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

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aluminium alloy wheel with splitter-bladed impeller and backswept blades for

high efﬁciency and a wide compressor map. Peak efﬁciencies of more than 84

per cent are obtainable.

Experience with the RR-type turbocharger was tapped by the designers

in creating the TPS series. The resulting conﬁguration is modular and offers

a high level of ﬂexibility with a minimum of sub-assemblies. A signiﬁcantly

reduced number of parts are used in comparison with the RR type, which itself

is a simple design. A modular conﬁguration fosters the easy integration or ﬁt-

ting of options, such as a jet assist system. Special attention was paid during

design and development to ease of maintenance and simple mounting of the

turbocharger on the engine.

Criteria for turbine development included the ability to operate at gas tem-

peratures of up to 750°C and yield a long lifetime on heavy fuel operation and

under extreme load conditions. The requirement for a large volumetric range

had to be met with a minimum number of parts. Considerable aerodynamic

potential was offered by the turbine of the RR..1 turbocharger, which had also

demonstrated excellent reliability and the highest efﬁciencies. Operation at

pressure ratios far above today’s levels was possible with the turbine for which

a nozzle ring was developed to satisfy the goals for the TPS turbocharger. A

new scroll casing and nozzle ring were designed using proven inverse calcula-

tion methods that ensure losses are kept very low and turbine blading is not too

strongly excited. Thermodynamic measurements showed that the turbine efﬁ-

ciency of the new design was as high as that of its predecessor. Blade vibration

excitations are even lower.

Previously, stress distribution for the turbine wheel was optimized by trial

and error: a geometry was deﬁned and the resulting stresses calculated, the

geometry then being varied until the stresses lay at an acceptable level. Using

the latest computer-aided tools for optimizing structures, the stress level was

reduced by around 30 per cent over the earlier version.

Turbocharger bearings must deliver a good load-carrying capability with

respect to both static and dynamic forces, good stability and minimal mechani-

cal losses from a cost-effective design fostering modest maintenance. The TPS

turbocharger bearings are lubricated directly from the engine lube oil system.

An increase in turbocharger pressure ratio means a rise in the load exerted

on the thrust bearing. A turbine wheel with a high back wall was chosen to

counteract the main thrust of the compressor as far as possible. Extensive cal-

culations and temperature measurements were performed on the thrust bearing,

both in steady state operation and with the compressor in surge mode, to opti-

mize its dimensions and to achieve the lowest possible bearing losses without

compromising on load-carrying capability.

The key design factor for the radial plain bearings is their stability charac-

teristic. Considered in terms of this criterion, ABB Turbo Systems notes that

a squeezed ﬁlm damped multi-lobe plain bearing would be the best choice.

But such a bearing has higher losses than that with freely rotating bushes. The

latter, however, exhibits an inadequate stability characteristic. A new bearing

TPs series 199

200 Pressure Charging

design with rotating hydraulically braked multi-lobe bearings was therefore

developed to blend the respective merits of the two types.

By providing a tangential lube oil supply, it is possible to reduce the

speed at which the ﬂoating bushes rotate by around 20 per cent compared

with freely rotating bushes. The designer says that this measure has ensured

a stability which is effectively as good as that with the squeezed ﬁlm damped

multi-lobe plain bearings, and mechanical losses can be reduced by more

than 20 per cent.

As noted earlier, a considerably higher boost pressure is needed to reduce

the temperature in the cylinders during the Miller process. Turbochargers offer-

ing even higher compression pressure ratios are therefore dictated. For such

engines, ABB developed three new TPS models covering an engine power

range from 500 kW to 3300 kW. The ﬁrst, designated the TPS-F33, was intro-

duced in 2000/2001 and followed two years later by the TPS-F32 and in 2004

by the TPS-F31. Based on the TPS-D/E platform—with the same outline

dimensions fostering interchangeability and engine upgrades—they achieve

full-load pressure ratios of up to 4.75, 5.0 and 5.2, respectively, using an alu-

minium alloy compressor wheel. The increased performance was sought while

retaining high efﬁciency, reliability, long lifetime and ease of maintenance

(Figure 7.17). The new compressors developed for the TPS-F series under-

wrote a 15 per cent increase in the ﬂow rates that could be covered by a given

impeller size.

A recent addition to the TPS-F family extended the application range down

to small high-speed and medium-speed heavy fuel-burning engines with ratings

Figure 7.17 Cross-section of aBB TPs57-F33 turbocharger

from 400 kW to 750 kW. This new TPS44-F model is the ﬁfth and the smallest

member of the compact series. Three radial compressor stages support opera-

tor efforts to reduce emissions and raise fuel economy while gaining higher

powers from their engines. The TPS44-F31 and F32 versions were introduced

to the market ﬁrst, offering full-load pressure ratios of up to 4.8; a TPS44-F33

variant delivers an enlarged volume ﬂow.

The TPS-F was the ﬁrst ABB turbocharger to feature recirculation technol-

ogy: a bleed slot around the compressor wheel, which, by improving the ﬂow

ﬁeld, increases the surge margin. The effect of the slot is to enlarge the map

width without compromising the compressor’s high efﬁciency.

Variable Turbine geometry

In the mid-1990s, developments in the diesel and gas engine markets led to

a TPS turbocharger version with VTG. One reason was the increasing popu-

larity of single-pipe exhaust systems for diesel engines. When conventional

turbochargers are used with these systems, part-load operation tends to be dif-

ﬁcult, load response is poor and smoke and particle emissions can be high. Gas

engine performance had also progressed impressively due to increased efﬁ-

ciency and bmeps, high-altitude capability and controlled air-to-fuel ratios.

It was not possible, however, to simply use conventional turbochargers with

these engines. Solutions ranged from installing a wastegate or throttle mecha-

nism to special matching of the turbocharger, but each had its drawbacks. An

‘adjustable’ turbocharger was considered the ideal solution for the candidate

diesel and gas engines. Apart from eliminating the losses associated with a

wastegate, a turbocharger equipped with VTG is more ﬂexible in applications

with changing operating or ambient conditions.

Precise control of the air-to-fuel ratio (so-called Lamda regulation) is

achieved with an innovative nozzle ring that enables the effective turbine area

to be varied without any signiﬁcant drop in turbine efﬁciency. The clearances

for the movable nozzle blade are reduced almost to zero by springs that push

the blades against the opposing casing wall. Numerous VTG turbochargers

have been supplied for Bergen gas engines speciﬁed for land-based power

plants.

ABB offers the VTG nozzle ring as an option for TPS turbochargers (frame

sizes 57 through 61), TPL65-A turbochargers and the new A100 series serving

diesel and gas engines but plans wider application of the technology. Precise

adjustment of engine operation to actual working requirements is facilitated

over a wide range of ambient conditions. Part-load operation, load acceptance

and engine emission levels can all be optimized by controlled rotation of the

movable nozzle ring vanes.

TPl series

A completely new generation turbocharger from ABB Turbo Systems—the

TPL series—was launched in 1996 to meet the demands of the highest output

TPl series 201

202 Pressure Charging

low- and medium-speed engines, the designer having set the following devel-

opment goals:

l High compressor pressure ratio for increased engine power output

l High turbocharger efﬁciency levels for reduced engine fuel consumption

and lower exhaust gas temperatures

l High speciﬁc ﬂow capacity, resulting in a compact design and low

weight

l High reliability, long lifetime and extended periods between overhauls

l Easy maintenance, even for machines operated under adverse conditions

(such as those serving engines burning low-quality heavy fuel oils)

The uncooled design features an overall number of components reduced by

a factor of six compared with the VTR series, contributing to easier mainte-

nance and extended times between overhauls (see Figure 7.18a–c).

A modular conﬁguration provides the TPL series with the ﬂexibility to

meet the turbocharging requirements of two- and four-stroke engines. Two-

stroke engines with outputs from 3000 kW to 28 000 kW per turbocharger are

served by the TPL-B variant introduced in 1999, while the original TPL-A

model addresses demands from four-stroke engines delivering from 2500 kW

to 12 500 kW per turbocharger.

Despite differences in their thermodynamics and design, the TPL-A and

TPL-B series share established features, for example, the basic modular TPL

concept and the central bearing housing with the complete bearing assembly.

Figure 7.18 (a) Cutaway of aBB TPl65 turbocharger

All TPL turbochargers consist of a central cartridge unit with the rotor assem-

bly. The casings on the compressor side and the turbine side are connected

by ﬂanges, and all casings are uncooled. Complete dismantling of the turbo-

charger, including the nozzle ring, is possible from the ‘cold side’, leaving the

exhaust pipes in place and untouched.

All TPL turbochargers feature the same bearing technology, with plain

bearings selected to secure a long lifetime. The non-rotating, radial bearing

bushes are suspended in a squeeze ﬁlm damper, which increases the stability

of the rotor while reducing the dynamic forces and hence the load on the radial

TPl series 203

(b)

(c)

Figure 7.18 (Continued) (b) Cross-section of aBB TPl65 turbocharger. (c) Modular

design concept of aBB TPl turbocharger: 1, lter silencer; 2, air volute; 3, rotor block;

4, gas inlet casing; 5, nozzle ring; 6, gas outlet casing

204 Pressure Charging

bearings. The main thrust bearing comprises a free-ﬂoating disc between the

rotating shaft and the stationary casing. This bearing concept halves the speed

gradient in the axial gap so that the losses and the risk of wear are signiﬁcantly

reduced; thanks to this technology, the thrust bearing is also very tolerant to

inclinations of the rotor.

Since two-stroke engines usually have a lubrication system driven by elec-

tric pumps rather than by the engine itself, an emergency oil supply has to be

provided to ensure that the turbocharger runs out safely in the event of a black-

out. The TPL-B turbocharger can be optionally equipped with an integrated

emergency oil tank mounted on top of the bearing casing. Since this system is

based on gravity, it does not require any auxiliary support.

Thermodynamic improvements from the TPL-B series derive from a new

axial turbine family (the TV10), which was especially developed for tur-

bocharging systems for two-stroke engines. Five turbine wheels and over 20

nozzle rings can be speciﬁed for each TPL-B model, these options allowing the

turbocharger characteristic to be adapted to the requirements of the application

within a wide range.

Two new radial compressor stages were developed for the TPL family. The

TPL-B compressor features a single-piece aluminium alloy wheel with split-

ter-bladed impeller design and backswept blades for high efﬁciency and a wide

compressor map. Peak efﬁciencies exceeding 87 per cent are reportedly obtain-

able. Enlarged compressor diameters further increased the volume ﬂow, thereby

fostering optimized matching of the turbochargers to the engine application.

Market studies led to ABB’s decision at the end of 1997 to develop a tur-

bocharger to boost low-speed engines required to propel the increasingly larger

container ships entering service, surpassing the output and performance of

what was then the world’s most powerful design, the TPL85-B. The resulting

TPL91-B turbocharger—which extended the volume ﬂow range of the estab-

lished TPL-B series by over 20 per cent—was designed to yield advanced

thermodynamic performance combined with the highest reliability and lowest

possible life-cycle costs. It was also optimized for integration and mounting as

well as for convenient servicing, important factors because of the heavier indi-

vidual elements and restricted engineroom space for onboard overhauling.

Built at the end of 2000, the ﬁrst prototype underwent extensive qualiﬁca-

tion tests on a burner test rig in the following year. Engine shop tests began in

2004 with three TPL91-B turbochargers boosting what was then the world’s

most powerful electronically controlled two-stroke engine, a 12-cylinder MAN

B&W K98ME model.

An engine power range from 20 000 kW to 28 000 kW per turbocharger

is covered by the TPL-91B (Figure 7.19), whose key performance data and

design features include:

l Maximum volume ﬂow rates: 56 m

/s at a compressor ratio of 3.5 m

and 59 m

/s at a ratio of 4.0

l Compressor pressure ratio: 4.2

l Turbocharger efﬁciency 70 per cent

l Compact frame and construction with short rotor and integrated lubrica-

tion oil tank

l Minimized speciﬁc length, volume and weight

l Inducer casing bleed system for wide compressor maps (no pulsating

noise at part load)

l Design optimized for easy servicing and long times-between-overhauls.

Turbocharger efﬁciencies are higher than 70 per cent for a wide range of

pressure ratios in both full-load and part-load operation, fostering low fuel con-

sumption and low engine-side component temperatures in those modes.

The conceptual design of the TPL-91B mirrors that of all the other models

in the TPL-B series, with a central cartridge unit and a rotor assembly, which

can be removed for servicing as an alternative to the standard method of dis-

mantling from both ends. A number of innovative features, however, reﬂect the

special area of application.

A two-stroke engine’s lubrication system is usually driven by electric pumps

rather than by the engine itself, so an emergency oil supply has to be provided to

ensure that the turbocharger runs out safely if the system shuts down. TPL-B tur-

bochargers normally have the emergency oil tank mounted on top of the bearing

casing. To signiﬁcantly reduce the outer dimensions of the turbocharger, however,

and give enginebuilders as well as shipyards more freedom in arranging machinery,

the TPL-91B has its emergency lube oil system integrated in the bearing casing.

ABB also developed a short rotor concept for the TPL-91B as a contribu-

tion to compactness. A new gas outlet conﬁguration and TV11 turbine allowed

the rotor to be made even 24 mm shorter than that of the TPL85-B turbo-

charger, the next largest one in the series. The complete TPL91-B turbocharger

is in fact only marginally (around 300 mm) longer than the TPL85-B, despite

its 20 per cent higher volume ﬂow rate.

TPl series 205

Figure 7.19 aBB’s largest series, the TPl91 turbocharger

206 Pressure Charging

ABB reports that a result of the very high compressor pressure ratios of

modern turbochargers is that loading is closer and closer to their physical lim-

its, with an obvious adverse effect on component lifetimes. Usually made of

aluminium alloy, the compressor wheel is especially susceptible to ageing.

Compressor cooling was introduced in the TPL91-B to lower the temperature

in the wheel’s outer area and hence slow the ageing process. This design fea-

ture allows a 3 per cent increase in turbocharger speed for the same exchange

interval of 100 000 h.

To simplify installation and provide better access for servicing, ABB

designers also positioned the oil inlet and outlet sideways in the lower part of

the bearing casing.

Large bore two-stroke engines are boosted by up to four turbochargers,

depending on the number of cylinders. Pulsating compressor noise, typically

registered at around 30–50 per cent engine load, can be an issue due to today’s

higher power outputs. ABB notes that although it has no critical inﬂuence on

turbocharger operation, this noise phenomenon is unacceptable to many cus-

tomers. Noise prevention was therefore a high priority in designing the TPL91-

B since the turbocharger was intended for the highest powered engines. To

solve the problem, an inducer casing bleed system already applied successfully

as an option in many TPL85-B installations was selected. Engine tests with

the system (standard on the TPL91-B) demonstrated that it almost completely

eliminated pulsating noise.

ABB’s ﬁrst TPL80-B12 turbocharger with a new CV14 compressor stage

was tested in 2007 on a Mitsui-MAN B&W 7S60MC-C low-speed engine. In

addition to this larger compressor stage, the turbocharger has an improved tur-

bine with increased stagger angle and a modiﬁed gas inlet casing with a larger

gas ﬂow area. The turbocharger design’s extended capacity allows engines

to be ﬁtted either with smaller models or with fewer units for a given duty.

Market introduction of these larger capacity versions of the TPL-B series was

planned to start from mid-2007 with the TPL80-B, with the TPL77-B, TPL73-

B and TPL85-B (featuring a CV16 compressor stage) following.

TPl-C series

Building further on the TPL series, ABB developed the TPL-C for advanced

medium-speed engines, delivering the ﬁrst example in early 2004. By mid-2006

over 250 units were in service or on order, typically serving Wärtsilä 32C and

46F, MaK M43C and HiMSEN diesel engines as well as Bergen gas engines.

TPL-C turbochargers are available in three sizes (TPL67-C, TPL71-C and

TPL76-C) covering an engine power range from 3000 kW to 10 000 kW per

unit. Easier maintenance was sought from the compact, modular design, the

lube oil inlet and outlet located at the bottom of the turbocharger to facilitate

servicing, especially in conﬁned spaces. Installation ﬂexibility was also pur-

sued, different casing types and a range of options promoting optimized match-

ing to the speciﬁc engine application.

Turbocharger efﬁciencies of up to 70 per cent are achieved, depending on

the TPL-C model size and speciﬁcation. Air ﬂow recirculation for an improved

surge margin, wide compressor maps and reduced compressor noise (particu-

larly at part load) are among the design characteristics.

Increasing adoption of Miller timing (see earlier) on new four-stroke

engine designs—contributing to cleaner emissions by reducing the temperature

in the cylinders—dictates very high boost pressures for a constant bmep. Such

demands are addressed by the TPL-C series with compressor pressure ratios of

up to 5.0 (and even 5.2 with optional compressor cooling).

Since the engines for which the TPL-C turbocharger is designed may

use a pulse or quasi-constant pressure charging system, two dedicated tur-

bine designs are offered. The turbine blading for the two smaller model sizes

(TPL67-C and TPL71-C) for quasi-constant and pulse charging is stabilized by

lacing wire. The turbine for the larger TPL76-C model in quasi-constant pres-

sure systems features wide-chord blading.

TPL-C turbochargers can be delivered with an axial or radial gas inlet cas-

ing with either single- or multi-entry for optimum matching to the engine’s

charging system. Three large-diameter radial compressors cover a broad range

of volume ﬂow rates, the innovative design features including a bleed slot in

the compressor wheel shroud for air ﬂow recirculation. ABB explains that by

improving the ﬂow ﬁeld, this measure increases the compressor surge margin

and enlarges the map width without compromising efﬁciency. Strong second-

ary ﬂows and separations are avoided, which also helps to reduce the compres-

sor noise.

Compressor cooling, available as an option, extends the ﬁeld of applica-

tion for aluminium alloy wheels, offering an economic alternative to titanium

impellers when the highest pressure ratios are required. Such cooling is also an

option for customers requiring longer exchange intervals for these key compo-

nents. Good mechanical behaviour with minimal vibration levels is promoted

by a sturdy foot and newly designed ﬁlter silencer, which further contributes to

a reduction in noise levels.

a100 series

ABB’s latest development, the A100 series, was launched in 2007 to offer

compressor pressure ratios of up to 5.8 for high- and medium-speed four-stroke

diesel and gas engines, and up to 4.7 for low-speed two-stroke engines (Figure

7.20). Such performance represents a signiﬁcant step in the development of

single-stage, high-efﬁciency, high-pressure designs with aluminium compres-

sor wheels.

Three A100 series (-H for high-speed engines, -M for medium-speed

engines and -L for low-speed engines) are designed to achieve the highest

compressor pressure ratios for four-stroke engines as well as the highest efﬁ-

ciency at high pressure ratios for two-stroke engines. The turbochargers can be

exploited to raise the power density of engines and/or lower NOx emissions.

a100 series 207

208 Pressure Charging

New compressor stages with further optimized impellers and new diffusers

are incorporated. Compressor cooling is standard for four-stroke engine appli-

cations to underwrite the highest pressure ratios while retaining compressor

replacement intervals comparable to standard turbochargers. Newly developed

turbine stages and gas inlet and outlet casings are also featured.

The ﬁrst A100 generation model, the A140-M/H for high- and medium-

speed engines, was released in 2008 to offer full-load pressure ratios of up to

5.8 in continuous operation. The A135, A145 and A130 sizes were due to fol-

low, ABB aiming to have the complete A100-M/H programme available for

series production by mid-2009. A100-series frame sizes have the same outer

dimensions as the TPS turbochargers, and also like the TPS design, have the

oil inlet and outlet ducts integrated in the foot. This enables existing TPS-tur-

bocharged engine platforms to adopt A100 solutions without major mounting

changes.

A100 turbochargers are of modular construction with a minimized number

of components, and designed to enable matching to individual engine appli-

cations. Different casing materials are available for different turbine inlet

temperatures.

Speciﬁc design and conﬁguration features allow A100-M models to serve

small medium-speed engines arranged for heavy fuel burning and pulse tur-

bocharging. Since exhaust gas temperatures associated with such engines are

usually lower than those with high-speed engines, the bearing casing of the

A100-M models can be supplied with or without water cooling. Coated nozzle

rings and multi-entry turbine inlet casings are among other options.

An ABB-developed cooling technology allowed the continued use of alu-

minium for the compressor wheels of the A100 series, even at very high pres-

sure ratios and without compromising the high reliability and long component

exchange intervals expected from the material by operators. A change to more

expensive titanium components was thereby avoided. Cooling with compres-

sor air was shown by an extensive test programme to be the most efﬁcient

as well as the easiest and least costly solution for the enginebuilder to implement.

Figure 7.20 aBB’s new generation a100 series turbocharger