We numerically study the self-compression of the optical pulses centered at 1.8-μm in a hollow-core fiber (HCF) filled with argon.It is found that the pulse can be self-compressed to 2 optical cycles when the input pulse energy is 0.2-J and the gas pressure is 500-mbar (1 bar=105 Pa).Inducing a proper positive chirp into the input pulse can lead to a shorter temporal duration after self-compression.These results will benefit the generation of energetic few-cycle mid-infrared pulses.