Yeah so I don't think it's WS-10C, and I don't see why the PLAAF would try to mount a AL-31F on a new J-20 when the entire force is so aggressively transitioning away to domestic engines (if this image is confirmed to be recent), It doesn't make sense to do so when they will be upgraded to WS-10C/WS-15 very soon, and since WS-15 has already entered LRIP, I'm inclined to belive it is a WS-15The WS-10C has a double ring structure at the nozzle exit. Doesn’t look like the engines in either of the pictures above have that.