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CHAPTER 4

CATALYTIC COMBUSTION IN SI ENGINE

FOR LEAN BURNING

4.1 TEST ENGINE

In the present work, tests were conducted on a single cylinder, air-cooled, four stroke, vertical, naturally aspirated, stationary, S.I engine with a displacement volume of 197cc, compression ratio of 4.5:1 and with a power output of 2.28 kW @3000 rpm. Test engine is a regular production engine used in stationary power generation. The normal operating range of the engine is between 2000 rpm and 3000 rpm. The fuel induction and ignition system is tuned for this speed range. Hence in the present work experiments are conducted in the speed range of 2200 rpm to 3000 rpm. The detailed technical specifications of the engine are given in Appendix 1.

4.2 LAYOUT OF THE EXPERIMENTAL SETUP

The engine is coupled with an eddy current dynamometer (20 kW) for loading. The fuel flow rate was measured using gravimetric system. The exhaust emissions such as hydrocarbon, oxides of nitrogen, carbon monoxide and carbon dioxide were measured using AVL make gas analyzer. The in-cylinder pressure was measured with the help of pressure transducer, which was flush mounted into cylinder head and the corresponding crank angle position was obtained by crank angle encoder. The specification of the gas analyzer is given in Appendix 3.

Figure 4.1 illustrates the schematic layout of the experimental set up. The details of the different measuring instruments are indicated in the figure.

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The pressure and crank angle positions were conditioned and

amplified using four channel charge amplifier (AVL indimeter 619). The

combustion parameters were analyzed with the help of inbuild software.

Figure 4.2 Photographic view of the experimental setup

Figure 4.2 shows the photographic view of the experimental set up.

A close view of the hole drilled to measure the in-cylinder pressure is shown

in Figure 4.3.

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Figure 4.3 View of pressure pickup mountings to measure cylinder

pressure

4.3 EXPERIMENTAL PROCEDURE

The following tests were conducted on the engine, operated by

petrol with various catalytic coating like copper, nickel and chromium.

Performance Test

Emission Test

Combustion analysis

4.4 PERFORMANCE TEST PROCEDURE

The overall view of the experimental setup is shown in Figure 4.1.

Petrol level in the fuel tank before starting the standard head engine has been

verified and then switched on the eddy current dynamometer control unit

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panel. The engine was allowed to run at a constant speed of 2500 rpm for

nearly 30 minutes to obtain steady state condition. Various measurements

were noted down. Fuel consumption was measured by stop watch for 50 cc of

fuel. In the same way the readings for 20%, 40%, 60%, 80% and full load

were taken. After taking the required readings the fuel supply is closed to stop

the engine, and the eddy current dynamometer control unit panel is also

switched off.

After completing the experiments with standard piston head similar

experiments were repeated with catalytic coated non-noble metal catalysts.

After completing the experiments with various load speed test have been

conducted at various speeds of 2200 rpm, 2400 rpm, 2600 rpm, 2800 rpm and

3000 rpm. For various coatings the test was repeated for a minimum of two

times for conforming the repeatability of the test.

4.4.1 Load and Speed Measurement

The test engine was coupled to an eddy current dynamometer. The

specification of the dynamometer is given in Appendix 2. A photo sensor

along with a digital rpm indicator was used to measure the speed of the

engine. The voltage pulses from the sensor were sent to the digital rpm meter

for pulse conversion and display of the engine speed with an accuracy of

± 1 rpm.

4.4.2 Fuel Supply Measurement

Fuel flow rate was measured on volume basis using a burette and

stop watch. Fuel was supplied to the engine from the petrol tank. When the

fuel cock is closed the fuel to the engine will flow from the burette and not

from the tank. The fuel flow rate can be obtained by noting the time taken for

metering known quantity of fuel and density of the fuel.

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4.4.3 Temperature Measurement

Temperature of the intake and exhaust gas was measured with

Chromel Alumel (K-Type) thermocouples. A digital indicator with automatic

room temperature compensation facility was used. The temperature indicator

was calibrated periodically.

4.5 EMISSION TEST PROCEDURE

1. The exhaust gas analyzer is switched on through the electrical

power supply. It is also allowed to stabilize down for

15 minutes at zero readings.

2. The engine is run according to the test procedure.

3. The sample probe is inserted in to the exhaust gas line for

measuring CO, HC and NOx. After the readings are stabilized,

the corresponding values of CO, HC, and NOx emission levels

are noted.

4. The sampling probe from exhaust pipe line is taken out and

the display is allowed to settle at zero reading.

5. The same procedure is repeated for different loads and

different catalytic coatings.

6. Finally the power supply is switched off to the exhaust gas

analyzer.

4.5.1 Measurement of HC, CO and NOx

Hydrocarbons, carbon monoxide and oxides of nitrogen were

measured as per the above procedure. An AVL gas analyzer was used for this

purpose. The exhaust sample to be evaluated was passed through a cold trap

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(moisture separator) and filter element to prevent water vapor. The gas

analyzer is periodically calibrated with standard gas. Hydrocarbons and

oxides of nitrogen were measured in parts per million (ppm), where as, the

carbon monoxide emissions were measured in terms of volume percentage.

4.6 COMBUSTION ANALYSIS

Combustion parameters were analyzed using AVL combustion

analyzer. The cylinder pressure, heat release rate and maximum pressure were

evaluated from the cylinder pressure data. The specifications of the

instrument used are given in the Appendix 4.

4.6.1 Pressure Measurement

In cylinder, pressure was measured with the help of a piezoelectric

air-cooled transducer. An AVL make transducer with a sensitivity of

16.11 pC/bar was used for the purpose. The transducer was flush mounted on

the cylinder head surface for avoiding passage effects. The pressure

transducer was located in a hole drilled through the cylinder head into the

combustion chamber. The change in value of compression ratio of the engine,

as a result of the additional volume formed by connecting passage, is

negligible. A piezoelectric transducer produces a charge output, proportional

to the cylinder pressure. The charge output was supplied to an AVL make

charge amplifier where it was amplified for an equivalent voltage that was

converted to the pressure.

4.6.2 Crank Degree Marker

For the measurement of cylinder pressure with respect to the crank

position, a crank degree marker, an electromagnetic pickup and signal-

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processing unit were used. The marker was fitted concentrically to the end of

the crankshaft.

4.6.3 Charge Amplifier

In order to obtain sharp, flicker free and stable signal of any desired

portion of the cylinder pressure trace, the charge amplifier was used. The

signal derived from the pickup that was suitably positioned with respect to

single pulse generator installed on the extension of the crank shaft was fed to

a charge amplifier. The output of the amplifier was sent to the monitor. The

detail of the charge amplifier is given in Appendix 5.

4.6.4 Data Acquisition System

The AVL 619 Indimeter software contains an easy to operate, menu

driven parameter editor for setting up the system, utilized for TDC detection.

The numerical monitor displays the calculated results like Indicated Mean

Effective Pressure (IMEP) or mass burn fractions as well as monitor program

for oscilloscope like curve display. This versatile software designed by AVL,

Austria was used for on-line data acquisition from the pressure transducer and

crank angle degree marker.

The Indimeter board, AVL INDIMETER 619 is a plug-in board for

standard PCs.

The features of this software are,

1. Acquisition on accurate crank angle basis.

2. Determination of top dead center.

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3. Signal calibration with dynamic offset correction for quartz

pressure transducers.

4. Calculation of engine specific results like indicated mean

effective pressure and mass burn fractions.

5. On-line numeric and graphic display of measured and

processed data are at user’s command immediately after

completing the installation.

4.7 EXHAUST GAS RECIRCULATION SYSTEM

Part of the exhaust gases from the engine were bypassed, regulated

and cooled by using a counter flow type heat exchanger in the EGR unit. The

flow rate of cooling water circulated through the EGR system was varied in

such a way that the cooled exhaust gas temperature was maintained around

atmospheric temperature. The cooled exhaust gas was allowed to pass through

a filtering device to remove the soot and particulate matter from the exhaust

gas. The schematic diagram of the EGR unit is shown in Figure 4.4. Engine

was run at constant speed during which the exhaust inlet flow was not

changing significantly. Hence constant flow rate was maintained in the heat

exchanger and also the inlet temperature of the cooling water was maintained

at atmosphere temperature.

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Figure 4.4 Schematic diagram of the EGR unit

4.8 EXPERIMENTAL PROCEDURE

The procedure adopted in the experimental work is given below;

1. Initial tests were conducted with standard surface at the rated

speed and variable load conditions to get the base line data of

performance, emission and combustion characteristics of the

engine.

2. Tests were conducted with different catalytic coated surface to

study the effects of coating on the performance, emission and

combustion characteristics of the engine.

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3. Tests were conducted with various catalytic coated surface at

different engine speed at full load to study the performance,

emission and combustion characteristics of the engine.

4. Experiments were conducted with exhaust gas recirculation

(0%, 5 % and 10% on volume basis) with various catalytic

coated surfaces to study the performance, emission and

combustion characteristics of the engine.

The test matrix indicating all the experiments conducted is given in

Table 4.1.

Table 4.1 Test Matrix

VARIABLES FUEL REQUIREMENT

Normal operation (Base engine)

Maintained constant load at

20%, 40%, 60%, 80% and 100%

at the rated speed of 2500 rpm.

Petrol Baseline reading for

comparison.

Normal operation (Base engine) with various catalytic coatings

Maintained constant load at

20%, 40%, 60%, 80% and 100%

at the rated speed of 2500 rpm.

Petrol Evaluation of performance,

emissions and combustion

parameters and selection of

an optimum catalytic

coating.

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Table 4.1 (Continued)

Normal operation (Base engine) with exhaust gas recirculation (EGR)

Maintained constant load at 20%, 40%, 60%, 80% and 100% at the rated speed of 2500 rpm. EGR flow rate varied between 5 % and 10 % .

Petrol Evaluation of performance, emissions and combustion parameters and optimisation of EGR flow rate.

Normal operation with various catalytic coatings and exhaust gas recirculation (EGR)

Maintained constant Brake Power at the different engine speed of 2200 rpm, 2400 rpm, 2600 rpm, 2800 rpm, and 3000 rpm. EGR flow rate varied between 5 % and 10 %.

Petrol Evaluation of performance, emissions and combustion parameters and optimisation of EGR flow rate.

4.9 EXPERIMENTAL ERROR AND UNCERTAINTY ANALYSIS

In the present work, many measurements are of single-sample type.

i.e. the measurements are made using only one instrument. Care has been

taken to maintain the original accuracy by frequent calibration. The

uncertainties for the basic measurements like barometer pressure, length,

weight, temperature, time etc., are equal to the least count of respective

instruments. The errors on quantities like gravity, gas constant, density,

viscosity, etc., are taken from handbooks and tables.

The uncertainty on the derived quantity is calculated by using the

method suggested by Holman (1998) which is based on the works of Kline

and McClintock. The uncertainties in the measured values like airflow, fuel

flow, engine power and pressure are calculated based on the work of

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Nedunchezhian (1993) and their results are presented in Table 4.2. The

procedure of error and uncertainty analysis carried out for the measured

parameters and is given in Appendix 8.

Table 4.2 Experimental Uncertainties

Variable Uncertainty %

Air-Flow Fuel Flow Engine Power Exhaust Temperature Viscosity Cylinder Pressure CO,HC

0.6481 0.7319 0.9434

50C 0.7

0.61644 1.5023

It can be observed from the Table 4.2, that the uncertainties

involved in the various parameters are less than 1.0% except for emission

measurement. The calculation of emissions involves many parameters such as

exhaust mass flow, temperature, power and the emission level. Hence, the

uncertainty increases in specific emission values. However, the uncertainty of

1.5% is still a small value and may not affect the accuracy of results.

Experiments were conducted and the results of engine performance,

emission and combustion data for both standard and catalyst engines are

discussed in Chapter 5.