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The early acceleration of protons and electrons in the nonrelativisticcollisionless shocks with three obliquities are investigated through 1Dparticle-in-cell simulations. In the simulations, the charged particlespossessing a velocity of $0.2\, c$ flow towards a reflecting boundary, and theshocks with a sonic Mach number of $13.4$ and a Alf\'{v}en Mach number of$16.5$ in the downstream shock frame are generated. In these quasi-parallelshocks with the obliquity angles $\theta = 15^\circ$, $30^\circ$, and$45^\circ$, some of the protons and the electrons can be injected into theacceleration processes, and their downstream spectra in the momentum space showa power law tail at a time of $1.89\times10^5 \omega_{\rm pe}^{-1}$, where$\omega_{\rm pe}$ is the electron plasma frequency. Moreover, the chargedparticles reflected at the shock excite magnetic waves upstream of the shock.The shock drift acceleration is more prominent with a larger obliquity anglefor the shocks, but the accelerated particles diffuse parallel to the shockpropagation direction more easily to participate in the diffusive shockacceleration. At the time still in the early acceleration stage, more energeticprotons and electrons appear in the downstream of the shock for $\theta =15^\circ$ compared with the other two obliquities; moreover, in the upstreamregion, the spectrum of the accelerated electrons is the hardest for$\theta_{\rm nB} = 45^\circ$ among the three obliquities, whereas the protonspectra for $\theta_{\rm nB} = 15^\circ$ and $45^\circ$ are similar as a resultof the competition of the effectiveness of the shock drift acceleration and thediffusive shock acceleration.

Early acceleration of electrons and protons at the nonrelativistic quasiparallel shocks with different obliquity angles