Influence of Key Properties of Pongamia Biodiesel on Performance Combustion and Emission Characteristics of a DI Diesel Engine

Abstract

The purpose of this study is to examine the influence of key properties of pongamia biodiesel on
engine performance, combustion, and emission characteristics of direct injection diesel engine. The key
properties of the pongamia biodiesel such as viscosity, density, bulk modulus, calorific value, iodine value,
cetane number, saturation% and oxygen% are considered for this study. Experiments were conducted in a
naturally aspirated, single cylinder, four-stroke, stationary, water cooled, constant rpm, in-line (pump-high
pressure tube-fuel injector) direct injection diesel engine with pongamia biodiesel (with and without
preheating), and petroleum diesel as fuels. The performance was evaluated in terms of fuel consumption, brake
specific energy consumption, and thermal efficiency. A significant improvement in thermal efficiency was
observed with preheated biodiesel. The peak pressures and peak heat release rates for biodiesel was slightly
higher than diesel fuel. The high peak pressures of the biodiesel are probably due to dynamic injection advance
caused by its higher bulk modulus. The higher values of peak heat release rates indicate better premixed
combustion with the biodiesel. However, the peak pressures for preheated biodiesel decreases due to late
injection and faster evaporation of the fuel. It was observed that at full load the nitric oxide emission of
biodiesel is increased by 6 %. The hydrocarbon emissions of the biodiesel are very low and are reduced up to 32
% as compared to that of diesel fuel. There is a significant reduction in all exhaust gaseous emissions. Also a
considerable reduction in nitric oxide emission is observed with preheated biodiesel due to change in premixed
combustion phase. However when the preheated biodiesel is used, the smoke emission was increased due to
prolonged combustion (diffusion) at lower viscosity. A considerable reduction in carbon monoxide emission
was also observed with the preheated biodiesel.

Full text

Influence of Key Properties of Pongamia Biodiesel on Performance
Combustion and Emission Characteristics of a DI Diesel Engine
CH. SATYANARAYANA1, AND P. V. RAO2
1Department of Marine Engineering, 2Department of Mechanical Engineering
Andhra University
Visakhapatnam-530 003, Andhra Pradesh
INDIA
prof.pvrao@gmail.com satyanarayanachaliki@gmail.com http://www.andhrauniversity.info
Abstract: The purpose of this study is to examine the influence of key properties of pongamia biodiesel on
engine performance, combustion, and emission characteristics of direct injection diesel engine. The key
properties of the pongamia biodiesel such as viscosity, density, bulk modulus, calorific value, iodine value,
cetane number, saturation% and oxygen% are considered for this study. Experiments were conducted in a
naturally aspirated, single cylinder, four-stroke, stationary, water cooled, constant rpm, in-line (pump-high
pressure tube-fuel injector) direct injection diesel engine with pongamia biodiesel (with and without
preheating), and petroleum diesel as fuels. The performance was evaluated in terms of fuel consumption, brake
specific energy consumption, and thermal efficiency. A significant improvement in thermal efficiency was
observed with preheated biodiesel. The peak pressures and peak heat release rates for biodiesel was slightly
higher than diesel fuel. The high peak pressures of the biodiesel are probably due to dynamic injection advance
caused by its higher bulk modulus. The higher values of peak heat release rates indicate better premixed
combustion with the biodiesel. However, the peak pressures for preheated biodiesel decreases due to late
injection and faster evaporation of the fuel. It was observed that at full load the nitric oxide emission of
biodiesel is increased by 6 %. The hydrocarbon emissions of the biodiesel are very low and are reduced up to 32
% as compared to that of diesel fuel. There is a significant reduction in all exhaust gaseous emissions. Also a
considerable reduction in nitric oxide emission is observed with preheated biodiesel due to change in premixed
combustion phase. However when the preheated biodiesel is used, the smoke emission was increased due to
prolonged combustion (diffusion) at lower viscosity. A considerable reduction in carbon monoxide emission
was also observed with the preheated biodiesel.
Key-Words: Pongamia, properties, bulk modulus, preheating, DI diesel engine, combustion, emissions
1 Introduction
Recent fuel crisis [1], increasing cost, and shortage
of petroleum diesel (PD) have stimulated the
economic feasibility studies of vegetable oils as a
fuel in diesel engines [2]. India has about 86 types
of oilseed- bearing perennial trees [2, and 3] of
which karanja seed (Pongamia glabra); mahua
(Madhuca Indica), neem (Azadirachta) and jatropha
(jatropha curcas) are the important ones.
2 Pongamia Oil
Pongamia, a medium sized glabrous tree, popularly
known as karanja is widely available in India. The
oil content of karanja seed is about 33 % [4].
Pongamia oil has a yellowish orange color. The feed
stock dependent fatty acid compositions
(hydrocarbon chains) of pongamia oil vary from
‘C
16
to C
24
’, with the long chain oleic acid (C
18:1
),
linoleic acid (C
18:2
), palmitic acid (C
16:0
), stearic acid
(C
18:0
), and behenic acid (C
22:0
) are the highest [4] as
shown in Fig. 1 and 2. The amount of fatty acids
present in pongamia oil is oleic acid: 49.4%, linoleic
acid: 19%, palmitic acid: 10.6%, stearic acid: 6.8%,
behenic acid: 5.3%. This pongamia oil contains
29.2% saturated fatty acids (SFA), 51.8% of mono-
unsaturated fatty acids (MUFA) and 19% of poly-
unsaturated fatty acids (PUFA) as shown in Fig. 3.
The carbon chain of PD fuel includes both medium
(C
8
-C
12
) and long (C
14
-C
32
) carbon chain. The
hydrocarbons in PD fuel range in size from 8 carbon
atoms per molecule to 32 carbon atoms per
molecule (C
8
-C
32
) [5]. The peak in the carbon-
number distribution occurs at about 13 to 19 carbon
atoms per molecule (C
13
-C
19
), as shown in Fig. 1.
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
34
Issue 2, Volume 4, April 2009

C8
C10
C12
C14
C16
C18
C20
C22
C24
C26
C28
0
10
20
30
40
50
60
70
80
Percentage
Carbon Number
PBD PD
Fig. 1: Carbon number distribution
0
10
20
30
40
50
Percentage
C16:0
C18:0
C18:1
C18:2
C20:0
C20:1
C22:0
C24:0
Fig. 2: Fatty acids in pongamia oil
29.2
51.8
19
10
15
20
25
30
35
40
45
50
55
Percentage
SFA MUFA PUFA
Fatty Acids
Fig. 3: Saturated and unsaturated fatty acids
in pongamia oil
5
10
15
20
25
30
35
40
45
Percentage
n- Paraffin
i-Paraffin
Naphthene
Aromatics
Fig. 4: Composition of PD
PD fuel typically contains over 400 distinct types of
organic compounds. Approximately 80 % (vol.) of
the PD fuel contains alkanes, with the remainder
(i.e. 20%) comprised of aromatic molecules. Typical
PD fuel contains approximately 44% of n-Paraffin,
29% of i-Paraffin and 7% of Naphthene as shown in
Fig. 4. The aromatics include polycyclic aromatic
compounds containing 2, 3, 4, and 5 fused benzene
rings. The aromatics containing multiple benzene
rings are known as poly-aromatic hydrocarbons
(PAHs). The aromatic benzene rings of the
polycyclic hydrocarbons act as nuclei for growth of
undesired soot [6].
3 Biodiesel Preparation
The BD fuel is produced by chemically reacting the
oil with an alcohol (methyl), in the presence of a
catalyst. A two-stage process [7, 8, and 9] is used
for the esterification of the pongamia oil. The first
stage of the process is to reduce the free fatty acids
(FFA) content in pongamia oil by esterification with
methanol (99% pure) and acid catalyst (sulfuric
acid-98% pure) in one hour time of reaction at 55
0
C. In the second stage, the triglyceride portion of
the pongamia oil reacts with methanol and base
catalyst (sodium hydroxide-99% pure), in one hour
time of reaction at 65
0
C, to form methyl ester and
glycerol. The raw fatty acid methyl ester is then
purified by the process of water washing with air-
bubbling. The biodiesel produced from pongamia oil
is known as pongamia oil methyl ester (POME) or
simply known as pongamia biodiesel (PBD).
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
35
Issue 2, Volume 4, April 2009

4 Biodiesel Characterization
Measurements of key properties (both physical and
chemical) were carried out according to ASTM
D6751-02 (Standard Specification for Biodiesel
Fuel (B100) Blend Stock for Distillate Fuels [10])
standards. The specifications and manufacturers of
the instruments were given in the following Table 1.
Table 1: ASTM methods and instruments used to
measure various fuel properties.
Fuel
Property
ASTM
method
Instrument Model
Density D 1298 Hydrometer
Petroleum
Instruments,
India
Flash and
Fire
Points
D92 Cleveland
Open-Cup
Flash
Tester
Petroleum
Instruments,
India
Calorific
Value
D 240 Bomb
Calorimeter
Parr, UK
Kinematic
Viscosity
D 445 Kinematic
Viscometer
Setavis,
UK
From the testing of the pongamia biodiesel, it is
observed that these properties are meeting the
specifications of ASTM biodiesel standards as
shown in Table 2, and PBD was found suitable for
usage as biodiesel. The importances of biodiesel key
properties are discussed as follows:
4.1 Oxygen and calorific value
The PD fuel made up of a mixture of various
hydrocarbon molecules and contain little oxygen (up
to 0.3%) and very small amount of sulfur, while the
pongamia biodiesel consists of three basic elements
namely: carbon, hydrogen and significant amount of
oxygen (11%) as shown in Table 2. The increase of
O
2
in biodiesel is related to the reduction of C and
H
2
, causes the lower value of lower calorific value
(LCV) of the biodiesel as compared to that of PD
fuel, because O
2
is ballast in fuel and ‘C and H
2
' are
the sources of thermal energy. The calorific value is
directly related to elemental composition of the fuel.
The LCV of PBD is lower than PD fuel because of
oxygen [11] and the biodiesel consists of esters of
fatty acids with a different degree of saturation. The
biodiesel has lower volumetric heating values (about
10%) than PD fuel. The stoichiometric air-fuel ratio
of biodiesel will be lower than PD fuel because of
O
2
is present in the biodiesel, as a result the
combustion efficiency of the BD fuel will be
increased [12].
Table 2: Properties of test fuels in comparison
to ASTM biodiesel standards.
Fuel
ASTM
Standards
Property Units PD
(HC)
PBD
(FAME)
Biodiesel
D 6751-02
Carbon
Chain
Cn C
8
-
C
28
C
16
-C
24
C
12
-C
22
Density
(ρ)
gm/
cc
0.825 0.875 0.87-0.89
Bulk
Modulus
(β)
@ 20
MPa [13]
MPa 1475 1800 -----
----
Kinematic
Viscosity
@ 40 0C
cSt 2.25 4.2 1.9-6.0
Cetane
Number
----- 48 55.84 48-70
Iodine
Value
g
Iodin
e/
100 g
38 81 120 max.
------
Oxygen % 0.3 11 11
Air/Fuel
ratio
(Stoichio
metric)
------ 14.86 13.8 13.8
Lower
Calorific
Value
kJ/kg 42
500
38 300 37 518
Sulfur % 0.25 0 0.05
Flash
Point,
(open
cup)
0
C 66 174 130 min.
Molecular
weight
226 281 292
Color
------
Light
yellow
Yellowish
orange ----
4.2 Cetane number
The ignition quality of the fuel is measured by
cetane number (CN) and it measures how easily
ignition occurs. The CN assists in smooth
combustion with lower knocking characteristics in
diesel engines. The CN requirement for the engine
depends on the design, size, speed, and load. Diesel
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
36
Issue 2, Volume 4, April 2009

engines that are run on low cetane fuels will suffer
from excessive CO, HC, PM and smoke emissions,
especially at low load and low temperature
operations. The CN depends on fuel composition
and influences the beginning of the process of
combustion and emissions. Cetane number of
biodiesel depends on fatty acids of feedstock [9].
The CN for PBD is 55.84 [4] and for PD is 48.
4.3 Iodine value
The iodine value (IV) shows the level of un-
saturation of the fuel, which means, higher the
percentage of unsaturation, larger will be the iodine
value [14]. The PBD with 70.8% unsaturation
(29.2% saturates) has an iodine value of 81; while
the PD with 40% unsaturation (60% of saturates)
has an iodine value of 38 as shown in Table 2.
4.4 Density and bulk modulus
The density (ρ) of biodiesel is more than that of PD
fuel and this compensates their lower values of
calorific value. For PBD, the density is lower than
that of water and its viscosity is low enough to allow
‘pump-ability’. The bulk modulus (β) of a liquid
fuel is defined as the pressure required to produce
unit volumetric strain and is given by the equation
(1) [11, 15]. The ‘β’ is a function of fuel
temperature, pressure, and density. The velocity (s)
of propagation of the pressure waves (or pulses)
through the fuel discharge pipe is given by the
equation (2) [16, 17, 18, and 19]. The values of ‘β’
and ‘ρ’ of PBD fuel is more than that of PD fuel as
shown in Table 2.
β = ρ. (∂p/ (∂ρ)
T
------------------- (1)
s = c. √ (β.g/ρ) -------------------- (2)
Where ‘c’ is velocity of sound and ‘g’ is
acceleration due to gravity
4.5 Flash point
The flash point temperature of PBD is higher
than that of PD fuel as shown in Table 2. The
higher value of flash point belongs to biodiesel,
because the biodiesel do not have the light
fractions. The safety of the biodiesel is ensured
due to higher flash point temperature.
4.6 Kinematic viscosity
The kinematic viscosity (KV) influences the
injection characteristics (spray pattern and depth of
penetration) of the fuel, and the quality of filtering.
Viscosity of the fuel decreases with the increase of
temperature, which in turn decreases the emissions
of non-combusted products. The viscosity of PD and
PBD at 30
0
C is 3.0, and 5.8 cSt respectively, as
shown in Figure 5. The high viscosity of PBD
reduces the leakage of fuel in the plunger and barrel
pair (Fig. 6) of the fuel pump [20] and minimum
viscosity limits are imposed to prevent the fuel from
causing wear in the fuel injection pump. The
viscosity of PBD at 50
0
C is 3.0 cSt and is equal to
that of PD fuel at engine room temperature of 30
0
C,
as shown in Fig. 5.
1
2
3
4
5
6
7
25 30 35 40 45 50 55
Temperature ( Deg.Cen.)
KV (cSt)
PD PBD
Fig. 5: Temperatures versus kinematic viscosity
5 Experimentation, Instrumentation
and Procedure
The experiments were performed on a naturally
aspirated, 4-stroke cycle, single cylinder, direct
injection diesel engine, with the specifications
shown in Table 3.
This engine employs the traditional, cam-driven, in-
line fuel injection system (Fig. 6). It consists of a
fuel pump (jerk pump), a high pressure tube (or fuel
discharge tube) of length 585 mm (23 inch.
approx.), and an injector (or atomizer). The pressure
pulses (or waves) are generated by the pump
plunger and the ‘column of fuel’ formed by the
pump chamber, discharge tube, and the injector.
This ‘column of fuel’ behaves like a stiff spring.
The pressure pulses propagate through the ‘column
of fuel’ to develop pressure at the nozzle end. When
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
37
Issue 2, Volume 4, April 2009

the fuel pressure reached a pressure more than that
required to open the needle valve of the injector, the
needle valve is lifted to inject the fuel into the
cylinder. For fuels with higher bulk modulus of
compressibility, a more rapid transferal of the
pressure wave takes place from pump end to the
injector needle valve and the earlier needle valve lift
causes an advanced (or early) injection. Therefore,
the fuel that is less compressible, such as PBD, will
inject prematurely in this system.
Table 3: Test engine specifications
Engine Make and
Model
Kirloskar (India),
AV1
Maximum Power
Output
3.72 kW
Rated Speed (constant) 1500
Bore x Stroke 80 mm x 110 mm
Compression Ratio 16.5
Fuel Injection System In-Line, Direct
Injection
Nozzle Opening
Pressure
205 bar
Method of Cooling Water cooled
BMEP @1500 rpm 5.42 kg/cm
2
Fig. 6: Conventional, cam driven, in-line fuel
injection system
The engine is tested with baseline PD fuel, and
PBD. Engine is also tested with preheated PBD
(PBD_H) to find the influence of reduced viscosity
on performance, combustion, and emission
characteristics. For preheating PBD fuels; heating
devices were placed along the fuel discharge tube.
The fuel injection was performed at a static injection
timing (optimum) of 23
0
BTDC set for PD fuel. The
engine is allowed to warm up at constant speed of
1500 rpm, until the cooling water temperature
reaches a steady state of 80
0
C. Eddy current
dynamometer is used to measure the power (or
torque). Engine brake load was varied in five steps
(at 0 kW, 0.93 kW, 1.86 kW, 2.79 kW, and 3.72
kW), ranging from 0% to 100% of the rated power
output of 3.72 kW. Apex innovations, Pune, India,
software: C7112 is used to record the in cylinder
combustion pressure. Pressure signals were obtained
using data acquisition system. The average pressure
data from 20 consecutive cycles were used for
calculating combustion pressure parameters.
6 Results and Discussion
6.1 Performance
The engine performance was evaluated in terms of
fuel consumption (FC), brake thermal efficiency
(BTE), and brake specific energy consumption
(BSEC).
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
0 0.93 1.86 2.79 3.72
Brake Power (kW)
FC (kg/hr)
PD
PBD
PBD_H
Fig. 7: Fuel consumption
6.1.1 Fuel consumption
The fuel consumption of PBD is more when
compared to PD at all loads as shown in Fig. 7. At
full load the FC for PD, PBD, and PBD_H are 1.03,
1.27 and 1.19 kg/hr respectively. PBD contains
more oxygen (11%) and less number of
hydrocarbons as compared to that of PD fuel.
Therefore the lower calorific value (LCV) is less for
Fuel discharge
tube
Fuel pump
chamber
Inlet
port
Cam
rotation
Needle
valve
Fuel
injector
Plunger
Barrel
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
38
Issue 2, Volume 4, April 2009

PBD than PD fuel. Consequently the FC is more for
PBD than PD. It is also observed that fuel
consumption is reduced at all loads for PBD_H
when compared to PBD. This is due to improved
spray characteristics and increased rate of fuel
evaporation of PBD_H at preheated temperature of
50
o
C.
10000
15000
20000
25000
30000
0.93 1.86 2.79 3.72
Brake Power (kW)
BSEC (kJ/kW-hr)
PD
PBD
PBD_H
Fig. 8: Brake specific energy consumption
11
16
21
26
31
0.93 1.86 2.79 3.72
Brake Power (kW)
B. Th. E. (%)
PD
PBD
PBD_H
Fig. 9: Brake thermal efficiency
6.1.2 Brake specific energy consumption
Brake specific energy consumption (BSEC) is an
ideal variable, because it is independent of the fuel.
The BSEC is the input energy required to develop
unit power output. Fig. 8 indicates the variation of
BSEC with power output. BSEC of PBD is higher at
all levels of power output compared to
corresponding PD values. This is presumably due to
lower value of LCV and higher value of kinematic
viscosity. Minimum BSEC of PBD and PBD_H are
13 060 kJ/kW-hr and 12 294 kJ/ kW-hr respectively,
against 11 868 kJ/kW-hr of PD fuel. The decrease in
BSEC of PBD_H may be attributed to increase in
combustion efficiency with preheating of biodiesel.
15
20
25
30
35
40
45
50
55
60
65
350 360 370 380 390 400 410
Crank Angle (degrees)
Pressure (bar)
PD
PBD
PBD_H
Fig. 10: Cylinder pressure
42
45
48
51
54
57
60
63
0 0.93 1.86 2.79 3.72
Brake Power (kW)
Peak Pressure (bar)
PD
PBD
PBD_H
Fig. 11: Peak pressures
6.1.3 Brake thermal efficiency
The Fig. 9 shows the variation of brake thermal
efficiency with power output. The brake thermal
efficiency increases as the output power increases,
for both the fuels. At full load, the efficiency of PD,
PBD, and PBD_H are 30.3%, 27.2% and 28.8%
respectively. According to thermodynamic analysis,
the degree of constant volume combustion increases
the indicated thermal efficiency. As shown in
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
39
Issue 2, Volume 4, April 2009

Fig.10, the premixed combustion of PBD is very
close to top dead center (TDC) and this behavior is
due to early injection caused by the higher bulk
modulus of PBD than that of PD fuel. The
improvement in thermal efficiency of PBD_H is
attributed to improved fuel spray characteristics, and
faster evaporation of biodiesel.
Fig. 11 shows that the peak pressures of the PBD_H
are less than those of PBD. When the engine is
running on PBD_H, the injection is slightly delayed,
due to decrease in bulk modulus of PBD with
increasing fuel temperature. Therefore the reason for
lower peak pressure attributed to early burning of
PBD_H due to its faster evaporation at its preheated
temperature (50
0
C), which leads to reduction in its
ignition delay.
6.2 Combustion analysis
The combustion process in diesel engines is mainly
divided into three phases as shown in Fig. 12.
Fig. 12: Three phases of combustion
The first phase of combustion is called as ignition
delay (ID), in which the tiny fuel droplets
evaporates and mixes with high temperature (or high
pressure) air. ID effects on rate of combustion. The
delay period depends mainly on fuel cetane number
(CN), and temperature of the air. The ID is also
influenced by the fuel temperature. The second
phase of combustion is called as period of rapid
combustion or premixed combustion. In this phase
the air-fuel mixture undergoes rapid combustion,
therefore the pressure rise is rapid and releases
maximum heat flux. The third phase of combustion
is called as period of controlled combustion. In this
period, the fuel droplets injected during the second
stage burns faster with reduced ID due to high
temperature and pressure. In this third phase the
pressure rise is controlled by the injection rate and
the combustion is diffusive mode, as shown in
Fig.12.
The lower calorific value (LCV) of PBD is less than
PD fuel. Fig. 10 shows the variation of cylinder
pressure with respect to crank angle at maximum
output of 3.72 kW. It is observed that, the PBD is
burning close to TDC and the peak pressure is
slightly higher than that of PD fuel; even though the
PBD is having lower value of LCV. The reason is
attributed to the higher bulk modulus of the PBD.
When, a high density (or high bulk modulus) fuel is
injected, the pressure wave travels faster from pump
end to nozzle end, through a high pressure in-line
tube [21]. This causes early lift of needle in the
nozzle, causing advanced injection. Hence, the
combustion takes place very close to TDC and the
peak pressure slightly high due to existence of
smaller cylinder volume near TDC. Therefore the
reason is attributed to the combined effect of
advanced injection and lower value of heat
rejection, which occurs due to prevalence of smaller
cylinder volume (or surface area) near TDC.
6.2.1 Net heat release rates
Fig. 13 shows the net heat release rate (HRR). A
noticeable change in combustion phases were
observed between PBD and PBD_H. The peak value
of premixed combustion was more for PBD, than
that of PBD_H, and the diffusive combustion phase
was more for PBD_H, than that of PBD. This is due
to poor mixing of PBD with the surrounding air
because of its high viscosity. At the time of ignition,
less quantity of air-fuel mixture is prepared for
combustion with PBD_H. This is due to faster
evaporation of the preheated biodiesel. Therefore,
more burning occurs in the diffusion phase rather
than in the premixed phase. The increase in heat
release is mainly due to better mixing and
evaporation of PBD_H, which leads to improved
burning.
Diffusion combustion
Premixed
combustion
Ignition
Delay
EOI
SOI SOC
TDC EOC
Crank angle (deg.)
Rate of heat release (J/deg.)
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
40
Issue 2, Volume 4, April 2009

-5
0
5
10
15
20
25
30
35
40
45
50
350 360 370 380 390 400
Crank Angle (degrees)
Net HRR (J/deg.)
PD
PBD
PBD_H
Fig. 13: Net heat release rates at maximum output
6.2.2 Exhaust gas temperatures
Fig. 14 shows the variation of exhaust gas
temperature (EGT). The exhaust gas temperatures of
PBD are lower than that of PD fuel, due to release
of lower levels of thermal energy. However, the
exhaust gas temperature of PBD_H is higher than
that of PBD, which indicates the improved
combustion due to high rate of evaporation and
improved spray characteristics.
75
125
175
225
275
325
0 0.93 1.86 2.79 3.72
Brake Power (kW)
EGT (deg.C))
PD PBD PBD_H
Fig. 14: Exhaust gas temperatures
6.3 Exhaust gaseous emissions
The exhaust gas emissions (NO, HC, CO, and
Smoke) of the engine are measured with the
following instruments, shown in the Table 4. The
table 5 shows the technical specifications of the
exhaust gas analyzer.
Table 4: Instruments used to measure exhaust
emission
Exhaust
Emissions
Instrument Model
NO, HC, CO MRU Exhaust Gas
Analyzer, Germany
Delta
1600 L
Smoke (soot) A V L Smoke Meter,
Graz-Austria
409 D
Table 5: Specifications of the Exhaust Gas Analyzer
Gaseous
Emission
Range
Precision
Resolution
NO 0-2000 ppm +/- 5 ppm 1 ppm
HC 0-20000 ppm
(n-hexane)
+/- 12
ppm
1 ppm
CO 0-1500 %
volume
+/- 0.06
%
0.01 %
6.3.1 Nitric oxide emission
In diesel engines, the combustion process mainly
forms nitric oxide (NO) emission. Therefore, only
NO is measured with the exhaust gas analyzer. The
NO emissions are plotted in the bar chart shown in
the Fig. 15 and the observations made are as
follows:
Results show that for all the fuels the increased
engine load promoting NO emission as shown in
Fig. 15. Since the formation of NO is very sensitive
to temperature, therefore higher loads promote
cylinder charge temperature, which is responsible
for thermal (or Zeldovich) NO formation. The
presence of oxygen (11%) in PBD leads to
improvement in oxidation of the nitrogen available
during combustion. This will raise the combustion
bulk temperature responsible for thermal NO
formation.
The PBD having long carbon chain (C
16
-C
24
) is
producing more NO than that of PD having both
medium (C
8
-C
14
) as well as long chain (C
16
-C
28
) as
shown in Fig. 1 and 15. The increase in NO
emission might be an inherent characteristic of PBD
due to the presence of 51.8 % of mono-unsaturated
fatty acids (MUFA) and 19% of poly-unsaturated
fatty acids (PUFA) as shown in figure 2 and 3. That
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
41
Issue 2, Volume 4, April 2009

means, the long chain fatty acids such as oleic
(C
18:1
) and linoliec (C
18:2
) are responsible for higher
levels of NO emission [22].
25
75
125
175
225
275
325
375
425
475
525
575
625
0 0.93 1.86 2.79 3.72
Brake Power (kW)
NO (ppm)
PD
PBD
PBD_H
Fig. 15: Nitric oxide emission
The production of more NO with PBD fueling is
also attributable to an inadvertent advance of fuel
injection timing due to higher bulk modulus of
compressibility, with the inline-fuel injection
system. Higher bulk modulus leads to a more rapid
transferal of the pressure wave from fuel-pump end
to the fuel-injector needle, causes an earlier needle
lift. The earlier needle lift causes an advanced (or
early) injection (or combustion), which contributed
towards large premixed combustion, and hence
responsible for thermal (or Zeldovich) NO
production.
The fuel spray properties may be altered due to
differences in viscosity and surface tension. The
spray properties affected may include droplet size,
droplet momentum, degree of mixing, penetration,
and evaporation. The change in any of these
properties may lead to different relative duration of
premixed and diffusive combustion regimes. Since
the two burning processes (premixed and diffused)
have different emission formation characteristics,
the change in spray properties due to preheating of
the PBD are lead to reduction in NO formation. The
reason is attributed to reduced intensity of premixed
combustion regime (Fig. 13) due to slightly retarded
injection, better evaporation, and well mixing of
PBD_H due to its low viscosity at preheated
temperature of 50
o
C.
6.3.2 Hydro carbon emission
Fig. 16 shows that for all fuels the unburned
hydrocarbon (HC) emissions are indicating, a
decreasing trend first and then increasing trend with
the power output. The reason for higher level of HC
at ‘0’ kW power output is due to the flame
quenching and cooled layer of the charge near the
cylinder wall during the cold start.
The HC emissions of the PBD are less than that of
PD fuel. The reason for lower HC emissions is due
to inherent presence of oxygen (11%) in the
molecular structure of the biodiesel. The PBD_H is
producing lower levels of HC emissions as
compared to that of PBD. The reason is attributed to
better spray pattern (due to its lower viscosity) and
evaporation (due to temperature of 50
0
C), which
leads to efficient combustion. Therefore, the lower
HC levels of PBD_H are due to the combined effect
of lower viscosity, presence of oxygen and higher
CN as compared to that of PD fuel.
60
75
90
105
120
135
150
165
180
195
0 0.93 1.86 2.79 3.72
Brake Power (kW)
HC (ppm)
PD
PBD
PBD_H
Fig. 16: Hydrocarbon emissions
6.3.3 Carbon monoxide
For both the fuels, the increasing trend of carbon
monoxide (CO) emission levels are observed with
power output as shown in Fig. 17. This increasing
trend of CO emissions is due to increase in
volumetric fuel consumption (due to its lower
calorific value) with the engine output power. The
CO emission level of PBD is less than that of PD
fuel. The CO emission levels are further reduced for
PBD_H, due to reduced viscosity, density and
increase in evaporation rate.
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
42
Issue 2, Volume 4, April 2009

0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
0.2
0 0.93 1.86 2.79 3.72
Brake Power (kW)
CO (%)
PD PBD PBD_H
Fig. 17: Carbon monoxide emission
6.3.4 Smoke emission
The Fig. 18 shows that, the smoke emission
increases with engine load for all the above fuels.
This increasing trend is attributed to the increase in
volumetric fuel consumption with the power output.
At lower power outputs (0 kW and 0.93 kW), the
PBD showed a slightly higher level of smoke than
that of PD fuel. The reason is attributed to poor
quality of air-fuel mixing. A portion of the fuel-rich
mixture may fail to burn, was emitted as smoke.
The PD fuel at higher loads showed a higher level of
smoke than PBD, the reason is due to presence of
aromatics (Fig. 4). Especially, the presence of
branched and ring (multi-ring or polycyclic)
structures of the PD fuel can increase the exhaust
smoke [23]. And this increase in smoke emission
was due to the higher boiling point and high thermal
stability of aromatic hydrocarbons [24]. The
increase in smoke of PD fuel is also because of the
lower levels of oxygen present in the PD fuel.
The biodiesel are emitting lower levels of smoke as
compared to that of PD fuel under similar operating
conditions. This is probably because of the inherent
oxygen present in the biodiesel, which improves the
combustion. The oxygen content in PD and PBD are
0.3%, and 11% respectively. Therefore, it is also
concluded that, the increase of oxygen in the fuel
tends to reduce the smoke (soot) emission for all
power outputs as shown in the Fig. 18. However, the
smoke emission is increasing for PBD_H, due to
late phase of combustion, particularly increase in
diffusive combustion (heat release) as compared to
that of PBD fuel.
0
1
2
3
4
5
0 0.93 1.86 2.79 3.72
Brake Power (kw)
BSU
PD
PBD
PBD_H
Fig. 18: Smoke emission
7 Conclusions
The present work confirms the influence of the
higher bulk modulus of biodiesel on injection and
combustion timing with the ‘in-line’ fuel injection
systems. The advanced injection timing results in
the increased NO emission with long chain
pongamia biodiesel.
The increase of NO emission is due to the combined
effect of higher bulk modulus, and presence of
unsaturated fatty acids (MUFA and PUFA) and
oxygen
The performance of the engine is increased, when
the biodiesel is injected at diesel fuel viscosity.
Decrease in premixed combustion and increase in
diffused combustion is observed with preheating.
The reduction in peak value of premixed
combustion leads to the reduction of NO emission.
The presence of oxygen in biodiesel improves the
combustion and hence lowers the exhaust emissions.
Except smoke (soot), all the remaining emissions
are reduced significantly with preheating of PBD.
Improvement in diffused combustion is responsible
for these increased smoke levels particularly at
higher loads.
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
43
Issue 2, Volume 4, April 2009

References:
[1] Divya Bajpai, and V.K. Tyagi, Biodiesel:
Source, Production, Composition, Properties
and Its Benefits, Journal of Oleo Science, Vol.
55, No. 10, 2006, pp. 487-502
[2] Mandal B., Majumdar S. G., Maity, C.R.,
Chemical and Nutritional Evaluation of
Pongamia glabra Oil and Acacia uriculaeformis
Oil, J. American Oil Chemists Society, Vol. 61,
No. 9, 1984, pp. 1447-1449
[3] Mitra, C.R., Development of Minor and Non-
edible Oils, Report of the Indian Central
Oilseeds Committee, Hyderabad, 1963, p.29
[4] Kumar, A., and Sharma, S., An evaluation of
multipurpose oil seed crop for industrial uses
(Jatropha curcas L.): A review, Journal of
Industrial Crops and Products, Vol. 28, No. 1,
2008, pp. 1-10
[5]T.H. APPLE WHITE, in Kirk-Othmer,
“Encyclopedia of Chemical Technology”, 3
rd
edition, John-Wiley & Sons, New York, NY,
Vol. 9., 1980, pp.795-811
[6] K. Akihama, Y.Takatori, K.Nakakita, Effect of
Hydrocarbon Molecular Structure on Diesel
Exhaust Emissions. Research Report, R&D
Review of Toyota CRDL, Vol. 37, No. 3, 2002.
[7] Jon Van Gerpen, “Biodiesel Production and
Fuel Quality”, University of Idaho,
Moscow, ID 83844, 2003.
[8] D. Tapasvi, D. wiesenborn and C. Gustafson,
Process Model for Biodiesel Production from
various Feedstock’s, Transactions of ASAE,
ISSN 0001-2351, Vol. 48(6): 2215- 2221.
[9] Aleks Kac, “The Two-Stage adaptation of Mike
Pelly’s Biodiesel Recipe”, 2003.
http://journeytoforever.org/biodiesel_aleks.html
[10] American Society for Testing and Materials,
Standard Specification for Biodiesel Fuel
(B100) Blend Stock for distillate Fuels,
designation D6751-02, ASTM International,
West Conshohocken, PA 2002.
[11] Van Gerpen, J.; Shanks, B.; R.; knothe, G.,
Biodiesel analytical methods, August
2002-January 2004. National Renewable Energy
Laboratory. NREL/SR-510-36240, 2004, 95 p.
[12] Lebedevas, S.; Vaicekauskas, A. Improvement
of the parameters of maintenance of medium
speed diesels applying the motor methods,
Transport, Vol XVI, No. 6, ISSN: 1648-4142.
2004, p. 252- 261.
[13] A. Boehman, M Alam., Fuel formulation
effects on diesel fuel injection, combustion,
emissions, and emission control. Proceedings of
DOE 2003, Diesel Engine Emissions Reduction
Conference, Newport, 2003.
[14] Heinrich Prankl, Manfred Worgetter, Josef
Rathbauer, Technical Performance of Vegetable
Oil Methyl esters with a High Iodine Number,
4
th
Biomass Conference of the Americas. BLT
Wieselburg, 1999.
[15] Edward F. Obert, Internal combustion engines
and air pollution, Harper International
edition (3/e). Harper & Row Publishers, Inc.
1973, Page no: 451-453
[16]Giffen, E. and A.W.Rowe, Pressure calculations
for oil engine fuel injection system.
Proceedings of the Institution of Mechanical
Engineers, 142:519-534., 1939.
[17] R.A. Bakar and T.Firoz. Numerical analysis of
pressure pulses in the jerk fuel injection
systems. American Journal of Applied Sciences
2(5), 2005, pp. 1003-1007.
[18] Brown, George W., Diesel Injection System
Calculations, A Thesis submitted to the
University of Nottingham for the degree of
doctor of philosophy, 1966.
[19] P V Rao, Pressure-Time Analysis of a Unit
Injector, A Thesis submitted to the Indian
Institute of Science, Bangalore, India, for the
degree of Master of Engineering in Mechanical
Engineering. 1993.
[20] Van Gerpen, J.; Shanks, B.; Pruszko, R.;
Clements, L.D.; knothe, G. Biodiesel analytical
methods, August 2002-January 2004. National
Renewable Energy Laboratory. NREL/SR-510-
36240, July 2004, 95 p.
[21] Yamane K., Ueta A., Shimamoto Y., Influence
of Physical and Chemical Properties of
Biodiesel Fuel on Injection, Combustion and
Exhaust Emission Characteristics in a DI-CI
Engine” Tran. Of the Japan Society of
Mechanical Engineers, Vol. 32, No: 2, 2001,
pp. 25-30.
[22] Thet Myo, “The Effect of Fatty Acid
Composition on the Combustion Characteristics
of Biodiesel”. A Thesis submitted to the
Kagoshima University for the degree of Doctor
of Philosophy in Engineering, 2008.
[23] Kazuhiro akihama, Yoshiki Takatori, Kiyomi
Nakakita, “Effect of Hydrocarbon Molecular
Structure on diesel Exhaust Emissions”. A
Research Report, R&D Review of Toyota
CSDL Vol. 37, No. 3, 2002.
[24] Tadao Ogawa, and Masanori Okada, “Influence
of Properties and Composition of Diesel Fuels
on Particulate Emissions” A Research Report,
R&D Review of Toyota CSDL Vol. 38 No. 4,
2003.
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
Ch. Satyanarayana, P. V. Rao
ISSN: 1790-5079
44
Issue 2, Volume 4, April 2009