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US-20260126013-A1 - METHOD AND SYSTEM FOR DUAL-VOLTAGE START OF AN AERONAUTICAL TURBINE ENGINE HAVING A FREE TURBINE AND A SINGLE-SPOOL GAS GENERATOR

US20260126013A1US 20260126013 A1US20260126013 A1US 20260126013A1US-20260126013-A1

Abstract

Method for starting an aeronautical free turbine and single-spool gas generator turbomachine of a twin-engine aircraft including two independent electrical networks each comprising a 28V battery selectively powering a starter-generator, in which, to ensure, under the control of a turbomachine regulation computer, the startup of the turbomachine first at a voltage of 28V by putting the two batteries in parallel and then at a voltage of 56V by putting them in series while avoiding too rapid acceleration of the gas generator, the serialization of the two batteries is ordered only once the combustion chamber of the gas generator is ignited and the speed of the gas generator is greater than a predetermined speed threshold N 1 for ensuring, through this serialization, a positive acceleration margin at the point of maximum drag of the gas generator.

Inventors

  • Vincent POUMAREDE
  • Sylvain Pierre Votie
  • Lucie Stéphanie APOSTIN

Assignees

  • SAFRAN HELICOPTER ENGINES

Dates

Publication Date
20260507
Application Date
20240213
Priority Date
20230214

Claims (10)

  1. 1 . A method for starting an aeronautical free turbine and single-spool gas generator turbomachine of a twin-engine aircraft including two independent electrical networks each comprising a 28V battery selectively powering a starter-generator, wherein to ensure, under the control of a turbomachine regulation computer, the startup of the turbomachine first at a nominal voltage of 28V by putting the two batteries in parallel and then at a nominal voltage of 56V by putting them in series while avoiding too rapid acceleration of the gas generator, the serialization of the two batteries is ordered only once the combustion chamber is ignited and the speed of the gas generator is greater than a predetermined speed threshold N 1 for ensuring, through this serialization, a positive acceleration margin at the point of maximum drag of the gas generator.
  2. 2 . The starting method according to claim 1 , wherein the speed threshold N 1 of the gas generator is comprised between 10 and 25% of a nominal speed NTOP of the gas generator.
  3. 3 . The starting method according to claim 1 , wherein the serialization of the two batteries is further ordered if, once the combustion chamber has been ignited and before the maximum drag point, the acceleration of the gas generator is smaller than a predetermined acceleration threshold DN 2 , so as to avoid a risk of stagnation of the startup.
  4. 4 . The starting method according to claim 3 , wherein the acceleration threshold DN 2 of the gas generator is comprised between 1 and 3% of a nominal speed NTOP/s of the gas generator.
  5. 5 . The starting method according to claim 1 , wherein, in order to avoid a possible overlap of the electrical contactors resulting in short-circuiting a battery during reconfiguration, the serialization of the two batteries is preceded by a dead time lasting between 150 and 300 ms.
  6. 6 . A system for starting an aeronautical free turbine and single-spool gas generator turbomachine of a twin-engine aircraft including two independent electrical networks each comprising a 28V battery selectively powering a starter-generator, a turbomachine regulation computer controlling the startup of the turbomachine first at a nominal voltage of 28V by putting the two batteries in parallel and then at a nominal voltage of 56V by putting them in series while avoiding too rapid acceleration of the gas generator, characterized in that the turbomachine regulation computer is configured to order the serialization of the two batteries only once the combustion chamber of the gas generator is ignited and the speed of the gas generator is greater than a predetermined speed threshold N 1 for ensuring, through this serialization, a positive acceleration margin at the point of maximum drag of the gas generator.
  7. 7 . The starting system according to claim 6 , further including a ground connection intended to be connected to a 28V ground power unit (GPU).
  8. 8 . The starting system according to claim 7 , wherein the turbomachine regulation computer is further configured to power a first starter-generator from the ground power unit and then by putting in series the ground power unit with one of the two batteries, once the combustion chamber is ignited and the speed of the gas generator is greater than a predetermined speed threshold N 1 for ensuring, through this serialization, a positive acceleration margin at the point of maximum drag of the gas generator.
  9. 9 . A rotary-wing or fixed-wing twin-engine aircraft turbomachine comprising a starting system according to claim 6 .
  10. 10 . The rotary-wing or fixed-wing twin-engine aircraft comprising two turbomachines according to claim 9 .

Description

TECHNICAL FIELD The present invention relates to the field of the control of the startup of the twin-engine aircraft turbomachines and more particularly concerns a method and system for the dual-voltage startup of 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 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. 26, 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 90 sufficient to compensate for the moderate drag torque 92 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 94 specific to this architecture exceeds the starting torque that such a 12 kW/400 A starter-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. Therefore there is also proposed 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 based on the