Reasonable Intake and Exhaust Processes Scheduling of Two-Stroke Free Piston Linear Generator for Intelligent New Energy Vehicles

Abstract

Considered a promising power plant offering 25% higher efficiency than conventional reciprocating engines, the free piston linear generator (FPLG) has garnered significant attention due to its breakthrough design that eliminates the crank-connecting rod, thereby achieving enhanced efficiency. However, this structural innovation is a double-edged sword, while having the advantages such as compact structure and short transfer path to reduce energy loss, it inevitably makes the stability of the system sensitive to the operating parameters of the intake and exhaust process, which is extremely easy to lead to instability shutdown or knock. Aiming at scheduling the intake and exhaust processes rationally for system stabilization, a fast numerical method is proposed, which is different from the existing research methods. It does not need to rely on extremely time-consuming and complex CFD models, while taking into account the intake and exhaust processes as a whole rather than treating each as a separate part. The fast numerical method mainly consists of four steps. First, the gas mass variations in-cylinder and in-port due to fuel injection quality are defined. Second, gas flow is established in the valve geometry and operation pressure. Employed gas mass and gas flow, the intake pressure, the exhaust pressure, the allowable duration, and the time consumption would be settled. Third, the total power subsection is used to compute certain fuel quality. Finally, the piston dynamics are applied to calculate piston displacement for objecting valve operation and piston velocity for simulating FPLG output power. The results show that the cyclic fuel injection quality is 42–53 mg for the output power about 12.5 kW, and total efficiency about 35.5%; the intake pressure would be not less than 1.83 atm when the compression ratio is from 8 to 10 and the exhaust pressure ranges from 3.78 to 6 atm.