Regarding the YF-75E LOX/LH2 upper stage engine. The torch ignition, if it is what I think it is,
As I understand torch ignition is to keep a small flame when the engine is shutdown, the small flame is used to re-ignite the engine. I guess this is what you thought?
is basically capable of multiple ignitions. This means the engine will be multiple restart capable. For example for putting satellite constellations into orbit with multiple satellites per launch. This is different from using expendable pyrotechnic ignition.
I think most ignition methods are able for multiple restart. Pyrotechnic (火药点火) is done by multiple cartridges such as YF-100M and YF-100N are able to re-ignited for the 2nd time using two cartridges. While YF-100(K) is one time ignition.
BTW, YF-75 (CZ-7A) and YF-75D (CZ-5) are all capable of two ignitions. I don't know if they are torch or pyrotechnic though. Pay attention, YF-75E is the first
low pressure torch ignition as the article said, it is the only torch ignition engine. I know YF-90 is torch ignition, so as the 200t methane engine.
Torch ignition's advantage is that the flame is maintained by the fuel, so there is unlimited number of times of re-ignition instead of the number of cartridges. It is like one can try to re-start the car in a cold day as long as there is electricity in the battery.
