Tests of Combustion of Rapeseed and Mineral Oils Mixtures

Tests of Combustion of Rapeseed and Mineral Oils Mixtures
A. Zajdel ∗ , A. Krzak
Silesian University of Technology, Gliwice, Poland
Abstract
The paper present investigation of combustion process of oil mixtures, which were the blend of raw rapeseed and
mineral oils. Experiments were performed in laboratory combustion chamber of 50kW thermal power. The standard
oil burner equipped with atomizer of pressure jet type was used for fuel burning. The experiments showed that in the
burner designed for combustion of mineral oil, it is possible to burn the oil mixtures included not higher than 50%
raw rapeseed oil. However the best results were obtained for about 30% mass fraction of rapeseed oil in mixture.
Introduction
Combustion of vegetable oils is considered as one of
possible way of extending the renewable energy sources
usage in fulfilling numeral human needs. From many
years esters of different vegetable oils are applied as a
component of Diesel engine fuel [1, 2]. That kind of
fuel can be also used in boilers for energy purposes [3].
However due to transesterification processes, the costs
of production of such fuels are higher than the fuels
obtained from petroleum. Unrefined vegetable oils,
because of their properties, especially high viscosity,
could not be directly used as the fuel in diesel engines.
But unrefined vegetable oil can be used for energy
purposes, e.g. to produce heat.
When conventional design of liquid fuel burners and
conventional heating installation are used combustion
of pure vegetable oil is not possible. In such conditions
combustion process can occur properly only when
vegetable oil is mixed with light mineral oil.
Results of tests of combustion of liquid fuels which
composition were varied by mixing in different
proportions two oils: rapeseed and mineral light oil are
presented in paper. Experiments allowed to evaluate the
influence of mass percentage of rapeseed oil in mixture
and fuel injection pressure on parameters achieved
inside combustion chamber.
Installation and test plan
Experiments were curried in laboratory, cylindrical
shape, consisted of two segments combustion chamber.
Each segment has own water coat with possibility of
establishing individual cooling water flow.
Cooling water
Combustion chamber
Measured slots Oil burner
Manometer
Water meters Oil pump Oil filter Oil meter Oil tank
∗ Corresponding author:antoni.zajdel@polsl.pl
Proceedings of the European Combustion Meeting 2009
Fig. 1. Scheme of laboratory installation.
Scheme of laboratory set is shown in figure 1.
Burner used for combustion of tested oil mixtures was
a conventional oil burner, made by the firm Körting,
equipped with atomizer of pressure jet type, designed
for combustion of mineral light oil.
In a chamber the combustion of earlier prepared
mixtures were performed. Preliminary tests showed that
combustion of mixtures, in which mass percentage of
rapeseed oil exceeds 70%, is practically impossible.
Flames lost stability and many unburned fuel droplets
fell on the bottom of chamber. Visually evaluation of oil
flame let to state that only if rapeseed oil fraction in
mixture not exceeds 50% the flame stability is proper.
Amount of oil droplets falling out of flame is smaller
and smaller when rapeseed oil percentage decrease (for
40 and 50% only individual droplets).
Therefore more detail experiments were carried for 6
variants of oil mixture, with following contents of
rapeseed oil: 0 (pure mineral oil), 10, 20, 30, 40 and
50%. Other varied parameter, besides composition of oil
mixture, was the pressure of fuel injection. Five
different values of pressure were applied: 8, 9, 10, 11
and 12 bar. The value of air excess ratio was kept
constant during all experiment on the level of 1,11-1,15.
It was observed that when rapeseed oil fraction was
increased (for the same value of injection pressure) the
flame dimensions also increased and colour of flame
was changed into more orange shade. It evidence that
the concentration of soot particles inside flame volume
raised with growing amount of rapeseed oil in mixture
what was the result of worsening the exactitude of fuel
atomization process because of growing viscosity of
mixture.
During each test, after attaining the steady thermal
state in chamber, many parameters were measured and
their values were recorded or several times noticed to
evaluate the average values. Measured parameters were
as follows:
- O2, CO, NO in fumes,
- flow rates of cooling water and fuel oil,
- temperature of cooling water in inlet and outlet
pipes of two chamber segments,
- temperature of fumes.

Values of some measured parameters were used to
calculate the other parameters, which characterize tested
process thermally, such as: thermal power of burner,
heat flux absorbed by water cooling the chamber walls
and effectiveness of energy transfer process inside
combustion chamber.
Physical characteristics of rapeseed oil were
measured by many investigators [4, 5]. Data from these
papers and our own measurements are very similar, e.g.
LHV of mineral oil is 42.5 MJ/kg and rapeseed oil 36.9
MJ/kg. These values were use for calculation of burner
thermal power.
Results and Discussion
Results of measurements and calculations are
presented in figures 2-7. Each graph shows the
influence of growing percentage of rapeseed oil (in
mixture with mineral oil) on the values of different
parameters. Particular curves on each graph refer to
different values of injection pressure.
In fig.2 it is seen how differed the oil burner
capacity with variation of rapeseed oil fraction in
mixture for different values of injection pressure.
oil burner capacity kg/h
4.0
3.5
3.0
2.5
2.0
0 10 20 30 40 50
rapeseed oil fraction %
&8 bar %9 bar C10 bar /11 bar "12 bar
Fig. 2. Effect of the composition of mixture and the
pressure of injection on burner capacity.
It is obvious that the higher oil pressure cause the
higher oil rate in the burner. When rapeseed oil
percentage rises the mixture has higher density and
higher viscosity. Higher fluid viscosity causes higher
resistance of flow. It is seen that, in tested range of
mixture composition, the influence of density growth
predominates the flow resistance growth and in
consequence the mass flow rate of mixture rises with
rapeseed oil percentage growth.
Value of mass flow rate of oil mixture leaving the
burner influences the thermal power of burner. In fig.3
the thermal power of burner for tested variants of
combustion process is shown. For each pressure of oil
injection the thermal power of burner, which is a
product of two values: oil mass flow rate and oil low
heat value, remains almost constant. In tested range of
2
mixture composition, as the fraction of rapeseed oil
rises, the product of oil mass flow rate, which also rises
burner thermal power kW
48
44
40
36
32
28
0 10 20 30 40 50
rapeseed oil fraction %
&8 bar %9 bar C10 bar /11 bar "12 bar
Fig. 3. Effect of the composition of mixture and the
pressure of injection on thermal power of oil burner.
and oil low heat value, which decreases, gains slight
maximum for about 30% of rapeseed oil in mixture.
Concentration of CO and NO in waste gases leaving
the chamber are presented in figures 4 and 5.
CO emission (3% O 2 ) ppm
700
600
500
400
300
200
100
0
0 10 20 30 40 50
rapeseed oil fraction %
&8 bar %9 bar C10 bar /11 bar "12 bar
Fig. 4. Concentration of CO in waste gases versus
rapeseed oil fraction for different values of injection
pressure.
It is seen that influence of pressure of oil injection
on CO and NO emission is not evident. From others the
results obtained for 8 bar, the lowest value of pressure,
distinguished most clearly. When pressure of fuel
injection has the lowest value the atomization of oil is
least fine and combustion of fuel occurs with small
intensity. Burner capacity is also lowest for this
pressure. From these reasons the temperature inside
combustion chamber, in that cases, have the lowest
level. When temperature in combustion area is low
more CO and less NO are created.

With growth of rapeseed oil percentage a viscosity
of mixture rises and atomization process goes worse. In
such conditions fuel burning can occur not complete and
NO emission (3% O2) ppm
60
50
40
30
20
0 10 20 30 40 50
rapeseed fraction %
&8 bar %9 bar C10 bar /11 bar "12 bar
Fig. 5. Concentration of NO in waste gases versus
rapeseed oil fraction for different values of injection
pressure.
amount of CO rises. Conditions, which are favorable for
CO creation as general cause NO emission decrease.
Main goal of fuel combustion process in a boiler is
transfer of energy to heated medium. Heat absorbed by
water cooling the chamber walls shows how intensively
this process occurs. Values of heat fluxes absorbed by
water flowing through cooling coat of chamber walls
are presented in fig. 6.
heat flux absorbed by water kW
22
21
20
19
18
17
16
15
0 10 20 30 40 50
rapeseed oil fraction %
&8 bar %9 bar C10 bar /11 bar "12 bar
Fig. 6. Heat absorbed by cooling water for different
values of rapeseed oil fraction and injection pressure.
Dependences showed in fig. 6. are very similar to
those ones showed in fig. 3. It results from fact that heat
fluxes transferred to heated medium depend, in
combustion chamber, first of all, on thermal burner
power at the moment. Higher burner power affords
higher values of heat fluxes inside combustion chamber.
However, the magnitude of heat fluxes did not
inform about thermal perfection of energy transfer
process. Effectiveness of energy transfer process taking
3
place inside combustion chamber is expressed by the
ratio of two values: heat flux transferred to heated
medium and burner power (release energy). In fig. 7
effectiveness of heating the water inside the chamber is
presented. The level of obtained effectiveness values is
rather low, however in that case the comparison of
tested variants is more important thing.
effectiveness %
54
52
50
48
46
44
42
40
0 10 20 30 40 50
rapeseed oil fraction %
&8 bar %9 bar C10 bar /11 bar "12 bar
Fig. 7. Effectiveness of energy transfer process
occurring inside chamber fired by oil mixtures.
It is seen that higher values of effectiveness are
achieved for lower values of oil injection pressure.
Explanation of such effect is as follows.
When the pressure of oil injection rises the
atomization process proceeds more exactly and obtained
oil droplets have smaller sizes. Combustion process
occurs more intensively and oil flame, in spite of higher
temperature, radiates less amount of heat. The main
reason of this is the lower concentration of soot particles
inside flame volume. Soot concentration inside the
flame influences decisively on intensity of flame
radiation. So it is seen that energy effects are higher
when atomization process occurs not very perfect. From
this point of view an increase of rapeseed oil in mixture
is also profitable.
Conclusions
On base of our investigation it can be stated that if
standard oil burner and standard combustion conditions
are applied the pure raw rapeseed oil can not be used as
substitute of mineral oil.
Combustion process can occur only when rapeseed
oil is mixed with light mineral oil. The best effects,
from thermally and ecologically point of view (CO and
NO emission, not complete fuel burning), were
observed when proportion of rapeseed oil to mineral oil
in mixture was 30% to 70%.
References
[1] Z. Szlachta, Using rapeseed fuels in Diesel engines,
Communication and telecommunication Publishing
House, Warsaw 2002, (in Polish).

[2] W. Lotko, Using vegetable and hydrocarbon fuels in
Diesel engines, Scientific-Technical Publishing
House, Warsaw 1997, (in Polish).
[3] G. Tashtoush, M. I. Al-Widyan, A. O. Al-Shyoukh,
Combustion performance and emissions of ethyl
ester of a waste vegetable iol in a water-cooled
furnace, Applied Thermal Engineering 23 (2003)
285-293.
[4] D. Jóźwiak, A. Szlęk, Evaluation of rapeseed oil as
a fuel for boilers, Power Engineering 6 (2006) 449-
451 (in Polish).
[5] J. San José Alonso, J.A. López Sastre, C. Romero-
Ávila, E.J. López Romero, Combustion of rapeseed
oil and diesel oil mixtures for use in the production
of heat energy, Fuel Processing Technology 87
(2006) 97-102.
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