Development ofHigh-efficiency Turbocharger
MET-MA Series for Large-BoreDiesel Engine
KEIICHI SHIRAISHI*1

YUKIHIRO IWASA*1

TAKANORI TESHIMA*1

YUICHIRO HIRANO*2

HIROSHI NISHINO*2

bocharger has undergone the model changes as shownin Fig. 1 to improve performance mainly by improving
the compressor impeller and turbine blade.
Fig. 2 shows the changes of aerodynamic designs.

1. Introduction

Compressor pressure ratio

A turbocharger is a machine that recovers exhaust gas
energy using a turbine and drives an axial compressor tofeed air required for combustion. To respond to high output of recent large-bore diesel engines, the turbocharger
must have a high pressure ratio of compressor and enhanced turbocharger efficiency.
Further, the turbo compound system that partially recovers exhaust gas energy as driving force is recently
attracting attention, with the need for high-efficiency turbocharger increasing.
This paper presents a report on the development of thelatest high-efficiency MET-MA turbocharger.

2. MET turbocharger overview
2.1 History of MET turbocharger
The MET turbocharger was first developed in 1965
for the Mitsubishi UE 2-cycle low speed diesel engine.
To respond to the need for higher engine output, the tur-

MET-S, SA
2 pieces wheel,
non-backward impeller(1973)

MET-S, SA
Impeller with damping wire
(1973)

4
MET-SC

MET-SD

MET-MASEIIMET-SE

MET-SB,-SBII
3

MET-S,-SA
MET .. O
Original MET

2

Water-cooled turbocharger
1960

1970

1980

1990

2000

YearFig. 1 History of Mitsubishi MET turbocharger

MET-SB
2 pieces, backward impeller(1982)

MET-SB, SC, SD
Free standing blade(1982)

MET-SC
one body impeller(1984)

MET-SD, SE, SEII
one body impeller
with split blade(1990)

MET-SE, SEII
Free standing blade,wide chord(1995)

Fig. 2 Changes in Mitsubishi MET turbocharger compressor impellers and turbine blades

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 1 (Jan. 2006)*1 Nagasaki Shipyard & Machinery Works*2 Nagasaki Research & Development Center, Technical Headquarters12.2 MET turbocharger features
The MET turbocharger features a bearing on the inner side of the impeller and turbine blade and a rotor
supported by a pedestal with less thermal deformation
as shown in the sectional drawing of turbocharger inFigFig.. 3 . Because of this, rotor support is not affected bythermal expansion of the turbine casing.
Furthermore, the bearing pedestal has an integrated
head tank to enable supply lubricating oil even after theengine comes to an emergency shut down. In addition,
the double wall structure of the gas inlet casing enables
removal of the inner casing without removing the pipe
connected to the engine, making it easy to check the turbine and nozzle.

Since the higher the turbocharger efficiency in theturbo compound system, the higher the energy yield, theturbocharger must have efficiency improved. To improveturbocharger performances, MET-MA was developed as
the new MET turbocharger series.
In developing MET-MA, the following items weretaken into consideration:(1) To respond to needs for high turbocharger performance, the turbine blade shape and exhaust gas
passage were reviewed to improve performance.
(2) A new series MET60 was added between MET53 andMET66 series as shown in Fig. 44, and MET60MA witha frame smaller than MET66 was applied to an engine
with output of approximately 10 000 kW, contributing
to the reduction of turbocharger size.
(3) The external dimensions were approximated with theconventional turbochargers to enable interchangeability.
Detailed below is turbine blade and gas casing design
closely linked to improved performance.

3. Purpose of MET-MA turbocharger development
For high engine output, high-efficiency supply of highdensity, i.e. high-pressure combustion air is needed, andthis is why the turbocharger requires high compressor
pressure ratio and high turbocharger efficiency. Further,for effective use of energy, the turbo compound system isdrawing attention, where the exhaust gas supplied tothe turbocharger is partially extracted and recovered as
driving force.

4. MET-MA Design
4.1 Turbine blade design
A new turbine blade is adopted to improve MET-MAturbocharger efficiency. Fig. 5 shows the external viewsof the turbine blades of MET-SE II and MET-MA turbochargers. Compared to the MET-SE II turbocharger
turbine blade where the leading and trailing edges of blade
are designed linearly, the MET-MA turbocharger turbine
blade adopts a three-dimensional curved form to optimize
the flow pattern in the direction of blade height.

Fig. 3 Section of MET83SE II turbocharger
MET90MA
MET90SE
MET83MA
MET83SE
83SEII
MET71MA
MET71SE
MET66MA
MET66SE

MET-MA

MET-SEII

MET-MA

MET-SEII

71SEII

66SEII

MET60MA
MET53MA
MET53SE
53SEII
MET42MA
42SE 42SEII
33MA
33SE
033SEII
5 000

10 000

15 000

20 00025 000Applicable engine output per unit turbocharger (kW)Fig. 4 Applicable engine output for MET-MA turbocharger

Fig. 5 External views of MET-MAand MET-SE II turbine blades

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 1 (Jan. 2006)

2Turbine performance difference (%)

Flowseparation(a) Conventional
casing(b) MET-MA
casing

43

Turbine Pressure Ration=2.5: MET-MA: MET-SEII

210-1-2-3
0.5

0.55

0.60.65

Total efficiency ofturbocharger (%)

7065: MET83MA: MET83SEII
2.0

2.5

3.0

3.5

4.0

Fig. 8 Section of MET83MA turbocharger

5.2 Turbocharger performance test
A MET83MA prototype was manufactured for turbocharger. performance tests. Fig. 8 shows the sectionalview of the MET83MA turbocharger.
Fig. 9 shows MET83MA turbocharger efficiency compared to the conventional MET83SE II, with MET83MAturbocharger efficiency indicating 70% or over at pressure ratio 3.8 (equivalent to scavenging air pressure 0.38MPa), approximately 2% higher than the conventional
type. The improved efficiency is considered to lead to ahigh-efficiency turbo compound system.

7555
1.5

0.75

Fig. 7 Efficiency of MET-MA turbine

Fig. 6 Analytical result of flow velocity
distribution in gas outlet casing

60

0.7

Theoretical velocity ratio

4.5

Compressor pressure ratio
Fig. 9 Comparison of overall efficiency of MET83MA turbocharger
and MET83SE II turbocharger

6. Conclusion
Based on the achievements of conventional turbochargers, the turbocharger turbine was improved toensure a drastic improvement in efficiency. It is expectedthat the newly developed high-efficiency MET-MA turbocharger will be applied to the new high-output engine
and exhaust heat recovery system, contributing largely
to the further improvement in the diesel plant efficiency.

4.2 Aerodynamic design of gas casing
Progress in calculation technology in recent years has
enabled analysis of large-scale flow fields comparativelyin a short time, making it an effective tool for design.
This tool was effectively used to optimize gas outlet casing and exhaust diffuser of the turbine.
Fig. 6 shows the analytical result of inner flow as compared to the conventional MET-SE II gas outlet casing.
In conventional design, flow was partial separated(Fig. 6-a), corrected by improving the gas outlet casing
shape (Fig. 6-b).

5. Performance test results
5.1 Independent turbine test
Fig. 7 shows the result of performance tests of an independent turbine, with the turbine efficiency inMET-MA confirmed to be improved approximately by 2%
at turbine pressure ratio 2.5 compared to the conventional MET-SE II.

Keiichi Shiraishi

Yukihiro Iwasa

Yuichiro Hirano

Hiroshi Nishino

Takanori Teshima

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 1 (Jan. 2006)

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