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CHAPTER 10

THE INTERNAL COMBUSTION ENGINE EXPERIMENTS

10.1 INTRODUCTION

Ceramic coating of IC engine components, especially the piston

head, skirt and the cylinder head of diesel engines has been practiced for some

years using YSZ (yttria stabilized zirconia) as the coating material. Results

have been encouraging and studies have shown improvement in the

performance parameters and emission levels of the engines. This study

pertains to the use of mullite as a coating material to coat on petrol engine

components, to study the performance and compare with those of the

uncoated engine.

10.2 TBC’S IN PETROL ENGINES

Metal substrates in petrol engine components such as cylinder head,

piston and valves are generally made of aluminum –silicon (eutectic and

hyper eutectic) alloys. Current research is focused on successful coating of

these components, especially to optimize the coating adhesion characteristics

during long duration performance on road. Coating of mullite on aluminum

poses a challenge, due to the mismatch in thermal expansion coefficients

between the substrate and the coating. Thus aluminum silicon alloys present

the most challenging task of adapting to the environment of engine with

insulated combustion chamber. Petrol engine TBC’s operate at much lower

temperatures compared to aircraft engines and hence it is not reasonable to

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expect any significant improvement in performance efficiency. However,

their effect on reducing the particulate emission is expected to be worth a

mention.

Thermal barrier coatings are highly advanced material systems

applied to metallic surfaces, such as gas turbine or aero-engine parts,

operating at elevated temperatures. These coatings serve to insulate metallic

components from large and prolonged heat loads by utilizing thermally

insulating materials which can sustain an appreciable temperature difference

between the load bearing alloys and the coating surface. In doing so, these

coatings can allow for higher operating temperatures while limiting the

thermal exposure of structural components, extending part life by reducing

oxidation and thermal fatigue.

Figure 10.1 Coated piston crown

The thermal barrier crown coating is applied to the top of the piston

as shown in figure 10.1 and is designed to reflect heat into the combustion

chamber, thereby increasing exhaust gas velocity and greatly improving

scavenging potential. The 300 m thick coating can also assist in extending

piston life by decreasing the rate of thermal transfer (Pierz 1993).

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Ceramic-based thermal barrier coatings are primarily used to control the

movement of heat. When applied to the top of a piston, heat is evenly

distributed across the dome. This reduces hot spots that cause detonation. The

coating protects and insulates the piston against heat soak and this keeps the

heat on top of the piston building more power, and at the same time reduces

the amount of stress on the piston rings allowing a better seal. The coating can

also be applied to the combustion chamber, valve faces, and exhaust ports. By

holding more heat in the combustion chamber power is increased. Detonation

can also be controlled by the following ways:

1. Using a higher octane fuel like grade 89 instead of the regular

87 grade.

2. Keeping the compression ratio within limits. A static

compression ratio of 9:1 is usually the recommended limit for

most naturally aspirated street engines.

3. Checking for over-advanced ignition timing. Too much spark

advance can cause cylinder pressures to rise too rapidly.

4. Using the correct heat range spark plug.

5. Checking for engine overheating. In coated engine, the engine

temperatures are lower and hence this may not be a problem.

6. Using a richer air fuel mixture.

10.3 EXPERIMENTAL WORK

In the present study, a two stroke petrol engine with components

plasma spray coated with mullite was evaluated for performance efficiency

and endurance on road. Mullite ceramics is a good alternative to stabilized

zirconia and in some characteristics even better than stabilized zirconia. The

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properties of mullite most critical for TBCs are a very low thermal

conductivity and a thermal expansion close to that of super alloys.The 100 µm

thick mullite coating on 100 µm nickel chrome ( NiCr) bond coat was

deposited on the top surface of the piston and the cylinder head of a two

stroke engine of a two wheeler. The engine with the coated piston and the

cylinder head was subjected to a preliminary performance evaluation on an

engine dynamometer. The fuel efficiency, brake specific fuel consumption

(BSFC) and hydrocarbon emission (HC) were measured and the performance

parameters were compared with those of standard combustion chamber

containing uncoated components. Six different sets of coated piston and

cylinder heads were used for the test. The engine was tested at different

speeds and load conditions. The compression and air fuel ratios were

maintained constant for all combinations. Engine performance tests were

performed at full throttle openings on a mechanical dynamometer, specially

designed and fabricated to handle lighter loads, applicable for a two stroke

petrol engine of a two wheeler. The carburetor was set to the richest condition

to prevent detonation from taking place.

The performance of the engine using uncoated engine components

and coated components were compared, the results plotted and the reasons for

improved performance of the coated engines highlighted.

10.3.1 Materials

10.3.1.1 Piston

Pistons are manufactured from cast aluminum alloy A356.0

containing silicon which makes the piston harder improving its strength and

wear properties. All pistons are heat treated by T6 (solution quenching and

aging) treatment to improve their strength before machining and helps retain

their shape. Generally, higher the silicon content, higher the strength and wear

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properties. In the present study, pistons are made of cast aluminum A 356.0,

T6 treated, silicon and magnesium alloy with an Fe (iron) content of 0.1 %,

which will impart good strength. The ceramic coating on the piston improves

the thermal shock resistance, wear resistance, oxidation and corrosion

resistance of the piston, thus enhancing the operating life of the piston.

10.3.1.2 Cylinder head

Similarly the cylinder heads are also manufactured from cast

aluminum alloy A 356.0 and T6 treated. The ceramic coating on the side

facing the combustion chamber helps retain the heat of combustion and

minimizes the heat transfer towards the inside of the head. The coating

imparts similar properties mentioned in the case of the piston.

10.3.1.3 Bond Coat

Bond coat of nickel chrome is applied on the aluminum substrate to

a thickness of 100 m + 50 m before applying the top coat of mullite to

improve the adhesion of the coating to the substrate.

10.3.1.4 Top coat

The top coat faces the hot combustion gases and hence should be a

thermal barrier.Mullite ceramic of 100 m + 50 m thickness is plasma

sprayed on the bond coat.

10.3.2 Coating process

The METCO ROBOT plasma spraying equipment was used to

fabricate the specimens in this study using optimized plasma spraying

parameters as detailed earlier. Six sets of pistons and cylinder heads supplied

by M/s TVS company, Hosur, were coated for the study.

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10.3.3 Experimental Setup

The experimental setup is shown in the Figure 10.2. The engine

setup is rigidly fixed on the chassis of the fixture. The carburetor setting was

set to the richest condition throughout the testing to avoid any chances of

detonation. The power is transmitted from the engine to the pulley of the

mechanical dynamometer through a V-belt. The loading arrangement is

mounted on a frame. The load is applied to the engine using spring balance

connected to a rope wound around the brake drum of the setup. The fixture

consists of a supporting block, which is a cylindrical hub that carries ball

bearings through which a shaft is inserted as it supports the transmission of

power from the pulley. The supporting block used here is a cylindrical hub

that is bolted to the chassis of the setup. It is made of cast iron to provide a

stronger support to avoid vibration of the test rig at higher speed runs of the

engine. A stop watch is used for measuring the time and a calibrated

thermocouple is used for the temperature measurements. The air inlet of the

carburetor is connected to a surge tank which in turn is connected to the

manometer to measure the air intake head. The surge tank has an orifice of

diameter 14 mm. A 500ml burette is filled with petrol through which the fuel

is supplied to the carburetor of the engine. The test rig constructed with IC

engine is operated to measure various test parameters namely, brake horse

power (BHP), total fuel consumption (TFC), specific fuel consumption (SFC),

heat transfer, indicated power (IP), brake thermal efficiency , indicated

thermal efficiency , mechanical efficiency and volumetric efficiency. This test

is conducted for both coated and uncoated component of the engine.

A comparative study is made between the two results and the performance

improvement is presented. The various graphs are charted like brake power vs

total fuel consumption, brake power vs efficiencies, specific fuel consumption

vs brake power, buildup of temperature vs duration of running the engine and

torque vs speed.

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Figure 10.2 Experimental setup

10.3.4 Engine specification

STROKE = 2

BORE = 46 mm

STROKE LENGTH = 42 mm

DISPLACEMENT = 69.9 cc

MAX. POWER@ 5000 rpm = 2.61 KW

TORQUE@ 3750rpm = 5.0 Nm

COMPRESSION RATIO = 8.3:1

10.3.5 Testing Arrangements

The experimental tests are carried out by constructing a test rig as

shown in Figure 10.3 with the following instruments. Manometer, stopwatch,

surge tank, thermocouple, spring balance, Brake drum, and burette.

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Figure 10.3 Fixture setup

10.3.6 Test Procedure

The various testing procedures are done between the coated and the

uncoated engine of same specification under similar conditions. These test

results helps us to compare the engine performance between the coated and

uncoated engines. Initially the air inlet of the carburetor is connected to a

surge tank setup. The manometer is connected to the surge tank which shows

the pressure difference. A 500 ml burette is filled with petrol through which

the fuel is supplied to the carburetor of the engine. The load is applied to the

engine using spring balance on the brake drum of the test rig setup.

10.3.7 Performance Testing

Initially the engine is run at no load. The time taken for fuel

consumption of 10 ml is observed and tabulated. The pressure

difference in manometer is observed and tabulated as h1 , h2.

The load of 1kg is applied on the brake drum and again the

time taken for fuel consumption for 10ml, and the pressuredifference is tabulated.

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Similarly for gradual increase in load the readings are noted

and tabulated.

Using the above readings the engine performance parameters

like BHP, Indicated power, SFC, TFC, mechanical efficiency,

thermal efficiency and volumetric efficiency are calculated.

The obtained results are charted like BP VS TFC, BP VS

efficiencies.

Fuel consumption at various speeds -The engine is made to

run at no load condition for testing the fuel consumption rate

at various speed. The speed is increased gradually and their

respective fuel consumption rate is calculated for every 10

ml.SFC vs speed graph is charted for comparison with coated

and uncoated engine performance.

Torque vs speed - The engine is initially let to run with no

load condition. The load is gradually increased and speed at

various load are observed and tabulated. The torque value for

the particular speed is calculated and thus a torque vs speed

graph is charted for comparison with coated and uncoated

engine performance.

10.3.8 Temperature Testing

10.3.8.1 Calibration of thermocouple

Initially a thermocouple is calibrated by keeping one of the

junctions in cold water and the other in hot water. The cold water is made

constant were as the temperature of the hot water is increased gradually. The

multi meter is made use for measuring the voltage at its terminals. The

observed value is tabulated to calculate the average ‘k’ value.

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10.3.8.2 Temperature testing procedure

The temperature of the engine is measured by keeping the cold

junction of thermocouple as water and the hot junction at the surface point

were the temperature to be measured. This is done by positioning the hot

junction probe on the surface of engine like head and cylinder portion, their

respective voltage are tabulated. The observed values are calculated for its

temperatures. Thus the results are tabulated for comparison and charted.

10.3.9 Emission Tests

Emission test was conducted for CO (carbon monoxide) and HC

(Hydrocarbon ) emissions for various speeds and graphs plotted for the coated

and uncoated engines and compared. The photos of the coated piston and

cylinder head are shown in Figure 10.4.

(a) (b) (c)

Figure 10.4 (a) Coated piston top view (b) Coated cylinder head(c) Coated piston elevation

10.3.10 Endurance Test of Coated IC Engine

An endurance test of the engine with coated piston and cylinder

head was conducted to make a feasibility study of the coating, viz its adhesion

strength after prolonged usage. The coated engine was mounted in a two

wheeler and was run on road for 1000 kms, at various speeds and loads.

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10.4 RESULTS AND DISCUSSION

In the present study, mullite TBC successfully withstood the severe

thermo-mechanical stresses during simulated and accelerated burner rig

conditions. The thermal shock resistance of the coating composition in an

actual working engine was required to be tested. This was done to understand

the endurance capabilities of the coating by not only carrying out the

performance evaluation (fuel efficiency, engine power) of the engine with

coated components but also by running a two wheeler on road with the coated

components. Petrol engine components are subjected to milder thermal

stresses and shocks in their combustion chamber environment compared to

those in diesel engines.

10.4.1 Visual Examination

The test fixture was run in the laboratory for 100 hrs at varying

speeds and loads. The coated surface of the piston was examined for surface

defects and signs of spallation. The visual examination of the piston surface

revealed no significant defect of the coating surface or the interface. The

surface had a deposit of carbon as expected.

10.4.2 Performance Tests

The performance curves of the petrol engine at different speeds and

load conditions are shown graphically and the tables of measurements taken

are shown. On examination of the various parameters evaluated the general

conclusions are drawn and summarized after each test.

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10.4.2.1 BP vs TFC characteristics

Brake horse power (BP) is the actual power delivered at the crank

shaft. It is obtained by deducting various power losses in the engine from the

indicated horse power. In other words, BP is the usable power produced by

the engine. (TFC)Total fuel consumed is the amount of fuel used by the

engine for one hour duration of running. The measured values are shown

graphically below in Figure 10.5.

(a)

(b)

Figure 10.5 BP vs TFC characteristics of a) uncoated and b) coated engine

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The results of the BP Vs TFC characteristics are shown below.

1. The total fuel consumption is more flat in the coated engine,

when compared to the uncoated engine. Also the fuel

consumption is lower (Chan and Khor 2000).

2. Generally, the TFC increases with increase in BP.

3. By extending the points to the second quadrant in the X-axis,

the friction power calculated is 1.5 kw for the uncoated engine

and 1.9 kw for the coated engine.

10.4.2.2 BP vs efficiency (mechanical, volumetric, indicated thermal and

brake thermal) characteristics

Mechanical efficiency is the ratio of the brake power (delivered

power) to the indicated power. Volumetric efficiency is an indication of the

breathing ability of the engine and is given by the ratio of volume of air

actually inducted at ambient conditions to the swept volume of the engine.

Indicated thermal efficiency is the ratio of the indicated power (IP) to the

input fuel energy in appropriate units. The power developed within the engine

cylinder is known as indicated power. In other words, it is the power the

engine can theoretically produce. Similarly brake thermal efficiency is the

ratio of the brake power (BP) to the input fuel energy in appropriate units.

The measured and calculated values are shown tabulated below in

Tables 10.1and 10.2 and the performance curves are shown in Figure 10.6.

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Table 10.1 Observed values of performance studies on uncoated engine

S.No. BP (kW) bt % It % mech % vol %1 0 0 48.5 0 842 0.1 3.2 50.5 6.3 853 0.2 5.7 48.2 12 904 0.3 8.5 50.8 16.7 875 0.4 9.9 46.9 21 866 0.5 12.4 49.6 25 867 0.6 14.2 49.8 28.6 888 0.7 16.9 53 31.8 889 0.8 18.5 53.2 34.8 86

10 0.9 20.5 54.5 37.5 8811 1 21.6 53.9 40 8812 1.1 22.4 53.1 42.3 8313 1.2 22.2 50 44.4 8914 1.3 23.7 51 46.4 8415 1.4 23.7 49.2 48.3 8916 1.5 24.6 49.2 50 85

Table 10.2 Observed values of performance studies on coated engine

S.No. BP (kW) bt % It % mech % vol %1 0 0 62.3 0 752 0.1 3.03 60.8 5 813 0.2 6.07 63.8 9.5 804 0.3 9.5 69.4 13.6 725 0.4 11.7 67.3 17.4 896 0.5 14.6 70.2 20.8 747 0.6 16.9 70.6 24 888 0.7 20 73.4 27 859 0.8 22.6 76.3 30 9110 0.9 24.6 76.5 32 8911 1 27.3 79 34 8412 1.1 29.1 79.4 37 8313 1.2 31.7 82 39 8014 1.3 33.3 82 40.6 7915 1.4 34.7 82 43.4 8016 1.5 36.1 82 44 83

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Figure 10.6 Comparison of brake horse power Vs efficiences for boththe coated and uncoated engines

The results of the BP vs efficiency characteristics are given below.

1. The maximum brake thermal efficiency bt is 24.6 % for theuncoated engine and 36.1 % for the coated engine.

2. The maximum Indicated thermal efficiency It is 54.5 % forthe uncoated engine and 82 % for the coated engine.

3. The maximum mechanical efficiency mech is 50 % for theuncoated engine and 44 % for the coated engine.

4. The maximum volumetric efficiency vol is 88 % for theuncoated engine and 91 % for the coated engine. Coating onthe piston and cylinder head has increased the combustiontemperature and hence the improvement in volumetricefficiency. James A. liedel (1997) and Tamil Porai (2003)have confirmed this in their study.

5. Reddy et al (1990), Taymaz et al (2005) , James A. liedel(1997) and Stephen Bernard (2009) in their study on coated diselengines confirm that the thermal efficiencies have improved.

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10.4.2.3 Speed vs SFC characteristics

The fuel consumption characteristics of an engine are generally

expressed in terms of SFC (Specific fuel consumption) in kilograms of fuel

per kW-hr. It is an important parameter that reflects the performance of the

engine.The Speed of the engine is varied and the SFC noted for each speed

and tabulated in table 10.3 and the performace curve is shown in figure 10.7.

Table 10.3 Speed vs SFC data a-uncoted engine, b- coated engine

Sl. No. Speed(rpm)

SFC(kg/kW.hr) Sl.No. Speed

(rpm)SFC

(kg/kW.hr.)1 950 0.22 1 950 0.222 1200 0.18 2 1200 0.183 1600 0.16 3 1600 0.164 1800 0.14 4 1800 0.155 2000 0.16 5 2000 0.186 2300 0.16 6 2300 0.18

Figure 10.7 Comparison of speed Vs specific fuel consumptioncharacteristics of coated and uncoated engines

There is no major change in the SFC vs Speed characteristics.

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10.4.2.4 Torque vs speed characteristics

The engine is loaded graduallyand the torque is calculated for each

load and the speed measured for various throttle openings. The measured and

calculated values are shown below in tables 10.4 and 10.5 and the

characteristic curves are shown in figure 10.8.

Table 10.4 Torque Vs speed observed values of the uncoated engine at25%,50 % and 100 % throttle openings

Speed (rpm)

Torque(Nm)

25 %throttleopening

50 %throttleopening

100 %throttleopening

0 1800 2000 2200

1 1730 1935 1922

2 1620 1620 1764

3 1421 1540 1630

Table 10.5 Torque Vs speed observed values of the coated engine at25 %, 50 % and 100 % throttle openings

Speed (rpm)

Torque(Nm )

25 %throttleopening

50 %throttleopening

100 %throttleopening

0 1800 2000 22001 1789 1960 21852 1750 1940 20313 1735 1917 1995

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(a)

(b)

(c)

Figure 10.8 Comparison of torque vs speed characteristics of coated anduncoated engines (a) 25 % throttle opening, (b) 50 %throttle opening, (c) 100 % throttle opening

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The results of the torque vs speed chracteristics are given below.

The coated engine performs better in providing a higher torque at

various throttle openings and also there is less variation in speed as load is

increased.Hence the power produced in the coated engines are higher.

10.4.3 Temperature Measurements

Measurements were done on the cylinder head and the cylinder

close to the conbustion chamber using thermocouples after calibration. The

measured values are tabulated and shown in tables 10.6 and 10.7 and also

shown graphically in Figures 10.9 and 10.10.

Table 10.6 Temperature measurements taken for the Uncoated engine

Duration (minutes)SpeedTemperature (°C) 10 20 30 40 50

Head 82 86.2 94.6 104.2 104.2

Cylinder 83.2 89.8 94.6 98.8 98.8

Head 120.8 130 134.2 137.8 137.8

Cylinder 124.6 124.6 127.6 129.4 129.4

Table 10.7 Temperature measurements taken for the coated engine

Duration (minutes)SpeedTemperature (°C) 10 20 30 40 50 60

Head 54.6 79.2 84.6 94.2 103.2 103.2

Cylinder 57.6 81.6 97.2 93 94.8 94.8

Head 103.2 110.4 113.4 118.8 122.4 122.4

Cylinder 97.2 102 106.8 110.4 118.8 118.8

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Figure 10.9 Comparison of temperature measurements on cylinder head

of coated and uncoated engines

Results : The temperature reduction of the coated cylinder head is apparent

from the graphs, indicating a higher combustion temperature.

Figure 10.10 Comparison of temperature measurements on cylinder ofcoated and uncoated engines

Results : The temperature reduction of the cylinder in the vicinity of the

combustion chamber is apparent from the graphs, indicating a

higher combustion temperature.

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10.4.4 Emission Tests

The CO (carbon monoxide) and HC (hydrocarbon) emission levels

are measured using in an engine emission test rig, for various speeds and

tabulated below, in table 10.8 and the characteristic curves are shown

graphically in Figure 10.11.

Table 10.8 Emission levels of CO and HC (a) CO % (b) HC (ppm)

Speed(rpm )

CO ( % vol ) HC ( ppm )Uncoated

EngineCoatedEngine

UncoatedEngine

CoatedEngine

0 2.6 2 1250 900500 2.65 2.05 1500 900

1000 2.7 2.1 1750 9001500 2.75 2.25 2100 9502000 2.8 3 2500 10002300 3.5 3.2 2900 900

(a)

Figure 10.11 Comparison of CO and HC emission characteristics of

coated and uncoated engines a) CO % b) HC ( ppm)

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(b)

Figure 10.11 (Continued)

The results of the emission tests are given below.

The CO and HC emissions are lower for the various speeds in thecoated engines. A trend of significant improvement in the carbon monoxideand hydrocarbon emissions is observed in the case of engine with coatedcomponents compared to that of the standard engine. The reduced hydrocarbon isseen to be more pronounced at higher engine speeds (> 1000 rpm) for theengine with coated components.

10.4. 5 Endurance Test of Coated IC Engine

The endurance test on road was completed for duration of 1000 kmsfor various speed and loads and the coated components were visuallyexamined for any peel off of the coating and any other coating defects. Onvisual examination, it was found that the coating was able to withstand thetemperature variations in actual use and found to be satisfactory.

10.5 CONCLUSION

1. The visual examination of the coated piston crown and thecylinder head showed no spallation of the coating after testingin the test rig.

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2. Petrol engines are not expected to exhibit superior performance

when incorporated with ceramic coated components, but the

results are encouraging and as such significant improvement is

observed in performance efficiency by a two stroke petrol engine

with coated components. The load carrying capacity of the coated

engine increased by 10 to 15 %, the brake thermal efficiency ( bth)

increased by 12 %, indicated thermal efficiency ( ith) increased by

28%, volumetric efficiency ( vol) increased by 3%.The

mechanical efficiency ( m) of coated engine reduced by 6%.

3. The maximum temperature of cylinder head and the cylinder

of coated engines were lower than that of uncoated engine by

20°C on an average, for the conditions described.

4. Also, it is very clear that the coating has not deteriorated the

performance of the petrol engine. Coating has in fact

improved the emission characteristics of the engine which is

due to the better burning of the fuel thereby reducing the

amount of unburnt fuel, ie. hydrocarbon in the exhaust. The

CO and HC emissions were lower by 30% for the various

speeds in the coated engines.

5. No visible defects were noticed after the endurance tests were

conducted on the petrol engine. Mullite duplex coatings on

engine components have withstood the long distance

endurance tests carried out. Mullite coatings have not failed as

anticipated due to the high creep strength of mullite. Similar

studies conducted on diesel engines by Pierz (1993), gave

good results. Hence, mullite coatings can be successfully

applied on spark ignition engines.