  A dual radiative heat engine is a device made of two facing optoelectronic
components (diodes) and capable of generating electrical power from heat. It
can operate in three different regimes depending on the component biases,
namely in thermoradiative-negative electroluminescent (TRNEL),
thermoradiative-photovoltaic (TRPV) or thermophotonic (TPX) regimes. The use of
dual engines gives access to operating conditions which are unachievable by
single radiative engines such as thermophotovoltaic systems: at the radiative
limit, TRNEL devices systematically reach the Carnot efficiency, while TPX
devices can achieve large power outputs by means of electroluminescent
enhancement. Upper bounds of the maximum power output and related efficiency
achieved by dual engines are derived analytically, and compared to usual
bounds. Spectral filtering and nonradiative recombinations are also briefly
considered. This work provides common framework and guidelines for the study of
radiative engines, which represent a promising solution for reliable and
scalable energy conversion.
