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

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uEC eco-engine 381

FigurE 11.19 Mitsubishi uEC 85LSii engine in six-cylinder form on test for VLCC

propulsion

Table 11.4 Small-bore uEC–LSE engines

35LSE 40LSE 45LSE

Bore (mm) 350 400 450

Stroke (mm) 1550 1770 1840

Output/cycle (mcr, kW) 870 1135 1245

Speed (rev/min) 167 146 130

Mean eective pressure (bar) 21 21 19.6

Mean piston speed (m/s) 8.6 8.6 7.97

Cylinders 5–8 5–8 5–8

Power range (kW) 3475–6960 4550–9080 6225–9960

35LSE and 40LSE engines jointly developed with Wärtsilä

382 Mitsubishi Low-Speed Engines

accumulator block at each cylinder. Pressure compensation during actuation is

effected by the volume in the accumulator chamber, making a pressurized gas

enclosed-type accumulator unnecessary.

Hydraulic power for fuel injection and exhaust valve actuation is

controlled by an on–off type solenoid valve unit and engine control system.

The timing of injection and exhaust valve opening/closing are also controlled

electronically to achieve the best solution for any operating mode and to match

changing conditions. The fuel injection pump is similar in structure to the con-

ventional mechanical unit but simpliﬁed. Two sets of on–off type solenoid

valves are mounted on the pump to control the injection pattern with respect to

the operating load and improve trade-off between thermal efﬁciency and NOx

emissions. Stricter emission regulations in the future could be met by MHI’s

stratiﬁed fuel–water injection system (see Chapter 3).

A feedback control function is applied in controlling the fuel injection

volume to compensate the equivalent thermal load and individual cylinder

control. The fuel pump stroke is monitored by twin gap sensors at each cycle,

underwriting system reliability (Figures 11.21 and 11.22).

Exhaust valve opening and timing are controlled by the electro-hydraulic

system using the on–off solenoid valve unit, the timings optimized to the oper-

ating load. For precise timing control, the feedback control function is applied

by monitoring the valve lift. The actuating mechanism is otherwise similar to

the conventional system, reportedly inheriting its reliability and maintenance

procedure. Solenoid valves are key elements of the eco-engine, the application

FigurE 11.20 Mitsubishi’s rst production eco-engine on test in 2005, an eight-

cylinder 60LSii model subsequently installed in a pure car/truck carrier

uEC eco-engine 383

FigurE 11.21 Schematic diagram of eco-engine fuel injection and exhaust valve

actuation and control systems

FigurE 11.22 Conguration of hydraulic oil power supply system for the eco-engine

384 Mitsubishi Low-Speed Engines

demanding a very quick response, high ﬂow rate and long life cycle. MHI

started developing suitable valves in 1999, the most important goal being reli-

ability. Endurance testing corresponding to around 6 years of actual operation

conﬁrmed satisfactory performance.

A conventional starting air control valve is eliminated, and solenoid valves

and a control air pipe added. Electronically controlled starting valves are said

to achieve a better performance and ﬂexibility in starting and crash-astern

procedures.

Hydraulic power for the systems is provided by an installation based on

engine-driven pumps, which supply pressurized oil mainly during engine oper-

ation, and electrically driven pumps, which maintain system pressure when the

engine is stopped. The engine-driven axial piston pumps are coupled through a

gear drive to the crankshaft.

An engine control system is prepared for the ‘eco main controller’ (EMC)

installed in the control room and interfaced with the remote control system.

A local control box and ‘eco cylinder controller’ (ECC) are mounted on the

engine and connected by a duplicated network line. For redundancy, the EMC

system comprises two duplicated units operating in parallel and performing the

same task. If the active EMC fails, the standby unit takes over control with-

out interruption. Among its functions, the controller carries out the following

tasks: speed governing; start/stop sequences; timing control of fuel injection,

exhaust valve and starting air system actuation; control of the hydraulic oil

supply system; alternative operation and control modes; network functioning

and monitoring malfunctions in the entire control system.

Each ECC, mounted on the individual cylinders, executes the orders

for fuel injection, exhaust valve actuation and starting air system timing. The

capability to control two cylinders provides redundancy: if one ECC fails, one

serving another cylinder can take over automatically.

Excellent experience is reported from the pioneering Lyra Leader instal-

lation, with better performance across the load range and lower operating

costs than camshaft-controlled engines. The electronically controlled cylinder

lubrication (ECL) system can be speciﬁed for the conventional UE engines to

reduce lube oil consumption and improve piston ring and cylinder liner run-

ning conditions.

MHI summarizes the beneﬁts of the eco-engine systems as follows:

l Environmental friendliness. Smokeless operation can be achieved by the

appropriate fuel injection pressure at any load; and reductions in NOx

emissions can be secured by tuning the fuel injection timing and pattern

at any load.

l Higher fuel economy. Fuel injection and exhaust valve actuation timing

can be optimized ﬂexibly by electronic control according to the engine

operating load, atmospheric conditions and fuel oil properties; lower

speciﬁc fuel consumption ratings can thus be achieved, particularly at

part load.

l Easier control (better manoeuvrability). Stable, continuous low load

operation (even at extremely low loads) with good engine perform-

ance is fostered by the improved combustion conditions arising from an

appropriate fuel injection pressure and optimized timing of injection and

exhaust valve actuation at lower loads.

l Higher reliability. A fuel injection pressure favourable to the combus-

tion condition at any load enhances reliability of the hot components

such as piston crown, rings, cylinder liner and exhaust valve.

l Flexible operation. Operating modes can be easily changed, and ﬁne

tuning is possible during engine running.

l Reduced maintenance. Electronic control signiﬁcantly simpliﬁes engine

assembly and servicing by eliminating some large mechanical elements

and their associated maintenance.

EMiSSiOnS rEduCTiOn

Two operating modes are selectable for the eco-engine: low emission and econ-

omy modes. If the former is selected, NOx emissions can reportedly be reduced

by 10–15 per cent without any penalty in fuel consumption; if economy mode

is chosen, the fuel consumption can be lowered by 1–2 per cent while retaining

the same level of NOx emissions.

New emission control technologies have been pursued by MHI for all UEC

engines to counter IMO third-stage NOx regulations, including two water

injection systems: a stratiﬁed fuel–water injection system (already installed in

stationary power plants) and an independent water injection system.

With water injection valves arranged separately from the fuel injection

valves, the independent system was tested on the bench before installation and

trials on a 6UEC 50LSE engine in the shop. Water is injected with appropriate

timing controlled by solenoid valves according to the crank angle; since the

electronic control system is similar to that of the eco-engine, the independent

water injection system is easy to integrate with that design.

Unlike a stratiﬁed fuel–water or emulsion injection system, it is not nec-

essary with the independent water injection system to increase the fuel pump

capacity or the size of the camshaft driving gears and cams; additionally, a

larger volume of water can be injected to achieve a greater reduction in NOx

emissions. NOx reduction is relative to the amount of water injected, MHI

reporting that a 69 per cent cut was achieved in the engine test, with a water

injection amount of 169 per cent to fuel quantity at 75 per cent load (the maxi-

mum weighting factors in E3 mode in the IMO NOx calculation formula).

Furthermore, a 68 per cent NOx reduction was obtained at 100 per cent load,

with a 134 per cent water injection to fuel ratio.

Although the targeted 80 per cent NOx reduction could not be achieved,

the results from an independent system—with higher than 50 per cent reduc-

tions—had never been secured by MHI with stratiﬁed fuel–water injection

or emulsiﬁed fuel. A remaining challenge was to reduce the amount of water

Emissions reduction 385

386 Mitsubishi Low-Speed Engines

injection required (e.g., by optimizing timing and the atomizer speciﬁcation)

and hence lower the volume of water to be generated or carried onboard for

this purpose.

CyLindEr LuBriCATiOn

MHI addressed the concerns of operators on cylinder lubrication costs by offer-

ing the swirl injection principle (SIP) lubricating system from Danish specialist

Hans Jensen Lubricators for UEC engines. Spray injection creates a thin and

uniform oil ﬁlm distribution on the liner surface, which is effective in reducing

waste oil splashed up and down by the piston ring movement. Additionally, the

system can reportedly achieve a reduction in ring and liner wear rates, improve

the liner condition and reduce particulate matter.

The cylinder lubricator pumps oil to the SIP valves mounted in the cylinder

liner wall. The valves are equipped with a nozzle for spraying tiny droplets of

oil tangentially to the liner wall, covering a large area above the next injection

valve. Spraying from all valves ensures coverage of the entire circumference

of the liner. Injection takes place when the exhaust valve is closing and well

before the piston passes the injection quills in the upward movement.

The centrifugal power of the scavenging air swirl ensures that the drop-

lets settle horizontally well distributed on the liner wall. This allows the piston

rings to effect the vertical distribution of the injected cylinder oil when they

pass in the continued upward movement. The designers claim that an optimum

distribution of oil is thus achieved with a minimum oil quantity injected. The

spring in the SIP valve works at a pressure of approximately 40 bar. Apart from

securing an adequate pressure for cylinder oil to become a suitable spray when

leaving the nozzle, it also ensures that the oil in the tube between cylinder

lubricator and SIP valve stays under pressure (Figure 11.23).

FigurE 11.23 Hans Jensen Lubricators’ SiP cylinder lubrication system benets

uEC engines 1 5 SiP valve, 22 5 Cylinder liner, 3 5 Pressure pipe, 4 5 Lubricator,

5 5 nozzle, 6 5 return pipe

387

C h a p t e r | t w e l v e

Wärtsilä (Sulzer)

Low-Speed Engines

Diesel engine pioneer Sulzer came under the umbrella of the Wärtsilä Corporation

in 1997, the Finland-based four-stroke specialist committing to sustained develop-

ment of the successful RTA low-speed two-stroke engines inherited from the

Swiss designer. Launched at the end of 1981, the uniﬂow-scavenged, constant pres-

sure turbocharged RTA series with a single poppet-type exhaust valve (Figures 12.1

and 12.2) represented a break with Sulzer’s traditional loop-scavenged valveless

two-stroke concept (see the last section of this chapter).

The original RTA series embraced six models with bore sizes of 380 mm,

480 mm, 580 mm, 680 mm, 760 mm and 840 mm, and a stroke–bore ratio of

2.86 (compared with the 2.1 ratio of the loop-scavenged RL series). These

RTA38, RTA48, RTA58, RTA68, RTA76 and RTA84 models—collectively

FigurE 12.1 uniow scavenging system for rTA engine series

388 Wärtsilä (Sulzer) Low-Speed Engines

termed the RTA-8 series—were supplemented in 1984 by the longer stroke

RTA-2 series comprising 520-mm and 620-mm bore models and the RTA84M

model. The RTA-2 series was extended again in 1986 by a 720-mm bore

model. An uprated 840-mm bore design, the RTA84C, was introduced in 1988

to offer higher outputs in the appropriate speed range for propelling large cel-

lular container ships (Figure 12.3).

A higher stroke–bore ratio (3.47) for the RTA-2 series secured lower engine

rotational speeds and hence higher propulsion efﬁciencies. The ratings of the

RTA-2 engines were increased in 1987 in line with the power level already

offered by the RTA72 model. Various design improvements, together with higher

ratings, were introduced for the RTA-2 series in 1988 at the same time that the

RTA84C engine was launched. A further upgrading of the RTA-2 series—to

RTA-2U status—came in 1992, with a 9 per cent rise in speciﬁc power output.

The RTA range was subsequently extended by the introduction in 1991

of the RTA84T ‘Tanker’ engine design, which, with a stroke–bore ratio of

3.75 and a speed range down to 54 rev/min, was tailored for the propulsion of

VLCCs and large bulk carriers. The ﬁrst production engine entered service in

1994. Even longer strokes (4.17 stroke/bore ratio) were adopted in 1995/1996

for RTA-T versions of the 480-mm, 580-mm and 680-mm bore models, whose

Rotating mechanism

Bolting connection

Air spring

Separate valve cage

Single centrally

positioned exhaust

valve made of heat-

resistant material

Rotationally symmetric

efficiently cooled valve

seat

Short piston skirt

Piston head bore

cooled with water

Hydraulic pushrod from

hydraulic valve actuator

Actuator piston

Fuel injection valves

with fuel circulation

without water cooling

Bore-cooled

cylinder cover

Bore-cooled

cylinder liner

Water guide

Dry cylinder jacket

FigurE 12.2 rTA engine combustion chamber components

key parameters addressed the power and speed demands of bulk carriers up

to Cape-size and tankers up to Suezmax size. These RTA48T, RTA58T and

RTA68T designs have more compact dimensions than earlier models, giving

ship designers more freedom to create short enginerooms, while reduced com-

ponent sizes and weights facilitate easier inspection and overhaul. Shipyard-

friendly features were also introduced to smooth installation.

In 1994 Sulzer anticipated demand for even higher single-engine outputs

from large and fast container ships by announcing the RTA96C engine, a short

stroke (2.6 stroke/bore ratio) 960-mm bore design.

RTA engines of all bore sizes have beneﬁted from continual design reﬁne-

ments to increase power ratings and/or enhance durability and reliability, based

on service experience. In early 1999 the RTA programme was streamlined by

phasing out some older types (such as the 380-mm bore model), which had

Wärtsilä (Sulzer) low-speed engines 389

max

comp

(bar)

max

comp

scav

2.0

1.5

1.0

0.5

Temp.(°C)

Spec. air

flow

(kg/kWh)

% load

rev/min

450

400

350

300

250

25 50 75 100 105

60 70 80 90 100 105

Temp. before turbine

Temp. after turbine

Spec. air flow

BSFC

(g/kWh) (g/bhph)

scav

(bar)

135

130

125

120

140

130

120

110

100

185

175

165

FigurE 12.3 Test results from a 9rTA84C engine equipped with an exhaust gas

power recovery turbine, according to a propeller characteristic. The engine develops

34 380 kW mcr at 100 rev/min

390 Wärtsilä (Sulzer) Low-Speed Engines

fallen out of demand, a measure also dictated by the need to ensure that all

engines could comply with the IMO Annex VI NOx emission regulations. In

mid-1999 the RTA60C model was introduced as the ﬁrst Sulzer engine designed

from the bedplate up to embody RT-ﬂex electronically controlled common rail

fuel injection and exhaust valve actuation systems. Starting with the 580-mm

and 600-mm bore designs, RT-ﬂex series versions progressively became avail-

able as options throughout the RTA programme (see the next section).

The current RTA/RT-ﬂex programme, summarized in Figure 12.4, embraces

10 bore sizes from 350 mm to 960 mm with various stroke–bore ratios, speed

and rating options covering an output band from around 3475 kW to 84 420 kW

with ﬁve-to-fourteen-cylinder in-line models.

Engine Selection

Selecting a suitable main engine model to meet optimally the power demands

of a given project dictates attention to the anticipated load range and the inﬂu-

ence that the operating conditions are likely to have throughout the entire life

of the ship. Every RTA engine has a layout ﬁeld within which the power/speed

ratio ( rating) can be selected. It is limited by envelopes deﬁning the area

where 100 per cent ﬁring pressure (i.e., nominal maximum pressure) is avail-

able for the selection of the contract maximum continuous rating (CMCR).

Contrary to the ‘layout ﬁeld’, the ‘load range’ is the admissible area of

operation once the CMCR has been determined. Various parameters have to

100000

80000

60000

40000

20000

10000

8000

6000

RT-flex48T-D

RTA48T-D

RT-flex58T-D

RTA58T-D

RT-flex96C

RTA96C

RT-flex82C

RTA82C

RT-flex60C-B

RT-flex50-D

RT-flex50-B

RT-flex35

RTA35

RT-flex68-D

RTA68-D

RT-flex40

RTA40

70 80 90 100 120 140 160 180

3000

4000

6000

8000

10000

20000

30000

40000

50000

60000

80000

Output (kw)Output (bhp)

Engine speed (rev/min)

RT-flex82T

RTA82T

RT-flex84T-D

RTA84T-D

FigurE 12.4 Wärtsilä rTA and rT-ex engine programme