Control and Influence of Valve Condition on Compression Stroke of Hydraulic Free Piston Engine

2018 ◽  
Author(s):  
Shengjie Fu ◽  
Haoling Ren ◽  
Tianliang Lin
Keyword(s):  
Piston Engine ◽  
Free Piston ◽  
Compression Stroke ◽  
Free Piston Engine

Tribological characteristics of piston rings in a single-piston hydraulic free-piston engine

2017 ◽  
Vol 69 (2) ◽  
pp. 131-141 ◽  
Author(s):  
Zhaoju Qin ◽  
Chenheng Yuan ◽  
Yanpeng Yuan ◽  
Yuanyuan Huang
Keyword(s):  
Numerical Simulation ◽  
Friction Loss ◽  
Piston Engine ◽  
Piston Motion ◽  
Piston Rings ◽  
Free Piston ◽  
Content Type ◽  
Compression Stroke ◽  
Free Piston Engine ◽  
Loss Efficiency

Purpose A free-piston engine (FPE) is an unconventional engine that abandons the crank system. This paper aims to focus on a numerical simulation for the lubricating characteristics of piston rings in a single-piston hydraulic free-piston engine (HFPE). Design/methodology/approach A time-based numerical simulation program was built using Matlab to define the piston motion of the new engine. And a lubrication mode of piston rings was built which is based on the gas flow equation, hydrodynamic lubrication equation and the asperity contact equation. The piston motion and the lubrication model are coupled, and then the finite difference method is used to obtain the piston rings lubrication performances of the FPE. Meanwhile, the lubrication characteristics of the new engine were compared with those of a corresponding conventional crankshaft-driven engine. Findings The study results indicate that compared with the traditional engine, the expansion stroke of the HFPE is longer, and the compression stroke is shorter. Lubrication oil film of the new engine is thicker than the traditional engine during the initial stage of compression stroke and the final stage of the power stroke. The average friction force and power of the hydraulic free piston engine are slightly lower than those of the traditional engine, but the peak friction power of the FPE is significantly greater than that of the traditional engine. With an increase in load, the friction loss power and friction loss efficiency decrease, and with a decrease in equivalence ratio, the friction power loss reduces, but the friction loss efficiency decreases first and then increases. Research limitations/implications In this paper, only qualitative analysis was performed on the tribological difference between conventional crankshaft engine and HFPE, instead of a quantitative one. Practical implications This paper contributes to the tribological design method of HFPE. Social implications No social implications are available now, as the HFPE is under the development phase. However, the authors are positive that their work will be commercialized in the near future. Originality/value The main originality of the paper can be introduced as follows: the lubrication and friction characteristics of the new engine (HFPE) were investigated and revealed, which have not been studied before; the effect of the HFPE’s special piston motion on the tribological characteristics was considered in the lubrication simulation. The results show that compared with the traditional crankshaft engine, the new engine shows a different lubrication performance because of its free piston motion.

Stability research of the compression process of two-cylinder four-stroke single-piston hydraulic free piston engine

2016 ◽  
Vol 231 (15) ◽  
pp. 2902-2911 ◽  
Author(s):  
Ren Hao-ling ◽  
Lin Tianliang ◽  
Xie Hai-bo ◽  
Yang Hua-yong
Keyword(s):  
Compression Ratio ◽  
Piston Engine ◽  
Compression Process ◽  
Free Piston ◽  
Compression Stroke ◽  
Pump Station ◽  
Free Piston Engine ◽  
Efficient Performance ◽  
Piston Assembly ◽  
Compression Chamber

An invariable compression ratio in certain conditions must be achieved to ensure a steady and efficient performance of the single-piston hydraulic free piston engine. The compression ratio is determined by the characteristics of the compression stroke. The mathematical models of the key components during the compression process are established. The kinematic characteristics of the free piston assembly are analyzed under two conditions. One condition is that free piston assembly is driven by the compression accumulator only and the other one is that free piston assembly is driven by the compression accumulator and the pump station. Pressures in compression accumulator and compression chamber are analyzed and compared in both conditions. According to the experimental results, pressures in the compression chamber and compression accumulator are not constant in both conditions during the compression process. The compression stroke and compression time vary with the changing of the pressure in the compression accumulator, which adds the complexity and changeability to the compression ratio control. An improved configuration is put forward to solve the pressure variation. The results show that the improved configuration can make the pressure invariable at the inlet of the compression chamber and the compression process keeps almost the same regardless of the pressure changing in the compression accumulator. With this new structure, there is about 2.5% energy loss, which is acceptable considering the stable compression stroke.

scholarly journals Research on the Operating Characteristics of Hydraulic Free-Piston Engines: A Systematic Review and Meta-Analysis

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3530
Author(s):  
Fukang Ma ◽  
Shuanlu Zhang ◽  
Zhenfeng Zhao ◽  
Yifang Wang
Keyword(s):  
Systematic Review ◽  
High Efficiency ◽  
Meta Analysis ◽  
Combustion Process ◽  
Research Progress ◽  
Future Research ◽  
Operating Characteristics ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine

The hydraulic free-piston engine (HFPE) is a kind of hybrid-powered machine which combines the reciprocating piston-type internal combustion engine and the plunger pump as a whole. In recent years, the HFPE has been investigated by a number of research groups worldwide due to its potential advantages of high efficiency, energy savings, reduced emissions and multi-fuel operation. Therefore, our study aimed to assess the operating characteristics, core questions and research progress of HFPEs via a systematic review and meta-analysis. We included operational control, starting characteristics, misfire characteristics, in-cylinder working processes and operating stability. We conducted the literature search using electronic databases. The research on HFPEs has mainly concentrated on four kinds of free-piston engine, according to piston arrangement form: single piston, dual pistons, opposed pistons and four-cylinder complex configuration. HFPE research in China is mainly conducted in Zhejiang University, Tianjin University, Jilin University and the Beijing Institute of Technology. In addition, in China, research has mainly focused on the in-cylinder combustion process while a piston is free by considering in-cylinder combustion machinery and piston dynamics. Regarding future research, it is very important that we solve the instabilities brought about by chance fluctuations in the combustion process, which will involve the hydraulic system’s efficiency, the cyclical variation, the method of predicting instability and the recovery after instability.

A review on the operating characteristics of free piston engine and its recent developments

2018 ◽  
Author(s):  
Evelyn Evelyn ◽  
A. Rashid A. Aziz ◽  
Firmansyah Firmansyah ◽  
Ezrann Zharif Zainal Abidin
Keyword(s):  
Operating Characteristics ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine ◽  
Recent Developments

scholarly journals Research of a Hybrid Diesel Locomotive Power Plant Based on a Free-Piston Engine

2020 ◽  
Vol 22 (3) ◽  
pp. 103-109
Author(s):  
Serhiy Buriakovskyi ◽  
Borys Liubarskyi ◽  
Artem Maslii ◽  
Danylo Pomazan ◽  
Tatyana Tavrina
Keyword(s):  
Internal Combustion Engine ◽  
Combustion Engine ◽  
Internal Combustion ◽  
Diesel Generator ◽  
Piston Engine ◽  
Diesel Locomotive ◽  
Free Piston ◽  
Electric Transmission ◽  
Free Piston Engine ◽  
Hybrid Transmission

This article describes one of the possible ways for improving the energy efficiency of shunting diesel locomotives. It means a replacing a traditional traction electric transmission with a diesel generator set with a hybrid transmission with a free-piston internal combustion engine and a linear generator. The absence of a crankshaft in an internal combustion engine makes it possible to reduce thermal and mechanical losses, which, in turn, leads to an increase in the efficiency of traction electric transmission of the diesel locomotive.

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