  We revisit the mathematics of exactly solvable Unruh-DeWitt detector models,
interacting with massless scalar fields under instantaneous interactions, to
construct a relativistic quantum Otto heat engine. By deriving the conditions
under which the thermodynamic cycle is closed we study the effects of motion on
the amount of work that can be extracted from the machine when the working
medium is moving at a constant relativistic velocity through the heat baths.
While there is a degrading effect with respect to speed in the hot bath, we
demonstrate that in the case of the cold bath, genuine enhancing effects are
sometimes present. For couplings the same order as the inverse frequency of the
detector and a specific value for the temporal separation between the two
instantaneous interactions--needed in order to be possible to cool the
detector--a non-monotonic dependence between speed and extracted work exists
raising the intriguing possibility of exploiting relativistic effects for the
enhancement of thermodynamic processes in tabletop experiments.
