  We present a spectral and timing study of the NuSTAR and Swift observations
of the black hole candidate IGR J17091-3624 in the hard state during its
outburst in 2016. Disk reflection is detected in each of the NuSTAR spectra
taken in three epochs. Fitting with relativistic reflection models reveals that
the accretion disk is truncated during all epochs with $R_{\rm in}>10~r_{\rm
g}$, with the data favoring a low disk inclination of $\sim
30^{\circ}-40^{\circ}$. The steepening of the continuum spectra between epochs
is accompanied by a decrease in the high energy cut-off: the electron
temperature $kT_{\rm e}$ drops from $\sim 64$ keV to $\sim 26$ keV, changing
systematically with the source flux. We detect type-C QPOs in the power spectra
with frequency varying between 0.131 Hz and 0.327 Hz. In addition, a secondary
peak is found in the power spectra centered at about 2.3 times the QPO
frequency during all three epochs. The nature of this secondary frequency is
uncertain, however a non-harmonic origin is favored. We investigate the
evolution of the timing and spectral properties during the rising phase of the
outburst and discuss their physical implications.
