I would assume a living emperor is not generally referred to by any name.
In the Chinese system, emperors before the Tang dynasty are referred to (now) by their posthumous name (汉武帝 Han Wudi, the "Han Martial Emperor"), from the Tang to the Yuan they are referred to by temple name (唐太宗 Tang Taizong, the "Tang Great Ancestor"), and from the Ming dynasty forward they are referred to by the name of their reign period (康熙帝 Kangxi Di, the "Kangxi Emperor").
They could not be referred to by the name of a reign period before then because the norm was for one emperor to reign over several named periods. And they are never referred to by their actual personal name (e.g. 李世民 Li Shimin, the name of the person who became Tang Taizong).
