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various carbon emission constraints have been, are being, or will be adopted by various states. Particularly, an ambitious standard applies at the same time to the new types of aircrafts and to those currently in operation, requiring the implementation of the technological solutions in order to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to contribute to the fight against climate change. Technological research efforts have already led to very significant improvements in the environmental performance of the aircrafts. The Applicant takes into account the impacting factors in all phases of design and development to obtain less energy-intensive and environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental impacts, with the aim of improving the energy efficiency of these aircrafts. Consequently, the Applicant is constantly working to reduce the climate impact through the use of virtuous development and manufacturing methods and processes that minimize the greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of the activity. These ongoing research and development works focus on the new generations of aircraft turbomachines, the aircraft weight reduction, in particular through the materials used and the lighter onboard equipment, the development of the use of the electric technologies ensuring the propulsion and, as an essential complement to the technological progress, the aviation biofuels. It is known that medium-powered turbomachines (typically comprised between 1,500 and 4,500 kW on the engine shaft) are complex to start because their gas generator has a large drag torque, due in particular to significant mechanical friction and to high compressor pressure ratio, air flow rate and power take-off due to the accessories driven by the gas generator (oil and fuel pumps in particular). The startup of these turbomachines therefore generally requires either a pneumatic starter or a high-powered high-voltage electric starter (for example powered with 115V AC/ 400 Hz). In both cases, the use of an auxiliary power generator (APU for Auxiliary Power Unit) as a source of pneumatic or electric power, on board the aircraft and previously started, is inevitable, which considerably complicates the architecture of the aircraft systems, therefore the overall mass and costs (in particular the costs of acquiring and overhauling the APU). To avoid the use of an APU to start such a medium-powered turbomachine, it is known to resort to a gas generator called two-spool gas generator, consisting of two distinct coaxial compressor-turbine shafts and of the bearing housings supporting these shafts, usually referred to as HP (High-Pressure) spool and LP (Low-Pressure) spool respectively. The starting torque required to start such a turbomachine is then equivalent to that of a low-powered single-spool turbomachine, since the starter only has to drive the HP spool of the gas generator. Thus, and as shown in FIG. 6, provided that it is powered by a battery of sufficient capacity, a 28V brushed starter-generator with a power of 12 kW/400 A nominal in generation is capable of providing a starting torque 80 sufficient to compensate for the moderate drag torque 82 of the HP spool characteristic of a two-spool architecture, in particular at the critical speed (point A) where this drag torque is maximum (positive acceleration margin M2). On the other hand, during the startup of an equivalent single-spool turbomachine, the larger drag torque 84 specific to this architecture may exceed the starting torque that such a 12 kW/400 Astarter-generator can provide, in particular under detrimental ambient conditions (such as very low air, fuel and oil temperatures that maximize the resisting torques of the compressor and pumps), resulting in a negative acceleration margin M1 at the point of maximum drag torque (point B) and therefore the impossibility of starting the turbomachine in its entire desired startup range. Furthermore, all things being equal, a two-spool turbomachine is significantly more complex from a mechanical point of view, more bulky, heavier, and more expensive than a single-spool turbomachine of equivalent performance, in particular due to the two coaxial shafts that constitute its gas generator. Thus, there is a need for a simpler starting system than the existing ones, that is to say not requiring the addition of an APU or a two-spool architecture, and which therefore requires, in particular wit