Journal of Power and Energy Engineering, 2013, 1, 77-83 Published Online October 2013 (
Copyright © 2013 SciRes. JPEE
Performance Characteristics of n-Butanol-Diesel Fuel
Blend Fired in a Turbo-Charged Compression Ignition
Lennox Siwale1, Lukács Kristóf2, Torok Adam2, Akos Bereczky2, Antal Penninger2,
Makame Mbarawa3, Kolesnikov Andrei1
1Department of Mechanical Engineering, Tshwane University of Technology, Private Bag X680, Pretoria, South Africa; 2Department
of Energy Engineering, Budapest University of Technology and Economics, Budapest, Hungary; 3Ministry of Communication,
Science and Technology, United Republic of Tanzania Department of Energy, Dar-es-Salaam, United Republic of Tanzania.
Received October 2013
In this study, n-butanol-diesel blends were burned in a turbo-charged, direct injection diesel engine where the brake
thermal efficiency, (BTE) or brake specific fu el consumption, (BSFC) was compared with that of ethanol-diesel or me-
thanol-diesel blends in another study by other authors. The test blends used were B5, B10 and B20 (where B5 is 5%
n-butanol by volu me and 95% diesel fuel-DF). In this s tudy, the BTE w as higher and the BSFC improved more than in
the other study. Because of improved BTE with increasing brake mean effective pressure, BMEP, the BSFC reduced,
however the increased shared volume of n-butanol in DF increased BSFC. Adding n-butanol in DF slightly dera ted the
torque, brake power output with increasing speed, and caused a fall in exhaust gas temperatures, (EGT) which improves
the volumetric efficiency and reduces compression work. Therefore, a small-shared volume of n-butanol in DF f ired in
a turbo-charged diesel engine performs better in terms of BTE and BSFC than that of ethanol or methanol blending in
Keywords: Brake Specific Fuel Consumption; Brake Thermal Efficiency; Exhaust Gas Temperature; n-Butanol/Diesel
1. Introduction
The depletion, price uncertainty and negative effect of
fossil fuels on the environment are some of the key is-
sues that have led to a worldwide search or move to-
wards alternative, renewable energy sources with lesser
and greener emissions. The transport sector consumes
about 58 percent of the primary energy consumption in
the world. These fossil fuels which are becoming ex-
hausted are the major contributors to greenhouse gas,
(GHG) and climatic change [1]. The promising alterna-
tive types of fuel for petroleum oil in transportation are
biofuels. These are biodegradable and do not have the
same negative effect as the petroleum based fuels on the
environment. Oxygenated fuels such as alcohols are one
of the biofuels that have attracted research for many
years because they burn cleaner than fossil fuels [2]. The
advantages of alcohol as a fuel includes the following [3].
Alcohols, (a) have a lower viscosity than diesel and so
improve injection, atomisation and vaporisation of the
charge,(b) have less emission to the environment than
diesel owing to a higher stoichiometric fuel-to-air ratio
than diesel fuel (DF); (c) have a high evaporative cooling
effect, resulting in cooler intake charge. This raises the
volumetric efficiency and reduces compression work, be-
sides alcohols (d) have higher laminar flame propagation
than DF [4]; shorten and enhance combustion and so
improve the brake thermal efficiency of the engine. Etha-
nol has received a wider application [5-8], although the
latter possesses better qualities than ethanol. Butanol has
a number of advantages over ethanol [9] such as a higher
cetane number (CN), less hydrophilic; and has a higher
miscibility factor in DF than ethanol [10]. Etha nol is un-
suitable to use in diesel engines because of its insufficient
auto ignition quality [11]. Butanol (IUPAC) is a colorless,
and may irritate the eyes and skin [6]. Lubricity, inter-
solubility, and corrosive effects of n-butanol have been
discussed in our earlier paper [12]. Researchers have
carried out studies to determine the effects of n-butanol
or isobutanol added to DF on performance characteristics.
Rakopoulos, et al. [7] reported that the potential of buta-
nol as a biofuel remains to be determined. The compari-
Performance Characteristics of n-Butanol-Diesel Fuel Blend Fired in a Turbo-Charged Compression Ignition Engine
Copyright © 2013 SciRes. JPEE
son of properties of n-butanol, ethanol with diesel is listed
in Table 1 [13,14]. Rakopoulos et al. [10] conducted
experiments on a hydra engine and found a higher brake
specific fuel consumption, (BSFC) at low brake mean
effective pressure (BMEP) than at high BMEP for all the
fuels using the blends 8%, 16% and 24% o f n-butanol in
DF. The BSFC slightly decreases with increasing load
for all the fuels whereas BSFC increases with retarded
main injection timing using the blends 8% and 16% of
n-butanol in DF [15]. The BSFC increases when main
injection timing is retarded using isobutanol, ISB15 and
ISB20. The brake thermal efficiency, (BTE), was similar
for all the fuels and increased with increasing BMEP
using blends 8% and 16% of n-butanol in DF. The BTE
slightly improved at high speed for blends up to 10%
isobutanol [16]. It can be observed from the preceding
cited studies that it is not quite clear which blends,
whether ethanol-diesel, methanol-diesel blends or n-bu-
tanol-diesel blends would produce superior performance
characteristics when burned in the compression ignition
(CI) engine.
The purpose of this work was to evaluate the perfor-
mance characteristics of the small volume ratios of n-bu-
tanol-in DF in a diesel engine and compare results with a
similar study by other authors [3] who used ethanol-di-
esel and methanol-diesel blends.
2. Methods and Mater i al s
2.1. Experimental Set up
Figu re 1 illustrates the e ngine layout for the exp eriments.
The study was conducted on a four-cylinder piston, 1.91
L - 66 kw Turbo-Direct Injection (TDI) Volks Wagen
diesel engine. This study is a continuation of the earlier
study carried out by the authors on combustion [12]. A
fixed electronic diesel control unit (EDU) was used to
maintain stiochiometric engine performance. The diesel
fuel, D2 was used as reference fuel. The test torque was
varied from 100%, 75% and 50% to 25% of full load.
The specifications of the measuring equipment used for
the experiments are listed in Tab le 2. The engine was ran
on steady state condition for about two minutes for every
measuring point before recording values. Three blends
were used namely: B5, B10, or B20, and reference fuel
B0 (B0 is the reference diesel, D2.
The blends were prepared on the same day using in-
Table 1. Properties of diesel, n-butanol and ethanol.
Fuel properties Diesel fuel n-butanol C4H9OH Ethanol C2H5OH
Density at 20 (˚C, kg/m3) 837 810 788
Cetane number 50 ~25 ~8
Lower calorific value, MJ/kg 43 33.1 26.8
Kinematic viscosity at 20˚C, mPas 3.4
Boiling point ˚C 180-360 118 78
Latent heat of evaporation, kJ/kg 250 585 840
Oxygen, %wt. 0 21.6 34.8
Stoichiometric air-fuel ratio 15.0 11.2 9.0
Molecular weight 170 74 46
Source [13,14]
Figure 1. Schematic diagram of engine arrangement and set up for data acquisition.
Performance Characteristics of n-Butanol-Diesel Fuel Blend Fired in a Turbo-Charged Compression Ignition Engine
Copyright © 2013 SciRes. JPEE
Table 2. Data measur i ng equipment.
Eddy current dynamometer Type: FE350s-BORGHI and SAUERI
Pressure transducer Type: KISTLER KIAG 600
TDC and crank angle speed pick up Type: OPTICAL ENCODER HENGSTLER RI 32-0/1024.ER.14KA
Thermocouple Type K
Fuel measurement Type: AVL 7131-12
tank method with standard laboratory glassware. Operat-
ing the engine for 20 to 30 minutes using the reference
fuel (D2) warmed it up. The initial fuel in the tank and
delivery system was nearly emptied before a new test
fuel was fed into the fuel tank. The engine was ran on
high load for a short period in order to speed up the re-
moval of the fuel in the fuel delivery lines. The engine
was ran using the test blend for another 20 minutes in
order to stabilize the engine on the new test fuel.
The fuel mass-flow rate was measured using the AVL
7131-12 dynamic fuel consumption measuring equip-
ment. The fuel balance works on the gravimetric mea-
suring principle. This instrument enables the highest
temperature stability of the fuel condition ing system with
measuring accuracy of 0.12%; including self-calibration
according to ISO 9001. Fuel is supplied to the engine
from a measuring vessel the weight of which is conti-
nuously measure d.
The torqu e was measured by a Borghi and Saveri eddy
current dynamometer, type FE-350S and the crank angle
and speed were measured by an encoder or sensor (placed
on the dynamometer shaft connected to the TDI diesel
engine). The engine parameters are listed in Table 3.
2.2. Materials
The n-butanol fuel was manufactured by VWR Prolabo
(BDH), of 99.99% purity, density of 809 kg/m3 (20˚C),
molecular formula:C4H9OH, molecular mass: MW 74.12
kg/kmol, boiling point: 118˚C (at 101.3 kPa), melting
point: 89.8˚C, and flash point: 30˚C. The type of DF
used for the experiments was: D2, standard EN 590, CN:
51, sulphur content of 10 mg/kg; water content of 200
mg/kg; and kinematic viscosity of 2.00 to 4.5 (mm2/s) at
40˚C, specific density at 15˚C, 0.82; and flash point
of >55˚C. The reference fuel was DF, (D2).
3. Results and Discussion
A study was conducted where a small-shared volume of
ethanol with diesel (E5 and E10) was compared with
methanol/diesel blends: M5, M10 (M5 is 5% by volume
of methanol in DF). The test was based on a naturally
aspirated engine with bore size of 98 mm and stroke 100
mm and compression ratio 17:1. [3]. The cited study is
hence designated as study A.
Figure 2 illustrates the effect of blends on BSFC. It is
well established that the lower energy content of the al-
Table 3. Engine parameters.
Bore 79.5 [mm]
Stroke 95.5 [m m]
Compression ratio 19.5 -
Maximum Torque 202 [Nm]/1800 [rpm ]
Maximum power 66 [kW]/4000 [rpm]
Fuel system:
Injector pump Distributor-type
(Bosh VP37)
Combustion chamber Bowl in piston
Injector type andpressure 5 hole, 180 [bars]
cohols increases the BSFC. Therefore, alcohols having a
higher heating value than others will have a lower BSFC.
For this reason, the minimum BSFC in study A was 298
g/kwh compared with 237 g/kwh in the current study
where n-biutanol/diesel blends were used at 1500 RPM.
Figures 3(a) and (b) depict the BTE at speeds 1500
and at 3000 RPM respectively. The oxygenated fuels such
as alcohols are well known to improve combustion when
blended with DF because of the oxygen atoms attached
to their structural composition. In order to determine
which blends have a better performance with regards to
thermal efficiency, the BTE between study A and this
study were compared. The value of BTE in study A was
in the range of: 0.22 to 0.28 for the speed range of 1000
to 1600 RPM. In the current study, the BTE fell into the
range: 0.25 to 0.35 with 1500 RPM.
The higher BTE of n-butanol/diesel blends is attri-
buted to their higher CN than ethanol/or methanol/diesel
blends. In the current study, BTE increased during the
testing of the fuels with BMEP. The ir regularity observed
on 3 and 6 bars, BMEP with 3000 RPM could probably
be attributed to the slower evaporation of the n-butanol
blends as a result of their lower CN than DF. The con-
stant BTE (see Figure 3) at a particular BMEP does not
correlate with the BSFC at the same BMEP (see Figure
2) with respect to the trends, according to this formula:
BTE is 1/(BSFC*LHV). This can be explained as follows.
The energy content, that is the Lower heating value,
(LHV) of the blend decreases with the increasing fraction
by volume (v/v) of n-butanol in DF. This causes the fuel-
mass flow to increase the BSFC. Thus, the two effects
compensate each other and maintain the same BTE. Im-
provement of BTE can be as a result of better atomisa-
tion of the blend, and effects on friction [17]. Atomisa-
tion of a fuel is affected by the fuel’s surface tension,
Performance Characteristics of n-Butanol-Diesel Fuel Blend Fired in a Turbo-Charged Compression Ignition Engine
Copyright © 2013 SciRes. JPEE
Figure 2. Brake specific fuel consumption (BSFC) vs. BMEP (a) at 1500 rpm (b) at 3000 rpm.
Figure 3. (a) Brake thermal efficiency (BTE) vs BMEP (a) at 1500 rpm (b) at 3000 rpm.
viscosity and density, jet diameter or Sauter Mean Di-
ameter (SMD), relative velocity of the jets and its sur-
roundings and turbulence [18]. High viscosity of the liq-
uid fuel, leads to poor atomisation and break-up, which
increases the SMD and reduces the spray angle. The
droplets reaching the surface of the cylinder wall can
cause dilution of the lubricating oil [18]. This can reduce
the friction torque by improving the lubricity around the
piston rings during the compression stroke [17]. Howev-
er, the spray of oxygenated fuel presents a finer droplet, a
stronger interface between the fuel spray and the sur-
rounding gas, and a more violent vortical motion. There-
fore, the viscosity of the oxygenated fuels exerts a sig-
nificant effect on the improvement of atomisation beha-
vior [19]. This action causes a slightly improved BTE.
Figu re 4 depicts the effect of the blends on torque and
power as the speed is increased. The lowered power and
torque with engines operating on n-butanol-diesel blends
is attributed to changes to the heating value (which is
lower than that of pure DF) brought about by the blends.
Another contributing factor is the control system. This
determines the level of the fuel-control ring position,
which changes depending upon the load applied to the
engine. Algorithms used for the maps of the EDC are
tailored for DF. When the fuel is changed, the EDC in-
terprets that the fuel in use is diesel if not modified. The
Figure 4. Torque (tb) and Brake power, (pb) vs speed.
EDC in this study was not modified. The drop in the
energy content of the fuel, (due to blending) causes a fall
in the power output or pressure, which is the signal mapped
to the EDC. The EDC changes the fuel-control ring posi-
tion to increase the mass of fuel injected into the com-
bustion chamber. However, the fuel mass quantity deli-
vered or the fuel-control ring level cannot be increased or
raised above the reference value set for the DF. This ex-
plains why the power was de-rated with the increase of
n-butanol shared volume in DF. The maximum torque
and the power output are both sensitive to the speed (see
Performance Characteristics of n-Butanol-Diesel Fuel Blend Fired in a Turbo-Charged Compression Ignition Engine
Copyright © 2013 SciRes. JPEE
Figure 4).
Figures 5(a) and (b) illustrate the effect on the EGT,
at 1500 and 3000 RPM respectively. Whereas the load
(BMEP) caused EGT to increase, blends, which have a
higher heat of evaporation than DF, lowered EGT through
evaporative cooling. Therefore, the EGT using DF was
higher than that of the blends. The lower EGT of the
blends than DF contributes to increasing the volumetric
efficiency and in turn reducing compression work during
the compression stroke.
Figures 6(a) and (b) illustrate the effect of the blends
on manifold boost (air) pressure at 1500 and 3000 RPM.
The boost (air) pressure level is a measure that helps to
improve the BTE as the fuel-air ratio is reduced. Air
pressure boosted in this way by the turbo-charged device
at the intake side of the engine is not a parasitic work
because the turbo-charged device as is well known is
driven by the waste exhaust gas. Therefore, the volume-
tric efficiency is again improved and the compression
work (parasitic work of the engine) reduced. This con-
sequently improves the BTE of the engine.
Figu r e 7 illus trates the effect of all the test fuels on the
injection timing or start of injection (SOI) in the crank
angle degrees, (CADs) with 1500 and 3000 RPM. The
injection timing was more advanced at the speed of 3000
RPM than at the speed of 1500 RPM. This was expected,
owing to the reduced (CADs) that the fuel mixture was
permitted to burn at high speed. However, the EDC re-
tarded the timing of SOI on partial loads in order to
match the operating conditions. The fuel-injection tim-
ings of the blends and DF controlled by the EDC for dif-
ferent speeds of 1500, 2500, 3000 and 3500 RPM were:
11˚ 11˚, 12˚ and 15˚ CAD before top dead centre (BTDC)
4. Conclusions
The purpose of this work was to compare the perfor-
mance characteristics of small fractions (v/v) of n-buta-
nol-diesel blends fired in a turbo-charged, direct injection
diesel engine with a similar study by other authors using
ethanol-and methanol-diesel blends.
The BSFC was lower and BTE was higher in our
study than in the other study.
The reduction of exhaust gas temperature (EGT) im-
proves the volumetric efficiency, which in turn re-
duces the compression work during the compression
Applying small-shared volumes of n-butanol to diesel
fuel improves the BTE and BSFC requiring no engine
modification compared with that of ethanol-or me-
thanol-diesel blends. The boost pressure improves brake
thermal efficiency (BTE) whereas the start of injec-
tion is retarded at low speed.
Figure 5. Exhaust gas temperature, (EGT) vs BMEP (a) at 1500 rpm and (b) at 3000 rpm.
Figure 6. Boost (air) pressure vs BMEP (a) at 1500 rpm (b) at 3000 rpm.
Performance Characteristics of n-Butanol-Diesel Fuel Blend Fired in a Turbo-Charged Compression Ignition Engine
Copyright © 2013 SciRes. JPEE
Figure 7. Crank angle advance for start of injection (SOI)
timing for DF and bl ends at different loads and speed.
5. Acknowledgements
The authors wish to acknowledge and are greatly indebted
for the financial support: (UID 72384 and TÉT_10-1-
2011-0005) and facilitation by the joint research colla-
boration between two Universities: Tshwane University
of Technology, Pretoria, South Africa and Budapest Uni-
versity of Technology and Economics, Budapest, Hun-
gary, where the engine experiments were conducted in
the laboratory facility, Jendrassik Gyorgy hotechnikai
Laboratorium in Budapest BME.
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