Numerical investigation on the cold-start/restart process of a linear range extender for faster response

The free-piston linear range extender (LRE) system is an innovative energy conversion system characterized by a simple structure, high reliability, superior conversion efficiency, minimized energy loss, and excellent adaptability to various fuels. This paper establishes a numerical model for the cold start process of the LRE system, and experimental data are utilized to validate the model's accuracy. Subsequently, the influence of cylinder wall temperature on the cold start of the LRE system is investigated. Results reveal that increasing the cylinder wall temperature from 300K to 600K enhances system performance, evidenced by increased peak cylinder pressure (from 8.18 bar to 12.46 bar), peak piston speed (from 1.54 m/s to 1.91 m/s), and operating frequency (from 9.76 Hz to 11.66 Hz), alongside a reduction in ignition time (from 0.462 s to 0.229 s). Additionally, the required motor force for ignition decreases from 219 N to 194 N, showing a linear relationship with cylinder wall temperature. The study indicates that employing the cylinder wall heating method can decrease the motor force needed for ignition, leading to a notable enhancement in the system's cold start capability. This presents a promising strategy for quickly restarting the system following a misfire.