The figure below depicts a simplified cross-sectional view of the TourEngine™ cycle:
- Intake – air and fuel enter the Cold-Cylinder through the open intake valve
- Compression – after the intake is completed, the intake valve closes and the left piston compresses the working fluid within the Cold-Cylinder.
Phase-lag – Notice that the power-piston (hot cylinder) is leading the compression-piston (cold cylinder) and has almost completed the exhaust stroke of the preceding cycle.
Transfer – After the power-piston reaches its TDC (Top Dead Center), the exhaust valve closes and the crossover valve opens to permit the Transfer of the compressed working fluid from the Cold-Cylinder to the Hot-cylinder.
- Combustion – Following closure of the crossover valve, the power stroke will progress in the Hot-Cylinder, while simultaneously in the Cold-Cylinder the next cycle will commence with the opening of the intake valve.
- Exhaust – following the completion of the power stroke, the exhaust valve opens and the power-piston moves back to its TDC to completely clear the burned working fluid.
At any given time the TourEngine™ is simultaneously performing two consecutive cycles - as combustion occurs in the Hot-Cylinder, the intake of the next cycle starts in the Cold-Cylinder.
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Notice that the two pistons of the TourEngine™ do not have any “clearance” at TDC. The power-piston continues its movement all the way to the cylinder head, clearing away completely the burned working fluid. Only after the power-piston reaches its TDC, the exhaust valve closes and the crossover valve opens to permit the transfer of the compressed working fluid. The compression-piston also does not have a “clearance”, therefore all the compressed working fluid is transferred to the combustion chamber, and then the crossover valve closes.