Which is not I understand on any other Chinese-made submarine. There's been no details of this engine's development and operational history.
How can engine viability be tested when there's no live operational parameters to compare performance, ie., on another similar submarine?
To be fair, the Chinese Defense Ministry had issued an industrial certificate for the CHD620 generator, and it also received a certificate of approval from Lloyd's Register (based solely on Chinese manufacturer representations?). CHD620 is actually a licensed-manufactured version of the German MTU396 engine aka based on reverse engineering?
However (I have no direct confirmation) the CHD620 engine may have been certified as a submarine electric generator, not serve as a propulsion engine. Maybe if Thailand requires China (versus Thailand) to conduct a month of sea trials for the new submarine, that might clear up any operational concerns.