Yes, the 4th generation single crystal superalloy DD15.
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Chinese Engine Development
- Thread starter jackbh
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Yes, the 4th generation single crystal superalloy DD15.
Great! thanks for the updated info. These advances in material science and casting + cooling tech explains the breakthroughs in performance. Any idea what the yield is for the SX castings for these? 80%? 90%?
Even the latest materials operate at gas temperatures far above their melting point in a Trent1000/GEnx type engine, so there's clearly more to it than merely metallurgy - cooling tech makes a huge difference. Blade internal passage design (pins, fins, turbulence ribs, number of entry points & passes, use of impingement), pre-swirl nozzles & coverplate, perhaps even heat exchangers to cool the cooling air (AL-31F)...
Very early AL-31Fs, PS-90As & RD-33s had DS blades, but got SC upgrades pretty soon - they also had pretty good internal passage design and (as mentioned) a heat exchanger for NGV cooling air in the AL-31F.
They all add that little bit but metallurgy is still king. For the same turbine entry temperature, if I can operate with uncooled blades then I am going to be able to squeeze that much more efficiency without diverting the gases through the cooling vanes, and my cost will go down. Like wise, with the same cooling tech and coating, my better material is gonna get that much higher TET and as a result either more life, more efficiency or more thrust. We are only talking 30-50 degrees here per generation but that is still significant.
I might be wrong here but to me metallurgy in a turbine, especially the SX is like the EUV of semiconductors. Its not the only hard part in the engine but it is definitely the hardest. I am sure its gonna be as a nasty shock for the west to know that China can grow themselves these blades of these specs as it was a surprise shock to me learning about these in the last 24 hours lol. Can imagine the face on CIA lab guy after stealing a blade from the J-10C engine overhaul in Pakistan. They will have realized that the gap is alot smaller than they thought haha.
broadsword
Brigadier
How about the manufacturing part? Is China good at it? Things like tight tolerances, friction reduction, etc.
It's clearly one of the major challenges in a modern aero engine. As mentioned though, even the best (metallic - and those are still the only ones mature enough to use in rotating parts) materials could not perform their function but for highly effective cooling. Permissible metal temperatures range around 75% of melting point, against gas temperatures that are well above the latter. This means cooling tech delivers reductions of several hundred K, and a more or less efficient implementation can easily account for 30 to 50K.
They don't "add that little bit", they make the difference between a turbine working thousands of hours and a pool of molten metal! Hardly negligible, in fact since there is no question of going for uncooled blades it's more like cooling does the heavy lifting, with a better material merely providing the luxury of saving a few % of bleed mass flow. Hell, the inception of air-cooled turbine blades can be traced to German manufacturers having to engineer their way round shortages in key high-temperature materials during WWII.
CFM is on record as stating the blade metal temperatures in the LEAP-1 are similar to the CFM56, all the while gas temperatures are likely to be at least 100K, more probably in excess of 200K higher. This in response to P&W claiming their higher-BPR engine cycle allowed them to relax turbine inlet [gas] temperature (accepting lower thermal efficiency) by 50K compared to the LEAP in favour of better durability. Which is to say there are marked differences in cooling tech even between Western OEMs - you can't assume everybody is on the same page in this regard, with material the only decisive factor.
Pratt earlier found that out to their detriment on the Boeing 757 competing against the RB211-535E4, which was giving the CFM56 a run for its money in time-on-wing stats until discontinued along with the aircraft. With its higher BPR, the PW2000 had a non-trivial SFC advantage, yet RR ended up powering 60% of the fleet (which would've been a lot higher still but for two disproportionately large customers in the P&W camp). And that certainly wasn't down to better materials!
In fact, cooling was so good that RR wasn't happy either, because they were failing to make the expected amount of revenue on spare parts, ultimately leading to the introduction of their TotalCare scheme. That way, as the engine remains RR's property, they benefit if the design turns out extremely durable, removing a perverse incentive to make a less sophisticated engine than they theoretically could.
lmao, capitalism sucks. Pardon the profanity. hahah
Actually cooling is king. Turbine inlet temperatures rose from 900 Celcius to 2000 Celcius in a span of 70 years. Around 750 Celcius of that increase came from better cooling. Rhenium was added to alloys primarily because it made more intricate structures much easier to achieve. Of course, metallurgy is important and plays an important part in cooling too. For example, better heat conductivity and castability are important. But reducing the jet engine performance to blade alloys is a massive oversimplification.
Compressor power and the corresponding engine cycle designs that enable them are actually the first order driver of engine performance. The role better materials play is as enablers to more powerful cycle design. Higher turbine temperatures follow greater compressor power, and both better cooling technologies and better materials play enablers to that factor. Then you have supplementary factors like combustor design and lighter structural materials. That said, because cycle design itself is much easier to iterate on than materials, employed material qualities are a good measuring stick for gauging how advanced capabilities are.
Not really - such perverse incentives are merely an indication that there is a distortion of some kind in effect, generally speaking capitalism rewards efficiency and sustainability. RR solved it in this instance by framing their business model differently under the TotalCare "power by the hour" scheme. They started selling engine flight hours to the airlines instead of engines, thereby ensuring they got their share of the benefit from excellent durability because they remained property of the company. Longer TBO and lower spares consumption then meant they could offer flight hours more cheaply.