To reconcile the difference between you two, which engine do you think the J-20 uses? Deino's stance is pretty clear, so what about you, b787?
Let me first tell you I am not an expert and by that i mean an aeronautics engineer or an expert in engines, i am an engineer, but not in that area, so i am a fanboy.
My opinion does not have any authority, so you can consider it non authoritative, just my opinion.
What do i know and what do i think?
Well looking at the United Engine corporation and Salyut and Saturn pages, i see Al-31F-M2/M3 are not in production, Salyut only has the Al-31F-M1 as in production and Al-31FN, thus i think is unlikely J-20 flies with Al-31F-M2/M3 engines, why? first these engines were intended for PAKFA, but by losing the competition 117 was chosen for production for Su-35 if we believe the United Engine corporation webpage.
M2 and M3 are supposedly 14,5 and 15.3 thrust tonnes engines.
What engine is used for PAKFA? that is classified but they think it is a variant of 117S.
Al-31FN series 3 could be used but it will mean all the engines will have the gear box bellow the engines, that will imply the Chinese will either need to re-modify to fit another engine with the gear box above the engine, that is highly unlikely so all engines will need a bellow gear box.
Since they want to buy Su-35 my opinion is they want 117S, why? first is production, 117S is in large scale production thus it is cheaper to make than engines that are not, M2/M3 are not in production if they were to be gotten by the Chinese, these engines would be quiet expensive and very likely Russia would demand a large quantity, very likely 200-500 engines to justify the production and investment.
Any engine to justify its production will demand large numbers, Russia will not sell even 117 without Su-35 unless China pays for the R&D costs, so they want to sell Su-35s with spare engines, the spare engines are not free, they get 4 engines for Su-35 but they are charged, a pair fitted in the aircraft and a pair as spare.
So, Al-31F-M2 in my opinion is out of the question, is not charity too, Salyut will not open a production line for 30 or 40 engines, and if they do each engine will be charge its weight in gold, it is like a car, a handmade car is more expensive than one built in series like a volkswagen Beetle.
So in my opinion either it uses regular Al-31Fs or a Chinese engine like WS-10, but it seems WS-10 is not the engine, so i think they are using Al-31Fs
