The operating regimes of a laboratory external combustion engine consisting of a catalytic heater, working cylinder, connection unit with hydroresistance, back pressure unit, and thermochemical recuperator have been studied. An experimental technique that provides an estimate of the power developed by an engine to perform mechanical work has been created. It has been shown that the efficiency can be increased by recu perating the heat of combustion products from the endothermic reaction of the steam that reforms the initial fuel, e.g., propane-butane, into syngas. The effect of the process parameters on an increase in the inner engine efficiency is analyzed. It has been shown that the maximum pressure in the working cylinder has the greatest effect on an increase in the inner efficiency.