  The formulation of models describing quantum versions of heat engines plays
an important role in the quest toward establishing the laws of thermodynamics
in the quantum regime. Of particular importance is the description of
stroke-based engines which can operate at finite-time. In this paper we put
forth a framework for describing stroboscopic, two-stroke engines, in generic
quantum chains. The framework is a generalization of the so-called SWAP engine
and is based on a collisional model, which alternates between pure heat and
pure work strokes. The transient evolution towards a limit-cycle is also fully
accounted for. Moreover, we show that once the limit-cycle has been reached,
the energy of the internal sites of the chain no longer changes, with the heat
currents being associated exclusively to the boundary sites. Using a
combination of analytical and numerical methods, we show that this type of
engine offers multiple ways of optimizing the output power, without affecting
the efficiency. Finally, we also show that there exists an entire class of
models, characterized by a specific type of inter-chain interaction, which
always operate at Otto efficiency, irrespective of the operating conditions of
the reservoirs.
