The too, as many parts within the engine

The aviation industry has always been eager to engage with promoting new innovations to ensure sustainability. One way to support sustainability is through continuous adaptations to jet engines, making them more efficient and thus emitting less pollutants to enter the atmosphere.  Ideally, operating engines at a higher temperature, leads to more burning of particulates which leads to less pollution. However, jet engines are limited to what temperatures they can be operated too, as many parts within the engine are temperature limited. In 2016, GE introduced a new material to be incorporated into a commercial jet engine. Ceramic Matrix Composites, also known as CMC’s. The introduction of silicon carbide shrouds offers multiple benefits to the engine. An increase in temperature limits from 1100 degrees Celsius to 1300. This burns more fuel particles, thus increasing the efficiency of the engine. The increase in efficiency of reportedly 15% is further supported by the CMC being only 1/3 the weight of traditional Nickel based superiod shrouds. The increase in fuel efficiency is clearly beneficial, however, questions remained regarding safety and practicality of manufacturing the new innovative material. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table of content

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Introduction……………………………………..…………………… 4

 

CMC Benefits….………………………………………..………….4-5

 

Identification of key challenges

Materials……………………………………………………………………………….5-6

Manufacturing…………………….…………………………………………………..6-7

Price economics…………………….…………………………………………………7-8

Reliability……………………………..………………………………………………….8

Future……………………………………………………………………………………8-9

 

 

Conclusion………………………………………………………… 10

Referencing …………………………………………………………10-11

Bibliography………………………………………………………… 11

Appendix 1…………….……………………………………….…… 12

 

 

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Introduction

Throughout the years, the aviation industry has seen unprecedented amounts of development in terms of aircraft design as well as reduction in the level of pollution created. In 2000, with the development of larger aircraft with more fuel-efficient engines, air travel became a greener, more cleaner form of transport compared to a car (APPENDIX 1). With BTU levels per passenger per mile expected to decrease each year, the aviation industry has never seen a demand from airlines who want more fuel-efficient aircraft until now. With the demand from airlines, it’s now up to the manufactures to ensure they can deliver. The answers to sustainability for the aviation industry is through development of new modern, cleaner aircraft whilst maintaining reliability ensuring safety margins are never compromised.

This report will look at an alternative to improve efficiency with the use of CMC materials, also known as Ceramic Matrix Composites. CMC’s are composed of hair like fibres which contain matrix’s and fibre’s composing of ceramic materials. Ceramic materials are normally associated with plates or plant pots which are heavy and very brittle, however innovative technology can produce bonding of the silicon carbide creating a CMC which is not only lightweight, heat resistant but also flexible. Making the CMC act more like a wood compared to traditional ceramics.     

 

CMC Benefits

In 2016, from successful results from the F136 military engine, GE announced the arrival of the LEAP engine, unlike many other Jet engines, the LEAP engine incorporates CMC silicon carbide shrouds, changed from the traditional nickel based super alloys previously used. GE claim the use of CMC material within the engine aid an increase in efficiency of 15%.

A benefit of the CMC shrouds is the lightweight material, 33% lighter than traditional materials. With the engine now being lighter, the required lift the aircraft needs to sustain flight is reduced and therefore less thrust is required which reduces fuel consumption and ultimately reduces the level of carbon dioxide emissions being released to the atmosphere.

Furthermore, with the 18 shrouds being positioned in the hottest section of the engine, the turbine, the CMC material needs to withstand temperatures above 1000 degrees Celsius. CMC’s offer a higher temperature limited rating of 1300 degree Celsius, 200 degrees higher than traditional materials previously used. A hotter engine requires less fuel to provide the same amount of thrust required for flight. With a reduction in fuel consumption comes less fuel used leading to less harmful pollutants emitted from the engine.

With the engine now able to operate at a higher temperature, the thermal efficiency increases. Thermal efficiency is the ratio of work done to heat supplied.

The formula shown is the thermal efficiency, tmax is the max temperature in the engine, and tamb is ambient temperature.

Because CMC materials provide unprecedent operating temperatures, less cooling air is needed in the hot section of the engine, thus more air can be directed through the natural flow path of the engine, which in turn increases the bypass ratio creating more thrust during the cruise. With more thrust being created per thrust setting, thrust can be reduced to maintain the required lift, reducing fuel consumption.

Finally, Silicon Carbide (SiC/SiC) offers the one of the most corrosive resistant materials in the industry, very important to keep maintenance cost down. Nickel based alloys currently used, are prone to cracks and scratches which can create deficiencies within the engine. Fig. 1.1 below shows how NI based super alloys strength linearly decreases with increasing temperature. Comparing this to SiC/SiC CMC’s which maintain strength over a range of temperatures.

Fig 1.1.

Testing temperature against strength of variety of materials.

 

 

 

 

 

 

 

Identification of key challenges and discussion

Materials

In the future, GE and US government investment for CMC materials to be able to withstand 1500 degrees Celsius compared to 1300 currently, will totally eliminate the need for engine cooling, however, around 1400-1600 degrees Celsius active oxidation may occur on SiC/SiC materials.  Active oxidation is the process where Silicon carbide material reacts with the exposer to oxygen and moisture creating corrosion, changing its appearance, strength, and permeability. CMC materials are usually coated in environment barrier coating (EBC) to mitigate the problems induced from oxidation. However long-term sustainability and effectiveness of the coating is a big concern. EBC on stationary parts, such as the shrouds, is certified for more than 1000 hours, whereas on moving parts, ie, the turbine, it’s less than 1000 hours. With the average aircraft doing 3000 hours a year, and more CMC parts predicted in the future, including moving parts, the feasibility of replacing the EBC coating on the CMC materials with the engine may be sustainable now, but certainly not in the future. With this said, EBC development has been focused on new coating composition and thin-layer composite coating systems for SiC/SiC, EBC coating systems with the temperature capability up to 1650 have been developed and won the 2007 R&D 100 award, however questions remain regrading availability, durability, and expensive costs. All of which will have an impact on the sustainability of utilising SiC/SiC materials in Jet engine aircraft.

Furthermore, aircraft parts are limited to flight hours, once the hours are met, the parts must be replaced with new ones. Recycling of CMC materials is notoriously difficult. Whilst recycling of CMC parts won’t be required for many years due to the short time they have been used in jet engines, the recycling process still needs careful attention. Legislations from the EU, indicates that end of life engineering products must be recycling in one form or another.  1 Recycling supports sustainability, whether that’s the reusing of old CMC materials or breaking down the CMC material to create a form of energy. However, the recycling process involved with CMC is expensive and the percentage recycled in small compared to traditional products. CMC materials are connected by matrix and fibres which are bonded together making the process of breaking up the material difficult. Combustion of CMC to create energy is a quick and easy method, however the primary principle of CMC materials is to create less pollution. Combustion of CMC would go against this principle. From research, there are very few companies out there who recycle CMC to create new parts of aircraft. This is due to the lack of profit margin due to the long process, it’s more cost effective for manufactures to buy or create new CMC products. One organisation called AFRA (aircraft fleet recycling association) promote the use of recycling within the aviation industry, working closely with manufactures and maintenance departments of airlines. AFRA carry out strict audits, ensuring materials are recycled to their full extent.

Manufacturing

With the CFM LEAP engine having a backlog of orders of over 12,000 engines supplying a variety of aircraft including the 737Max and A320NEO, the manufacturing process of the CMC shrouds must be effective to be able to meet demand. Whilst the shrouds are static, the end goal for GE is to introduce CMC parts throughout the engine, including compressor, combustion lining and turbine. The moving parts will not only benefit from the lightness of SiC/SiC but the lightness also leads to less inertia in the moving parts, meaning for example, the compressor can be span more efficiently. GE believe that the use of CMC throughout the engine is a step in the right direction, and hope the new GE9X engine will incorporate moving CMC parts. GE projections show that from 2012-2020, there will be a 10 fold increase from 100 parts to 32,000 parts of CMC materials within an engine. This leads to the question regarding manufacturing and whether GE can produce CMC materials on mass production. With this said, GE seem to be acting promptly on the ensure they can meet the demand from CMC materials from building 2 brand new facilities in Alabama in a £200 million-dollar investment and creating 300 new jobs. These facilities will be solely used for development and production of CMC materials and is expected to be operational in the first half of 2018. 2

Price economics

It’s very difficult to understand price economics of the new CMC LEAP engine without knowing the price of an engine. The LEAP 1A engine is RRP at just under £13million dollars, however, it’s common practice for airlines to routinely pay 70% lower than list price for single-aisle engines. Bringing to cost down to $3.7 million dollar per engine.

From an airlines point of view, the LEAP engine offers excellent fuel economy of 15%. However according to analyst ‘Leeham co’ from Washington, the engine is missing its book figures by 3-4%.

Calculations

For calculation purposes we can assume that the figure of 12% fuel savings per year per aircraft. (assuming two engines per aircraft)

·         A Boeing 737-800 burns 2500kg/h on average with “standard CFM 56” engines.

·         Specific gravity of Jet A1 is close to 0.80

·         A conventional 737-800 will therefore burn 2000 litres of Jet A1 per hour.

·         With the average aircraft at a popular airline, doing around 6 hours of flight time per day, that’s a total of 2184 flying hours per year.

·         That’s 4,368,000 litres per year

·         Jet A1 costs about 65p

·         Total yearly cost of fuel would be £2,839,200

If the aircraft had the new LEAP 1A engine, the yearly fuel cost would be £2,498,496.

·         A saving of £340,704 per year.

 

 Comparing the LEAP to the standard CFM 56.

·         LEAP costs $3.7 million.

·         CFM costs $2.8 million.

These figures are based off listed price with a 70% discount.

$900,000 = £652,851 (based on current exchange rates)

Therefore, it would take a mere 99 weeks to start earning the rewards and save money from using the LEAP engine.

 

Further calculations

If a airline has just started up or they require an aircraft to be used just for summer, working out the break even hours is an important indication of the worthwhileness of having the LEAP engine over the similar CFM 56.

Using the calculations above it can be said that;

·         1 hour of operation of the GE LEAP engines (2 engines) costs £1144

·         1 hour of operation of the GE CFM 56 engines costs £1300 

 

·         A saving of £156 per hour from the LEAP engine.

 

With the LEAP engine being £652,821 more expensive than the CFM 56.

·         If an airline keep the aircraft for 15 years

·         £652,821 / 15yrs = £43,521 per year extra for the LEAP engine.

·         £43,521/ 156 (cost saving) = 279 hours per year required to break even.

·         Or 5.3 hours per week.

What this means that if an airline can fly an aircraft for more than 5.3 hours per week, its more beneficial to them to use the new LEAP engine over the traditional CFM 56.

 

NOTE= This is not factoring depreciation or sell on value of the engines or maintenance costs of each engine. Figures may be slightly inaccurate as engine pricing is from third party information.

 

Reliability

Reliability of the CMC engines to date is unknown, due to the short time they have been available.  However, questions regarding durability from airlines is a key question, as any teething issues on the new engine may ground the aircraft and in turn cost the airlines valuable income. It was known from early October various flight crews noticed a shift in the EGT margin during flight. An inspection revealed the coating of the CMC shroud had started to flake off. Allowing air to escape. Although it is common for new designed engines to suffer from small issues, it will be a concern to future customers that the newly added CMC materials with their coating are already starting to cause problems. GE have started to change the EBC used, and overall, CMC materials should not impair the engines lifespan or reliability.

Future

Moving into the future, engines are going to become hotter and hotter with the need to actively increase efficiency within air travel. It has been discussed the potential issues with SiC/SiC with temperatures above 1600 degrees Celsius. If EBC coating for these kind of temperatures is not approved and feasible, the engine won’t be able to support the high temperatures required.  An innovative new polymer has the potential to replaced SiC/SiC in the future. This “Waterlike Polymer” can withstand temperatures up 1700 degrees Celcuis, replacing the need of EBC coating. and is 3-6 times lighter than any other ultra high tempceramic currently available. This polymer comprises of a complete random structure containing nitrogen, baron, carbon which provides heat stability with delayed oxygen reaction. The polymer has nanotubes of SiC fibres which provide interlocking connections, increasing damage tolerance. The result of which is a micro Velcro like material, where exposed parts of the fibre are curly and act like hooks, leading to less cracking and a more sealed material, which prevents oxygen changing the composition.   

 

 

 

Fig 1.2- Shows the structure of the waterlike polymer.

 

 

 

 

 

 

 

Fig 1.3- Shows the curly hooks on the polymer which prevents oxidation.

 

 

 

 

 

 

 

 

 

The dynamic use of this polymer can be greatly beneficial to the aviation industry with the polymer able to be poured into complex moulds or even sprayable on to object which require temperature protection. With the diverse uses, this polymer can be incorporated into other industries which would increase the demand, leading to more investment, bringing down production costs as the polymer becomes widely available.

Conclusion

It’s undoubted the multiple benefits CMC materials bring when used in the aviation industry. Reducing fuel consumption is what manufactures are continuous striving to achieve, however it’s important that, in the search for less emissions, safety and reliability of the engines aren’t comprised. Question marks over the use of CMC materials are still out there, especially with problems of the EBC coating used on the LEAP engines. GE will hope that this is just teething issues. With that said, providing the reliability remains strong, the price economics of the new LEAP do work, and nearly every airline operator would be better off overall using the LEAP engine over nickel based engines. With the new investment, supply will meet demand, and moving into the future, CMC products will be used throughout the engines. What the future holds for SiC/SiC CMC products is unclear, especially with new composite polymers being created, it wouldn’t be surprising if SiC/SiC CMC’s are replaced, with more heat resistance and cheaper products (as they don’t require coating) especially in search of increasing engine temperatures to satisfy emission targets. 

 

Referencing