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

Ziwei Zhang,Huihua Feng,Zhengxing Zuo

doi:10.3390/en13184685

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.

Highlights

The free-piston internal combustion engine linear generator (FPELG), as a novel fuel-to-electricity energy conversion device, has been studied by many groups in the whole world because of the unique operation characteristics [1,2,3,4,5,6]
Due to the unique physicochemical properties during the gasoline with hydrogen as the fuel input during the combustion process and the operation characteristics of the FPELG, the simulation method of the coupled zero-dimensional dynamic models and multi-dimensional CFD combustion model was applied during the simulation process
The mover operation characteristics and the performance of the gasoline FPELG with various hydrogen volume fractions increases from 0% to 4.5% in intervals of 1.5% are compared

Summary

Introduction

The free-piston internal combustion engine linear generator (FPELG), as a novel fuel-to-electricity energy conversion device, has been studied by many groups in the whole world because of the unique operation characteristics [1,2,3,4,5,6]. The FPELG consists of the free-piston engine and the linear generator directly [3]. According to the FPELG operation principle, it is found that the FPDLG shows many differences with the conventional internal combustion engines (ICEs) in terms of the construction, operation performance, combustion characteristics, etc. Compared with the conventional ICEs, the FPELG has many advantages, such as the high indicated thermal efficiency, the short energy conversion-chain, multi-fuel, and multi-combustion modes feasibility [8]. The only moving component of the FPELG is the mover so that the friction loss is reduced significantly [9,10]

Objectives

Results

Conclusion