Effects of Design Parameters on Fuel Economy and Output Power in an Automotive Thermoelectric Generator
Abstract
:1. Introduction
2. Thermoelectric Generators
3. Experimental Analysis
3.1. Automotive Thermoelectric Generator
3.2. Experimental Set-Up
3.3. Experimental Cases
3.4. Effective Thermal and Electrial Properties of the Thermoelectric Modules
4. Numerical Model
4.1. Simulation Set-Up
4.2. Model Validation
5. Results and Discussion
5.1. Water Heat Sink: Effects of Changing the Geometry and Flow Rate
5.2. Heat Absorber: Effects of Changing the Diameter of the Cylindrical Holes
5.3. Configurations with Maximum Power and Maximum Fuel Economy
6. Conclusions
- Engine operating points of maximum output power did not coincide with those of maximum fuel economy.
- Designs that maximized output power differed substantially from those that maximized fuel savings.
- While an increase in the cooling flow rate enhanced the output power, it also increased the power required to pump the cooling flow. Therefore, a compromise between gaining generated power and the loss of power needed to drive the water pump must be made. From the design point, a maximum value of flow velocity in the cooling system should be imposed to assure that energy losses are not excessive. Changes in the cross-sectional area of the water cooling channel had a similar effect. From the initial layout, a reduction in flow rate was preferred over an increase in the cross-sectional area of the channel, since the former implied greater decrements of the required pumping power.
- The design of the heat absorber was critical in two opposing aspects: (1) to maximize the heat transfer, and (2) to minimize the back pressure. The back pressure was the main limiting factor in determining success in terms of fuel economy. Its value may vary several orders of magnitude depending on the type of heat absorber design. In order to have increments in fuel consumption <0.2% due to the effect of the back pressure, a value lower than 5 mbar should be attained.
- A heat absorber with cylindrical holes is not a recommended geometry since it leads to large back pressure values. For this type of heat absorber, the main three terms that contributed to fuel savings could be analytically expressed as a function of the diameter of the cylindrical holes with a high degree of accuracy. The analytical equations could be used to determine the minimum efficiency of the thermoelectric modules (figure of merit) in order to obtain positive fuel savings.
- The maximization of fuel savings cannot only rely on reducing back pressure values because this would result in trivial designs with very low back pressure and very low heat transfer being proposed. The feasibility of an ATEG requires a minimum value of electrical output power generated and this value should be kept as a constraint in the minimization study of the back pressure values.
Author Contributions
Acknowledgments
Conflicts of Interest
Nomenclature
A | area of the aluminum channel in contact with the water (m2) |
Ab | block surface area (mm2) |
ATEM | TEM surface area (mm2) |
D | diameter of the cylindrical holes (m) |
Fe | fuel economy (%) |
Fe,ATEG | fuel economy resulting from the power generated by the ATEG (%) |
Fe,BP | fuel consumption (<0) due to overcome the back pressure (%) |
Fe,m | fuel consumption due to increase in weight (%) |
g | acceleration of gravity (m·s−2) |
h | heat transfer coefficient (W·K−1·m−2) |
ITEM | electrical current (A) |
kb | block thermal conductivity (W·K−1·m−1) |
ke | TEM effective thermal conductivity (W·K−1·m−1) |
L | height of the cooling channel (mm) |
Lb | block height (mm) |
LTEM | TEM height (mm) |
mATEG | ATEG mass (kg) |
exhaust gas mass flow rate (g·s−1) | |
N | number of samples in the data series |
PATEG | ATEG electrical output power (W) |
Pe | engine-shaft power (W) |
Pn,ATEG | net ATEG electrical output power (W) |
PTEM | TEM electrical output power (W) |
Pwp | power consumed by the water pump (W) |
Qc | heat flow on the cold side of the TEM (W) |
Qh | heat flow on the hot side of the TEM (W) |
r | ratio of figure of merits |
Rc | thermal contact resistance (cold side) (m2·K·W−1) |
Rh | thermal contact resistance (hot side) (m2·K·W−1) |
Rie | TEM effective internal electrical resistance (Ω) |
RL | external electrical load resistance (Ω) |
(Th + Tc)/2 (K) | |
Tc | TEM cold side temperature (°C) |
Tg | exhaust gas temperature (°C) |
Th | TEM hot side temperature (°C) |
Tw | coolant temperature (°C) |
v | vehicle velocity (m·s−1) |
Voc | open-circuit voltage (V) |
volumetric flow of the ATEG coolant (L·h−1) | |
ZTe | effective figure of merit |
confidence range | |
αe | TEM effective Seebeck coefficient (V·K−1) |
Δpbp | back pressure increase due to the ATEG (Pa) |
εe | uncertainty of the equipment |
εs | uncertainty of the mean values |
εt | total uncertainty of data |
η | ATEG efficiency |
ηG | efficiency of the alternator |
ηPCU | efficiency of the power converter unit |
λ | air–fuel equivalence ratio |
ξ | vehicle rolling resistance |
ρe | effective electrical resistivity (Ω·m) |
σ | standard deviation |
Subscripts
i | inlet |
max | maximum conditions |
o | outlet |
Abbreviations
AFR | air–fuel ratio |
AFRs | stoichiometric air–fuel ratio |
ATEG | Automotive thermoelectric generator |
CAE | computer-aided engineering |
CI | compression ignition |
CSHE | cold-side heat exchanger |
EGR | exhaust gas recirculation |
HDV | heavy-duty vehicle |
HexS | hexagonal cross-section |
HP | heat pipes |
HSHE | hot-side heat exchanger |
ICE | internal combustion engine |
OctS | octagonal cross-section |
PCU | power converter unit |
SI | spark ignition |
TEG | thermoelectric generator |
TEM | thermoelectric module |
2PP | two parallel plates |
4SSP | four square section plates |
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Engine 1 | ATEG Design 2 | Number of TEMs 3 | Tg,i (°C) | Tw,i (°C) | mATEG (kg) | PATEG (W) | Fe (%) | Reference |
---|---|---|---|---|---|---|---|---|
1.4 L SI | 2 PP | 12 | 709 | 74 | 7 | 111 | [5] | |
1.6 L SI | 2 PP | 80 | 719 | 50 | 137 | 1.1 * | [6] | |
1.8 L CI | Radial | 10 | 540 | 28 | 4.8 | 40 | 0.0 * | [7] |
1.8 L CI | 2 PP | 12 | 526 | 34 | 7 | 64 | 0.0 * | Present |
1.9 L CI | 4 SSP | 8 | 427 | 7 | 30 | [8] | ||
2.0 L SI | 20 | 650 | 25 | 266 | [9] | |||
2.0 L SI | HexS | 18 | 611 | 80 | 99 | [10] | ||
3.0 L SI | HP | 8 | 350 | 30 | 38 | [11] | ||
3.7 L CI | 6 | 650 | 30 | 42 | [12] | |||
3.9 L CI | 2 PP | 240 | 290 | 80 | 200 | 618 | [13] | |
5.3 L SI | 2 PP | 16 | 550 | 88 | 40 | 177 | 2.0 ± 1.5 | [14] |
6.6 L CI | 2 PP | 4 | 200 | 10 | 8 | [15] | ||
HDV CI | 2 PP | 224 | 80 | 416 | [16] | |||
14 L CI | OctS | 72 | 1068 | [17] |
Equipment | Accuracy | Ref. |
---|---|---|
Current (NI 9227) | ± (169.7 mA + 5% of reading) | [36] |
Voltage (NI 9215) | ± (85.3 mV + 1.05% of reading) | [36] |
Temperature (NI 9211) | ± 0.6 °C | [36] |
Type K thermocouple | ± 1.5 °C | [37] |
Sensus 405 S water meter | ± 0.05 L | [38] |
Manometer | ± 10 Pa | |
Fuel Calibrated volume cylinder | ± 0.5 cm3 |
Case | Regime (rpm) | Torque (N·m) | (g/s) | Tg,i (°C) | (L/h) | Tw,i (°C) | λ |
---|---|---|---|---|---|---|---|
1 | 2500 | 69.9 ± 0.1 | 43.4 ± 0.3 | 444.7 ± 2.0 | 580 ± 3 | 26.4 ± 2.0 | 1.68 |
2 | 2500 | 67.3 ± 0.1 | 42.8 ± 0.3 | 428.7 ± 2.0 | 280 ± 3 | 31.2 ± 2.0 | 1.68 |
3 | 2500 | 71.9 ± 0.1 | 43.0 ± 0.3 | 450.1 ± 2.1 | 160 ± 3 | 33.6 ± 2.0 | 1.63 |
4 | 2800 | 75.1 ± 0.1 | 46.1 ± 0.3 | 521.6 ± 2.1 | 580 ± 3 | 29.6 ± 2.0 | 1.50 |
5 | 2600 | 82.2 ± 0.1 | 44.4 ± 0.3 | 547.4 ± 2.0 | 140 ± 3 | 33.4 ± 2.0 | 1.43 |
6 | 3000 | 79.2 ± 0.1 | 48.3 ± 0.3 | 598.8 ± 2.0 | 580 ± 3 | 28.0 ± 2.0 | 1.34 |
7 | 3200 | 76.1 ± 0.1 | 51.0 ± 0.3 | 598.5 ± 2.0 | 180 ± 3 | 34.5 ± 2.0 | 1.36 |
Tc (°C) | Th (°C) | αe (V·K−1) | ke (W·m−1·K−1) | Rei (Ω) | |
---|---|---|---|---|---|
38 | 140 | 0.0255 | 3.17 | 0.759 | 0.157 |
39 | 160 | 0.0263 | 2.94 | 0.781 | 0.180 |
42 | 180 | 0.0272 | 2.90 | 0.814 | 0.192 |
50 | 160 | 0.0267 | 3.00 | 0.806 | 0.179 |
51 | 170 | 0.0274 | 3.02 | 0.838 | 0.183 |
55 | 181 | 0.0280 | 2.97 | 0.829 | 0.199 |
55 | 201 | 0.0280 | 2.84 | 0.834 | 0.212 |
65 | 201 | 0.0279 | 2.87 | 0.787 | 0.214 |
65 | 226 | 0.0296 | 2.73 | 0.922 | 0.232 |
70 | 140 | 0.0261 | 3.15 | 0.729 | 0.179 |
70 | 160 | 0.0267 | 3.11 | 0.760 | 0.186 |
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Comamala, M.; Cózar, I.R.; Massaguer, A.; Massaguer, E.; Pujol, T. Effects of Design Parameters on Fuel Economy and Output Power in an Automotive Thermoelectric Generator. Energies 2018, 11, 3274. https://doi.org/10.3390/en11123274
Comamala M, Cózar IR, Massaguer A, Massaguer E, Pujol T. Effects of Design Parameters on Fuel Economy and Output Power in an Automotive Thermoelectric Generator. Energies. 2018; 11(12):3274. https://doi.org/10.3390/en11123274
Chicago/Turabian StyleComamala, Martí, Ivan Ruiz Cózar, Albert Massaguer, Eduard Massaguer, and Toni Pujol. 2018. "Effects of Design Parameters on Fuel Economy and Output Power in an Automotive Thermoelectric Generator" Energies 11, no. 12: 3274. https://doi.org/10.3390/en11123274