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CHAPTER 6

EXPERIMENTAL INVESTIGATION

6.1 GENERAL

The compression engine basically works by the intake of air during

the intake stroke. At part load condition, the fuel admitted inside the

combustion chamber consumes a limited quantity of air and some quantity is

left behind. But when the load is increased, the combustion process requires

more and more quantity of air which is not readily available through the

intake stroke. During this stage, the injected fuel is not fully oxidized

resulting in low efficiency with the production of smoke to a large extent.

During this period, the increased blend of algal oil methyl ester releases

oxygen which takes part in the combustion process which is readily available

within the blended fuel. The main objective of this research is to

experimentally investigate the technical feasibility of AOME blends to be

used in compression ignition engine. The AOME is blended with diesel at

5%, 10%, 15% and 20% ratios and ASTM methods were used to analyze the

results of the investigation in detail.

6.2 DETAILS OF INVESTIGATION

The AOME-Diesel are blended at 5%, 10%, 15% and 20% ratios to

balance the content of oxygen present in AOME (5% to 9% of O2) which

leads to better combustion efficiency and lower emission formation. The ester

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of AOME was identified as Hexadecanoic acid-methyl ester (Palmitic acid),

6,9,12,15 Docosatetraenoic acid Methyl ester (Linoleic acid), 16 Octadecenoic

acid methyl ester (Oleic acid), Heptadecanoic acid 16 methyl methyl (Stearic

acid) ester using spectral studies and confirmed using Infrared analysis.

6.3 EXPERIMENTAL SETUP

A schematic layout of the experimental setup is shown in

Figure 6.1. The Figure 6.2 shows the photographic views of experimental

setup and sensors used for measurements. The specification of the engine is

tabulated in Table 6.1.

Table 6.1 Specification of engine

Name Description

Make and Model Kirloskar DM 10

Bore and Stroke 102 mm X 116 mm

Compression Ratio 17.5 : 1

Rated Speed 1500 rpm

Cubic Capacity 0.948 liters

Power 7.4 kW at 1500 rpm

Injection timing 26o bTDC

Injector opening pressure 210 bar

Valve timing

Inlet valve opening ( bTDC) 4.5 o

Inlet valve closing ( aTDC) 35.5 o

Exhaust valve opening (bTDC) 35.5 o

Exhaust valve closing (aTDC) 4.5 o

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Figure 6.1 Schematic line diagram of Experimental setup

1. Kirloskar DM 10 Test engine 4. Data acquisition system 2. Engine Flywheel 5. Dynamometer control unit 3. Eddy current Dynamometer 6. Electronic fuel flow meter

Figure 6.2 Pictorial view of Experimental setup

ENGINE Exhaust

5 Gas Analyzer

Probe

Smoke Meter Probe

5 Gas Analyzer

Smoke Meter

Data Acquisition system

Fuel Measurement

Power Supply

PressureTransducer

DynamometerControl

Slotted Disc

CRO

Crank Angle Sensor

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6.4 TEST INSTRUMENTS FOR MEASUREMENTS

The following instruments were used for the measurements during

the investigation

1. Electronic flow meter for measuring fuel consumption

2. Air flow measurement system for measuring intake air

3. Eddy current dynamometer for applying torque

4. Pressure transducer for measuring In-Cylinder pressure

5. Bosch smoke meter for measuring smoke intensity

6. Gas analyzer for detecting and measuring CO, CO2, HC and

NOx with GB 1.OX

6.4.1 Instruments for Performance Analysis

The performance analysis and quality control techniques need

continuous improvements because of advancement in engine design,

construction and compactness. An eddy current dynamometer is used for this

purpose. The eddy current dynamometer is designed based on application

parameters like power, torque, speed and moment of inertia. The eddy current

dynamometer is a dry gap rotor machine which operates in an air gap and

capable of bi-directional operations. It consists of steel rotor with thin spokes

and houses the field coil and a heat exchanger. Upon excitation, current is

generated in the field coil producing a magnetic flux. An equal and opposite

magnetic field is produced by the heat exchanger wall facing the rotor inside

the casing. The field thus produced is directed as a pulsating wave by the

arrangement of spokes in the rotor. This changing field produces eddy current

in the heat exchanger walls and opposes the excitation field. This causes the

retarding act to the rotor. Water is allowed to pass through the water jackets in

the heat exchanger to remove excess heat. The pressure variation of the water

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will not affect the system; hence the loading control purely depends upon the

level of excitation.

The eddy current dynamometer is equipped with a controller which

acts as the dashboard as in Figure 6.1. It controls the supply of direct current

necessary to excite the dynamometer. Very accurate and reliable loading is

achieved using eddy current dynamometer at various loads and speeds.

Figure 6.3 Engine coupled with eddy current dynamometer

6.4.1.1 Measurement of Air flow

‘U’ tube manometer equipped with 20mm diameter orifice is

used for measuring the actual air intake. The difference in the water column

of the manometer is noted and equivalent air column is calculated using

Equation (6.1). The co-efficient of discharge was verified though calibration.

The volume of air VA through the orifice is given by

= 2 (6.1)

where Cd is Co-efficient of discharge (0.62), A is the cross-sectional area of

orifice (m2), HA is the height of air column (m3) and g is acceleration due to

gravity (9.81 m/s2).

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6.4.1.2 Measurement of Fuel flow

Electronic fuel flow meter is employed for measuring the quantity

of fuel intake during testing of AOME in compression ignition engine as

shown in Figure 6.4. The electronic fuel flow meter was attached with eddy

current dynamometer and its controls are integral part of dynamometer

controller. A toggle switch in the panel can be set to record 100 cc, 200 cc and

300 cc of fuel consumed. The switch can be also set in auto mode and the

timers automatically records the starting and stopping time of fuel flow into

the test engine. The time taken for total fuel consumption is noted for

calculation purpose.

Figure 6.4 Electronic fuel flow meter

6.4.1.3 Measurement of Exhaust and Coolant Temperature

The temperature sensors are employed for measuring the coolant

and exhaust temperature. Exhaust gas temperature is measured by placing the

sensors at the start of the exhaust manifold and coolant temperature is

measured by placing the sensor at water inlet point.

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6.4.2 Instrument for Pressure Measurement

A Kistler 701 A type pressure transducer is used for measuring In-

cylinder pressure as shown in Figure 6.5 and technical details given in

Table 6.2 . It is very precise and robust in construction with a built in charge

amplifier. It works at a power supply between 7V to 32V direct current with a

range of 1 to 100 bar pressure and 5s time constant. The quartz element is

placed in a high sensitive chamber welded hermetically to the body. The

pressure measured through the steel diaphragm on the measuring element and

transforms the pressure into electrostatic charges. It converts the electrostatic

charge into proportional voltage. It has a stable temperature input stage and a

differential input together provides better condition for operations. Latest

hybrid techniques are incorporated to make it safe, reliable and vibration

proof. At every one degree crank angle, it measures the cylinder pressure for

all strokes. The pressure values are acquired and analyzed on computer with

the help of combustion analysis software and interface. The pressure

transducer was mounted on the cylinder head with a adopter whose signal

cable is connected to the charge amplifier through a high temperature VITON

cable for cylinder pressure measurement.

Figure 6.5 Kistler Pressure transducer

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Table 6.2 Technical details of pressure transducer

Details Description

Pressure range 0 to 110 bar

Sensitivity (±0.5%) 40 mV/bar

Calibration at 200 o C 0-100 bar

Time constant 5s

Signal output 4.4 to 5 V (max)

Supply current 6 mA

6.4.3 Instrument for Emission Measurement

All the emissions are measured using Hartridge smoke unit of

Diesel tune DX 230 smoke meter and five gas analyzer as shown in Figure

6.6. The smoke meter is a partial flow opacimeter suited for free acceleration

and full load test for all types of compression ignition engine. It works on the

principle of sending a light beam through the exhaust to determine the density

of exhaust. It consists of a sampling head and a interface unit operating at low

voltage and temperature. The measuring tube and the photodiode assemblies

are heated to 70oC to prevent the condensation of oil and water. The sampling

head is maintained at 7.5 mbar so that it can draw smoke samples into it.

Measuring errors are minimized by providing rings to eliminate reflection of

ambient light. The interface unit is connected to the sampling head by a

continuous single, 2 channel cable upto 20m in length. All the signals are

combined in the interface unit and sent to the PC through a link. The diesel

tune smoke meter gives smoke reading on percentage (i.e) 0% denotes clean

air and 100% denotes total black smoke. Therefore, light intensity is

expressed as ‘K’, coefficient of light absorption by the Equation (6.2).

(1 ) (6.2)

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where L is the path of light (m) and N is percentage of light obscuration (%)

Before starting the measurement, the initial settings are made as 0%

by sensing clean air and 100% by sensing at no light rays. The smoke meter

automatically calibrates itself at the start of each test and the tolerance on

midpoint calibration between 34% to 40%. The conversion chart

(ULX900HSU manual) is used to determine the level of particulates in the

exhaust which includes compensation for the temperature of smoke. The other

emissions like HC, NOx, CO and CO2 were obtained directly from five gas

analyzer.

Figure 6.6 Emission measuring device

6.5 TEST PROCEDURE FOR PERFORMANCE AND

EMISSION PARAMETERS

Before starting the experiment, the test engine is started and

allowed to warm up for 20 mins. The base reading from eddy current

dynamometer, time taken for 100 cc of fuel consumption, pressure-crank

angle value from PC based data acquisition system and emission reading from

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diesel tune smoke meter for straight diesel are recorded. The experiment was

repeated thrice to minimize the errors in the analysis.

The experiment is initiated by starting the engine and allowing a

warm up time for 20 mins. The loading is done by eddy current dynamometer.

The time taken for 100 cc fuel consumption is noted using electronic fuel

flow meter. The eddy current dynamometer is set to constant mode so that

when the engine speed is fixed, the load or torque can be varied by increasing

or decreasing the throttle. An input signal from the transducer is given to the

controller. The indicator display is calibrated with standard weight to indicate

torque in desired units (Nm or Kgm).

When the field coil is excited, load is given to the engine to stop

and as a result equal and opposite excitation is exerted by the dynamometer

stator assembly and gives a torque value. This results in reduction of engine

speed which is recorded and the corresponding power developed is calculated.

This procedure was repeated by changing the load from no load to full load

(BMEP) and the performance characteristics are recorded. The various

performance parameters like indicated power, brake power, brake specific

fuel consumption, brake specific energy consumption and torque are

calculated. Graphs are plotted between BSEC, BTE and BMEP to study the

variation of performance and emission parameters using various blends of

algal oil. The pressure readings are taken from the signal obtained from

pressure transducer through the data acquisition system. The computer plots

the pressure and crank angle to a minimum scale of 1 bar and 1 degree

respectively. The rate of heat release is then calculated based on the pressure-

crank angle data. The above entire test procedure is performed using straight

diesel as base reading and repeated for AOME 5%, 10%, 15% and 20%

blends to evaluate the effect of AOME addition.

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Smoke reading is obtained from bosch smoke unit of diesel tune

smoke meter interfaced with PC. The smoke meter is capable of measuring

particulates derived from smoke in mg/m3. The other emission like HC, NOx,

CO and CO2 are measured using 5 gas analyzer interfaced with computer

which is a self calibrating type. CO and CO2 are measured in % by volume

while HC and NOx. Five sets of readings are taken at each stage to ensure

accuracy. This procedure is repeated from No load to Full load condition.

6.6 TEST PROCEDURE FOR CYLINDER PRESSURE AND

HEAT RELEASE ANALYSIS

The period between inlet valve closing and exhaust valve opening

plays a very significant role in analyzing the combustion characteristics;

hence maximum power is developed during this period. The pressure inside

the closed system (i.e) the cylinder changes because of change in cylinder

volume, combustion rate, flow of air and fuel around the crevice region, heat

transfer to cylinder walls and leakage past the piston and valves. The effect of

pressure on combustion cannot be accurately calculated because nearly 70%

to 92% of fuel is in vapor state during start of injection. After 1 ms, the

vaporization rate reaches 95%, since only 25% to 35% of vapourized fuel is

burnt within the flammability limits.

The rate of change in pressure rise is directly proportional to the

amount of heat energy released. The rate if heat release is formulated based

on first law of thermodynamics incorporating the leakage of gases past the

cylinder, effect of heat transfer because they affect the change in pressure

during combustion. A suitable mathematical model is used to formulate the

above data.

Based on first law of thermodynamics as given in Equation (6.3)

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= + + + (6.3)

where, Q = Heat transfer through the walls

Q = Chemical energy released during combustion

W = Work of piston = p.dV

h d = Flow across the system boundary

Assuming that U = Mu(T)

where, T = Mean gas temperature

m = Mass

Then

= + (6.4)

In Equation (6.4), the leakage past the cylinder is very minimal and

can be neglected.

Therefore, the equation becomes as given below [Equation (6.5)]

= + ( ) + . + (6.5)

where, dm > 0 when flow is out of the cylinder and dm <0 when flow is

from the crevice into the cylinder, h is specific enthalpy.

By neglecting the gas constant in the ideal gas equation

= + ( + ) + (6.6)

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and the heat transfer rate considering the gas temperature and wall

temperature becomes as given in Equation (6.7)

= ( ) (6.7)

where T = Mean gas temperature (Kelvin)

T = Mean wall temperature (Kelvin)

h = Instantaneous co-efficient of convective heat transfer

A = Surface area of chamber (m2)

T and T are calculated using ideal gas equation (pV=mRT) and averaging

the gas and coolant temperature respectively.

In the present combustion study, considering the engine

dimensions, pressure and piston speed, Woschni correlation of heat transfer

was found to be more suitable.

= 3.26 . . . (6.8)

The above Equation (6.8) of instantaneous heat transfer is derived

from relationship between Nusselt, Reynolds and Prandtl number below as

given in Equation (6.9)

= ( ) ( ) (6.9)

where Nu = Nusselt number

Re = Reynolds number

Pr = Prandtl number

a, m and n are proportionality constants.

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Neglecting the leakage through the cylinder, crevice volume

and fuel vaporization because the enthalpy of vaporization is less than 1%

and heating of fuel vapour is 3% of fuel heating value, the Equation (6.10)

becomes

= 1 + + +

= + + (6.10)

where

= (6.11)

The adiabatic isentropic process was found to be close before and

after the combustion process. Therefore a polytrophic relation PV =

constant is derived for compression and expansion process where ‘n’ is the

polytrophic index. In diesel engine, the value of ‘ ’ as given in Equation

(6.11) is more important because, it always operates with lean fuel air mixture

is used. For diesel engines, the ratio of specific heat values is expected to be

appropriate to ambient air at the end of compression stroke which was found

to be 1.35 (approx) to the overall equivalence ratio of the burned gases after

combustion which is found to be 1.26 to 1.3 (approx). However, the accurate

heat release value which was derived from the ratios of specific heat during

combustion is not clearly defined. For the conventional fuel, ‘n’ value is 1.3.

it is larger than specific heat ratio after combustion for burned gases during

expansion stroke and lies close to the ratio of specific heat before combustion

process. By taking the above consideration, the ‘n’ value for algal oil methyl

ester is taken as 1.32, since the appropriate range of specific heat for heat

release analysis is 1.3 to 1.35.

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By plotting the log values of ignition delay and 1/Tg , we can get

the value of ‘n’ as given in Equation (6.12)

= + + (6.12)

The net heat release, Qh is determined by calculating the difference

between gross heat release, Qch and the heat transfer through the wall, Qht.

The net heat release was also equal to the summation of change in internal

energy and work done on the piston.

The volume of the cylinder at any time of the engine cycle can be

determined using Equation (6.13).

) = [ + ((2 ) ) (6.13)

where S = Stroke length (m)

L = Length of connecting rod

r = Compression ratio

6.7 ESTIMATION OF UNCERTAINTY

The uncertainties and errors can arise from instruments selection,

environmental condition, calibration, testing, observation and taking readings.

Uncertainty in any instrument may be caused by two factors. One is fixed

errors which can be accounted by its repeatability and the other is random

errors which can be calculated analytically. In this research, the uncertainty of

any measured parameters ( xi) was estimated by Gaussion distribution

method as given in Equation (6.14) with a confidence limit of ±2 (95% of

measured value lie within the limits of 2 of mean).

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= 100 (6.14)

where is the number of reading, is standard deviation and is

experimental values. The experiment was conducted with commercial diesel

and five sets of readings were taken for speed, load, torque, temperature,

pressure and exhaust emissions. The uncertainties of computed parameters

were evaluated using the below expression as given in Equation (6.15).

R = f(X , X , X … … X )

where R is the function of X , X , X … … X

R = X + X X (6.15)

The uncertainties of measuring instruments are given in Table 6.3. Tiegang

et al. (2009), Senatore et al. (2000) suggested the root mean square technique

to get the magnitude of uncertainties and errors as given in Equation (6.15)

which is used to estimate the uncertainty in brake power, brake thermal

efficiency, fuel flow, speed, load and voltage as in Table 6.4.

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Table 6.3 Uncertainties of instruments

S.No Instruments Range Accuracy % of

uncertainties

1 Pressure transducer 0-110 bar ±0.1 bar 0.1

2 Manometer - ±1mm 1.0

3 Speed Measurement 0-10000 rpm ±10 rpm 0.1

4 Smoke meter BSU 0-10 ±0.1 1.0

5 Exhaust temperature 0-900oC ±1oC 0.12

6 Stop watch - ±0.5 Sec 0.2

Table 6.4 Uncertainties of measured parameters

S.No Measured parameters Uncertainties %

1 Brake Power ±0.24

2 Brake thermal efficiency ±0.25

3 Flow rate of air ±0.60

4 Flow rate of Diesel ±0.72

5 Speed ±0.10

6 Load ±0.45

7 Oxides of nitrogen ±1.20

8 Hydrocarbons ±0.01

9 Carbon Monoxide ±0.60

10 Smoke ±2.00