Measured pressure traces from the 1 kW Tour engine developed with support of the ARPA-E GENSETS program. The measured pressure traces illustrate the fluid transfer between cold- and hot-cylinder and follows the complete Tour cycle: The reciprocating shuttle alternately connects through the ‘Input Port’ (IP) during phase with the cold-cylinder and through the ‘Expansion Port’ (EP) with the hot-cylinder during phase . Ignition during phase initiates combustion at a crank angle of -6° (red arrow). During phase , almost the entire trapped mass in the cold-cylinder is compressed into the shuttle volume (blue arrow) where it combusts during phase and expands into the hot-cylinder during phase . The induction and exhaust through conventional poppet valves occur during phases and , respectively. Note that there is no pressure drop during the fluid transfer through both ports as the shuttle pressure coincides with both cold- and hot-cylinder pressures during phases 1, 3.