Chinese Engine Development

thunderchief

thunderchief

Senior Member
Re: Shenyang J-31 Fighter

latenlazy said:
Absence of evidence is not evidence of absence. Just because we have been spoiled with comprehensive leaks with some programs does not mean we should expect comprehensive leaks of all programs. This is especially the case with Chinese engines. You mention how much we now know about the Taihang, but the Taihang was pretty incognito for most of its development. Only when they were ready for production did we actually see the engine. (Of course ready for production should be put in quotes, because the program had hiccups after that point). If we follow the same pattern of leaks as the WS-10, we actually should not expect any visual confirmation of the WS-15 until the engine is on the tail end of testing and is being readied for production. If the rumour that they've only just built a complete prototype for testing, we should still not expect to see photos of the engine for another 3 to 5 years.
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Well, we actually don't have absence of evidence ;) We have core tests in 2006 and prototype tests in 2014, with 8 years of pause between them . We have another circumstantial evidence and that is continuing import of Russian engines . All that tells me that China still has some catching up to do , and since original discussion was about supposed improved RD-93 engines on JF-17 and J-31 (far beyond specs Russians have achieved with their own improvements) I would say I'm still highly skeptical of that . Lacking further evidence, I don't think I would change my opinion and you won't change yours, so let's leave it at that , at least for a time being .
 
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latenlazy

Brigadier
Re: Shenyang J-31 Fighter

thunderchief said:
Well, we actually don't have absence of evidence ;) We have core tests in 2006 and prototype tests in 2014, with 8 years of pause between them
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None of which back your original claim that they don't have the turbine blades at that specific performance ready (let's not forget the original contention here)! If they went from core testing to a full blown prototype that basically means the turbine blades are ready. Granted, 8 years of core testing is pretty long, but even an expedited timeline for core testing would have taken at least 3 years. The fact that they moved on from core testing to build a full prototype literally means everything that has to do with the engine core is okay, including the turbine blades.

As for the rest of the stuff about buying Russian engines, there's a mix of evidence (such as the 5+ regiments of Taihang equipped J-11s), and a number of potential reasons that they continue to buy Russian not related to engine readiness.
 
broadsword

broadsword

Brigadier
Here are some links on the development of single crystal turbine blades in China. The best they have is the DD6, second generation, that will be used on WS-15. They are also trying to move away from using rhesium to other less costly materials.


High-Performance Turbofans Jet Engine in A Final Step Toward
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A LOW-COST SECOND GENERATION SINGLE CRYSTAL SUPERALLOY DD6
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Fourth-generation single-crystal high temperature alloy with high strength and stable structure and preparation method thereof
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thunderchief

thunderchief

Senior Member
t2contra said:
Here are some links on the development of single crystal turbine blades in China. The best they have is the DD6, second generation, that will be used on WS-15. They are also trying to move away from using rhesium to other less costly materials.
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Thanks t2contra, very informative, although I doubt they will use DD6 for WS-15 (serial production) . DD6 is 2nd generation, or to be correct 2+ generation, with melting point somewhere around 1350-1400 C , which correspond to inlet temperature of WS-10A of 1477C (turbine blades always operate somewhat above melting temperature) . Btw, previous generation (DD3 ) was probably used in development of WS-10 .
 
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latenlazy

Brigadier
thunderchief said:
Thanks t2contra, very informative, although I doubt they will use DD6 for WS-15 (serial production) . DD6 is 2nd generation, or to be correct 2+ generation, with melting point somewhere around 1350-1400 C , which correspond to inlet temperature of WS-10A of 1477C (turbine blades always operate somewhat above melting temperature) . Btw, previous generation (DD3 ) was probably used in development of WS-10 .
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A single crystal's melting point is not the same as the temperature which it's cast. Not sure how much higher the melting point is once the crystal has set but...

EDIT: One more thought. I'm pretty sure the inlet turbine temperature does not dictate what temperature the blades will be at operation. There's going to be a temperature differential in the turbine based on a multitude of factors, and the temperature of the blades should be based on how much local heat energy is being absorbed by the materials (which is not going to be the same as the inlet temperature).
 
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SamuraiBlue

SamuraiBlue

Captain
latenlazy said:
A single crystal's melting point is not the same as the temperature which it's cast. Not sure how much higher the melting point is once the crystal has set but...
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It doesn't matter if it reaches melting point or not since at very high temperatures beyond a certain point metal starts losing structural integrity and bend or elongate through centrifugal force.
 
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latenlazy

Brigadier
SamuraiBlue said:
It doesn't matter if it reaches melting point or not since at very high temperatures beyond a certain point metal starts losing structural integrity and bend or elongate through centrifugal force.
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Sure, which is why I followed up with the second point about how the inlet temperature may not be the same as the blade's temperature. That seemed more relevant in explaining how matching inlet temperature and melting point of the turbine blade didn't make much sense.
 
thunderchief

thunderchief

Senior Member
latenlazy said:
Sure, which is why I followed up with the second point about how the inlet temperature may not be the same as the blade's temperature. That seemed more relevant in explaining how matching inlet temperature and melting point of the turbine blade didn't make much sense.
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Melting point of material is measured in controlled environment with constant pressure and no airflow . Blades operate at high rpms and at high airflow . Also, they are specially crafted to dissipate heat , therefore they could and do operate at temperatures above melting point of alloy . Some articles mention even 400 degrees above melting point, but this has to be taken with grain of salt .

The blade lives in the high-pressure turbine, where the gas temperature is at least 400 degrees above the melting point of the blade’s alloy. It sits in a disc that rotates at more than 10,000 rpm. This means that the force on the blade root is the same as hanging a London double-decker bus from its tip. Every time the plane takes-off this single blade develops the same horsepower as a Formula 1 racing car, and yet it can travel 10 million miles before it needs replacing.
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broadsword

broadsword

Brigadier
I think this quote from Wikipedia
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explains more clearly why blades can operate at temperatures above melting point.

Nickel-based superalloys are used for HP turbine blades in almost all modern jet engines. The temperature capabilities of turbine blades have increased mainly through four approaches: the manufacturing (casting) process, cooling path design, thermal barrier coating (TBC), and alloy development.

Although turbine blade (and vane) materials have improved over the years, much of the increase in (HP) turbine inlet temperatures is due to improvements in blade/vane cooling technology. Relatively cool air is bled from the compression system, bypassing the combustion process, and enters the hollow blade or vane. The gas temperature can therefore be even higher than the melting temperature of the blade. After picking up heat from the blade/vane, the cooling air is dumped into the main gas stream. If the local gas temperatures are low enough, downstream blades/vanes are uncooled and not adversely affected.

Strictly speaking, cycle-wise the HP Turbine Rotor Inlet Temperature (after the temperature drop across the HPT stator) is more important than the (HP) turbine inlet temperature. Although some modern military and civil engines have peak RITs of the order of 1,560 °C (2,840 °F), such temperatures are only experienced for a short time (during take-off) on civil engines.
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