CHAPTER 3 EXPERIMENTAL SETUP AND...
Transcript of CHAPTER 3 EXPERIMENTAL SETUP AND...
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CHAPTER 3
EXPERIMENTAL SETUP AND PROCEDURE
3.1 METHODOLOGY
The step by step methodology that was followed is given below:
Selection of non edible vegetable oil (Rubber seed oil)
Selection of a suitable single cylinder diesel engine and
development of an experimental set-up with necessary
instruments to study the performance, emission and
combustion characteristics.
Mounting a piezo-electric pressure transducer on the cylinder
head and developing an optical TDC position sensor and
circuits for obtaining pressure-crank angle data.
Fabrication of a set-up for the production of methyl ester of
vegetable oil (biodiesel) by the transesterification process and
preparation.
Conducting experiments with RSO and its ester to study
performance, emission and combustion characteristics and
comparison with that of the base diesel engine.
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Studying the effect of blending RSO with diesel and compare
the performance, emission and combustion parameters with
neat RSO fuel operation.
Modifying the experimental set-up to preheat the RSO using
exhaust gas to different temperatures in order to lower the
viscosity. Conducting experiments with exhaust preheated
RSO to study the effect of reducing their viscosity.
Modifying the engine to operate in the dual fuel mode and run
it with RSO, rubber seed oil methyl ester (RSOME) and diesel
as main fuels and hydrogen as the inducted fuel.
Modifying the setup to study the effects of DEE injection into
the intake manifold to improve the performance of RSO
fuelled diesel engine.
The test matrix indicating all the experiments conducted is given in
Table 3.1.
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Table 3.1 Test Matrix
VARIABLES FUELS USED REQUIREMENT Normal operation
Maintained constant load at 25 %, 50 %, 75 % and 100 % at the rated speed of 1500 rpm
1. Diesel 2. Rubber seed oil
(RSO) 3. Rubber seed oil
methyl ester (RSOME)
Compare the performance, emission and combustion characteristics of base fuels
Normal operation with blends Maintained constant load at 25 %, 50 %, 75 % and 100 % at the rated speed of 1500 rpm
1. RSO + diesel
Evaluation of performance, emissions and combustion parameters and selection of an optimum blend
Normal operation with preheating using exhaust gas Maintained constant load at 25 %, 50 %, 75 % and 100 % at the rated speed of 1500 rpm
1. RSO
Evaluation of performance, emissions and combustion parameters
Dual fuel operation with Hydrogen Maintained constant load at 25 %, 50 %, 75 % and 100 % at the rated speed of 1500 rpm Hydrogen flow rate was varied from zero to knock limit at each load
1. Diesel 2. RSO 3. RSOME
Estimation of performance, emissions and combustion parameters and Optimization of inducted hydrogen quantity at different loads
Operation with RSO + DEE injection Maintained constant load at 25 %, 50 %, 75 % and 100 % at the rated speed of 1500 rpm DEE injection pressure was maintained at 3 bar Injection timing was varied from 10º bTDC-30º aTDC and injection duration was varied from 10ºCA-60ºCA for each load.
1. RSO Optimization of DEE injection timing and duration. Estimation of performance, emissions and combustion parameters and selection of the optimum DEE fraction to be used
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3.2 EXPERIMENTAL SET-UP
An experimental set up was developed to conduct the experiments
on the selected compression ignition engine in single fuel and dual fuel modes
to evaluate the performance, emission and combustion parameters at different
operating conditions. The schematic of the experimental setup is shown in
Figure 3.1 and the overall view of the experimental set-up is shown in
Figure 3.2.
3.2.1 Test Engine
A single cylinder, 4-stroke, air-cooled, direct injection diesel engine
with a displacement volume of 661.5 cc, compression ratio of 17.5:1,
developing 4.4 kW at 1500 rpm with a centrifugal type governor was used for
the present research work. The details of the engine are given in Appendix 1.
The injector opening pressure recommended by the manufacturer was 200
bar. The governor of the engine was used to maintain a constant speed of
1500 rpm. The combustion chamber is hemispherical in shape. The exhaust of
the engine was collected and sent out by a central facility, which maintained a
constant pressure close to ambient in the exhaust manifold. A provision was
made to mount a piezoelectric pressure transducer flush with the cylinder
head surface in order to measure cylinder pressure. The injection system of
the engine was periodically cleaned and calibrated as recommended by the
manufacturer. This engine was modified to operate in the dual fuel mode by
fitting a gas carburetor in the intake manifold.
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1. Engine
2. Electrical dynamometer
3. Diesel fuel tank
4. RSO fuel tank
5. Cylinder pressure transducer
6. Charge amplifier
7. Analog to digital convertor card
8. Computer
9. TDC pickup
10. Exhaust gas analyzer
11. Air surge tank
12. Fly wheel
Figure 3.1 Schematic diagram of the experimental setup
3.2.2 Load Measurement
The engine was coupled to an electrical dynamometer for loading.
The specifications of the dynamometer are given in Appendix 2. The
dynamometer used to load the engine comprised a shunt wound DC generator
and a load bank. In electrical dynamometer, the shaft rotation drives some
form of electrical generator. The strength of the electromagnetic field
coupling the rotating and stationary parts of the dynamometer can be adjusted
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in order to increase or decrease the resistance offered to the engine rotation.
Dynamometer load was varied from 0 amp. to 16 amps. in steps of 4 amps.
Figure 3.2 Photographic view of experimental set-up
3.2.3 Air and Fuel Flow Measurement
An orifice meter connected to an air surge tank was attached to the
inlet manifold of the engine to measure airflow. The fuel flow rate was
measured on volume basis using a burette and a stop watch.
3.2.4 Exhaust Gas Temperature Measurement
The temperature of the exhaust gas was measured with Chromel
Alumel (K-Type) thermocouples. A digital indicator with an automatic room
temperature compensation facility was used and it was calibrated periodically.
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3.2.5 Measurement of Smoke
The exhaust smoke level was measured by using a standard BOSCH
smoke measuring apparatus. This measuring instrument consists of a
sampling pump that draws a definite quantity of exhaust sample through a
white filter paper. The reflectivity of the filter paper was then measured using
a standard Bosch smoke meter that consists of a light source and an annular
photo detector surrounding it. Before every sampling, it was ensured that the
exhaust from the previous measurement was completely driven off from the
tube and pump. The specifications of the smoke meter are given in
Appendix 3.
3.2.6 Measurement of Exhaust Gas Emissions
An exhaust gas analyzer (Qrotech QRO-401) was used for
measuring the exhaust pollutants where NOx and Oxygen concentrations
were measured and it is an electro chemical cell. Hydrocarbons, Carbon
Monoxide and Carbon dioxide were measured in NDIR type analyzer. The
exhaust gas analyzer was calibrated periodically and used. The details of the
exhaust gas analyzer are given in Appendix 4.
3.2.7 Cylinder Pressure Measurement
In cylinder pressure was measured with a water-cooled piezoelectric
transducer. The charge output of the transducer was amplified into an
equivalent voltage using a suitable charge amplifier. The transducer was
flush mounted on the cylinder head surface for avoiding passage effects. A
KISTLER make transducer with a sensitivity of 80.5 pC/bar was used for the
purpose. The details of the pick up and charge amplifier are given in
Appendix 5 and Appendix 6 respectively. The piezoelectric transducer
produces a charge output, which is proportional to the in cylinder pressure.
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The system was periodically checked for drift and corrected suitably
(Lancaster 1975). Since the signals from a piezoelectric transducer indicate
only relative pressures, it is necessary to have a means of determining the
absolute pressure at some point in the cycle. Hence, it had to be referenced to
get the actual pressure. This was done by assuming that the cylinder pressure
at suction BDC is equal to the mean intake manifold pressure (Lancaster
1975). The pressure transducer mounted on the engine is shown in Figure 3.3.
Figure 3.3 Photographic view of pressure transducer fitted in the
cylinder head
3.2.8 Optical TDC Position Sensor
An electro optical sensor was developed and used to indicate the
position of TDC by providing a voltage pulse exactly when the TDC position
was reached. This sensor consists of a matched pair of infrared diode and
phototransistor so that infrared rays emitted from the diode fall on the
Pressure transducer
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phototransistor when it is not interrupted. A continuous disc with a small cut
at the TDC position with respect to optical sensor point was made to get the
signal when the piston reaches TDC exactly. At this point the output voltage
from phototransistor rises to 5 volts and at all other points it is zero. Voltage
signals from the optical sensor were fed to an analog to digital converter and
then to the data acquisition system along with pressure signals for recording.
A photograph of the encoder is shown in Figure 3.4 and the circuit is given in
Figure 3.5.
3.2.9 Digital Data Acquisition System
A 12-bit analog to digital converter (A/D Converter) was used to
convert analog data to digital form on a Personal Computer (PC). The data
acquisition system worked on special software, which incorporated the library
functions given by the manufacturer of the data acquisition system. This
software could set the sampling speed and the total number of samples that
were to be taken continuously and stored the same in the PC. Signals were
stored in a file. One channel was fed with signals from the pressure transducer
while the voltage was fed to the other from the TDC position encoder.
Specifications of the A/D converter are given in Appendix 7. The A/D
converter had external and internal triggering facility with sixteen single
ended channels. Data from 100 consecutive cycles were stored continuously
at each operating condition. Recorded signals were processed to obtain
combustion parameters like peak pressure, maximum rate of pressure rise,
heat release rate etc. The heat release rate was obtained based on the method
outlined by Hayes et al (1986).
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Figure 3.4 Photographic view of optical encoder
Figure 3.5 Circuit for the optical encoder
Optical encoder
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3.2.10 Calculation of Heat Release Rate
A piezo-electric pressure transducer was flush mounted on the
cylinder head and the signals are recorded on a data acquisition system. Along
with the pressure signal the TDC position signal was also acquired by the A/D
converter installed in the personal computer. These voltage signals were
stored in two columns in a file at uniform time intervals. Since a piezo-
electric transducer provides only relative pressures, it is necessary to know the
absolute pressure at some point in the cycle so that the pressure at all other
points can be had. For this the cylinder pressure at suction BDC was assumed
to be equal to mean manifold pressure (Lancaster et al 1975). Software was
used to compute the average pressure crank angle values for 100 consecutive
cycles. From this peak pressure, occurrence of peak pressure, maximum rate
of pressure rise and heat release were calculated.
The rate at which combustion occurs i.e., the rate of heat release,
affects the efficiency, power output and emissions of an engine. The heat
release rate curve provides a good insight into the combustion process that
takes place in the engine. A program was used to compute the heat release
rate based on the first law of thermodynamics.
app w1Q PdV VdP Q
1 1
(3.1)
where Qapp - Apparent heat release rate (J)
- Ratio of specific heats p
p
CC R
R - Gas constant in (J / kmol-K)
Cp - Specific heat at constant pressure (J / kmol-K)
V - Instantaneous volume of the cylinder (m3)
P - Cylinder pressure (bar)
Qw - Heat transfer to the wall (J)
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For this calculation the contents of the cylinder were assumed to
behave as an ideal gas (air) with specific heats dependent on temperature and
the specific heat was calculated using the equation given below (Hayes et al
1986);
2 3 4
p 6 9 121.33736T 3.29421T 1.91142T 0.275462TC 3.6359 R
1000 1 10 1 10 1 10
(3.2a)
for T < 1000 K
2 3
p 6 91.338056T 0.488256T 0.0855475TC 3.04473
1000 1 10 1 10
4
120.00570127T R
1 10
(3.2b)
for T > 1000 K
The heat transfer was calculated based on the Hohenberg equation
(Hohenberg 1979) given below and the wall temperature was assumed to be
723oK (Hayes et al 1986).
h = C1 V-0.06 P0.8 T-0.4 (Vp + C2)0.8 (3.3)
where h - Heat transfer coefficient in W/m2 K
C1 & C2 - Constants, 130 & 1.4
V - Cylinder volume in m3
P - Cylinder pressure in bar
T - Cylinder gas temperature in K
Vp - Piston mean speed in m/s
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Start of combustion was determined from the heat release rate curve.
The crank angle at which there is a sudden rise in heat release rate was taken
as the start of combustion. End of combustion was determined from the
cumulative heat release curve. It was taken as the point where 90% of heat
release had occurred. Ignition delay is the time lag between the start of
injection to the start of combustion. The dynamic injection timing was used to
calculate the ignition delay.
3.2.11 Fuels Used
Diesel, rubber seed oil (RSO), rubber seed oil methyl
ester (RSOME) were used as fuels in the present work. The rubber tree
– Hevea brasiliensis Muell, Arg, (Euphporbiaceae) is grown mostly in the
costal regions of Kerala, Karnataka, Tamil Nadu, Andhra Pradesh and West
Bengal. The important natural rubber producing countries in the world are
India, Srilanka, Philippines, Malaysia and Indonesia. Fresh oil is pale yellow
but commercial oil is dark in colour. It is semi-drying oil used in surface
coatings for making alkyl resins. It is a partial substitute for linseed oil in
paints and varnishes. It is effective against house flies and lice, used upto 30
% in soap making. The rubber seed production in India is about 150 kg/ha per
annum. The estimated availability of rubber seed is about 30000 MT/year. At
present rubber seed oil has not found any major application and hence the
natural production of seeds remains underutilized. The properties of the fuels
are given in Table 1.1 of chapter 1.
3.2.12 Hydrogen Supply Systems
A gas carburetor of the venturi type was used to induct hydrogen
into the engine. The induction system consists of a high-pressure gas cylinder,
high-pressure valve, pressure regulator and a control valve. The hydrogen was
allowed to flow through the pressure regulator where the pressure was
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reduced to atmospheric value. A needle valve was used to control the fuel
flow rate. The gas from the needle valve was made to flow through the
positive displacement gas flow meter into the gas carburetor. The carburetor
was fitted in the intake pipe of the engine. A manometer was also connected
in the intake side of flow meter to get the pressure of gas. A flame trap of the
wet type and another flame arrester of the dry type were also provided to avoid
flash back. Figure 3.6 shows the hydrogen fuel supply system.
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4
3
2
1
1. Hydrogen tank
2. Pressure regulator
3. Gas flow meter
4. Flame trap
5. Flame arrester
6. Gas carburetor
8. To engine cylinder
Figure 3.6 Hydrogen supply system
3.2.13 DEE Injection System
An electronically controlled DEE injection system was developed to
inject a known quantity of well-atomized spray of DEE into the inlet manifold
of the engine. It consists of a high-pressure pump to feed DEE to a solenoid-
operated injector, which is normally used to inject gasoline. A bypass valve
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and a pressure gauge were provided to maintain the pressure constant at 3 bar.
The amount of DEE injected was controlled electronically by changing the
pulse width of the signal fed to the injector. The equipment was calibrated out
side before fitting it into the system. The engine was allowed to run at a
constant speed of 1500 rpm and for a particular DEE pressure, the amount of
DEE injected for a period of time was collected in a jar to get the DEE flow
rate. This experiment was repeated at various injection durations and at
different injection pressures. The important properties of DEE (Brent Bailey
et al 1997) compared with RSO and diesel (Ramadhas et al 2005) is shown in
Table 3.2. The block diagram of the injection system is as shown in
Figure 3.7. The photographic view of the injector mounted on the inlet
manifold is shown in Figure 3.8.
Table 3.2 Properties of Diethyl Ether (DEE)
Property Rubber seed oil (RSO)*
Diesel Diethyl ether
(DEE)
Specific gravity 0.91 0.83 0.714
Viscosity (mm2/s) at 40oC, c St 33.91 3.01 0.23
Flash point (ºC) 224 45 -40
Calorific value (kJ/kg) 37500 42500 33857
Iodine value 135.3 38.3 -
Acid value 26 0.062 -
Cetane number 37 47 >125 * Values measured
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98
7
6
5
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2
1
1. Switch
2. ECU
3. Battery
4. DEE tank
5. Pump
6. Pressure Regulator
7. Pressure gauge
8. DEE injector
9. Inlet manifold
Figure 3.7 DEE injection system
Figure 3.8 Photographic view of injector mounted on the inlet manifold
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3.2.14 Transesterification of Rubber Seed Oil
Transesterification is an effective way to reduce the viscosity of
vegetable oils. A setup as shown in Figure 3.9 and the photographic view
shown in Figure 3.10 and Figure 3.11 was made for the process of
transesterification. It consists of a 5-litre capacity round bottom flask with
three necks. An electrical heater with a thermostat was used to heat the oil in
the flask. A variable high-speed motor with a special type of stirrer was used
to stir the contents vigorously.
It is difficult to transesterify the high FFA rubber seed oil using the
commercially available alkaline catalyst process. The percentage of FFA
content in RSO is 12.19. If RSO is directly used in the alkaline
transesterification process, it is necessary to avoid these soap formation which
greatly affects the transesterificaton efficiency. Two step processes are
involved namely, acid esterification and alkaline esterification to convert
biodiesel from RSO.
Acid Esterification: Acid esterification is the chemical reaction
between FFA and methanol in the presence of acid catalyst for the conversion
of FFA into mono alkyl methyl ester. The first step reduces the FFA value of
raw rubber seed oil to about 2 % using acid catalyst. One litre crude rubber
seed oil requires 200 mL of methanol for the acid esterification process. The
rubber seed oil is poured into the flask and heated to about 50ºC. Then
methanol was added with the preheated rubber seed oil and stirred for a few
minutes. 0.5 % of sulphuric acid was also added with the mixture. Heating
and stirring was continued for 20-30 minutes at atmospheric pressure. On
completion of this reaction, the product was poured into a separating funnel
for separating the excess alcohol. The excess alcohol, with sulphuric acid and
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impurities moved to the top surface and was removed. The lower layer was
separated for further processing. The acid esterification reaction is represented
by the following reaction:
RCOOH + CH3OH → RCOOCH3 + H2O (3.4)
Alkaline Transesterification: Alkaline transestrification is the
chemical reaction between triglyceride (triester) and methanol in the presence
of alkaline catalyst to produce mono ester. The long and branched chain of
triglyceride molecules are transformed into monoesters and glycerin. The
transesterification reaction is represented by the following reaction:
CH2OOCR1 R1COOCH3 CH2-OH
│ │
CHOOCR2 + 3 CH3OH → R2COOCH3 + CH-OH (3.5)
│ │
CH2OOCR3 R3COOCH3 CH2-OH
The products of acid catalyzed esterification were preheated to the
required reaction temperature of 45 ± 5ºC in the flask. Meanwhile 5 gm KOH
was dissolved in 300 mL methanol and was poured into the flask. The mixture
was heated and stirred for 30 min. the reaction was stopped and the products
were allowed to separate into two layers. The lower layer, which contained
impurities and glycerol, was drawn off. The ester remained in the upper layer.
Methyl esters were washed to remove the entrained impurities and glycerol.
Hot distilled water (10 % by volume) was sprayed over the surface of the
ester and stirred gently. Lower layer was discarded and the upper layer was
separated.
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Figure 3.9 Transesterification set-up
1. Power supply 2. Heater 3. Thermostat 4. Flask 5. Stirrer 6. Connecter
7. Thermometer 8. Stirrer motor 9. Slider 10. Speed control 11. Cap 12. Stirrer stand
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Figure 3.10 Photographic view of transesterification set-up
Figure 3.11 Photographic view of separating funnel
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3.3 EXPERIMENTAL PROCEDURE
All the tests were conducted at the rated speed of 1500 rpm. All the
readings were taken only after the engine attained stable operation. All the
instruments were periodically calibrated. The injector opening pressure was
kept at the rated value throughout the experiments.
The engine output was varied in steps from no load to full load in
the normal operation of the engine. In the dual fuel mode, the engine output
was varied 25 %, 50 %, 75 % and full load. At each load, fuel flow rate,
airflow rate, exhaust gas temperature, emissions of carbon monoxide,
hydrocarbons, oxides of nitrogen and smoke readings were recorded. The
pressure crank angle history of 100 consecutive cycles was also recorded by
using the data acquisition system and the personal computer. This data was
processed to get the average pressure crank angle variation.
3.3.1 Experiments
Initial tests were conducted with diesel, rubber seed oil (RSO)
and its biodiesel at the rated speed and variable load
conditions to compare the performance, emission and
combustion characteristics of base fuels.
Tests were conducted with different blends of rubber seed oil
with diesel to study the effects of blending RSO on the
performance, emissions and combustion parameters of the
engine.
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Experiments were conducted with exhaust pre heated RSO
upto a temperature where the viscosity of this oil became the
same as the viscosity of diesel and RSOME at 40°C.
In the next phase, the engine was operated in the dual fuel
mode with hydrogen as the secondary fuel and diesel, RSO
and its methyl ester (RSOME) as the main fuel. In each case,
the flow rate of hydrogen was controlled with a needle valve
from zero to the maximum amount which the engine could
tolerate. At low loads, the hydrogen flow rate was limited by
misfire and at high loads the amount of hydrogen was limited
by knocking. The inducted fuel supply was varied from 0 to
the maximum possible limit. Experiments were conducted at
different loads of 25 %, 50 %, 75 % and full load.
Finally the effects of DEE injection in the inlet manifold along
with air were studied with RSO in order to improve the
combustion of RSO. Experiments were conducted at all loads
with different amounts of DEE. The injection pressure of DEE
was maintained not more than 3 bar. Experiments were
conducted with various injection timings and durations. The
injection timings and durations were controlled electronically
by varying the pulse width.