Personally, I find the architecture of the GE9X
engine (F+3 -11 ^ 2 - 6) to be more similar to that of the GE90
engine with the 123˝ fan (F+3 -10 ^ 2 - 6) than to that of the larger GE90 engine with the fan of 128˝ (F+4 - 9 ^ 2 - 6), and which is, in turn, more similar to that of EA
engine architecture (F+5 - 9 ^ 2 - 6)…
Replacing the certain metal components in the hot section of the engine by those made of the CMC
material brings a lot of advantages to the new GE9X engine. CMC material itself, made as strong as the metal, at the same time beeing much lighter, and withstanding higher temperatures, allows lower fuel burn and the lower emissions of NOx and CO
, while increasing the efficiency of the engine. This material can withstand some 110-170°C (200-300ºF) higher temperatures compared to the ceramic coated nickel/titanium superalloys. Combined with a new swirl pattern and increased air volume through the combustor, it eliminates the need for cooling bleeds. The higher temperature capability and simpler component´s cooling requirements allow a more spacious combustor design so it can be run more efficiently. Less cooling flow to the component enables more HPC´s flow to be put into the combustion process through the combustor mixing nozzles. Present-day metal parts of the HPTs need extensive amount of the cooling air, directly taken from the primary engine airflow, thus reducing engine´s SFC, CR, OPR and TIT. CMCs can operate with the much less or even no cooling, providing a significant efficiency boost to the cycle and simplifying a complex cooling system of the engine´s hot sections. CMCs, also one-third the weight of the nickel, deliver a truly revolutionary leap in temperature capability, beyond any advanced metal alloy and its durability has been already proven through the significant testing in the GE
´s aeroderivative gas turbine engines. The biggest benefit of CMCs is in the significant weight savings they can give, as well as CFRP fan blades and Ti-Al HPC´s and LPT´s blades.
The main advantage of using CMC materials is not in enabling higher peak cycle temperatures of the engine, but in the improving cycle efficiency, and that, by reducing the thermal losses caused by the bringing the compressed air into the hot sections of the engine. The peak combustion cycle temperatures in commercial TFs are currently limited by NOx formation, and NOx compounds only form in the presence of too high amount of the oxygen at the front of the flame and with the temperatures greater than some 1.560°C (2.800°F). In the order for the combustion system to operate with the lowest emissions, it must operate at a specific flame temperature, balancing the generation of NOx with the generation of CO
. This is very difficult to achieve if fuel and air are injected directly into the combustion chamber, and therefore a pre-mixing of the fuel and air has to be accomplished just to create a uniform mixture that, once it enters the combustion chamber, is ideal for complete low emissions combustion.
Specifically, the GE9X
engine will incorporate a new disc alloy in the last stage of the HPC and in the first of the 2-stage HPT. Both HPT´s stages will be air-cooled, while the second stage will incorporate a new blade design. CMC material will be used for the first-stage nozzle guide vanes and shroud, the second-stage nozzles as well as for the, already mentioned, inner and outer combustion liners (TAPS 3 combustion liner has no air dilution holes like previous generation combustors). The lightweight LPT´s blades will be made of TiAl, but I do not exclude a possibility that the 1st-stage HPT´s blades could be also made of CMC material. Compared to the CR of 19:1 on the GE90-115 engine and 23:1 on the 10-stage HPC unit in the GEnx-1B / 2B engine, GE9X compressor (11-stage HPC) pressure ratio will be 27:1, raising TIT by around 100 degrees.
While I would not dare to say that the GE
was, for the last decades, at the forefront in the development of the turbofan engines in the sense of particular technical and design solutions, but when it comes to the development of the advanced materials, especially for the turbine applications, the GE
´s invention of the Rene-family of nickel-based super-alloys led to continuous improvement in the engines´ temperature capabilities, the same way as the thermal barrier coatings and internal cooling system were delivering incremental improvements in the engines´ efficiency ...
Assuming that the LPC
´s (3-stage booster) geometry of the GE9X
engine will remain unchanged (somehow, I expect GE9X engine to have scaled-down core´s geometry in compare with the GE90 engine), it is, due to the larger 134˝ fan with the fewer (16) and thinner blades with the more sweep and wider chord, compared to the 128˝ fan with the 22 blades, realistic to expect GE9X engine to have higher BPR than the GE90 engine, making it even more efficient and significantly quieter…