high temperature corrosion on turbochargers

Motor Ship Conference 2000, 29th & 30th March, Amsterdam

MET Motoren- und Energietechnik GmbH Rostock

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MECHANISMS OF HIGH TEMPERATURE CORROSION IN

TURBOCHARGERS OF MODERN FOUR-STROKE MARINE ENGINES

S. Bludszuweit, H. Jungmichel, B. Buchholz; Motoren- und Energietechnik GmbH

K. Prescher, H. G. Bünger; Universität Rostock, Institut für Energie- und Umwelttechnik

Abstract

Solid deposits with high vanadium and sodium contents as well as corrosion phenomena at

nozzle rings and blades of exhaust gas turbo chargers of 4-stroke diesel engines operated

with heavy fuel have been reported in an increasing number. At the same time, salt deposits

inside the intake and charge air channels have been found.

The investigation presented in this paper served the purpose to find the connections and

interrelations between sodium and vanadium contents in the charge air and in the fuel, and

fouling and high temperature corrosion at turbo chargers.

A series of test runs has been carried out using a heavy fuel operated test bed engine. During

this test runs the Na/V ratios inside the cylinder have been manipulated by injection of NaCl –

brine into the charge air or addition of sodium to the fuel. The fuel itself had a vanadium

content of 322mg/kg.

The results showed that corrosion phenomena could be reproduced within few operation

hours. The extent of corrosion was related to the Na/V ratio obtained inside the cylinder. It

has been found, that charge air channels, exhaust pipes and the circulating oil can act as

depots for sodium and vanadium making an accurate control of fouling and high temperature

corrosion at real engines extremely difficult.

At the end of the investigation a number of recommendations can be given to avoid or retard

turbo charger damage due to high temperature corrosion.

Introduction

An increasing number of failures at nozzle rings and blades of exhaust gas turbo chargers of

modern 4-stroke diesel engines (auxiliary engines mainly) operated with heavy fuel and at

high exhaust gas temperatures has been reported. Characteristic features of this damage are

the clogging of the nozzle rings (up to complete congestion) and the formation of firm

deposits of high vanadium and sodium content as well as formation of coke deposits.

This leads to increased exhaust gas temperatures, to destruction of the nozzle ring and blade

materials by corrosion and eventually to breakdown of turbo chargers.



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The causes and conditions for the formation of the contamination and the deposits, also called

fouling in shipping terms, and the consequences of it have so far never been analysed

thoroughly; and therefore no certified statements are available.

The corrosion observed together with high degrees of vanadium in the deposits and with

exhaust gas temperatures well above 500°C point to the high temperature corrosion, an effect

known for a long time in heavy fuel engines.

Departing from the above mentioned facts, experts of the ship owner A. P. Møller developed

the research task to investigate and determine whether the observed turbo charger damages

are due to high temperature corrosion and to which extent the sodium content in the intake air

is responsible for the damage. ABB Turbo Systems Ltd, Wärtsilä NSD AG (Switzerland) and

Octel Deutschland GmbH joined A. P. Møller to build an interest group looking for a

thorough investigation of the high temperature corrosion mechanism inside engines in order

to prevent future turbo charger damage.

The MET Motoren- und Energietechnik GmbH was commissioned to carry out this research

project. MET developed a research concept for the investigations necessary. The research

tasks were carried out together with the University of Rostock, Institut für Kolbenmaschinen

und Verbrennungsmotoren.

A study of the conditions leading to high temperature corrosion was undertaken at a test bed

engine by burning a vanadium-rich heavy fuel and by injecting NaCl brine of varying

concentrations into the intake air.

At the same time, condensate water taken from the intake air of engine plants in sea-going

ships (samples taken by Octel Deutschland GmbH) was to be analysed to determine the Na-

content.

High Temperature Corrosion

When burning ash-rich and sulphur-containing fuels in engines the exhaust gases cause

considerable corrosion at the metal surfaces they come into contact with. The degree of

corrosion is dependent on the composition of the fuels, on the material used, on the O2

contents of the exhaust gas and on the local temperatures.

Vanadium and sodium are mainly responsible for corrosion at high temperatures. Vanadium

and sodium are (apart from sulphur - up to 5%) contained in heavy fuels at ratios of up to 600

ppm and 200 ppm respectively. During the combustion process vanadium oxidises to V2O5

mainly, sodium forms Na2O and sulphates (NaSO4) which are able to further react with

vanadium oxides. The formation and structure of these sodium-vanadyl-vanadates are



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extensively described in the relevant literature /1//2//3//4//5/. Some of these compounds have

properties such as low melting point and oxygen transitions which are of decisive influence

on the corrosion. The following table shows some melting points of ash components resulting

from burning heavy fuel /6/:

Table 1.: Melting points of ashes from HFO

chemical composition melting points °C

V2O5 670

Na2O ⋅ V2O5 682

2Na2O ⋅ V2O5 643

Na2O ⋅ V2O4 ⋅ 5V2O5 535

5Na2O ⋅ V2O4 ⋅ 11V2O5 535

Na3Fe (SO4)3 543

Na2SO4 887

Fe2(SO4)3 720 (decomposition)

The melting characteristics of the system Na2O-V2O5 were studied by Pollman /1/ and

Wagner /7/. The results were summarised by Vögtle /2/ and are presented in Fig. 1.

Fig. 1: Melting temperature of HFO-ash dependent on Na2O ⋅ V2O5 ratio of the ash



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The behaviour of the compounds Na2O ⋅ 6V2O5 and 5Na2O ⋅ 12V2O5 is especially important.

According to: Na2O ⋅ 6V2O5 ⇔ Na2O ⋅ V2O4 ⋅ 5V2O5 + ½ O2 and

5Na2O ⋅ 12V2O5 ⇔ 5Na2O ⋅ V2O4 ⋅ 11V2O5 + ½ O2

a liberation of atomic oxygen takes place at the moment of solidification. This oxygen loosens

up the whole melting cake by forming bubbles and attacks the metal surface. During the

melting process the oxygen is absorbed again from the surrounding exhaust gas. The sodium-

vanadyl-vanadates thus act as an oxygen transmitter (oxygen pump) and transports the oxygen

to the metal surface during the processes of melting and solidifying at a temperature range of

530 - 600 °C.

The iron oxide formed in this process - nickel oxide in case of Cr-Ni steel - diffuses in the

melting cake. The result is an uninhibited attack of corrosion on the metal surfaces which are

exposed to the described temperature range. In heavy fuel engines the parts specially

concerned are outlet valves, piston crowns, nozzle rings and blades of the turbo charger.

The process of the slag deposits and the temporary corrosion attack on the engine components

partly depend on the total content of ash-forming elements and partly on the ratio they have

amongst themselves. Considering the melting behaviour mentioned above and the

examinations of diesel engine outlet valves, a Na/V-mass ratio between 0.08 and 0.45 is

especially dangerous /9/.

The range of the strongest corrosion corresponds to a Na/V-mass ratio of 0.15 to 0.30.

These and further examinations on the temperature dependant corrosion of iron and

chromium-nickel steels of different composition /3/ allow two main conclusions to be drawn:

• The ratio of Na2O : V2O5 and of Na : V has a decisive influence on the melting behaviour

of slag.

• The temperature of the components of an engine operated with heavy fuel decisively

determines the corrosion intensity.

Measurements at the outlet valves of diesel engines /9/ and at pistons /5/ confirm this finding.

The SO2 present in the exhaust gas also has an influence on the high-temperature corrosion. It

is bound by Na2O/V2O5 melting according to SO2 + V2O5 → SO3 + V2O4 and SO3 + Na2O

→ Na2SO4 and is found in all melting layers. Sodium sulphate once formed can however not

exist in melting of sodium vanadates and is set free, so it can also attack the surface of

materials. In addition surplus acid SO3 in a sulphurous deposit has the tendency to dissolve

oxides so that protecting oxide layers are destroyed.



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Electro-chemical examinations according to /3/ show that sulphates cause an increase in

corrosion at temperatures above 600°C which again is considerably increased when vanadyl-

vanadates are present.

An analysis of marine fuels on the market shows that the content of sulphur, vanadium and

sodium is fluctuating widely within the permitted range according to ISO 8217.

A comprehensive survey of fuels available world wide is published in the periodical ”Fuel

Quality Statistics” /15/ by DNV Petroleum Services. In Figure 2 the Na/V ratios in the

different fuels are shown for the years 1994/1995.

Fig 2.: Na-V ratio in heavy fuels according to DNV /15/

The composition of most of the fuels offered on the international bunkering markets are - as

far as their Na/V ratio is concerned in the range that enhances high-temperature corrosion.

On the way between bunkering and injection into the combustion process the analysis values

of the fuels can be changed by settling and separation treatment.

Fig. 3 presents a survey of the qualitative and quantitative changes during these processes.

The samples were taken from ships owned by A. P. Møller and analysed by DNV. It is

evident that between the bunker analysis and the analysis before separation the water contents

remains constant or can become lower presumably by settling processes. Both can be stated

for the Na content as well but not in proportion to the water contents. The separation process



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always brings about a reduction of Na content as well as a reduction of the water content. For

the single case of dry fuel analysed the separation also results in an Na fallout. A complete

elimination of Na particles in the fuel could, however, not be obtained in the samples

presented.

Figure 3.: Changes in Na and H2O content of heavy fuel during storage and separation aboard

ships

The contents of Na and H2O found in heavy fuel of a viscosity >400 cSt and reported in ”Fuel

Quality Statistics” 1994/1995 (15) were analysed. They do not show a connection or fixed

relation between the two contents, the partly considerable Na ratios, however, underline the

necessity of careful separation.

Analysis of Condensed Water in Intake Air

To analyse the salt input into the charge air 119 probes of condensate were taken from the

charge air of a number of ships on different routes. These probes were analysed for their

contents of sulphate, chloride and nitrate as well as potassium, sodium, calcium and

magnesium.

According to the schedule the following samples of charge air condensates were taken and

examined:



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1. 13 samples of condensate from the charge air cooler of MV ”Washington Senator” on the

route Japan – Europe. The analysis results are shown in Figure 4.

2. MV ”Kate Maersk” on route between Europe - East Asia and back

- 58 samples from the charge air flow of the main engine MAN B&W 12K90 MC, the

condensate being obtained by means of an Octel Deutschland GmbH cooling trap.

- 38 samples from the condensate drain pipe of the auxiliary diesel engine of the type

MAN B&W Holeby 7L32/40

3. 10 condensate water samples from MV ”Maersk Flanders” under heavy sea conditions on

the route Scheveningen - Folkstone.

The analysis was carried out to show which magnitude the sodium portions take in form of

aerosols, i.e. in finely christalline form in the sea air. They precipitate in the cooling trap

together with the condensed water vapour parts of the air.

The portion is obviously very small and a noticeable portion can therefore only get into the

engine with liquid sea water in spray form.

Figure 4.: Results of condensate water analyses. Samples taken from the charge air cooler of

MV “Washington Senator”.

Engine analysis



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A study of the conditions leading to high temperature corrosion was undertaken at a test bed

engine by burning a vanadium-rich heavy fuel and by injecting NaCl brine of varying

concentrations into the intake air. The effects of fouling and high temperature corrosion were

analysed by means of a test probe body (particle catcher) inside the exhaust channels.

Test bed layout

A heavy fuel burning diesel engine of the type 3VDS24/24 was used for all engine analyses.

Table 2 shows the main engine parameters.

The Na salts were injected in the intake air as a watery solution through a pin-jet impinging

nozzle. By means of special entering holes the nozzle could be arranged before or after the

charge air cooler. The brine tank connected to the nozzle was kept under a defined pressure

during all tests. The brine tank was placed on a weighing apparatus. The injected amounts

could at all times be observed.

Table 2.: Main parameters of test bed engine 3VDS24/24 AL-1

Typ 3VDS24/24 AL-1Mixture formation procedure direct InjectionCharging exhaust gas turbo chargerStroke s [mm] 240Diameter D [mm] 240Compression ratio ε [ ] 13Effective power Pme [kW] 500Maximum pressure pmax [MPa] 14Effective mean pressure pe [MPa] 1,80Rotation per min. n [min-1] 1000Strokes 4Charge air pressure pL [MPa] 0,27Charg. air temp. before cooler TLvK [°C] 170Charg. air temp. after cooler TLnK [°C] 50Exh. gas temp. before turbine TAVT [°C] 540Specific fuel consumption [g/kWh] 199Air flow rate le [kg/s] 2,23Combustion air ratio λv 2,2

A heavy fuel oil with a high metal content was taken for the performance of all test runs in

order to obtain a high Na2O-V2O5 concentration in the exhaust gas at short engine runs and

thus obtain visible Na2O-V2O5 deposits in a short a time as possible. The vanadium content in

the fuel was 322 mg/kg, the sodium content was 56 mg/kg. These, like all the other

characteristic fuel values were within the ISO norm 8217. The preparation of the fuel was

done by means of a separation. During this procedure the vanadium concentration changed

but little compared with the raw fuel, the sodium content decreased, however, clearly.



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The cleaned fuel for all test runs was kept in a large tank from which the amount needed for

each test run was discharged into a day tank. Here the dose of watery Na-salt solution was

added to obtain a defined Na/V ratio (Test run No. 3 and 4 only). The fuel homogenisation

was obtained by constant recirculation using a gear pump.

To analyse the fouling and corrosion effects obtained during the different test runs a particle

catching device was to be entered into the exhaust channels. The particle catcher was to be

removed after each test run and the deposits to be analysed regarding weight, composition and

corrosive effect. The particle catcher was a specially built test probe in a purpose-built holder

which was placed in the exhaust gas duct immediately in front of the nozzle rings of the

exhaust gas turbo charger in such a way that an ash layer was formed under the same

temperature conditions as at the nozzle rings. The electric heating of the probe which was

considered first proved to be unnecessary as preliminary tests did not show a difference in

temperature of more than 1°C between exhaust gas and particle catcher. To prevent soot

deposits during the starting phase a protective pipe was arranged over the probe body which

could be easily removed once the required temperature was reached.

To keep the test bed engine runs as economic i.e. as short as possible examinations were

carried out to optimise the shape of the probe body for catching the deposit of Na2O-V2O5.

Variants considered were a circular form and a semi-circular form flattened in the counterflow

direction. Both were tested regarding their suitability for the catching of Na2O-V2O5 particles.

The examination included a Computational-Fluid-Dynamics analysis (CFD analysis) of the

exhaust gas flow around the probe body to show the velocity field, the particle flow lines as

well as the amount of particles landing on (and sticking to) the body. When summing up the

particles that stuck to the probe parts and their percentage there was a difference of 1% in

favour of the semi-circular probe. This is a minimum difference and since the circular probe is

easier to produce and as heating as well as temperature measuring are more conveniently to be

placed in the circular probe the decision was taken in favour of the circular form.

The knowledge about the flow pattern around the probe which was obtained from these CFD

analyses (see Figure 5) proofed to be very important for the later explanation of the fouling

layers around the probe bodies.

Seven probe bodies were manufactured. They were made from the original axial nozzle ring

of a turbo charger VTR 304 of ABB.



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Figure 5.: Flow pattern around the circular particle catcher inside the exhaust channel (in front

of the turbo charger

During the test runs residues from the burning process were deposited on the probe bodies and

corrosion products were formed. In order to determine the value of the corrosion the deposits

and corrosion products had to be completely removed from the probe body. This was done by

means of an etching process that did not attack the probe material but completely removed the

deposits. The corrosion effects were determined by weighing the probe body before the test

run, after the test run, and after the etching procedure.

The ash particles carried in the exhaust gas flow and their amount and composition compared

to the ash components on the probe body are worth knowing. Therefore a partial exhaust gas

flow was taken and analysed using an ICP-OES device.

Test bed runs and results

8 test runs of 4h to 10 hours each were carried out with the following aims:

Table 3: Test bed runs carried out within the investigation

Test scope of test run

1 check of test bed set-up, critical Na/V-ratio by injection of NaCl- brine in charge air

2 Na/V-ratio adjusted by injection of NaCl- brine in charge air, NaCl surplus to



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compensate for deposits in the charge air ducts

3 effect of the critical Na/V ration in the fuel

4 effect of the critical Na/V ration in the fuel

5 effect of the critical Na/V ration in the charge air, brine injection after charge air

cooler, investigation of demister effect of charge air cooler

6 effect of the critical Na/V ration in the charge air, brine injection before charge air

cooler, investigation of demister effect of charge air cooler

7 examination of the effect of the heavy fuel additive PLUTOcen FW-M

8 comparison run with diesel fuel without addition of sodium or vanadium

In all engine examinations the vanadium content in the fuel amounted to 322 mg/kg. The Na

content resulted from the ratio contained in the fuel and the amount added by additional

doses. Table 4 shows the pertaining ratios in the initial fuel, the theoretically obtained

composition and the place of addition/injection together with the corrosion results.

During all test bed runs the probe body acting as particle catcher had a temperature of

between 550° and 560° C.

Table 4.: Na/V ratios for different test bed runs and material losses due to corrosion

NR. Na/V ratio

in fuel

location of

NaCl-addition

Na/V ratio

obtained

loss due to

corrosion mg

1 0.15 after intercooler 0.23 2.02 0.15 after intercooler 0.27 3.03 0.15 fuel 0.24 5.14 0.08 fuel 0.22 2.55 0.17 after intercooler 0.34 deposits could not be

removed completely

6 0.17 before intercooler 0.34 0.27 0.17+PLUTOcen before intercooler 0.34 0.28 0 (DK) without 0.00 0.3

Test bed run 1

The sodium concentration in the initial fuel was 56 mg/kg. Further Na was added by injection

of a NaCl brine into the charge air behind the charge air cooler up to the critical Na/V ratio =

0.23.

After 10 hours of operation marked salt deposits were visible in the intake duct (Fig. 6).



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Figure 6.: Salt deposits inside intake ducts after test bed run 1

This means that part of the injected sodium-chloride brine hits the duct wall prior to its

evaporation in the intake air flow and only evaporates later from this wall leaving the sodium

chloride as a deposit on the duct wall. Because of this process of an uncontrolled precipitation

of sodium chloride from the charge air an exact determination of the Na/V ration inside the

cylinder (i.e. during combustion) is problematic.

Ash particles were deposited on the whole probe body, their colour changed very clearly

depending on the position at the probe with respect to the flow direction of the exhaust gas.

Whereas the deposit showed a dark brown colour on the side of the direction of the flow it

showed a light brown colour on the reverse side and a yellowish one in the transition area.

The structure and adhesion strength of the deposit also showed considerable local differences.

The deposits were of crystalline character, and they were loose, soft and less adhesive in the

efflux area and dense, hard and strongly adhesive in the inflow area.

After etching the deposit away there were no optically visible changes due to corrosion to be

found on the probe surface. Nevertheless a loss of mass of 2 mg was registered.

Test bed run 2



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Because of the salt deposit created during test bed run 1 the desired Na/V ratio of 0.24 could

not be obtained in the combustion chamber of the engine. Therefore a higher salt

concentration in the brine was injected. The other conditions remained unchanged.

After 5 hours of operation a deposit had formed on the probe body but in contrast to test run 1

the colours were more clearly differing.

In spite of the shorter operating time a loss of mass of 3 mg was registered after etching off

and the surface showed corrosion effects in the form of pitting. The rough surface (processed

by cutting) favoured the corrosion attack. The changes in the surface structure were, however,

only found at an angle of 90° of the efflux flow direction of the exhaust gas.

Test bed runs 3 and 4

The Na/V ratio in the fuel in test bed run 3 was set to 0.24. There was no NaCl-brine added to

the intake air.

The picture of the deposit formation on the probe body did not differ from that of test bed run

2 (Fig. 7), the loss of mass due to corrosion was, however, distinctly higher and amounted to

5.1 mg after only 5.5 hours of operation.



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Figure 7.: Deposit formation around the test probe

Compared to test bed run 2 this run shows clear traces of corrosion attack at an angle of 60° -

90° of the inflow direction ( Fig. 8) whereas the areas of 0 and 180° show almost no visible

corrosion. A picture taken by means of a raster electron scan microscope (REM) clearly

shows the beginning of pitting (Fig. 9).



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Figure 8.: Corrosion marks at the probe body after test bed run 3



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Figure 9.: Corrosion traces at probe body 3, enlargement 40:1 (REM)

The repetition of test bed run 3 in test bed run 4 but with insignificantly smaller Na content

(Na/V = 0.22) and a shorter operation time of only 4 hours confirmed the results. The loss of

mass of the probe body incurred due to corrosion was 2.5 mg.

The composition of the ash deposit was locally analysed and photographed by means of an

energy dispense x-ray spectroscope (EDS). The analysis shows that at angles of 90° and 270°

in the inflow direction the Na/V ratio of the deposit is much closer to the critical value than

the composition at 0° and 180°.

Test bed run 5

Departing from a Na/V ratio of 0.17 in the fuel, a clear surplus of NaCl brine was injected

into the intake after the charge air cooler. The theoretical amount was 0.34. The colour of the

ash deposited on the probe body did show almost no changes compared with the previous test

runs.

The composition of the slag deposit obtained by means of EDS resulted in the following data:

Table 5.: Composition of deposits at probe body 5

element in inflow direction

% (m)

90° of inflow direction

% (m)

O 73.7 71.2

Na 2.4 1.5

S 4.0 3.8

V 13.5 17.7

Ni 2.8 2.4

Na/V 0.18 0.08



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The etching procedures to remove the deposit carried out twice as often as in the other tests

could not remove a very fine layer of dark colour. Only very tiny traces of corrosion were

visible.

Test bed run 6

The test run conditions corresponded to those of test bed run 5 the only difference being that

the brine was injected before the charge air cooler.

Considerable less ash than in test run 5 was deposited on the probe body. The colours did not

show any difference. After etching off a completely clean surface was obtained. There was no

loss in mass registered.

Test bed run 7

Test bed run 7 corresponded in all but one condition to test bed run 6 the difference being an

addition of the heavy fuel additive PLUTOcen FW-M to the fuel.

A bright, very loosely adhering deposit was obtained on the probe body the major part of

which could easily be removed mechanically. An one-time melting in the etching liquid

resulted in a complete removal of the deposit. An unchanged clean surface was obtained

showing no loss of mass due to corrosion.

Test bed run 8

This test bed run was carried out with pure diesel fuel and without sodium salt brine added to

the intake air. It produced a yellow-white deposit on the probe body. The volume of the

deposit was, however, little and consisted mainly of calcium and sodium sulphates with but a

few vanadium parts. The EDS analysis showed 0.8 % vanadium. The particle emission was

0.19 g/kWh.

An analysis of the lubricating oil carried out for control purposes yielded the following

results:

Table 6: Results of lubricating oil analysis before and after all test runs

elements used oil after tests fresh oil prior totests

Na 49 mg/kg 9 mg/kgV 24 mg/kg 0

The exhaust gas turbo charger was dismounted and examined after all tests had been carried

out. The deposits on the nozzle rings had reached a considerable volume (Fig. 10).



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Figure 10.: Deposits on nozzle ring

Also the exhaust gas manifold before the turbo charger and the turbine wheel showed deposits

containing mainly vanadium. Whereas the brown deposits on the nozzle rings and the exhaust

manifold did not contain any soot components, there were small amounts of soot on the

turbine rotor visible by its black colouring.

The following element composition was measured:

Table 7.: Composition of deposits on different engine components

element nozzle ring

%(m)

turbine vane/blade

%(m)

exhaust manifold

%(m)

V 16.8 13.8 19.4Ca 4.8 10.4 7.5Fe 4.8 5.6 3.5

sulphate 1.6 1.9 1.8Na 3.9 1.9 3.8Ni 2.9 1.3 2.5

Summary

The results obtained in the individual test bed runs and the deposits on the particle catchers in

the exhaust gas duct and on the nozzle rings are a convincing proof that the exhaust gas turbo

charger of a heavy fuel operated engine is subject to considerable corrosive loads depending

on the ash particles emitted.

At exhaust gas temperatures between 530 and 560°C the amount of the adhesive ash and the

extent of corrosion are visibly depending on the vanadium and sodium ratio present. This is

clearly seen in test bed runs 3 and 4 where the rate of corrosion correlates very closely with

the melting behaviour of the sodium-vanadates.



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When adding NaCl brine to the engine intake air after the charge air cooler beginning

corrosion was also found (see test bed runs 2 and 5), albeit considerably less than in test bed

runs 3 and 4.

A new finding is that during the engine operation the relevant elements Na and V from the

fuel and the Na from the charge air are deposited at different places where they form depots or

buffers. Vanadium particles are found in the lubricating oil and bound to ash in the exhaust

gas duct. Sodium is found in the lubricating oil and the intake air ducts.

From these depots sodium and/or vanadium can be released uncontrolled at a later time and

possibly at another operation state of the engine and enter the combustion process and cause

fouling and/or high-temperature corrosion. The storing or depots areas for sodium and

vanadium are shown in Fig. 11.

Because of this depot mechanism high-temperature corrosion can even take place when the

Na and V salts entering the engine with the fuel and the intake air do not possess a critical

ratio. This is hinted at by the results of test bed run 8 where deposits of a high Na content

were formed on the probe body although the test was run with ash-free diesel fuel and without

any NaCl brine injection.

Due to the load depending depot formation (temperature state of the engine, conditions of the

charge air) the appearance of fouling or of high-temperature corrosion cannot directly be

controlled, i.e. the time of their appearance can not be predicted from the Na and V particles

introduced through the fuel and the charge air. The decrease of the Na content in the newly

bunkered fuel by means of separation also cannot prevent a depot formation but it may delay

it in time. At other critical load states, e.g. at high exhaust gas temperatures, fouling or high-

temperature corrosion can occur even if the fuel used and/or the charge air do not show any

critical Na-V values at the time.

Summing up the project results can be stated as follows:

• The influence of salty aerosols in the intake air of heavy fuel engines on the formation ofdeposits, i.e. fouling which are considered to be the starting basis for high temperaturecorrosion could be detected.

• Addition of NaCl-brine as aerosol to the charge air to obtain critical Na/V ratios did notshow the same effect as analogous additions to the fuel.

• Deposits of a high content of Na (on the test probe body) were generated also at engineoperation with ash free diesel fuel and without NaCl addition to the charge air.

• Ratios of Na and V were discovered in the lubricating oil and in deposits in the exhaustgas tract of the engine, so that it can generally be assumed that ratios of vanadium arepresent in the lubricating oil as well as in the exhaust gas tract and ratios of sodium are



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present in the charge air channel, in the lubricating oil and in the exhaust gas tract in theform of deposits.

• When PLUTOcen FW-M was added to the fuel the deposits on the probe showed a veryloose, mechanically removable structure and there were no corrosion effects to be found.This shows the favourable effect of the additive due to the increase of the reactiontemperature of the vanadium-vanadate.

• The engine run no. 8 with diesel fuel and the analyses of the lubricating oil as well as ofthe deposits in the exhaust gas tract yield the following conclusions:The lubricating oil and the deposits practically form depots for sodium and vanadiumwhich are formed or increased by any Na-V input from the outside. At another engineoperation state these deposits can uncontrollably release sodium and/or vanadium into thecombustion process, form deposits and cause high temperature corrosion even if thepresent ration of the Na-V admission from the outside, from the fuel or the air is notcritical (Figure 11).

charge air cooler

Intake air

exhaust gas

test probeturbo charger

charge air channel

Exhaust gas channel

NaV,

Fuel

Na

lubricating oil

charge air channelexhaust gaschannel

Na

V

fuel

Charakter explanation:

Feeding: Na by charge airand fuel

V by fuel

Depots: Na

Na , V

Figure 11.: Sodium and vanadium depots inside the engine

Conclusions and Recommendations

To prevent or redeem fouling and/or high-temperature corrosion from melt layers in diesel

engines operated with heavy fuel (the formation of which cannot be predicted exactly because



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of the existence of sodium and vanadium depots) the following statements and suggestions

can be made at the present stage of knowledge:

• Use of uncritical fuels wherever possible, i.e. fuels with a low content of vanadium and an

uncritical Na/V ratio as is shown in Figure 2.

• Decrease of the Na content in the heavy fuel to the lowest level possible by separation.

• In practical engine operation prevent exhaust gas temperatures higher than 500°C

(remember that cylinders may deviate from the mean value).

• Installation of efficient demisters in the charge air duct system minimises Na entry in form

of aerosol or over-saturation through spray.

• Addition of Mg-salt based heavy fuel additive (PLUTOcen FW-M of Octel Deutschland

GmbH) showed a favourable effect by pushing the reaction temperatures upwards. A long

term study should be carried out and the results should be made available.

These generalised statements can be made with sufficient conviction from the results obtained

in the project. It has to be underlined, that the tests as far as influencing factors, operation

parameters of the engine and sodium-vanadium ratio are concerned, were carried out under

conditions which are realistic but not often to be found under practical engine operation

conditions and which are not often to be encountered on board in such an “optimum”

combination regarding high temperature corrosion. The choice of these conditions served the

sole purpose to obtain reliable results of the engine runs in a short time span, that is in a time-

lapse motion. The results obtain confirm the correctness of the conditions chosen. The same

processes will take place on board sea-going ships, but slower.

4-stroke engines operated with heavy fuel will for a long time continue to be a main

propulsion and energy system in shipping, some trends are even indicating their extension.

Therefore the issue of turbo charger fouling and high-temperature corrosion will continue to

exist until solutions will have been found for their complete prevention (of damage). It is to be

expected that fuel and engine producers/manufacturers as well as users/operators will have to

co-operate in this task.

Literature/1/ S. Pollmann, Mineralogisch-kristallografische Untersuchung an Schlacken und Rohrbelägen

aus dem Hochtemperaturbereich ölgefeuerter Großkessel; Mitteilungen der VGB(1965), H.94,S. 1-18

/2/ G. Vögtle, Einsatz von Kraftstoffen schlechter Qualität in Dieselmotoren; Schiff &Hafen(1978), H.8, S .690-692

/3/ A.J.B. Cutler, Die derzeitigen Probleme durch rauchgasseitige Korrosionen bei der CEGB undneuere Forschungen zu deren Lösung; VGB Kraftwerkstechnik (1974), H.9, S. 611-619

/4/ H. Pleiming, W. Vormstein, Auslaßventile für Schwerölmotoren; Hansa (1975) H.8, S. 583-588



22

/5/ D. Schlager, Materialabtrag an Kolben von Großmotoren, MTZ 55 (1994), H.5, S. 300 – 307/6/ D. C. Lewis, H. J. Goldberg; Richtlinien für ein erfolgreiches Brennstoffaufbereitungs

programm; Archiv für Energiewirtschaft (1979), H.5, S. 471 – 485/7/ E. Wagner, Diss. Hannover (1964)/8/ W. Lowe, High-output medium speed engine for marine propulsion using residual fuel;

Combustion Engine Progress (1966), S. 46 – 52/9/ P. Burmester, Diss. Rostock (1971)/10/ Gröber / Erk, Die Grundgesetze der Wärmeübertragung; Springer-Verlag,

Berlin/Göttingen/Heidelberg, 1963, S.246/11/ Jedlicka, H., Werkstoffschädigung durch Hochtemperaruekorrosion bei Dieselmotoren, VDI-

Bericht 236, 1975, S. 163/12/ Kurze, K., Probleme des Schwerölbetriebes von mittelschnellaufenden Vietakt-

Tauchkolbenmotoren, Zeitschrift Seewirtschaft, 1974, Heft 8, S.474/13/ Buch-Übersetzung : Gas Turbine Principles and Practice, Kapitel: Mechanismus der

Ablagerungsbildung, London,/14/ New Sulzer Diesel, Maintenance- Documents, RTA72U, 1993, Air Cooler / Demister/15/ DNV Petroleum Services, Fuel Quality Statistics, September 1995, Vol. 15, Nr. 3