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

Подождите немного. Документ загружается.

The concept was already proven in the ﬁeld, having been offered as an optional

feature for the larger ABB TPL-C turbochargers for a number of years.

The A100 turbocharger casings reﬂect the much higher mechanical

demands imposed on them. In designing the casings, ABB worked closely

with enginebuilders to secure the same compactness as the TPS units as well

as optimum mounting of the turbocharger on the engine console. The safety

of the containment concept—vital in view of the signiﬁcantly increased power

density—was conﬁrmed both numerically and experimentally on the test rig.

A stronger shaft (required because of the higher power transmission) was

also a factor in designing the A100 bearing assembly, which was based on

TPS turbocharger bearing technology. On the turbine side, the casing cen-

tring concept which had proved successful with the TPS-F turbocharger was

retained.

Three completely new compressor stages, each with different wheel blad-

ing, allow the compressor volume ﬂow range of the TPS-F turbochargers to

be covered by the A100-M/H models with signiﬁcantly higher pressure ratios.

New high-pressure diffusers and compressor blading were developed in addi-

tion to innovative wheel cooling to facilitate the full-load pressure ratios of

around 5.8 with a single-piece aluminium compressor wheel.

A range of compressor stages is available for every turbocharger frame

size, allowing optimum matching in every application. The compressor map

shows high efﬁciencies, excellent map widths and more than adequate over-

speed margins. An 80 per cent compressor efﬁciency is attained on a typical

generator line for a full-load pressure ratio of 5.8.

A new generation of mixed-ﬂow turbines was developed for the A100 tur-

bochargers in addition to the existing TPS mixed-ﬂow turbine stage. A char-

acteristic of the new turbine family is the larger operating range, allowing the

high pressure ratio potential of the new compressor stage to be exploited over

an even wider range of application. The turbine design is optimized in each

speciﬁc volume ﬂow range so that the individual stages exhibit higher turbine

efﬁciencies than the current TPS turbine stages. Further development of the

sealing technologies has reduced the bypass ﬂows so that ﬂow losses are also

lower. In particular, this has allowed a substantial improvement in turbocharg-

ing performance at higher boost pressures.

ABB designed the A100-L programme for advanced two-stroke engine

generations planned or under development, taking special account of the mar-

ket’s increasing focus on reducing emissions. The A100-L series was headed

in 2008 by the A175-L model for boosting medium bore low-speed two-stroke

engines designed to beneﬁt from compressor pressure ratios of up to 4.7 at the

highest turbocharger efﬁciencies. (ABB continues to supply its TPL-B family

for engines requiring pressure ratios of up to 4.2.)

New compressor stages with further optimized impeller blading, new dif-

fusers and new air casings are incorporated. Turbines and gas chambers are

also new, along with an integrated emergency lube oil tank originally devel-

oped for larger TPL-B turbochargers. VTG is available as an option.

a100 series 209

210 Pressure Charging

naPier TurBoChargers

UK-based Napier Turbochargers, which was acquired from the Siemens group

in 2008 by Primary Capital, offers its Napier 7-series and 8-series designs for

application to two- and four-stroke engines developing up to 10 500 kW per

turbocharger.

Based on the designer’s original cartridge construction, Napier 7-series tur-

bochargers are suitable for engines with outputs from 2000 kW to 6500 kW per

turbocharger. Developed from the company’s earlier generation, these NA297,

NA307, NA357 and NA397 models achieve pressure ratios of up to 5:1 and

an overall efﬁciency exceeding 70 per cent. Optimization for different applica-

tions and fuels is facilitated by alternative compressor options, and an innova-

tive lip seal secures effective turbine end sealing at all operating loads.

Cost and complexity is reduced by the air-cooled operation, while the car-

tridge construction enhances on-site maintenance and cuts downtime. Service

life is extended and through-life costs reduced by a squeeze ﬁlm bearing

system.

Proven features from the 7-series, including cartridge construction and

lip seal turbine sealing, were retained for the new generation 8-series, whose

development was stimulated by the need to offer turbochargers capable of

yielding pressure ratios in excess of 5:1 and serving engines with outputs of

up to 10 500 kW per turbocharger. Exploiting aerodynamic and mechanical

advances, the new axial-turbine series (Figure 7.21) comprises NA298, NA358,

NA398 and NA498 models. A pressure ratio of 5.5:1 can be achieved in con-

tinuous operation with an overall efﬁciency of up to 70 per cent, while report-

edly maintaining a service life similar to the 7-series products.

Enhanced levels of component durability are also claimed, while the air-

cooled design contributes to a reduced overall weight. Inboard bearings were

Figure 7.21 Cross-section of napier 458 turbocharger for medium-speed engines

applied for the ﬁrst time on a Napier turbocharger of this size, the hydrody-

namic units securing stable rotor dynamic performance and underwriting a long

life. The new bearing arrangement facilitates the use of axial and radial exhaust

gas ﬂow into the turbocharger, extending the options for the enginebuilder.

Two separate compressor wheel designs are offered to provide differing

characteristics for optimized efﬁciency in diverse applications. Other features

include a circular exhaust ﬂange (eliminating the need for transition pieces)

and a mounting ﬂange incorporating both the lube oil inlet and outlet. Another

concept pioneered by Napier—cartridge construction—beneﬁts serviceability

of the 7-series and 8-series, this conﬁguration allowing operators to remove

and repair the rotor and bearings through a simple procedure without disturb-

ing the exhaust connections. Good access is also provided to key functional

areas such as the nozzle ring.

Titanium compressors, offering enhanced aerodynamic potential and

mechanical properties, were initially planned to replace the aluminium compo-

nents, but design reﬁnements enabled the required performance to be attained

with aluminium.

Smaller engine requirements are addressed by the Napier 047, 057 and

067 all-radial air-cooled turbochargers in the 7-series, which are suitable for

engines developing outputs from 500 kW to around 1700 kW and yield pres-

sure ratios of up to 5. Typical applications include the Wärtsilä 20 engine and

other circa-200 mm bore genset engines. The 047 model features inboard bear-

ings and is uncooled. In common with other turbochargers in the series, the

bearings are designed to run on the engine’s lube oil system and to yield an

extremely long life, even when operating on contaminated lube oil. The 047

model incorporates 50 per cent fewer parts than its predecessor, the Napier

CO45. Cost savings result from using a reduced number of components, and

maintenance is simpliﬁed, with no special tooling required or clearances to set.

Simple clamps are used to hold the casings together and provide total index-

ability of connecting ﬂange positions.

Earlier axial-ﬂow turbine Napier 457 and 557 models, which serve engines

from 4000 kW to 10 000 kW output, featured long-life outboard plain hydrody-

namic bearings fed directly from the engine lube oil system and water-cooled

casings.

High efﬁciency at all pressure ratios was sought from the 5- and 7-series

through advanced compressor and turbine aerodynamic designs. The com-

pressor stage features a one-piece aluminium alloy wheel manufactured on

ﬁve-axes milling machines (Figure 7.22). Vanes with sweepback and rake are

speciﬁed to secure high performance, and a divergent circular arc (DCA) dif-

fuser design yields maximum pressure recovery from a compact conﬁguration.

A high-efﬁciency fabricated nozzle with proﬁled blades serves the turbine sec-

tion of the small and large axial-ﬂow turbochargers.

Napier turbochargers exploit the heavy fuel bearing design to secure a long

service life, even when operating with the poorest quality engine lubricating

oil: a bearing life exceeding 20 000 h is reportedly common.

napier turbochargers 211

212 Pressure Charging

napier turbocharger series performance data

7-Series 8-Series

Pressure ratio capability 5:1 5.5:1

eciency at 5:1 65% 70%

design point pressure

ratio

4:1 4.5:1

design point eciency 70% 75%

eciency at 2.5:1 65% 70%

Man diesel

A full range of turbochargers for two- and four-stroke engines is offered by

MAN Diesel of Germany, its PBS Turbo subsidiary in the Czech Republic and

overseas licensees. The current programme embraces the older NR/R series, the

NR/S series and the NA/S/T9 series, and the new generation TCR radial series

and TCA axial series; in addition, the PT/ PTG power turbine series is avail-

able for turbo compound systems.

na and nr series

The NA/S and NR/S series turbochargers were progressively introduced to the

market in the 1990s, their uncooled casings and inboard plain bearing features

subsequently being adopted by other turbocharger manufacturers.

The radial-ﬂow turbine NR/S series was designed for safe control of the

charge air pressure ratio of up to 4.5, adequate extension of the application

Figure 7.22 a 3d Cad visualization of the napier 457 turbocharger impeller, show-

ing the one-piece intervaned swept-back design with tip rake

range, a higher efﬁciency level, improved reliability in all operating ranges,

unrestricted heavy fuel capability and reduced maintenance demands. Seven

models—the NR12/S, NR14/S, NR17/S, NR20/S, NR24/S, NR29/S and

NR34/S—formed the programme, which overlapped with the smallest of

the established axial-ﬂow turbine NA/S series. The totally water-free series

(Figure 7.23) was a further development of the established NR/R turbo-

charger, featuring a revised compressor and turbine wheel. MAN Diesel’s

proven system of internal plain bearings was retained, the axial thrust now

being absorbed by a separate thrust bearing. The ﬁve models in the radial-ﬂow

turbine NR/R series serve engine outputs from around 400 kW to 4400 kW

per turbocharger.

The development targets for the axial-ﬂow turbine NA/S and NA/T9 series

turbochargers listed the following performance criteria:

l Medium-speed four-stroke engines: a compressor ratio in excess of 4,

and a turbocharger efﬁciency in excess of 60 per cent

l Low-speed two-stroke engines: a compressor ratio in excess of 3.6, a

turbocharger efﬁciency of at least 64 per cent (without an associated

power turbine system) and a turbocharger efﬁciency of at least 69 per

cent (with a power turbine system)

l A pressure ratio of up to 4.5 for the NA/S and 4 for the NA/T9

Man diesel 213

1 Turbine rotor with shaft

2 Compressor wheel

3 Bearing casing

4 Bearing bush

5 Gas inlet casing

6 Nozzle ring

7 Outlet diffuser

8 Compressor casing

9 Diffuser

10 Silencer

Figure 7.23 Man diesel nr/s radial-ow turbocharger

214 Pressure Charging

MAN Diesel carried out extensive theoretical and experimental investiga-

tions on the key individual turbocharger components: the compressor, turbine

and bearings. Apart from higher efﬁciencies from the turbine and compressor,

the goals included the attainment of high vibratory stability for the bladings

and a smooth running performance at low bearing temperatures.

A one-piece radial compressor wheel with continuously backswept blades

was selected to secure an uprated pressure ratio and ﬂow rate, and improved

vibratory stability. The wheel carries 10 main blades and 10 splitter blades.

The introduction of splitter blades reportedly yielded a marked increase in efﬁ-

ciency for pressure ratios 3.5, and an adequate safety margin against surging

in the part-load range was maintained. Various coatings, such as Keplacoat and

Alumite, have been investigated to protect the compressor wheels against cor-

rosive attack undermining the fatigue strength under reversed bending stresses.

A few percentage points improvement in efﬁciency was also gained by

the development of a new turbine blade and by optimizing the outlet diffuser.

The investment-cast turbine blade offers a signiﬁcant cost reduction over a

forged blade, while retaining the material properties and the fatigue strength

under reversed bending stresses. The resistance of the blading to vibrations and

‘exceptionally smooth’ running at pressure ratios of up to 4.5 were promoted

by the incorporation of a ﬂoating bush in the turbine bearing system.

The S-type turbochargers are characterized by uncooled turbine casings

and bearing housings, dispensing with the previous double-walled heavy cas-

ings and cooling connections. The water-cooled bearing casing was retained,

however, for the NA/T9 turbocharger. Tests with an NA57/T9 turbocharger

serving a MAN B&W 6L60MC low-speed engine achieved an efﬁciency of

around 67.5 per cent at the 100 per cent load point; the charge air pressure

ratio was around 3.6. The maximum efﬁciency measured at near-70 per cent

engine load was around 69 per cent. A high efﬁciency level over the remaining

load range was also logged.

Axial-turbine NA series and radial-turbine NR series turbochargers are still

manufactured by MAN Diesel and its licensees to serve appropriate engines

that remain in production. The NA series now embraces six models cover-

ing maximum supercharged engine outputs per turbocharger from 3600 kW

to 24 500 kW. The seven-model NR series covers an engine power range from

670 kW to 5400 kW per turbocharger.

TCa series

In 1999/2000 MAN Diesel decided to develop a completely new turbocharger

generation to replace the NA series, resulting in the launch in 2002 of the TCA

series with radial-ﬂow compressor wheel and axial-ﬂow turbine blading. The

designers pursued the following goals: high speciﬁc ﬂow rates, high efﬁcien-

cies, low noise emissions, ease of maintenance and reduced servicing times,

ease of engine mounting and high reliability with a long service life.

The six-model TCA series addresses two- and four-stroke engines requir-

ing from around 3000 kW to 30 000 kW output per turbocharger. All elements

of the design were optimized with regard to ﬂow control and stress reduction

using 3D CFD and FEM calculations.

The TCA series was headed into production by the TCA77 model (Figure

7.24) with additional frame sizes from the TCA33 to the TCA99 planned to fol-

low progressively and cover the requirements of the highest powered two- and

four-stroke engines. The largest projected model was subsequently deemed

unnecessary, thanks to the performance of the TCA88-25 model, which can serve

two-stroke engines with 27 300 kW output per turbocharger (Figure 7.25).

Fewer turbochargers to boost a given low-speed engine are thus enabled.

An 8-cylinder MAN B&W K98MC/ME or MC-C/ME-C engine, for example,

can be speciﬁed with two TCA88-25 turbochargers instead of the previous out-

ﬁt of three, and 12-cylinder engines of the same type can be boosted by three

such turbochargers instead of the previous four.

Man diesel 215

TCA77

NA57/TO10

1 2 3 4 5

Compressor pressure ratio

1.1

1.0

0.9

Reference efficiency

Figure 7.24 eciency map of the prototype Man diesel TCa77 turbocharger plot-

ted against the maximum eciency of the earlier na57 design

Figure 7.25 Man diesel’s axial-ow TCa series turbocharger

216 Pressure Charging

Most TCA models are available in three versions:

1. Two-stroke version—pressure ratio of up to 4.2, primarily for two-

stroke engines

2. Four-stroke version—pressure ratio of up to 4.7, for both four- and two-

stroke engines

3. High-pressure version—pressure ratio of up to 5.2, for future four-

stroke engines with very high mean effective pressures.

Increased efﬁciency was secured by newly developed wide-chord turbine

blades, which are very stiff and highly wear resistant, and supported in the tur-

bine disc with ﬁr-tree feet. A damping wire thus became unnecessary, easing

maintenance work. Efﬁciency was also raised by a new optimized turbine out-

let diffuser and turbine inlet casing, while a new turbine nozzle ring extended

durability.

Running on two internal radial bearings with ﬂoating bushes and a sepa-

rate thrust bearing, the advanced rotor design achieves higher safety margins.

Bearing points with small diameters were realized by optimizing both the

rotor dynamics and the shaft/hub connection of the compressor wheel and

turbine shaft. The resulting low circumferential speeds of the bearing bushes

and minimization of friction losses contribute to a higher total efﬁciency. Very

quiet running and minimal bearing wear are cited for the ﬂoating journal bear-

ing bushes, which optimize damping behaviour, and the bearing body has an

expected service life of up to 50 000 h.

Mechanical losses are minimized by a reduced shaft diameter and high-

performance thrust bearings. Easy handling and short maintenance times were

sought from the support design; neither the compressor casing nor the turbine

rotor, for example, has to be disassembled when removing the thrust bearing.

Very high centrifugal forces result from a compressor wheel operating

at a circumferential speed of well over 500 m/s. A standard aluminium alloy

design and a specially adapted machining process ensure a long service life for

a component subjected to high-pressure conditions. An optimized geometry is

said to secure high efﬁciency at a safe surge margin over the whole operating

range, and noise is considerably reduced. A new type of force and form lock-

ing compressor wheel attachment on the turbine shaft enables assembly and

disassembly of the wheel without the need for an unwieldy hydraulic tool. The

new MAN Diesel-patented shaft/hub connection substantially reduces replace-

ment times and eases maintenance.

Efﬁciency is enhanced by the newly developed compressor volute and com-

pressor diffuser vanes, while optional internal recirculation (IRC) increases the

surge margin, and optional jet assistance provides fast rotor acceleration.

TCA nozzle rings are manufactured from high-resistance materials to

secure a long service life. Optimum matching of the turbocharger to the spe-

ciﬁc engine is smoothed by individually adapting nozzle rings. A new vari-

able turbine area (VTA) option, however—detailed in the section Variable

Turbine Area Technology—enables the ﬂow cross-section to be adapted to the

corresponding load condition of the engine, thereby reducing fuel consumption

and emissions, especially in part-load operation.

Optimized mounting to the engines is facilitated by enabling all casings to

be installed and turned in 15° steps, and newly developed one- and two-socket

compressor spirals and diffusers foster optimum matching of the turbocharger

to the engine.

A modular design allows the turbocharger to cover as broad a range of

applications as possible. Air is sucked in either via an intake air silencer, a

90° intake casing or an intake manifold; exhaust gas ﬂows into the turbine via

either an axial- or radial-ﬂow casing. The design features the separate casing-

base concept proven in the NA series. The compressor volute is available with

either one or two opposing thrust pieces: the single-piece variant has advan-

tages for two- and four-stroke in-line cylinder engines, while the two-piece

volute offers advantages when attaching a single turbocharger to V-type four-

stroke engines.

Both the compressor wheel and the turbine can be adjusted to engine

requirements by choosing from a range of meridians and blading conﬁgura-

tions. Diffusers and nozzle rings that are very ﬁnely stepped in their mass-ﬂow

areas allow the turbochargers to be ﬁne-tuned to the engine. A nozzle ring

capable of adjustment during operation is available optionally for maximum

variability.

A minimal number of external connections were sought. On the engine side

and in the plant system itself the only additional connections—apart from the

air and exhaust gas connections—are an oil inlet and drain pipe, together with

a breather connection for the bracket. No cooling water, or lock-air connec-

tions, additional oil overﬂow piping or external lube oil supply are required. A

special emergency operation facility is integrated into the turbocharger to allow

continued operation under emergency conditions. All the hot casing compo-

nents are equipped with a new temperature- and noise-reducing casing with

a sheet metal cover, signiﬁcantly reducing the risk of engineroom personnel

coming into contact with excessively hot surfaces.

Uncooled casings are designed in accordance with the ‘pipeless engine’

principle, all supply pipes being fully integrated within the casing. Only one

oil supply and discharge pipe and a venting pipe have to be connected exter-

nally. A robust structure and the material thickness of the casing walls means

that additional burst protection is not required. Safety is further enhanced by

the rigid connection of the turbine outlet, bearing and compressor casing using

tie rods.

In order to limit bearing losses, the shaft diameter of the rotating assem-

bly was reduced, paying special attention to rotor dynamics so that, despite

the reduction, it was possible to increase rotor stability compared with the NA

series turbochargers. The rotating assembly is mounted in the bearing casing

on two ﬂoating-sleeve radial bearings. Since the ﬂoating-sleeve design signiﬁ-

cantly reduces the rate of shear in the bearing gaps, in comparison with the

ﬁxed-sleeve type, both bearing losses and bearing wear are reduced.

Man diesel 217

218 Pressure Charging

The thrust bearing is equipped with a ﬂoating centre plate which acts in the

same way as the ﬂoating-sleeve radial bearings. The thrust bearing is located

outside the radial bearing on the compressor side, facilitating removal with-

out having to dismantle the radial bearing and rotating assembly. MAN Diesel

notes that the fact that the thrust bearing is subject to far greater stresses than

radial bearings (because of the axial thrust of the turbine and compressor)

makes this a signiﬁcant feature for ease of maintenance.

Bearing points are supplied with oil by a ring channel arranged in the

inside of the bearing casing. Oil feed, either from the right or left side of the

turbocharger, lube oil distribution to all the bearing points and the supply from

the emergency lube oil service tank are via this ring channel.

No bearing case is water cooled. The heat input from the compressor and

turbine is dissipated in the lube oil ﬂung off the shaft of the rotating assembly.

The oil mist thus generated can drop down the walls of the generously dimen-

sioned interior of the bearing casing, thereby evenly absorbing the heat to be

dissipated. The bearing casing has its own air vent, ensuring that the leakage air,

which the compressor inevitably forces into the casing through the shaft seal of

the rotating assembly, does not increase crankcase pressure in the engine but

dissipates it directly.

All airﬂow components were optimized with regard to ﬂow conﬁguration

and stress reduction using 3D CFD and FEM analyses. The result was a turbine

with wide-chord blades arranged in a ﬁr-tree root in the turbine disc. A charac-

teristic feature of such blades is their very high chord-to-height ratio, this cre-

ating a compact, very stiff and hard-wearing blade. The turbine blades can be

of varying angles and lengths. With the aid of advanced design tools, it is now

possible to dispense with lacing wire to dampen exhaust-generated vibrations,

even in four-stroke engine applications. MAN Diesel explains that apart from

improving the blade proﬁle, this has signiﬁcantly boosted efﬁciency.

As in the NA series, the turbine shaft is friction-welded to the turbine disc.

The disc (which in the case of the TCA77 turbocharger must absorb a centrifu-

gal force per blade equivalent to the weight of a fully loaded truck and trailer)

is made from a forged steel alloy. The nozzle rings, with a new blade proﬁle

design, and a carefully matched turbine outlet diffuser, also contribute to efﬁ-

ciency gains. A key element of the development work was designing the pat-

ented turbine outlet diffuser, which effectively converts kinetic energy remaining

downstream of the turbine wheel into pressure. Simultaneously, the outlet dif-

fuser acts as an integrated burst protection within the turbine (see later).

The compressor wheel is operated at circumferential speeds well in excess

of 500 m/s, generating considerable centrifugal forces. To withstand these

forces, the wheel is made of a high-strength aluminium alloy. For applications

where the components will come into contact with corrosive media, a special

corrosion-resistant coating can be applied to the compressor wheel.

A new design of compressor volute and new nozzle ring designs contribute

to optimized turbocharger matching and high efﬁciency, while a new compres-

sor mounting system was developed to ease removal. The compressor wheel is