Stable Operation and Electricity Generating Characteristics of a Single-Cylinder Free Piston Engine Linear Generator: Simulation and Experiments
Abstract
:1. Introduction
2. Simulation Modelling and Methodology
2.1. Linear Motor Force Profiles
2.2. Simulation Model
2.2.1. Dynamic Modeling
2.2.2. Linear Generator Modeling
2.2.3. Thermodynamic Modelling
2.2.4. Frictional Modelling
2.3. Simulation Method
Parameters | Value |
---|---|
Bore | 34.0 mm |
Piston assembly mass | 5.0 kg |
Spark ignited position | 3.0 mm |
Intake port open position | 28.0 mm |
Exhaust port open position | 25.0 mm |
Initial pressure in cylinder | 1.013 × 105 Pa |
Load constant | 100 Ns/m |
Design stroke | 45 mm |
Parameters | Value |
---|---|
Combustion duration | 4.5 ms |
Combustion quality factor | 2 |
Average velocity y of piston | 3 m/s |
Specific heat ratio in compression stroke | 1.33 |
Specific heat ratio in expansion stroke | 1.30 |
Lower heating value of fuel | 4.4 × 107 J/kg |
2.4. Simulation Results and Discussion
2.4.1. Different Motor rebound Forces and Positions
2.4.2. Different Motor Force Types
3. Electricity Generating Characteristics of the Linear Generator
3.1. FPELG Prototype
Parameters | Linear Motor/Generator |
---|---|
Maximum stroke | 180 mm |
Actual stroke | 50 mm |
Width of air gap | 7.2 mm |
Width of the permanent magnet | 12 mm |
Turns per coil | 180 |
Mass of permanent magnet | 1.6 kg |
Peak force | 1300 N |
Force constant (25 °C) | 44.7 N/A |
Continuous stall force | 440 N |
Peak current | 41.5 A |
Back EMF constant (ph-ph, °C) | 25.8 V/(m·s−1) |
Resistance | 12 s |
Peak velocity | 19.2 m·s−1 |
Test Device | Accuracy |
---|---|
Linear generator | 0.01 mm |
Electric machine controller | 0.01 mm |
Electric machine driver | 0.01 mm |
Linear displacement transducer | 0.1% |
3.2. Test Results
3.2.1. Variation of Intake Pressures
3.2.2. Variation of Frequency
3.2.3. Variation of Load Resistance
4. Conclusions
- (1)
- In the simulation, the peak value of displacement increases with the increase of motor rebound force. There is a minimal value of brake output power when the motor rebound force is approximately 500 N. When the motor rebound position increases, the maximum displacement and brake output power of the linear generator both increase.
- (2)
- Compared to a motor rebound force with a triangular profile, a parabolic motor rebound force profile has advantages such as higher values of the maximum positive velocity, shorter time to reach the TDC, and higher peak cylinder pressure.
- (3)
- Experimentally, the maximum velocities and peak output power were not stable after the starting process until the intake pressure reached 4 bar. As the gas intake pressure increased, the system output power rose continually. However, the system reached its maximum efficiency before reaching maximum output power, which rose slowly.
- (4)
- The parameters of frequency and load resistance could be adjusted to achieve a special peak line voltage, peak power, and efficiency, which is one of the ways to control the system. The output power reached 25.9 W and the system efficiency reached 13.7%.
Nomenclature
Abbreviations
BDC | Bottom dead center |
TDC | Top dead center |
Symbols
Fp | Combustion-gas pressure [N] |
Ff | Frictional force [N] |
Fm | Motor force [N] |
Fe | Electromagnetic force [N] |
F0 | Maximum motor force [N] |
R | Resistance [Ω] |
L | Inductance [H] |
Φ | Coil magnetic flux |
eg | Induced electromotive force [V] |
c | Constant of load |
X1 | Rebound position [mm] |
X2 | Bottom dead center position [mm] |
S | Maximum displacement [m] |
P | Brake output power [w] |
m | Piston assembly mass [kg] |
Qht | Heat transfer at cylinder [J] |
h | Heat transfer coefficient |
Ū | Mean piston speed [m/s] |
x(t) | Fuel mass fraction burned [%] |
t | Time [s] |
ma | The sum of the gas [kg] |
mi | The gas mass of i constitutent [kg] |
U | Internal energy [J] |
u | Specific heat |
p | Pressure in cylinder [MPa] |
V | Gas volume in cylinder [m3] |
R | The gas constant [J/kg K] |
T | Gas temperature [K] |
Tw | Wall temperature [K] |
Q | Total input energy [J] |
cv | The specific heat capacity at constant volume [J/kg K] |
γ | Specific heat ratio |
Qc | Heat released in combustion [J] |
a、b | Shaping factors |
t0 | The time combustion begins [s] |
tc | The combustion duration [s] |
fmep | Mean frictional pressure [Pa] |
Acknowledgments
Author Contributions
Conflicts of Interest
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Feng, H.; Song, Y.; Zuo, Z.; Shang, J.; Wang, Y.; Roskilly, A.P. Stable Operation and Electricity Generating Characteristics of a Single-Cylinder Free Piston Engine Linear Generator: Simulation and Experiments. Energies 2015, 8, 765-785. https://doi.org/10.3390/en8020765
Feng H, Song Y, Zuo Z, Shang J, Wang Y, Roskilly AP. Stable Operation and Electricity Generating Characteristics of a Single-Cylinder Free Piston Engine Linear Generator: Simulation and Experiments. Energies. 2015; 8(2):765-785. https://doi.org/10.3390/en8020765
Chicago/Turabian StyleFeng, Huihua, Yu Song, Zhengxing Zuo, Jiao Shang, Yaodong Wang, and Anthony Paul Roskilly. 2015. "Stable Operation and Electricity Generating Characteristics of a Single-Cylinder Free Piston Engine Linear Generator: Simulation and Experiments" Energies 8, no. 2: 765-785. https://doi.org/10.3390/en8020765