Woodyard D. (ed.) Pounders Marine diesel engines and Gas Turbines

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uEC design details 371

1955

1963

1965

1970

1975

1979

1982

1983

1985

1986

1987

85 75

65 52

45 39

Impulse Water cooled Accumulator

Impulse Water cooled Bosch

Impulse

Non-cooled MET-OO

Bosch

Impulse MET-OOO Bosch

Constant pressure MET-S Bosch

Constant pressure MET-SB Bosch

Constant pressure MET-SC Bosch

Two-stage impulse MET-OOO Bosch

3 exhaust valves

1 FOV

1 exhaust valve

2 FOVs

* Controllable opening pressure system † Controllable injection timing

LSII

85 65

52 45

39 33

(COP)*

Water-cooled seat

(COP)*

Water-cooled seat

(COP)*

(COP)* (CIT)

†

Type

Cylinder

bore

(cm)

Turbocharging

system

Turbocharging

Fuel

system

Valve

arrangement

FigurE 11.8 design history of uE engine, 1955–1987

372 Mitsubishi Low-Speed Engines

l Easily maintained fuel injection valves.

l High-performance piston gland packing (stufﬁng box drainage of

10 litres/day/cylinder, and a low wear rate scraper ring).

Mitsubishi’s R&D priorities mirror those of its two rivals in the low-speed

engine arena, with emphases on further upratings of designs, enhancing reli-

ability and durability, and reducing noxious emissions. Its resources include

the group’s main research centre at Nagasaki. Mitsubishi has investigated all

aspects of exhaust gas de-NOxing technology including the direct injection of

water into the combustion chamber. Its stratiﬁed injection system based on a

fuel valve designed to inject fuel–water–fuel sequentially has achieved NOx

m/s

g/P

140

120

100

1955 1960 1965 1970 1975 1980 1985 1990 1995

Year

4.0

3.0

2.0

160

150

140

130

120

Stroke–bore ratio

Mean effective pressure

Maximum cylinder pressure

Specific fuel oil consumption

8.0

7.0

6.0

kg/cm

Mean piston speed

FigurE 11.9 Changes in uEC engine parameters and performance since its

introduction

reductions of around 50 per cent without signiﬁcantly increasing fuel con-

sumption and is offered as an option for UEC–LSE engines (see Chapter 3 and

more in the Emissions Reduction section in this chapter).

uEC-H TyPE EnginE

Although superseded by the LA, LS and LSII designs, and no longer in pro-

duction, the UEC-H type engine remains in service and warrants more detailed

description. The UEC-H type engine (Figure 11.16) is of cast iron construc-

tion with the three separate blocks of bedplate, entablature and cylinder block

secured to one another by long tiebolts. Unlike other designers of two-stroke

engines, Mitsubishi retained the solid cast iron construction (Figure 11.17)

to achieve greater rigidity with less deformation in service and lower vibra-

tion and noise levels. The shell type main bearings are supported in housings

machined in the bedplate. The running gear is of straightforward conventional

design using shell type or white metal–lined large end bearings and a crosshead

of traditional table type (Figure 11.18) with four guide slippers and twin white

metal–lined top end bearings and the piston rod bolted direct to the crosshead

pin. The connecting rod itself is machined from forged steel.

Compared with the two-stage turbocharged E type engine, the constant

pressure turbocharged UEC-H engine has a delayed exhaust valve opening and

consequently more effective work done during each power stroke.

Exhausting and Scavenging

Referring to the cross-sectional drawing (Figure 11.16), the exhaust gases leave

the engine by way of a diffuser type pipe to enter the exhaust gas manifold.

The Super MET non-water-cooled turbocharger, or two chargers in the case of

a large number of cylinders, is located above this manifold on a pedestal. The

uEC-H type engine 373

Table 11.3 Mitsubishi uEC programme

LSii LSE

Bore (mm) 330

370

430

500

600

750

850

450

500

520

600

680

–

Stroke–bore ratio 2.8–3.9 4.1–4

Mean eective pressure (bar) 17–18 19–20

Mean piston speed (m/s) 8 8/8.5

374 Mitsubishi Low-Speed Engines

air from this turbocharger is delivered to the intercooler and then to the scavenge

air trunk by way of non-return valves and then into the cylinder via ports

uncovered by the piston. During low load operation, the turbocharger air deliv-

ery is passed through two auxiliary blowers before entering the cylinders.

The diffuser-type exhaust pipe is of a three-branch construction where it

connects to the engine cylinder. The gas ﬂows from the three cylinder exhaust

valves are merged into one to enter the exhaust manifold through the diffuser

section. The exhaust manifold is actually made up of many short sections,

*CIT: Controllable injection timing

Welded

monobloc column

One-piece guide shoe

Hydraulic valve

driving system

Air spring

Lube oil quill

Water jacket

Dry jacket

Welded monobloc

bedplate

Shell metal

crosshead bearing

High camshaft

CIT*

Fuel inj. pump

FigurE 11.10 Construction of uEC 75LSii

each corresponding to one engine cylinder, joined together by ﬂexible joints to

accommodate longitudinal thermal deformation.

The scavenge air trunk, however, is divided into two compartments. Charge

air from the intercooler enters the outer chamber and passes through the multi-

cell non-return valves to the scavenge air entablature surrounding the cylinder

jackets.

The two motor-driven auxiliary blowers consume approximately 0.6 per

cent of the rated engine output and as a matter of standard practice they are

uEC-H type engine 375

FigurE 11.11 improvements in piston design from the original uE engine compo-

nent (left) to the HA model (centre) and the current L and LS types (right)

A-A

B-B

C-C

Exhaust valve

Piston

Previous type

Piston

CSS

Exhaust valve

Gas flow

Residual gas

FigurE 11.12 Comparison of gas ow in cylinder with original uE engine scaveng-

ing and with controlled swirl scavenging (CSS)

automatically brought into operation when the engine operates at 50 per cent

load or less. Start-up of the blowers is by a sensed drop in scavenge air pres-

sure. An emergency feature for engines equipped with only one turbocharger

is the facility to operate both auxiliary blowers in series to achieve the required

scavenge air pressure for continuous engine operation. This emergency hook-up

FigurE 11.13 CiT fuel oil pump

F.O.

Fuel nozzle tip

FigurE 11.14 Lightweight (20 kg) non-cooled fuel injection valve for uEC LSii

engine

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Manoeuvring &

display

FigurE 11.15 A uEC engine served by an AFr control system

378 Mitsubishi Low-Speed Engines

is a simple process of adjusting some partition plates in the scavenge box

(Figure 11.19).

new 350-mm and 400-mm Bore Models

A joint venture by MHI with the Wärtsilä Corporation to design and develop

a new low-speed engine was announced at end-2002. The Japanese group has

been a proliﬁc licensed builder of Sulzer engines since 1925, a marque now

under the Wärtsilä umbrella. The resulting 500-mm bore/2050-mm stroke

design was realized in two versions: the conventional camshaft-controlled

Sulzer RTA50C and the electronically controlled RT-ﬂex50C (see Chapter 12

for design details.)

A strategic alliance forged between the groups in September 2005 resulted

in the launch of a new range of 350 mm and 400 mm-bore designs in 2008, in

both mechanically and electronically controlled versions. The engines cover the

power ratings and running speeds associated with propelling diverse small-to-

medium size cargo tonnage. Tapping experience from earlier and contemporary

generations of small bore two-stroke engines, the designers sought compliance

FigurE 11.16 Cross-section of the uEC 52/125H engine

with IMO Tier II emission regulations, low fuel consumption and cylinder oil

feed rates, high reliability and long times-between-overhauls. Electrical power

requirements, weight and dimensions were other development factors as well

as competitive manufacturing costs.

Mitsubishi’s programme was thereby extended with the UEC 35LSE and

40LSE designs (see Table 11.4), which exploit a traditional camshaft for

mechanical actuation of the fuel injection pumps and exhaust valve operation.

uEC ECO-EnginE

Mitsubishi followed MAN Diesel and Wärtsilä in dispensing with the tradi-

tional large camshaft and developing a UEC eco-engine engine with electronic

control of fuel injection, exhaust valve actuation, starting air valve and cylinder

lubrication.

uEC eco-engine 379

FigurE 11.17 Exploded view of uEC-H engine showing cast iron construction

380 Mitsubishi Low-Speed Engines

Studies on electronic control solutions for two-stroke engines were started

by MHI in 1988, the fundamental systems subsequently veriﬁed on single-

cylinder 330-mm and 450-mm bore research engines at the group’s Nagasaki

R&D centre over almost 15 years. Based on the test results, the eco-engine

project was initiated in early 2000. A seven-cylinder UEC 33LSII stationary

engine at MHI’s Kobe shipyard retroﬁtted to eco status in the late 2001 proved

system functionality and reliability in daily service under various operating

modes for over 2 years.

The ﬁrst commercial production engine, an eight-cylinder 600-mm-bore

UEC 60LSII-eco model developing 16 360 kW at 105 rev/min, completed

tests in 2005 before delivery for powering the large pure car/truck carrier Lyra

Leader. Design work extending the concept to other bore sizes has been com-

pleted, but no further eco-engines had entered service by end-2008. The current

programme offers eco-engine versions of the UEC 85LSII, 60LSII, 50LSII,

68LSE, 60LSE, 52LSE and 50LSE models (Figure 11.20).

In an eco-engine, the fuel injection pump and exhaust valve driving gear are

actuated by hydraulic oil at a pressure of 320 bar, the pressurized oil stored in an

FigurE 11.18 Connecting rod and crosshead of uEC-H engine