Mitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
1Turbocharger Joint Research Organization with Imperial
College London

YASUAKI JINNAI*1

SEIICHI IBARAKI*2

TORU HOSHI*3

MOTOKI EBISU*4

TAKAO YOKOYAMA*5NOBUHITO OKA*6

In Europe, which is a major market for turbochargers, Imperial College London (ICL) andthe Mitsubishi Heavy Industries (MHI) Group have a history of nearly 20 years of joint research,people-to-people exchanges and other activities. Amid calls for decarbonization and theelectrification of passenger cars, a joint research organization (UTC: University TechnicalCentre) was established with ICL in 2019 to intensively carry out innovative and targeted
research. In this report, we describe the results of our research with the university that contributed
to the improvement of MHI turbocharger technology, the activities of the newly establishedorganization and our involvement in the turbocharger business of Mitsubishi Heavy Industries
Engine & Turbocharger, Ltd. (MHIET).

|1. Introduction
The MHI Group has been mass-producing turbochargers for passenger cars since the 1970sand initially developed the technology in Japan. Since the main turbocharger market is in Europe,
our turbocharger business has gradually shifted its focus to Europe, where the business has grownby developing and manufacturing turbochargers for local automobile manufacturers. We
recognized the necessity of developing turbocharger technology in accordance with therequirements of the European market at an early stage and the MHI Research & Innovation Centerhas been conducting joint research with European universities and research institutes. Mitsubishi
Turbocharger and Engine Europe B.V. (MTEE), which produces turbochargers at its Europeanbase, acquired engineering functions in the late 1990s and research and development functions forturbochargers in the 2010s.
There is an ever increasing need decarbonization in countries around the world, Europe, ishome to many environmentally-advanced nations and where industry-academia cooperation
between automotive manufacturers and universities is active. MHIET has developed a system todisseminate Mitsubishi turbocharger technology by establishing a strong development partnershipthere utilizing MTEE, which has grown its engineering functions, as well as cooperative networks
developed mainly by the MHI Research & Innovation Center.

|2. Cooperation in Global Development of MitsubishiTurbochargers
The MHI Group is developing turbochargers not only at the MHI Research & Innovation
Center and overseas bases of the MHI Group, but also in cooperation with universities and research
institutes in various regions. The development system is shown in Figure 1. Our bases in Europe*1

Deputy Director, Engineering Department, Turbocharger Division, Mitsubishi Heavy Industries Engine & Turbocharger, Ltd.

*2

General Manager, Turbomachinery Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*3

Turbomachinery Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*4

Chief Staff Manager, Engineering Department, Turbocharger Division, Mitsubishi Heavy Industries Engine & Turbocharger,*5

Chief Staff Researcher, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*6

Engineering Department, Turbocharger Division, Mitsubishi Heavy Industries Engine & Turbocharger, Ltd.

Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
2and China, which are major markets for turbochargers, have engineering and development
functions, and also conduct exchanges with local universities and research institutes. Each base,university and institute are developing products that meet the needs of each market, while taking
advantage of their characteristics and fields of expertise, aiming to improve their overallcapabilities by leveraging each other. Technological innovation in turbocharging systems forpassenger car powertrains requires research and development in a wide range of fields including:
fluid mechanics, thermodynamics, tribology, electrical control and development needs. It becomesdifficult to advance our development in the light of the speed of the market change, as such,collaboration with external research institutes is becoming increasingly important.

QMUL：Queen Mary Univ. of LondonQMUL
VKI：von Karman Institute for Fluid DynamicsVKI
TU Delft：TU Delft Univ. of Technology
UTM：Universiti Teknologi Malaysia
LoCARtic：Low Carbon Transport
MHIET: Mitsubishi Heavy Industries Engine & Turbocharger, Ltd.
MHI R&D: Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.
MTA: Mitsubishi Turbocharger Asia Co., Ltd.
SMTC: Shanghai MHI Turbocharger Co., Ltd.
MTEA: Mitsubishi Turbocharger and Engine America, Inc.
MTEE: Mitsubishi Turbocharger and Engine Europe B.V.

Figure 1 Global bases for Mitsubishi turbochargers and cooperation in global
development with universities and research institutes|3. History of collaboration with Imperial College London andachievements to date
ICL was established in 1907 through the merger of the Royal College of Science, the Royal
School of Mines and the City & Guilds College and is currently ranked among the top three
universities in the EU and in the top ten universities worldwide (The Times Higher Education
World University Rankings 2020). ICL is a science and engineering university which consists ofengineering, medicine, science, and business faculties. In particular, social contribution throughinnovative research and development is being promoted, as is practical research focusing on
industrial applications. Professor Ricardo Martinez-Botas of the Thermofluids Division of theFaculty of Engineering at ICL focused on the importance of unsteady performance of radialturbines used in turbochargers for the first time anywhere in the world. He proposed ideas for theeffectiveness and performance enhancement of mixed flow turbines under pulsating flow byelucidating unsteady phenomena and developing a one-dimensional performance evaluation
method using a test device developed by ICL that can measure performance and flow phenomena
under pulsating flow as shown in Figure 2. In 2003, the MHI Research & Innovation Center held
an exchange meeting with the professor and officially started joint research on the unsteady
performance of radial turbines in 2005. Since then, joint research on performance innovation ofturbocharger turbines and compressors has continued. As a representative result, in order toimprove turbine efficiency under pulsation of the engine, a new turbine volute and a mixed flow

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
3turbine were developed by optimizing the rate of change of a cross sectional area in thecircumferential direction and high performance was achieved in a turbine unit test and engine
test(1). The technology was jointly developed as patent in 2013 and mass-produced in 2016,
contributing to the reduction of CO2 emissions from automobiles. In the case of the compressor, thetest equipment shown in Figure 3 was constructed to simulate pressure pulsation accompanying air
supply to the actual engine. With the equipment, performance and surge characteristics underpulsation, which had been difficult to understand in the past, were measured and internal flow wasclarified by unsteady flow analysis(2). Figure 4 shows the pressure-flow characteristics of thecompressor with and without pulsation. It was found that under pulsation, the surge flow rate
decreased by about 8% from the steady flow due to the inertial effect of the flow accompanying theunsteady increase/decrease of the flow rate and surging was suppressed. This result is also being
applied to the design of high efficiency compressors of mass-produced products that are actuallyaffected by pressure pulsation. In this way, MHI group has established an effective transfer cycle inwhich the innovative technologies created through joint research with ICL are rapidly applied toactual products. MHI group has also realized social contributions, which is our joint mission withICL, and also created a strong relationship of trust. In 2019, MHIET and ICL established a joint
research organization (UTC) in order to further strengthen cooperation and enhance the researchand development capability. Figure 5 is a photo of officials from ICL and MHI group at the UTC
founding ceremony held in Tokyo.

Figure 2Turbine pulsating flow test equipment at ICL,Figure 3

Compressor pulsating flow test equipmentMitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
4Figure 4 Relationship between presence of pressure pulsation and surge flow rate

Figure 5UTC funding ceremony, group photo of ICL and MHI Group officials|4. Joint Research Organization and System
In addition to the MHI Research & Innovation Center, which has built a deep relationshipthrough various joint research efforts with ICL on turbochargers for a long time, MTEE, which is a
European development base and MHIET, which has a turbocharger business division, haveestablished the MHIET-Imperial Future Boosting Innovation Centre, a joint research organization(University Technical Centre) with the university, under the leadership of the MHI Group. Incollaboration with Universiti Teknologi Malaysia (UTM), ICL has also established Low Carbon
Transport in Cooperation with Imperial College London (LoCARtic), a research organization
which has engine test bench and the system for various verification tests, at UTM to develop
turbocharger technology and other low-carbon technologies for transportation equipment. As
shown in Figure 6, a virtual organization was established to bind these elements. Dr Maria
Esperanza Barrera-Medrano (ICL) is the manager of the centre and leading the organization. In thisorganization, research is conducted on multiple themes at the same time and regular steering
meetings are held to confirm the progress of research and review the development strategy.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
5Figure 6

Joint Research Organization and System|5. Contents of Activities
In the joint research with ICL, the flow phenomenon was clarified by unsteady performancemeasurement under exhaust pulsation and large-scale flow analysis as described above and this led
to the development of new high-performance turbines and compressors. At present, in order torespond to the diversification of technical requirements, the scope of the joint research has been
expanded from performance enhancement of turbines and compressors to supercharging systems,engine systems and vehicle systems. Examples of research and development at UTC are introduced
below.
Since a turbocharger drives a compressor by turning a turbine using the exhaust energy of anengine, air cannot be instantaneously supplied to the intake side and turbo lag occurs. To suppress
this, it is effective to improve the transient response performance of the turbocharger and it isparticularly important to improve the low flow rate performance of the compressor. To solve thisproblem, a new compressor cover has been developed by making the cross section distribution of
the scroll in the circumferential direction nonlinear. As shown in Figure 7, the pressure ratio in thelow flow rate region has been improved compared with that of the conventional compressor cover.
In order to evaluate this effect on the engine, the ECU (Engine Control Unit) setting including theignition timing was optimized using the engine verification test facility at LoCARtic shown in
Figure 8, and the engine response was evaluated. As a result, as shown in Figure 9, the newcompressor improved the transient response performance by 20% to 60% in all region. This wasthought to be caused by an increase in the air density required when the throttle opening was large
and the operating point of the compressor shifted to the high pressure ratio side, that is, to the low
flow rate side. It was confirmed that the efficiency improvement effect of the new compressor
contributed to the improvement of the engine response(3).
In engines for automobiles, performance enhancement in starting and transition is important
to improve the environmental performance of the product. For example, in the case of aturbocharger, the thermal management technology downstream of the turbine contributes to thepurification of exhaust gas from the engine, from the perspective of shortening the catalyst
activation time when the engine is cold-started(4). As shown in Figure 10, there are multiple heatsources inside the turbocharger, such as turbines, compressors, bearings, lubricating oil and coolingwater. Therefore, it is necessary to estimate the transient heat transfer state of each part andevaluate the effect on performance by considering the system as a whole. For this, we aredeveloping a transient performance simulation method considering heat transfer and pulsation withICL.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
6Figure 7Compressor performance test result

Figure 8Engine test facility at LoCARtic

Figure 9 Comparison of engine response between conventional
compressor and new concept compressor

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
7Figure 10 Unsteady turbine CHT（Conjugate Heat Transfer）analysis result atcold start

The realization of the optimum matching of the engine and turbocharger in the development
stage of the engine is important for achieving good transient performance and low fuelconsumption, which leads to the shortening of the development period. In general, the engine
model is treated as quasi-steady instead of considering the transient behavior of the turbocharger.
Although this conventional approach can adequately predict steady-state engine performance, there
are challenges in accurately predicting transient engine performance. Regarding unsteady
low-dimensional models for evaluating the transient behavior of turbochargers, several researchefforts have been conducted in the past(5)(6). However, there are still few examples in which thesemodels have been integrated into a one-dimensional engine model for detailed analysis andsufficient knowledge has not been obtained. In order to solve this issue, we are working on thedevelopment of a one-dimensional engine simulation method, by which engine performance underexhaust pulsation can be instantaneously predicted and the optimum turbocharger will be proposed
according to the customer's engine, as shown in Figure 11.

Figure 11
Development flow of engine performance evaluation method
considering turbine unsteady performance

In recent years, there has been a high need for the adoption of a double entry turbine fordirect injection supercharged engines. In particular, there is an advantage in that the pulsationenergy generated from the engine exhaust gas is used for a four-cylinder engine or a six-cylinder
engine to reduce the exhaust interference between cylinders in the exhaust stroke and to reduce
pump loss.
As shown in Figure 12, there are two types of double entry turbines, a twin scroll turbine inwhich the scroll is arranged in the axial direction and a double scroll turbine in which the scroll isarranged in the circumferential direction. Until recently, the comparison of performanceMitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
8

characteristics of these two types of turbines has been widely discussed. The scroll connection
valve (SCV) shown in Figure 13 is used as a flow rate control mechanism of the double scroll
turbine and performance characteristics similar to a single scroll can be obtained by opening thevalve in a high speed region while realizing the performance characteristics of a divided flow pathin the low speed region of an engine. Thus, the matching of the engine and the turbocharger can beimproved by making the performance at a small flow rate compatible without sacrificing the engine
performance at a large flow rate. However, because it is used in a high-temperature exhaust gas
pulsation environment, it is difficult to achieve both performance and reliability and development isbeing conducted to solve this issue.

Figure 12

Comparison of double entry turbines structures

Figure 13 Cross-Sectional view of double scroll turbine SCV andfunctional description

The MHI Group has been developing electric compressors to improve the fuel efficiency ofvehicles through high supercharging pressure and high responsiveness. We have also developed anelectric supercharging system in which a turbocharger on the high or low pressure side is replacedwith an electric compressor for a normal two-stage turbocharger(7). In the electric supercharging
system, energy management of the engine and the battery is important. Therefore, in view of thedevelopment trend of the powertrains of passenger cars and the electrification of vehicles such as
hybrid systems, we are working on the development of a modeling method of the whole vehicle
system in consideration of in-vehicle power supply performance, higher voltage and energy
regeneration efficiency. Figure 14 shows an analysis and control model of the entire hybridvehicle. In the future, we would like to propose the optimum energy management of the vehicle
system by combining it with the fuel efficiency improvement technique of the engine such as themirror cycle and lean combustion, which are actively being developed.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
9Figure 14 Structure of vehicle system model for hybrid vehicle|6. Conclusion
In the past, MHI and ICL started out with a single joint research project and by increasing thenumber of research themes and achieving results, the foundation for a partnership with the MHIGroup was created. The partnership was not limited to research and development, but also
developed into people-to-people exchanges by sending young engineers from MTEE to ICL where
they obtained doctoral degrees in turbocharger research. As mentioned above, the research anddevelopment of UTC, which was launched this time, covers component technologies and overallturbocharger technology and the range is even expanding to powertrains and the whole vehicle
system with an eye to the rapidly-changing development trend of powertrains of passenger cars andthe electrification of vehicles. By having this organization, development with a sense of unity
among each base was made possible and outcomes from this cooperation are being delivered.
Mitsubishi Turbocharger technology from Europe will be introduced to the world by utilizing thisUTC.

References
(1)

(2)
(3)
(4)
(5)
(6)
(7)

T. Yokoyama et al., Technology for Enhancement of Turbine Performance Under Exhaust Pulsation for
High-Performance Automotive Turbocharger, Mitsubishi Heavy Industries Technical Review Vol. 55 No.
2 (2018)
I. Tomita et al., Flow Field of a Turbocharger Centrifugal Compressor under Pulsating Conditions,
Mitsubishi Heavy Industries Technical Review Vol. 56 No. 2 (2019)
M. S. Chiong et al, "On-Engine Performance Evaluation of a New-Concept Turbocharger Compressor
Housing Design", SAE Technical Paper 2020 - 01 -1012 (2020)
T. Kitamura et al, "Study on Analytical Method for Thermal and Flow Field of a Turbocharger with theCatalyst Unit", ASME Turbo Expo, GT 2019 -90451
M. S. Chiong et al, "Assessment of Cycle Averaged Turbocharger Maps Through One Dimensional andMen-Line Coupled Codes", ASME Turbo Expo, GT 2013 -95906
T. Cao et al, "A Low-Order Model for Predicting Turbocharger Turbine Unsteady Performance",
Proceedings of ASME Turbo Expo, 2014
B. An et al., Development of Two-Stage Electric Turbocharging System for Automobiles, Mitsubishi
Heavy Industries Technical Review Vol. 52 No. 1 (2015)