Dynamic modeling of SI/HCCI free-piston engine generators

For the purpose of model-based analysis and control design, a dynamic physics-based model for free-piston engine generator is developed in this paper. The physics-based model contains 16 states, which include piston dynamics, port and cylinder gas filling dynamics and thermal dynamics. Homogeneous charge compression ignition (HCCI) combustion is employed for better efficiency and reduced emissions, whereas spark ignition (SI) combustion can be used for quick start. Equipped with electric mechanical valves (EMV) and direct injection, the free-piston engine generator is deemed to achieve optimized and clean combustion. Key features in this dynamic model include the port and cylinder filling dynamics and cycle-to-cycle coupling between the piston motion and combustion process. The effects of the amount of fuel, valve timings and load constant on the important performance variables such as piston dynamics and combustion timings are evaluated via simulation.