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  Volume 10, Number 1 • January/February 2002 • Aerospace Technology Development

NASA Glenn Helps Engines Last Longer

Electronic controllers for current commercial aircraft engines provide high performance and operational stability to an engine. However, the standard method of operation results in significant wear and tear on the engine, and negatively impacts the on-wing life—the time between cycles when the engine must be physically removed from the aircraft for maintenance. The resulting engine wear and damage must be monitored closely and portions of the engine regularly replaced and rebuilt in order to provide safe and reliable flight.

Top: It is possible to apply ILEC technology to existing commercial turbine engines without modifying hardware or adding sensors, making it possible to retrofit existing engines by changing only the controller (FADEC) software. Bottom: A demonstration used a hardware-in-the-loop simulation to show the feasibility of integrating new ILEC logic into a flight-grade commercial engine controller. Photos courtesy of Glenn Research Center.

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NASA’s Glenn Research Center (GRC), along with its industrial and academic partners—Scientific Monitoring, Inc., Honeywell Aerospace, General Electric Aircraft Engines and Penn State University—has been working toward a new control concept that will include the consideration of engine damage as part of the control function. The resulting controller will be able to significantly extend the engine’s on-wing life with almost no impact on engine performance and operability. The new controller design will utilize damage models to estimate and mitigate the rate and overall accumulation of damage to critical engine parts. The control methods will also provide a means for assessing trade-offs between performance and structural durability based on mission requirements and remaining engine life.

GRC originated the development of Life-Extending Control for Reusable Rocket Engines in the early 1990s. The concept was demonstrated in a simulation study with limited success due to the rigid operating envelope. These control methods, however, are now being adapted and extended to commercial turbine engine technology, where significant improvements in on-wing engine life are expected.

The IT Base Program at NASA Ames has funded Intelligent Life-Extending Control (ILEC) research since 1998 as part of its Intelligent System, Controls and Operations Project. Goals of the ILEC effort are to identify the relationships between engine performance, life usage and cost of operation for commercial engine systems; to quantify the trade-off between life usage and other parameters; and to develop and demonstrate control laws that take advantage of component life estimates to extend the on-wing engine life.

Recent efforts have been focused on applying ILEC technology to an existing commercial turbine engine, and doing so without modifying hardware or adding sensors. This approach makes it possible to retrofit existing engines with ILEC technology by changing only the controller (FADEC) software. Based on this approach, System Monitoring Inc. and Honeywell Aerospace successfully demonstrated a life-extending control at NASA Glenn in Cleveland, Ohio. The demonstration used a hardware-in-the-loop simulation to show the feasibility of integrating new ILEC logic into a flight-grade commercial engine controller.

This represented completion of a Level I mile-stone for the IT Base Program and paved the way for the migration of ILEC technology to an engine test phase. The significance of the demonstration includes:

  • Demonstrating a 25–35 percent creep/rupture damage reduction in the engine’s hot section by using smart optimization to define cruise conditions during flight. The demonstration also showed an estimated fuel savings of 2.1 percent. The trade-off is an increase in flight time of 1.3 percent.
  • Demonstrating a 20–30 percent reduction in thermo-mechanical fatigue (TMF) damage to the hot section by developing and implementing smart acceleration logic during the take-off. The trade-off is an increase, from 5.0 seconds to 5.2 seconds, in the time required to reach maximum power from ground idle.
  • The smart acceleration logic was successfully implemented in a flight-grade engine controller and demonstrated against Honeywell’s full-envelope, real-time simulator for the Teledyne Continental TFE731-20/40/60 engine. This hardware-in-the-loop demonstration is an important step in assuring that the ILEC logic is compatible with flight-grade engine controllers.

Bob McCarty, senior principal engineer of Honeywell Engines, said that “Honeywell is very pleased with the ILEC simulations conducted in 2001. It is clear that developing the algorithms that predict engine hot-section damage, in terms of controllable parameters such as rate of change of temperature and speed, can allow new control laws that will dramatically increase engine on-wing life. We are hopeful of obtaining a go-forward program to confirm and demonstrate this technology through engine cyclic testing.” Q

For more information, contact Ten-Huei Guo at Glenn Research Center, 216/433-3734, Ten-Huei.Guo@grc.nasa.gov. Please mention you read about it in Innovation.

 

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