Vegetable oils as Diesel Fuels for Rebuilt Vehicles

44th International Petroleum Conference, Bratislava, Slovak Republic, September 21-22, 2009 1

Vegetable oils as diesel fuels for rebuilt vehicles
1
Kleinová A., 2Vailing I., 3Franta R., 3Mikulec J., 1Cvengroš J.

1
Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9,
812 37 Bratislava, Slovak Republic,
e-mail: andrea.kleinova@stuba.sk; jan.cvengros@stuba.sk
2
RASOL, Nitra, Slovak Republic, e-mail: info@rasol.sk
3
Slovnaft VÚRUP, Bratislava, Slovak Republic,
e-mail: jozef.mikulec@vurup.sk; franta.robert@vurup.sk

Abstract
Vegetable oils and animal fats are applicable as fuels in standard diesel engines after
having adapted the fuel system for electronically controlled dual fuel (oil/fat – fossil diesel)
regime. In this study, performance and emission characteristics of the engine running on
rapeseed oil or chicken fat are given and compared to those of fossil diesel. The results of
engine tests of these fuels show a decrease in maximum power and maximum torque in
comparison with fossil diesel. When compared to fossil diesel, the opacity of vegetable oil or
animal fat based fuels is lower for an engine with higher injection pressures. The level of both
controlled and uncontrolled emissions is low for all tested biofuels and it is low also for the
reference fossil diesel. The results of performance and emission tests for rapeseed oil
containing 3 and 6 vol. % of anhydrous ethanol are comparable to those obtained for pure oil.

Key words: Vegetable oils, animal fats, bioethanol, alternative fuels, diesel engine, dual fuel
operation

1 Introduction
Pure plant oils and also animal fats (PPO) represent promising alternative in the field of
biofuels [1], they are renewable and environmentally friendly. Utilization of this group of
natural products leads to further diversification of liquid fuel resources for transport, in
a simple and easily accessible form [1–4].
PPO are non-toxic incombustible liquids with the flash point above 170 °C, i.e. with
minimum risk for storage, handling or transport. Their cetane number is relatively low,
ranging from 39 to 44. When PPO are used as fuels for diesel engines, some qualitative
parameters must be fulfilled and also the vehicle fuel systems must be appropriately adapted


for this kind of fuel. The qualitative requirements for PPO are defined in the DIN V 51605
standard [5]. The content of free fatty acids, phosphorus, calcium and magnesium need to be
monitored. For trouble-free engine run, these parameters should reach the lowest possible
levels. Their increased values indicate the necessity of appropriate PPO treatment before
using as fuel [6].
The main drawback of PPO for direct utilization as fuel in conventional diesel engines is
related to their high viscosity [7, 8] which causes incomplete fuel atomization, formation of
carbon deposits on injectors, piston ring sticking, engine oil deterioration, etc. [9, 10]. Despite
these problems, literature data [11–18] show that PPO are applicable for conventional diesel
engines without their adaptation. Moreover, some benefits appear: reduced PAH emissions,
reduced opacity [19] and lower NOx values [20–22].
There are several approaches to solve the viscosity problem in an effective and simple
way, such as blending, microemulsions, transesterification, and cracking [10, 22–26]. Various
mixtures of PPO and conventional diesel fuel (DF) with a low (5–30 %) [16, 18, 19] and high
share (up to 75 %) of PPO [17, 22] are discussed. Heating of PPO before its input into fuel
injection system [27–31] also leads to viscosity decrease. Temperatures about 70 °C [31], 100
°C [27], but even 150 °C [32] are mentioned. These approaches cause low emission, reduced
opacity and positive performance. Alcohols-PPO blend represents other way of fuel viscosity
decrease [20, 33, 34]. A low-viscosity solvent decreases significantly the mixture viscosity
and opacity when compared to run on pure oil.
Dual fuel operation of engines represents a new approach in the use of PPO [35–37]. Here,
electronically controlled dual fuel (DF-PPO) system is built and PPO is pre-heated to reduce
its viscosity. Without any engine adjustments, the vehicle fuel system contains a fuel pre-
heater and the dual fuel tank. System allows switching over between DF and PPO, both
controlled by a microcomputer. The engine is started and runs on DF for the first few minutes
while the PPO is heated. The engine is then switched over to the second tank and runs on
PPO. At the end of operation, the engine runs again on DF. The optimal operation on
individual fuel is ensured by an automatic control system [38]. Literature related to tests
performed using animal fats as fuel in diesel engines with modified fuel system is scarce.
Nowadays, there is an extensive know-how for optimized adjustment of standard vehicles
with the diesel engine running on PPO. It is estimated that in Germany, there is about 60 000
vehicles adjusted in such way (situation in 2006). The fuel consumption of these vehicles
approaches 300 000–400 000 t/y rapeseed oil, i.e. about 0.5 % of the liquid fuel consumption


in Germany. Demand for this fuel is considerable [39], in the next years a yearly increase by
10 % is anticipated.
Although ethanol (EtOH) does not belong to typical and optimal components of diesel
engine fuel, there are tendencies to exploit it as a component of diesel fuels [40, 41], in spite
of its negative properties, such as low cetane number, decreased flash point, worsened
lubricity, low energy content. However, addition of EtOH to PPO can improve its low-
temperature flow properties. The results in [40, 41] show that addition of EtOH to DF up to 5
vol. % does not lead to substantial worsening of the fuel performance properties, with
exception of flash point. Therefore, we decided to pay attention to test EtOH as a part of
blended fuel.
In this work, we studied the performance and emission characteristics of standard engines
with unit injection system in vehicle with adapted fuel system running on PPO as main fuel.
Obtained results were compared with those of the same engine running on DF. Tests were
performed also using animal fat. A further objective lies in analogous investigation using the
mentioned engine running on the blended fuel consisting of PPO and anhydrous EtOH.

2 Experimental part

2.1 Testing vehicle
To provide all performance and emission tests, a passenger car VW Touareg R5 2.5 UI
(Unit Injection System), year of production 2007, was chosen. Basic characteristics of the
used all-wheel drive car are given in Tab. 1. Testing vehicle was equipped with a RASOL
[38] system for dual fuel regime and all the necessities, too.

Tab. 1 Characteristics of testing engine
Type of engine 2.5 UI
Cylinder number 5
Bore (mm)×Stroke (mm) 81×95.5
Volume (L) 2.5
Compression ratio 19.5:1
Maximal power output (kW/rev) 128/3500
Maximal torque (N m/rev) 400/2000
Injection pressure (bar) 2050
Vehicle weight (t) 2.4

2.2 Tested fuels – characteristics and preparation
The reference fuel, DF, was provided by Slovnaft Bratislava. Parameters of DF are given
in Tab. 2. Low-temperature properties of the used diesel fuels were modified by commercial
additives, detergent (200 ppm) and depressant (300 ppm).


The properties of the used alternative fuels are summarized in Tab. 3. Rapeseed oil (RO)
was cold pressed, subsequently adsorbed by clay, filtered through a filter press and re-filtered
through a 1 μm filter. Its acid value (AV) was 1.7 mg KOH/g. To prepare blends of PPO with
EtOH, anhydrous denaturated EtOH (Slovnaft VÚRUP Bratislava) containing less than 1000
ppm water was used. Chicken fat (CF) with AV = 4.0 mg KOH/g was supplied by JAV-AKC
Vlčany. Viscosity/temperature plots for tested fuels are shown in Fig. 1.

Tab. 2 Characteristics of used diesel fuel
Characteristic Unit Value Method
Density at 15 °C kg m-3 832.6 EN 12185
Viscosity at 40 °C mm2 s-1 2.376 EN 3104
Cetane index 50.7 EN 4264
Cetane number 50.6 EN 5165
Water content mg kg-1 26.2 EN 12937
Flash point °C 70 EN 2719
Cloud point °C - EN 23015
Filterability (CFPP) °C -30 EN 116
Lubricity μm 605 EN 12156-1

2.2 Performance and emission tests, fuel consumption measurements
All measurements of performance characteristics were carried out using the chassis
dynamometer MAHA LPS 2000 (MBH Haldenwang/Allgäu, Germany). Emission
measurements were performed with an exhaust gases analyzer MAHA MGT 5 by means of
the emission determination at steady-state regime during idle running and the constant speeds
of 60, 90 or 120 km/h. Diesel engine opacity determination was performed by the method of
free acceleration with a dynamometer AVL DiSmoke 435. Aldehydes and ketones were
determined as described in [42, 43]. Fuel consumption measurements were done by weighting
of tested fuel samples in the regime of engine run in-town and non-city cycles following the
ECE 83 method. The results of individual tests are compiled in the corresponding tables. The
values in the tables represent an average of five measured values.

3 Results and discussion

3.1 Viscosity of tested fuels
Objections to the direct use of PPO as fuels for unmodified diesel engines relate mainly to
their higher viscosity in comparison with that of DF. In Fig. 1 temperature dependences of the
used PPO (rapeseed oil and chicken fat) viscosities are shown together with the dependence
for DF. It is obvious that in spite of increased temperature, a substantial decrease in the
viscosities was not achieved and they are still higher than that of DF. According the literature


data, the temperature of PPO about 70 °C is already sufficient for the study of performance
and emission characteristics. Addition of 3 and 6 vol. % of EtOH does not decrease viscosity
of RO significantly when compared to DF. Further increase in temperature induces viscosity
decrease [32]. However, the presence of a volatile component with the boiling point of 78 °C
is limiting factor. Viscosity decrease may be reached also by increasing the EtOH content in
the blend. In general, it is not expected to add more than 7 % of EtOH permitted by
the standard. In separate study of the low-temperature behavior of blended fuel RO–EtOH
containing 3 and 6 % EtOH at –10 °C, a high phase stability was manifested at long-term test
lasting several tens of hours. The system was permanently homogeneous without any
indication of the phase separation.

45
DF
40 RO
RO+3% EtOH
35 RO+6% EtOH
CF
viscosity [mm s ]
-1

30
2

25

20

15

10

5

0
35 40 45 50 55 60 65 70 75

temperature [°C]

Fig. 1 Viscosity/temperature dependence of tested fuels

3.2 Engine performance tests
The results of performance tests of the investigated fuels using unmodified diesel engine
2.5 UI indicate lower obtained values of peak performance and torque when compared to DF
(Tab. 3), which proved their potential to act as alternative diesel fuel. At the performance
characteristics in the Tab. 4, the different fuel densities are respected. The highest values of
performance and torque were obtained for DF. For the other fuels, the obtained values of the
peak performance are lower by 12–13 %. The decrease in the peak performance is associated
with a decrease in maximum torque. The obtained values of maximum torque are decreased


by 12–14 %. In general, a decrease in the engine performance characteristics is related to
a lower energy content of such fuels due to a higher share of oxygen in TAG molecule (cca 10
%).
The presence of a small share, 3 and 6 vol. %, of EtOH leads to a negligible increase of
oxygen content (by 1–2 %). Based on the measured data (Tab. 3), EtOH has no effect on the
performance characteristics when compared with RO. Lower performance characteristics of
the engine fueled with tested biofuels relate to their lower energy content. At the performance
characteristics in the Tab. 3 the different fuel densities are respected.

Tab. 3 Performance characteristics of tested fuels
RO RO
Fuel DF RO CF
+ 3 % EtOH + 6 % EtOH
Max. output
127 112 110 114 113
(kW)
Max. torque 476 418 410 416 412
(N m)

Reached accelerations were similar for TAG based fuels and DF. Within acceleration tests
in the given speed ranges (Tab. 4), shorter time intervals were measured for the fuels with a
small content of EtOH in spite of unchanged performance characteristics of the engine. The
speed ranges in the Tab. 4 are as follows: 40→80 km/h, 60→100 km/h and 80→120 km/h.

Tab. 4 Accelerations in seconds for tested fuels
RO RO
Fuel DF RO CF
+ 3 % EtOH + 6 % EtOH
40→80 (2nd gear) 5.28 5.48 5.44 5.32 5.12
60→100 (3rd gear) 10.2 10.5 10.4 10.14 9.52
80→120 (4th gear) 21.7 22.5 22.4 20.32 19.52

3.3 Emission tests
Based on the previous study [44], opacities of tested alternative fuels exceed 3.5–4 times
those measured for DF. Higher opacity values are probably related to the presence of a
glycerol moiety in the TAG molecule. Obtained opacity values (Tab. 5) are lower in the case
of engine with higher injection pressures. This is achieved in engines with modern injection
conception, equipped with a common rail (CR) injection or unit injection system UI (pump-
nozzle). Here, the injection pressures reach 2050 bar while in TDI engines [44] these
pressures reach 850 bar only. Such an engine fueled by DF does not need so higher pressures
since low opacity is obtained even at lowered injection pressures. The engines manufactured
after 2000 use almost exclusively these types of injection, where in one cycle several fuel


injections are realized. Higher opacity values can be reduced using in-series produced and
commercially available filters of solid particles. Applying this approach, the opacity reaches
values lower than those permitted by a standard. Measured opacity values (Tab. 5) are the
lowest for CF. The filters for solid particles were not used during the mentioned tests.
Opacities of the engine fueled with the RO containing EtOH are lower than those using
reference DF, however, the differences in the values for pure RO and RO–EtOH blends are
not relevant (Tab. 5).

Tab. 5 Opacities of tested fuels at free acceleration
Opacity
Fuel
(%)
DF 17.0
RO 13.9
CF 11.7
RO + 3 % EtOH 13.8
RO + 6 % EtOH 13.4

The contents of CO, CHx and NOx in exhaust gases are given in the Tab. 6. The content of
CO was very low, practically at determination limit. There are no substantial differences in
CHx content for all tested fuels. Generally, the level of unburned hydrocarbons in exhaust
gases is low. The content of NOx is the lowest in conditions of idling and increases with the
increased speed. Higher content of NOx is usually connected with higher operational
temperatures in the cylinder. In cases of all tested PPO, the content of NOx is lower in
comparison with DF, the differences are decreasing with the speed increase.

Tab. 6 CO, CHx and NOx emissions of tested fuels
DF2 RO CF RO RO
+ 3 % EtOH + 6 % EtOH
Idling 0 0.052 0 0 0
60 km/h 0 0 0 0 0
CO 90 km/h 0 0 0 0 0
120 km/h 0 0 0 0 0
Idling 0 4.8 1.6 11.6 3.6
60 km/h 19.6 15 17.2 22 16.8
CHx 90 km/h 31 25.4 23.8 25.4 26.2
120 km/h 20 20 17.2 20.6 22.6
Idling 44 30.2 27.4 29 9.2
60 km/h 87.6 76.8 116.2 124.6 94
NOx
90 km/h 294.6 302.8 337.2 340.2 285
120 km/h 476.2 472.8 491 475.8 426


In Tab. 6, the values of CO, CHx and NOx emissions of the tested fuels with the small
share of EtOH are also given. The CO content in the exhaust gases was very low. Contents of
CHx and NOx are almost identical for RO containing EtOH as those for DF, the emission
profile is not influenced by EtOH content.
The concentrations of uncontrolled emissions (aldehydes and ketones) are at level of
determination by all tests and the results are not presented in the table form.

3.4 Fuel consumption measurements
Fuel consumption determined within the test cycle ECE 83 was most favorable for DF
(Tab. 7). Consumption of PPO based fuel was higher by 12–16 % than that of DF. The
consumption of fuels containing small amount of EtOH are higher by 14–20 % comparing to
DF and by 2–7 % comparing to pure RO.

Tab. 7 Consumptions of tested fuels according to ECE 83
Fuel consumption
Fuel
(g/cycle ECE 83)
DF 780.5
RO 873
CF 904
RO + 3 % EtOH 889.5
RO + 6 % EtOH 937.0

4 Conclusions
Performance and emission tests of investigated fuels based on natural triacyglycerols of
vegetable and animal origin documented that the parameters of these fuels are comparable to
those of fossil diesel. The presence of ethanol in PPO has no negative impact to the
performance and emission characteristics, with exception of flash point. Operation of a
vehicle fueled with chicken fat was, from technical viewpoint, trouble-free. In this case,
noteworthy results of performance and emission tests, fuel consumption including, were
achieved. A remarkable potential is anticipated in the case of animal fats use for stationary
engines in cogeneration units operation.

Acknowledgement
This work was supported by the Slovak Research and Development Agency under the contract
No.APVV-20-037105.


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