  The introduction of the quantum analogue of a Carnot engine based on a bath
comprising of particles with a small amount of coherence initiated an active
line of research on the harnessing of different quantum resources for the
enhancement of thermal machines beyond the standard reversible limit, with an
emphasis on non-thermal baths containing quantum coherence. In our work, we
investigate the impact of coherence on the thermodynamic tasks of a collision
model which is composed of a system interacting, in the continuous time limit,
with a series of coherent ancillas of two baths at different temperatures. Our
results show the advantages of utilising coherence as a resource in the
operation of the machine, and allows it: (i) to exhibit unconventional
behaviour such as the appearance of a hybrid refrigerator, capable of
simultaneous refrigeration and generation of work, and (ii) to function as an
engine or a refrigerator with efficiencies larger than the Carnot bound.
Moreover, we find an effective upper bound to the efficiency of the thermal
machine operating as an engine in the presence of a coherent reservoir.
