Analysis of the Scavenging Process of a Two-Stroke Free-Piston Engine Based on the Selection of Scavenging Ports or Valves

Boru Jia,Anthony Roskilly,Andrew Smallbone,Yaodong Wang

doi:10.3390/en11020324

Boru Jia, Anthony Roskilly + Show 2 more

Open Access

https://doi.org/10.3390/en11020324

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Journal: Energies	Publication Date: Feb 2, 2018
Citations: 13	License type: CC BY 4.0

Affiliation: Newcastle University, Beijing Institute of Technology

Abstract

The free-piston engine generator (FPEG) is a linear energy conversion device with the objective of utilisation within a hybrid-electric automotive vehicle power system. In this research, the piston dynamic characteristics of an FPEG is compared with that of a conventional engine (CE) of the same size, and the difference in the valve timing is compared for both port scavenging type and valve scavenging type, with the exhaust valve closing timing is selected as the parameter. A zero-dimensional simulation model is developed in Ricardo WAVE software (2016.1), with the piston dynamics obtained from the simulation model in Matlab/SIMULINK (R2017a). For the CE and FEPG using scavenging ports, in order to improve its power output to the same level as that of a CE, the inlet gas pressure is suggested to be improved to above 1.2 bar, approximately 0.2 bar higher than that used for a CE. If a CE cylinder with exhaust valves is adopted or referred to during the development of an FPEG prototype, the exhaust valve is suggested to be closed earlier to improve its power output, and a higher intake pressure is also suggested if its output power is expected to be the same or higher than that of a CE.

Highlights

The free-piston engine (FPE) is a novel power device system, and the main difference from a conventional crankshaft engine is that the piston motion is linear and free to move between its dead centers [1,2]
The FPE connected with a linear electric generator is selected for future application in hybrid-electric automotive vehicles
FPEGisiscompared compared withport that of conventional enginethe of the same size, and thecharacteristics difference in theof valve for both scavenging engine type andofvalve scavenging type,the with the exhaust valve closing timing selected as the a conventional the same size, and difference in the valve timing is compared for both parameter

Summary

Introduction

The free-piston engine (FPE) is a novel power device system, and the main difference from a conventional crankshaft engine is that the piston motion is linear and free to move between its dead centers [1,2]. For the FPEs, the elimination of the crankshaft system and the reduction of mechanical components significantly reduces the complexity of the engine [3]. This gives a number of advantages: the heat transfer losses and NOx generation are supposed to be reduced due to faster expansion stroke; the frictional losses should be reduced due to the simplified mechanism and the elimination of the piston side force in conventional reciprocating engines; potentially lower maintenance cost due to a compact design; and multi-fuel/combustion mode possibility due to a possibility of variable compression ratio [4].

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