Energy and exergy analysis of hydraulic free-piston engines

2018 ◽  
Vol 233 (12) ◽  
pp. 3074-3087 ◽  
Author(s):  
Lei Wang ◽  
Zhenfeng Zhao ◽  
Chuncun Yu ◽  
Fujun Zhang ◽  
Changlu Zhao
Keyword(s):  
Thermal Efficiency ◽  
Waste Heat ◽  
Energy Utilization ◽  
Injection Timing ◽  
Characteristic Parameters ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis

A hydraulic free-piston engine is an unconventional reciprocating piston internal combustion engine in which the piston assembly motion is determined by in-cylinder gas pressure and load force. Fuel combustion energy is directly converted into hydraulic energy. These affect the work process of cylinder and efficiency of energy conversion. In order to study the energy utilization efficiency and to explore the recovery potential of waste heat energy of hydraulic free-piston engine, in this paper, the energy distribution and waste heat energy characteristics of hydraulic free-piston engine have been studied by combining energy and exergy analysis. The thermal efficiency was analyzed by the first law of thermodynamics, and exergy balance was analyzed by the second law. The effect of the characteristic parameters on the thermal and exergy efficiency was studied through the simulation analysis comparing the energy utilization of hydraulic free-piston engine and conventional engines. The results show that control of the injection timing parameter is effective for optimizing efficiency because the cycle characteristic parameters can be controlled by changing the injection timing. The experimental results show that the thermal efficiency is 40.8% and the exergy efficiency is 46.3%. The simulation result show that the thermal efficiency of hydraulic free-piston engine is 38.0% and the conventional diesel engine is 33.0%.

New Free-Piston Topping Cycle for Gas-Turbine Power Plants

2003 ◽  
Author(s):  
William L. Kopko ◽  
John S. Hoffman
Keyword(s):  
High Performance ◽  
Power Plants ◽  
Waste Heat ◽  
Combustion Engine ◽  
Complete Recovery ◽  
Combined Cycle ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine ◽  
Topping Cycle

A proposed topping cycle inserts a free-piston internal-combustion engine between the compressor and the combustor of a combustion turbine. The topping cycle diverts air from the compressor to supercharge the free-piston engine. Because the free-piston engine uses gas bearings to support the piston and is built of high-temperature materials, the engine can increase the pressure and temperature of the gas, exhausting it to a small expander that produces power. The exhaust from the topping-cycle expander is at a pressure that can be re-introduced to the main turbine, allowing almost complete recovery of waste heat. A capacity increase exceeding 35% is possible, and overall cycle efficiency can approach 70% when incorporated into a state-of-the-art combined-cycle plant. The cost of per incremental kW of the topping cycle can be dramatically lower than that of the base turbine because of the high power density and simplicity of the engine. Building on decades of progress in combustion turbines systems, the new cycle promises high performance without the engineering risks of manufacturing a completely new cycle.

Multi-Dimensional Analysis of NOx and Soot Formation in a Diesel-Fueled Hydraulic Free Piston Engine

2013 ◽  
Vol 690-693 ◽  
pp. 2800-2804
Author(s):  
Ying Xiao Yu ◽  
Zhao Cheng Yuan ◽  
Jia Yi Ma ◽  
Shi Yu Li
Keyword(s):  
Mass Fraction ◽  
Soot Formation ◽  
Combustion Process ◽  
Injection Timing ◽  
Swirl Ratio ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine ◽  
Minor Influence ◽  
A Minor

This paper is aimed at simulating and analyzing emission NOxand Soot formation in the hydraulic free piston engine (HFPE) designed and constructed by Jilin University. The combustion process of HFPE is simulated by using the commercial CFD software AVL FIRE, and the flow field and factors that influence NOxand Soot formation were analyzed. The simulated results indicate that NO is mainly distributed in the burned zone, whereas the distribution of Soot acts in accord with high unburnt equivalence ratio and high temperature burned zone. Injection timing increases, the amount of the formation of NO is reduced, whereas the mass fraction of Soot rises to a peak and descends. And small swirl ratio exerts a minor influence on emission mass fraction of HFPE.

Study on the Motion Characteristics of a Hydraulic Free-Piston Engine

2014 ◽  
Vol 889-890 ◽  
pp. 390-393
Author(s):  
Shi Yu Li ◽  
Zhao Cheng Yuan ◽  
Jia Yi Ma
Keyword(s):  
Fuel Injection ◽  
Fuel Efficiency ◽  
Injection Timing ◽  
Piston Engine ◽  
Free Piston ◽  
Fuel Injection Timing ◽  
Free Piston Engine ◽  
Center Position ◽  
Working Frequency ◽  
Motion Characteristics

Hydraulic free-piston engines have potential advantages of cost and fuel efficiency. Due to no crankshaft system, it is difficult and important to control the piston motion and working frequency precisely. This paper studies on the motion characteristics for the hydraulic free-piston engine effects of operation parameters, and results are presented. The TDC (Top Dead Center) position and CR (Compression Ration) are great influenced by starting pressure and fuel injection timing, and working frequency is mainly influenced by piston mass, starting pressure and fuel quantity.

Realizing Trajectory-Based Combustion Control in a Hydraulic Free Piston Engine via a Fast-Response Digital Valve

2018 ◽  
Author(s):  
Chen Zhang ◽  
Zongxuan Sun
Keyword(s):  
Chemical Kinetics ◽  
Thermal Efficiency ◽  
Fast Response ◽  
Combustion Control ◽  
Piston Engine ◽  
Free Piston ◽  
Frictional Loss ◽  
Switching Strategy ◽  
Hcci Combustion ◽  
Free Piston Engine

Previously, the authors have proposed the concept of piston trajectory-based combustion control enabled by a free piston engine (FPE) and shown its advantages on both thermal efficiency and emissions performance. The main idea of this control method is to design and implement an optimal piston trajectory into FPE and optimizes the combustion performance accordingly. To realize the combustion control in practice, it is obvious that the design of the optimal trajectory should consider the dynamic behaviors of the FPE’s actuation systems as well as variable load dynamics and fuels’ chemical kinetics. In this paper, a comprehensive model describing the operation of a hydraulic FPE fueled by diesel under HCCI combustion mode is developed. Such a high fidelity model includes four parts, i.e. the piston dynamics, the hydraulic dynamics, the thermodynamics and the fuel’s chemical kinetics. Extensive simulation results are produced, showing that by varying the switching strategy of a fast-response digital valve, the hydraulic FPE can operate at different working loads in a stable manner. Additionally, analysis has been conducted to quantify the thermal efficiency as well as the frictional loss and throttling loss of the FPE. At last, a feedback control is developed to generate optimal switching strategies for the digital valve aimed to achieve the HCCI combustion phasing control. The resulted switching strategy of the digital valve not only increases the thermal efficiency by 0.76%, but also reduces frictional loss by 9.8%, throttling loss by 6.5% as well as NOx emission by 85.6%, which clearly demonstrates the effectiveness of the trajectory-based combustion control.

Operation of a turbine-compound free-piston linear alternator

2021 ◽  
pp. 146808742110159
Author(s):  
Chang-Ping Lee ◽  
Claus Borgnakke ◽  
Russell Durrett
Keyword(s):  
Injection Timing ◽  
Actual Behavior ◽  
Piston Engine ◽  
Combustion Chambers ◽  
Free Piston ◽  
Free Piston Engine ◽  
Linear Alternator ◽  
Mechanical Models ◽  
Control Volumes ◽  
Engine Map

A free-piston linear-alternator combined with combustion chambers has been examined in many studies. However, only simplified thermodynamic and mechanical models were developed to mimic the actual behavior of the free-piston engine. The purpose of this study is to establish a fully dynamic model that can calculate the energy transformation under the operation of the free-piston engine. The Matlab/Simulink® model uses non-constant-volume combustion event, the piston transient dynamics, flow, heat losses, and thermodynamics as bridges to connect control volumes. The model successfully captured the behavior and measurements of a GS-34 free-piston engine, based on a thermodynamic calculation calibrated with experimental data. The resulting model is used for a series of parametric studies to understand the very complex system behavior, including low load operation. Operation parameters (injection timing and bounce chamber mass) are optimized to generate the engine map for different alternator sizes. At the end, the advantages of the opposed free-piston engine with a linear alternator are presented through the energy analysis.

scholarly journals Two-Stroke Thermodynamic Cycle Optimization of a Single-Cylinder Free-Piston Engine Generator

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Houliang Yu ◽  
Zhaoping Xu ◽  
Qinglin Zhang ◽  
Liang Liu ◽  
Ru Hua
Keyword(s):  
Simulation Model ◽  
Performance Optimization ◽  
Thermodynamic Cycle ◽  
Prototype System ◽  
Injection Timing ◽  
Connecting Rod ◽  
Piston Engine ◽  
Free Piston ◽  
Single Cylinder ◽  
Free Piston Engine

A free-piston engine generator (FPEG) is a new type of energy converter, which eliminates the crankshaft and connecting rod mechanism. In order to achieve efficient energy conversion, the two-stroke thermodynamic performance optimization of a single-cylinder free-piston engine generator is investigated in this paper. Firstly, the components, four-stroke thermodynamic cycle, two-stroke thermodynamic cycle, and prototype system of the FPEG are presented in detail. The one-dimensional flow simulation model of the FPEG is created based on the gas dynamics equation, Weber combustion function, and heat transfer function, and then the model is validated by the data tested from the prototype system. According to the four-stroke experimental results of the FPEG, an effective power of 4.75 kW and a peak pressure of 21.02 bar have been obtained. Then, the two-stroke thermodynamic cycle is simulated and compared under the different control parameters of intake air pressure, injection timing, ignition timing, and valve timing through the simulation model. The optimized results show that an indicated thermal efficiency of 27.6%, an indicated power of 6.7 kW, and a maximal working frequency of 25 Hz can be achieved by the prototype system, when the two-stroke thermodynamic cycle is used.

Motion Characteristics and Influence Factors of Piston Assembly in a Compression-Ignition Hydraulic Free-Piston Engine

2013 ◽  
Vol 860-863 ◽  
pp. 1761-1765
Author(s):  
Ying Xiao Yu ◽  
Zhao Cheng Yuan ◽  
Jia Yi Ma ◽  
Shi Yu Li
Keyword(s):  
Fuel Injection ◽  
Influence Factors ◽  
Basic Structure ◽  
Injection Timing ◽  
Compression Ignition ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine ◽  
Motion Characteristics ◽  
Piston Assembly

The advantages and basic structure of hydraulic free-piston engine (HFPE) were presented. And the operation principle of a single piston compression-ignition HFPE was analyzed. Based on the basic theory of thermodynamics, hydraulic fluid mechanics and dynamics, the system simulation model for a single-piston compression-ignition HFPE was established in the environment of MATLAB/SIMULINK. The simulation results, which accord with the related literature data, indicate that the asymmetric characteristics of piston motion in the entire cycle are very obvious, the compression stroke duration is longer than the expansion stroke, the time at around the top dead center (TDC) is short. The piston assembly motion is a process when the energy balance is fulfilled, and some factors must be taken into account for design optimization, such as the piston assembly mass, compression accumulator pressure, fuel injection timing and fuel injection quantity.

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.

Sign in / Sign up

Export Citation Format

Share Document