scholarly journals Investigations for a Trajectory Variation to Improve the Energy Conversion for a Four-Stroke Free-Piston Engine

2021 ◽  
Vol 11 (13) ◽  
pp. 5981
Author(s):  
Robin Tempelhagen ◽  
Andreas Gerlach ◽  
Sebastian Benecke ◽  
Kevin Klepatz ◽  
Roberto Leidhold ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Alternative Fuels ◽  
Internal Combustion Engines ◽  
Combustion Process ◽  
Optimal Operation ◽  
Combustion Engines ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine ◽  
Future Work

Internal combustion engines with a crankshaft have been successfully developed for many years. They are lacking in the fact that the piston trajectory, i.e., position as a function of time, is limited by the crankshaft motion law. Position-controlled electric linear machines directly coupled to the piston allow to realize free-piston engines. Unlike the crankshaft-based engines, they allow for a higher degree of freedom in shaping the piston trajectory, including adaptive compression ratios, which enables optimal operation with alternative fuels. The possibility of adapting the stroke course results in new degrees of freedom with which the combustion process can be optimized. In this work, four-stroke trajectories with different amplitudes and piston dynamics have been proposed and analyzed regarding efficiency. A simulation model was created based on experimental measurements for testing the proposed trajectories. It could be proved that the variation of the trajectory resulted in an improvement of the overall efficiency. The trajectories were described analytically so that they can be used for a prototype in a future work.

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.

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.

A Virtual-Cam Control Methodology for Free-Piston Engines

2011 ◽  
Author(s):  
Chao Yong ◽  
Eric J. Barth
Keyword(s):  
Internal Combustion Engines ◽  
Control Method ◽  
Piston Engine ◽  
Piston Motion ◽  
Stroke Length ◽  
Free Piston ◽  
Physical Context ◽  
Spark Timing ◽  
Free Piston Engine ◽  
Timing Belt

In conventional internal combustion engines, valves are opened and closed using a cam surface. The cam is kinematically related to the piston positions through the crankshaft and timing belt. In contrast, there is no crankshaft or kinematic cam surface in a free-piston engine to physically realize this mechanism. As a consequence, a free-piston engine has variable stroke lengths, which presents a challenge for active piston motion and precise stroke length control. This paper presents a virtual-cam based approach to relate free-piston motion to actuated engine valve control within a clear and familiar intuitive physical context. The primary functionality of the virtual cam control framework is to create a variable index, which is adjustable from cycle to cycle, for the exhaust/injection valves and spark timing similar to the function of physical cams in conventional engines. Since the cam is virtually created, it can be dynamically rebuilt to comply with cycle-to-cycle variations such as amount of the air/fuel supply, engine load and stroke length. This index rebuilding process is based on a cycle-to-cycle adaptive control method that uses the knowledge obtained from previous cycles to adjust the cam parameters. Preliminary experimental results are presented for a novel liquid-piston free-piston engine intended as a compact and efficient energy source for untethered power dense pneumatic systems such as untethered robots.

Experimental investigation of the cycle-to-cycle variations in combustion process of a hydraulic free-piston engine

Energy ◽  
2014 ◽  
Vol 78 ◽  
pp. 257-265 ◽  
Author(s):  
Zhenfeng Zhao ◽  
Dan Wu ◽  
Zhenyu Zhang ◽  
Fujun Zhang ◽  
Changlu Zhao
Keyword(s):  
Experimental Investigation ◽  
Combustion Process ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine

Effect of Piston Motion on Combustion of CNG Free Piston Engine (FPE)

2014 ◽  
Vol 889-890 ◽  
pp. 501-506
Author(s):  
Ning Xia Yin ◽  
Zhao Ping Xu ◽  
Si Qin Chang ◽  
Ji Ming Lin
Keyword(s):  
Heat Transfer ◽  
Combustion Process ◽  
Engine Performance ◽  
Expansion Ratio ◽  
Nox Emissions ◽  
Piston Engine ◽  
Piston Motion ◽  
Free Piston ◽  
Beneficial Effects ◽  
Free Piston Engine

CNG is thought to be one of the most promising alternatives to traditional fuels. The multi-fuel ability is another characteristic of the FPE. The piston motion can be controlled to have beneficial effects on the engine performance. This article investigates the effect of piston motion on combustion of four-stroke CNG FPE using a multidimensional simulation model. It is found that the high piston acceleration and velocity at top dead center increases expansion ratio and fasting combustion, reduces the heat transfer losses and decreased NOx emissions formation. At the same time, the turbulent kinetic energy of the gas during the combustion process is added.

Modeling of Piston Trajectory-Based HCCI Combustion

2014 ◽  
Author(s):  
Chen Zhang ◽  
Ke Li ◽  
Zongxuan Sun
Keyword(s):  
Lawrence Livermore National Laboratory ◽  
National Laboratory ◽  
Combustion Process ◽  
Gas Temperature ◽  
Piston Engine ◽  
Free Piston ◽  
Active Motion ◽  
Motion Patterns ◽  
Bottom Dead Center ◽  
Free Piston Engine

Previously, the authors have designed and implemented an active motion control “virtual crankshaft” for a free piston engine, which enables precise piston tracking of desired trajectories. With this mechanism, the volume of the combustion chamber can be regulated, and therefore the pressure, temperature and species concentrations of in-cylinder gas can be adjusted in real-time which affect the combustion process directly. This new degree of freedom enables us to conduct trajectory-based combustion control. In this paper, a model of the free piston engine running homogeneous charge compression ignition combustion under variant piston trajectories is presented. The variant piston trajectories have the ability to change the compression ratio and accommodate different piston motion patterns between the top dead center and the bottom dead center. The Lawrence Livermore National Laboratory reduced n-heptane reaction mechanism is employed in the model in order to describe the chemical kinetics under various piston trajectories. Analysis of the simulation results is then presented which reveals the piston trajectory effects on the combustion phenomena in terms of in-cylinder gas temperature trace, indicated output work, heat loss and radical species accumulation process.

Research of Micro Free-Piston Engine Generator Performance

2011 ◽  
Vol 199-200 ◽  
pp. 198-202
Author(s):  
Qian Wang ◽  
Jin Hua Yang ◽  
Jin Bai ◽  
Jun Jie Chen ◽  
Ze Chen
Keyword(s):  
Dynamic Model ◽  
Combustion Process ◽  
Engine Performance ◽  
Combustion Efficiency ◽  
Operating Characteristics ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine ◽  
Engine Combustion ◽  
Ignition And Combustion

Based on the operating characteristics of a micro HCCI (Homogeneous Charge Compress Ignition) free-piston engine, a multidimensional model which coupled CFD code, chemical dynamic model and piston dynamic model has been established. Using this model, an ignition and combustion process of the micro engine is simulated, the cylinder pressure and temperature profiles are obtained, and the influence of leakage and heat lost on micro engine combustion process is analyzed. Meanwhile, working characteristics of micro engine generator are evaluated by employing the simulation result. Power, combustion efficiency, etc of the micro engine are obtained. Lastly, the micro engine working characteristics with different load, fuel and piston mass are compared and effects of those varying conditions on engine performance are investigated. Simulation result provides essential requirements for micro free-piston engine control and design.

scholarly journals Effects of Injector Spray Angle on Performance of an Opposed-Piston Free-Piston Engine

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3735
Author(s):  
Qinglin Zhang ◽  
Zhaoping Xu ◽  
Shuangshuang Liu ◽  
Liang Liu
Keyword(s):  
Combustion Engine ◽  
Fluid Dynamic ◽  
Combustion Process ◽  
Three Dimensional ◽  
Mixture Distribution ◽  
Combustion Efficiency ◽  
Spray Angle ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine

A free-piston engine is a novel internal combustion engine which has the advantages of a variable compression ratio and multi-fuel adaptability. This paper focuses on numerical simulation for combustion process and spray angle optimization of an opposed-piston free-piston engine. The working principle and spray-guided central combustor structure of the engine are discussed. A three-dimensional computational fluid dynamic model with moving mesh is presented based on the tested piston motion of the prototype. Calculation conditions, spray models, and combustion models were set-up according to the same prototype. The effects of spray angle on fuel evaporation rate, mixture distribution, heat release rate, in-cylinder pressure, in-cylinder temperature, and emissions were simulated and analyzed in detail. The research results indicate that the performance of the engine was very sensitive to the spray angle. The combustion efficiency and the indicated thermal efficiencies of 97.5% and 39.7% were obtained as the spray angle reached 40°.

Piston Rings Friction Comparison in a Free Piston and Conventional Crankshaft Engines

2018 ◽  
Author(s):  
Mehar Bade ◽  
Nigel N. Clark ◽  
Terence Musho ◽  
Parviz Famouri
Keyword(s):  
Film Thickness ◽  
Internal Combustion Engines ◽  
Asperity Contact ◽  
Combustion Engines ◽  
Power Losses ◽  
Piston Rings ◽  
Free Piston ◽  
Oil Film ◽  
Frictional Losses ◽  
Free Piston Engine

The conventional internal combustion engines driven by crankshafts and connecting rod mechanisms are restrained by combustion, thermal and mechanical inefficiencies. The Oscillating Free Piston Linear Engine Alternator (OFPLEA) produces electric power with no need to modify the reciprocating motion to rotary motion. In the most common geometry it consists of a linear alternator driven cyclically by one or two internal combustion engines. With the elimination of crankshaft mechanism linkages, the free piston engine offers potential benefits over crankshaft engines in terms of total mechanical losses. A significant proportion of 5% to 12% of total fuel energy in conventional engines is consumed to overcome the frictional losses. This research investigation addresses an analytical and numerical model to simulate the tribological performance of piston rings in an OFPLEA engine. The results are then compared with results from an equivalent conventional crankshaft driven engine. This axisymmetric, mixed lubrication tribological model is developed on the hydrodynamic process defined by Patir and Cheng’s modified Reynolds equation and an asperity contact process as defined by Greenwood and Tripp’s rough surface dry contact model. The asperity contact pressure distribution, hydrodynamic pressure distribution, lubricant oil film thickness, frictional force and frictional power losses are calculated using an explicit finite difference approach. In the absence of spring-dominated OFPLEA system, dissimilarity in the piston motion profile for compression and power stroke exhibited two different oil film thickness peaks. Whereas a similar oil film thickness peaks are observed for conventional engine due to the controlled and stable operation maintained by crankshaft mechanism. The simulation results state that the frictional losses due to piston ring - cylinder liner contact are found to be lower for a free piston engine than for those of a corresponding crankshaft engine. The simulated piston ring frictional power losses are found to be 342.8 W for the OFPLEA system and 382.6 W for the crankshaft engine. Further, an overall system efficiency improvement of 0.6 % is observed for an OFPLEA engine due to these reduced frictional losses from piston rings.

Investigating Trajectory Based Combustion Control Using a Controlled Trajectory Rapid Compression and Expansion Machine (CT-RCEM)

2021 ◽  
pp. 1-23
Author(s):  
Abhinav Tripathi ◽  
Zongxuan Sun
Keyword(s):  
Combustion Engine ◽  
Optimal Operation ◽  
Temperature History ◽  
Control Input ◽  
Combustion Control ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine ◽  
Compression And Expansion ◽  
Rapid Compression

Abstract This work presents a systematic framework for the real time implementation of a new combustion control strategy – trajectory-based combustion control – for the operation of free piston engines. The free piston engine is an alternative architecture of IC engines which does not have a mechanical crankshaft and hence allows extreme operational flexibility in terms of piston trajectory. The key idea of trajectory-based combustion control is to modulate the autoignition dynamics by tailoring the pressure and temperature history of the fuel-air mixture inside the combustion chamber, using the piston trajectory as the control input, for the optimal operation of the free piston engine. Here, we present the experimental investigation of trajectory-based combustion control using a novel instrument called controlled trajectory rapid compression and expansion machine (CT-RCEM) that can be used for studying a single combustion cycle of an internal combustion engine with precisely controlled initial and boundary conditions. The effect of the shape of the piston trajectory on the combustion phasing, combustion efficiency and the indicated thermal efficiency has been found to be significant. The experimental results indicate that the trajectory-based combustion control is an effective strategy for combustion phasing control for FPE operation.

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