CHAPTER 6 SURFACE TEMPERATURE...

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CHAPTER 6

SURFACE TEMPERATURE PREDICTION

6.1 LOW HEAT REJECTION ENGINES - AN OVERVIEW

Energy conservation and efficiency have always been the quest of

engineers concerned with internal combustion engines. The diesel engine

generally offers better fuel economy than its counterpart petrol engine. Even

the diesel engine rejects about two thirds of the heat energy of the fuel, one-

third to the coolant, and one third to the exhaust, leaving only about one-third

as useful power output. Theoretically if the heat rejected could be reduced,

then the thermal efficiency would be improved, at least up to the limit set by

the second law of thermodynamics. If combustion gas energy can be

contained through the expansion cycle, then the efficiency of the engines can

be increased. To increase the efficiency of IC engines and generate higher

combustion chamber temperatures, low heat rejection concept is investigated.

Low Heat Rejection engines aim to do this by reducing the heat lost to the

coolant.

The diesel engine with its combustion chamber walls insulated by

ceramics is referred to as Low Heat-Rejection (LHR) engine. The LHR

engine has been conceived basically to improve fuel economy by eliminating

the conventional cooling system and converting part of the increased exhaust

energy into shaft work using the turbocharged system. Adiabatic engine

implies a no heat loss engine, as adiabatic process is defined as a no-heat loss

process since the combustion chamber walls have no thermal capacity or

inertia. But, under such imaginary cases, there would be no heat flow relative

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to the cylinder walls. The ways and means of realization of such a combustion

chamber are not realistic in practice. However the insulated combustion

chamber either partially or fully can be assumed to have a large thermal

capacity or inertia. The surfaces of the combustion chamber remain at a

constant temperature throughout the operation. Such an engine is called a

Low Heat Rejection (LHR) engine. In the development of LHR engine, the

reduction of heat loss to the coolant system has always been of considerable

interest to engine designers because, this would reduce the cost, weight,

power requirement and size of the cooling system. In gasoline engines, the

thermal insulation will increase the wall temperature which will lead to

unwanted detonation. Because of this, insulation of the combustion chambers

could be done only to diesel engines. This has two important purposes-to

reduce the size of coolant system & to increase the exhaust energy available

for turbo charging and thereby increasing power and efficiency.

In the insulated engines, the wall temperatures increase. Hence in a

natural aspirated engine the intake air gets heated and reduces the volumetric

efficiency. To maintain the volumetric efficiency, the insulated engines are

usually turbo charged. This maintains the volumetric efficiency and hence the

power output. The excess energy in the exhaust is used to drive turbines and

the combination gives the highest efficiency.

In LHR engine the combustion chamber is insulated with high

temperature materials which makes the engine operate at hotter environment

with less heat transfer. The components that are normally insulated include

piston, cylinder head, valves, cylinder liner, and exhaust ports. It is expected

that additional power and improved efficiency is possible with engine

insulated because thermal energy that is normally lost to the cooling water

and exhaust gas is converted to useful power through the use of turbo

machinery and high temperature materials. Insulation of the combustion

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chamber is done by coating it with ceramics. Partially stabilized zirconia and

aluminium titanate are used for coating. The coating is mainly done by

plasma spraying. The spraying parameters are very important in determining

the reliability of the coating. A 0.5mm layer of zirconia will reduce the heat

rejection to the coolant by 48%, while a 1mm layer is required to reduce the

heat flow by 78%. The engine components which are commonly coated are

cylinder head, valves, liners and piston crown.

According to the first law of thermodynamics, and energy which is

not rejected the coolant remains available to produce useful piston work.

According to second law of thermodynamics, combustion taking place at

higher temperature is also more efficient as irreversibility decrease with

increasing temperature. The reduction in heat losses also results in increased

exhaust enthalpy. This extra exhaust energy can be utilized to drive a

compounding turbine or a bottoming cycle, thus improving the overall

efficiency. From the above, it is expected that the insulated diesel engine

should easily outperform the standard cooled engine. However, experiments

reveal that in many cases, the performance of LHR engine is only slightly

better, in a few cases worse than the cooled version of the same engine.

A more likely cause for the performance changes is that the introduction of

insulation in the cylinder could significantly alter the combustion process.

In a LHR engine, shorter ignition delays are expected, thus leading

to a decreased premixed fraction and a corresponding increase in the amount

of fuel burned during the diffusion phase of combustion. With the heat

release shifted later in the cycle, less useful work would be extracted from the

insulated engine. In other words, in order to realize the benefits of the LHR

engine, the combustion system has to be modified to maintain a desirable heat

release profile. The changes in the combustion process due to insulation also

affect exhaust emissions. Higher gas temperatures are supposed to reduce the

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concentration of incomplete combustion at the expense of increase in nitric

oxide.

The combustion chamber wall temperature of an LHR engine is

higher than that of a conventional water-cooled engine. Hence the charged air

in a cylinder absorbs heat emanating from the high temperature chamber wall.

Therefore the charged air expands, this lessening the amount of intake air.

However if the increase in power output is to be realized, a turbocharger using

higher exhaust energy and which increase the amount of intake air, or better

still, a turbo compound system that recovers that exhaust energy and converts

it into additional power should be connected with the LHR diesel engines.

The excess air ratio also decreases by about 1 to 7.6% compared to that of

water cooled, turbocharged base engine. Cooling the liner with water even in

the case of a naturally aspirated insulated engine can moderate the

deterioration in volumetric efficiency. The rate of heat release in the diffusion

combustion phase shows a decreasing trend from the early to middle period

and lengthening of the subsequent after-burning period.

6.2 EFFECT OF COATING ON ENGINE PERFORMANCE

PARAMETERS

6.2.1 Volumetric Efficiency

Volumetric efficiency is an indication of breathing ability of the

engine. It depends on the ambient conditions and operating conditions of the

engine. Reducing heat rejection with the addition of ceramic insulation causes

an increase in the temperature of the combustion chamber walls of an LHR

engine. The volumetric efficiency thus drops, as the hotter walls and residual

gas decrease the density of the inducted air. The deterioration in volumetric

efficiency of the LHR engine can be prevented by turbo charging, and that

there can be more effective utilization of the exhaust gas energy.

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6.2.2 Thermal Efficiency

Thermal efficiency is the true indication of the efficiency with

which the chemical energy input in the form of fuel is converted into useful

work. Improvement in engine thermal efficiency by reduction of in-cylinder

heat transfer is the key objective of LHR engine research. Much work has

been done at many research institutes to examine the potential of LHR

engines for reducing heat rejection and achieving high thermal efficiency.

Researches indicate improvement in thermal efficiency with LHR engine.

They attribute this to in cylinder heat transfer reduction and lower heat flux.

However investigations of others report that thermal efficiency reduces with

insulation. They all attribute this to an increase in the convective heat transfer

coefficient, higher heat flux (increase in in-cylinder heat transfer) and

deteriorated combustion. The in-cylinder heat transfer characteristics of LHR

engine are still not clearly understood. Thus the effect of combustion chamber

insulation on reducing heat rejection and hence on thermal efficiency is not

clearly understood as on date.

6.2.3 Specific Fuel Consumption

Numerous investigators have modeled and analyzed the effects of

in-cylinder thermal insulation on fuel consumption and have reported

improvement in the reduction of fuel consumption in LHR engine. The level

of improvement that has been predicted ranged from 2 to 12 %. They attribute

this to insulation of in-cylinder components. It has been predicted that

insulation of in-cylinder components is a more effective means of reducing

heat rejection and reducing fuel consumption. Some attribute this to reduced

friction due to increased wall temperature. Some investigations indicate

higher fuel consumption of LHR engine which is attributed to the increase in

reciprocating mass. In general, it has been reported that fuel consumption of,

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naturally aspirated LHR engine is in the range of 0 to 10% higher,

turbocharged LHR engine in the order of 0 to 10% lower and turbo

compounded LHR engine in the order of 0 to 15% lower, when compared

with the conventional cooled engine.

6.2.4 Injection Characteristics

In heavy-duty diesel engines, rather than air motion, the momentum

and energy of the injected fuel are the major physical factors, which control

the air fuel mixing process. Accordingly it is necessary to optimize the fuel

injection system of the heavy-duty un-cooled LHR diesel engines. The

investigations show that the fuel economy of the LHR engine is of the same

level as that of water cooled engine at the medium load, but deteriorated

significantly at the high load condition which is attributed to increased

temperature of the combustion chamber walls, thus also increasing the

temperature of the fuel issuing from the heated nozzle orifice resulting in the

reduced fuel viscosity which causes a heavy leakage fuel inside the nozzle

and extended injection duration as well. Some experimental data show that

higher insulated temperature in the insulated engine alters both the needle lift

and line pressure. It has been shown that with proper adjustment of the

injection timing it is possible to partially offset the adverse effect of insulation

on heat release rate. The data shows that reducing heat rejection from the

cylinder, shift the combustion from pre-mixed towards diffusion and by

advancing the timing; the LHR engine achieves the same pre-mixed heat

release rate. Injection pressure and rate can also offset the adverse effect of

insulation.

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6.3 EFFECT OF COATING ON ENGINE EMISSION

PARAMETERS AND NOISE

6.3.1 Unburned Hydrocarbon

The emission of unburned Hydrocarbon from the LHR engines is

more likely to be reduced because of the decreased quenching distance and

the increased lean flammability limit. The higher temperatures both in the

gases and at the combustion chamber walls of the LHR engine assist in

permitting the oxidation reactions to proceed close to completion. However

some investigations indicate increased level of HC emissions which is

attributed to deterioration in diffusion combustion. The burning of lubricating

oil due to high wall temperature is believed to be the other reason for

increased UBHC level.

6.3.2 Carbon Monoxide

LHR engines produce less carbon monoxides, for reasons similar to

those for unburned Hydrocarbon which is attributed to high gas temperature

and combustion chamber walls. The reduced level of pre-mixed combustion

in the insulated engine decreases the initial production of CO and the higher

temperatures during diffusion combustion accelerate the oxidation of CO.

6.3.3 Oxides of Nitrogen

NOx is formed by chain reactions involving Nitrogen and Oxygen

in the air. These reactions are highly temperature dependent. Since diesel

engines always operate with excess air, NOx emissions are mainly a function

of gas temperature and residence time. NOx emission from LHR engines is

generally higher than that in water-cooled engines due to higher combustion

temperature and longer combustion duration. Many investigations report an

increase in the LHR engine NOx emissions and concluded that diffusion

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burning is the controlling factor for the production of NOx while other

investigations indicate reduction in NOx level due to the shortening of the

ignition delay that decreases the proportion of the premixed combustion.

6.3.4 Smoke and Particulates

It is expected that LHR engines would produce less smoke and

particulates than standard engines for reasons such as high temperature gas

and high temperature combustion chamber wall. Also enhanced soot

oxidation, which was made possible by both the high combustion temperature

and the intense turbulence created by the reversed squish reduces smoke.

Factors such as short ignition delay, poor air-fuel mixing are also responsible

for the formation of smoke and particulates.

6.3.5 Noise

Ceramics are light weight materials when compared with the

common metals and alloys, because they are less dense in nature. So it is

generally expected that use of such material for engine components would

decrease the noise generated in an engine. The rotating and the reciprocating

masses can be lighter, decreasing response time, noise and the required spring

forces for successful operation. Lighter materials will decrease vibration

created in the system. Friction would also be decreased as would the resultant

friction or sustaining work required and decrease the noise at that interaction.

6.4 USE OF CERAMIC MATERIAL IN IC ENGINES-AN

APPROACH

The choice of metal as the material from which heat engines are

made is an unfortunate one. This is because metals are relatively low

temperature materials for heat engines and they are also good thermal

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conductors, two properties that are detrimental to efficient combustion.

Historically, when the internal combustion engine was first

being developed, it was an unavoidable choice because metals were the only

suitable material available at that time. Development of new materials for IC

engines is now being encouraged worldwide.

The maximum service temperature of many metals is less than

6000C, and thus metal engines are required to operate at temperatures too low

for fuel to be burnt completely. Also, as metals are good thermal conductors,

the heat generated within the metallic combustion chamber is asily conducted

through the metallic casing. Liquid cooling is thus required to prevent the

metallic engine from overheating and this hastens heat loss (about 30% of the

heat generated is lost to the coolant or radiator water). Furthermore, resulting

incomplete combustion products are discarded through the exhaust adding to

airborne pollution. This temperature trade-offs required of metallic internal

combustion engines result in low combustion and low thermal efficiencies.

Thus, metallic internal combustion engines suffer primarily from three

problems namely Low combustion efficiency (due to the lower operating

temperatures of metals), Substantial heat loss (due to the high thermal

conductivity of metals), and Wear (resulting in some limited metal component

life).

As ceramics are high temperature materials, a ceramic engine

should be able to operate at higher temperatures enabling combustion of

fuel to be more complete resulting in increased combustion efficiency. This

should increase performance, decrease fuel consumption and reduce pollution.

This should also enable various fuels to be used. A suitable engine material

should have twin capabilities; namely be able to operate at high temperatures

and also contain the heat generated within the combustion chamber. Ceramic

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is such a material. It is a high temperature material and it also possesses a low

thermal conductivity.

The following are the advantages of using ceramics in IC engines -

(1) Ability to operate at higher temperatures resulting in more

complete combustion of fuel and increased thermal and

combustion efficiency (and could lead to decreased fuel

consumption)

(2) They are relatively good thermal insulators and are thus able

to reduce the heat lost to the surroundings (e.g. the thermal

conductivity of zirconia ceramics is about 2 W/m.K).

(3) It reduces the heat rejected from the working chamber of an

internal combustion engine to the engine's cooling system and

thus improves engine efficiency.

(4) It eliminates the need for continuous lubrication of the

engine's cylinder walls.

(5) It eliminates the need to consider the wear resistance of the

thermal barrier material to be used, thus providing a greater

selection thereof.

Therefore making the combustion chamber of an internal

combustion engine entirely out of a ceramic or else insulating the surface of

the combustion chamber with ceramic tiles should improve the engine's

combustion characteristics and reduce heat loss. This could lead to higher

engine performance and lower exhaust emissions.

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6.5 VARIOUS CERAMIC MATERIALS USED IN IC ENGINES

The following ceramics have long been used for coating on the

combustion chamber of IC engines.

6.5.1 Silicon Nitride

Among the various engineering ceramics that have been developed

over the decades, silicon nitride has received the most attention for use in

internal combustion engines and turbines. It has good thermal

shock resistance (ΔT ~ 6000C) and good creep resistance. Though very

desirable as an engine material, their poor mechanical strength (low fracture

toughness) has precluded their use in load-bearing applications. As the

brittleness of silicon-based ceramics is considered an intrinsic characteristic

of such materials by virtue of their strong bonding, covalent and ionic,

only limited increases in the fracture toughness of silicon nitride is believed to

be attainable. The development of ceramic matrix composites (CMC) is

considered to be a more attractive alternative, but success in this approach has

been limited. Although some progress has been made over the years, the

processing of silicon nitride remains a problem and larger higher-strength

silicon nitride components have yet to be fabricated. Silicon nitride cannot be

heated over 18500C to densify because it dissociates into silicon and nitrogen.

Also its covalent bonding does not allow it to easily sinter and fully densify.

Furthermore, silicon nitride ceramics in a hot, corrosive and humid oxidizing

atmosphere (such as during fuel-air combustion in internal combustion and

turbine engines) are prone to degradation. When they are subject to oxidation,

water vapor and high temperatures they form a thermally-grown silicon oxide

layer which continually volatilizes as hydroxide species affecting the integrity

of the silicon-based ceramic surface. Despite the persistent and seemingly

intractable problems of degradation and poor mechanical strength as well as

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the difficulties in fabricating and processing larger higher-strength load-

bearing components, silicon nitride ceramic remains surprisingly the preferred

high temperature material for turbines, pumps, blowers and many other such

applications.

6.5.2 Silicon Carbide

A material with a very high hardness, silicon carbide has, in the last

few years, been receiving some attention from the Micro Electro-Mechanical

Systems (MEMS) community in their quest to develop a miniature engine.

However, the same problems that plague silicon nitride would also apply to

silicon carbide, and the fracture toughness of silicon carbide is even lower

than that of silicon nitride. Silicon carbide still has many other uses that do

not require mechanical integrity and strength.

6.5.3 Alumina

A much used ceramic, mainly as electrical insulators, they have

seldom been considered as suitable materials for engines possibly because of

their low fracture toughness and high thermal conductivity. However, there

has been some recent interest in fabricating alumina components for micro-

engines though they find less use in IC engines.

6.5.4 Zirconia

These engineering ceramics were once dubbed as "ceramic steels"

because of their very high fracture toughness among ceramics. Also, zirconia

ceramics have one of the highest maximum service temperatures (~20000C)

among all of the ceramics and they retain some of their mechanical strength

close to their melting point (27500C). However, their low creep resistance and

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their low thermal shock resistance (ΔT ~ 3500C) could pose a problem.

Zirconia ceramics have been used in heat engines because of two very

notable properties they possess: a high temperature capability and a low

thermal conductivity. None of the other ceramics possess a thermal

conductivity as low as the zirconia’s. This means that engines made out of

zirconia would retain much of the heat generated in the combustion chamber

instead of losing it to the surroundings (approaching near adiabatic

conditions). Thus the need for a cooling system could also be eliminated by

using these coatings on the IC engines.

6.6 CHOICE OF THE CERAMIC MATERIAL

The choice of a ceramic is complicated by particular attributes that

are present in some ceramics and not in others.. Some properties of ceramic

materials promise considerable improvement in the performance of IC

engines. Their capability to withstand high thermal load conditions and higher

operating temperatures can be used to replace metal alloys. The low thermal

conductivity of some ceramics could result in higher efficiencies or better

operating characteristics though low heat losses. The low density could lead to a

reduction of inertia of the components and improve the engine response. Non

oxide ceramics like silicon nitride and silicon carbide have higher strengths than

metallic alloys above 13000C and their density is around 1/3rd as that of metallic

alloys which offers inertia in rotating and oscillating parts.

A careful consideration on the above properties revealed the use of

a yttrium-based zirconia engineering ceramic for the following reasons:

(1) Its relatively good mechanical strength (i.e. combination

of high fracture toughness and high bond strength), high

hardness, high elastic modulus and resistance to corrosion and

wear.

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(2) A high temperature capability and a low thermal conductivity.

None of the other ceramics possess a thermal conductivity

as low as the zirconia’s. This means that engines made out of

zirconia would retain much of the heat generated in the

combustion chamber instead of losing it to the surroundings

(approaching near adiabatic conditions). Thus the need for a

cooling system could also be eliminated.

(3) Tests show that zirconia ceramic does not suffer from

hydrothermal degradation which plagues several other

ceramics;

(4) Being an oxide, zirconia is unlikely to be further oxidized.

(5) Low ductility, low tensile strength and low bending strength

have impeded the direct replacement of metal with ceramics.

Considering that many fuels contain chemically-active and

corrosive substances, resistance against hydrothermal degradation and

resistance against oxidation are highly desirable attributes of a ceramic for

an internal combustion engine. In this present work, PSZ + 8% Yittria have

been coated for a thickness of 65 microns over the cylinder head, valves and

the piston crown.

There are three types of Zirconia that are used in coating industry.

They are;

6.6.1 Unstabilized (Pure) Zirconia

Pure Zirconia (Zirconium dioxide) has a high melting point (2,7000C)

and a low thermal conductivity. Its polymorphism, however, restricts its

widespread use in ceramic industry. During a heating process, zirconia will

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undergo a phase transformation process. The change in volume associated

with this transformation makes the usage of pure zirconia in many

applications impossible. Pure zirconia is an important constituent of ceramic

colors and an important component of lead-zirconia-titanate electronic

ceramics. Pure zirconia can be used as an additive to enhance the properties of

other oxide refractories. It is particularly advantageous when added to high-

fired magnesia and alumina bodies. It promotes sinter ability and with

alumina, contributes to abrasive characteristics. Pure zirconia is monoclinic at

room temperature and changes to the denser tetragonal form at about 1,0000C,

which involves a large volume change and creates cracks within its structures.

Due to the inversion, pure zirconia has low thermal shock resistivity.

6.6.2 Partially Stabilized Zirconia (PSZ)

Addition of some oxides, such as CaO, MgO, and Y2O3, into the

zirconia structure in a certain degree results in a solid solution, which is a

cubic form and has no phase transformation during heating and cooling. This

solid solution material is termed as stabilized zirconia, a valuable refractory.

Partially stabilized Zirconia is a mixture of zirconia polymorphs, because

insufficient cubic phase-forming oxide (Stabilizer) has been added and a

cubic plus metastable tetragonal ZrO2 mixture is obtained. A smaller addition

of stabilizer to the pure zirconia will bring its structure into a tetragonal phase

at a temperature higher than 1,0000C, and a mixture of cubic phase and

monoclinic (or tetragonal)-phase at a lower temperature. Therefore, the

partially stabilized zirconia is also called as tetragonal zirconia polycrystal

(TZP).Usually such PSZ consists of larger than 8 mol% (2.77 wt %) of MgO,

8 mol% (3.81 wt %) of CaO, or 3-4 mol% (5.4-7.1 wt %) of Y2O3. PSZ is a

transformation-toughened material. Partially Stabilized Zirconia has been

used where extremely high temperatures are required. The low thermal

conductivity ensures low heat losses, and the high melting point permits

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stabilized zirconia refractories to be used continuously or intermittently at

temperatures of about 2,200°C in neutral or oxidizing atmospheres. Zirconia

is not wetted by many metals and is therefore an excellent crucible material

when slag is absent. It has been used very successfully for melting alloy steels

and the noble metals. PSZ is also used experimentally as heat engine

components, such as cylinder liners, piston caps and valve seats.

6.6.3 Fully Stabilized Zirconia

Generally, addition of more than 16 mol% of CaO (7.9 wt %), 16

mol% MgO (5.86 wt %), or 8 mol% of Y2O3 (13.75 wt %), into zirconia

structure is needed to form a fully stabilized zirconia. Its structure becomes

cubic solid solution. Its structure becomes cubic solid solution which has no

phase transformation from room temperature up to 2,500 °C. As a good

ceramic ion conducting materials, fully Yittria stabilized Zirconia (YSZ) has

been used in oxygen sensor and solid oxide full cell (SOFC) applications. The

SOFC applications have recently been attracting more worldwide attention,

due to their high energy transfer efficient and environment concerns.

6.7 PREPARATION OF Y2O3 STABILISED PARTIALLY

STABILISED ZIRCONIA (PSZ)

Zirconia is usually produced from the zircon, ZrSiO4. To produce

zirconia from zircon, the first step is to convert zircon to zirconyl chloride. It

can be done by the following series of reaction:

Zircon (ZrSiO4) + NaOH Na2ZrO3 (upon melting) (6.1)

Na2ZrO3 + HCl ZrOCl2 8H2O (6.2)

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Solution + NH4OH Co-precipitated intermediates Zr(OH)4 +Y(OH)3

OH)

Wet powders Zr(OH)4 + Y(OH)3 (Filtration) Cl- -free Precipitate

(Wash)

(Freezing Dry (Liquid Nitrogen))

Dry Powder Zr(OH)4 + Y(OH)3 (Calcination) Stabilized ZrO2 + Y2O3

Once the zirconyl chloride (ZrOCl2 8H2O) is heated to 2000C, it

starts dehydration and becomes dehydrated ZrOCl2. Zirconia lumps obtained

from the calcination then undergo a size reduction process, such as ball

milling, into the particle size range needed, usually up to 325 mesh. This

method is associates with low production cost. However, it is not easy to

produce zirconia powders with high purity and fine particle size by the

method. In order to achieve the requirement of the presence of cubic and

tetragonal phases in their microstructure, stabilizers (magnesia, calcia, or

Yittria) must to be introduced into pure zirconia powders prior to sintering.

Stabilized zirconia can be formed during a process called in-situ stabilizing.

During the firing (sintering), the phase conversion takes place. High quality

stabilized zirconia powder is made by co-precipitation process. Stabilizers are

introduced during chemical processing, before zirconium hydroxide's

precipitation.

ZrOCl2 8H2O + Stabilizer (Y2O3) + HCl Solution (6.3)

(6.4)

A cubic (or tetragonal) phase zirconia is formed during calcination

of chemically precipitated intermediates. These powders have chemically

higher uniformity than in-situ stabilizing powder and can be used in

applications such as refractories, engineering ceramics and thermal barrier

coatings. By substituting the host cation sites with either rare earth or an

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alkaline earth element, just as with Yittria-stabilized zirconia (YSZ), an

increase of ionic conduction can be achieved. Zirconia (zirconium dioxide,

ZrO2) in its pure form has a high melting temperature and a low thermal

conductivity. The applications of pure zirconia are restricted because it shows

polymorphism. It is monoclinic at room temperature and changes to the

denser tetragonal phase from circa 1000°C. This involves a large change in

the volume and causes extensive cracking. Hence zirconia has a low thermal

shock resistivity. The addition of some oxides results in stabilizing the cubic

phase and the creation of one oxygen vacancy. Stabilized zirconia (PSZ) is a

mixture of zirconia polymorphs: a cubic and a metastable tetragonal ZrO2

phase is obtained, since an insufficient amount of stabilizer has been added.

PSZ is also called tetragonal zirconia poly-crystal (TZP). PSZ is a

transformation-toughened material since the induced micro cracks and stress

fields absorb energy.

6.8 STEPS INVOVED IN THE COATING PROCESS

6.8.1 Pre-Cleaning Using Brush

This method involves cleaning of the surface of the cylinder head,

valves and the piston using carbon tetra chloride and ethyl alcohol bath and

then drying the component. In this method, polished surface is obtained when

the component is in contact with the brush which is supplemented by flow of

non-acid electrolyte (carbon tetra chloride or ethyl alcohol bath) at constant

flow wherein maximum desired level of cleaning is achieved.

6.8.2 Mechanical Processing

Pre machining using wheel grit blasting technique-For further

removal of any rust, scale, sand, paints, burrs and carbon deposits etc,

abrasive particles (fused alumina or dry steel grit) are pneumatically

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accelerated by a centrifugal wheel and forcefully directed against the surface.

These high speed abrasive particles remove contaminants from the materials

surface and condition the surface for subsequent finishing. The Figure 6.1

shows the photographic view of the pre machining equipment and the

abrasive sand used for cleaning.

Figure 6.1 Pre Machining Equipment and Abrasive Sand

6.8.3 Masking

Masking techniques are normally adopted for components that only

need specific areas coated. Application of reagents over the surface of the

cylinder head and valves (usually where coating is not to be done) to prevent

these surfaces to react with the coating powder at higher temperature.

6.8.4 Application of Metallurgical Bond Coat

Application of metallurgical bond coat over the metal substrate is

done to promote good adherence, good oxidation resistance, and good

corrosion resistance and to favour a deposition of a controlled porosity, highly

thermal resistive zirconia outer layer. The bond coat material is of M-Cr-Al

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chemical composition; where M is Co, Ni, Fe or combinations of these

elements (Applied for a thickness of 10-15 microns).

The composition used in the present work consists of Ni+10-30%

weight Chromium+3-13 wt. % aluminum+ 0.05 to 1.0 wt. % cobalt. The bond

coat is applied using thermal spray processes using flame .In this method , the

metal surface is heated to a temperature of 600- 800 0C and the material in the

form of powder is fed into the flame by a stream of compressed air where it

gets heated due to high temperature and is directed towards the surface.

6.8.5 Application of the Powder over the Surface Using Plasma

Spraying Technique

This method uses a DC electric arc to generate a stream of high

temperature ionized plasma gas (argon), which acts as the heat source. In

plasma the electrons are stripped from the atoms creating a substance that

resembles a gas but that conducts electricity. The arc is struck between a

tungsten cathode and a copper anode within the torch. The torch is fed with a

continuous flow of inert gas, which is ionized by the DC arc and is

compressed and accelerated by the torch nozzle so that it issues from the torch

as a high velocity (500-600 m/sec), high temperature (12000-16000K) plasma

jet. The coating material in powder form is carried in an inert gas stream into

the plasma jet where it is heated and propelled towards the substrate. The

schematic setup of plasma spray technique used for the coating as shown in

Figure 6.2.

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Figure 6.2 Plasma Spraying Technique

Parameters - Porosity %= 2-5 , Coating Adhesion= 40-70 MPa,

Current rating = 800-1000A

6.8.6 Final Machining and Grinding

Final machining process using abrasive grinding wheel or a

precision diamond cutting tool to remove excess ceramic powders adheres

over the surface.

Velocity of the cutter / RPM of grinding wheel-525 m/s (3000 rpm)

6.8.7 Polishing and Cleaning

Since the surface of the coated component will be rough after the

plasma spraying process, the surface is polished using fine abrasive over a

rotating grinding wheel. The excess coating powder is cleaned by using a

spray of compressed air at low pressure.

6.8.8 Lapping

It is a machining operation in which the two mating surfaces are

rubbed together by insertion of an abrasive material in between them to

remove any burrs, dirt etc between them and to ensure a perfect mating

87

contact between them. Lapping is done for the valves using fine and coarse

abrasive paste. The following Table 6.1 shows the physical properties of the

various ceramic materials. The Table 6.2 shows the comparison of the desired

properties of various zirconia based ceramics.

Table 6.1 Physical Properties of Ceramics

Properties Si3N4 SiC Al2O3 Al2O3.TiO2

Thermal conductivity (W/ m K) 12 40 18 2.5

Maximum temp withstanding capacity (0C) 1850 1754 1025.5 1025.5

Fracture Toughness (MPa m1/2) 6.1 6.1 3.7 9.2

Density ( g/cc) 3.1 3.1 3.5 3.-3.4

Ultimate tensile Strength ( MPa) 300 450 250 55

Modulus of elasticity (MPa) 256 400 151.4 20

Co-efficient of thermal expansion (/K) 3.2 4.5 7 0.001

Table 6.2 Comparison of Various Zirconia Based Ceramics

Property Zirconia

Toughened Alumina

Magnesium Stabilized Zirconia

Yittria Stabilized Zirconia

Thermal conductivity ( W/ m K) 27 2.2 2.2

Maximum service temperature (0C ) 1500 500 1500

Density (g/cc) 4.05 5.72 6.02

Hardness (GPa) 14.4 11.8 12.7

Tensile Strength at 250C (MPa) 290 352 -

Fracture toughness(MPa/m2) 5-6 11 13

Co-efficient of thermal expansion (10-6/k) 8.3 10.1 10.3

Colour white ivory ivory

Specific Heat (J/kg K) 885 400 400

Crystal size (microns) 2 35 1

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6.9 MATERIAL PROPERTIES AND BOUNDARY CONDITIONS

A generalized thermal boundary condition is derived to include all

thermal effects of a thin layer which is in thermal contact with an adjacent

domain. The thin layer may be a stationary or moving solid-skin or fluid-film.

The included thermal effects of the thin layer are the thermal capacity of the

layer, thermal diffusion, enthalpy flow, viscous dissipation within the layer,

convective losses from the layer, and other effects. Six different kinds of

thermal boundary conditions can be obtained as special cases of the

generalized boundary condition. The generalized boundary condition is given

for perfect and imperfect thermal contact between the thin layer and its

adjacent domain.

The ANSYS program supports six types of thermal boundary

conditions:

1. Constant temperatures

2. Constant heat fluxes

3. Applied heat transfer (film) coefficients with associated

ambient temperatures

4. Ambient radiation with associated surface emissivities and


5. Surface-to-surface radiation with associated emissivities and

enclosure number.

6. Adiabatic boundaries (the default condition)

In addition, constant volumetric heat sources may be located in

both fluid and non-fluid regions. The main aim of the thermal analysis of the

cylinder head, piston and the valves involves the calculating the convective

89

heat transfer coefficient around the combustion chamber, outer surface and

around the cooling jackets.

The following Table 6.3 gives the various loading methods used in

thermal analysis.

Table 6.3 Various Loading Types in Thermal Analysis

Load Type Solid Model Entity

Temperature Finite Element Nodes

Convection, Heat Flux, Ambient Radiation, or Surface-to- surface Radiation

Solid Model

Solid Model

Finite Element

Finite Element

Lines

Areas

Nodes

Elements

Heat Generation Rates

Finite Element

Solid Model

Solid Model

Solid Model

Elements

Lines

Areas

Volumes

6.10 MATERIAL PROPERTIES AND BOUNDARY CONDITIONS

FOR THE PROBLEM

Mean speed of the piston, Cm=stroke (mm)/1000*rpm/60*2 (m/sec)

For engine speed of 800 rpm, the maximum load, Cm=1.813 m/sec

The following Table 6.4 describes the material properties of the

cylinder head, valves, piston and the coating material.

90

Table 6.4 Material Properties of the Engine Components

Component Material Density (kg/mm3)

Specific Heat (kJ/kg K)

Thermal Conductivity (W/ mm K)

Cylinder head Al alloy 2.689X10-6 0.916 246.86X10-3

Ceramic coating

PSZ+Y2O3 6.02 X10-6 0.400 2.2 X10-3

6.10.1 Heat Transfer Coefficient Calculation for Conventional

Cylinder Head

6.10.1.1 Outside the combustion chamber

By assuming air flows over the outer surface of the chamber and at

the sides, the heat transfer coefficient can be determined as a condition of free

convection for fins.

Pmax = 73 bar (expt) AT 70 aTDC

Compression ratio = 18

B/S = 0.078/0.068

Vs = Л/4*B*B*S=3.25X10-4 m3

C.R. = (VS+VC)/VC

VC = 1.91X10-5 m2

Piston travel for 70 aTDC = 5.289x10-3 m2

Vmax = 1.91X10-5 + Л /4*0.078 *0.078

*5.289x10-3 =0.437 X 10-5 m3

Mass flow rate at full load = 2.038 X10-3 kg/sec (expt)

Pmax *Vmax = mR Tmax

Tmax = 553.86 K

Bulk temperature inside the

combustion chamber = t0 =1273K

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and ,temperature exposed to

outer surface (air) = ta =300 K

t= max temp = 553.86 K

(t-ta)/(t0-ta) = e-mx

=> mx = 1.3436

X= average length of the fin = 0.0475m

=> m = 28.286

Fin thickness ti = 4.33 X10-5 m

Average perimeter value = p =2(l+b)

Ac = average c/s area

Upon measurement, Ac/p = 2.164 X10-5 m

M = (p*h)/(K*Ac)

H = 4.275 X10-6 W/mm2K

6.10.1.2 Inside the Combustion Chamber

The fluid properties at the combustion chamber temperature are

given below in the following table.

According to Annand’s equation ,

hinner=a*(k/B)* Re 0.7+C/(Tg-Tw)*((0.01*Tg)4 -(0.01*Tw)4)kcal/hr m2 K

where,

a = 0.35 to 0.8 increasing with increased engine speeds

B = bore of the cylinder (m)=0.078 m

C = 2.81 for CI engines

k = thermal conductivity of the gas in kcal/hr m2 k

= 0.0871W/m

k = 0.0694 kcal/hr m2 K

ν = kinematic viscosity of the gas = 178 X 10-6 m2/sec

Tg = 1273 K

92

Tw = 553.86K

Re = B *Cm / ν = 0.7945*103

Using this

equation, hinner = 151.3807 kcal/hr m2 K = 1.76*10-4 W/mm2 K

6.10.2 Heat Transfer Coefficient Calculation for Conventional Cylinder

Head


Pmax = 77 bar (expt) AT 70 aTDC


B/S = 0.078/0.068

Vs = Л /4*B*B*S=3.25X10-4 m3

C.R. = (VS+VC)/VC

VC = 1.91X10-5 m2

Piston travel for 70Atdc = 5.289x10-3 m2

Vmax = 1.91X10-5+ Л /4*0.078*0.078*5.289x10-3

= 4.437 X 10-5 m2

Mass flow rate at full load = 1.941 X10-3 kg/sec (expt)


Tmax = 613.3 K

Bulk temperature inside

the combustion chamber = t0 =1273K

temperature exposed to

outer surface (air) = ta =300 K

t = max temp =613.3 K


mx = 1.133

x = average length of the fin = 0.0475m

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m = 23.86


Average perimeter value = p =2(l+b)


Upon measurement, Ac/p = 2.164 X10-5 m

m = (p*h)/(K*Ac)

h = 3.041 X10-6 W/mm2K

Inside the combustion chamber




hinner = a*(k/B)*Re0.7+C/(Tg-Tw)*((0.01*Tg)4-(0.01*Tw)4)kcal/hrm2 K

where,




k = thermal conductivity of the gas in kcal/hr m2 K

= 0.0871 W/m K= 0.0694 kcal/hr m2 K


Tg = 1273 K

Tw = 613.3 K

Re = B *Cm / ν = 0.7945*103

hinner = 158.27 kcal/hr m2 K = 1.84*10-4 W/mm2 K

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6.10.3 Heat Transfer Coefficient Calculation for Coated Cylinder

Head with Pre Combustion Chamber


Pmax = 78.3 bar (expt) AT 70 aTDC


B/S = 0.078/0.068

Vs = Л /4*B*B*S=3.25X10-4 m3

C.R. = (VS+VC)/VC

VC = 1.91X10-5 m2

Piston travel

for 70 Atdc = 5.289x10-3 m2

Vmax = 1.91X10-5 + Л /4*0.078*0.078*5.289x10-3

= 4.437 X 10-5 m2

Mass flow rate at

full load = 1.882 X10-3 kg/sec (expt)


Tmax = 634.11 K

Bulk temperature

inside the combustion

chamber = t0 =1273K and ,

temperature exposed

to outer surface (air) = ta =300 K

t = max temp =634.11 K


mx = 1.0689

x = average length of the fin = 0.0475m

m = 22.503


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Average perimeter

value = p =2(l+b)


Upon measurement,

Ac/p = 2.164 X10-5 m

m = (p*h)/(K*Ac)

h = 2.705 X10-6 W/mm2K

6.10.3.2 Inside the combustion chamber




hinner = a*(k/B)*Re0.7+C/(Tg-Tw)*((0.01*Tg)4-(0.01*Tw)4)kcal/hr m2 K

where,




K = thermal conductivity of the gas in kcal/hr m2 K

= 0.0871 W/m K= 0.0694 kcal/hr m2 K


Tg = 1273 K

Tw = 634.11 K

Re = B *Cm / ν = 0.7945*103

hinner = 160.84 kcal/hr m2 K

= 1.87*10-4 W/mm2 K

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6.10.3.3 Catalytic plug

Length = 0.25 m

Area of the wire = 1.59*10-7 m2

Resistivity = 0.000000106 ohm-m

Hence, Resistance R = ρ *l /A =0.167 ohms

Voltage = 12 V

Hence , Current I = 12/0.167 = 72 Amps

6.11 INTRODUCTION TO FINITE ELEMENT ANALYSIS

ANSYS is general-purpose finite element analysis (FEA) software

package. Finite Element Analysis is a numerical method of deconstructing a

complex system into very small pieces (of user-designated size) called

elements. The software implements equations that govern the behaviour of

these elements and solves them all; creating a comprehensive explanation of

how the system acts as a whole. These results then can be presented in

tabulated or graphical forms. This type of analysis is typically used for the

design and optimization of a system far too complex to analyze by hand.

Systems that may fit into this category are too complex due to their

geometry, scale, or governing equations. ANSYS provides a cost-effective

way to explore the performance of products or processes in a virtual

environment. This type of product development is termed virtual prototyping.

With virtual prototyping techniques, users can iterate various

scenarios to optimize the product long before the manufacturing is started.

This enables a reduction in the level of risk, and in the cost of ineffective

designs. The multifaceted nature of ANSYS also provides a means to ensure

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that users are able to see the effect of a design on the whole behavior of the

product, be it electromagnetic, thermal, mechanical etc.

Often, the solution for the temperature distribution throughout the

flow field is of interest. If fluid properties do not vary with temperature, we

can converge the flow field without solving the temperature equation. In a

conjugate heat transfer problem, the temperature equation is solved in a

domain with both fluid and non-fluid (that is, solid material) regions. In a

natural convection problem, the flow results mainly or solely from density

gradients brought about by temperature variations. Most natural convection

problems, unlike forced convection problems, have no externally applied flow

sources.

A thermal analysis calculates the temperature distribution and

related thermal quantities in a system or component. Typical thermal

quantities of interest are the temperature distributions, amount of heat lost or

gained thermal gradients and thermal fluxes. Thermal simulations play an

important role in the design of many engineering applications, including

internal combustion engines, turbines, heat exchangers, piping systems, and

electronic components. In many cases, engineers follow a thermal analysis

with a stress analysis to calculate thermal stresses (that is, stresses caused by

thermal expansions or contractions).

The ANSYS program supports six types of thermal boundary

conditions: Constant temperatures

1. Constant heat fluxes

2. Applied heat transfer (film) coefficients with associated


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3. Ambient radiation with associated surface emissivities and


4. Surface-to-surface radiation with associated emissivities and

enclosure number.

5. Adiabatic boundaries (the default condition)

ANSYS supports two types of thermal analysis:

1. A steady-state thermal analysis determines the temperature

distribution and other thermal quantities under steady-state

loading conditions. A steady-state loading condition is a

situation where heat storage effects varying over a period of

time can be ignored.

2. A transient thermal analysis determines the temperature

distribution and other thermal quantities under conditions that

vary over a period of time.

6.11.1 Solid 90 Element

SOLID90 is of the 3-D eight nodes thermal element .The element

has 20 nodes with a single degree of freedom, temperature, at each node. The

20-node elements have compatible temperature shapes and are well suited to

model curved boundaries. The 20-node thermal element is applicable to a 3-

D, steady-state or transient thermal analysis.

6.11.2 Assumptions

1. The element must not have a zero volume. This occurs most

frequently when the element is not numbered properly.

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2. A prism or tetrahedron shaped element may be formed by

defining duplicate node numbers as in Triangle, Prism and

Tetrahedral Elements.

3. The specific heat and enthalpy are evaluated at each

integration point to allow for abrupt changes (such as for

melting) within a coarse grid.

4. If the thermal element is to be replaced by a SOLID45

structural element with surface stresses requested, the thermal

element should be oriented such that face I-J-N-M and/or face

K-L-P-O is a free surface.

5. A free surface of the element (that is, not adjacent to another

element and not subjected to a boundary constraint) is

assumed to be adiabatic.

6. Thermal transients having a fine integration time step and a

severe thermal gradient at the surface will also require a fine

mesh at the surface.

The element is defined by 20 node points and the material

properties. A prism-shaped element may be formed by defining duplicate K,

L, and S; A and B; and O, P, and W node numbers. A tetrahedral-shaped

element and a pyramid-shaped element may also be formed as shown in the

Figure 6.3. Orthotropic material directions correspond to the element

coordinate directions. The element coordinate system orientation is as

described in Coordinate Systems. Specific heat and density are ignored for

steady-state solutions. Convection or heat flux (but not both) and radiation

may be input as surface loads at the element faces as shown by the circled

numbers on the Figure 6.3. Heat generation rates may be input as element

body loads at the nodes. If the node I heat generation rate HG (I) is input, and

all others are unspecified, they default to HG (I). If all corner node heat

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generation rates are specified, each mid side node heat generation rate

defaults to the average heat generation rate of its adjacent corner nodes.

6.11.3 Input Data

1. Nodes : I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z, A, B

2. Degrees of Freedom: TEMP

3. Real Constants: None

4. Material Properties: KXX, KYY, KZZ, DENS, C, ENTH

5. Surface Loads: Convection or Heat Flux (but not both) and

Radiation

face 1 (J-I-L-K), face 2 (I-J-N-M), face 3 (J-K-O-N),

face 4 (K-L-P-O), face 5 (L-I-M-P), face 6 (M-N-O-P)

6. Body Loads: Heat Generations --

HG(I), HG(J), HG(K), HG(L), HG(M), HG(N), HG(O),

HG(P), HG(Q), HG(R),

HG(S), HG(T), HG(U), HG(V), HG(W), HG(X), HG(Y),

HG(Z), HG(A), HG(B)

Figure 6.3 Solid 90 Element

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6.11.4 Output Data

The solution output associated with the element is nodal

temperatures included in the overall nodal solution. Convection heat flux is

positive out of the element; applied heat flux is positive into the element. The

element output directions are parallel to the element coordinate system. The O

column indicates the availability of the items in the file Job name OUT. The

R column indicates the availability of the items in the results file. In either the

O or R columns, Y indicates that the item is always available, a number refers

to a table footnote that describes when the item is conditionally available, and

a hyphen indicates that the item is not available Table 6.5 shows the output

definition for the solid 90 eliment.

Table 6.5 Solid 90 Element Output Definitions

Label Definition O R EL Element Number Y Y NODES Nodes - I, J, K, L, M, N, O, P Y Y MAT Material number Y Y VOLU Volume Y Y

HGEN Heat generations HG(I), HG(J), HG(K), HG(L), HG(M), HG(N), HG(O), HG(P), HG(Q), ..., HG(Z), HG(A), HG(B)

Y -

TG:X,Y,Z,SUM Thermal gradient components and vector sum at centroid Y Y

TF:X,Y,Z,SUM Thermal flux (heat flow rate/cross-sectional area) components and vector sum at centroid Y Y

HFILM Film coefficient 1 - TAVG Average face temperature 1 1 TBULK Fluid bulk temperature 1 - HEAT RATE Heat flow rate across face by convection 1 1 HEAT RATE/ AREA Heat flow rate per unit area across face by convection 1 -

HFLUX Heat flux at each node of face 1 - HFAVG Average film coefficient of the face - 1 TBAVG Average face bulk temperature - 1

HFLXAVG Heat flow rate per unit area across face caused by input heat flux - 1

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6.12 STEPS INVOLVED IN THERMAL ANALYSIS

The following steps are involved in solving the cylinder head and

valves for thermal analysis:

6.12.1 Specify the Type of Analysis

Since we are interested in knowing the temperature distribution

around the cylinder head and valves, click “PREFERENCES” and check

“ON” the “Thermal” radio button.

6.12.2 Importing the Model from 3d Modelling Software

The model created in Solid works 2005 is saved as an “iges” or

“igs” file. Then the required file is imported in ANSYS using the following

commands:

(a) Go to “FILE” pull down menu bar and Click “IMPORT

IGES”.

(b) Set import option as “de-feature model” and click “OK” and

Specify the path name of the “iges” file to be imported.

6.12.3 Preprocessing

This refers to the various input data required for thermal analysis.

They may include type of the element (basic form of the model), material

properties, modeling (if required), meshing to the precise mesh density and

creating nodes and elements by meshing the model. The following parameters

are required in preprocessing:

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6.12.3.1 Define Element Type

Select thermal element “SOLID 90” which possesses all the

characteristics required to perform the analysis. Choose

PREPROCESSORELEMENT TYPEADD/EDIT/DELETE. Select

Thermal Solid 20 node 90 element.

6.12.3.2 Define Material Properties

Define the material with the following properties as input:

(i) Thermal conductivity (k) (ii) Specific heat (C) and (iii) Density (ρ).

Since the model created in Solid works followed the dimensioning

with “mm” as the units, the following units are to be followed for consistency.

The Table 6.6 shows the variables used for the analysis and their units.

Table 6.6 Consistent unit systems to be followed

Quantity Units

Temperature K

Thermal conductivity W/mm K

Specific heat kJ/kg K

Density kg/ mm3

Convective film coefficient W/mm2 K

6.12.3.3 Meshing

Once the solid model is imported and established with element

attributes it is ready to generate the finite element mesh. Meshing is an

integral part of the CAE analysis process. The mesh influences the accuracy,

convergence and speed of the solution. More importantly, the time it takes to

create a mesh model is often a significant portion of the time it takes to get

104

results from a CAE solution. Therefore, the better and more automated the

meshing tools, the better the solution.

As an assembly drawing is being imported, select the volumes

individually for which the meshing has to be done. The following steps are to

be followed:

(i) Specify the properties for that volume i.e. the element

properties .Choose MESHING MESHED ATTRIBUTES

PICKED VOLUME. Select the volume. Apply the element

properties and click OK.

(ii) Mesh the given model: Choose MESH TOOL and move the

smart size tab to “1” for increased accuracy and then click

MESH option. Select the volume (as in step (i)) to be meshed

by clicking OK. The geometry is meshed using tetragonal

elements with free meshing. Repeat steps (i) and (ii) for all the

volumes and change the element properties as desired.

6.13 LOADS AND BOUNDARY CONDITIONS

Apply thermal convection boundary conditions on the areas

exposed to the combustion chamber, cooling water jackets and to the

atmospheric air.

Choose LOADS DEFINE LOADS APPLY THERMAL

CONVECTION ON AREAS.

Select the areas and enter the values of convective heat transfer

coefficient and bulk temperature. Enter the values of film co-efficient and

bulk temperature on areas. Click OK.

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Apply the convection boundary conditions for other areas. Check

the load values on each surface using the option:

LIST LOADSSURFACE ON ALL AREAS

6.14 SOLUTION

In the solution phase of the analysis, the computer takes over and

solves the simultaneous set of equations that the finite element method

generates. The results of the solution are:

Nodal degree of freedom values, which form the primary

solution.

Derived values, which form the element solution.

Several methods of solving the system of simultaneous equations

are available in the ANSYS program: sparse direct solution, Preconditioned

Conjugate Gradient (PCG) solution, Jacobi Conjugate Gradient (JCG)

solution, Incomplete Cholesky Conjugate Gradient (ICCG) solution, frontal

direct solution, and an automatic iterative solver option (ITER).

Choose SOLUTION SOLVE CURRENT LS OK in the

“solve Current load step” dialog box.

During solving, the computer forms the element matrices, solves it

using any one of the iteration process, calculates the element results and

displays the solved model. Click OK when the note “solution is done!”

appears.

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6.15 POST PROCESSING

After building the model and obtaining the solution, the answers to

some critical questions like how does the temperature of this part vary with

time, what is the heat loss across this face of the model etc will be answered

by the postprocessors . Post processing means reviewing the results of an

analysis. It is probably the most important step in the analysis, because we are

trying to understand how the applied loads affect the design, how good the

finite element mesh is, and so on. Post processing helps to plot the

temperature distribution across the model. Choose GENERAL

POSTPROCPLOT RESULTS CONTOUR PLOT NODAL SOLU

DOF SOLUTION and pick “Temperature TEMP”, and then click OK.

6.16 RESULTS-TEMPERATURE DISTRIBUTION PLOTS

The thermal analysis of the cylinder head considering no coating

and with coating is performed by applying the material properties and the

boundary conditions. The Figures 6.4 and 6.5 illustrates the temperature

distribution around the cylinder head of a conventional engine while the

Figures 6.6 and 6.7 shows for a LHR engine and Figures 6.9 and 6.10

illustrates for the coated engine with pre combustion chamber.

It can be concluded that the combustion chamber surface

temperature is highest in the case of coated head with pre combustion

chamber. The maximum temperature after the coating is around 613 K. For

the coated head with pre combustion chamber, due to the presence of catalytic

plug, maximum temperature is 634.11K. The self ignition temperature of

Aquanol is around 820 K. But the surface temperature is sufficiently lower

than the self ignition temperature of the fuel. So it will avoid the pre ignition

of the fuel and the coating will improve the vaporization of the fuel.

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Figure 6.4 Temperature Distribution Around the Combustion

Chamber of the Cylinder Head of an Ordinary Engine

Figure 6.5 Temperature Distribution Around the Outside Surface of

the Cylinder Head of an Ordinary Engine

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Chamber of the Cylinder Head of a Coated Engine

Figure 6.7 Temperature Distribution Around the Outer Surface of the

Cylinder Head of a Coated Engine

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Figure 6.8 Coated Engine with Pre Combustion Chamber


Chamber of the Cylinder Head of a Coated Engine With Pre

Combustion Chamber

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Figure 6.10 Temperature Distribution Around the outer Surface of the

Cylinder Head of a Coated Engine with Pre Combustion

Chamber

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