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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.
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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.