Use of Electrical Coolant Pumps in Scania’s Cooling System

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Use of Electrical Coolant Pumps in Scania’s Cooling System

SAI ASWIN SRIKANTH

Master of Science Thesis TRITA-ITM-EX 2019:589 KTH Industrial Engineering and Management

Machine Design SE-100 44 STOCKHOLM

SEPTEMBER 2019

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ii

Abstract

The automotive industry is currently traversing through the electrification wave. Numerous manu- facturers are directing focus to electrify their lineup and reduce emissions. In the frontier of heavy duty diesel trucks, electrification of auxiliary units remains an unexplored potential. An optimized cooling system functioning in sync with a controllable electric coolant pump attempts to reduce parasitic losses and emissions. The cooling flow requirements in challenging conditions may also be fulfilled. Although electric coolant pumps are found increasingly in passenger cars, the implication of independently operating them in a heavy duty diesel truck is an important objective to be explored.

The purpose of this project is to generate different cooling system layouts coupled with electrical coolant pumps. The performance of these layouts is compared with the volume flows in a standard cooling system. Refined layouts which fulfill the cooling system requirements are chosen for

verification. 1-D Simulation is used to correlate and verify the trends of the test rig data.

The results show an adequate gain in the total volume flow across distinct layouts with the electric coolant pumps. However, numerous challenges are required to be overcome.

Keywords: Electrical coolant pumps, advanced cooling system layouts, controllable cooling system,

GT-Suite simulation

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Sammanfattning

Bilindustrin befinner sig mitt i en våg av elektrifiering. Flertalet tillverkare fokuserar på att elektri- fiera sitt produktutbud och att minska utsläppen. Inom forskningen kring tunga transporter med dieseldrivna lastbilar, är elektrifiering av kylsystemet ett outforskat område. Ett optimerat kylsystem som är reglerbart med en elektrisk kylvätskepump skulle potentiellt kunna minska energiförluster och utsläpp. Kravet på flödet av kylvätska vid utmanande driftsfall skulle också kunna bli bättre uppfyllda än för dagens system. Trots att det blir allt vanligare att personbilar har elektriska kylvätskepumpar, så har det inte utforskats vad det innebär att ha reglerbara elektriska kylvätskepumpar i dieseldriva lastbilar. Därför är detta ett viktigt område att utforska.

Målet med detta projekt är att skapa olika kylsystemskoncept, där den elektriska kylvätskepumpen är en systemkomponent. Prestandan hos dessa principlösningar jämförs sedan med volymflödet i ett standard kylvätskesystem. Koncept som uppfyller kraven för kylvätskesystemet kommer att bli utvalda för vidare verifiering. 1-D simuleringar används för att hitta samband och verifiera mot tren- derna som hittas i resultat från en testrigg.

Resultaten visar en förbättring i det totala volymflödet för flera av lösningarna, som har en elektrisk kylvätskepump. Men det finns fortfarande flera utmaningar som behöver övervinnas.

Nyckelord: Elektrisk kylvätskepump, avancerade kylsystemkoncept, reglerbart kylvätskesystem, GTSuite-

simuleringar

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Acknowledgment

This thesis work was carried out from January 2019 to June 2019, in partial fulfillment of the Master of Science degree in Engineering Design at KTH Royal Institute of Technology, Stockholm. I would first like to thank my manager, Magnus Hulten at Scania CV AB, for entrusting me with this exciting thesis project. I would also like to express my gratitude to my supervisor, Stig Hildahl, for sharing his valuable expertise in rig testing of coolant pumps, encouragement, and continual support. Mattias Strindlund for his regular feedback on the simulation results. David Panero for offering his construc- tive opinions throughout my project.

I would also like to thank Zoltan Kardos, for helping me with the connections for operating the elec- trical pump.

I extend my gratitude to Ulf Sellgren, my thesis supervisor, and examiner at KTH for his timely guid- ance and support.

Sai Aswin Srikanth Stockholm, Sweden

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viii

Nomenclature

ABBREVIATIONS

ECP Electrical Coolant Pump HDD Heavy Duty Diesel

MCP Mechanical Coolant Pump IC Internal Combustion EGR Exhaust Gas Re-circulation CAN Controller Area Network BTE Brake Thermal Efficiency

HC Hydrocarbon

CO Carbon monoxide

STP Scania Testbed Platform

NOTATIONS

m ˙

_f

Mass flow rate of fuel, kg/s

˙

m

_a

Mass flow rate of air, kg/s h ˙

_f

Specific Enthalpy of fuel, J/kg h ˙

_a

Specific Enthalpy of air, J/kg

Q

_{equi v}

˙ Energy corresponding to input fuel

N

_b

Effective engine brake power, W

Q ˙

_c

Heat transfer rate to coolant, W

Q ˙

_f

Heat flux of fuel, W

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ix

Q

mi sc

˙ Summation of heat rejected to oil, convection and radiation, W Q

_exh

˙ Exhaust gas energy

m ˙

c

Mass flow rate of coolant, kg/s C

_pc

Specific heat of capacity Coolant, J/K T

_c^out

Coolant temperature at engine outlet, K T

_c^{i n}

Coolant temperature at engine inlet, K T

_exh

Exhaust gas temperature, K

T

_{i nt}

Intake gas temperature, K

P

_{eng i ne}

Power consumption of engine, kW

T Torque, Nm

n Engine Speed, Rpm

η Engine Brake Efficiency

k Fraction of Heat Flux to Coolant

∆T

eng i ne

Max Temperature of Engine at Peak Load, K

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List of Figures

1.1 A MCP coupled to an Engine. (Source: Scania) . . . . 3

1.2 Thesis Methodology . . . . 5

2.1 Automotive Engine Cooling System . . . . 9

2.2 Pilot Thermostat in Cooling Circuit . . . . 10

2.3 Engine Energy Balance Representation . . . . 11

2.4 Example of Pump vs System curve.[5] . . . . 12

2.5 Cross section of ECP[6] . . . . 13

2.6 A WP29-Electric Water Pump. . . . 16

2.7 Thermostat Valve Configuration [23] . . . . 19

3.1 Cooling system test rig with a pressure sensor in Retarder circuit . . . . 23

3.2 Schematic illustration of pressure and volume flow sensor locations . . . . 23

3.3 Mechanical Coolant Pump- Low Powered . . . . 24

3.4 Pump Map of MCP at System Pressure - 0.7 bar . . . . 24

3.5 Cooling System Requirements . . . . 25

3.6 Electrical Coolant Pump prototype . . . . 26

3.7 ECP Control Methodology . . . . 27

3.8 Layouts tested in the rig . . . . 28

3.9 Illustration of Static Line Modification . . . . 29

3.10 Components in Engine Block . . . . 29

3.11 Layout-1 Schematic and Assembly in Test Rig . . . . 30

3.12 Layout-2 Coolant System Schematic . . . . 31

3.13 Layout-3 Assembly in Test Rig . . . . 31

3.14 Layout-3 Coolant System Schematic . . . . 32

xiv

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LIST OF FIGURES xv

3.15 Layout-4 Coolant System Schematic . . . . 33

3.16 Layout-4 Assembly in Test Rig . . . . 33

3.17 Layout-5 Coolant System Schematic . . . . 34

3.18 Layout-5 Assembly in Test Rig . . . . 35

3.19 Preferred Measurement Setup- Milling . . . . 36

3.20 Layout-5 Simulation Model . . . . 36

3.21 Single ECP configuration . . . . 37

4.1 Result: Cooling System Layout-1 . . . . 40

4.2 Result: Cooling System Layout-2 (Test 1-2) . . . . 40

4.3 Result: Cooling System Layout-2 (Test-3) . . . . 41

4.4 Result: Cooling System Layout-3 (Test 1-2) . . . . 42

4.5 Result: Cooling System Layout-3 (Test 3-4) . . . . 42

4.6 Result: Cooling System Layout-4 (Test 2) . . . . 43

4.7 Result: Cooling System Layout-4 (Test 3-4) . . . . 44

4.8 Result: Cooling System Layout-5 (Test 2) . . . . 45

4.9 Result: Cooling System Layout-5 (Test 3.1-3.3) . . . . 45

4.10 Result: Cooling System Layout-5 (Test 4.1-4.3) . . . . 46

4.11 Simulation: Cooling System Layout-5 (Test Setup 2) . . . . 47

4.12 Simulation: Cooling System Layout-5 (Test Setup 3.1-3.3) . . . . 48

4.13 Simulation: Cooling System Layout-5 (Test Setup 4.1-4.3) . . . . 49

4.14 Pump Map: GT-Suite vs Supplier Data . . . . 50

4.15 Power Consumption: Electrical Pumps . . . . 51

4.16 Power Consumption: Mechanical Pump . . . . 51

4.17 Result: Single ECP configuration . . . . 53

A.1 Project Plan . . . . 64

B.1 Risk Assessment . . . . 65

B.2 Risk Assessment Matrix . . . . 65

C.1 Electrical Coolant Pump- Drawing . . . . 66

C.2 Electrical Coolant Pump- CAN Database . . . . 67

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LIST OF FIGURES xvi

C.3 Electrical Coolant Pump- CANalyzer Setup . . . . 67

D.1 2.4 kW Power Supply Specifications . . . . 68

E.1 Layout - 1 . . . . 69

E.2 Layout - 2 . . . . 70

E.3 Layout - 3 . . . . 71

E.4 Layout - 3 . . . . 71

E.5 Layout - 4 . . . . 72

E.6 Layout - 4 . . . . 72

E.7 Layout - 5 . . . . 73

E.8 Layout - 5 . . . . 73

E.9 Layout - 5 . . . . 74

F.1 Layout - 5 . . . . 75

F.2 Layout - 5 . . . . 76

F.3 Layout - 5 . . . . 76

G.1 Q Total Correlation- Test 1 . . . . 77

G.2 Q Total Correlation- Test 3.1 - 3.3 . . . . 78

G.3 Q Total Correlation- Test 4.1 - 4.3 . . . . 78

H.1 Schematic: Layout A . . . . 79

H.2 Schematic: Layout B . . . . 80

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List of Tables

3.1 Flow Requirements: Tabular Data . . . . 25

3.2 Electrical Pump Specification . . . . 26

3.3 Layout 3 - Test Setup . . . . 32

3.4 Layout 4 - Test Setup . . . . 34

3.5 Layout 5 - Test Setup . . . . 35

4.1 Layout2: Flow Enhancement from ECP . . . . 41

4.2 Layout 3: Flow Enhancement from ECP . . . . 43

4.3 Layout 4: Flow Enhancement from ECP . . . . 43

4.4 24 V Truck Battery Specification . . . . 52

4.5 Result: Single ECP configuration . . . . 52

5.1 Test Cases Satisfying System Requirements . . . . 55

5.2 Power Consumed by Pumps . . . . 57

xvii

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Chapter 1 Introduction

The automotive sector is currently undergoing a rapid transformation. Numerous manufacturers are directing focus to electrify their lineup and minimize environmental impacts. SCANIA CV AB is aim- ing to be a global leader in sustainable transport. Thus, bearing the objective to fulfill the ever requir- ing demands of reduced fuel consumption and simultaneously progress towards obeying stringent emission regulations. The advancement in mechatronics has paved the way for the development of enhanced powertrain components, thereby optimizing the thermal management system in vehi- cles. To enable demand-driven cooling and enhance passenger comfort, the adaptation of electrical coolant pump(ECP) in the cooling system is beginning to be explored by researchers.

1.1 Background

The traditional cooling system in heavy-duty trucks comprises of a mechanical coolant pump (MCP) driven by the engine. The pump speed and therefore, the coolant flow rate is directly proportional to the engine speed, which is not an optimal method of control in numerous cases. Excessive frictional losses are prevalent in the belt transmission drive, and parasitic losses are experienced due to the aux- iliary components continually driven by the engine crankshaft.

In the scenario of heavy traffic during summer, numerous start-stop events lead to high engine tem- perature. However, the speed of the coolant pump is low. The coolant circulation is not adequate to help reduce the engine temperature. Hence, due to incomplete combustion, the formation of NO

_x

particles are accelerated [1]. During cold starts, the warm-up time of the engine is longer than ex- pected, impacting the HVAC performance negatively.

2

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CHAPTER 1. INTRODUCTION 3

Figure 1.1: A MCP coupled to an Engine. (Source: Scania)

Considering all the following disadvantages, significant fuel savings can be achieved by reduc- ing the coolant pump’s absorbed power. The advancement in the development of electrical coolant pump technology can hence play a significant role in assisting to accomplish this objective. If the MCP is replaced with its electrical counterpart possessing similar packaging dimensions, weight and nominal overall cost increase, the pump’s operational performance dependence with respect to the engine speed can hence be eliminated. The ECP can also work as a booster pump together with an optimized smaller sized MCP. The flow boost can help fulfill the requirements during braking appli- cations when the truck is heavily loaded.

Passive cooling components operating in a traditional cooling system are designed considering low coolant flows at hot ambient temperatures. High design load scenarios are considered to prevent ther- mal fatigue. Hence, the system components can help prevent system failures at extreme operational limits but are unavoidably oversized for loads occurring in a moderate or light operational driving cy- cle.

The ECP’s speed can however be controlled based on the coolant temperature rather than the engine

speed, indicating flexibility in designing cooling system components in the future. An ECP operating

in sync with a smart thermostat valve is the primary step in electrification of the cooling system.

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CHAPTER 1. INTRODUCTION 4

1.2 Purpose

The major focus in this study is to examine the implications if the traditional mechanical coolant pump in a SCANIA 13-Litre, 6 cylinder diesel engine can be replaced by an electrical coolant pump, maintaining equivalent characteristics of packaging and reduced power consumption. A better un- derstanding of the interaction between the coolant pump and different components of the cooling systems is consequently necessary to understand if electrification can contribute to improved per- formance and function, parallelly reducing fuel consumption. Generating different cooling system layouts and analyzing their performance is a major step towards achieving a robust system.

Research Questions

1. Can one electrical coolant pump guarantee the coolant flow requirements in a heavy duty diesel vehicle’s cooling system or two coolant pumps may need to operate in parallel to fulfill the re- quirements ?

2. Is life length of the electrical coolant pump suitable with respect to the life length of a truck ? 3. What is the power consumed by the electrical pump in comparison to the mechanical pump ?

1.3 Delimitations

Following are the boundaries of the thesis work.

1. Only the cooling system in a SCANIA 13 litre, 6 cylinder diesel engine is considered for study.

2. As a primary step, the effectiveness of the electrical coolant pump in a simple cooling circuit comprising of a radiator, HVAC system and thermostat is investigated. The brake compressor and gearbox cooler circuits are not initially considered.

3. Retarder cooler, Turbo cooler and Exhaust Gas Re-circulation (EGR) components are not con- sidered in any of the generated layouts.

4. Evaluation of the engine warm-up time will not be performed.

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CHAPTER 1. INTRODUCTION 5

1.4 Methodology

The following section describes the methodology which is to be adopted while carrying out the thesis work. The flowchart shown in the figure 1.2 highlights the major steps which are elaborated further below.

Figure 1.2: Thesis Methodology

Literature Study

Gathering knowledge on existing cooling system components from research journals and technical documents. Major focus on investigation of cooling systems with electrical or clutch based coolant pumps. Control strategies employed for regulation of coolant pumps is a subject to be explored. State of the art ECPs from suppliers is also to be analyzed, life length of the pump being a primary weighable factor.

Formulation of research questions

Based on existing literature, a boundary has to be defined highlighting the goals to be achieved in this

thesis. The first step is to identify and ascertain the research questions to be answered. This step is

followed by definition of the delimitation factors inorder to help assess the research questions in an

effective manner.

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CHAPTER 1. INTRODUCTION 6

Analyzing electrical coolant pumps in today’s markets

Tabulation of ECP specifications from various suppliers in the market today is to be performed. Prop- erties such as life length, flow rate, power requirements are to be analyzed. This section will provide engineers with relevant information on performance tested pump prototypes currently available on demand.

Generation of different cooling system layout concepts

Different situations are to be investigated wherein the requirement of coolant flow through the engine or oil cooler are not satisfied, an example of a truck driving on a hilly terrain during a hot day can be considered. The engine warm-up time of the truck in extreme cold weather can also be cited wherein the cab heating is not effective. After researching on the case studies, different cooling system layouts overcoming the identified challenges are to be generated.

Testing the Performance of the generated layouts in the test rig

The layouts are to be constructed to characterize the required configurations. The ECP’s speed is to be regulated by CAN protocols. Volume flow, pressure drop will have to be recorded with the aid of sensors mounted in the rig at appropriate channels. This step is to be carried out in iteration until cooling system layouts with enhanced performance are obtained.

Selection of layouts and Simulation of performance

The layouts demonstrating enhanced cooling performance are to be shortlisted from the test rig re- sults for verification, with the aid of GT-Suite simulations. The existing cooling system model with the MCP in GT-Suite is verified with physical test rig data. This circuit is to be modified to account the adjustments made in the test rig for mounting the ECP.

Verification of results and future work

The data obtained from physical testing and simulation are to be compared to corroborate the trends.

The results will be further elaborated in the final section, accounting for the deviations in results and

highlighting future work.

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Chapter 2 Frame of Reference

This chapter elucidates the necessary concepts and background knowledge that is to be gained while carrying out this thesis work. The chapter begins with an illustrative description of the current cooling system in Heavy Duty Diesel(HDD) vehicles, followed by the performance criteria to be obeyed by a MCP in supplying coolant to different components in the cooling system.

The chapter further elaborates on market research, highlighting current ECP designs, performance, and reliability. The conclusive part touches upon on the knowledge gained by researchers whilst em- ploying ECP in current cooling systems.

2.1 Cooling System in Diesel Engine

A traditional automotive engine cooling system comprises of coolant expansion vessel, thermostat, coolant pump, engine, radiator, fan, hoses and pipes. The coolant system circuit coupled to an in- ternal combustion (IC) engine plays a significant role in maintaining overall energy balance, curbing emissions and guaranteeing engine auxiliary units to perform reliably. The core of the engine archi- tecture has not undergone any comprehensive transformations over the last few decades. Certain additions such as the cab heater circuit, exhaust gas recirculation (EGR) cooler, retarder cooler cir- cuits have been introduced. The wax-type thermostat is however challenging to replace owing to its cost-effectiveness and ease of operation with a MCP driven by the IC engine.

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CHAPTER 2. FRAME OF REFERENCE 9

2.1.1 Working Principle

In conventional cooling systems, the engine start-up results in the coupled MCP to also begin its function. The MCP is mounted adjacent to the engine inlet to ensure that the pressurized coolant is delivered to the engine with minimum losses. Frictional losses are also minimized. During initial piston strokes after engine start-up, the coolant circulates continuously, travels through the oil cooler and enters the engine through the inlet water jacket. The coolant flow branches and flows through the turbo and gearbox coolers, subsequently flowing into the inlet of the coolant pump. The other part of the branched flow circulates through the outlet water jacket and passes through the catalytic reduc- tion circuit and the retarder cooler, subsequently flowing into the thermostat. The temperature of the wax in the thermostat is critical to determine the flow path of the coolant. Considering the low coolant temperature during the initial vehicle start-up, the coolant flow is completely diverted towards the in- let of the MCP through the bypass channel. Numerous combustion cycles result in an increase in the coolant temperature. The temperature of the wax in the thermostat also undergoes thermal expan- sion thereby allowing a part flow of the coolant through the radiator and bypass channel. When the thermostat valve is in a fully open position, the coolant starts to flow completely through the radiator tubes. The viscous clutch fan is engaged by the engine control unit to aid in reducing the temperature of the coolant.

Figure 2.1: Automotive Engine Cooling System

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CHAPTER 2. FRAME OF REFERENCE 10

2.1.2 Pilot Thermostat

A semi-pilot thermostat in a cooling circuit, as illustrated below in Figure 2.2 aids in streamlining a pilot flow from the outlet of the coolant pump into the wax body of the thermostat. The semi-pilot thermostat concept from Scania consists of 2 discs functioning in tandem. The melting temperature of wax in the respective discs are 89°C and 96°C. Thus, facilitating a stabilized thermostat hysteresis behaviour. The cooling down period after a retarder brake engagement cycle is also effectively re- duced.

An electric wax thermostat design was also recently developed and tested [2]. The prototype yielded positive results when coupled to an existing cooling system, indicating future developmental poten- tials.

Figure 2.2: Pilot Thermostat in Cooling Circuit

2.1.3 Energy Balance Fundamentals

An IC engine obeys the first law of thermodynamics. A part of the heat loss after combustion is trans- ferred to the coolant, another part exits out of the system in the form of exhaust gases [3]. The energy conservation equation for the engine control volume during warm-up is described in equation 2.1.

The thermal energy rejected to the coolant by the process of convection is described in equation 2.2.

The thermal energy transported by exhaust gases is described in equation 2.3.

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CHAPTER 2. FRAME OF REFERENCE 11

˙

m

_f

h

_f

+ ˙ m

_a

h

_a

= ˙ Q

_equiv

+ ˙ m

_a

h

_a

= N

b

+ ˙ Q

_c

+ ˙ Q

_misc

+ ˙ Q

_exh

(2.1)

Q ˙

_c

= ˙ m

_c

C

_pc

(T

_c^out

− T

ci n

) (2.2)

Q ˙

_exh

= ( ˙ m

_f

+ ˙ m

_a

)[h

_exh

(T

_exh

) − h

int

(T

_int

)] (2.3)

The schematic describing the parameters influencing the energy balance of an IC engine is illus- trated below in figure 2.3.

Figure 2.3: Engine Energy Balance Representation

2.2 Mechanical Coolant Pumps

A centrifugal type MCP is often the most important component of an engine cooling system. Sealed

in a compact mechanical casing, the pump ensures adequate circulation of coolant to different com-

ponents in the system. The coolant entry is through the pump inlet. It is then forced to circulate and

exit through the pump outlet. The MCP is driven by the crankshaft of the engine via belt drives with

a fixed transmission ratio. The pump performance is an important criterion to be considered during

the optimization of engine cooling system. Coolant pumps are exposed to temperatures between -

40°to +120°. The MCP is usually over-sized to accommodate the cooling demands during maximum

torque applications.

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CHAPTER 2. FRAME OF REFERENCE 12

2.2.1 Pump Performance

In order to ensure that the chosen pump fulfills distinctive demands of the cooling system in a HDD truck, it is pivotal to conduct tests at different speeds [4]. Suitable speeds to start a run is usually at 500 rpm of engine speed. With steps of 200 rpm, a targeted 2500 rpm of engine speed is to be achieved.

The critical parameters to be tested are as follows :

• Inlet and outlet pressure.

• Coolant flow, internal torque, power consumption

The test results are summed up in a diagram collectively with the system curve. The system curve shows the pump capacity on one engine type or cooling system. It is hence necessary to obtain the characteristics for each engine type despite having a similar operational pump. The pump curve is a way to graphically depict the pump behaviour for a certain flow rate and pressure increase. It is important to measure the internal torque of the pump during various driving cycles. The obtained torque is used for the calculation of power consumption and static efficiency. Properties of Pump Power, Efficiency, and Net Positive Suction Head (NPSHR) as a function of flow rate are also impor- tant. An example of a pump curve imposed with the system curve is illustrated below in figure 2.4.

The operational point of the system is always located at the point at which the two curves intersect.

Figure 2.4: Example of Pump vs System curve.[5]

Numerous fail-safe tests such as cavitation analysis [4], CFD simulation, corrosion, noise and vibra-

tion tests are performed on the pump before certifying them suitable for mass production.

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CHAPTER 2. FRAME OF REFERENCE 13

2.3 Electrical Coolant Pumps

Extensive resources are continually allocated for the development of ECPs due to their functionality in electric and hybrid vehicles. They can facilitate demand-driven cooling of the engine, enhance fuel economy and passenger comfort, contribute to efficient cooling of power train components. Fig- ure 2.5 shows the main components of ECP in a cross-sectional view. Similar to a MCP, the impeller plays the most crucial role in increasing the head and delivering coolant at the requested flow rate.

Since the flow angles at ECP impeller’s entry and exit are similar to that of MCP, the design method- ology implemented in the design of mechanical components in an ECP are similar. However, the extreme parameters dictating the pump’s design points can be down-sized. The main components of

Figure 2.5: Cross section of ECP[6]

an ECP are, a wet rotor, stator core, a separator in the motor structure, an impeller which is coupled to rotor assembly, a shaft is used to drive the rotor, the motor housing for the control system.

In this paper [6], the methodology for designing the critical electrical components such as the stator core and rotor are highlighted categorically. Optimal manufacturing techniques can help curb loses due to friction, aid in reducing costs and limiting the overall size of the motor. Performance of radial field and claw pole concepts in an ECP are necessary to be evaluated.

There are no mechanical seals in an ECP. The BLDC motor reduces frictional losses. The coolant en-

ters the ECP through the inlet and pressurized coolant is exited through the outlet. However, some

volume of coolant passes through the small gap between the impeller and involute housing inorder to

be circulated through the stator core. The rotor assembly housed in the stator is continually cooled by

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CHAPTER 2. FRAME OF REFERENCE 14

the circulation of coolant through this channel. However, this small gap can lead to the accumulation of debris from the circulating coolant. Since the rotor assembly is a critical component, selection of the optimal magnet material can help in realizing cost savings. The rotor bearings are the only compo- nent which may limit the lift length of the ECP. According to a NHTSA report[7], millions of passenger vehicles were recalled due to an ECP failure which the thermal management software could not de- tect. The root cause analysis concluded that the overheating due to accumulation of debris caused a short circuit and resulted in fire of the passenger car.

2.3.1 Current Product Trends

High Performance electrical coolant pumps are widely available for passenger cars. However, pump manufacturers have recently started developmental projects for HDD trucks. The expected perfor- mance of a coolant pump operating in heavy duty trucks is generally superior. An ECP in Scania’s HDD cooling system is required to satisfy the following demands:

• Voltage: 24 V

• Power: 800-1000 W

• Coolant flow: 300-450 litres/minute

Suppliers manufacturing ECPs were explored and their product specifications are listed below.

1. Hybrid Coolant Pump with Electrical and Mechanical Drive

This hybrid coolant pump combines the advantages of an ECP and a MCP operating in a single system[8].

Demand-driven control of the pump is possible in the electrical mode of engagement. High pump ef- ficiency is achieved in the mechanical mode of engagement. Hence, high variability is achieved in mid-power areas. Speed range of the pump was 7000 rpm, satisfying a maximum driving power of 2 kW.

2. WP29 – Electric Water Pump

This heavy duty performance ECP is specifically developed for electric and hybrid trucks[9]. Coupled

with an intelligent CAN enabled controller, a superior flow rate is deliverable. This pump is ideal

for enhancing the coolant circulation in the radiator circuit when MCP is ineffective in heavy load

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CHAPTER 2. FRAME OF REFERENCE 15

applications. This ECP is also suitable to circulate low-temperature coolant through the charged air cooling circuits on a heavy-duty diesel engine. The specifications of the pump are given below:

• Operating Voltage: 12V Model, 18 to 32 Volts (24V Model)

• Power: 500 W

• Coolant flow: 110 litres/minute

• Life Cycle: 10,000 Hours

3. PCE Coolant pump

This electric centrifugal type pump can be controlled via a CAN interface[10]. It has a brushless mo- tor drive and a robust design. The hydraulic operational power range enables it to be mounted as a booster pump to the MCP driven by the IC engine. The specifications of the pump are given below:

• Operating Voltage: 12 V or 24 V

• Input Power: 13 - 25 W

• Life Cycle: 8,000 Hours to 30,000 Hours (dependent on temperature profile)

4. Electric Coolant Pump for 48-Volt Systems

The following pump has the ability to deliver a maximum power of 950 Watt [11]. The speed can be controlled via CAN or PWM. Operating at 48 Volts, the pump builds on the previous range of 450 Watt variants which are beginning to be used in automobiles. Achievable flow rate is 220 litres/minute.

5. Circulation DC Water Pumps

The following pump features sine wave silent technology, functioning at less than 40 dB[12]. Equipped with water shortage and congestion protection functions, it operates with a magnetic driven, brush- less DC motor. The specifications of the pump are given below:

• Operating Voltage: 12 V or 24 V

• Input Power: 120 W

• Life Cycle: 20,000 Hours

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CHAPTER 2. FRAME OF REFERENCE 16

• Maximum Flow Rate: 105 litres/minute

6. Electric Coolant Pump ECP 160

The BLDC motor of this pump can be controlled by CAN or PWM method [13]. The spiral housing is realized by additive manufacturing. The specifications of the pump are given below:

• Operating Voltage: 12 V

• Released Output Power: 750 W

• Maximum Flow Rate: 240 litres/minute

7. Electrical 48-V Coolant Pump to Reduce CO

₂

Emissions

This 48-V electrically driven pump offers a potential to save 96 grams of CO

2

per kilometer[14]. Three design points at 400 W, 800 W and 1 kW are chosen for testing the pump in different operational areas.

Thus, achieving a balance between pump size, weight with respect to operation at elevated coolant temperature.

Figure 2.6: A WP29-Electric Water Pump.[9]

8. Auxiliary Electrical Water Pump

The ECP from Continental [15] is ideal for fulfilling the cooling requirements of engine and electronics

in light and medium duty vehicles. Beside this functionality, turbocharged air in passenger cars can

also be cooled. Remaining on par with all other ECPs in the market, this pump also supports on-

demand energy management and independent operation from IC engine.

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CHAPTER 2. FRAME OF REFERENCE 17

2.4 Cooling Systems With Controllable Pumps

• In this paper, a 12 volt ECP was implemented in the low temperature cooling circuit, two 48 volt ECPs were implemented in parallel in the high temperature cooling circuit in order to eval- uate emissions [16]. Although it resulted in a reduced cooling performance at higher speeds, demand-driven cooling improved the brake thermal efficiency (BTE) by 5%. The engine warm- up time decreased by 5 minutes, impacting HC, CO emissions positively and NO

_x

emissions negatively. The input power to the ECP in the engine-stop phase was reduced by 50%. The ther- mostats in the low temperature circuits were also removed. Thus, improving fuel economy and reducing parasitic losses.

• Investigations implementing pumps with electromagnetic clutch concepts were undertaken[17].

Two types of pumps, planetary gear based and an on/off type pump to completely stop the ro- tation of the impeller were designed. Coolant temperature was monitored by placing k-type thermocouples at cylinder wall jacket and at the bottom of the engine oil pan. By implementing a suitable control system, engine warm-up time and emissions were investigated. The on/off pump could warm-up the engine significantly faster in comparison to planetary gear pump which constantly circulated the coolant at lower volume flow rates. This was measured by ob- serving the time taken by the coolant to reach 80 °C. Although the fuel economy in on/off pump system was superior due to continually minimizing engine frictional losses, the emission of NO

_x

particles were slightly higher.

• Implementation of ECP required a modified thermostat hysteresis. A control unit with 2 elec- tronically controlled valves was developed to replace the thermostat [18]. Two new cooling strategies were proposed. Ensuring that no coolant circulation occurred through the engine during a warm-up cycle resulted in a rapid increase of engine temperature. Significant reduc- tion in warm-up time was also achieved by closing the valve between the engine and oil cooler.

HC and CO particle emissions were decreased due to complete combustion in different cycles,

however, emission of NO

_x

particles was higher due to increased temperature in cylinder liners,

a downside of demand-driven cooling. The cost feasibility of the above system was also not

computed. A study accounting the dynamic behaviour of pressure rise in ECP after switching

from high to low speed was also not performed.

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CHAPTER 2. FRAME OF REFERENCE 18

• In order to minimize fluctuations of temperature in the combustion chamber due to engine speed, a suitable coolant control approach, was described [19]. Mathematical models which interpreted the thermal behaviour of engine components were presented. In the first assess- ment, a linear control strategy was implemented to represent the thermostat valve functional- ity, coolant temperature being the key regulation factor. The fluctuations in the engine were steep. In the second assessment, the smart thermostat valve and ECP were regulated by PI con- trollers. Large temperature swings were again observed in the exhaust valve and piston while variation in middle cylinder wall was similar. In the final assessment, the smart thermostat and ECP were regulated by using the weighted cylinder head and wall temperature. a 44% reduc- tion in fluctuations were observed. This method may curtail peak-to-peak fluctuations in the engine components but may rapidly escalate fluctuations in coolant temperatures. An idea of integrating the thermostat valve into the ECP was also proposed.

• In this paper[20], The MCP was replaced by its electrical counterpart in the cooling circuit and its performance was simulated in GT-Cool. An estimated that 87% power saving could be achieved during the FTP 74 driving cycle by adopting an ECP. Analyzing coolant flows, the ther- mostat hysteresis was modified by reducing the opening temperature by 5°C, thus minimizing the ECP’s effort. Radiator downsizing was another important exploration. The inlet velocity of the radiator was obtained by correlations from the vehicle speed. Considering the MCP and ECP operating at their highest speed and coolant temperature at 90°C, the maximum cooling capac- ity under extreme load application was evaluated. Upon Inferring that the maximum coolant temperature was lower during the operational cycle of ECP, the size of the radiator was reduced by almost 27%. Thus the maximum coolant temperature of ECP circuit matched the range of the conventional system.

• This paper outlined the design, physical rig testing, wind tunnel vehicle testing of an advanced

cooling system which comprised of an electric water pump, flow control valve and a control

system to satisfy the cooling demand of a HDD engine [21]. The control system operated on the

feedback loops from the electric valve and pump which were dependent on the coolant tem-

perature at the engine outlet. The ECP could significantly overcome the engine parasitic losses

and sufficiently meet cooling demands. Up to 5% overall fuel efficiency benefits could be antic-

ipated by implementing the proposed thermal management system. Other benefits of adopting

the ECP included, packaging benefits owing to the freedom of mounting the ECP at the chassis

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CHAPTER 2. FRAME OF REFERENCE 19

and not fundamentally at the engine inlet. Radiator erosion could be prevented by controlling the flow valve. Leakage through the radiator or bypass could be prevented. Coolant tempera- ture could be controlled by engaging the electric valve and ECP. Enhanced heater performance was also achieved.

• In this paper [22], an optimal nonlinear control strategy for controlling the cooling system of a military M-ATV engine’s was presented. This strategy was also bench-marked against conven- tional state flow control and classic PI control methods. Smaller tracking errors and temperature fluctuations were realized in the nonlinear control strategy.

2.4.1 Advanced Cooling System Layouts

• The thermostat valve’s primary role was examined and system performance with four different valve configurations was investigated [23]. The configuration has been illustrated in the figure below 2.7. Mechanical components in the first layout experience high rotational speeds, lead- ing to an increase in fuel consumption. Over-cooling or under-cooling may occur due to the MCP’s speed varying as a function of the engine speed. In the second layout, the smart valve blocks the coolant flow from entering the external channel. However, a considerable volume of coolant is directed through the radiator, impacting the warm-up temperature negatively. The performance of the three-way valve is similar to a two-way valve. Except, the three-way valve controls coolant flow through the bypass and radiator circuit. The coolant flow can hence be completely blocked from entering the radiator or bypass, aiding in decreasing the engine warm- up time.

Figure 2.7: Thermostat Valve Configuration [23]

Enhanced thermal management is possible, but the introduction of complex valve hardware

with greater functionality can be expensive. In the final circuit, the valve is potentially elimi-

nated. The flow is only regulated with the electric water pump.

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CHAPTER 2. FRAME OF REFERENCE 20

During warm-up conditions, the pump speed is minimal. Upon the engine reaching the desired temperature, the pump speed can be adjusted in accordance with the engine load. The study concluded that, the three-way valve configuration provided excellent temperature control char- acteristics, reduced power consumption, and warm-up time in comparison to the other config- urations.

• In the following paper [24], different cooling system layouts were evaluated in KULI (1-D simu- lation tool). The first layout consisted of electrically powered fans, pump, and valve controlled by CAN protocols. An array of BLDC fans were prevalent in the second layout. The third lay- out consisted of an ECP and smart valve. It was concluded that impressive power savings in a low voltage HDD vehicle’s powertrain can be realized by replacing the standard mechanical fan with an array of small electrically driven fans. Replacement of the low voltage battery with its higher capacity counterpart can help in electrification of all the cooling system components.

Thus ensuring proportional fuel savings to be realized.

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Chapter 3 Implementation

This chapter describes the necessary details with regard to the conventional cooling system test rig setup with MCP, illustrating the flow and pressure sensor locations. Further, the ECP specifications from the supplier are tabulated and the control strategy is elaborated. Different cooling system lay- outs that are performance tested by modifying the conventional rig setup are chronologically pre- sented. Consequently, the chapter concludes with the simulation methodology adopted in GT-Suite for simulating performance of layouts with ECPs operating in parallel.

3.1 Conventional Cooling System Test Rig Setup

The coolant system rig consists of a computer, a mobile panel that contains Profibus modules to es- tablish master communication and record measurements. The electric motor and torque sensors are interfaced to the Profibus panel by suitable connections. The pressure, torque and temperature sen- sors are connected to the panel box. The PWM that controls the speed of the electric motor is also connected to the panel box. The panel box is connected to the 220 V power supply. The V-belt from electric motor drives the MCP, thus imitating an IC engine assembly, driving the MCP by the rotation of the crankshaft. Pressure and flow sensors are placed in the circuit as depicted in figure 3.2. The flow sensors installed at the cab heater circuit, static line and radiator outlet play an important role in analyzing the flow characteristics in the generated layouts. The pressure sensors aid in ascertaining the pressure drop across critical branches due to modifications in existing optimized layout connec- tions. Scania Test-bed Platform (STP) software is implemented in order to establish communication and record measurement of parameters during test runs.

22

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CHAPTER 3. IMPLEMENTATION 23

Figure 3.1: Cooling system test rig with a pressure sensor in Retarder circuit

A 6 cylinder HDD engine block is mounted in the test rig in figure 3.1, the objective to investigate the coolant flow in the retarder circuit during the thermostat open and closed conditions.

Figure 3.2: Schematic illustration of pressure and volume flow sensor locations

The coolant composition used for tests in the rig comprises of glycol and water mixed at a 20:80 pro-

portion. The kinematic viscosity of this composition at 30°C is similar to the conventional 50:50 glycol

and water composition at 100°C. In our setup, the inlet flange to MCP is always following the ECP out-

let and suitable pressure sensors are situated in this region. The radiator, oil cooler and additional

cooling system elements are modelled as pressure drop components in GT-Suite.

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CHAPTER 3. IMPLEMENTATION 24

3.2 Coolant Pumps and Flow Requirements

3.2.1 Low Powered Mechanical Coolant Pump

The coolant flow characteristic thorough the MCP is linear through the engine speed range 600-2400 rpm with 0,7 bar system pressure. Without system pressure, cavitation can be detected when the engine speed exceeds 2000 rpm. Coolant flow at normal driving speed (1100 rpm) is about 200 L/min which will demand a pump power about 0.27 kW. Coolant pump efficiency at rated speed (1800 rpm) is about 54 %. The pump maps are also further tabulated in figures below.

(a) MCP- Inlet and Outlet (b) MCP mounted to Engine Block

Figure 3.3: Mechanical Coolant Pump- Low Powered

Figure 3.4: Pump Map of MCP at System Pressure - 0.7 bar

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CHAPTER 3. IMPLEMENTATION 25

3.2.2 Cooling System Requirements

The fundamental cooling system requirements across engine speeds 600-1800 rpm have been tabu- lated below. Recommended coolant pumps operating in the system should fulfill the benchmark limit by producing maximum volume flow of 300 L/min. The volume flow rate at normal driving speed is approximately 200 L/min at 1000-1200 rpm of engine speed. This corresponds to 0.36 kW of power consumed by the MCP. In figure 3.5, the volume flows produced by the low powered MCP is shown.

At engine speed of 1500 rpm, volume flow of 300 L/min is produced.

Max Coolant Flow: 300 L/min Engine Speed

(Rpm)

Coolant Flow (L/min)

Delta P (bar)

Power Consumed (kW)

600 100 0,1 0,05

800 130 0,2 0,10

1000 170 0,33 0,21

1200 208 0,5 0,36

1400 243 0,68 0,56

1600 280 0,88 0,82

1800 318 1,1 1,18

Table 3.1: Flow Requirements: Tabular Data

Figure 3.5: Cooling System Requirements

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CHAPTER 3. IMPLEMENTATION 26

3.2.3 Electrical Coolant Pump

The two 24-Volt ECP prototypes are purchased from the supplier- Concentric AB. The pump has a BLDC motor, no mechanical sealing. The coolant pumps fulfilled a torque requirement of 2.4 Nm at 3400 rpm, producing optimal flows of 300 [L/min]. The image of the pump prototypes is presented below. The inlet and outlet diameters are 65mm and 60 mm respectively. The specifications are also further tabulated in table 3.2. The speed of the ECP can be controlled and monitored by CAN signals.

(a) Pump Inlet and Outlet (b) Pump- Tab housing with Electrical Interface

Figure 3.6: Electrical Coolant Pump prototype

Electrical Interface Pump Performance Characteristics

Voltage Rating 24 V Flow, Maximum Speed 300 L/min, 3400 rpm CAN Control SAE J1939 Pressure Increase 0.76 bar

Environmental Protection IP6K9K Fluid Water/Glycol

Table 3.2: Electrical Pump Specification

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CHAPTER 3. IMPLEMENTATION 27

3.2.4 Control Strategy

The pump utilizes SAE J1939 protocols in order to establish communication. CANalyzer software is used in creating a CAN database of the necessary signals namely, pump switch on and off, torque, temperature, electric motor speed monitoring and speed control.

Figure 3.7: ECP Control Methodology

The ECP is powered by a bench power supply device from Mean Well. The device produces a maxi-

mum output voltage of 230 Volts and 2.4 kW of power. Since the device has a single output point, a

secondary power supply device of a similar characteristic is used in order to power the second ECP

in later layouts. The CAN High, CAN Low, shield and wake-up ports from the ECP are interfaced with

Vector V1630A device. The device is configured to be operated in CANalyzer software. The laptop is

used to send signals and control the status of the pump, concurrently also monitor the pump param-

eters during its wake condition. It is crucial to use the CAN trace data in order to analyze the torque,

speed and temperature of the electric motor at different input speeds and requested conditions. The

primary computer in the rig, installed with STP software is configured to record measurements and

to drive the MCP through the electric motor from a speed range of 500 rpm to 2400 rpm as discussed.

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CHAPTER 3. IMPLEMENTATION 28

3.3 Performance testing of layouts

A total of five aggregate layouts are tested in the exiting system rig. A brief specification of each layout is illustrated in figure 3.8 below. Each successive layout was improvised in comparison to the existing built configuration.

Figure 3.8: Layouts tested in the rig

Inorder to successfully test the layouts, following changes are to be implemented across all the layouts:

• The static line inlet to the coolant pump has to be relocated to the radiator channel, contrary to the existing position at the mechanical pump’s inlet flange. Hence, reverse pumping of coolant to the expansion vessel is prevented. This has been further illustrated in 3.9

• The engine water jacket is optimally designed for a single directional flow from the oil cooler

block. However, Inlet 1, Inlet 2 has to be modified to ensure that the pressurized coolant from

the ECP can converge with the flow from the MCP and continue to be introduced into the engine

block, further illustrated in 3.10

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CHAPTER 3. IMPLEMENTATION 29

(a) Original Position of Static line inlet to Mechanical Pump

(b) New Position of Static line- preceding the ECP Inlet

Figure 3.9: Illustration of Static Line Modification

(a) Engine Block Interfaces

(b) Illustration of coolant flow from MCP outlet to engine

Figure 3.10: Components in Engine Block

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CHAPTER 3. IMPLEMENTATION 30

3.4 Coolant System Layouts

3.4.1 Layout 1

In the following layout, the ECP is connected in series with the MCP by modifying the pipe network in radiator channel. The impeller from the MCP is detached. Major volume of coolant from the outlet of the radiator is pumped through the ECP and into the engine inlet block. The ECP is operated at a speed range of 1000 to 3200 rpm, via CAN signals. The pressure drop is measured across the MCP section using suitable pressure sensors. This pressure drop data is pivotal for the GT-Suite simulation in future layouts. Thermostat is always open to prevent reverse flows across the bypass channel.

Figure 3.11: Layout-1 Schematic and Assembly in Test Rig

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CHAPTER 3. IMPLEMENTATION 31

3.4.2 Layout 2

A comparable configuration as the above layout is retained. The current MCP (without impeller) is replaced with its low powered counterpart, specifications as mentioned in section 3.2.1. The speed of MCP is successively increased from 500 to 1500 rpm across the three respective tests.

Figure 3.12: Layout-2 Coolant System Schematic

3.4.3 Layout 3

The ECP and MCP are coupled in a parallel configuration. The flow is bifurcated at radiator outlet.

The coolant flow from the outlet of ECP is introduced into the engine block through Inlet-1 (Figure 3.10). The diameter of Inlet-1 is Φ 16 mm. The assembly in the test rig is shown in the image below.

Figure 3.13: Layout-3 Assembly in Test Rig

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CHAPTER 3. IMPLEMENTATION 32

A mechanical ball valve is supplemented at the ECP outlet, to study the feasibility of a future smart valve to be operational in the ECP circuit. This controllable valve can be opened when the pump is to be engaged by the engine control system. In the future, a smart operational valve can be embedded inside the ECP itself. The valve can be designed to automatically open if the pump’s motor is engaged.

Hence, reducing the complexity of the control system. In the test rig, a check valve is assembled at the junction of the ECP outlet preceding Inlet-1 in the oil cooler. The diameter of the check valve is Φ 20 mm. Cracking pressure drop is 1 bar. The ability of the one-way check valve to help prevent reverse flow is investigated. The test setup in this layout is shown in table 3.3.

Figure 3.14: Layout-3 Coolant System Schematic

MCP Speed ECP Speed Mechanical Valve 1 500-1500 rpm ECP Status: Off Valve Closed 2 500 rpm 1000-3200 rpm Valve Open 3 1000 rpm 1000-3200 rpm Valve Open 4 1500 rpm 1000-3200 rpm Valve Open

Table 3.3: Layout 3 - Test Setup

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CHAPTER 3. IMPLEMENTATION 33

3.4.4 Layout 4

The parallel configuration of ECP and MCP is retained. The ball valve is disassembled. The coolant flow from the outlet of ECP is introduced into the engine block through Inlet-2 (Figure 3.10). The diameter of Inlet-2 is Φ 22 mm. The engine electrical heater is originally located in this position.

However, this interface is modified in order to accommodate the flow from ECP. The outer diameter of the electric heater interface is Φ 29 mm. It is evaluated if the increase in diameter of Inlet-2 can help in enhancing volume flow performance.

Figure 3.15: Layout-4 Coolant System Schematic

Figure 3.16: Layout-4 Assembly in Test Rig

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CHAPTER 3. IMPLEMENTATION 34

MCP Speed ECP Speed 1 500-1500 rpm ECP Status: Off 2 500 rpm 1000-3200 rpm 3 1000 rpm 1000-3200 rpm 4 1500 rpm 1000-3200 rpm

Table 3.4: Layout 4 - Test Setup

3.4.5 Layout 5

In the following layout, two ECPs and the low power MCP are coupled to the cooling circuit. The right angled T-split is assembled down-stream, near radiator outlet. This enables parallel divergence of coolant in ECP-1–MCP and ECP-2 flow branches, converging at the location of the engine inlet block.

The sensors at ECP-1 channel facilitates the measurement of pressure drop trends. The assembly of the layout in the test rig is shown below. The setup of runs is as tabulated in 3.5. An attempt to study milling and reverse flow conditions in the ECP is also carried out.

Figure 3.17: Layout-5 Coolant System Schematic

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CHAPTER 3. IMPLEMENTATION 35

Figure 3.18: Layout-5 Assembly in Test Rig MCP Speed ECP-1 Speed ECP-2 Speed 1 1000, 1500 rpm ECP-1 Status: Off ECP-2 Status: Off 2 MCP Status: Off 1000-3200 rpm 1000-3200 rpm 3.1 1000 rpm 1000-3200 rpm ECP-2 Status: Off 3.2 1000 rpm ECP-1 Status: Off 1000-3200 rpm 3.3 1000 rpm 1000-3200 rpm 1000-3200 rpm 4.1 1500 rpm 1000-3200 rpm ECP-2 Status: Off 4.2 1500 rpm ECP-1 Status: Off 1000-3200 rpm 4.3 1500 rpm 1000-3200 rpm 1000-3200 rpm

Table 3.5: Layout 5 - Test Setup

Milling And Reverse Leakage Measurements

Milling and reverse leakage data are an essential input to Electric Pumps template in GT-Suite, playing a major role to help obtain robust simulation results. By accounting this occurrence in ECPs, the overall flow rate results in the simulation can be better regulated. The phenomenon of milling occurs in an ECP when a pressure drop is experienced contrary to a conventional pressure rise trend. The milling speed, volume flow rate and pressure drop data are essential to be measured.

Consider a test setup in illustration 3.19. The second coolant pump is to be in off condition. The first

coolant pump is to be engaged across a range of speeds from 500 to 3200 rpm. A pressure drop will

now be observed across the ECP-2, contrary to a pressure rise. The coolant flow through ECP-2 will

also cause the impeller to freely spin. This free spin of the impeller, also termed as milling speed is to

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CHAPTER 3. IMPLEMENTATION 36

be recorded by the speed sensor embedded in the pump. Extending the similar test case in layout 5, the MCP and ECP-1 are in an off condition. The sensors are attached to ECP-1 (Figure 3.17). ECP-2 is engaged at different speeds. However, the drawback of an embedded speed sensor to measure milling speed in ECP-1 led to an incomplete array of test data.

To measure reverse leakage data in layout 5, ECP-1 and ECP-2 are kept in off condition and MCP is engaged at different speeds to measure the reverse flow of coolant across ECP-1. The pressure rise across ECP-1 is nominal.

Figure 3.19: Preferred Measurement Setup- Milling

GT-Suite Simulation

Figure 3.20: Layout-5 Simulation Model

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CHAPTER 3. IMPLEMENTATION 37

The conventional 1-D cooling system model for the 6 cylinder HDD Engine is verified with test rig results. This validated model is used for the simulation of this layout. The position of electric pumps in the model is illustrated in 3.20. The static line inlet to the coolant pump is modified, ad- ditional pressure drop data from test rig is implemented and ECPs are modelled using the electric pump templates. The Pump characteristic curve at maximum rpm, 3200 rpm is linearly extrapolated using GT-Suite due to insufficient data points from the supplier’s test runs. The reverse leakage data from the test rig is implemented. Milling conditions are ignored. The convergence of volume flow at water-jacket inlet block is achieved by using volume split component features.

To obtain simulation results from tests 3.1 and 4.1, ECP-2 is deleted from the branch. This also en- sured implicit flow convergence criterion during the simulation. Similarly, ECP-1 is deleted from its corresponding branch while simulating conditions in tests 3.2 and 4.2. However, the pressure drop across this channel is included in the model. MCP is completely removed in simulation of test setup 2. The corresponding pressure drop data across the MCP channel is instead included.

3.4.6 Supplementary System Layout

Some cooling system layout configurations are not implicit to be realized for performance testing in the cooling system rig. However, the layout concepts can be simulated in GT-Suite. It is not possible to replace the MCP with the current ECP prototype, owing to the mounting interfaces in engine block.

Hence in the 1D model, the MCP specifications and pump map are replaced with the data from the ECP supplier. The layout has been illustrated in figure 3.21.

Figure 3.21: Single ECP configuration

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Chapter 4 Results and Discussions

The respective results obtained from the test rig is presented in this chapter. A comparison of simu- lation results with physical test data is carried out in layouts 5. Further, the power consumed by the ECP is contrasted with that of a traditional MCP.

4.1 Performance Results

4.1.1 Layout 1

The overall coolant flow through the radiator linearly increases with the ECP’s speed. The flows across the radiator, HVAC, static line are measured in the test rig. As shown in the result in figure 4.1, an optimal flow is achieved when the ECP is operated at a speed of 3000 rpm, producing a total volume flow of 217 L/min. An escalated flow rate is not obtained with this pump operating at its highest speed of 3200 rpm. The maximum volume flow achieved is 238 L/min.

The single ECP in operation does not guarantee the benchmark coolant flow requirement of pro- ducing 300 L/min. However from the flow requirements table 3.1, the demands at engine speed of 1400 rpm, requiring volume flow of around 243 L/min is satisfied. The cooling requirements at higher range of engine speeds (greater than 1400 rpm) are not fulfilled.

The pressure drop across the MCP passage also plays a major role in reducing the overall flown into the engine. However, an improvement in performance can be realized if the engine block can be redesigned in order to mount the ECP in proximity to the MCP. Hence, pressurized coolant can be delivered effectively with minimal losses.

39

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CHAPTER 4. RESULTS AND DISCUSSIONS 40

Figure 4.1: Result: Cooling System Layout-1

4.1.2 Layout 2

The ECP operating in series with MCP enables in enhancing the overall volume flow through the lay- out. The results from tests 1, 2 are presented below. It is evident that the volume of flow enhancement linearly increases with the MCP operating at 500 rpm, 1000 rpm.

Figure 4.2: Result: Cooling System Layout-2 (Test 1-2)

From the results shown in figure 4.3, the volume flow enhancement obtained at MCP speed of 1500 rpm is slightly reduced. In the table shown below in 4.1, the benchmark coolant flow at engine speeds 500-1500 rpm is compared with the enhanced volume flow. Maximum flow enhancement is obtained at test 2, MCP engaged at 1000 rpm. The decrease in volume flow can be attributed to numerous factors, owing to the differences in the operation of MCP and ECP.

In circuits involving pumps operating in series, the overall pressure rise in the system is elevated. The

irregular variations in pressure and velocity of the coolant across the pumps may result in turbulent

mixing of flows. The pump work required to overcome these losses will also be high.

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CHAPTER 4. RESULTS AND DISCUSSIONS 41

Figure 4.3: Result: Cooling System Layout-2 (Test-3)

A thorough investigation of the MCP’s and ECP’s pump operational map is hence required to be carried out if they are to function in series configuration. The engagement strategy of the ECP is also to be analyzed in order to obtain maximum volume flow enhancement. The overall volume flow is maximal in Test Setup-3. The requirement to obtain volume flows higher than 300 L/min is fulfilled.

Test-Setup Engine Speed Benchmark Flow (L/min)

Test Rig

Total Flow (L/min)

Flow Enhancement (L/min)

1 500 100 243 43

2 1000 170 274 107

3 1500 255 326 71

Table 4.1: Layout2: Flow Enhancement from ECP

4.1.3 Layout 3

The results in this layout are obtained by engaging the ECP and MCP in a parallel configuration. In

test 1, the engagement of only the mechanical pump from 500 rpm to 1500 rpm results in a total flow

of 240 L/min. This is below the required benchmark maximum flow specification. The benchmark

flow criterion is also not fulfilled at the alternative two lower speeds of 500, 1000 rpm. The reduction

in the flow across MCP can be attributed to the removal of auxiliary cooling sub systems, indicated in

the project delimitations. The coolant circulation occurs only through the cab-heat system, static line

and radiator. It is hence mandatory to consider volume flows across test 1 as the new guideline.

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CHAPTER 4. RESULTS AND DISCUSSIONS 42

Figure 4.4: Result: Cooling System Layout-3 (Test 1-2)

The results obtained from test setup 3 and 4 are shown below.

Figure 4.5: Result: Cooling System Layout-3 (Test 3-4)

Hence, the flow enhancement achieved across tests 2, 3 and 4 have been compared and contrasted with respect to the modified guideline volume flows in table 4.2 shown below. Pumps can be arranged in parallel configuration to suitably enhance the volume flow through the cooling layout channels. If the ECP is not engaged, reverse flows are prevented by the one-way check valve at Inlet-1. The low volume flow enhancement can be attributed to the small diameter of Inlet-1 (Φ12 mm) in the oil cooler. This small diameter can also cause turbulence convergence of flows, thereby inducing power losses in the pump.

In the conventional system, the coolant flow in the oil cooler bifurcates through the water jacket and Inlet-1. Through Inlet-1, coolant is delivered to the auxiliary subsystems located near the engine. At higher speeds of MCP, volume flow through Inlet-1 will also be high.

Although the ECP may operate at maximum speed, the turbulent mixing of coolant flows in the oil

Use of Electrical Coolant Pumps in Scania’s Cooling System