151

1 INTRODUCTION

Vegetable oilcan be used as analternative fuelfor

diesel engines and for heating oil buners. When

vegetable oil is used directly as a fuel, in either

modified or unmodified equipment, it is referred to

asstraightvegetableoil(SVO)orpureplantoil(PPO).

SVOshavesomeadv

antagesincomparisonwithfuel

oils such as: renewability, local availability, lower

sulphur content, avoiding the environmental issues

causedbysulphuricacid,loweraromaticcontentand

high biodegradability [1,2]. However, SVOs also

attach several disadvantages suchas: high viscosity,

lowheatingvalue,highfattycontent,influencingon

injection process and causing engine  coking if

misused.

Table1.Featuresofblendedpalmoil

________________________________________________________________

No FuelcharacteristicBlendedfuelsandDO

DO PO10 PO20 PO30 PO100

________________________________________________________________

1 Densityat15

C,[kg/dm

]0.8464 0.8538 0.8599 0.8668 0.9225

2 Viscosityat40

C,[cSt] 2.63.42 5.31 6.45 40.24

3 Cetanenumber 42.89 50.13 50.91 52.11 52.92

4 Flashpoint,[

C] 72 73 75 77 135

5 Freezingpoint,[

C] ‐6‐1 1 2 16

6 LowerHeatingValue,[MJ/kg] 43.4 39.72 39.55 38.69 37.11

________________________________________________________________

Fuel Continuous Mixer

–

an Approach Solution to Use

Straight Vegetable Oil for Marine Diesel Engines

D.VanUy&T.TheNam

VietnamMaritimeUniversity,Haiphong,Vietnam

ABSTRACT:Thevegetableoiliswellknownasgreenfuelfordieselenginesduetoitslowsunphurcontentand

renewable stock. However, there are some problems raising when vegetable oil  is used as fuel for diesel 

engines such as highlyeffected by coldweather, lower generalefficiency, separation in layer if mixed with

dieseloilandsoon.Toovercometha

tdisadvantiges,theauthorsproposeanewideathattouseacontinuous

fuelmixer to blend vegetableoil with diesel oiltomake so called a  mixedfuelsupplying to diesel engines

inline.Inordertoensureaqualit

yofthemixedfuelcreatedbycontinuousmixer,ahomogeneoustestingwas

introducedwithbelievableresults.Then,thecontinuousmixerhasbeeninstalledintofuelsupplysystemof

dieselengine6LU32atalabofVietnamMaritimeUniversityintermsofcheckingarealoperationofthefuel 

continuousmixerwithdieselengine.

http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 12

Number 1

March 2018

DOI:10.12716/1001.12.01.17

152

To prevent such bad effects, a blended fuel

between SVOs and diesel oil is one of potential

solutions. Table 1 shows the physical features of

mixeddieseloilwithpalmoil[3].

InordertoapplyblendedSVOsfordieselengines

and particularly for marine diesel engines, there

shouldneed

apropermodificationoftheenginefuel

supply system. In this paper, there will introduce a

methodtocreateafuelcontinuousmixingsystem(or

fuelcontinuousmixer) to produceonlineablended

fuelormixedfuel(SVOandDO)usedasalternative

fuelformarineapplication.

2 FUEL

CONTINUOUSMIXERDESIGN

Based on the theory of mixing fluid and the

requirements of the fuel quality for marine diesel

engines[4,5],theauthorshavedevelopedatheoretical

methodtodesignafuelcontinuousmixer.Thequality

ofamixedfuelcanbeunderstoodonbase ofalevelof

homogeneousness

 of mixed fluids. The higher is

degreeofhomogeneousness,thebetterisqualityofa

mixed fuel. To assess the quality of mixed fluid or

effectivenessofthecontinuousmixer,itnormallyhas

to use a concept so called a “mixing time”. So, in

general, the quality of the fuel

continuous mixer is

definedasfollowing[5]:





,, ,,

Q f t V N impeller type



  (1)

where:Q—qualityofmixing;t

m—mixingtime[s];V —

volume of mixing fluid [m

]; N—speed of impeller

[rpm];μ—dynamicviscosity[cP].



Figure1.Continuouslymixingmechanism

Toensurethequalityofamixingprocess,aflow

pattern created by the impellers must be selected

properly. Therefore, a type of impeller must be

chosen properly and then the fluid flow pattern, as

well as the mixing mechanism will be visible as

shown in Fig.1. In this article, a

 proper type of

impelleristheturbineflatblade,becauseitcancreate

twozonesofafluid flow: one is aboveandotheris

belowtheimpeller.Thankstosucharrangement,the

mixing quality will not be affected by the input of

fluids.

Anideaofafuelcontinuous

mixeristhataninput

offluidsmustbeequaltooutputoneandisalsoequal

tothefuelconsumptionofadieselengine.

.[/]

in out f e e

QQ GNgkgh





 (2)

where: Q

in and Qout — input and output of fluids 

respectively [kg/h or m

/h];

—output of diesel

engine [kW];

—specific fuel consumption

[kg/kWh].

Asmentionedabove,themixingqualitydepends

on some factors, but the mixing time is a main one

anditisalsoafunctionofacirculationtimeoffluid

insidemixing tank. Therefore, in order to assess the

mixingquality,anumberoftimesoffluid

circulation

mustbetaken into consideration. For asingle‐phase

liquidinamixing tank withsome baffles and small

impeller, the relationship between mixing time and

circulationtimeisasfollow[6,7]:

4[]

tts



 (3)

where:

—mixingtime[s];

—circulationtimeand

it can be determined by a formula as:













, ρ—

density of mixed product; Δρ—difference of density

between the liquids to be mixed; N—number of

revolutions of impeller per minute [rpm]; d—

diameter of impeller[m]; H—height of liquid in

mixing tank; g—gravity acceleration [m/s

]; a—

constantdependingonatypeofimpeller.

However,inrealityoffluidcontinuousmixer,the

circulation time is very difficult to be measured.

Therefore,morepraticallythecirculationtimewillbe

subtitutedbya“remaining time”[3].Theremaining

timeisatime,inwhichanelementofmixed

product

willberemainedinsideofmixingtankforcirculation

untillitsdischargeout.Lettakeanyelementofmixed

producttobeconsideredand foundthatanelement

ofmixedproducthasagoingwayfromthetoptothe

bottomofmixing tankasshowedintheFig.1

andthe

elementofamixedproductisaffectedbytwoforces.

OneisthecentrifugalforceF

Randanotherisasumof

the gravity force and additional force created by

liquid moving down due to output of the mixed

product.So,therecansummarizethattheelementof

mixed product will be affected mainly by a level of

mixed product moving down with a velocity /v

down/.

Therefore, a remaining time of the product element

insidethemixingtankcanbecalculatedasfollow:

tan

[]

remain

down



 (4)

In which:

remain

—remaining time of mixed

product in mixing tank [s];

down

—velocity of the

productlevelmovingdown[m/s];

tan

—volumeof

mixingtank[m

];G —outputofmixedproduct[m

/s].

Finally, the remaining  time can be determined as

follow:

153

.. .

[]

remain

CDH





 (5)

and

[/]

3,600.

Gms





 (6)

here: D—diameter of mixing tank [m];

—specific

fuel consumption of a diesel engine [g/kWh]; ρ—

density of mixed product or fuel [kg/m

]; C‐storage

coefficientoftankcomplyingwithclassificationrules

withvaluefrom1.5to2.

Inaccordancewithexperimentalresults,aquality

ofmixedproductwillbesatisfied,ifthemixingtime

issmallerthanfrom2to3timesofremainingtimeof

product[3].



23.

mremain

tt

 (7)

Therefore, the remaining time /

remain

/ is a key

factor that must be taken into consideration during

designofafuelcontinuousmixer.

For design application, there must use shape

factorsfromS1toS9asdefinedinTable2andFig.2

[6,7].

Table2.Shapefactors

_______________________________________________

Shapefactor RatioValues

_______________________________________________

S1T/D3

S2Z/D0.75‐1.3

S3L/D0.25

S4D/W5

S5T/B6

S6H/D2.7‐3.9

S7Numberofimpeller6

S8Pitch/angle0deg

S9Numberofbaffles 4

_______________________________________________



Figure2.Shapeparameterofmixer

Designingofthefuelcontinuousmixermeansthat

ithastocalculateallparametersasmentionedinthe

Table2,aswellastomeettheconditionasmentioned

in Eq. (7). To complete design process, it must go

throughseveralstageswhichshouldneedacomputer

supportfor calculation. A

 calculation algorithm of a

fuelmixerparametersispresentedinFig.3.

3 USINGCFDSIMULATIONFOREVALUATING

THEMIXTUREQUALITY

Inthescopeofstudyondesigningafuel continuous

mixer, a computational fluid dynamics (CFD)

simulationis usedto evaluate the qualityof blends,

optimizing the mixerʹs performance.

ANSYS Fluent

softwareis the most powerful and suitable that

includes well‐validated physical modeling

capabilitiestodeliverfast,accurateresultsacrossthe

widestrangeofCFDandmultiphysicsapplications.



Figure3.Calculationalgorithmofmixerparameters

Applying for mixing liquids in the cylinder type

mixer, CFD simulation is built upon the primary

equations:

 Continuityequation:

uvw

xyz









 (8)

 Navier–Stokesequations

1dV

F gradp v V









 (9)

154

In which:

),,( wvuV



‐ velocity vectorof survey

liquid element;



‐ strain tensor; : Laplacian

operator.

The simulation focuses on distribution of two

undissolved liquid phases, including vegetable oil (

let take palm oil‐PO) and diesel oil. Based on the

designed parameters of fuel continuous mixer

(temparature, impeller profile, positions of impeller

anddischargemouth,etc.),thephasehomogeneityof



a mixed fuel depending on impeller speed and PO

ratiointhe mixture,  shall be reviewed,specially the

optimummixturetime.

3.1 Typicalcasestudy:

1 Case of constant impeller speed (60rpm) and

variablemixtureratioleadstotheresultsinFig.4.

Itcanbeseenclearlythatat

mixingratioof20%,

PO molecules dispose in the diesel oil with high

density and occupy a large portion of

experimentedarea.



Figure4.Casestudywithimpellerspeedof60rpm

2 Case of constant mixing ratio at 20% PO and

adjusted impeller speed brings to the Fig.  5. The

results show that at speed of 50rpm, almost PO

phaselocatesnearbythevalueof20%butstillhigh

amplitude.Whenthespeedofimpllerisincreased,

theamplitudewillbemore

concentratedatcenter.

However, there is not much diffrence between

60rpm and 70rpm or more, so the result can be

acceptableinordertosaveenergyprovidingtothe

mixer.



Figrue5.Casestudywithmixingratioof20%PPO

4 TESTOFFUELCONTINUOUSMIXER

The above study is impemented in regards to using

palmoilasalternativefuel formarineapplication.A

marine diesel engine selected to be an investigation

objectisHANSHIN6LU32(Japan)whichisnormally

used as main engine of vessels with capacity from

1,500 to 2,500

 DWT. The technical specifications of

this diesel engine are shown in the Table 3 and

physicalfeaturesofthepalmoilinTable1.

Table3.Technicaldataofdieselengine

_______________________________________________

TechnicalparametersValue

_______________________________________________

Numberofcylinders6

Revolution[rpm]340

Effectivepower[kW]970

Cylinderbore[mm]320

Stroke[mm]510

Specificfuelconsumption[g/kWh] 200

Max.pressure[kG/cm

]90

_______________________________________________



Onabaseofthecalculationalgorithm(Fig.3)and

the technical data of diesel engine 6UL32 together

withthephysicalfeaturesofpalmoiland dieseloil,

required parameters of a fuel continuous mixer

applied for this diesel engine is calculated and

presentedinTable4.

The fuel continuous

mixer then was built and

installed in fuel supply system of marine diesel

engine6UL32attheCenterforMarineDieselEngine

Research (Vietnam Maritime University) upon the

diagramonFig.6.

Therealproductionsystemandsamplesofmixed

fuel(blendedfuel)areshowedinFig.7.



10%PPO

Mixingtime:54s



20%PPO

Mixingtime:92s

30%PPO

Mixingtime:138s

50rpm

Mixingtime:54s

60rpm

Mixingtime:92s

70rpm

Mixingtime:95s

155

Table4.Theparametersoffuelcontinuousmixer

_______________________________________________

TankdiameterD[m]0.6

Impellerdiameterd[m]  0.2

Numberofblades6

WidthofimpellerW[m] 0.05

LengthofimpellerL[m]  0.1

WidthofbafflesB[m]  0.06

HeightofliquidH[m]1.0

Distancefromimpellertotankbottom0.2

_______________________________________________



Before running the engine with blended fuel,

samples of mixture were taken to scientifically

examine on homogeneity by a microscope Axio Lab

A1. At each mixing ratio, there were two samples

collectedatdifferenttime:T1andT2.

The Table 5 and Fig.8 shows the result of visual

experiment.

Table5.Testingresultoffuelsamples

_______________________________________________

MixingMixing Maximummolecule

ratiotime[s] ofpalmoilinblendedfuel[μm]

_______________________________________________

PO10‐T16042

PO10‐T212015

PO15‐T110047

PO15‐T220051

PO20‐T112015

PO20‐T22408

PO20Online‐T1 18035

PO20Online‐T2 36012

_______________________________________________



Beforemixing Beforeonlinemixing



PO10‐T1 PO10‐T2



PO20‐T1 PO20‐T2



PO20Online‐T1 PO20Online‐T2



Figrue8.SamplesseenbymicroscopeAxioLab.A1

Itcanberecognizedthat:

 As homogeneity of palm oil in diesel fuel over

95%,thequalityofblendedfuelisconfirmedand

acceptableforoperatingtheengines;

 At continuous proces (online supply), maximum

sizeofpalmoilwas35μmafter3minutemixing

and 12μm at

 6 minutes. Actually, these sizes do

notaffect to injection nozzle (200μm) of engine

6LU32.

5 EXPERIMENTALRESULTS

Experimental research on real marine diesel engine

6LU32 with support of high accuracy measuring

equipmenthave been at two regimes: 50% loadand

75%load.

 Peakpressure

The characteristics of

the combustion pressure

changes are showed in Fig.9, 10 and the details are

alsopresentedinTable6.



Figure9.Pressureincylinderat50%load



Figure10.Pressureincylinderat75%load

Table6.Peakpressureatdifferentengineloads 

_______________________________________________

Engineload Peakpressure[bar]Difference[%]

DO PO10  PO20

_______________________________________________

50%65.808 64.352 64.106  2.59

75%76.321 73.555 72.068  5.58

_______________________________________________



Changes of pressure in cylinders of all blended

fuelsandDOarethesame.Thebiggestdifferenceof

peak pressure is recognized for PO20 and DO with

thevalueof5.58%.

 Ignitiondelay

The results of ignition delay of blended palm oil

are showed in Fig.  11. The

research team tried to

enlarge the pictures of ignition start moment for all

After

156

kind of testblendedfuels and realvalues measured

arepresentedinTable7.



Figure11.Ignitiondelayofblendedpalmoils

Table7.Ignitionstartoffuelsbeforetopdeadcenter(TDC) 

_______________________________________________

No EngineIgnitionstartofblendedfuelsbeforeTDC[s]

load[kW] DO PO10  PO20

_______________________________________________

1 4850.0017 0.0017 0.0008

2 7300.0021 0.0016 0.0012

_______________________________________________



Figure12.Ignitionstartandburningoffuels

ItcanbeseenthattheignitionstartofPO10before

TDC is the same as that of DO at low load and

delayed 1.31 times at higher one. Also,  the delay

increasesapproximatelylinearlywithraisingvolume

ofpalmoilintheblendedfuels.

To demonstrate this judgment, the Video

 Scope

equipment was used to observe combustion process

incylinder,especiallyignitionstartofdifferentkinds

of blended fuels including DO, PO10, PO15, PO20.

ExperimentalresultsareshowninFig.12.

 Emissions

Emissionsinexhaustgasofthedieselenginesuch

as CO, CO

2, HC and NOx are analyzed by special 

measuring system AVL AMA i60 R1. The results of

experimentareplottedinFig.13.



Figure13.Emissionsdependingonkindoffuels

Among emissions, for marine field,  IMO focuses

seriously on the NO

x content control. The absolute

values of NO

x in the experiment associated with

differentfuelsareshowninTable8.

Table8.NOxemissionsofdieselengine6LU32

_______________________________________________

NOxemissions

_______________________________________________

DOPO10PO20

ppm g/kWh ppm g/kWh ppm g/kWh

_______________________________________________

940.45 19.4  894.06 18.6  576.62 13.6

_______________________________________________



Theresultsshowthatthemorevolumeofpalmoil 

intheblendedfuels,thelowertheNO

xemissionsin

theexhaustgasofthetesteddieselengine.Specially,

the NO

x emissions of PO20 is only 13.6 [g/kW.h]

which is lower than allowable NOx emissions

requestedby IMO fortest diesel engine6LU32 with

nominalrevolution320rpm(requestedNOxemission

forthetestengineis14.19g/kW.h).

6 CONCLUSIONS

To use straight vegetable oils as alternative fuel for

marine diesel engines

is very potential due to their

importantadvantagesinenvironmentprotectionand

renewablepossibility.However,SVOswhichisused

directlyas fuel formarine diesel  engines may cause

some troubles for engines themselves like bad

combustion, coking engines, significantly lower

output and so on. Therefore, to avoid above

157

mentioned problems, there is recommended that

blendedSVOsshouldbeapplied.

The fluid continuous mixing is not new but the

fuelcontinuousmixerappliedinmarinesectorisvery

few. As demanding on using the straight vegetable

oils as alternative fuel for the marine application, a

groupofresearchersof

VietnamMaritimeUniversity

has been developing the fuel continuous mixer and

being applied for marine diesel engines. Based on

reaserchresults asqualityofmixedfuel,possibilityof

thefuelmixerworktogetherwithfuelsupplysystem,

lowemissionsandsoon,therearesomeconclusions

asfollows:

 The

ideawhichhasbeendevelopedasmentioned

above is potential method to design and make a

fuelcontinuousmixerformarineapplication;

 The quality of the mixed fuel made by the fuel

continuous mixer is satisfied the requirements of

themarinefuel;

 The real fuel supply system with the

 fuel

continuousmixerbuiltin canbe acceptabletobe

appliedformarineapplication.

Itishopefulthatthefuelcontinuousmixerwillbe

appliedandinstalledwidelyonboardshipsinorder

toplayaroleinevironmentprotectioninnearfuture.

REFERENCES

[1]Krzysztof Kołwzan, Marek Narewski, Polski Rejestr

Statków, “Study on Alternative fuels for marine

applications”,CleanShippingCurrentsVol1,No3,2012;

[2]J. Blin, C.Brunschwig, A.Chapuis, “Characteristics of

vegetable oils for use as fuel in stationery diesel engines‐

towards specification for a standard in west Africa”, HAL