The YF-23 is a liquid rocket vernier engine, burning N<sub>2</sub>O<sub>4</sub> and UDMH. It is used in along the YF-22 to form the YF-24 and YF-25 propulsion modules.
The basic engine has been used since the Feng Bao 1 rocket and has been the vernier propulsion of the Long March 2, Long March 3 and Long March 4 families second stage.
This engine is bundled into modules along the YF-22 upper stage engine.
The relevant modules for second stage application are: