Internal of the engine. The diesel engines are

Internal
combustion engines (IC Engines) were invented in the 19th century,
and ever since they are used as primary power systems for both stationary and
mobile applications. As time progresses, IC engines went through remarkable
changes in terms of combustion, performance and emissions, and there is
substantial development because of electronic control in engine management
system. Now a days new development in engines are inspired by better fuel
economy and meeting stringent exhaust emission norms. Because of this, it is
very crucial to make cleaner and fuel-efficient engine without sacrificing the
performance of the engine. The diesel engines are popular because of their high
fuel economy, robustness ad mechanical durability. In addition to this, overall
fuel-lean operation and typically higher expansion ratio results in high
thermal efficiency in diesel engine. Further, at part load lack of throttling
is advantageous for fuel economy. The biggest challenge facing CI engines is
difficulty in simultaneously reducing NOx and Smoke. As emission limits get
more and more stringent, manufactures have to look for new ways to reduce
emissions this is one problem. Another problem is availability of fossil fuels
and there prices, as resources for fossil fuel is conserve. However, demands
are increasing because energy is important key for economic growth and
development of any country.   

One
of the routes is to modify the engine so that the combustion process can be
improved in order to reduce formation of pollutants within the cylinder itself.
Many new technologies like Common Rail Direct Injection (CR-DI), exhaust gas recirculation
(EGR), intake air boosting, and Variable Valve Timing (VVT) are used these
days. Exhaust after treatment like Selective Catalytic Reduction (SCR), Three
Way Catalytic (TWC) converter, and De-NOx converter are being implemented along
with the above mentioned technologies. CO2 is major pollutant which
is responsible for global warming.    

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Another
approach is to look for renewable alternative fuels which can emit low levels
of harmful components and enhance their performance through the use of modern
fuel injection and control strategies. According to a report published by EIA
renewable energy the world’s fastest growing forms of energy and it will grow
in future at a faster rate. Renewable alternative fuels like alcohols, biogas,
biodiesel and hydrogen have been and are being evaluated for application in
both in compression ignition (CI) and spark ignition (SI) engines with slight
modification or no modification. Alternative fuels are cleaner in burning then
fossil fuel so lower tail pipe emission. They are produced form biomass sources
so reduces dependency on fossil fuels.      

1.1.
ALTERNATIVE FUELS FOR ENGINES

Alternative
fuels can be divided into two categories based on their form of availability:

1.      Gaseous
alternative fuels

2.      Liquid
alternative fuels   

1.1.1. Gaseous alternative fuels

Use
of gaseous fuels like natural gas, liquid petroleum gas, hydrogen and biogas
are explored in both CI and SI engines. As it is available in gas form it mix
well with air and forms homogenous mixture which results in lower smoke and CO
emissions provided not form overall rich mixtures. Gaseous fuel has high octane
number and higher auto-ignition temperature as compared to gasoline so they can
be used in SI engines with increase in compression ratio in order to take
advantage of higher octane number. However, energy density is low and storage
and refilling is an issue, because of this range is an issue. Mostly gaseous
fuels which are used in diesel engine use dual fuel mode of combustion.

1.1.2. Liquid alternative fuels –

Liquid
alternative fuels like alcohols, biodiesel, Fischer-Tropsch diesel, di-methyl
ether (DME), di-ethyl ether (DEE) have been studied in both CI and SI engines.
Liquid alternative fuels are popular because of their ability to easily stored
and transport. Some of liquid alternative have properties very close to diesel fuel,
which makes them suitable for CI engine. Alcohols are quite attractive and
promising because it can be easily stored, can be produced from renewable
sources and can be handled easily. Brazil, India,
United States of America and Canada are the major countries producing the ethanol from their
bio-resources like sugarcane molasses, corn and agricultural wastes. Fuels
with less carbon content and high energy density are preferred as they emit
less CO2 on combustion.

1.2.
ALCOHOLS AS ENGINE FUELS

Use of alcohols has gained importance because of their ability and
superior combustion characteristics. In SI engine alcohols have been used as a
sole fuel and also in the blended form along with gasoline. However, blends
stability depends upon type of alcohols, ambient temperature and water content
in blend. Methanol and ethanol have been used in SI engine extensively.
Countries like Brazil and USA use blends of ethanol and gasoline is mandatory. Use
of alcohols in CI engine is gaining importance.

Conventional fermentation process is used to produce acetone,
n-butanol and ethanol (ABE fermentation) in the ratio of 3:6:1. Fermentation is
basically a metabolic reaction of bacteria or yeast in the absence of oxygen. In
this process Starch and glucose are converted into alcohols and other by-products
like carbon-di-oxide, hydrogen and acids etc. Synthetic gas formed when lignite
or municipal solid wastes are made to react with steam or oxygen use to produce
methanol (Wagner et al., 1979). Methanol was used earlier in engines. However,
it is not preferred currently due to its limited availability.

1.3. ADVANTAGES IN USING ALCOHOLS AS ENGINE FUELS

Alcohols have superior antiknock quality which can lead to high torque
and power in SI engines or compression ratio can be increased as they have high
octane and self-ignition temperature this helps in improve the efficiency of SI
engines. This is because knock free operation of the engine even at high
compression ratios can be realised. Increase in compression ration can led to
reduce in fuel consumption because better BTE. Alcohols has higher flame speed
which results in shorter combustion duration which means that more part of
combustion is occurring in constant volume process which leads to higher torque
and better thermal efficiency. Alcohols have high latent heat of evaporation
which led to cool the charge, which results in higher volumetric efficiency. In
addition to this, reduction in charge temperature leads to lower peak
combustion temperature which lowers the oxides of nitrogen (NOx) (Starkman
1964; Brinkman 1975). Further, adiabatic flame temperature of alcohols is lower
than diesel which once again helps in lower the NOx emissions (Gu et al., 2010).

Alcohols are oxygenated which means that they contain oxygen in
their molecule. This is known as fuel bound oxygen which can reduce the smoke, hydrocarbon
(HC) and carbon monoxide (CO) emissions (Kumar et al., 2009, Rakopoulos et al.,
2010). Agricultural and municipal solid wastes are used to produce alcohols.
They are viable solution for low cost renewable fuels to balance the price fluctuation
of fossil fuels because their sources are depleting (Kumar et al., 2012).

 

1.4. PROBLEMS IN USING ALCOHOLS AS ENGINE FUELS

Following are the major problems with using alcohols as a fuel:

·        
Phase separation while using
as blends of alcohols in fossil fuels

·        
Corrosion and water
contamination

·        
Cold startability

·        
Use of alcohols along with diesel in
different proportions based on operating conditions

Alcohols can be used in CI engines and by blending or emulsifying
them with diesel. However, the miscibility of alcohols in diesel depends on the
type of alcohol. The stability of alcohol diesel blends depends on mainly two
factors: water content and temperature. Increase in temperature improves
miscibility while the presence of water decreases it. At a temperature of 25ºC
the miscibility of methanol is less than 5 vol% and that of ethanol is less
than 20 vol% in the absence of water. However, butanol can be mixed in any
proportion with diesel at this temperature when there is no water Lapuerta et.
Al, 2010 1-SAE-WX. Addition of water reduces the amount of alcohol which
can be blended with diesel. To overcome this problem additives (Co solvents)
are used and in some cases the quantity of additive may be considerable Adelman,
H., 1979. Blends of diesel and butanol are less susceptible to separation in
the presence of water than diesel-ethanol blends because of the lower
solubility of butanol in water and water in butanol Hajba et al., 2011, 3.

Alcohols are more corrosive than gasoline and diesel. Ethyl-sulphate
leads to corrosion of the metals that are in contact. The sulphur dioxide which
is used as an antioxidant and antiseptic during the production of ethanol is
source of ethyl-sulphate. This issue can be mitigated by changing the material
used in fuel injection system. Polymeric tubes and “O” rings are affected by
the high chemical reaction rate of alcohols which results in loss of weight, swelling
and brittleness of the polymer components. Fluorosilicone and fluorocarbon
elastomer polymers are very suitable for alcohol fuel applications (Nersasian
(1), 1980; Nersasian(2), 1980). Additives for enhancing lubricity and corrosion
resistance will be required in the case of ethanol and methanol. Additives can
have a significant effect on the heating value of the blends Waterland et al.,
2003 6.

 

Alcohols has high latent heat of evaporation which can led to
problem in starting engine in cold condition and also increase emissions in
such conditions. This happens because during vaporization process alcohols
takes heat from surrounding air and this drops the temperature and it also
affects evaporation also. Further, this affects mixture formation and
combustion (Wallner et al., 2009; Kumar et al., 2009). For solving this issue
preheating of air or fuel can be used as a viable solution.

Dual fuel mode of operation is an effective was of using alcohols
and it gives flexibility of using different proportions of it base on operating
conditions.

1.5. DUAL FUEL ENGINE

Dual-fuel engine operation is another promising technology; it
allows the use of high self-ignition temperature fuels like alcohols by
igniting them after compression by a spray of high reactivity fuel like diesel.
A primary fuel is inducted through intake manifold or by port injection along
with air, this homogeneous air-fuel mixture is compressed during the
compression stroke but cannot auto-ignite on its own due to lean homogenous
mixtures and high self-ignition temperature of the primary fuel. Hence, the
need for secondary fuel arises; pilot injection of diesel like fuels leads to
the ignition process. Wide range of fuels like biogas, natural gas, LPG and
alcohols can be used in conjunction with diesel in a dual fuel engine. However,
only limited studies have been reported on few operating points.

1.6.
BUTANOL

Though
ethanol and methanol have been the widely investigated by researchers for
powering internal combustion engines, the use of butanol is gaining importance.
Butanol is a viable renewable fuel as it can be produced by the fermentation process
from agricultural feed stock that are normally used for producing ethanol. In
addition, butanol has several properties that are closer to both gasoline and
diesel as compared to methanol and ethanol. It is a more complex alcohol as
compared to ethanol and methanol as it has a four carbon atoms in its molecule.
It has oxygen which can lead to reduction in soot. Its latent heat of
vaporisation is high which helps in reducing temperature and NOx emission. Butanol
has higher heating value and density as compared to the other alcohols. Its low
vapour pressure leads to problems in starting in SI engines. Butanol is less corrosive
and less prone to water contamination than ethanol so it is easy to be
transported and distributed using existing fuel supply infrastructure. Butanol
is found to be a viable alternative renewable fuel. N-butanol is being
evaluated for its suitability for use in CI engines as its properties are close
to those of diesel and gasoline. The properties of
methanol, ethanol, n-butanol, gasoline and diesel are discussed later.

1.7. MOTIVATION

Use
of alternative fuels in dual fuel operation along with common rail direct
injection of diesel carries a promising future in terms of improvement in fuel
economy, reduction in emissions and dependence on fossil fuels. In existing
diesel engines alternate fuel like alcohols can be used with minimum
modification. Strategies for controlling the dual fuel operation, identifying
the range of operation and implementing in production engine are very
essential. Modification of a common rail direct injection diesel engine for
dual-fuel operation and experimental study on dual-fuel operation is therefore
very challenging and rewarding. Only few studies are reported in this context
that too at a limited engine operating loads and energy shares.  

1.8. PRESENT WORK

In this work a
turbocharged three cylinder automotive common rail diesel engine was modified
to operate in the n-butanol diesel dual fuel mode. Detailed experiments have
been done using this system to study the effect butanol to diesel energy share
(BDES) and BMEP on combustion, performance and emission characteristics of a
turbocharged common rail duel fuel engine. Influence of different injection
strategies of diesel, injection timing of diesel and their offsets, rail
pressure and power output on performance, emissions and combustion of an automotive
compression ignition engine was studied in dual fuel mode of operation. Since
butanol is an emerging renewable alternative fuel has properties that are close
to those of diesel and not much work is available in literature on its use in
engines, it was chosen as the main fuel along with diesel in this work. Experiments
were also conducted with manifold injection of blends of water-butanol and
ethanol-butanol under certain operating conditions in dual fuel mode of
operation

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