Simulation methodology and numerical comparison of boxer and opposed free piston linear generator configuration in 0D/1D environment

Abstract

Free Piston Linear Generators (FPLGs) are thermal machines suitable for both stationary power generation unit (PU) and vehicle propulsion. They convert chemical energy from the fuel into electric energy to charge a battery using a linear electric generator. Due to the reduction of friction losses and the ability to work with different compression ratios, FPLGs are potentially characterized by high overall global efficiency with respect to a conventional alternative internal combustion engine. Like conventional internal combustion engines, FPLGs have several configurations: single piston, dual piston, opposed piston and boxer are the configurations considered in this work. Two configurations are compared in this paper from a functional and energetic perspective: opposed piston (Opposed) and Boxer. This is done with the aim to highlights pro and cons of these configurations. They are modelled using the 0D/1D modelling coupling GT-Power® and Simulink®. The comparison between the two configurations was done modelling the architecture with the same size and in two-strokes operating mode. The comparison of the two configurations highlights differences between them in terms of scavenging process, thermodynamic efficiency and global energy efficiency, putting in evidence what aspects need to be improved for each configuration and what are their advantageous features. Boxer configuration can provide less power due to lower volumetric efficiency compared to the Opposed configuration. Boxer configuration can provide 102.2 kW while Opposed can provide 110.0 kW at full load with a frequency of 20 Hz (equivalent to 1200 rpm). The Opposed configuration results in lower heat loss but higher energy lost at the exhaust. The final balance shows that Boxer configuration has a slightly higher brake efficiency (equal to 28.9 %) compared to the value found for Opposed (27.6 %).