  In this paper we consider the 3D Euler equations and we first prove a
criterion for energy conservation for weak solutions with velocity satisfying
additional assumptions in fractional Sobolev spaces with respect to the space
variables, balanced by proper integrability with respect to time. Next, we
apply the criterion to study the energy conservation of solution of the
Beltrami type, carefully applying properties of products in (fractional and
possibly negative) Sobolev spaces and employing a suitable bootstrap argument.
