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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.

33

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

35

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

37

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.

38

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.

39

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

40

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)

43

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.

7

65

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

46

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

47

98

7

6

5

43

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

49

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.