Simulation
Porsche 6-Stroke Engine Dynamics
Parametric multibody model of Porsche's patented 6-stroke planetary engine, coupling single-zone thermodynamics with an 8-DOF drivetrain model to optimize power density, torsional vibration and higher-order inertia balancing across RPM and throttle.
Links & Resources
The Concept
Porsche's 6-stroke engine, covered by a patent filed in 2024, adds an extra compression and power stroke to the conventional four-stroke cycle. The result is two power strokes per cylinder for every three crankshaft revolutions. To achieve this, the conventional crankshaft is replaced by a planetary gear set, with a connecting rod linked eccentrically to the orbiting planet gear. The piston therefore sees two distinct top dead centres and two distinct bottom dead centres per cycle, with scavenge ports between the two BDCs enabling the additional combustion stroke.
Modelling
With over 50 design parameters to optimize simultaneously — covering cylinder layout and phasing, gear geometry, air-fuel mixture ratio, and valve timing — computational efficiency drove every modelling decision.
The thermodynamic model uses a single-zone formulation with 3 degrees of freedom per cylinder: cylinder pressure, gas mass, and oxygen mass. Heat release follows a Wiebe function, heat transfer uses the Woschni model, and compressible nozzle flow handles intake, exhaust and scavenge port flows. The model is coupled to an 8-DOF multibody drivetrain: rotational degrees of freedom for the planet gears, planet carrier, and output shaft, plus a dual-mass flywheel between engine and gearbox to suppress raw torque fluctuations.
Equations of motion are integrated in the crank-angle domain from 0 to 1080 degrees. A cycle-to-cycle fixed-point iteration finds the periodic steady state.
Design Objectives
Beyond power density, two critical objectives shaped the parametric study. The first is torsional vibration: the planetary gear transmission error excites torsional modes of the drivetrain, and its harmonic content depends strongly on gear geometry and phasing. The second is inertia balancing: the non-sinusoidal piston motion generated by the planetary mechanism introduces higher-order inertia harmonics that must be carefully managed across the range of operating speeds.
Notes on the Animation
The engine in the animation is simulated at 2000 rpm and visualized in slow motion — at its fastest, it still rotates about 20 times slower than a real Porsche engine. A public version of the model has been shared on GitHub for those interested in the implementation details.