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.
Model and Assumptions
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.
Significance
A trimmed, public version of the model is shared on GitHub. The modelling choices — single-zone thermodynamics at three DOFs per cylinder, integration in the crank-angle domain, and a cycle-to-cycle fixed-point search for the periodic steady state — keep the full coupled engine–drivetrain model cheap enough to sweep more than 50 design parameters across the RPM–throttle map. That turns an unconventional architecture, with its non-sinusoidal piston motion and planetary transmission error, into something that can be balanced and optimized at the design stage rather than discovered on a test bench.