Journal of Environmental Management 86 (2008) 427434 [627460]

Journal of Environmental Management 86 (2008) 427–434
Usability of food industry waste oils as fuel for diesel engines
Russ Winfrieda,/C3, Meyer-Pittroff Rolanda, Dobiasch Alexanderb, Lachenmaier-Ko ¨lch Ju ¨rgenc
aTechnische Universita ¨tM u¨nchen, Chair of Energy and Environmental Technology of the Food Industry, Weihenstephaner Steig 22,
D-85350 Freising-Weihenstephan, Germany
bAD Hard- und Softwareberatung, Postfach 1116, D-85311 Freising, Germany
cEVA Fahrzeugtechnik, Heidemannstra Xe 41a, D-80939 Mu ¨nchen, Germany
Received 23 November 2004; received in revised form 5 October 2006; accepted 8 October 2006
Available online 15 February 2007
Abstract
Two cogeneration units were each fitted with a prechamber (IDI) diesel engine in order to test the feasibility of using waste oils from
the food industry as a fuel source, and additionally to test emissions generated by the combustion of these fuels. Esterified waste oils and
animal fats as well as mustard oil were tested and compared to the more or less ‘‘common’’ fuels: diesel, rapeseed oil and rapeseed methyl
ester.
The results show that, in principle, each of these fuels is suitable for use in a prechamber diesel engine. Engine performance can be
maintained at a constant level. Without catalytic conversion, the nitrogen oxides emissions were comparable. A significant reduction in
NO xwas achieved through the injection of urea. Combining a urea injection with the SCR catalytic converter reduced NO xemissions
between 53% and 67%. The carbon monoxide emissions from waste oils are not significantly different from those of ‘‘common’’ fuelsand can be reduced the same way as of hydrocarbon emissions, through utilization of a catalytic converter. The rate of carbon monoxide
reduction by catalytic conversion was 84–86%. A lower hydrocarbon concentration was associated with fuels of agricultural origin. With
the catalytic converter a reduction of 29–42% achieved. Each prechamber diesel engine exhibited its own characteristic exhaust, whichwas independent of fuel type. The selective catalytic reduction of the exhaust emissions can be realized without restriction using fuels of
agricultural origin.
r2007 Elsevier Ltd. All rights reserved.
Keywords: Emission reduction; Waste oils; Food industry; Alternative fuels; Diesel engine
1. Problem description and definition of goals
In recent years, the application of vegetable oils as a source
of fuel has been extensively researched. For prechamber(IDI) diesel engines straight vegetable oils can be used after
minimal processing, while for direct injection (DI) diesel
engines the oils must undergo esterification. The use of IDIdiesel engines in the experiments was appropriate because oneach engine tests with both, straight vegetable oils andesterified oils, had been carried out. IDI diesel engines arenot widespread in vehicles, but standard in combined heatand power plants (CHP). DI diesel engines are not suitablefor running in CHP with vegetable oils or blends ( Jones and
Peterson, 2002 ). The use of biofuels in CHP becomes more
and more common, also because these engines are often usedin more rural areas and powered with self-produced fuels.
Unlike fossil fuels, the combustion of vegetable oil is
regarded as CO
2neutral and environmentally friendly. The
limiting factor hindering their more widespread implemen-tation is the amount of land available for the cultivation ofthese crops.
In many countries, cul tivation of oil-producing crops is only
economically feasible if the government subsidizes them, andwhere there is excess land for this purpose, which is not neededfor the cultivation of comestibl es. Triglycerides (fats and oils
in the following) generated as waste by the food industry must
either be disposed of or recycled in some way. From theviewpoint of sustainability, the use of this type of waste as fueloffers a plausible means by which it can be recycled.ARTICLE IN PRESS
www.elsevier.com/locate/jenvman
0301-4797/$ – see front matter r2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jenvman.2006.12.042/C3Corresponding author. Tel.: +49 8161 71 3865; fax: +49 8161 71 4415.
E-mail addresses: winfried.russ@wzw.tum.de (R. Winfried) ,meyer–
pittroff@wzw.tum.de (M.-P. Roland) ,dobiasch@web.de (D. Alexander) ,
lachenmaier@web.de (L.-K. Ju ¨rgen) .

The goal of this research is to determine the nature of the
emissions created through the combustion of waste oilsfrom the food industry and to compare them with thosefrom ‘‘common’’ fuels such as rapeseed oil, rapeseed oil
methyl ester (RME) and diesel fuels. The experiments were
conducted using two prechamber diesel engines, one ofwhich was modified for combustion of vegetable oil.Furthermore, the efficacy of purifying waste oil exhaustemissions was to be proved.
2. Status of the current research
It is state of the art that stationary as well as automobiles
diesel engines are capable of running on vegetable oil-basedfuels, and recent modifications have also extended andoptimized this applicability. Examples for these modifica-
tions were improvement of fuel injection time and volume,
coating of the prechamber (at IDI diesel engines) andreplacement of the fuel injector nozzles. Prechamber (IDI)diesel engines are capable of running with straightvegetable oils, while DI diesel engines need previouslytransesterification of the oils ( Jurisch and Meyer-Pittroff,
1994;Birkner, 1995 ;Schumacher, 1996 ;Graboski and
McCormick, 1998 ).
Vegetable oils possessing a higher viscosity can be
utilized in non-modified IDI diesel engines, if the triglycer-ides have been converted to methyl esters throughtransesterification as well in non-modified DI dieselengines.
Currently in Europe almost exclusively RME is pro-
duced for use as a fuel. In USA soybean oil is the principaloil being utilized for biodiesel. In Japan the availability of
used cooking oil and fat as a raw material reached its limits
in the last years and so more and more Japanesemunicipalities now cultivate rapeseed ( Schmidt ). The main
world biodiesel sources were in 2002: rapeseed oil (84%)and sunflower oil (13%), furthermore soybean oil (1%),palm oil (1%) and many others (1%) were used ( Cyberlipid
Center—Resource Site for Lipid Studies ).
The motivation behind using vegetable oils as fuels:
/C15Environmental concerns : Unlike fossil fuels, vegetable oil
fuels are renewable and are CO 2neutral ( von Weizsa ¨ck-
er et al., 1997 ;Sheehan et al., 1998 ).
/C15Economic advantages : Oil-producing plants not intended
for use as food are eligible for subsidies within theEuropean Union and are exempt from petroleum andCO
2taxes.
/C15Agreements on emissions reducing and fossil fuelsreplacement : An action plan of the EU-Commission
intend to replace fossil fuels by biogenous fuels
from 2% in 2005 to 5.75% in 2010 ( Bockey, 2002 ). In
the Kyoto protocol, the EU member countries havecommitted to a reduction of their CO
2emissions by 8%
relative to 1990 levels by the year 2010 ( Franke and
Reinhardt, 1998 ).The concept of using waste triglycerides from plant and
animal sources as fuel emerged for obvious reasons(Iglhaut et al., 1998 ;Russ and Meyer-Pittroff, 2004 ).
Utilizing this waste as fuel removes it from the food
production cycle, because it will not be added to animal
feed, as has been traditionally the case. Using thesesubstances as fuel instead of additives to animal feedwould eliminate any potential danger and therefore preventfood scandals such as in Belgium ( van Larebeke et al.,
2001) from occurring. Since the bovine spongiform
encephalopathy (BSE) scandal addition of meat-and-bonemeal or other animal remains to animal feed is forbidden in
the European Community (EC) ( Regulation, 2001 ).
Though also recent regulations continuing this trend(Regulation, 2002a ), it is still allowed to use some animal
by-products in feed ( Regulation, 2002b ) and also illegal
utilization is taken place. The more alternative ways ofefficient and safe reusing animal waste will be available, theless misuse of these risk products will occur.
In a variety of studies, it was determined which emissions
arise from the usage of rapeseed oil and RME as fuel
(Jurisch and Meyer-Pittroff, 1994 ;Birkner, 1995 ;Schuma-
cher, 1996 ;Graboski and McCormick, 1998 ;Hemmerlein
et al., 1991 ;Widmann and Kern, 1999 ). The emissions were
measured on production and modified diesel engines usingvarious experimental parameters. Production engines areconventional engines that are not used for locomotion.This diesel fueled engines are mostly used in CHPs and in
agriculture. The results obtained from these studies were
summarized by Dobiasch, (2000) and are presented in
Tables 1 and 2 .
Particulate filters aid in the reduction of emissions from
diesel engines, and catalytic and non-catalytic processes areemployed for reducing the CO and NO
xcontent. The non-
selective catalytic chemical reduction (i.e. three-waycatalytic converter) is not feasible in diesel motors, because
they operate with an excess of air.
In addition to a catalytic converter, selective catalytic
reduction incorporates a reducing agent. Metal oxides suchas V
2O5,W O 3and MoO 3serve as catalysts. However, ifARTICLE IN PRESS
Table 1
Differences in the emissions of unmodified rapeseed oil in production
engines and engines modified for rapeseed oil use, compared to diesel fuel
Emissions Production engines Motors modified for
rapeseed oil fuel
CO ++ /C0
NO x oo
Hydrocarbons ++ /C0
Soot particles ++ /C0
Aldehydes andketones++ +
Polycylic aromatic
hydrocarbonsIndifferent /C0
+, Emissions increased.
/C0, Emissions decreased.
o, Emissions remained the same.R. Winfried et al. / Journal of Environmental Management 86 (2008) 427–434 428

only reducing agents such as ammonia or urea are used,
this is referred to as selective catalytic reduction. Regulat-ing the temperature to remain between 200 and 350 1Ci s
necessary in order to achieve the high rate of conversion
desired ( Kind, 1998 ).
3. Materials and methods3.1. Fuels used
Rapeseed oil, RME and diesel ( DIN e.v., 2004 ) were
chosen as the more or less ‘‘common’’ fuels, and thefollowing three types of waste oils from the food industry
were selected:
3.1.1. Used cooking oil collected from various sources
This type of oil is commonly collected and cleaned by
recycling companies and afterwards made available forreuse. It is collected from industrial kitchens, restaurantsand food producers, where it was primarily used for frying.After collection, the used oil is transferred to large holding
tanks where it is blended with other waste oils; however the
quality is very inconsistent. The impurities present in theused oil consist primarily of free fatty acids, polymers,chlorides and phospholipids, which cannot be adequatelyremoved through the cleansing process. To use this oil asfuel a transesterification process must be performed whichchanges the molecular structure and decreases viscosity.The separation steps during this process leads to purifica-
tion of the methylester fraction and the impurities are
enriched in the glycerine fraction.
3.1.2. Mustard oil from mustard production
Mustard seeds contain 22–42% oil, which is primarily
extracted by pressing. The oil consists of up to 60% erucicacid and between 110 and 115 mmol/g glucosinolates, both
of which prevent mustard seed oil from further use in the
food industry ( Weiss, 1999 ).
3.1.3. Animal fat from rendering plants
In rendering plants, the ground animal parts are heat-
treated for hygienic reasons, and afterwards the fat portionis separated. For the same reasons as with the waste oils,
only the esterified form of this fat can be used. Because ofpotential BSE contamination of animal material differentprocessing steps compared to plant feedstock have to take
place. In the last years processing methods for fuels from
animal fats like sterilization, separation, purification,washing and distillation had been modified to reach riskreduction of 10
3–105(Alm, 2004 ). Based on that develop-
ments the European Food Safety Authority concluded thatthe production of biodiesel, including the by-productspotassium sulphate and glycerine, is safe for the treatmentof fats of category 1 animal by-products (high risk) ( Panel
on Biological Hazards of the European Food Safety
Authority, 2004 ).
3.2. Experiment design and measuring techniques
Two cogeneration units were selected as the diesel
engines for this experiment, because their load profile canbe regulated in such a way that it remains constant.
Automobile diesel engines were not tested because
stationary engines are more easily adapted for the varyingfuel quality of waste oils. Hence, future applications of thistechnology focus chiefly on stationary diesel engines.Cogeneration unit 1 with a swirl chamber diesel enginewas set up to run on diesel fuel, while cogeneration unit 2with a prechamber diesel engine was specially modified toburn plant oils (see Table 3 ). The modifications of unit 2
included adjustment of fuel injection time and volume as
well as replacement of the fuel injector nozzles.
For the data logging at the test stations a Almemo data
logger (Ahlborn Mess- und Regelungstechnik) was used.Temperature was measured by Pt-100 and NiCr-Nisensors, volume flow by a Turbotron VTP 15 MS-40(VSE) and electrical real power using a MU-P4Wu/stransducer (Mu ¨ller&Weigert). The manufacturers of the
emission measuring devices as well as their technical data
are given in Table 4 . Data output was imported auto-
matically into a Microsoft Excel file.
Fig. 1 shows the placement of the diesel engines and their
integration into the system designed for measuring theirexhaust emissions. If desired, a catalytic converter could beinstalled on cogeneration unit 2 in front of the heatexchanger, where urea could to be injected for denitrifica-
tion of the exhaust. The amount of fuel consumption as
well as the amount of injected urea was measuredgravimetrically. The catalytic converter contained anextruded honeycomb catalyst composed of titaniumdioxide (TiO
2), vanadium oxide (V 2O5) und tungsten oxide
(WO 3).
The standard deviation of the test setup was ascertained
in preliminary tests ( n¼9) for each analyzed parameter.
Because most fuels were not available in huge amounts, the
tests in advance were conducted with waste oil methyl ester(WOME) and outcomes were utilized for general errorestimation. For the fuel trials, the cogeneration units had a4 h forerun with WOME before every test. After changingARTICLE IN PRESS
Table 2
Differences in the emissions of rapeseed oil methyl ester in production
engines compared to diesel fuel
Emissions Production engines
CO /C0
NO x +
Hydrocarbons /C0
Soot particles /C0
Aldehydes and ketones /C0
Polycyclic aromatic hydrocarbons /C0
+, Emissions increased.
/C0, Emissions decreased.
o, Emissions remained the same.R. Winfried et al. / Journal of Environmental Management 86 (2008) 427–434 429

fuel there was an initial break-in phase of at least 30 min
for stabilizing of measurands.
3.3. Fuels and their properties
Diesel was selected as the standard fuel, and rapeseed oil
and RME as the fuels of agricultural origin, because of
their widespread availability. Mustard oil could be used inthe non-ester form because of its purity. WOME wasobtained from a supplier. The animal fat methyl ester(AFME) for the experiment was produced in the labora-tory. Because of high free fatty acid content of the animalfat compared to other raw materials a modified methodusing ammonia for deacidification was applied ( Dobiasch,
2000). The most important properties of each of these fuels
are listed in Table 5 .
The density and viscosity of unmodified vegetable oils
are significantly higher than those of other types of fuel.Esterification reduces the viscosity and therefore eliminatesthis problem. The impurities according to the reference
method DIN 51419 (like sand, rust and organic com-pounds) in oil and the ash content of the emissions aredirectly related. The contamination level (impurities) ofAMFE is more than ten times higher than recommended
for continuously operating according to engines specifica-
tions. The implications of high contents of undissolved anddissolved impurities could result in different seriousproblems. For example impurities like sand, rust and otherundissolvable matters can plug up filters or nozzles.Organic compounds, often containing nitrogen, can alsoblock nozzles and cause carbon deposit in the combustionchamber and on outlets. Free fatty acids can impede the
transesterification and form soaps. Not esterified free fatty
acids and different kinds of salts (Ca
2+,N+,K+) can
cause corrosion in the engine and catalyze oxidationprocesses.
The fatty acid spectra of the vegetable oils in this
experiment are typical for rapeseed oil and mustard oil (seeARTICLE IN PRESS
Table 3
Specifications for both engines
Cogeneration unit 1 Cogeneration unit 2
Manufacturer/Model Icemaster GmbH/ Fischer Panda 10 Vereinigte Pflanzeno ¨lwerk-sta ¨tten/KW 5-3 AP
Engine 3 cylinder swirl chamber Kubota industries 3 cylinder prechamber Lombardini S.I.
Cylinder and piston 64 /C268 mm 72 /C275 mm
Volume 719 cm3916 cm3
Injection pump Bosch MD Type Mini Pump Lombardini LDW 903
Injection pressure 13,73 MPa 13–14 Mpa
Injection time 21 1before TDC 22 1before TDC
Compression ratio 23:1 22.8:1Max. mechanical power 12.4 kW at 3000/min 13.7 kW at 3600/min
Generator Asynchronous Asynchronous
Max. electrical power 9.5 kW 8.4 kWNominal electrical output 6 kW 5 kW
Table 4
Technical information for the devices used in the emissions testing
Measuring device Manufacturer Gas Range Accuracy relative
to final valueDetection limit Zero drift relative
to final value
Oxynos 100 Rosemount O 2 0–5% by vol.
0–100% by vol.71% 0.05% by vol. 70.5%
MCS 100 Perkin Elmer
Bodensee-werkNO 0–200 mg/m372% 1% of final value
for all gases70.5% for all
components 0–10000 mg/m372%
CO 0–140 mg/m372%
0–700 mg/m372%
NH 3 0–30 mg/m372%
N2O 0–50 mg/m372%
H2O 0–20 vol.-% 72%
FID Bayer Diagnostics HC 0–105mg/m3n. g. 0.2 mg/m3n. g.
GC Siemens N 2O Peak height 1:108 71% 10 ppm n. a.
CIMS 500 V&F NO 0–1000 ppm 75 10 ppm n. a. for all
NO 2 0–1000 ppm 75 10 ppm components
NH 3 0–1000 ppm 75 10 ppm
n. g., no information given.
n. a., not applicable (based on measurement method).R. Winfried et al. / Journal of Environmental Management 86 (2008) 427–434 430

Fig. 2 ). The amounts of stearic acid and palmitic acid were
noticeably high in the AFME.
4. Discussion of results
The amount of electrical power generated by the diesel
engines served as the measure for engine performance. Thiswas approximately the same for all the fuels in theexperiment ( Fig. 3 ).
The exhaust temperature provided a direct means for
measuring the fuel performance, because the electricalpower and therefore the mechanical power were heldconstant. A performance controller was set to keep about5.5 kW at cogeneration unit 1 and about 4 kW atcogeneration unit 2. To keep constant electrical power at
constant revolution, fuel supply was regulated by thecontroller. Thus a change in temperature is an indicationfor a different performance of the fuel. The AFME did notburn as well in the diesel engine, as was evidenced by theincreased temperature of the exhaust ( Fig. 4 ). From previous
experiments, it was determined that the optimal temperaturefor the catalytic NO
xconversion lies between 200 and 350 1C.
Cogeneration unit 2 was within this range, with an operating
temperature between 300 and 350 1C. Injection of a urea
solution resulted in lower temperatures in contrast tomeasurements taken without urea ( Lachenmaier, 2002 ).
As can be seen in Fig. 5 , the levels of NO
xemissions
from the AFME were markedly low. It could beARTICLE IN PRESS
-COMS
-COMS
-COMS
-MS
TC returncoolant
returnVW.electronic
data recordingcooling
unitVCO2.
TC feedcoolant
feedPelgas
chromato-graphmass
spectrometer
particulate
filterexhaust
emissionspolycyclic
aromatic
hydrocarbon
filter
T
filter
synthetic
air
Tfg after
Tfg beforeheat
exchanger3cylinder swirl
chamber motorasynchro-
nous
generatorcooling
unitheated
CO2
NOCOSO2CO2N2ONH3H2OFID O2 GC
flame
ionisation
detector
mfuel.Tfa
Fig. 1. Integration of the measuring devices used in the experiment into the test setup.
Table 5
Properties of the fuels
Density (15 1C) Net calorific
valueViscosity Carbon
residueImpurities Neutralization
numberAsh content Iodine value Phos-phorus
content
Reference
methodDIN EN
ISO 3675DIN
51900DIN EN
ISO 3104DIN EN
ISO 10370DIN 51419aDIN EN
ISO 660DIN EN
ISO 6245DIN
53241ASTM D
3231
Measurement
unitkg/m3MJ/kg mm2/s % by
massmg/kg mg KOH/g % by
massg/100 g mg/kg
Diesel fuel 822 43.2 2.4 0.08 11.9 0.97 0.001 n. a. n. a.
Rapeseed oil 918 37.6 36.7 0.70 32.4 1.66 0.007 106 11
RME 880 37.5 4.8 0.11 30.8 1.11 0.002 107 0Mustard oil 911 37.8 46.1 0.34 36.4 1.11 0.007 86 2
WOME 883 37.2 5.4 0.07 30.4 0.97 0.001 100 0
AFME 876 37.0 4.3 0.03 305.0 0.23 0.039 97 0
n. a., not applicable (based on measurement method).
aIn the meantime replaced by DIN EN 12662.R. Winfried et al. / Journal of Environmental Management 86 (2008) 427–434 431

hypothetical possible, that the higher exhaust emission
temperature is a result of a different combustion processwhat influences the NO
xformation. Furthermore, the
scores of impurities could theoretically contain catalytic
compounds which are reducing NO xemissions. The
nitrogen oxides emissions from cogeneration unit 1 werehigher than those from cogeneration unit 2, even whenburning the same type of fuel. This was due to the
modifications made to the diesel engine for the combustionof vegetable oils. As expected, in the absence of a ureainjection, the SCR catalytic converter had almost no effect.The rate of reduction (with catalytic converter and ureainjection) in NO
xemissions using diesel fuel was 67%,
which was somewhat better than that of the renewable fuels(54% and 61%).
For the catalytic conversions of NO
xto N 2the
availability of not complete oxidized compounds areimportant. Therefore, the engine of cogeneration unit 2was calibrated in a way that at any rate enough CO forcatalytic reduction process is present. On this account therewill be always a minimum of CO in the exhaust emissionsARTICLE IN PRESS
0%10%20%30%40%50%60%70%Fatty acids [% by mass]100%
90%80%
Rapeseed
oilRapeseed
oil
methyl
ester
(RME)Mustard
oilWaste
oil
methyl
ester
(WOME)Animal
fat
methyl
ester
(AFME)Palmitic acidStearic acidOleic acidLinoleic acidLinolenic acidArachidonic acidBehenic acidErucic acidOther
Fig. 2. The most important fatty acids present in the selected fuel types.
3.03.54.04.55.05.56.0
Diesel
Rapeseed oil
RME
Mustard oil
WOME
AFME
Diesel
Diesel + C
Diesel + C + U
Rapeseed oil
Rapeseed oil + C
Rapeseed oil + C + U
WOME
WOME + C
WOME + C + UElectrical power [kW]Cogeneration unit 2 Cogeneration unit 1
Fig. 3. Electrical power generated by both cogeneration units using
different fuels (C: converter; U: urea).290300310320330340350360370
Diesel
Rapeseed oil
RME
Mustard oil
WOME
AFME
Diesel
Diesel+ C
Diesel+ C + U
Rapeseed oil
Rapeseed oil + C
Rapeseed oil + C + U
WOME
WOME+ C
WOME + C + UTemperature [ °C]Cogeneration unit 1 Cogeneration unit 2
Fig. 4. Temperatures of the exhaust emissions measured before the heat
exchanger (C: converter; U: urea).
020040060080010001200140016001800
Diesel
Rapeseed oil
RME
Mustard oil
WOME
AFME
Diesel
Diesel+ C
Diesel+ C + U
Rapeseed oil
Rapeseed oil + C
Rapeseed oil + C + U
WOME
WOME + C
WOME + C + UNOx [mg/m3]Cogeneration unit 1 Cogeneration unit 2
Fig. 5. Nitrogen oxides emissions based on residual oxygen content of 5%
by volume in exhaust emissions (C: converter; U: urea).R. Winfried et al. / Journal of Environmental Management 86 (2008) 427–434 432

after the catalytic converter left. Without catalytic con-
verter this setting appears in high CO levels ( Fig. 6 ).
However, this higher emission level allowed the amount ofconversion taking place in the SCR catalytic converter tobe measured. The rate of reduction was 84–86%, depend-
ing on the used fuel. Through the injection of urea, a
further small improvement of the reduction rate wasattained.
The hydrocarbon (HC) concentration functions well as a
measure for the accuracy of injection, distribution anddegree of combustion in a diesel engine. Both cogenerationunits showed a typical increase in HC emissions ( Fig. 7 )o f
diesel fuel compared to fuels of agricultural origin
(Schumacher, 1996 ;Graboski and McCormick, 1998 ;
Dobiasch, 2000 ;Lachenmaier, 2002 ). In cogeneration unit
1, a more complete combustion and lower HC concentra-tion was associated with all non-diesel fuels ( Birkner,
1995). At cogeneration unit 2 the higher HC emissions of
fuels combusted without installed catalytic converter showsalso that the fuel injection was calibrated to reach a certainlevel of not complete combusted compounds for NO
x
conversion. Here, it is even more apparent that the dieselengine was adapted for use with oils possessing a higherviscosity. The HC concentration was better in cogenerationunit 2 with rapeseed oil than with other fuels. The fuel-depending reduction rates of 29–42% by the catalyticconverter were not significantly improved by the injectionof urea.
5. Conclusion
The use of plant and waste oils as fuel is possible. Both
engines (adapted to triglycerides or not) show a goodperformance regarding the exhaust gases. The catalyticconversion of NO
xand CO is possible with triglycerides aswith diesel. Regarding the emissions catalytic systems
should be preferred. The injection of urea leads to adecrease of the emissions, but is not feasible in mobileengine systems (e.g. cars, HGV etc.).
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Diesel
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