CFM INTERNATIONAL (CFMI)
CFM International is a 50/50 joint venture between French Snecma Moteurs and American General Electric. They develop, produce and sell the new advanced-technology LEAP engine and the world’s best-selling CFM56 engine.
1974: Snecma + GE = CFMI
CFMI – 50/50 joint company
– Safran Aircraft Engines (France)
– GE (USA)
CFM is not an acronym, so it doesn’t stand for anything. The company (CFM), and product line (CFM56), got their names by a combination of the two-parent companies’ commercial engine designations: GE’s CF6 and Snecma’s M56.
Snecma’s M56 – its 56th project.
The “CF” in CFM is derived from GE’s use of the letters to designate “commercial turbofan.” The “M” is from M56, Safran’s original designation for the new engine.
Engines – Turbofan
- CFM56-2 series : First variant (-2A, -2B, -2C) – DC-8, KC-135, …
- CFM56-3 series : (-3B, -3C) B737 Classic
- CFM56-4 series : A320 family (later project was scrapped due to V2500 competition)
- CFM56-5 series : (-5A, -5B, -5C) – A320 family
- CFM56-7 series : (-7B) – Boeing 737NG
CFM56-5 Series – 1988
The CFM56-5 series is designed for the Airbus aircraft and has a very wide thrust rating of between 22,000 and 34,000 lbf.
It has three distinct sub-variants; CFM56-5A, CFM56-5B and CFM56-5C.
- -5A : 22,000 – 26,500 lbf – A320 & A319
- -5B : 22,000 – 33,000 lbf – A320 family
- -5C : 31,200 – 34,000 lbf – A340
CFM56-7 Series – 1995
Only one sub-variant: -7B
- Improved design from CFM56-3.
- Aircraft – Boeing 737NG
- Thrust range : 19,500 – 27,300 lbf
- 24 fan Blade
- Double-annular combustor (DAC) as an option
- Compressor –
- 5A, 7B – 1 fan, 3 LP, 9 HP
- 5B, 5C – 1 fan, 4 LP, 9 HP
- Combustor –
- Annular (SAC)
- DAC option for -5B and -7B (-5B/2 and -7B/2)
- Turbine –
- 1 HP, 4 LP (-5C – 5LP)
- Control –
- Dual FADEC
- Bypass Ratio –
- 5A – 6.0-6.2
- 5B – 5.4-6.0
- 5C – 6.4-6.5
- 7B – 5.1-5.5
The CFM56 is a two-shaft (or two-spool) engine, meaning that there are two rotating shafts, one high-pressure and one low-pressure. Each is powered by its own turbine section (the high-pressure and low-pressure turbines, respectively). The fan and booster (low-pressure compressor) evolved over the different iterations of the engine, as did the compressor, combustor, and turbine sections.
Most variants of the CFM56 feature a single-annular combustor.
Fuel injection is regulated by a Hydromechanical Unit (HMU), built by Honeywell.
In 1989, CFMI began work on a new, double-annular combustor. Instead of having just one combustion zone, the double-annular combustor has a second combustion zone that is used at high thrust levels. This design lowers the emissions of both nitrogen oxides (NOx) and carbon dioxide (CO2). The first CFM56 engine with the double-annular combustor entered service in 1995, and the combustor is used on CFM56-5B and CFM56-7B variants with the suffix “/2” on their nameplates.
GE started developing and testing a new type of combustor called the Twin Annular Premixing Swirler combustor, or “TAPS”, during the Tech 56 program. This design is similar to the double-annular combustor in that it has two combustion zones; this combustor “swirls” the flow, creating an ideal fuel-air mixture. This difference allows the combustor to generate much less NOx than other combustors. Tests on a CFM56-7B engine demonstrated an improvement of 46% over single-annular combustors and 22% over double-annular combustors.
The high-pressure compressor (HPC), which was at the center of the original export controversy, features nine stages in all variants of the CFM56.
As part of the Tech-56 improvement program, CFMI has tested the new CFM-56 model with six-stage high-pressure compressor stages (discs that make up the compressor system) that was designed to deliver the same pressure ratios (pressure gain 30) similar to the old nine-stages compressor design. The new one was not fully replacing the old one, but it offered an upgrade in HPC, thanks to improved blade dynamics, as a part of their “Tech Insertion” management plan from 2007.
CFMI tested both a mixed and unmixed exhaust design at the beginning of development; most variants of the engine have an unmixed exhaust nozzle. Only the high-power CFM56-5C, designed for the Airbus A340, has a mixed-flow exhaust nozzle.
Mixed Exhaust Flow refers to turbofan engines (both low and high bypass) that exhaust both the hot core flow and the cool bypass flow through a single exit nozzle. The core and bypass flows are “mixed”.
Unmixed Exhaust Flow refers to turbofan engines (usually, but not exclusively high-bypass) that exhaust cool bypass air separately from their hot core flow. This arrangement is visually distinctive as the outer, wider, bypass section usually ends mid-way along the nacelle and the core protrudes to the rear. With two separate exhaust points, the flow is “unmixed”.
“One of the most recent noise-reducing technologies shepherded through the research process by NASA and now making a difference on commercial jet engines is chevrons.
Chevron is the name for sawtooth cutouts that are sometimes applied to the exhaust nozzles of jet engines to reduce jet noise.
Chevrons are the sawtooth pattern seen on the trailing edges of some jet engine nozzles. As hot air from the engine core mixes with cooler air blowing through the engine fan, the shaped edges serve to smooth the mixing, which reduces turbulence that creates noise.”
GE and Snecma also tested the effectiveness of chevrons in reducing jet noise.
The chevrons reduced jet noise by 1.3 perceived loudness decibels during takeoff conditions, and are now offered as an option with the CFM56 for the Airbus A321.
Fan and booster
The CFM56 features a single-stage fan, and most variants have a three-stage booster on the low-pressure shaft, with four stages in the -5B and -5C variants. The booster is also commonly called the “low-pressure compressor” (LPC) as it sits on the low-pressure shaft and compresses the flow initially before it reaches the high-pressure compressor. The original CFM56-2 variant featured 44 tip-shrouded fan blades, although the number of fan blades was reduced in later variants as wide-chord blade technology developed, down to 22 blades in the latest variant, the CFM56-7.
The CFM56 fan features dovetailed fan blades which allows them to be replaced without removing the entire engine, and GE/Snecma claims that the CFM56 was the first engine to have that capability. This attachment method is useful for circumstances where only a few fan blades need to be repaired or replaced, such as following bird strikes.
The fan diameter varies with the different models of the CFM56, and that change has a direct impact on the engine performance. For example, the low-pressure shaft rotates at the same speed for both the CFM56-2 and the CFM56-3 models; the fan diameter is smaller on the -3, which lowers the tip speed of the fan blades. The lower speed allows the fan blades to operate more efficiently (5.5% more in this case), which increases the overall fuel efficiency of the engine (improving specific fuel consumption by nearly 3%).
The CFM56 is designed to support several thrust reverser systems which help slow and stop the aircraft after landing. The variants built for the Boeing 737, the CFM56-3, and the CFM56-7, use a cascade type of thrust reverser. This type of thrust reverse consists of sleeves that slide back to expose mesh-like cascades and blocker doors that block the bypass airflow. The blocked bypass air is forced through the cascades, reducing the thrust of the engine and slowing the aircraft down.
The CFM56 also supports pivoting-door type thrust reversers. This type is used on the CFM56-5 engines that power many Airbus aircraft. They work by actuating a door that pivots down into the bypass duct, both blocking the bypass air and deflecting the flow outward, creating the reverse thrust.
All variants of the CFM56 feature a single-stage high-pressure turbine (HPT). In some variants, the HPT blades are “grown” from a single crystal superalloy, giving them high strength and creep resistance. The low-pressure turbine (LPT) features four stages in most variants of the engine, but the CFM56-5C has a five-stage LPT. This change was implemented to drive the larger fan on this variant. Improvements to the turbine section were examined during the Tech56 program, and one development was an aerodynamically optimized low-pressure turbine blade design, which would have used 20% fewer blades for the whole low-pressure turbine, saving weight. Some of those Tech56 improvements made their way into the Tech Insertion package, where the turbine section was updated. The turbine section was updated again in the “Evolution” upgrade.
The high-pressure turbine stages in the CFM56 are internally cooled by air from the high-pressure compressor. The air passes through internal channels in each blade and ejects at the leading and trailing edges.
Tech56 – CFM Tech Insertion Program
In 1998, CFMI launched the “Tech56” development and demonstration program to create an engine for the new single-aisle aircraft that were expected to be built by Airbus and Boeing.
When it became clear that Boeing and Airbus were not going to build all-new aircraft to replace the 737 and A320, CFMI decided to apply some of those Tech56 technologies to the CFM56 in the form of the “Tech Insertion” program which focused on three areas: fuel efficiency, maintenance costs, and emissions.
The “Tech Insertion” program launched in 2004, the package included redesigned high-pressure compressor blades, an improved combustor, and improved high-pressure and low-pressure turbine components which resulted in better fuel efficiency and lower nitrogen oxides (NOx) emissions. The new components also reduced engine wear, lowering maintenance costs by about 5%.
The engines entered service in 2007, and all new CFM56-5B and CFM56-7B engines are being built with the Tech Insertion components. CFMI also offers the components as an upgrade kit for existing engines.
Evolution Upgrade – CFM56-7B Evolution
In 2009, CFMI announced the latest upgrade to the CFM56 engine, the “CFM56-7B Evolution” or CFM56-7BE. This upgrade, announced with improvements to Boeing’s 737 Next Generation, further enhances the high-pressure and low-pressure turbines with better aerodynamics, as well as improving engine cooling, and aims to reduce overall part count.
Airbus and CFM International will begin delivering A320-family aircraft equipped with a performance upgrade developed from the Boeing 737’s CFM56-7BE Evolution engine.
The CFM56-5B/3 PIP (Performance Improvement Package) engine includes these new technologies and hardware changes to lower fuel burn and lower maintenance costs. Airbus A320s were to use this engine version starting in late 2011.
View CFM56 Engine at cfmaeroengines.com
The LEAP is a new engine design based on and designed to replace the CFM56 series, with 16% efficiency savings by using more composite materials and achieving higher bypass ratios of over 10:1. LEAP entered service in 2016.
- the successor of the successful CFM56 (-5B, -7B)
- power narrow-body aircraft
- competing with the Pratt & Whitney PW1000G
The LEAP delivers a 15% improvement in fuel consumption, compared to today’s best CFM56 engines, and maintains the same level of dispatch reliability and life-cycle maintenance costs.
The LEAP engine’s fan blades are manufactured from 3D woven RTM (Resin Transfer Molding) carbon fiber composite, an industry first for CFM. This technology results in fan blades that are not only lightweight but so durable that each individual blade is strong enough to support the weight of a wide-body airplane like the Airbus A350 or Boeing 787.
The LEAP engine features the second generation Twin-Annular, Pre-Mixing Swirler Combustor (TAPS II).
TAPS II reduces NOx emissions by 50% versus CAEP/6 standards.
Unlike traditional combustors that mix fuel and air inside the combustion chamber, the LEAP nozzle pre-mixes these elements to provide what our engineers call lean-burn combustion. We just call it revolutionary.
The unique LEAP debris rejection system provides the best erosion protection, preventing sand, dirt, and other harmful items from reaching the core. As a result, the highly durable, more efficient LEAP engine stays newer for longer.
High Bypass Ratio – Optimum propulsive efficiency
Fan Blade – 3-D woven carbon fiber composites – Lightweight, increased durability
3-D WOVEN CARBON FIBER COMPOSITES
The 3-D woven RTM (Resin Transfer Molding) carbon fiber composites used for the fan blades and fan case on the LEAP engine are revolutionizing the single-aisle market. This material helps reduce engine weight by 500 lbs per engine. The 3-D RTM technology is high impact resistant and, thus, reduces maintenance requirements.
Debris rejection system – Airfoils protection against erosion
High technology compressor – Optimum thermal efficiency
High Pr. Turbine Shroud – Ceramic composites, new cooling & 3-D aerodynamics – Reduced weight, cooling optimization
CERAMIC MATRIX COMPOSITES (CMCs)
Composite materials, such as CMCs, are made from separate materials that are joined together. CMCs are produced from silicon carbide fibers 5 times as thin as human hair embedded in a silicon carbide matrix and coated in a proprietary coating creating a part that is stronger than metal.
CMCs are incorporated in the LEAP engines in the high-pressure turbine shroud, one of the hottest sections of the engine. CMC materials have a 20% better thermal resistance (reducing cooling needs), two times the material strengths and are 2/3 lighter vs the metallic alloys they replace (contributing to engine weight reduction), all of those contributing to better fuel efficiency.
The LEAP family of engines is designed to power commercial aircraft requiring 20,000 TO 35,000 POUNDS OF THRUST.
LEAP family members
- LEAP – Leading Edge Aviation Propulsion
- Series – LEAP
- Model – 1A, 1B, 1C
- A – Airbus
- B – Boeing
- C – COMAC
LEAP-1A – Airbus A320neo
– 24,500 – 35,000 pounds thrust
LEAP-1B – Boeing 737 MAX
– 23,000 – 28,000 pounds thrust
LEAP-1C – COMAC C919
– 27,980 – 30,000 pounds thrust
-1A24 : 24000 lbf (for example)
LEAP family Configuration
- Twin-spool, high bypass turbofan
- Compressor – 1 fan, 3-stage LP, 10-stage HP
- Combustor – Second generation Twin-Annular, Pre-Mixing Swirler Combustor (TAPS II)
- Turbine – 2-stage HP, 7-stage LP (-1B: 5-stage LP)
- Pr. Ratio – 40:1
- Bypass Ratio – 11:1 (-1B: 9:1)
View LEAP Engine at cfmaeroengines.com