Numerical Investigation of a Free-Piston Hydrogen-Gasoline Engine Linear Generator

Abstract

The free-piston engine linear generator (FPELG) is being investigated by many researchers because of its high thermal efficiency and its variable compression ratio. However, all researchers focused on the FPELG characteristics with mono-fuel. Therefore, in this paper, the performance of the FPELG that has adopted gasoline with hydrogen as fuel is investigated. The method of coupling the zero-dimensional dynamics model with the multi-dimensional CFD (Computational Fluid Dynamics) combustion model was applied during the simulation process. According to the results, the piston TDC (Top Dead Center), the piston peak piston velocity, and the system operation frequency show a negative correlation with the increase of hydrogen fractions. However, the peak in-cylinder pressure was increased with the hydrogen volume fraction increase, due to the fast flame speed and short combustion duration characteristics of hydrogen. Meanwhile, the indicated efficiency of the free-piston engine was increased from 32.3% to 35.3% with the hydrogen volume fraction change from 0% to 4.5%, when the free-piston engine operates at stoichiometric conditions with fixed ignition timing. In addition, with the ignition timing advance increase, the piston TDC was decreased. The peak piston velocity and the peak in-cylinder pressure were in negative correlation with the ignition timing advance. While the engine indicated that the efficiency was increased with the equivalent degree of ignition timing from 20° to 16°. Therefore, the ignition timing of the FPELG under the spark-ignition combustion mode is supposed to be an effective and practical control variable.

Rectification and converter control of the FPSLGs for energy storage applications

“…According to recent research, thermal-electrical energy conversion can make considerable contributions to renewable energy globally. Thermal electrical energy converters with improved performance can compete with other types of fossil fuels and renewable energy sources in the energy market [3,4].…”

Effect of Nonlinear Spring Characteristics on the Efficiency of Free-Piston Engine Generator

“…In FPEGs without a crank mechanism, the piston motion can be changed. As a result, the compression ratio (CR) can be changed to accommodate a variety of fuels, including hydrogen, which is a zero-carbon alternative fuel [8][9][10]. In addition, FPEGs have advantages such as reduced frictional loss because they have no crank mechanism [11,12] and improved thermal efficiency by varying the piston motion [13][14][15].…”

The effect of electromagnetic load fluctuation on the gas exchange stability of a free-piston hybrid power system

“…The study also found that increasing the effective stroke of the cylinder increased the capture rate of fresh charge, but the scavenging efficiency decreased. Zuo et al 21,22 intend to effectively control the cylinder pressure of the free-piston internal combustion generator, a variable load control method is proposed to restrain the piston movement, and a closed-loop control strategy of variable load control is designed. The simulation results show that the variable load control based on the control strategy can make the piston movement tend to be stable, so as to realize the stable control of the cylinder pressure.…”