First registered in September 1974, CFM International was developed by GE Aircraft Engines and Snecma to create competitive turbofan engines in the 20,000 lb thrust class. The company received its first order in 1979, when Delta Airlines selected the CFM56-2 to re-engine the McDonnell Douglas DC-8. Since then the company has developed the CFM56-3, -5A, -5B(/P), -5C, and -7 engines, which serve a number of Airbus and Boeing aircraft. CFM retains the same basic architecture for all its engines while tailoring them for specific applications.
The CFM56-5C, which has a thrust rating of 31,200-34,000 lb, is one of several CFM engines that may benefit from the technologies developed in the TECH56 program. This high-bypass turbofan engine powers many A340-200 and -300 aircraft.
The CFM56-7 is a high-bypass turbofan engine with a thrust rating of 18,500-26,300 lb. This engine, which has already benefited from several advancements, may also gain technologies from the CFM Project TECH56.
The CFM56-5B dual spool test rig allows the placement of the high-pressure turbine with the low-pressure turbine for full-scale testing. This test is performed to optimize the aerodynamics and minimize interaction loss between counterrotating turbines.
To prepare for future markets, the company established TECH56 to develop new technologies for its existing engine architecture. The design philosophy of the program includes simplified designs, better performance, higher efficiency, lower noise and emissions, lower operational costs, and good quality. The first year (1998) of the program involved the development of a low-speed compressor, design of a high-pressure compressor (HPC) rig, twin annular pre-swirl (TAPS) mixer testing, and high-pressure turbine (HPT) vane solidity cascade testing. In 1999, the company plans to conduct swept fan blade tests, fan/structure design, HPC rig fabrication and assembly, and HPT aero rig testing. The final year of the program will involve a TAPS engine demonstration and high-pressure (HP) sealing, HPC rig, fan, and dual spool testing.
The swept fan blade design allows for the potential for more thrust growth in the engine, better fuel burn (1% improvement), lower weight (150 lb savings), and lower noise. Fatigue, large bird impact, and initial containment testing have been completed to date with performance, stability, and crosswind testing scheduled for this year.
A load reduction device is also under development to lower structural weight (200 lb savings) of the engine and reduce imbalance in a blade-out situation. The company has completed proof-of-concept and full-scale testing and is currently planning to establish technical requirements, complete detailed design of the fan module, and complete static and fatigue testing.
CFM compressor development has employed the use of its low-speed research compressor, which allows the testing of many different configurations of parts to verify the efficiency of the blading. The company is also trying to reduce the number of stages in its compressor from nine to six using a new blade design. This stage reduction will provide increased pressure rise across the compressor while lowering maintenance costs and the number of parts. The compressor stage loading has been validated and aerodynamic stability enhancements and performance improvements of the swept blades have been demonstrated. The company plans to complete the design and producibility, reliability, and maintainability trade studies in 1999 along with conducting rig testing.
The TAPS combustor builds on the company's dual annular combustor (DAC) experience and it improves the overall emissions while simplifying the design. The TAPS will not only improve NOx emissions, which is usually the primary focus of engine designers, but also it will reduce hydrocarbons. "Normally when you work on the high
end of thrust,
you work on NOx," said Dr. Mike J. Benzakein, General Manager of Advanced Engineering Programs at GE Aircraft Engines. "You try to get the NOx down. If anything, you can compromise the hydrocarbons, and here we're trying to do both at the same time." The company has completed TAPS single-cup testing, preliminary design and analysis, and flame tube testing, which validates low-power emissions. Future analysis includes full annular rig, single-cup module, and sector (five cup) rig testing.
Development work is also being conducted on the company's single-stage HPT. Such work includes enhanced aerodynamics, improved sealing, advanced materials, and dual spool rig testing. Aerodynamic enhancements to the HPT consist of a 3-D aerodynamic turbine vane and convergent-divergent blade. A 0.5% fuel burn improvement and a 6-10�C benefit in exhaust gas temperature (EGT) margin are realized from these aerodynamic enhancements.
Brush seal technology is being used in the HPT to reduce aerodynamic losses and produce higher efficiency. According to Bill Clapper, Executive Vice President of CFM International, better sealing improves engine efficiency. "The trick with brush seals is to make them work long term and to make sure that they are sealing after 14,000 hours in much the same way they did after 200 hours," said Clapper. "That's what we're trying to demonstrate with this. We've got some work going on at some facilities in Russia to help demonstrate that. We want to do some validation work on the -5B (CFM56 variant). Plus we want to do the ring seal test on the -5B and prepare for full engine endurance test, which goes a long way."
The dual spool rig allows the engineer to put the HPT and low-pressure turbine (LPT) together and run a full-scale test to optimize the aerodynamics to better understand how to cut down the interaction loss between the counterrotating turbines. "We've been very successful in getting good performance out of the single-stage high-pressure turbine," said Clapper. "However, if you do all of the analysis, when you look at the interaction loss between the high-pressure turbine and the low-pressure turbine, there is still about two points there that we can't really explain. And what we're trying to do with this rig test is use the analytical plus the measurement techniques to get that interaction loss down and take that to a different level."
Fuel burn, higher bypass ratio, and lower parts count result from improvements made to the LPT airfoils. A 2% fuel burn improvement is realized with the new airfoil technology. The bypass ratio increases from 5.5 to 9 with four LPT stages and 20% fewer airfoils. The HP/LP transition sections and LPT rig design are completed along with HPT low solidity tests. In 1999, the company plans to complete baseline -5B dual spool testing, initiate HPT rig testing, and finish LPT rig testing.
Noise reduction is another issue being addressed by TECH56. CFM has conducted some testing on the Chevron nozzle, which has jagged edges to improve the mixing of air entering the engine. The tests demonstrated a 3.5 dB in jet noise reduction and an acoustic energy reduction greater than 50%.
CFM engines will gain several benefits from the TECH56 program such as 15-20% lower cost of ownership, 15-20% lower maintenance costs, 4-7% better fuel burn versus the CFM56-7 and -5B, noise levels approximately 20dB cumulatively below Stage III noise levels, and emissions 40-50% below current ICAO levels. "We believe that with TECH56 that we have identified the needs from a technology point of view to meet the needs of the next decade," said Clapper. "We believe that will advance the state-of-the-art of the -5B/P and -7. And we believe we can back-flow that technology, help that product line (-5B/P and -7), and improve our installed base. We also believe that if there is a requirement for a new engine, that (TECH56) will set the foundation that we can build on and get to the market on time. And that program is under way, producing results and allowing us to have the capability to provide value to the customer in a lot of different ways."