DESIGN AND OPTIMIZATION OF INTEGRATED TURBO-GENERATOR AND THERMOELECTRIC GENERATOR FOR VEHICLE EXHAUST ELECTRICAL ENERGY RECOVERY

DESIGN AND OPTIMIZATION OF INTEGRATED TURBO-
GENERATOR AND THERMOELECTRIC GENERATOR FOR
VEHICLE EXHAUST ELECTRICAL ENERGY RECOVERY

by

Prasert Nonthakarn

A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of
Doctor of Engineering in Mechatronics

Examination Committee: Dr. Mongkol Ekpanyapong
Assoc. Prof. Erik L.J. Bohez
Dr. Udomkiat Nontakaew

External Examiner: Prof. Jose Carlos Fernandes Teixeira
Mechanical Engineering Department,
University of Minho, Portugal

Nationality: Thai
Previous Degree: Master of Science in Technical Education
in Mechanical Technology
Scholarship Donor: King Mongkut’s Institute of Technology
North Bangkok, Bangkok, Thailand

Rajamangala University of Technology
Srivijaya, Thailand.

Asian Institute of Technology
School of Engineering and Technology

Thailand
May 2020

ACKNOWLEDGMENTS

This dissertation completed with the help of Assoc. Prof. Mongkol Ekpanyapong the
dissertation advisor for giving advice, and comments, particularly helpful in the research,
and also support for solving the problems that arise during the research. Thanks to Assoc.
Prof. Erik L. J Bohez for giving guidance on how to do research in the design phase,
including the knowledge for doing the dissertation. Special thanks to Assoc. Prof. Udomkiat
Nontakaew for giving advice from the beginning, including providing places in research
operations and I am highly grateful for the counseling. Thanks to all ISE officials who
facilitate the process of various procedures, and thanks for the advice, and help in all
aspects of research. Also, thank you to all friends in the Mechatronics laboratory who
encourage, and assist in doing this dissertation. I would like to thank Rajamangala
University of Technology Srivijaya that grants scholarships, and provides time for
studying.
Finally, I am grateful to my parents, and family for providing opportunities to study and
encourage me to complete my research.

ii

ABSTRACT

The design of a power turbine plays a key role in turbo generator engine performance. In
addition, the thermoelectric generator can further convert waste heat into another source of
energy. This research aims to design, and optimize for an integrated turbo-generator, and
thermoelectric generator for diesel engine. The goal is to generate electricity form vehicle
exhaust gas. The pressure, and flow of the exhaust gas from combustion engine, and waste
heat are used to drive the generator to generate electrical energy. For the turbo-generator,
and thermoelectric generator, the system automatically adjusts the power provided by an
inverter. Typically, vehicle exhausts are discarded to the environment. Hence, the proposed
conversion to electrical energy will reduce the alternator charging system. This work
focuses on design optimization of turbo-generator, and thermoelectric generator for 2,500
cubic centimeters diesel engines due to widely usability. The concept can be applied for
gasoline engines. Moreover, this model is designed for hybrid vehicles. Charging on
running will save time on charging station. The optimization by variable van angle 40,
50, 62, 70 , and 80 showing the best output power is 62 as it was identically calculated.
The design prototype can generate a maximum power output of about 1,456 watts when
operating at exhaust mass flow rate of 0.1024 kg/sec at 3,400 rpm (high performance of the
engine). This research aims to better utilize fuel consumption, and reduce pollution from
exhaust especially for hybrid vehicles.

iii

CONTENTS

ACKNOWLEDGMENTS Page
ABSTRACT ii
LIST OF FIGURES iii
LIST OF TABLES iv
CHAPTER 1 INTRODUCTION
viii
1.1 Background and Motivation 1
1.2 Statement of the Problem 1
1.3 Overview of System Design 3
1.4 Objectives 4
1.5 Scope and Limitation 6
1.6 Contributions 6
1.7 Publications Related to the Dissertation 6
CHAPTER 2 LITERATURE REVIEW 7
CHAPTER 3 METHODOLOGY 8
3.1 The Cycle of Engine and Turbine 13
3.2 Exhaust Gas 13
3.3 Basic for Turbine Design 16
3.4 Specific Design Turbine 22
3.5 Drawing Turbo-Generator 33
3.6 Drawing and Construction of a Thermoelectric Generator
CHAPTER 4 RESULTS AND DISCUSSION 37
4.1 Turbine Performance Calculations 38
4.2 Pressure and Path Line of Flowing 43
4.3 Experimental Setup 43
4.4 Rotation Speed of Turbo-Generator Test 46
48
49

iv

Page

4.5 Power of Turbo Generator Test 50
4.6 Voltage of Turbo Generator First Test 51
4.7 Temperature of Exhaust Turbo Generator 53
4.8 Pressure of Exhaust Turbo Generator Measurement 54
4.9 Rotation Speed of Turbo-Generator Test on Variable Vane 54

Angle 55
4.10 Power of Turbo-Generator Test on Adjust Vane Angle 56
4.11 Power of Thermoelectric-Generator Test 57
4.12 Power of Turbo-Generator and Thermoelectric-Generator
59
Driving Test 59
CHAPTER 5 CONCLUSION 59
60
5.1 Conclusion 61
5.2 Contribution 64
5.3 Recommendations for Future Work
REFERENCES
APPENDIX

v

LIST OF FIGURES

Figures Page
Figure 1.1 Typical Energy Path for Vehicles with Internal Combustion 1

Engines 2
Figure 1.2 The Energy Flow Distribution of a Typical Engine Under
4
Full-Load 4
Figure 1.3 Position to Install the Turbo-Generator Module 9
Figure 1.4 Concept of the Exhaust Recovery Module 13
Figure 2.1 The Turbo Generator Gas Energy Recovery 14
Figure 3.1 T-s and P-v Diagrams for Diesel Cycle 15
Figure 3.2 Idealized Brayton Cycle 15
Figure 3.3 Energy at Exhaust 16
Figure 3.4 Idealized Turbo-Generator 16
Figure 3.5 The Control Volume Surrounding the Engine 17
Figure 3.6 Volume of the Engine 18
Figure 3.7 Engine Rotation Speed 19
Figure 3.8 Engine Rotation Speed 21
Figure 3.9 Engine Rotation Speed on Driving Time 24
Figure 3.10 Cross Section of Exhaust Tube 25
Figure 3.11 Radial Inflow Turbine 26
Figure 3.12 T-s Diagram for a Radial Inflow Turbine 27
Figure 3.13 Summary of Number Rotor Vanes 33
Figure 3.14 The Ratio of Mean Rotor Exit Radius to Rotor Inlet Radius 34
Figure 3.15 Dimensional Calculation for Rotor and Stator 36
Figure 3.16 One Dimensional Calculation 37
Figure 3.17 Velocity Triangles for Rotor and Stator 37
Figure 3.18 Rotor and Volute Design
Figure 3.19 The Turbo-Generator Component

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Figure 3.20 Heat Transfer Correlation of the Thermoelectric Module Page
Figure 3.21 Thermoelectric Generator Module 41
Figure 4.1 Model Preparation (A) CFX-Design Modeler and (B) CFX- 42
43
Meshing
Figure 4.2 CFX-Pre Simulation 44
Figure 4.3 Moment on the Turbine 44
Figure 4.4 Variables Vane Angle; 40°, 50°, 62°, 80° and 85° 45
Figure 4.5 (A) Result Showing Vane Angle and Power; (B) Result 46

Showing Rotation Speed and Power 46
Figure 4.6 Pressure at All Turbine Walls 47
Figure 4.7 Pressure at Turbine Blade 47
Figure 4.8 Path Line of Flowing at Turbine Blade 48
Figure 4.9 Sound Speed at Turbine Blade 49
Figure 4.10 Rotation Speed of Turbo-Generator Testing 49
Figure 4.11 Rotation Speed of Turbo-Generator Testing 50
Figure 4.12 Power of Turbo-Generator Testing 51
Figure 4.13 Power of Turbo-Generator Testing 52
Figure 4.14 Voltage of Turbo-Generator Testing 52
Figure 4.15 Voltage of Turbo-Generator Testing 53
Figure 4.16 Real Internal Combustion Engine Test 53
Figure 4.17 Inlet and Outlet Exhausts Temperature 54
Figure 4.18 Inlet and Outlet Exhaust Pressure 55
Figure 4.19 Rotation Speed of Turbo-Generator Test 56
Figure 4.20 Inlet and Outlet Exhausts Temperature 56
Figure 4.21 Inlet and Outlet Exhaust Pressure 57
Figure 4.22 Total Output Powers 58
Figure 4.23 Total Output Powers 58
Figure 4.24 Total Output Powers

vii

LIST OF TABLES

Tables Page
Table 3.1 Mass Flow Rate and Flow Velocity of Exhaust Gas on 22

Difference Engine Rotation Speed 28
Table 3.2 Design Parameters for 90° IFR Gas Turbines 34
Table 3.3 The Result from Calculation in One Dimensional
45
Calculation of Radial Turbine 49
Table 4.1 Turbine Performance 51
Table 4.2 The Result of Rotation Speed of Turbo-generator Testing 52
Table 4.3 The Result of Power of Turbo-Generator First Testing
Table 4.4 The Result of Voltage of Turbo-Generator First Testing

viii

CHAPTER 1
INTRODUCTION

1.1 Background and Motivation
Nowadays, vehicle fuel consumption is continuously increasing and this results in

a huge impact on the environment. Therefore, it is important to develop an environmentally
friendly energy system that consumes less energy and minimal energy disposal. Moreover,
recovering discharged energy becomes a very important challenge for recycling. The
recoverable energy such as heat-discharged energy can be recycled by importing into the
vehicle's electrical system or to be charged in the battery. This can reduce fuel consumption
and vehicle waste emissions.

Besides, an increase in global demands of fuel consumption causes higher fuel
prices. There is more concern about the impact of greenhouse gases from carbon dioxide
that the engine is discharging into the environment. These problems bring about the use of
burned fuel as much as possible. There have been many efforts for designing and
developing new engine models and power transmission systems. These technologies were
developed to provide the most efficient fuel consumption in the transport system. However,
to date, the recycling of energy concerning exhaust gas is not widely investigated. The
recycled energy includes energy in the exhaust and water in the cooling system. It has been
found that 40 percent of the energy used to burn the fuel was released with exhaust gas and
30 percent was discarded with water in the cooling system through the radiator. The
remaining energy would be the power for driving vehicles (Figure 1.1) [1].

Figure 1.1
Typical energy paths for vehicles with internal combustion engines.

1

The efficiency of the fuel consumption in combustion engines inside both diesel,
and gasoline engines, as well as hybrid engines, is only 25 percent. While most energy is
wasted on the heat of exhaust gases around 40 percent [2], it will result in an increase of
internal combustion engine performance up to 20 percent if heat around 10 percent can be
recycled.

The built-in combustion engine works using power from the combustion of fuel
burning. Some part of energy will be sent to the cooling system, and the other part is
released with exhaust gas [3]. All the energy in the exhaust, and cooling system, including
water, and oil, has a volume of up to twice of the energy to be used to drive the engine.

Vehicle power consumption is built from energy that transformed from the fuel to
drive the alternator. Using such energy is the primary purpose for converting energy to
driving force. The main problem of low engine power conversion is the energy to be used,
and the efficiency of alternator is high, but the ratio of the power output, and the fuel
consumption rate are very low. The electrical load of the vehicle is also increased due to
comfort, efficiency of driving, and transmission power. This trend results in the load of the
engine power, and the volume of engine weight. If about 6 percent of heat from the exhaust
gas can be converted into electric power, it is possible to reduce fuel consumption by
approximately 10 percent [4].

Figure 1.2 shows the power distribution of conventional engines under full working
conditions. The figure demonstrates that the function of internal combustion engine with
heat loss, and energy in the exhaust gas has a similar number. The thermal energy is the
waste of the engine, including the loss of heat, and energy in the exhaust gas, with more
than 60 percent of total energy. In conclusion, this illustrated that it is necessary to recover
the heat, and waste energy of the engine by increasing the heat efficiency [6].

Figure 1.2
The energy flow distribution of a typical engine under full-load

2

The exhaust gas in the engine consists of pressure energy, and thermal energy. These two
types of energy released continuously with high pressure, and temperature. The remaining
pressure energy is a very high mechanical energy and is able to be directly obtained from
the expansion of the gas, which will be used in direct return. Other energy resources are the
heat energy that low-grade thermodynamic energy can be recycled indirectly. Each type of
energy has different approaches for re-using.

An interesting solution to meet these energy requirements is energy recovery that
may be wasted into heat exhaust gases using a switched reluctance-powered generator with
a high-speed exhaust turbine. Using potential power makes it possible to increase overall
engine performance, and may be able to replace conventional alternator as well as new
technology instead of using the drive belt alternator [9].

1.2 Statement of the Problem

Normally, 40 percent of the energy released from fuel combustion was carried away
along with exhaust gas at temperatures around 190-380°C (Diesel engine), and 100-280°C
(Gasoline engine). Since this large amount of energy was released as waste energy,
therefore, it is interesting to find out how to bring it back for re-using. In the past, there were
many research studies on the design, and construction of equipment that could convert
exhaust energy from the internal engine to energy recovery. These previous works focused
on designing, and building devices to bring the energy back with only one type of
conversion: converting exhaust from stationary engine or power plant into electrical energy
or converting the pressure of the exhaust gas into electrical energy. Consequently, there
was still some part of energy released uselessly, resulting in low power. Moreover, these
papers were not designed for engine rotation or vehicle engine. Therefore, the purpose of
this research is to investigate the methodology for bringing two forms of energy back for
re-using. The brought back energy is in the form of electrical power that can be applied
with electrical system of vehicles. This study aims to convert thermal, and flow energy to
electrical power that can be re-used for vehicles. Besides, this article is designed to bring
flow, and pressure discharged from the exhaust of vehicles on driving conditions for
converting back into electrical power. The achieved energy can be used for power electric
vehicles such as charging the battery, power supply for the electrical system, and interior
lights. This results in energy consumption reduction.

3

Figure 1.3
Position to install the turbo-generator module.

Figure 1.4
Concept of the exhaust recovery module

1.3 Overview of System Design
The overall picture of system design is bringing energy waste around 30 percent

from the exhaust to produce electrical power used in car. With this system, waste energy
from the exhaust of an internal combustion engine passes through the combustion stroke
process of four-stroke engines. The intake is burned, and expanded. Then, it will be released

4

from the cylinder on exhaust stroke. The exhaust gas flows through exhaust manifold. This

gas has high pressure, and flow rate enough for pressing turbine blade that leads to rotation
of the turbine. Consequently, the generator will be rotated because both turbine, and
generator are connected by shaft. The rotation of generator leads to generating electrical

power that can be used for electrical devices in cars, and can be kept by battery charging.
The thermo-electrical generator acts as a role for changing heat energy in the exhaust into
electric power. The set of thermo-electrical generator was set up at exhaust pipe. Whenever
the exhaust flows through the designed pipe, it will transmit heat to the thermo-electrical
generator set. After that, the heat is transformed into electricity by the thermoelectric series
sheet. The electric discharge from this kit will be combined with the electricity from
turbine, and generator. This system will be different from any traditional turbochargers that
use a turbine for rotating, and spinning the compressor. With the traditional system, the

blades of compressor create a vacuum state to suck intake through air filter, and release
intake gas into the cylinder. The intake gas in cylinder has higher density than gas in the
normal engine. This affects increasing pressure in combustion stroke. When the expansion
of the gas at explosion stroke is increased, it will cause the engine to have higher torque.

Therefore, the difference between the designed turbo generator and typical turbocharger is
that turbocharger increases engine power by adding the intake of combustion process while
turbo generators produce electricity directly. In addition, the typical system does not bring

heat in the exhaust for re-using, but the proposed system will bring a lot of energy in the
exhaust back in the form of electric power. To summarize, the proposed system is designed
to bring the flow energy, and heat in the exhaust back for utilizing in the form of electrical
power.

Turbo-generator, and thermo-electrical generator are designed to generate electrical
power directly. It can run similar functions as electrical charged system (alternator).
Therefore, it can be used interchangeably. The designed turbo- generator, and thermo-
electrical generator also has the same weight as the old system, hence it will not affect car
load. This designed system takes power from the exhaust, and is different from the
traditional system which is driven directly by the engine via a belt, and pulley. It also
removes the drive power charger system. Accordingly, this system will decrease fuel
consumption, and parts of the transmission for running charging system.

This work focuses on diesel engines because of various characteristics of engine,
such as exhausts with higher pressure, higher temperature, compression ratio, and higher
combustion pressure expansion than gasoline engines. Besides using diesel engines without
turbo, there is no obstacle that will reduce the pressure, and flow rate of the exhaust outlet
from the combustion. This results in achieving maximum benefit from energy waste for
further use. The concept of both systems is different in terms of two steps.

5

1.4 Objectives

This method uses a turbine wheel in the exhaust system. Normal speed generator is
assembled onto the shaft of the turbine, an assembly known as a turbo- generator, and
thermoelectrical generator is assembled onto exhaust pipe. Electrical power is generated
when exhaust gas flows.

• To optimize design of the turbo-generator module for generating electrical
power by converting power from exhaust flow.

• To design the thermo-electrical generator module for generating electrical
power by converting power from exhaust temperature.

• To build, and install the exhaust recovery prototype module with diesel 2,500
cubic centimeters.

• To assess the effectiveness of the designed prototype by measuring amount of
electrical power recycling.

1.5 Scope and Limitation

This study focuses on the design optimization of the exhaust recovery module
capable of producing the maximum energy. The scope of this study will cover the following
issues:

• Energy from exhaust is the only power source.
• The exhaust recovery module is the prototype for internal combustion engine.
• The optimized geometry of turbo-generator module will be provided by

research, and calculation.
• The turbo- generator and thermo-electrical generator are designed for the

internal combustion engine without turbo.
• The designed exhaust recovery module has diesel engine displacement of 2,500

cubic centimeters.

1.6 Contributions

The contributions of this dissertation are as follows:
• Designing suitable components with diesel engine size 2,500 cubic

centimeters.
• Designing the gas energy recovery system using two systems: turbo-generator

and thermoelectric generator.
• Designing and installing real engine.

6

1.7 Publications Related to the Dissertation
Some parts of the dissertation have been published as follows.
Nonthakarn, P.; Ekpanyapong, M.; Nontakaew, U.; Bohez, E. Design and

Optimization of an Integrated Turbo-Generator and Thermoelectric Generator for Vehicle
Exhaust Electrical Energy Recovery. Energies 2019, 12, 3134.

7

CHAPTER 2

LITERATURE REVIEW

This dissertation proposes an approach for recycling exhaust vehicle energy that is
usually wasted into the environment. The approach uses the principles of turbo-generator
and thermoelectric generator. The development process focuses on designing and
developing turbo-generator and thermoelectric generator, which are suitable for internal
combustion engine using diesel engine size of 2,500 cubic centimeters. The development
is divided into two main parts: mechanical and electrical design. The process proposed by
this approach consists of the transformation of heat energy from exhaust to mechanical
energy, the transformation of mechanical energy to electrical power through the turbine
series, and changing the energy form to direct electrical power. The energy recovered from
the engine exhaust is transformed into electric power through a set of inverters to improve
the output energy produced that is appropriate to be used by connecting the vehicle's main
electrical system or electric charge into the battery for further use.

Controlled Power Technologies Ltd. is a company that develops tools for recycling
of wasted exhaust gas. The company has developed a turbo-generator named Turbo-
generator Integrated Gas Energy Recovery System [11] as shown in Figure 2.1. The
developed turbo-generator consists of a set of turbines which uses exhaust gas as a driver,
rotates, and then is directly connected to the generator with cooling water system. The
turbo-generator is designed into small size, and is equipped with another exhaust pipe with
the inlet control valve of exhaust gas. The valve is connected to the engine control system
for providing an exhaust flow rate suited to turbo-generator. One part of exhaust flows
through the turbine series to rotate and then transmit the energy through the driver
generator. The amount of energy outputted from the system depends on the burden of the
engine, that is, if the burden is high, then energy produced is also high. The system power
can be produced at a maximum of 600 watts. This research brings the energy of the flow in
the exhaust back for the rotation of turbine blade and transmits power for driving power
generation.

8

Figure 2.1
The turbo generator gas energy recovery [11]

Melanie Michon [12] has a comparative study of using the turbo-generator for re-
using the energy from the vehicle exhaust gas back to usable energy. The study compares
high voltage electric power machines with low voltage installed with the generator directly
connecting to the power turbine for recovering purpose. The maximum recovered energy
is approximately 1.8 kW. This research is aimed to design a turbine for driving high voltage
power generator.

Bowman Power Group LTD [13] proposed a system for bringing energy from the
exhaust gas back to use with power plant engines using turbo-generators. The system uses
Bowman Power Electronics that the energy is directly inputted into the electrical system in
a way that is parallel to the alternator of the main engine. The turbo-generator is installed
with the exhaust pipes at the position after the original turbocharger. The produced power
output is 250 kW to 1 MW when the increasing power is around 10 to 20 percent. This
research designed the tool for bringing exhaust energy back to use in turbo, and transmit
power generator for generating electricity.

Aman M.I. Mamat [14] developed high-performance turbine running at low
pressure. The turbine is applied to the gasoline engine with 1,000 cubic centimeters engines
used in small, and medium-sized individual private cars. The turbine is designed as mixed-
flow turbine to change passive energy in the exhaust gas with a low-pressure ratio of 1.05-
1.3, and to drive small electric. The turbo-compounding series can produce up to 1 kW of
energy. In addition, the turbine series is designed to run at a speed of turbine 50,000 rpm.
The design of the built-in powerful low-pressure turbine set was simulated through using a
computational fluid dynamics (CFD) software. After that the turbine was used to conduct
the cold-flow test trial in the Imperial College turbine test rig. This research is a turbine
design that can be run at low pressure for driving a small generator. For the design process,
it uses a CFD program to perform experiments, and simulate cold-flow work.

9

Caterpillar is the concept for designing a system for taking the exhaust back to use
[15-16]. Taking the concept can reduce the fuel consumption rate (Brake specific fuel
consumption) around 5 percent to normal usage. In addition, it is also possible to reduce
fuel consumption by 9-10 percent when used at optimum performance. The series consists
of electrical turbo-compounding, and turbo-compound. The turbo-compound is served as
receiving direct exhaust gas, and then is connected to high-speed generator to change
energy from rotation to electricity. In this case, the turbine produces more power compared
with the use of the compressor driver for the turbocharge system. The excess power is
converted to electrical power by high speed generator in the same series as the turbo-
generator. This research is designed to build the electrical turbo-compounding that makes

exhaust able to drive turbo rotation, and transmit power to high-speed generator.
X. Liu [17] proposed the model of the simulation, and testing of the placement of

thermoelectric generators. The study found that the location installed between catalytic
converter, and muffler is appropriate to support the exhaust flow scheme, low- back
pressure, and maximum thermal surface area. This research simulates, and installs

thermoelectric units with exhaust pipes in various positions in comparison with the
produced electrical power.

Tae Young Kim [18] has investigated the efficiency of heat waste recovery using
thermoelectric generator. The study made by building a system that consists of

thermoelectric 40 modules installed on the top, and bottom of rectangular exhaust gas
channel. The system has been validated using an experimental installation with a six-
cylinder diesel engine with turbo charger. The experiments are performed at the rotation
cycle of three levels of the engine: 1,000, 2,000, and 3,000 rpm, respectively. The results of

the trial illustrated that the outputted power is increased in proportion directly to the load
or speed of the engine. The maximum is 119 watts at 2000 rpm. This research created a

thermoelectric series installed in various positions of the designed exhaust gas channel
series to generate electricity.

Xiuxiu Sun [19] has explored a comparison of generators with a series of
thermoelectric generators with serial, and dual-stage parallel. The study revealed that the
performance of thermoelectric generators one step is better than two steps. This research

examined the installation of a variety of thermoelectric generators kits to find the most
power generation.

Hua Tian [20] presented what affected the energy outputted, and efficiency of
energy transformation in thermoelectric generator. The study concluded the key as follows:

to provide high output power, it must increase the heat source temperature, and decrease
the temperature of the cool source, and the efficiency of thermoelectric generator based on
the ratio of two types of material. The advantages of thermoelectric generator are simple,
feasible, and reliable. This work made a comparison of the elements that had an effect on

the amount of power that came out from the thermoelectric generator.
Ilker Temizer [21] has developed a generator prototype for thermal recovery using

thermoelectric equipped with diesel engines. In the test phase, the speed is determined by
the five-level engine rotation, and the two different engine load settings for each speed

10

level. The experimental result indicated that the maximum output power was 156.7 watts at
the highest speed of the engine, and the maximum load of the engine. This research created

a prototype of thermoelectric series that was suitable with various speeds of the engine.
B. ORR [22] proposed two technologies used with exhaust heat recovery were

thermoelectric generators, and heat pipes, both of which had the advantages of no moving
parts, and no noise, can modify the size, and sustain long service life. This research has

outlined the benefits of recycling exhaust by thermoelectric series.
Nyambayar Baatar [23] brings the development of thermoelectric low thermal

generator applied to engine water coolant of size 2.0 liters. This series has the capacity to
produce more than 75 watts in a running state with a speed of 80 km/h, and has 28 watts
during idle condition. Dimension has a width of 80 mm, a height of 250 mm, and a length
of 740 mm of thermoelectric 72 modules. This research has developed thermoelectric with

low heat by applying to engine water coolant.
S. Pratheebha [24] used thermoelectric and turbocharger to convert power from

exhaust to power generation to charge the battery for consumption to use turbine connected
to dynamo in production power. This research employed the thermoelectric, and

turbocharger kits to bring back the energy in the exhaust.
S. V. Chavan [25] investigated the potential of power generation with

thermoelectric, and found 8 percent efficiency performance increased when adding engine
load, exhaust temperature, and flow rate of cooling water. This research offers guidance on

the optimization of electrical energy by thermoelectric series.
K. T. Zorbas [26] developed prototype by investigating the efficiency of

thermoelectric generators using thermoelectric 2.5 x 2.5 cm Bi2Te3 module of 31 sheets.
Thermoelectric generators can produce electricity 2.6 watts at the heating temperature of
220 C with the performance of 5.4 percent. This research has presented the use of Bi2Te3

to convert heat energy into electricity.
Chethan R Reddy[27] examined the thermoelectric generator system in the car

operating using the temperature difference between exhaust gas (hot side), and liquid
coolant engine (cold side) by mathematical equations, and simulation working with the
engine diesel 1.4 liters can reduce the function of alternator , and increase the efficiency of
the 4-7 percent engine. This work has studied the difference between hot, and cold side by

simulating the operation with diesel engines.
Tzer-Ming Jeng [28] has explored the technique of high-performance heat transfer,

and thermoelectric adapted to generate electricity by thermoelectric, installed at the exhaust
pipe of four-stroke engines of 35.8 cubic centimeters, power generating 2.5 watt at 5,400

rpm of a speed. This work has been designed to transmit heat from exhaust pipes to
thermoelectric.

Based on the hybrid electric charge, it was found that the average electric charge
would be 1-5 hours per 100 km distance. On charging, the car is parked at the power station

to charge the electricity, which will waste time in this step, and the average speed of a used
car driving on the highway is 80 km/h. At that speed, the engine speed is 3,500 rpm.

11

From the previous works, two types of recycling exhaust energy are used: turbo
generator, and thermoelectric. These devices are set up at the exhaust pipe. The turbo
generator recycles flow energy to generate electrical power. On the other hand, the
thermoelectric recycles heat energy to generate electrical power. The previous works have
used only one type of energy to produce electricity which makes it partially used to bring
energy back from the exhaust. Therefore, this work proposes concepts that work together
with the two types, starting from bringing back the flow energy, and using the remaining
energy in form of heat for re-using.

This work focuses on designing optimization of turbo-generator, and thermoelectric
generator for 2,500 cubic centimeters diesel engines because of engine characteristics, such
as exhausts with higher pressure, compression ratio, and pressure expansion of the
combustion, and they are widely deployed as passenger cars, and light commercial trucks.
In addition to using diesel engines without turbo, there is no obstacle that will reduce the
pressure, and flow rate of the exhaust outlet from the combustion. Power can generate the
different turbine geometry component such as volute, nozzles, and rotor. Electricity
produced can collect during the driving time. The paper is presented as follows. First, turbo-
generator model, and thermoelectric generator are presented. Next, simulation result is
illustrated. Then, the experimental result to validate the idea has been discussed. Finally,
the paper is summarized, and recommended for further investigations.

12

CHAPTER 3
METHODOLOGY

3.1 The Cycle of Engine and Turbine
The diesel cycles

The diesel cycle is a life cycle for constant pressure heat enhancement (pressure
constant). This cycle is the theoretical cycle of the diesel engine with low cycle speed. The
cycle started with air sucked into the cylinder by the adiabatic compression. This increases
the air temperature to 600 C (process 1 – 2). Then, the fuel is injected to the cylinder. This
causes burning while the fuel is gradually sprayed slowly. This process occurs under
constant pressure until the 3rd state. After that, the fuel supplying stopped (process 2 – 3).
The burning effect results in adiabatic expansion from the 3rd to the 4th state. In this cycle,
the compression ratio is not equal to the magnification ratio (processes 3-4). In general, the
thermal performance of this diesel engine is in range of 35 to 40 percent.

Figure 3.1
T-s and P-v diagrams for diesel cycle

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The gas turbine cycle

The simplest gas turbine follows the Brayton cycle (Figure 3. 2) which consists of
4 sub-processes: 1-2 is reversible adiabatic compression, 2-3 is reversible constant pressure
heat addition, 3-4 is reversible adiabatic expansion, and 4-1 is reversible constant pressure
heat rejection.

Figure 3.2
Idealized Brayton cycle

Brands et al. [3 2 ] has reported the ability to drive mechanical turbo-compound of
engine in a real drive cycle. At the beginning, the power outputted from the engine
increases due to the suitability of the turbocharger. The power of turbine can be calculated

by

P = tsmC Tp 0,in  −  pout ( −1)/  3.1
1  p0,in  
 
 

The level of energy recovery wasted on diesel engines achieved from the turbo

generator in the pressure, and the scale of the Otto with increasing pressure to the air using
the turbocharger or super rechargeable engine for four-stroke engines is detailed as follows:

(Figure 3.3)
The overall work of the systems is area B-C-D-E-B.
The task of stamping is area B-F-G-A-B.
The exhaust gas is area F-G-H-I-F.
The induction work is area A-B-I-H-A.
The energy of exhaust gas is area F-G-H-I.
The energy emitted is area E-J-I-E.
The expanded pressure in Turbocharge is E-K.
The pressure of the exhaust gas from the turbocharger to the atmosphere is K.

14

The remaining energy in the exhaust gas that is able to be recovered by the installation of
Turbo Kit generator is point at J- K, corresponding to the energy in exhaust gas area K- J-
H-L-K.

Figure 3.3
Energy at exhaust

Turbo-generator cycle
The turbo-generator cycle is similar to the gas turbine cycle (Figure 3.4) by catting

cycle steps 1-2, 2-3, and 4-1 and only stilling cycles 3-4 is entropy constant. Exhaust gas
from combustion flow to rotate the turbine flows out to exhaust pipe ( to environment) .
Work out is made on rotation turbine step.

Figure 3.4
Idealized turbo-generator.

15

3.2 Exhaust Gas

Mass ( m ) passing through the control volume surrounding the engine is shown in
Figure 3.5.

Figure 3.5
The control volume surrounding the engine

Control

volume
Fuel

Exhaust

Air Engine gas

Engine displacement is the volume swept by the pistons inside the cylinders of a

reciprocating engine in a single movement from top dead center (TDC) to bottom dead
center (BDC).

Volume of 1 cycle of engine (Figure 3.6)
Where V is volume, A is area, L is piston stroke) , and D is diameter.

V = A L =  D2  L 3.2
4

Figure 3.6
Volume of the engine

16

The availability of waste heat from internal combustion engine is explained as follows:

The quantity of waste heat contained in an exhaust gas is a function of both the
temperature, and the mass flow rate of the exhaust gas:

Q = mcpT 3.3

Where Q is the heat loss (kJ/min), m is the exhaust gas mass flow rate (kg/min), cp is the
specific heat of exhaust gas (kJ/kg K), and T is temperature gradient (K).

From this formula, the temperature range has important functions for the selection
of waste heat recovery system designs.

Engine rotation speed

Rotation speed is a measure of the frequency of crankshaft rotation, specifically the
number of rotations around a fixed axis in one minute (rpm). Rotation speed is the cause of
amount exhaust mass flow rate.

Figure 3.7
Engine rotation speed

PC/Laptop OBD connecter

OBD cable

Engine rotation speed obtains the value by reading the data from on-board diagnostics OBD
port, and transfers them to program on computer (Figure 3.7). OBD is an automotive term
referred to as a vehicle's self-diagnostic, and reporting capability. Receiver fluctuates value
when starting an engine, and moving. It stops recording when switching off the engine. The
average engine rotation speed brings about designing 1D turbo-generator.

17

Figure 3.8 6,000 RPM
Engine rotation speed 5,000 RPM
4,000 RPM
Engine Rotation Speed 3,000 RPM
2,000 RPM
4% 1% 1,000 RPM
2%

17%

21% 55%

Normally, the engine rotation speed of driving car on the road is shown in Figure
3.8, and 3.9. The ratios of driving time are mostly control pedals at 4,000, and 3,000 rpm
and other driver speeds have a few distance, and period. Therefore, the design point at 4,000
rpm is used in this work because of its greatest rotation speed. This graph shows the driver
engine rotation speed characteristic at Nakhon Si Thammarat Province, Thailand.

18

Figure 3.9
Engine rotation speed on driving time

Engine rotation speed(x1,000) Driver characteristic

7

Driver1

6 Driver 2

Driver 3
Driver4
Driver5

5 Driver6

Driver7
Driver8

4 Driver9

Driver10
Driver11
Driver12

3 Driver13

Driver14
Driver15

2 Driver16

Driver17
Driver18
Driver19

1 Driver20

0
Time(Sec)
10
30
50
70
90
110
130
150
170
190
210
230
250
270
293
310
330
350
370
390
410
430
450
470
490

Exhaust heat loss through diesel engine
Engine displacement includes the total volume of the combustion chamber.

Vr = Vc + Vs 3.4
Vc

Where Vr is compression ratio,Vc is compression volume, Vs is displacement volume, and

Vt is total volume.
Displacement of engine is 2,499 cc, and Compression ratio is 18.4:1.

18.4Vc = Vc + 2.49910−4 3.5
Vc = 0.0001358 m3 3.6

Vt =Vc +Vs = 0.002499 + 0.0001358 = 0.0026348m3 3.7

19

( )Mass flow rate of fuel (on the basis of specific fuel consumption) m f

s. f .c = m f 3.8
power

Power is 90 hp (67 kW) at 4,200 rpm (higher power of this engine).

. . is 200g/kW ∙ h(0.2kg/kW ∙ h) *from Internal Combustion Engine Fundamentals, John
B. Heywood [26]

mf = s. f .c  power = 0.2 67.1129884 =13.42259kg / hr 3.9

volume rate = swept volume  speed 3.10

V = Vs  N = 0.002499  4,200 = 5.2479m3 min = 0.087465m3 / sec 3.11
2
3.12
Volumetric efficiency (v ) 13.42259 3.13

v = voiumeof air = mair
swept volume air  n Vs

mair =v  air  n Vs

Volumetric efficiency (v ) is 0.8 to 0.9.
Density air fuel is 1.167kg m3

mair = 0.9 1.167  4,200  2.499 10−3 = 5.512kg min = 91.5333 g sec 3.14
2

Engine 2,499cm3 , 4 stroke engines is 2 rounds per cycle.

volume = 2,499 = 1,250cm3 round 3.15
2

At rotation engine speed is 2,000 rpm.
Volume flow rate (Q)

Q =V n = 0.002499  2, 000 = 0.04165m3 sec 3.16

(2  60)

Flow velocity (v)

Exhaust tube area is 0.0014m2

20

v = Q = 0.04165 = 29.75m sec 3.17
A 0.0014

Mass flow rate (m) :  (mass density)
Density air is 1.109kg m3
Area of inner exhaust tube ( A)

Figure 3.10
Cross section of exhaust tube

A =  D2 =  102 = 78.5cm2 = 0.00785m2 3.18
44 3.19

mair = Q air = 0.041651.109 = 0.04618985kg sec 3.20
3.21
Fuel/air ratios for CI engine with diesel fuel is 18  A F  70(0.014  F A  0.056) 3.22

( F )A = mfuel 3.23
3.24
mair 3.25
mfuel = 0.056 mair = 0.056 0.0468985 = 0.0025866316kg sec 3.26
mexhaust = mair + mfuel = 0.0468985 + 0.00258663 =1.264kg min = 0.04877kg sec

At 4,200 rpm is highest rotation is 90hp(611.948kW )

Q =V  n = 0.002499  4, 200 = 0.087468m3 sec

(2  60)

v = Q = 0.0877486 = 62.6775714285m sec
A 0.0014

mair = Q air = 0.0874681.109 = 0.096998685 kg sec

(mfuel = F )A  mair = 0.056 0.096998685 = 0.005431962kg sec

21

mexhaust = mair + mfuel = 0.096998685 + 0.005431926 = 0.1024kg sec 3.27

Specific heat of exhaust gas is 1.1−1.25kJ kgK

Temperature of exhaust gas is 450 °C.

Q = m  cp  T = 33.41.25 (450 − 30) = 292.25kJ sec(kW ) 3.28

Therefore, the total energy loss in exhaust gas from 611.948 kW diesel engines is
292.25 kW (47.75percent) as shown in Table 3.1.

Table 3.1
Mass flow rate, and flow velocity of exhaust gas on difference engine rotation speed

Engine rotation speed (rpm) ( )mexhaust kg sec v(m min)

1,000 0.0243 14.87
2,000 0.0487 29.75
3,000 0.0731 44.62
4,000 0.0975 59.50
4,200 0.1024 62.67
5,000 0.1219 74.37

3.3 Basic for Turbine Design

R.K. Turton [2 7 ] has presented a degree of vane, and no vane of the system with
nozzles. In general, the angle of guide vane is in the range of 10-30. In the case of a small

turbocharger, it is designed to have no vane for economical design, and makes the steam
flow with wide range, but its performance will be less. The blade at the entrance has an
angle of 90 , and the formulas to design the number of blades ( Z ) are as follows:

For pumps by Stepannof

Z = 2 3.29
3

By Pfleiderer

Z = 6.5 D2 + D1 sin m 3.30
D2 − D1

22

By Eckert and Schnell

Z = 2 sin m D2 D1 3.31

(0.35to 0.45)logc

Where 2 is the flow angle of relative velocity, m is the mean flow angle of relative

velocity, D1 is the inlet diameter , and D2 is the outlet diameter.

A Whitfield and NC Baines [28] presented the design that reduces cost, and sizes
of the turbine installation, specifically applied to the turbocharger by reducing the number
of row nozzle vanes. The flow rate of mass depends on the neck area of the nozzle. The area

of nozzle turbine or the shape of volute for turbine without the nozzle blade angle
calculated by using radius is as follows:

r3 = constant 3.32
tan B3

The minimum number of blades,

The Jamieson equation

ZB min = 2 = 2 tan2 3.33


Glassman considered that the Jamieson

ZB =  (110 −2 ) tan2 3.34

30

Where r3 is the mean exit radius, B3 is the flow angle of relative velocity, ZBmin is the
mean flow angle of relative velocity, ZB is the number of rotor vanes , and 2 is the flow
angel at inlet rotor blade.

The volute

The flow enters the volute in a direction which is tangential, or nearly so, to the
rotor in the volute. A radial pressure gradient is set up in order to turn the flow towards to
rotor. In vaneless volute, the flow is subjected to pressure pulsations linked to the passing
of the rotor blade.

The volute inlet to exit area ratio is then given by

A1 = 2  P02 3.35
A2 1 P01

Where A1 is inlet area, A2 is exit area,1 is inlet volute angle,2 is exit volute angle, P01 is inlet
pressure , and P02 is exit pressure.

23

H Cohen [29] presents the velocity triangles are drawn for the normal design
condition in which the relative velocity at the rotor tip is radial, and the absolute velocity
is at axial (Figure 3.11 and 3.12). The specific work output W becomes simply.

Figure 3.11
Radial inflow turbine

( )W = cp = = 2 3.36
T01 − T03 CW 2U2 U 2 3.37
3.38
C2 =U2 cosec2 3.39
3.40
V3 =U2 cosec2
3.41
C3 = U3 cot 3

U3 = U2 r3
r2

( )cp T01 − T03 = U22

WhereW is work output, cp is specific heat of exhaust gas, T01 is temperature of gas involute
, T03 is temperature of gas out volute, U2 is the blade speed at mean inlet radius, V3 is the

24

absolute velocity at outlet, C3 is exit velocity, U3 is the blade speed at mean exit radius, 3
is the flow angle of relative velocity at outlet, r3 is the mean exit radius, and r2 is the mean
inlet radius.
The best overall efficiency is obtained if velocity ratio lies between 0.68 and 0.71.

Figure 3.12
T-s diagram for a radial inflow turbine

A.S. Rangwala [31] presents a ratio of diameter at the hub, and at the tip of the rotor
exit must be greater than 0.3. The ratio of blade tip diameter at the exit to the outer disk
diameter must not exceed 0.7 to limit curvature of the rotor blades. A/R ratio values tend to
range between 0.3 and 1.0.
S.L.Dixon [32] presents equation of continuity

m = 1c1An1 = 2c2 An2 = cAn

3.42

Where c is stream velocity, An1and An2 are the areas normal to the flow direction at station 1
and 2.

Wx = Wt = m(h01 − )h02 3.43

( ) A = m r2c 2 − r1c1 3.44

25

The rotor vanes in IFR turbines are assumed to be radial; the angle 2is an angle depending
upon the number of rotor vanes (Z ) this angle may be between 20 − 40

tan 2 =  2  U2 
 Z   cm 2 


3.45

The minimum number of rotor blade is

Z min = 2U 2 3.46
w2 3.47

Zmin = 2 tan2 3.48

Glassman preferred to use

Z =  (110 −  2 ) tan 2
30

Jamieson, Glassman and Whitfield result are plotted a summery in table (Figure 3.13).

Figure 3.13
Summary of number rotor vanes

Flow angle at rotor inlet as a function of the number of rotor vanes
For designing a number of rotors to select rotor 11 number of blades by using graphical
in Figure 3.13

26

Figure 3.14
The ratio of mean rotor exit radius to rotor inlet radius

r2
r3
r3/r2<0.7

Rohlik suggested that the ratio of mean rotor exit radius to rotor inlet radius (r3 r2 ) should

not exceed 0.7 (Figure 3.14).
A. Seppo [33] presents the increasing of work by increasing the inlet velocity C2 .

Orientation of the stator blades that flow into the rotor at a large nozzle angle 2 resulting
in the increase of velocity. The same reasoning leading to the design of the exit velocity C3
is axial. Therefore, as small as possible, the relative velocityV3 is large. Increasing the work
delivery by a small U3 , and large U2 means the ratio, r2 r3 ought to be reasonably large.
Using mass balance for determining the height of blade as follows:

b2 = m cos2 3.49
2 r22V2 3.50
3.51
The rotor shroud r3s = 0.75r2
The hub radii
The mean rotor outlet r3h = kr3s

r3 = r32h + r32s 3.52
2

27

All design parameters for 90° IFR gas turbines are presented in Table 3.2.

Table 3.2
Design parameters for 90° IFR gas turbines

Parameter Recommended range Source

2 68-75 and 0-30(vaneless) Dixon,Rohlik
3 50-70 Whitfiel&Baines
D3h D3s <0.4
D3s D2 <0.7 Dixon,Rohlik
D3 D2 Dixon,Rohlik
b2 D2 0.53-0.66 Whitfiel&Baines
U2 C0 0.05-0.15 Whitfiel&Baines, Dixon,Rohlik
W3 W2 0.55-0.80
V3 U2 Balje
R 2-2.5 Ribaud&Mischell
N 0.15-0.5 Whitfiel&Baines
0.4-0.8
0.06-0.24 -

Dixon

Formula for one dimensional calculation
Delivery of power

w = power 3.53
mexhaust 3.54
3.55
The blade speed at inlet
3.56
u2 = w

The absolute velocity at inlet

v2 = u2
sin  2

Where 2 is absolute gas angle at radius
The radius at inlet

r2 = 60u2
2 n

28

The relative velocity at inlet

w2 = v22 − u22 3.57
3.58
The rotor shroud radius 3.59

r3s = 0.75r2 3.60
3.61
The rotor hub radius 3.62

r3h = kr3s 3.63
3.64
Where k is the hub-tip ratio at the inlet blade 3.65

The hub blade speed u3h = 2 r3h n
The shroud blade speed 60
The mean exit radius
u3s = 2 r3s n
60

( )r3 = 0.5 r32s + r32h

The blade speed at the mean exit radius

u3 = 2 r3 n
60

The blade width at outlet

b3 = r3s − r3h

The area at outlet

( )A3 =  r32s − r32h

29

The isentropic inlet static temperature

Ts 2 = 1 + T2  3.66
M 22 R  3.67
2C p 3.68
3.69
The inlet static pressure 3.70
3.71
 3.72
3.73
p2 = po1 T2s To2   −1

The density at inlet

2 = p2
RT2

The inlet blade height

b2 = mexhaust
2 r2v2 cos2

The static temperature at inlet

T3 = To3 ( 1)

 − M 2 
1 + 3 

2

The number of Mach at outlet of rotor

M 4 +  2 1 M 2 − 2RT03m2 = 0
3 − 3 
( −1) p32 A32

The absolute velocity at outlet

v3 = M3  RT3

The flow angle of relative velocity at outlet

3 = tan −1  u3 
 v3 
 

30

The flow angle of relative velocity at hub

3h = tan −1  u3h  3.74
  3.76
 v3  3.77

The flow angle of relative velocity at shroud

3s = tan −1  u3s 
 
 v3 

The density at outlet

3 = p3
RT2

Assumption for One Dimensional Calculation:

The assumptions of combustion gas are the initial values to use for in various
design sizes with the following details:
- Density air ( ) is 1.109 kg m3

- Specific heat of exhaust gas (cp ) is 1.148 kJ (kg  K)

- The ratio of specific heats ( ) is 1.35
- The gas constant (R) is 287 J (kg  K)

Specification of engine
- Capacity (Vs ) =2,499 cc
- Power = 90 hp. (67.113kW)
- Rotation speed of engine = 4,200 rpm
- Fuel/air ratio for CI diesel engine (F/A) is 0.056
Specification of Turbine
- Total temperature of gas in volute (T01) = 400 Celsius (673 K)
- Total temperature of gas leaving stator (T02) = (T01)
- Speed of rotor (n) = 52,000 rpm
- Exit pressure is atmospheric ( p3) = 101.325 kPa
- The stator loss efficiency = 0.08

- The ratio of the blade radii at the exit (k = r3h r3s ) is 0.35
- We assume the pressure ratio of the turbine is ( p01 p3 ) = 2

- The number of Mach at inlet of impeller (M2 ) = 0.69

31

- The flow angel at inlet of impeller 2 = 68 degree
- Delivery of power (power) = 2.7 kW

Mass flow of exhaust to design turbine
Flow chart for calculate mass flow of exhaust gas from engine.

Volume rate 2, 499 4, 200
2  60
Q= = 87, 468 mm3 s = 0.087468 m3
s

Mass flow of air mair = 0.0874681.109 = 0.096998685 kg s

Mass flow of fuel mfuel = 0.056 0.096998685 = 0.005431926 kg s
Mass flow of exhaust mexhaust = 0.005431962 + 0.096998685 = 0.102430611kg s

32

3.4 Specific Design Turbine
The flow chart for one-dimension calculation is used for calculating the size of

turbine (Figure 3.15). All these equations are in the past.
Figure 3.15
Dimensional calculation for rotor and stator

MATLAB calculates the parameters and dimensions.
The process knows the value of one-dimensional calculation of turbine by using

MATLAB, because the parameter values are associated with other parts. The details are
shown in Figure 3.15, using the calculator to simplify and complicate the connection of
each section's values as follows:

33

Figure 3.16
One dimensional calculation

The results of the calculation of the values required for the design of the sections are
displayed in Table 3.3.

Table 3.3
The results from calculation in one dimensional calculation of radial turbine

No Description Abbreviation Unit Value
kg / m3 1.109
1 Density air air 1,148
2 Specific heat of exhaust gas cp J / (kg  K ) 4/3
3 The ratio of specific heats  287
4 The gas constant J / (kg  K )
5 Capacity of engine R 2,499
6 Power of engine vs cc 90
7 Speed of engine hp hp
n 4,200
rpm

34

No Description Abbreviation Unit Value

8 Fuel/air ratio for CI engine with diesel fuel f /a K 0.056
rpm
9 Total temperature of gas involute T01 kPa 673
10 Rotational speed of rotor n kPa
30,000
11 The outlet static pressure p3 degree 101.325
12 The inlet stagnation pressure to stator p01 kW 202.65
13 The stator loss efficiency s m3 / s
14 The number of Mach at inlet of rotor M2 kg / s 0.08
15 The ratio of the blade radii at the exit K 0.69
k 0.35
kJ / kg 0.58
16 The ratio between blade radii outlet and inlet 2 m/s
17 The flow angel at inlet of impeller power 62
18 Delivery of power K 2.7
kJ / kg 0.0875
19 Volute flow rate Q 0.1024
m/s 565.9233
20 Mass flow of gas m m/s
m/s 122.92
21 The isentropic static temperature at the exit T3s 495.8307
22 The isentropic work ws K 623.5234
23 The spouting velocity v0 26.359
24 The static temperature at inlet T2 kPa 162.3555
25 The specific work kg / m3 183.879
w 86.3259
m 622.3453
26 The blade speed at inlet u2 m 148.1877
27 The absolute velocity at inlet v2 0.8281
28 The relative velocity at inlet w2 K 0.0298
29 The isentropic inlet static temperature T2 s 0.0076
30 The inlet static pressure p2 m 650.0389
31 The density at inlet 2 m 0.0175
32 The radius at inlet r2 m 0.0075
33 The inlet blade height b2 0.0134
34 The exit stagnation temperature T03 m/s
35 The rotor shroud radius r3 s m/s 0.4744
36 The rotor hub radius r3h m/s
37 The mean exit radius r3 73.2037
K 95.1403
38 The number of Mach at outlet of rotor M3 40.8152
626.5349
39 The blade speed at mean exit radius u3
40 The shroud blade speed u3s
41 The hub blade speed u3h
42 The static temperature at exit T3

35

No Description Abbreviation Unit Value
43 The absolute velocity at outlet m/s 232.3041
44 The relative velocity at outlet v3 m/s 243.5651
45 The flow angle of relative velocity at outlet w3 degree 17.4907
46 The flow angle of relative velocity at shroud 3 degree 22.2716
47 The flow angle of relative velocity at hub 3s degree
48 The area at outlet 3h m2 9.9650
49 The blade width at outlet A3 0.0008
b3 m 0.01

Figure 3.17
Velocity triangles for rotor and stator

36

3.5 Drawing Turbo-Generator
Turbo-generator CAD models drawing on referencing the volute of dimensional

calculation are shown in Figure 3.18.
Figure 3.18
Rotor and volute design

The main part of Turbo generator model consists of volute, vane, turbine, and plate.
Figure 3.19
The turbo-generator component

37

3.6 Drawing and Construction of a Thermoelectric Generator (thermoelectric plate just
select from market)

The output voltage is directly proportional to the temperature change, which is the
principle of a thermoelectric generator using the phenomenon characteristics known as the
Seebeck effect, and the following equation is displayed as

V = T 3.78

Where α is the Seebeck coefficient (VK )−1 , T is the temperature difference of two sides of

the surface in K .
The Reynolds number derived from the value of the heat source from the engine exhaust
gas

Re = vD /  , 3.79

Where  is the density,  is viscosity, D is the equivalent diameter, and  is the viscosity

of the fluid flowing through the tube.
The heat transfer coefficient of the hot side

he = Nuke / Dh . 3.80

The Nusselt number is defined as the ratio of convection heat transfer to fluid conduction
heat.

Nu = he Dh 3.81
ke

Where Nu is Nusselt number, ke is thermo conductivity of exhaust, and Dh is the hydraulic
diameter.
The convection on the plate

( )Nu = 0.664 Re0.5 Pr0.33 3.82

Where Re is the Reynolds number, and Pr is the Prandtl number.
The heat conversion efficiency of waste heat recovery

Poutput 3.84
( ) =
mC p Tin − Tout

38

where  is the conversion efficiency, Poutput is the thermoelectric generator power output,

m is the exhaust gas mass flow rate, Cp is the exhaust gas specific heat, Tin is the exhaust
gas system inlet temperature, and Tout is the exhaust gas system outlet temperature.
The power generated by the thermoelectric generator

P = N pnITleg − I 2NRpn 3.85

Where N is the number of thermoelectric couples employed,  pn is the Seebeck coefficient,
I is the electric current, Tleg is the thermoelectric leg temperature difference, and Rpn is
the value of the thermoelectric resistivity couple.
The equation for the system efficiency

 = pTEG 100% 3.86
Pengine

Where pTEG is the thermoelectric generator maximum output power, isPengine the power of

the engine.
The efficiency of a TE module
Where Z is a material property, Tc is cold temperature, Th is hot temperature, and T is
(Th + Tc ) / 2 .

TE max = Welec = T 1 + ZT −1 3.87
Qh . 1 + ZT + Tc 3.88

Th

Th

p −n 2
p p 1/2 + nn 1/2 2
(( () ) )( )Z =

Where  p is the Seebeck coefficient corresponding to p , n is the Seebeck coefficient
corresponding to n , p is thermal conductivity corresponding to p , n is thermal
conductivity corresponding to n ,  p is electrical resistivity the corresponding to p , and
n is electrical resistivity corresponding to n .
The power output

P = Qh − Qc = I 2RL 3.89

Where I is the electrical current in the generator circuit, RL is the electric resistance of
semiconductor couple, Qh is the heat absorbed from heat source, and Qc is the heat
absorbed from the cold source.

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Power outputs, and conversion efficiencies

P = N  pn (Th − Tc ) I − I 2R 3.90
3.91
( )R = L
A
n + p

= P 3.92
Qh

Where P is the output power, N is the number of thermoelectric elements in the module,
and  pn is the Seebeck coefficient. L is the length of the legs, and A is the cross-sectional

area.

The equation for the thermocouple conversion efficiency

 = P Qh 3.93

Where Qh is the absorbed, P is the output power.

Another important part of the process for designing a thermo-electric generator is
finding the heat transfer correlation, which is calculated from the heat of the engine exhaust
flowing through the exhaust pipe. The design focuses on the suitability, and ease of
installation with real engines in a limited space to make the best heat transfer efficiency,
and not to extremely affect the pressure of the exhaust. Figure 3.20 illustrates the heat
transfer correlations of the thermo-electric generator.

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Figure 3.20
Heat transfer correlation of the thermoelectric module

Energy balance of cooling heat exchanger

( )Qc = mccp Tc+1 − Tc 3.94

( )( )Qc = hc Ac Tc − Tc + Tc+1 / 2 3.95

where hc is the heat transfer coefficient for the coolant heat exchanger, Ac is the heat
transfer area for the coolant side, mc is the mass flow rate, Tc is the coolant water
temperature, and Tt is the temperature of the cold side of the thermoelectric module.
Energy balance of exhaust heat exchanger

( )Qh = mhcp Th − Th+1 3.96

( )( )Qh = hh Ah Th − Th + Th+1 / 2 − Ti 3.97

where hh is the heat transfer coefficient for the exhaust heat exchanger, Ah is the heat
transfer area for the exhaust side, mh is the mass flow rate, cp is the specific heat of the
exhaust, Th is the temperature of the exhaust, and Ti is the temperature of the hot side of
the thermoelectric module.

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Heat and cooling transfer of the system 3.98
Qc = SITc + K (Th − Tc ) − 0.5I 2R

Qh = SITh + K (Th − Tc ) − 0.5I 2R 3.99

Where S is the Seebeck coefficient, R is the internal resistance, K is the thermal
conductance of the module, and I is the total current of the generator.
Calculations for efficiency of a thermo-electric generator
The exhaust gas mass flow rate was 0.1024 kg/s, the exhaust gas specific heat cpg was

1kJ / kgK , and the supplied heat was:

the exhaust gas = mgcpgT = 0.1024  1.148  (110 − 115) = 587.776 W ,

electrical power output = VI = 16  5 = 80 W

efficiency of thermoelectric generator= electrical power output = 13.61 3.100
heat sup plied by the exhaust gas

Figure 3.21
Thermoelectric generator module

The thermoelectric module is composed of 2 units with dimensions: 240 x 100 x
300 mm. It is a combination of three main parts: water cooling box, heat exchange box, and
thermoelectric plate (TECI-12706). Water cooling box has 8 parts with dimensions 70 x 40
x 300 mm. It was used as thermo-electric plate to reduce the heat by removing the heat from
the water using the radiator. Heat exchange box has dimensions 100x100x300 mm to
transfer heat from hot water to thermoelectric 80 plates.

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