24

CHAPTER 2

LITERATURE REVIEW

2.1 GENERAL

In the recent years efforts have been made by several researchers to

use biofuel as fuel to the engines. During use of biofuel some measures has to

taken to solve the problems of long-term operational and durability problems

e.g. poor fuel atomisation, piston ring- sticking, fuel injector coking and

deposits, fuel pump failure and lubricating oil dilution, etc..These problems are

avoided by adopting of two different possibilities: adaption of fuel to the

engines, and adaption of engines to the fuel.

In this present work adaption of engines to the fuel has been tried and

given in the following categories:

1. Biofuel with standard diesel blends operated in direct injection

diesel engine with standard and various compression ratios.

2. Biofuel with standard diesel blends in direct injection diesel

engine with exhaust gas recirculation.

3. Biofuel with standard diesel blends operated in thermal barrier

coated diesel engine.

25

2.2 BIOFUEL WITH DIESEL BLENDS OPERATED IN DIRECT

INJECTION DIESEL ENGINE WITH STANDARD AND

VARIOUS COMPRESSION RATIOS.

The use of biofuel in diesel engines has to be widely investigated

because of their availability and their inherent proprieties. The biofuel

(Eucalyptus and Turpentine) used in this study has low cetane number as

compared to the standard diesel fuel. As part of attempt to understand better,

the performance, combustion and emission benefits of biofuel (Low cetane

fuel) and their diesel blends as fuel in diesel engines, many literatures were

studied and it is summarised in this section.

Poola et al (1994) investigated the performance, combustion and

exhaust emissions characteristics of spark-ignition engines at two different

compression ratios of 7.4 and 9.0 using eucalyptus oil and orange oil as

alternative fuels. It was reported that most of their properties were similar in

nature to those of gasoline and they were miscible with gasoline without any

phase separation. Eucalyptus oil is an effective co-solvent that prevents the

alcohol-gasoline blended fuel from undergoing phase separation. One of the

reasons is the fact that, eucalyptus oil is quite similar to the naphthenic base in

its chemical structure. It was found that the octane value of the eucalyptus oil-

gasoline blend was higher compared to that of gasoline. Tests were conducted

using 20% volume of orange oil and eucalyptus oil that were blended

separately with gasoline and the performance, combustion and exhaust

emission characteristics were evaluated at two different compression ratios.

The results indicated that the performance of the fuel blends was much better

than that of gasoline fuel, in particular, at higher compression ratio.

Hydrocarbons and carbon monoxide emission levels in the engine exhaust

were considerably reduced with fuel blends at both the Compression Ratios

26

(CRs) tested. Between the two fuel blends tested, the eucalyptus oil blend

provided better performance than the orange oil blend. Maximum

improvement in brake thermal efficiency was obtained at the higher

compression ratio of 9. In comparing the two fuel blends tested, the

eucalyptus oil blend provided the potential for a high brake thermal efficiency

concomitant with low exhaust emissions.

Purushothman and Nagarajan (2009) investigated the use of orange

oil in single cylinder compression ignition engine. The orange oil exhibits a

longer ignition delay than diesel fuel. The heat release rate and brake thermal

efficiency are higher as compared to diesel fuel .Smoke emission such as HC,

CO and smoke emission were reduced considerably except NOX emission.

Murat Karabektas and Murat Hosoz (2009) conducted test on single

cylinder, direct injection diesel engine powered by diesel fuel and isobutanol

blends .Four different isobutanol-diesel fuel blends containing 5, 10, 15 and

20% isobutanol were prepared in volume basis and employed in the

experiments along with pure diesel. The experiment was conducted at full load

condition and at the speeds between 1200 and 2800 rpm with the intervals of

200 rpm. The test results showed that there is increase in the BSFC in

proportional to the isobutanol content in the blends. Break thermal efficiency

was higher for diesel fuel as compared to four blends. Emission such as CO

and NOX emissions decreased with the use of the blends, whereas HC

emission increased considerably.

Ashok et al (2008) conducted experiments on single cylinder direct

injection diesel engine powered by diesel and emulsified fuel in the ratios of

90D: 10E, 80D: 20E, 70D: 30E and 60D: 40E and tested at different load

conditions. Brake thermal efficiency increased by 3.45% for emulsified fuel as

27

compared to the diesel fuel. From the results, it was also revealed that there

was reduction in specific fuel consumption and smoke emission and

simultaneously there was increase in NOX and particulate matter. 80D: 20E was

much suitable for getting good performance and low emission of the engine.

Takeda (1984) conducted experiments on the utilisation of

eucalyptus oil and orange oil in small passenger cars. It was reported that

eucalyptus oil obtained from leaves by means of steam extraction, contains

1.8-cincole (C10 H18O) as the main ingredient. It was reported that in using

100 % of eucalyptus oil, there existed a difficulty in the engine starting under

the low atmospheric temperature because of the high flash point of eucalyptus

oil. He also conducted experiments using eucalyptus oil, gasoline, ethanol and

their blended fuels. The various distilation curves were obtained from the use

of six kinds of fuels, based upon the distilation curve; eucalyptus oil presented

some difficult in starting the engine. It was also reported that the distilation

temperature for eucalyptus oil is 167°C and 45° C for gasoline. This

difficulty, however, was not experienced in the case of a blended fuel of

gasoline and eucalyptus oil. It was further reported that the phase separation

problem was not noticed when the eucalyptus oil was blended with ethanol

and gasoline. One of the reasons citied for this fact was that, as eucalyptus oil

(C10 H18O) is quite similar to the napthenic base in its chemical structure, it

played the role of a third material, which can easily combine both the

materials. The flame propagation velocity of eucalyptus oil appears to be

slightly higher than that of gasoline. In the second part of the paper, results of

the road test were reported. This included the study on the wear and carbon

deposit in the engine parts while the car tested in road conditions. It was

founded that there were no critical problems on start ability and drivability

while driving the vehicle. However, carbon deposits were found on the

position head, exhaust port and combustion chamber. The carbon deposit

28

consisted of 60% carbon and a few percent of CaSO4 Fe, and Zn. The carbon

deposit caused by eucalyptus oil on the piston head was less than that found

when the gasoline was used. It was also observed that no abnormal conditions

were found including oil leakage of fuel system, deformation of the fuel

system and cracks on the cylinder head. Carbon deposit was found slightly on

the piston head and exhaust manifolds.

Ajav E. A. and Akingbehin O.A. (2002) have made a study on some

of the fuel properties of ethanol blended with diesel fuel. Some properties have

been experimentally determined to establish their suitability for use in CI

engines. The results showed that both the relative density and viscosity of the

blends decreased as the ethanol content in the blends has increased. Based on

the findings of their report, blends with 5 &10% ethanol content are found to

have acceptable fuel properties for use as supplementary fuels in diesel

engines.

Naveenkumar et al (2004) have explained in detail the use of

ethanol-diesel emulsion as a diesel fuel extender. Ethanol has emerged as one

of the viable biofuel. They have made an attempt to use ethanol-diesel blends

as a fuel for unmodified diesel engine. Various fuel samples have been

prepared and their physico-chemical properties evaluated. Tests have been

conducted on a single cylinder, direct injection diesel engine to compare these

fuels in terms of performance and exhaust gaseous emissions. Finally, the

authors have concluded that thermal efficiency improves by using ethanol with

standard diesel.

Keith et al (2003) reviewed the existing public data from previous

exhaust emissions tested on ethanol (E) diesel fuel. They conducted

experiments at different engine loads, engine speeds and on different engine

29

designs. The variations in performance under these various conditions were

observed and discussed. They observed that the emissions of E diesel relative

to diesel fuel varied widely with respect to different engine sizes, engine

design, and cetane number and operating conditions. Increasing the cetane

number of the E diesel blend resulted in improvements in the emissions. They

further reported that, generally, regardless of the cetane number, diesel

resulted in increased HC and CO emissions, without any change in NOx

emissions and reduction in PM emissions.

Agarwal (2007) reviewed the production, characterisation and

current status of the research work on ethanol, vegetable oil and bio-diesels.

He also reviewed the properties and specifications of ethanol blended with

diesel gasoline fuel. He observed that ethanol as an additive to gasoline

improved the engine performance and exhaust emissions. He further reported

that ethanol-diesel blends up to 20 % (E20) could be used in a constant speed

CI engine without any engine modifications. The exhaust gas temperature and

lubricating oil temperature were lower for ethanol-diesel blends. The engine

could be started normally both in hot and cold conditions. A significant

reduction in CO and NOx emission was observed while using ethanol-diesel

blends. The E20 blend improved the peak thermal efficiency of the engine by

2.5 % along with a reduction in exhaust emissions. He also conducted

experiments with a blend of up to 20 % of methyl ester of rice bran oil with

diesel and found a satisfactory performance without any engine modifications.

He further reported that the 20 % bio-diesel blend (B20) produced better

thermal efficiency and lesser smoke emissions. He concluded that the overall

combustion characteristics were quite similar for B20 when compared to those

of mineral diesel.

30

Pramanik (2003) studied the use of jatropha oil and its diesel fuel

blends in a compression ignition engine. Blends of varying proportions of

jatropha oil and diesel were prepared, analysed and compared with diesel fuel.

He reported that the high viscosity of jatropha oil decreased when it was

blended with diesel. He found that 70% to 80% of diesel may be added to

jatropha oil to bring the viscosity close to that of diesel fuel, and thus blends

containing 20% to 30% of jatropha oil can be used as engine fuel without

preheating. He also studied the effect of temperature on the viscosity of

jatropha oil. The viscosity of the blends containing 70% and 60% vegetable

oil came close to that of diesel in the temperature ranges of 70°C to 75°C and

60°C to 65°C respectively. He also reported that the higher density of blends

led to more discharge of fuel for the same displacement of the plunger in the

fuel injection pump, thereby increasing the specific fuel consumption. A

significant improvement in engine performance was observed for blends

compared to that of neat vegetable oil. He further reported that the specific

fuel consumption was comparable for the 50:50 J/D blend. Acceptable

thermal efficiencies of the engine were obtained with blends containing up to

50% volume of jatropha oil. He concluded from the properties and engine test

results, that 40% to 50% of jatropha oil can be substituted for diesel without

any engine modification and preheating of the blends.

Humke and Barsic (1981) evaluated the performance and emission

characteristics of crude soybean oil, a 50% mixture of crude soybean oil and

degummed soybean oil, and these data were compared with those of diesel

fuel using a naturally aspirated, direct injection diesel engine. They reported

that injection nozzle deposits with vegetable oil and vegetable oil blends with

diesel fuel caused engine performance to decrease and emissions to increase as

a function of test time. They also reported that vegetable oil densities were

10% higher than that of diesel fuel and resulted in a greater mass flow to the

31

engine because the fuel injection pump controlled volume delivery. Since

vegetable oil viscosities were 8 to 10 times higher than that of diesel fuel, the

internal pump leakage was reduced which also contributed to an increased flow.

They found that degummed vegetable oil performs better than crude vegetable oil.

Robert Fanick and Ian Williamson (2002) have reported on the

comparison of emissions and fuel economy characteristics for the emulsified

fuel for the heavy duty diesel engine. Also, three emulsified fuels have been

prepared with the help of oxygen enriched additives. Results obtained are

based on the fuel properties such as cetane number, lubricity, emissions and

fuel consumption compared with diesel fuel. Further, continuing result of

lubricity, FC and emission have been decreased, when a cetane improver has

been implemented for preparing the emulsified fuel.

Wang et al (2008) studied the combustion characteristics of a

methanol-diesel dual-fuel compression ignition engine. They investigated the

combustion characteristics of the engine, with measured cylinder pressures,

using a single cylinder, naturally aspirated, four stroke, and direct injection

diesel engine, operated on pure diesel and on dual fuel (methanol-diesel).

They reported that the static injection timing of pilot diesel was kept constant

at 21 BTDC and engine speed at 1600r/min. They introduced methanol until

the engine load was higher than 15 percent of the maximum torque, since,

methanol has a low cetane number and high latent heat. They found that the

ignition delay of the methanol-diesel dual-fuel engine increases with an

increase in the methanol mass fraction. Methanol has a faster flame speed;

hence, the shorter flame propagation distance. These aspects make the rapid

combustion duration shorter. They further reported that the engine smoke

showed a sharp decrease with an increase in the methanol mass fraction as

methanol contains no heavy hydrocarbons and no carbon- carbon bonds. They

32

concluded that with an increase in the methanol mass fraction, both CO and

HC increased but smoke and NOX decreased simultaneously under all

operating conditions.

Irshad Ahmed (2001) has investigated the study of emissions and

performance characteristics of ethanol-diesel blends in CI engines. It has been

found that the formation of NOX, smoke and other harmful emissions could be

significantly reduced by mixing oxygenate additives in to diesel fuel. The

overall results have established that the ethanol-diesel blends are compatible

with the existing technology, fuel distribution, use and blending infrastructure.

The report finally states that fuel performance, long term storage ability,

emissions, durability, materials compatibility, environmental biodegradability

and other engine characteristics have been established to meet the required

emulsified fuel specifications.

Murayama et al (1984) investigated the feasibility of rapeseed oil

and palm oil for diesel fuel substitution in a naturally aspirated D.I. diesel

engine, and also found the means to reduce the carbon deposit buildup in

vegetable oil combustion. The engine performance, exhaust gas emissions,

and carbon deposits were measured for a number of fuels, namely, rapeseed

oil, palm oil, methyl ester of rapeseed oil and blends of these oils with ethanol

and diesel fuels at different fuel temperatures. They found that both the

vegetable oils generated an acceptable engine performance and exhaust gas

emission levels for short-term operation, but they caused carbon deposit

buildups and sticking of piston rings after extended operation. They suggested

practical solutions (to overcome these problems) such as increasing the fuel

temperature to over 200°C, blending 25% by volume of diesel fuel in the

vegetable oil, blending 20% by volume of ethanol in the fuel, or converting the

vegetable oils into methyl esters. They found that a blend of 25% diesel and

33

75% rapeseed oil gave better engine performance, lower emissions, carbon

deposit build up and piston ring sticking. They also established empirical

equations to estimate the density and viscosity of rapeseed oil, palm oil and

their blends at different temperatures.

Senthilkumar et al (2001) operated a dual fuel diesel engine using

vegetable oils as primary and pilot fuels. They conducted experiments with

orange oil as an induction fuel and jatropha as a pilot fuel. They varied the

energy share of orange oil up to 35% of the total energy share. They also tried

methyl ester of jatropha oil and diesel as pilot fuels for comparison. They

reported that dual fuel operation with orange oil induction reduced the smoke

level and improved the thermal efficiency with all pilot fuels. The NOX

emission is lower with all pilot fuels in the dual fuel mode as compared to that

in single fuel operation. They concluded that the use of jatropha oil and

methyl ester of jatropha oil as pilot fuels and orange oil as the inducted fuel

will improve the performance of the diesel engines.

Li et al (2008) analysed the combustion characteristics of a

compression ignition engine fueled with diesel-ethanol blends with and

without the cetane improver using a single cylinder DI diesel engine. They

showed that for the same brake mean effective pressure and engine speed, the

maximum cylinder pressure, the ignition delay, premixed combustion duration

and the fraction of heat release in premixed combustion phase increased, while

the diffusive combustion duration, the fraction of diffusive combustion phase

and the total combustion duration decreased with an increase in the ethanol

fraction in the blends. The centre of the heat release curve moves close to the

top dead centre, and the maximum rate of heat release and maximum rate of

pressure rise increased with increase in the ethanol fraction in the blends.

34

They reported that the addition of ethanol to diesel fuel decreases the cetane

number of the blends, increasing the ignition delay and the amount of

combustible mixture available within the ignition delay period, subsequently

increasing the amount of fuel burned in the premixed burning phase, which

increases the rate of pressure rise, and the combustion noise when operating on

diesel – ethanol blends by reducing the amount of combustible mixture within

the delay period. They revealed that the amount of the premixed combustion

heat release for diesel-ethanol blends decreased by adding a cetane number

improver to the blends.

Armbruster et al (2003) conducted experiments with on-board

conversion of alcohols to ethers for fumigation in compression ignition

engines. For the use of methanol in compression ignition engines, DME

fumigation has been found to be a promising alternative, which gives excellent

performance and emission results. However, they found an increase in CO

and HC emissions. They evaluated the heat release and ignition delay based

on the cylinder pressure data and reported that precombustion creates

appropriate conditions for the main fuel (Methanol) to facilitate ignition and

enhance the main combustion. They concluded that the use of ethers as

ignition improves in alcohol engines gives comparable performance and

emissions.

Bhattacharya et al (2006) have conducted the experiment on

stationary, constant speed compression ignition engine, using an alcohol fuel

in diesel emulsions. The performance of the engine has been evaluated in

terms of brake power, FC, brake thermal efficiency and emission of NOx. The

result shows that the brake thermal efficiency of the engine and the emission

part increased have been increase and decreased respectively. Finally they

conclude that the performance of the engine with respect to efficiency and

35

emissions, emulsion fuels could be used in a CI engine, during periods of lean

supply of diesel.

Agarwal and Rajamanoharan (2009) investigated the performance

and emission characteristics of a compression ignition engine fueled with

karanja oil and its diesel blends of 10%, 20%, 50% and 75%. The effect of

temperature on the viscosity of karanja and diesel blends was also

investigated. They reported that significant improvements were obtained both

in the performance and emission characteristics with preheating or without

preheating the vegetable oil. Higher brake thermal efficiencies than those of

mineral diesel were obtained for all blends except 100% karanja oil. However,

it was reported that preheating the oil improved the brake thermal efficiency

for all the blends including 100% karanja oil. They concluded that the karanja

oil blends with diesel up to 50% with or without preheating, and could replace

diesel for running the CI engine for lower emissions and also improve the

performance.

Abolle et al (2009) proposed empirical modelling to interpolate

viscosity to any kind of diesel oil/straight vegetable oil blend. They reported

that when viscosity increased the spray angle decreases. This property of

straight vegetable oil induces a reduction of the spray angle, and this may

cause the fuel droplets trajectory to collide with the combustion chamber

walls. This leads to the formation of carbon deposits and/or the engine wall

lubricant dilution. They also reported that viscosity can be varied to a great

extent when blending diesel oil with vegetable oil.

Patterson et al (2006) experimentally studied the performance and

emissions of a four cylinder, four stroke DI diesel engine using methyl esters

derived from three different vegetable oils, namely rapeseed, soybean and

36

waste cooking oils. They conducted experiments at five conditions and at two

different speeds. They reported that the engine performance and emission for

all the 5% bio-diesel blends were indistinguishable from those of mineral

diesel. However, at higher blends, the rapeseed oil fuel exhibited better

emission and performance characteristics than those of either the soybean or

waste cooking oil fuels. They reported that the soybean oil bio-diesel has the

lowest NOX emission and lowest fuel borne oxygen content. They reported

that the reason for lowest NOX emissions is the higher viscosity of the fuels

leading to poor spray characteristics that reduced combustion efficiency and

hence maximum combustion temperature. They reported that for 50% and

100% blends, ignition delays were increased at low loads; with the longest

ignition delay being observed for S100 (neat soybean bio-diesel) and the

shortest for rape seed oil bio-diesel. They conducted that in an unmodified

engine, rapeseed oil gave the best combustion and emission performance.

Jose and Desantes (1999) carried out experimental investigation in a

single cylinder direct injection (DI) diesel engine fueled with rapeseed oil

methyl ester at three different pressures and reported that the droplet size of

methyl ester was more than that of diesel due to higher viscosity and resulted

in increased combustion duration.

Carraretto et al (2004) investigated the potentiality of biodiesel as

an alternative fuel in boilers and diesel engines installed in urban buses.

Investigation monitored the distance, fuel consumption and emissions (CO2,

CO, HC and NOX) and also checked the wear and tear, oil and air filter

dirtiness and lubricant degradation. The results revealed a slight reduction in

the performance, notable increase in specific fuel consumption (SFC), reduced

CO and increased NOX emissions.

37

Eugene Ecklund et al (1984) demonstrated various methods of

using alcohol fuels in diesel engines. They reported the various techniques of

using alcohol fuels in diesel engines like solutions, emulsions, fumigation,

dual injection, spark ignition, and ignition improvers. They also reported that

power output, thermal efficiency, and exhaust emissions can change

significantly depending on the techniques employed. The easiest method by

which alcohols can be used in diesel engines is in the form of solutions. But

this method is limited due to its limited solubility in diesel. The dual-fuel

techniques (fumigation and dual injection) are better suited to moderate length

shortages and could allow relatively easy switching back to straight diesel fuel.

They further reported that the use of spark ignition or ignition improving

additives allow total displacement of diesel fuel in situations in which total

substitution of diesel fuel is desired. Physical properties like viscosity, cetane

rating, and lower heating value were reduced when alcohol was added to

decrease in brake thermal efficiency. They observed that Unburned

Hydrocarbons (UBHC) and carbon monoxide (CO) increased slightly whereas

there was a fluctuation in the trend of NOX emissions and smoke emission

with alcohol content in the solution.

Lakshmi Narayana Rao et al (2008a) analysed the combustion,

performance and emission characteristics of Used Cooking Oil Methyl Ester

(UCME) and its blends with diesel in a direct injection diesel engine. They

found a minor decrease in thermal efficiency with a significant improvement

in the reduction of particulates, carbon monoxide and unburnt hydrocarbons

compared to those of diesel. An increase in the oxygen content in the UCME

blend resulted in better combustion and increase in the combustion chamber

temperature, which leads to an increase in NOX emission. They reported a

significant reduction in smoke intensity, especially at higher loads even with

20% UCME. The engine developed the maximum rate of pressure rise and

38

maximum heat release rate for diesel, compared to those of 100% UCME and

other blends. The ignition delay of UCME and its diesel blends was found to

be lesser compared to that of diesel. They mentioned that used cooking oil as

feedstock for tranesterification reduced the production cost of bio-diesel.

They concluded that UCME satisfies the important fuel properties as per the

ASTM specification of bio-diesel and improves the performance and emission

characteristics of the engine significantly.

Nwafor and Rice (1995) evaluated the performance of Rapeseed

Methyl Ester (RME) in an unmodified diesel engine. They compared the

effect of using RME in a diesel engine with the baseline test on diesel fuel. It

was reported that the maximum power output of the engine running on RME

was slightly lower than that running on diesel fuel, due to the low heating

values of plant oil. The thermal efficiency of the engine was higher at high

load levels when operating on RME. The carbon deposits on the injector were

similar to those observed with diesel fuel. They reported lower cylinder peak

pressure and longer ignition delay for RME compared to those of diesel fuel.

They also reported that the start of fuel injection was the same for RME and

diesel, but the injection duration for RME operation was longer due to its

higher fuel viscosity and perhaps to compensate for the low heating value of

plant fuels.

Banapurmath et al (2008) investigated the performance and

emission characteristics of a DI compression ignition engine operated on

honge, jatropha and sesame oil methyl esters using a single cylinder four

stroke DI diesel engine. They reported that poor mixture formation, lower

volatility, and higher viscosity lead to lower brake thermal efficiency for

Jatropha Methyl Ester (JOME) among the biodiesel tested. The HC, CO and

smoke opacity for JOME are higher in comparison with those of other fuels

39

due to the heavier molecular structure, higher viscosity and poor atomisation

of jatropha oil. They observed that NOX emissions were higher for diesel

operation compared to those of biodiesel. The heat release rates of biodiesel

were lower during the premixed combustion phase, and led to lower peak

temperature. They further reported longer ignition delay and combustion

duration for biodiesel compared to those of neat diesel.

From the literature survey on usage of low cetane biofuels in diesel

engine, it has been found that bio-fuel with diesel fuel can be used in long term

operation without affecting engine performance and exhaust emissions. The

properties of bio-fuel blends are similar to those of diesel fuel. Bio-fuel can be

blended with any proportion and injected as in a conventional injection

system. It is evident that many researchers attempted to use different kinds of

low cetane biofuels as alternative fuels to diesel engines and spark ignition

engines. And it is also reported that the low cetane fuel was used in diesel

engine with or without any modifications. There are still only a few literature

reporting experimental results on the combined use of low cetane bio-fuel with

diesel fuel, while there is certainly need to obtain more such experimental

data.

40

2.3 BIOFUEL WITH STANDARD DIESEL BLENDS IN

DIRECT INJECTION DIESEL ENGINE WITH

EXHAUST GAS RECIRCULATION

Oxides of nitrogen (NOX) are formed during combustion when

localised temperatures in the combustion chamber exceed the critical

temperature which makes molecules of oxygen and nitrogen to combine.

Exhaust Gas Recirculation (EGR) system has received attention as a potential

solution. Many research work results showed that EGR is one of the most

effective methods used in the modern engines to reduce the NOX emissions.

These studies are summarised and given in this section.

Pradeep and Sharma (2007) reported exhaust gas recirculation is an

effective method to reduce the NOX. He conducted experiment in direct

injection diesel engine powered by jatropha based bio-diesel. From the

research it is found that the NOX emissions were reduced when the engine was

operated with 5- 25% and the brake thermal efficiency is reduced beyond 15%

EGR level. And also, quoted that 15% EGR is the optimum level which results

in minimum possible Smoke, CO, HC and reasonable brake thermal

efficiency. Hot EGR technique reduces the practical difficulty faced in the

cooled EGR system viz. corrosion of gas cooler, cooling capacity at higher

loads and extra weight are avoided. Further it is noted that combustion

parameters were found comparable with JBD and standard diesel fuel.

Abd-Alla (2002) in his work reviewed the potential of exhaust gas

recirculation (EGR) to reduce the exhaust emissions, particularly NOX

emissions, and to delimit the application range of this technique. A detailed

analysis of previous and current results of EGR effects on the emissions and

performance of diesel engines, spark ignition engines and duel fuel engines is

41

introduced. From the detailed analysis, it was found that adding EGR to the

air flow rate to the diesel engine, rather than displacing some of the inlet air,

appears to be a more beneficial way of utilising EGR in diesel engines. This

way may allow exhaust NOX emissions to be reduced substantially. EGR also

reduces the combustion rate, which makes stable combustion more difficult to

achieve. At constant burn duration and brake mean effective pressure, the

brake specific fuel consumption decreases with increasing EGR. The

improvement in fuel consumption with increasing EGR is due to three factors:

firstly, reduced pumping work; secondly, reduced heat loss to the cylinder

walls, and thirdly, a reduction in the degree of dissociation in the high

temperature burned gases. In dual fuel engines, with hot EGR, the thermal

efficiencies improved due to increased intake charge temperatures and

reburning of the unburned fuel in the recirculated gas. Simultaneously, NOX is

reduced to almost zero at high natural gas fractions. Cooled EGR gives lower

thermal efficiency than hot EGR but makes possible lower NOX emissions.

The use of EGR is therefore, believed to be most effective improving exhaust

emissions.

Agarwal et al (2006) chosen constant speed, two-cylinder, four-

stroke cylinder, direct injection diesel engine generator set of 9 kW rated for

his research and used biodiesel extracted from rice bran oil as fuel. From the

results, it is noted that biodiesel-fueled engine produced less CO, unburned

HC, particulate emissions and higher NOX emissions as compared to mineral

diesel. They have also reported that EGR was effective to reduce NOX from

diesel engines and could be effectively employed for biodiesel applications.

And also reported that 20% biodiesel with 15% EGR is found to be optimum

concentration for biodiesel, which improves the thermal efficiency, reduces

the exhaust emissions and the BSEC.

42

Ladommatos et al (1998) reported that the EGR is one of the most

effective techniques to reduce NOX emissions in internal combustion engines.

However, the application of EGR also incurs penalties. In the case of diesel

engines, they include worsening specific fuel consumption and particulate

emissions. From the results it is found that at high loads, EGR aggravates the

trade-off between NOX and particulate emissions. The application of EGR can

also affect adversely the lubricating oil quality and engine durability. Also,

EGR has not been applied practically for heavy duty diesel engines because

wear of piston rings and cylinder liner is increased by EGR. It is widely

considered that sulphurdioxide in the exhaust gas strongly relates to the wear.

The results showed that the sulfur oxide concentration in the oil layer is related

strongly to the EGR rate, inversely with engine speed and decreases under

light load conditions. It was also found that as the carbon dioxide levels are

increased due to EGR, the combustion noise levels also increase, but the effect

is more noticeable at certain frequencies.

Lazaro et al (2002) analysed dual cooled EGR prototype and tested

in four steady state operating conditions in a direct injection diesel engine.

The prototype was characterised on test flow and thermal efficiency rigs and

also studied on the engine test bed. From the results it is concluded that under

steady partial load conditions small reduction in CO and HC emission with a

small increase of NOX emission. There were significant reductions of HC and

CO emission with slight increases of NOX emission were obtained during

engine warm-up tests. This showed a potential to reduce CO and HC emission

during the first stages in the emission certification test in Europe. This

technique can be used to improve catalyst light-off, temperature particle trap

regeneration and other engine functions.

43

Miller et al (2007) employed four strokes, single cylinder, water

cooled, and naturally aspirated direct injection diesel engine developing

3.73KW at 1500 r.p.m fueled by L.P.G. EGR flow rates were varied in steps

of 5%, 10%, 15% and 20%. The test results showed that brake thermal

efficiency increased by about 2.5% at part loads for all EGR percentages, but

at full load higher EGR percentage affected the performance of the engine. HC

and NO concentrations were lowest at full load at 20% EGR. The rate of

pressure rise was marginal for all EGR percentages at part loads however the

rate of pressure rise reduced significantly at higher loads.

Raheman and Phadatare (2004) conducted performance and exhaust

emission analysis in a diesel engine supplied with Karanja Methyl Ester

(KME) and its blends with diesel from 20% to 80% by volume. They noticed

increase in torque, brake power, brake thermal efficiency and reduction in

brake specific fuel consumption and CO, NOX emissions and smoke density.

They also concluded that blend with 20% and 40% biodiesel could be replaced

with diesel.

Nidal and Abu-Hamdeh (2003) studied spiral fin exhaust pipe that

was designed to analyse the effect of cooled EGR on diesel engine. In this

study, emissions such as NOX , CO2 and CO were analysed. In addition; O2

concentration in the exhaust was also measured. The two designs adopted in

this study were with solid exhaust pipes and hollow fins around them. First

model used airflow around the fins to cool the exhaust gases where as second

model consisted of hollow fins around the exhaust pipe to allow cooling water

to flow in the hollow passage. Different combinations and arrangement of the

solid and hollow fins exhaust pipes were analysed. From the results it is

44

inferred that decreasing in the EGR temperature results reductions in the NOX,

CO2 emissions and increased CO emission in the exhaust gases.

Alain Maiboom et al (2008) studied the influence of cylinder – to –

cylinder variations in EGR distribution on the NOX - PM trade off had been

experimentally investigated on an automotive high speed direct injection

diesel engine. The test results showed that suppression of unequal EGR

distribution results in decreased NOX and PM emissions, especially when

running with high EGR rates.

Ming Zheng et al (2004) reported that EGR was effective to reduce

NOX emission from diesel engines because it lowered the flame temperature

and the oxygen concentration of the working fluid in the combustion chamber.

However, as NOX emission reduced, particulate matter increased, resulting

from the lowered oxygen concentration. When EGR ratio further increased,

the engine operation reached zones with higher instabilities, increased

carbonaceous emission and even power losses. They also studied oxidation

catalyst converter with EGR that eliminated the recycle combustible thus

stabilising the cycle’s variations.

Saleh (2009) investigated the effect of exhaust gas recirculation on

exhaust emission and performance in a diesel engine operating with jatropha

methyl ester. For all operating conditions, a better trade–off between HC, CO

and NOX emissions can be attained within a limited EGR rate of 5 – 15% with

little economy penalty.

Spring and Onder et al. (2007) addressed the problem of EGR

occurring when pressure-wave superchargers were used as boosting devices of

IC engines. During accelerations, critical situations arise whenever large

45

amounts of exhaust gas were recirculated over the charger from the exhaust to

the intake manifolds of the engine. Such recirculation's caused the engine

torque to drop sharply and thus severely affected the driveability of the

vehicle. A new Pressure Wave Supercharged (PWS) controller system was

designed and experimentally verified that prevented the above mentioned

problems. The control concept was based on the fact that the EGR rate was

linked to the scavenging rate, an indicator for the amount of fresh air leaving

through four channels of the PWS.

From the above literature review, it is evident that many researchers

have investigated the effect of exhaust gas recirculation on diesel engine

performance. Hot EGR technique is preferred because it reduces the practical

difficulty faced in the cooled EGR system. And also it is inferred that there is

better trade – off between HC, CO and NOX emissions can be attained with

15% EGR and without reduction in brake thermal efficiency. In research, we

use 15% of exhaust gas recirculation to analyse the performance, combustion

and emission characteristics of direct injection diesel engine powered with

standard diesel fuel, eucalyptus oil with diesel fuel blends and turpentine oil

with diesel fuel blends.

46

2.4 BIOFUEL WITH STANDARD DIESEL BLENDS

OPERATED IN THERMAL BARRIER COATED

DI DIESEL ENGINE

In the recent researches there are only limited numbers of technical

papers available in the area of application of metal matrix composites and

ceramic based thermal barrier coating on automobile engine components.

Can Hasimoglu et al (2008) used biodiesel produced from

sunflower oil in the Low Heat Rejection (LHR) engine and analysed its

performance and emission characteristics. In this work Mercedes – Benz /

OM364A type, four cylinders, turbocharged DI diesel engine. The tests were

performed at full load condition for the engine speeds of

1100,1200,1400,1600,1800,2000,2200,2400,2600 and 2800 rpm. Yttria

Stabilised Zirconia with a thickness of 0.35 mm over a 0.15mm thickness of

NiCrAl bond coat was used to convert the test engine into LHR engine. The

results revealed that the specific fuel consumption and the brake thermal

efficiency were improved in LHR engine.

Hanbey Hazar (2009) conducted experiment on four stroke, single

cylinder, direct injection, naturally aspirated, air cooled 6LD 400 Lombardini

model diesel engine was used. The cylinder head, exhaust and inlet valves of

the engine were coated with MgO-ZrO2 to a thickness of 0.35mm over a

0.15mm thickness of NiCrAl bond coat by plasma spray method. The fuels

used for this test are canola methyl ester with diesel fuel mixed at ratios of

20% and 35% respectively. The engine power was increased by 8.4%, 3.5%

and 1.6% for Diesel fuel and 80D: 20C and 65D: 35C respectively. Emission

such as CO and Smoke density decreased considerably whereas NOx emission

increases by 11.4%,5.4% and 2.6% for Diesel fuel and 80D:20C and 65D:35C

respectively.

47

Ramu (2009) conducted an experiment on single cylinder direct

injection diesel engine where the cylinder head, valves, piston crown were

coated with ZrO2 and Al2O3 with particle sizes ranging from 38.5 to 63 µm

and Ni-20Cr-6Al-Y metal powder with particle sizes ranging from 10 to 100

µm were used. The results revealed that the thermal efficiency was increased

and NOx emission was reduced by 500 ppm for ZrO2 and Al2O3 and 800 ppm

for Ni-20Cr-6Al-Y.And also results showed that the smoke density was higher

for thermal barrier coated engine. Heat release rate and peak cylinder pressure

was also reduced.

Buyukkaya et al (2004) studied the effect of ceramic coatings on

diesel engine performance and exhaust emissions. The cylinder head and

valves of an engine were coated with a 0.35 mm thickness of CaZrO3 over a

0.15 mm thickness of NiCrAl bond coat and pistons were also coated with

MgZrO3 by using atmospheric plasma spray technique. The result showed that

specific fuel consumption was lower for the insulated engine when compared

to standard engine. Due to better combustion efficiency in the coated engine,

particulate emissions were lower (about 48%) than the standard engine.

Hejwowski and Weronski (2002) reported the effect of thin thermal

barrier coating diesel engine to analyse the performance, temperature, stress

distribution and wear analytically evaluated by means of Cosmos/Works FEM

code. From the FEM calculation, the optimum coating thickness for the engine

components was identified. The components were coated with (i) NiCrAl

bond coat 0.15 mm thick, Al2O3 – 40% TiO2 0.35 mm thick (ii) NiCrAl bond

coat 0.15 mm thick, ZrO2 – 8% Y2O3 0.3 mm thick. They concluded that the

optimum coating thickness for ZrO2 – Y2O3 and Al2O3 – TiO2 was slightly

below 0.5 mm. Effect of coatings on stress and temperature distributions

48

decreased with increasing distance from the free surface. In this work thermal

fatigue and wear test were also discussed.

Taymaz et al (2005) evaluated experimentally the effect of ceramic

coating on diesel engine with different engine speeds and loads. Experiments

were conducted with six cylinder direct injection, turbocharged, inter-cooled

diesel engine. The combustion chamber surfaces like cylinder head, piston and

valves were coated with CaZro3 and MgZrO3, by using plasma – coating

method onto the base of the NiCrAl bond coat. The thickness of coating is

0.35 mm. The result showed that the increase of the combustion temperature

caused the effective efficiency to rise from 32% to 34% at medium load and

from 37% to 39% at full load and medium engine speeded for ceramic-coated

engine while it increases only from 26% to 27% at low load. It was seen, that

the values of the effective efficiency are slightly higher for the ceramic-coated

engine compared to the standard engine (without coating).

Ekrem Buyukkaya and Muhammet Cerit (2008) conducted a test in

a six cylinders, indirect injection diesel engine with an intercooler system .Al

bond coat and pistons were also coated with MgZrO3 by using atmospheric

plasma spray technique. For the original injection timing of the 200 before top

dead centre, the brake specific fuel consumption value of the LHR engine was

approximately 6% lower than the original engine. NOx emissions were also

higher. In this investigation to reduce the NOx emission, the two injection

timing 180 and 160 crank angle BTDC was used. The results showed that

BSFC and NOx emission were reduced by 2% and 11%, respectively by

retarding the injection timing and optimum injection timing was obtained

through decreasing by 20 BTDC.

49

Adnan Parlak (2005) conducted a test in a single cylinder, indirect

injection Ricardo E6 – MS/128/76 type diesel engine. Supercharging was

applied to test engine with an external compressor. Intake pressure and

exhaust back pressure were controlled with a regulator valve, thus permitting

an intake to exhaust gas pressure ratio to be maintained constant through the

tests. The tests were conducted with variable load at various engine speeds

and at the static injection timings of 380, 360, 340 and 320 CA. Atmospheric

plasma spray coating method was used to coat the combustion chamber

components. As for plasma gas, a mixture of Ar + 5% H2 was used. The

combustion chamber components (cylinder head, valves and piston) were

coated with MgO – ZrO2 layer of 0.35 mm thickness over a NiCrAl bond coat

of 0.15 mm thickness. In this study, optimum injection timing was found with

crank angle (340 CA) retarded bTDC. When the LHR engine was operated

with the injection timing of the 38 CA, which is the optimum value of the

standard engine, it was shown that oxides of nitrogen emission increased about

15%. When the injection timing was retarded to 340 CA in the LHR engine, a

decrease in the NOx emission (about 40%) and the brake specific fuel

consumption (about 6%) compared to that of the standard engine were

observed. By retarding the injection timing, an additional 1.5% saving in fuel

consumption was obtained.

Ekrem Buyukkaya et al (2006) conducted an experimental

investigation on a six cylinders, direct injection and turbocharged diesel

engine. The pistons were coated with a 350 micron thickness of MgZrO3 over

a 150 micron thickness of NiCrAl bond coat. The cylinder head and valves

are coated with CaZrO3. The result showed almost 65 C increases in the

combustion gas temperature in the LHR engine compared to standard engine.

The brake specific fuel consumption was lower by 6% in the LHR engine and

50

NOx emission levels were found to be higher by about 9% when compared to

standard engine.

Yhuda Tzabari et al (1990) conducted an experimental investigation

on Petter AV1 diesel engine. In this work the piston was covered by silicon

nitrite cup with the help of aluminum adaptor connected to the aluminum

piston and supported by the specially fitted gasket. The aluminum alloy/silicon

nitride joint was formed by integral casting of an aluminum alloy threaded

sleeve which was screwed into the aluminum piston. Insulation was created

by an air gap and ceramic fiber washer which provides a flexible support to the

piston cap attachment. The test was conducted at various loads to analyse the

thermal shock and heat transfer characteristics. The temperature of cylinder

head, linier and exhaust valve obtained by finite element models were

compared with measured temperature. The test results showed that non

uniform displacement occurs between the ceramic cup and piston. In order to

improve the piston cup attachment to that aluminum piston the characteristic

of the gasket has been changed.

Katsuyuki Osawa et al (1991) studied the effect of aluminum

engine block without iron sleeve was coated with Zirconium and chrome oxide

in the cylinder head, piston crown and valves. The investigation was carried

out in single cylinder air cooled diesel engine coupled with AC generator. In

this work, injection timing was retarded by 2 degrees before TDC. They

conclude that 10% improvement in fuel consumption was recorded for thermal

barrier coated engine. From the temperature data analysis, 5% decrease in

brake fuel consumption for the coated engine. Coating of the cylinder liner

only gives the best performance on comparison to coated piston and cylinder.

51

Martin R. Myers et al (1991) investigated the mechanical properties

of aluminum, Silicon alloy reinforced ceramic fiber metal matrix composite.

Tensile and fatigue tests were carried out over a range of temperatures typical

of those experienced during engine operation. The development of metal

matrix composites (MMCs) which are of low cost can be produced to near net

shape, and be used to selectively to reinforce critical areas of components.

These composites may have much improved properties in terms of strength,

wear resistance and thermal stability, making them very attractive for use in

heavy duty diesel engines. They concluded that, ceramic fibers substantially

improve the tensile and fatigue characteristics of the current material at

temperatures in the range of the maximum engine operating conditions. The

thermal fatigue durability of diesel engine piston may be substantially

improved by the incorporation of ceramic fibers.

Dennis Assanis et al (1991) conducted the detailed study of effect

of ceramic coating on diesel engine performance and emission. Tests were

carried out at different engine speeds with a standard metal piston and two

pistons insulated with 0.5 mm and 1.0 mm thick ceramic coatings. They

reported that the thinner (0.5 mm) ceramic coated piston provided 10% higher

thermal efficiency than the metal piston and thicker coated piston resulted in 6

% higher thermal efficiency than the conventional engine. It showed 30% to

60% lower CO levels, 35% to 40% lower unburned hydrocarbon levels, and

10% to 30% lower NOx levels and lower smoke levels when compared to

baseline engine. They reason for this is more complete combustion in the

insulated version.

Matthew Winkler et al (1992) reported on thermal barrier coated

diesel engine. In this work they used plasma thermal spray method to coat the

piston, cylinder head and liner by Zirconium oxide. In this process, metallic

52

bond coat was followed by ceramic coat. The thickness of coating was

optimised by analytical method. The total coating thickness was 100 microns

approximately. The paper analysed the bond coat material with various

combinations of nickel, cobalt and chromium with additions of Aluminum and

yttrium. The combination of nickel cobalt and chromium provided the high

melting temperature (1,538 C) of the coating alloy while aluminum and

yttrium protect the alloy from oxidation by forming a thin adherent layer of

aluminum oxide.

Adnan Parlak et al (2003) experimentally studied the effect of

reducing the compression ratio on the performance and exhaust emissions in a

Low Heat Rejection (LHR) indirect injection diesel engine. The compression

ratio was lowered from 18.20 to 16.10 in 0.7 intervals. The experiment was

carried out in a Ricardo E6 type engine. It is a single cylinder, four stroke,

water cooled pre-combustion chamber engine. The combustion chamber

components (cylinder head, valves and piston) were coated by 0.35 mm

thickness of MgO-ZrO2 over a 0.15 mm thickness of NiCrAl bond coat. They

concluded that, at the compression ratio of 17.50 and 16.80 in the LHR engine,

the specific fuel consumption and NOx emissions are decreased about 2.9 %

and 15%.

Shuji Kimura et al (1992) reported that effect of combustion

chamber insulation of diesel engine to analyse the thermal efficiency. The

experiment was conducted with 4-cylinders and single-cylinder direct injection

diesel engines to examine the effects of combustion chamber insulation on

heat rejection and thermal efficiency. The combustion chamber was insulated

by using a silicon nitride piston cavity that was shrink-fitted into a titanium

alloy crown. The effect of insulation on heat rejection was examined on the

basis of heat release calculations made from cylinder pressure time interval.

53

High-speed photography was used to investigate combustion process. The

results showed that heat rejection was influenced by the combustion chamber

geometry and swirl ratio and it was reduced by insulating the combustion

chamber. Slight improvement in thermal efficiency was observed in the

insulated engine. High-speed combustion photographs revealed that the

application of heat insulation reduced the angular velocity of the flame in

combustion chamber by 10 – 20%. This reduction in the angular velocity of

the flame was due combustion deterioration when heat insulation is applied to

the combustion chamber.

Matthew Winkler et al (1993) had studied the thermal barrier

coating applied to piston and valves to control the diesel engine emission. In

this investigation Zirconium oxide used as a ceramic material to coat the

piston, cylinder head and liner by plasma spray process. The effect of coating

reduced the exhaust gas temperature and particulate emission and to improve

the mechanical efficiency. They concluded that the coating reduces the

lubrication oil consumption and improved the life of the piston and piston

rings.

Ernest Schwarz et al (1993) studied the combustion and

performance characteristic of low heat rejection engine. The test was

conducted with different pistons coated with different materials. The first

piston was coated by zirconium by plasma spray method about 1.016 mm

thickness and the second, the same except that the surface was impregnated

with chrome oxide which acted as a seal coat. They concluded that, the

ignition delay was shorter, premixed fraction was less and heat release

duration greater for the LHR engine. The volumetric efficiency was less for

the LHR engine however, differences were not substantial (3% or less).

Exhaust temperatures were greater in all LHR cases. LHR engine performance

54

results were mixed. From the investigation, at full load conditions the

indicated specific fuel consumption was better at the high speed conditions

and very low was observed at the low speed condition.

Sun et al (1993) conducted experiments on turbocharged large-bore

single cylinder engine, both with and without insulation in order to enable a

direct comparison. The LHR engine featured a ceramic High Pressure Silicon

Nitride (HPSN) insert in a cast iron piston. Plasma Sprayed Zirconium (PSZ)

was applied to the cylinder head, liner, and valves. Insulation resulted in a

shortened ignition delay followed by an increase in the combustion duration

and a lower pressure rise. This was reflected in the heat release by a less

marked premixed combustion peak and a more pronounced diffusion burn.

The volumetric efficiency went down from 91%to 85% as a result of applying

the insulation. Heat transfer was measured with a set of thermocouples in the

cylinder wall as well as in the inlet and exhaust manifolds. The peak flux was

found to be approximately 40% lower in the LHR engine However, the fuel

consumption increased by about 9%.

Walter Bryzik et al (1993) studied the low heat rejection engine

coated with ceramic slurry using titanium alloy as a thermal barrier coating.

The investigation was carried out in single cylinder, water cooled, 4 strokes DI

diesel engine. The cylinder liner, head plate and the piston crown were coated

with ceramic slurry coating. In this work, three coating methods were

described (i) Plasma sprayed with slurry top coating (ii) Plasma sprayed with

slurry densifier and hardener (iii) using an all slurry coating. They concluded

that increase in brake fuel consumption for insulated engine and also analysed

the tribological condition.

55

Afify et al (2008) investigated the effect of selective insulation on

DI diesel engine to analyse the performance, combustion and emission

characteristics. In this work KIVA II code was used to model the engine with

and without the selective insulation. In this study, piston crown, cylinder head

and valves coated by PSZ by 0.2 mm thickness were considered. The

experiment was conducted at different operating conditions of speed, load and

injection timing for base engine and ceramic coated engine. The experimental

result showed that insulation of the piston crown was more effective than

insulation of the cylinder head in improving the brake specific fuel

consumption and NO emission of the engine compared to the baseline engine.

Coating the piston crown lowered the NO emission under all operating

conditions and consistently improved BSFC at the maximum load and

maximum speed conditions.

Kamo et al (1999) experimentally determined the performance of

thermal barrier coated engine with high pressure fuel injection system. In this

work six cylinder turbo charged DI diesel engine was used. The cylinder

head, piston and valves were coated with thin layer of thermal barrier

Zirconium oxide (ZrO2) with Nickel chrome boron (NiCrB) about 0.13 mm

thickness. The study revealed improvement in specific fuel consumption for

thermal barrier coating engine. The peak pressure and heat release rate

increased for thermal barrier coated engine because of high combustion

chamber temperature. Thin thermal barrier coating offers 5% to 6% higher fuel

efficiency.

Dickey (1989) studied the performance and emissions with a LHR

engine where ceramic coated steel capped aluminum composite piston with

ceramic coated valves, found a reduction in indicated thermal efficiency (ITE)

by 3.4 %. An increase in smoke and particulate emissions and 30% reduction

56

in heat loss to coolant were attributed to degraded combustion with longer

combustion duration and lower peak heat release rates.

Miyari (1988) conducted an experimental work in a single cylinder

DI diesel engine indicating improved engine performance, reduced HC

emissions but increased NOx emissions and decreased volumetric efficiency.

They also reported reduction in brake specific fuel consumption by 7% under

naturally aspirated conditions. They attributed this to more efficient use of the

in-cylinder air. The engine used for investigation was selectively insulated

with monolithic ceramics such as partially stabilised zirconia and sintered

silicon nitride. In the experiments, the fuel injection system and the fuel

injection amount were kept the same as that of the base engine. Temperature

of the jacket cooling water and the lubricating oil are maintained at 80 C

throughout the experiments. The cylinder liner was water cooled to prevent the

sliding surface suffering tribological problems and to prevent deterioration of

volumetric efficiency caused by the liner surface getting too hot.

Bryzik et al (1991) results showed that the LHR engine when

tested with the retarded injection timing had no change in fuel economy

compared to base engine. However, if full advantage was taken of the

potential improvement in fuel economy the NOx emissions were increased.

Nevertheless comparing the NOx / SFC trade off, the LHR engine performed

better than the base engine.

Morel et al (1986) predicted that the liner insulation offers only a

small benefit in efficiency improvement and main benefit was obtained by

insulating piston top and head only. Its main influence was to redirect the

flow of heat from the liner coolant to oil cooling. They suggested that a

substantial reduction in combustion chamber heat transfer could be achieved

57

by using Partially Stabilised Zirconium (PSZ) insulating layers. The resulting

benefits in BSFC can be quite favorable when compared to those obtainable

using hypothetical limits with material of zero conductivity.

Hideo Kawamura et al (1995) tried the heat insulation structure

referred to as thermos structure in a diesel engine. This was constructed by a

combustion chamber wall made of Si3N4 (silicon nitride) monolithic ceramics

and heat insulation layers combined with air gap and gaskets with low thermal

conductivity that were located behind the combustion chamber wall. They

found that improvement in fuel economy and exhaust emissions could not be

realised in case of Direct Injection (DI) diesel engines. The work revealed that

a pre-combustion chamber had good potentials for LHR engine by having high

combustion chamber wall temperature that improves fuel consumption and

controls exhaust emissions. New type of pre-combustion chamber was

installed in the LHR engine which had located at the center of cylinder, throat

holes radiating to cylinder wall having the throat area 3% or more and

insulated by an air gap and gaskets had achieved 5 to 10% lower fuel

consumption compared with direct injection water-cooled diesel engine. The

combustion chamber with thermos structure consisted of monolithic Si3N4

sintered ceramics, which had high fracture toughness and bending strength.

Thus it has good reliability and durability for the long hard testing. The fuel

consumption in the case of the new types of energy recovery system was

180gm/kwh or less for light duty diesel engine with the new combustion

chamber.

Thring (1986) concluded from the experiments on an insulated

engine, that improvement in fuel economy of naturally aspirated engine is

marginal and about 7% improvement in turbo compound engines. These

values differed vastly in literature mostly because of the different modes of

58

insulation and differences in the basic engines used for experimentation and

comparison. It is essential to have an exhaust energy recovery system to fully

reap the benefits of making engine adiabatic.

Yoshimitsu et al (1983) reported theoretical benefits in fuel

economy of 14% due to perfect heat insulation of a turbo compound engine

and 6% from the turbo compounding, making a total of 20%. The

experimental results, however, only showed a maximum improvement of

13.5% at rated power. Reducing heat rejection causes an increase in the

temperature of the internal surfaces of the engine, which causes a loss in

volumetric efficiency. Since the maximum power output of naturally aspirated

diesel engine is normally limited by the maximum tolerable smoke level,

power output was directly reduced. Typically the volumetric efficiency

reduction in smoke-limited power is of the order of 25%. For turbocharged

engines, power was of the order of 25%. For turbocharged engines, power

output can be maintained by increased boost pressure.

From the above literature review, it is evident that many researchers

have investigated the effect of thermal barrier coating on diesel engine

components. The ceramic coating offers very good heat resistance

characteristics, but they are brittle in nature. It has very poor bonding with the

metal. Generally ceramic coatings are subjected to large thermal shock due to

large thermal gradient in the thickness direction and results in damages in the

coated surface due to the high brittleness of ceramic materials. To overcome

the above problems the metal matrix composite coating is the best alternative

of the ceramic coating. In metal matrix composite, the matrix phase is highly

ductile and the reinforcement phases are extremely hard in nature. It must be

superior in wear resistance, heat resistance and corrosion resistance when

compared to the base alloy. Metal matrix composites have good thermal

59

stability and chemical resistance properties. From the output of various

researches, it is found the partially stabilised zirconia – alumina alloy works

better than other ceramic materials. For our research work, partially stabilised

zirconia- alumina alloy was chosen to coat the cylinder head, piston crown and

valves of about thickness 3mm. Plasma spray method is used to provide

thermal barrier coating on diesel engine components.

60

2.5 BY USING OF COMPUTER MODEL TO ANALYSE

THE COMBUSTION AND EMISSION CHARACTERISTICS

OF THE THERMAL BARRIER COATED DIESEL ENGINE

POWERED BY BIOFUEL AND DF BLENDS.

In the recent research to develop a computer model, there are

limited numbers of technical papers available in the area of application of

using biofuels in thermal barrier coated direct injection diesel engine

components.

Hountalas et al (2006) reported the potential benefits in engine

performance and exhaust emissions by varying compression ratio in heavy-

duty diesel engines. The investigation was conducted using a simulation code.

This has been validated against experimental data to ensure its ability to

predict adequately performance and engine emissions. The theoretical

analysis revealed that the increase of compression ratio results in reduction of

brake specific fuel consumption due to the improvement of the operating cycle

thermodynamic efficiency. The improvement was significantly lower

compared to the standard engine and was in the order of 1% per unit increase

of compression ratio. The increase was lower at part load operation.

Canakci et al (2006) studied the applicability of an artificial neural

network (ANN) to investigate the performance and exhaust-emission values of

a diesel engine fueled with biodiesel from different feedstock and petroleum

diesel fuels. Experimental results of two different petroleum diesel fuels

(No.1 and No.2), biodiesel (from soybean oil and yellow grease), and their

20% blends with No. 2 diesel fuel were used in the work. After the

investigation on the Artificial Neural Network (ANN) applicability, the

61

performance and exhaust emissions of a diesel engine fueled with blends of

biodiesel and No. 2 diesel up to 20% have been predicted using the ANN

model.

Franz Tanner and Seshasai Srinivasan (2009) performed engine

simulations on KIVA-3-based code which was equipped with well-established

spray, combustion and emission models. The computation was done for a

sulzer S20 diesel engine which, for the simulations, was equipped with multi-

orifice, asynchronous injection systems. The computations showed that, in

opposition to the conventional split injection method. The reasons for the

improvement over the standard split injection lied in the fact that the

asynchronous injection allowed an overlap of the two injection pulses, which

supplied the total fuel in a much shorter time to the cylinder. This allowed a

long injection delay which, together with the internal EGR effect, led to low

NOX emission and reduction in soot formation.

Tamilporai et al (2010) conducted experiment on four cylinders,

four strokes, turbocharged water cooled engine powered by biodiesel derived

from jatropha. The engine combustion chamber was coated with Partially

Stabilised Zirconia (PSZ) of 0.5 mm thickness, including the piston crown,

cylinder head, valves and outside of the cylinder liner. To validate the

theoretical results, experiments were conducted on a turbocharged direct

injection diesel engine and LHR engine using diesel and biodiesel under

identical conditions. A mathematical model was developed for analysing the

performance and combustion characteristics. The modelling results shows that

with increase in speed the peak pressure, peak temperature and brake thermal

efficiency increases and decreases the specific fuel consumption. LHR engine

powered with diesel fuel shows better performance than LHR biodiesel

operation but not upto the extent of the lower level. This model predicted the

62

engine performance characteristics in closer approximation to that of

experimental operations.

Semin (2008) uses GT-POWER a simulation tool to predict the

performance and emission characteristics of a diesel engine operated with com

pressed natural gas. GT-POWER a simulation tool used by the engine and

vehicle makers and suppliers and it was suitable for analysis of a wide range of

engine issues. From the simulations, it is found that there was reduction of

44% in brake power, 49% in brake torque and addition of 49% in brake

specific fuel consumption.

Jamil Ghojel and Damon Hennery (2005) developed single zone

method to calculate the heat release characteristics in internal combustion

engines using diesel oil emulsion and standard diesel fuel. The model is a

suitable tool for quick evaluation and interpretation of the performance of

different engines with different configurations or fuels and for the same engine

under variable operating conditions .It is also useful when used to monitor the

real-time engine heat release characteristics for diagnostic purposes.

Miyairi (1988) developed a low heat rejection diesel cycle

simulation consisting of a gas flow model, a heat transfer model and a two-

zone combustion model. The heat transfer model was used to determine

convective and radiative heat transfer between the gas and the cylinder valve.

Using combustion model the temperature and the chemical equilibrium

compositions were determined. The gas flow model was used to determine the

gas flow rates between the intake system, the cylinder and the exhaust system.

The simulation was run at different loads, speeds and with different insulation

materials such as iron, PSZ and ZrO2. The investigation indicated

improvement in thermal efficiency ranging from 2 to 2.7% compared to the

63

base line engine. The gain in thermal efficiency due to insulation varied with

different insulation materials. The investigation also indicated materials with

low thermal conductivity and lower heat capacities are advantageous in the

trade off between thermal efficiency and NO emission. It indicated increase in

adiabaticity increases the emission of NO.

Rafiqul Islam (1997) developed a computer simulation model for a

single cylinder direct injection diesel engine for neat diesel operation, ethanol-

diesel dual fuel operation in fumigation and dual injection mode operating in

conventional and low heat rejection version. The developed simulation model

was validated using an available experimental data. The results revealed that

the engine operating with ethanol-diesel dual fuel mode either in fumigation

or dual injection resulted in an increase in power, improvement in brake

specific energy consumption, reduction nitric oxide emission and soot

concentration. The low heat rejection engine in all operating conditions

provided a marginal improvement in engine power output with a slight

increase in nitric oxides emission and reduction in soot concentration.

Timothy Jacobs and Dennis Assanis (2007) focused on an

experimental investigation, modelling issues were considered by assessing

how valuable the measurements were for model development. A predictive,

physically-based model for NOX formation, implemented in the engine system

simulation, could contribute significantly to the advanced development and

evaluation of strategies for reducing NOX emissions. A particular aspect that

seemed to be critical in any analysis of NOX emissions is the gas temperature

during combustion. Engine cycle simulations often utilise the bulk gas

temperature to predict NOX emissions. However, the bulk mean gas

temperature and flame temperature do not necessarily correlate very well.

64

From the literature review, it is found that due to insulation of the

engine components, a high degree of thermal gradients will exist inside the

combustion chamber. It is estimated that for every 3 mm a thermal gradient of

100 C is reached. Under these conditions models are required to predict the

local-in-cylinder conditions such as temperature, gas flow and composition. A

synthesis of the equations describing the various engine process mechanisms

in conjunction with simple expression for energy and mass conservation yield

results for instantaneous values of air entrainment rates, cylinder pressure, rate

of heat release, heat transfer etc.. Computer modelling is a useful adjunct to

this process in reducing the amount of test work required and in providing the

ability to generalise results in a quantitative manner.