CHAPTER-I

Literature Survey and Introduction to the problem

CHAPTER-I

Literature Survey and Introduction to the problem

Particulate matter (PM) and oxides of nitrogen (NOx emissions) are the two

important harmful emissions in diesel engine. Fuel companies and the researchers around

the world are devoted to reduce such emissions with different ways. Fuel modification,

modification of combustion chamber design and exhaust after treatment are the important

mean to alleviate such emissions. In this context, engine researchers are hunting suitable

alternative fuels for diesel engine. Among different alternative fuels, oxygenated fuel is a

kind of alternative fuel. Diethylene glycol dimethyl ether (DGM), dimethoxy methane

(DMM), dimethyl ether (DME), methyl tertiary butyl ether (MTBE), dibutyl ether (DBE),

dimethyl carbonate (DMC), methanol, ethanol and diethyl ether (DEE-a Cetane

Improver) have played their role to reduce diesel emissions. These fuels can either be

used as a blend with conventional diesel fuel or as a neat fuel.

The presence of oxygen in the fuel molecular structure plays an important role to

reduce PM and other harmful emissions from diesel engine. The present work reports on

the effect of oxygenated fuel on diesel combustion and exhaust emissions. It has been

found that the exhaust emissions including PM, total unburnt hydrocarbon (THC), carbon

monoxide (CO), smoke and engine noise were reduced with oxygenated fuels. NOx

emissions were reduced in some cases and were increased depending on the engine

operating conditions. The reductions of the emissions were entirely depended on the

oxygen content of the fuel. It has been reported that the combustion with oxygenated fuels

were much faster than that of conventional diesel fuel. This was mainly due to the oxygen

content in the fuel molecular structure and the low volatility of the oxygenated fuels.

1.1 Review on additive application in general:

This review was to investigate the effect of several oxygenated fuel additives,

having a range of boiling points and other properties, on emissions from diesel engines

with alternate fuels and petro-diesel. As per Ullman T and Mason R (1990) the

oxygenates were blended with no. 2 diesel fuel at 1 and 2 wt % oxygen, and the effect on

emissions was measured by the hot start portion of the heavy-duty transient test 40 CFR,

Part 86, Subpart N. Testing was performed in both 2-stroke and 4-stroke diesel engines.

The hardware is typical of current on-road engine technology and has been extensively

used for fuel emission studies. According to EPA Complex Model. Fed. Regist. (1994)

the oxygenated fuels have a history of reducing exhaust emissions from motor vehicles.

Additions of methyl tertiary butyl ether (MTBE) and ethanol have been successful in

reducing CO and non-evaporative hydrocarbon emissions from gasoline engines. The

success of oxygenated gasoline has sparked interest in the use of oxygenated compounds

as particulate matter (PM) emissions reducing additives in diesel fuel. Bennethum and

Winsor (1991) examined the oxygenated compound diglyme diethylene glycol dimethyl

ether in a 2-stroke engine.

Heavy- duty transient test results with the treated fuel showed a 6% CO and PM

reduction at 0.5 vol % diglyme. At 5% diglyme, a 13% CO reduction and a 20% PM

reduction were observed while HC and NOx remained unchanged. Winsor R.E. (1993)

reported further work in which dimethyl carbonate was added to diesel at 3.5 wt %

oxygen. PM and CO reductions were approximately 15%. NOx emissions showed a 1.8%

increase while HC emissions were unchanged. The neat methyl esters of rapeseed oil and

soybean oil were also tested. HC, CO, and PM were decreased approximately 75%, 50%,

and 30%, respectively, for both methyl esters. NOx emissions have increased by

approximately 18%. Graboski M. S. et al. (1996) in their paper measured emissions from

100% methyl esters of soy bean oil and blends of this material with no. 2 diesel in a 4-

stroke engine. Substantial particulate emissions reductions were observed at all oxygenate

levels. They observed a statistically significant 1% increase in NOx at 2 wt % oxygen in

the fuel and higher NOx increases at higher oxygen levels.

Liotta and Montalvo (1993) investigated the emissions effects of three glycol

ethers, an aromatic alcohol, an aliphatic alcohol, and a polyether polyol using a 4-stroke

engine. The actual structures of these compounds were not revealed. Methyl soy ester and

diglyme were also included for comparison to previous results. Based on heavy-duty

transient testing, CO was generally reduced and NOx showed an increase with all

oxygenates studied. The PM reduction experienced appeared to be related to the amount

of oxygen in the fuel. Unregulated emissions of aldehydes and ketones were reported to

decrease. Nikanjam (1993) examined ethylene glycol monobutyl ether acetate as a diesel

additive based on cost, fuel blending properties, and toxicity concerns. Emissions results

from a 4-stroke engine showed CO and PM reductions of approximately 18% and a NOx

increase of 3% for 3 wt % oxygen in the fuel. More recently, Ullman et al. (1994)

reported the effect of oxygenates and other fuel properties on emissions from a 1994

Model Detroit Diesel Series 60, 4-stroke engine. Monoglyme and diglyme were used as

oxygenates at the 2% and 4% oxygen levels. The engine was run with 5 and 4 g/bhp.h

NOx calibrations 1994 and 1998 emissions standards, respectively.

Statistical models of the emissions dependency on fuel composition were

developed with weight percent oxygen as the oxygenate variable. At 2% Oxygen and

constant aromatic content and Cetane number, the model predicts a 1.5% increase in NOx

for the 5-gram calibration and a 0.9% increase for the 4-gram calibration. FEV Engine

Technology (1994) investigated various soy ester blends with diesel in comparison to

diesel using a 13-mode steady-state test with the Navistar 7.3 L engine. FEV found that

NOx increased with biodiesel under all conditions of speed and load. Soy ester blends

reduced particulate at high speed and at all loads. At lower speeds, particulate was

reduced at light and heavy loads but was increased at intermediate loads. McDonald et al.

(1995) examined emissions from blends of diesel and soy bean oil methyl esters for off-

road mining applications using the ISO 8178-C1 8 mode off- highway test. Mutagenicity

with soy ester and a diesel oxidation catalyst was reduced to half that of conventional

diesel. The reduction in muta-genicity is due to a reduction in PAH. Formaldehyde

emissions were not significantly increased using soy ester blends with the diesel oxidation

catalyst. Rantanen et al. (1993) report similar results. These studies, combined with results

on aldehydes and ketone emissions reported by Liotta and Montalvo (1993) suggest that

the use of oxygenates in diesel does not lead to an increase in emissions of reactive

aldehydes and similar species. Krahl et al. (1996) in their recent studies, however,

indicates substantial increases in engine out aldehydes emissions. Clearly, aldehydes

emissions are a major concern for diesel oxygenates and should be measured in all future

studies.

The studies cited above clearly indicate that substantial reduction in particulate

emissions can be obtained through the addition of oxygenates to diesel fuel. Because

diesel particulate is essentially all smaller than 1 micron and Johnson et al. (1994) some

studies relate ambient fine particulate levels to adverse health effects (Schwartz, J1996),

National Resources Defense Council, New York (1994), Health Effects Institute,

Washington(1995), and Environment Protection Agency Washington-(1993) the addition

of oxygenates to diesel fuel could have significant public health benefits. However, many

oxygenates also appear to increase emissions of NOx. Nitrogen oxides can be a limiting

reactant for Ozone formation in some areas (Sloss L -1991) and, in other areas, are an

important source of fine secondary particulate (Bowman-1992). Therefore, fuels

producing an increase in emissions of NOx will be unacceptable under the are to be-

proposed. Substantially Similar Rule for diesel fuels (Kortum -1995). Many of the

oxygenates tested to date, especially vegetable oil methyl esters, have a number of

properties not typical of diesel fuels such as higher boiling point, viscosity, and surface

tension that may contribute to the increased NOx emissions.

In the (Robert et al. 1997) investigation, it was tested several oxygenates with a

range of properties as part of an effort to discover oxygenates or properties of oxygenates

that produce a particulate reduction without increasing NOx. The testing was performed

in Denver, CO, at an altitude of 1609 m (5280 ft) above sea level. Previous works at this

laboratory (Graboski M. G et al. 1996) as well as high-altitude simulation studies reported

by Southwest Research Institute (Human, D. M et al. (1990), Chaffin, C.A et al. 1994)

indicate that heavy-duty transient PM emissions can be much higher at altitude than

observed at sea level. For turbo-charged engines, the PM increase noted in all three of the

cited studies was in the range of 50-100%. CO emissions are also observed to increase.

However, altitude has not been observed to effect NOx emissions from turbo- charged

engines. The effect of diesel fuel Cetane number and aromatic content on NOx and PM

emissions is proportionally the same at altitude as at sea level (Graboski, M. G et al.

1996) although, as noted, the level of PM emissions is much higher.

1.2 Literature about Oxygenated fuels and mixed trials to reduce pollution levels:

Due to price hike in 80’s and the rapid depletion of fossil fuels researchers

concentrate their research on alternative fuel. Methanol and ethanol were proved to be

effective alternative fuels long ago for internal combustion (IC) engines. The oxygen in

the methanol and ethanol molecule helps to make complete combustion when combusted

with atmospheric oxygen. Most recently, DME, oxygen content of 34.7% has been

noticed as one of the promising alternative fuels for IC engine. DME can be derived from

natural gas, coal or even from biomass sources. Zhang et al. (2008) reported lower diesel

emissions including smoke, THC, carbon dioxide (CO2), NOx, while slight increase in

CO was noticed with DME compared to those of conventional diesel fuel. Authors

reported the reason of reducing exhaust emissions were the presence of oxygen in the

DME, absence of C-C bond, shorter ignition delay and the instantaneous vaporization of

DME. Like DME, DEE is another oxygenated fuel that has a very high Cetane number.

Masoud et al. (2008) reported lower smoke and THC emissions due to higher

Cetane number and Oxygen content of DEE. Authors also found lower CO emissions at

high load condition, but higher at low load condition. Also lower NOx emissions were

realized with DEE-diesel blends. Kapilan et al. (2008) conducted experiments with 5 %

DEE and found lower CO, THC and smoke emissions while a slight improvement in

thermal efficiency was observed. Yeh et al. (2001) investigated the effect of fourteen

different oxygenated fuels on diesel emissions, especially PM and NOx emissions.

Authors found that for PM reduction, the most effective oxygenates on equal oxygen

content basis were the C9 – C12 alcohols in both the engine and vehicle testing.

(source: Nurun Nabi)

No significant NOx emissions was increased with the oxygenates. The effects of

liquid oxygenated fuels on diesel combustions are discussed in this work as many

researchers worked on liquid oxygenated fuels. The advantages of using liquid fuel are:

easy transportation, easy injection to the combustion chamber and require less space to

store. The role of fuel oxygen on PM and NOx emissions is investigated with the previous

research works. The target of the work is to make a correlation between fuel oxygen and

the exhaust emissions.

Fujia et al. (2008) investigated the effect of fuel oxygen on total PM and other

exhaust emissions. THC emissions with all biodiesel reduced from 45-67%. Like THC,

CO emissions were reduced by 4-16% with the biodiesels. On the other hand, NOx

emissions were increased with the addition of fuel oxygen content. Authors extended

their research with three oxygenated fuels like ethanol, DMC and DMM. 10-30% ethanol

was blended with PME, 10-20% DMC was added to WME and 10-20% DMM was added

to DMM. The reductions in PM, THC and CO emissions and the increase in NOx

emissions were due to the oxygen content in the fuel.

Zannis et al. (2004) conducted engine experiments with oxygenated fuels. They used

two oxygenated fuels, such as Diethylene Glycol Dimethyl Ether Diglime (C6H14O3) and

Diethylene Glycol Dibutyl Ether Butyl-Diglime (C12H26O3), and one biodiesel (RME).

These two oxygenated fuels and RME were blended with conventional diesel fuel (DF)

maintaining oxygen content of 3 to 9%. The effect of fuel oxygen content on exhaust

emissions at various engine loads was investigated. Authors reported relative changes of

emissions between base fuel (diesel fuel) and oxygenated fuels. Soot, CO and THC

emissions were reduced with increasing oxygen content for all loads. The reductions were

higher for higher percentage of oxygen (9%) in the fuel blends and at high load condition.

Authors reported that the reduction of soot, THC and CO emissions with increased fuel

oxygen, which prevent to form soot emissions as less available carbon in fuel molecule.

Authors also reported that the increase of local oxygen concentration enhances soot

oxidation. On the other hand, NOx emissions were increased for higher oxygen content in

the fuel. The additional oxygen in fuel rich region in conjunction with the increase in gas

temperature due to the increase of cylinder pressure during combustion phase favors the

formation of thermally generated NOx emissions.

(source: Nurun Nabi)

Nabi et al. (2006) performed engine experiments with different oxygenated fuels.

The author investigated the effects of fuel oxygen on diesel emissions and combustion. In

Figure 1.2, PM emissions were shown with soluble organic fraction (SOF) and insoluble

fraction (ISF), which is actually termed as dry soot. The results in Figure 1.2 show the

PM with neat diesel fuel, DGM100 and ENB100. In Figure 1.2, only DGM was added to

the conventional diesel fuel at volumetric percentages of 0, 25, 50, 75 and 100. Author

concluded that it was oxygen, not the kinds or the chemical structures of the oxygenated

fuels, was responsible for lower exhaust emissions. NOx emissions were also reduced

with the oxygenated fuels Figure 1.3. The author also found the lower adiabatic flame

temperature which caused the lower NOx emissions with oxygenated fuels. Author

extended their research applying EGR in the exhaust system. Using EGR and an

oxygenated fuel DGM, remarkable reductions in both smoke and NOx emissions were

realized compared to those of diesel fuel.

(source: Nurun Nabi)

Nabi et al. (2006) also attempted smokeless stoichiometric diesel combustion with

a combination of high EGR, highly oxygenated fuels and a three way catalyst. Figure 1.4

shows the smoke emissions with Dimethoxy methane (DMM) and different kinds of

highly oxygenated liquid fuels at stoichiometric and high 30 vol % EGR conditions. The

smoke emissions formed easily at these conditions. Neat DGM and DGM based fuels

blended with ordinary diesel fuel or different kinds of oxygenated fuels shown in Table

1.1 Table 1.1 Oxygen content and molecular formula of different oxygenated fuels

Oxygenates Oxygen Molecular Formula

Dimethyl carbonate (DMC) 53.30 C3H6O3

Diethyl Ether (DEE) 21.00 C4H10O

Diethylene glycol diemthyl ether (DGM) 35.82 C6H14O3

Di-n-butyl ether (DBE) 12.30 C8H18O

Dimethoxy methane (DMM) 42.10 C3H8O2

Ethyl hexyl acetate (EHA) 18.60 C10H20O2

Methyl tert-butyl ether (MTBE) 18.18 C5H12O

Ethylene glycol di-t butyl ether (EDTB) 18.40 C6H14O2

Dimethoxy propane (DMP) - CH3)2COCH3)2

2-Methoxyethyle acetate (MEA) 40.70 CH3COOCH2CH2OCH3

Methanol (MeOH) 50.00 CH4O

Ethanol (EtOH) 34.78 C2H6O

Palm oil methyl ester (PME) 11.20 -

Waste cooking oil methyl ester (WME) 11.30 -

Cottonseed oil methyl ester (CME) 10.60 -

Rapeseed oil methyl ester (RME) 10.50 -

PME 90% +EtOH 10%) (PE10) 13.50 -

PME 80% +EtOH 20%) (PE20) 15.50 -

PME 70% +EtOH 30%) (PE30) 17.70 -

WME 90% + DMC10% (WDMC 10) 16.20 -

WME 80% + DMC20% (WDMC 10) 21.10 -

WME 90% + DMM10% (WDMM 10) 14.20 -

WME 80% + DMM 20% (WDMM 20) 17.30 -

(source: Nurun Nabi)

From Figure 1.4 it is observed that smoke emissions decreased sharply and

linearly and became zero at an oxygen content of 38%. The smoke free diesel combustion

was also confirmed with two other oxygenated fuels of oxygen content of 40 and 42%.

From this study it was suggested that DGM80+MeOH20 oxygen content of 38%,

DGM80+DMC20 oxygen content of 40% and DMM100 oxygen content of 42% were

suitable for partial load high EGR and high load stoichiometric diesel combustion.

(source: Nurun Nabi)

Figure 1.5 shows the influence of EGR on NOx emissions using DMM100.

DMM100 realizes smoke free diesel operation at any engine conditions as discussed in

Figure 1.4. The extreme right end points of Figure 1.5 represent to the stoichiometric

condition where a three-way catalyst is believed to be effectively reduce NOx emissions.

High reductions in NOx emissions with a three-way catalyst are difficult but significantly

low NOx emissions were achieved by applying high EGR 30% at different excess air

conditions. It can be seen also from the Figure1.5 that 30% EGR produces NOx

emissions below 100 ppm at any excess air condition. With oxygenated fuel and

stoichiometric diesel operation significantly increase the maximum BMEP, which was

found to be as high as 0.9 MPa without applying EGR. To achieve ultra low diesel

emissions, author incorporated a three way catalyst in a diesel exhaust system. Figure 1.6

shows the influence of a three way catalyst on three diesel emissions in partial load high

EGR and high load stoichiometric diesel operation using DMM100. It can be seen from

the Figure 1.5 that the NOx emissions were reduced to as low as 100 ppm, while the

THC and CO emissions were found to be about 200 ppm even at stoichiometric condition

and without applying EGR. Thus it can be concluded that extremely low NOx and smoke

free diesel operation was realized with the combination of a three way catalyst, high EGR

and DMM100.

Anand et al. (2007) investigated the influence of EGR and oxygenated fuel on

diesel combustion and exhaust emissions. Authors used DEE as oxygenated fuel and

blended with diesel fuel up to 30 vol%. Authors incorporated 5% EGR using 20 vol%

DEE to diesel fuel. Without applying EGR, lower NOx emissions were resulted from

DEE blended fuels compared to diesel fuel, while higher smoke emissions were realized

with the same blends. NOx emissions were reduced maximum with 15% EGR using 20

vol% of DEE to diesel fuel. At full load under 15 vol% EGR conditions with 20 vol%

DEE, the smoke emissions were reduced to 2.1 Bosch smoke units (BSU) from the

baseline smoke level of 4.2 BSU. The reductions were due to the oxygen availability in

DEE, which supplies oxygen during combustion.

Figure 1.6. Influence of a three way catalyst on diesel emissions (source: Nurun Nabi)

Miyamoto et al. (1996) conducted experiments with eight kinds of oxygenated

fuels to investigate the effect of low content oxygenate additive maximum of 10 vol% on

diesel emissions. The oxygen contents of the neat oxygenated fuels were ranging from

12.3 to 53.3 wt%. When blended these oxygenates with conventional diesel fuel,

particulate and smoke emissions were oppressed significantly without increasing NOx.

THC and CO emissions were also decreased slightly. Oxygen content in the blended fuels

and the low volatility of the fuel were the reasons for decreasing the emissions.

Sathiyagnanam et al. (2008) conducted diesel engine experiments with DMM

and dimethoxy propane (DMP). Authors blended 1 ml to 3 ml of DMM & DMP as

additives to diesel fuel. They conducted the experiments by introducing a diesel

particulate filter (DPF). The experimental results were compared with and without DPF

using the two oxygenated additives DMM and DMP and diesel as a base fuel. It was

found that smoke and PM emissions were reduced with the addition of DMM and DMP to

diesel fuel. Smoke and PM emissions reduction was higher with DPF. NOx emissions, on

the other hand were higher with DMM and DMP blended fuels. It was reported that NOx

emissions were higher by 13 g/kWh with DMM and 16 g/kWh by DMP. Lu et al. (2005)

investigated the spray characteristics and diesel exhaust emissions with three oxygenated

fuels, namely ethanol, DMC and DMM.

1.3. Hybrid fuels application:

Authors investigated the spray characteristics Sauter mean diameter (SMD) and

axial mean velocity distribution) with DMM-diesel hybrid fuels, while the engine

experiments were performed with DMC-diesel hybrid fuels. For spray analysis DMM was

blended to diesel fuel at blending ratios of 25 and 50 vol%, while for DMC the ratios were

10, 20 and 30 vol%. It was found that the droplet diameter of the DMM-diesel hybrid

fuels decreased with increased axial distance from the injector tip. Compared to diesel

fuel, the mean axial velocities of DMM-diesel hybrid fuels were higher. The lower SMD

and higher axial mean velocity with DMM-diesel hybrid fuels were due to the inherent

properties of lower kinematic viscosity and surface tension of neat DMM. Concerning

exhaust emissions it was reported that the smoke and NOx emissions were reduced

markedly with DMC-diesel hybrid fuels. The reductions were higher with the higher

percentages of DMC to diesel fuel. The reduction of NOx emissions was due to the

shorter combustion duration, while presence of oxygen in hybrid fuels was additional

reason for reduction in smoke emissions.

Wang et al. (2009) carried out engine experiments with several oxygenated fuels

like biodiesel, ethanol, DMM and DMC. They made different oxygenated blends with

diesel fuel. The biodiesels used in the experiments were derived from palm oil, waste

cooking oil and acidified oil. It was found that the dry soot in PM emissions decreased

significantly as the fuel oxygen content increased. SOF, which is a constituent of PM

were found to be higher. Authors also investigated the effect of Cetane number on SOF

emissions. It was found that with the increase in fuel Cetane number SOF emissions

decrease. Authors found that an oxygenated fuel blend of 50% biodiesel, 15% DMC and

35% diesel fuel oxygen content of the blend is 15.46%) met the Chinese 4th stage

standard, which is equivalent to Euro IV for heavy duty engines without modifying or

using any after treatment device. Yanfeng et al. (2007) did experiments with a new kind

of oxygenated fuel, 2-methoxyethyl acetate (MEA) of oxygen content of 40.7 wt%.

Authors reported significant reduction in smoke emissions with MEA blends. THC and

CO emissions were also reduced with higher blending percentages of MEA to diesel fuel.

However, the MEA blends had almost no effects on NOx emissions. Authors suggested

that 15% MEA blend is suitable for diesel emissions, engine power and fuel economy.

Guo et al. (2005) attempted engine experiments with a new oxygenated fuel,

methyl 2-ethoxyethyl carbonate (MEEC) by introducing an ether group to DMC

molecule. MEEC was blended with diesel fuel from 15 to 25 vol%. For a 25% MEEC

blend with full load condition, CO was lessened by 29.2 to 40.5%, smoke by 0.3 to 0.5

BSU. NOx emissions were also lessened by 15.9% when the 15% MEEC was blended

with diesel fuel. Output power of the engine was not noticeably changed with MEEC

blends; however 2.5 to 5.5% fuel consumption was increased with 20% MECC. BSEC

was improved by 10% when the engine was fuelled with 20%MECC. Cheng et al. (1999)

carried out experiments with two oxygenates, DMM and DEE blended with conventional

diesel fuel and a Fischer-Tropsch (F-T) diesel fuel to investigate their exhaust emissions

reduction potential. Both DMM and DEE reduced PM emissions. Like PM, NOx

emissions were also reduced with these blends. 35% less PM was observed with DMM30,

while 30% less PM emissions were resulted in with DEE30. Compared to diesel fuel, F-T

fuel also reduced PM emissions by 29%. NOx emissions, on the other hand were reduced

by 1-10% with F-T, DMM and DEE blends. Fuel conversion efficiency (thermal

efficiency) was reduced with the tested fuels compared to diesel fuel.

Chen et al. (2008) investigated the effect of fuel oxygen on diesel emissions and

performance. Authors blended ethanol and biodiesel to diesel fuel. The blending

percentages of ethanol to diesel fuel were 10, 20 and 30%, while the biodiesel percentages

were 5 and 10%. Engine torque was reduced and BSFC was increased with blended fuels.

Using the diesel ethanol and biodiesel blends the PM was reduced significantly and the

reduction was found to be significant at higher percentages of oxygen in the fuels. NOx

emissions were slightly increased or the same as baseline diesel fuel. THC emissions with

oxygenated blends were reduced under most operating conditions. CO emissions were

increased at low to medium load conditions, but reduced at high load condition. Tat et al.

(2007) investigated diesel exhaust emissions with biodiesel. Authors used soy methyl

ester soy (biodiesel) and high oleic methyl ester to investigate the brake specific NOx,

THC, CO and smoke emissions. Both biodiesels are some sort of oxygenated fuels as

approximately 11 wt% of oxygen is contained in their molecular structures. The brake

specific THC and the smoke emissions were lower with the two biodiesels compared to

diesel fuel. The brake specific NOx emissions with two biodiesels were higher than those

of diesel fuel. The reasons of higher NOx emissions with biodiesels are as follows: the

higher proportion of unsaturated fatty acid compositions in the biodiesels, advance

injection timing leads to earlier ignition, which leads to higher peak cylinder

temperatures. Biodiesels produce less soot than diesel fuel, which may increase NOx

emissions.

1. NOx, smoke and PM emissions with oxygenated fuels were reduced in most cases.

However, the increase in NOx emissions were also reported with oxygenated fuels. The

reductions in emissions were mainly dependent on fuel oxygen. The reductions were

found maximum at the maximum percentage of fuel oxygen.

2. There is an increase in NOx emissions and decrease of soot emissions in the case of

biodiesel which is also an oxygenated fuel with higher percentage of unsaturated fatty

acid compositions. Advance injection timing with biodiesels lead to earlier ignition.

Earlier combustion with biodiesels resulted in higher peak cylinder temperatures which

eventually lead to higher NOx emissions.

3. CO emissions were reduced with all oxygenated fuels at wide operating load ranges.

The reductions were significant at higher load range. The fuel oxygen, which was

responsible for reducing CO emissions made complete combustion in the fuel rich region.

4. Like CO emissions, THC emissions were also reduced with oxygenated fuels for all

loading conditions, but a few reports showed higher THC emissions at lower load

condition.

5. It is established that the reductions in smoke, PM, CO and THC emissions were

dependent on fuel oxygen content. Lower boiling points and lower volatility of

oxygenated fuels were the additional factors for the reduction in these emissions.

6. The engine thermal efficiency was reduced and in some cases increased with

oxygenated fuels.

1.4. Biodiesel with additive application:

The use of Biodiesel in conventional diesel engines results in substantial reduction

of un-burnt hydrocarbons, carbon monoxide and particulate matters. Biodiesel is

considered to be a clean fuel since it has almost no sulphur, no aromatics and has about

10% built-in oxygen, which helps it to burn fully. Its higher cetane number improves the

ignition quality even when blended with the petroleum diesel. Biodiesel has comparable

energy density, Cetane number, heat of vaporization, and stoichiometric air/fuel ratio with

diesel oil. However it suffers from higher viscosity, cold starting problems and increased

nitrogen oxides (NOx) emissions when compared with diesel oil (Agarwal et al. (2007),

Daisuke Kawano et al (2008), Shailendra Sinha et al. (2005), Mustafa et al.( 2007),

Omprakash Bhardwaj et al. (2008), Baiju et al (2009), Dilip Kumar Bora et al.(2009),

Edwin Geo et al. (2008), Iman K et al (2007), Senthil kumar et al. (2001).

The addition of Di-Ethyl Ether (DEE) has been used as an oxygenated additive to

the biodiesel fuel, Jatropha oil methyl ester (JOME) appears to be a promising approach

to reduce emissions especially, NOx or soot and particulate emission, due to its bound

oxygen content 21% (by weight), decrease viscosity. This oxygenate fuel can be

produced easily by dehydration of ethanol, which is a renewable bio-fuel. DEE is

considered as an excellent compression ignition engine fuel having higher energy density

and much higher Cetane number (>125) than ethanol. Though DEE has long been known

as a cold start aid for engines, its knowledge as usage of significant component of a blend

for biodiesel is limited. To identify the potential of DEE as a transportation fuel a

comprehensive literature review was carried out by Baily et al. (1997). Considering the

advantages and obstacles of DEE and biodiesel. Properties of DEE are tabulated in Table

1.2.

The author Masoud Iranmanesh et al (2008) has used 5 to 20 vol% DEE as a

supplementary oxygenated fuel with KOME (Karanja oil methyl ester) The results have

shown a significant reduction in NOx emissions especially for DEE addition of more than

10% on a volume basis and a little decrease in smoke of DEE blends compared with neat

KOME. It has been found that the 15% DEE-KOME gives better performance and

emission characteristics. Anand & Mahalakshmi (2007) have shown that a 20% DEE in

diesel along with 5% EGR result in the simultaneous reduction of smoke and NOx

emission. The purpose of this investigation is to analyze the effect of DEE as a

supplementary oxygenated fuel along with JOME as baseline fuels on reduction of NOx

and smoke emissions simultaneously. It is also desired to find out optimum amount of

DEE to blend with JOME on the basis of performance and emissions characteristics.

1.5. Focus on DEE application:

Masoud Iranmanesh et.al (2008) conducted experiments on the potential of

Diethyl Ether (DEE), which is a renewable bio-based fuel has been identified as a

supplementary oxygenated additive to improve fuel properties and combustion

characteristics of biodiesel Karanja oil methyl ester – (KOME) like its high viscosity,

cold starting problems and a high level of NOx emissions through an experimental

investigation. The tests were conducted on a single cylinder DI diesel engine fueled with

neat KOME as a base fuel and blends of 5, 10, 15 and 20% DEE on a volume basis. Some

physicochemical properties of test fuels such as heating value, viscosity, specific gravity

and distillation profile were determined in accordance to the ASTM standards. The results

obtained from the engine tests have shown a significant reduction in NOx emissions

especially for DEE addition of more than 10% on a volume basis and a little decrease in

smoke of DEE blends compared with neat KOME. A global overview of the results has

shown that the 15% DEE-KOME blend is the most effective combination based on

performance and emission characteristics. Biodiesel has comparable energy density,

Cetane number, heat of vaporization, and stoichiometric air/fuel ratio with diesel oil

(Agarwal A.K., 2007). However it suffers from higher viscosity, cold starting problems

and increased nitrogen oxides NOx) emissions when compared with diesel oil.

Utilization of Diethyl ether (DEE) as an oxygenated additive supplementary fuel)

to the biodiesel Karanja oil methyl ester – (KOME) fuel appears to be a promising

approach to reduce emissions especially NOx or soot and particulate emission due to its

bound oxygen content 21% (by weight), and decreased viscosity. This oxygenate fuel can

be produced easily through dehydration of ethanol which is a renewable bio-fuel. Among

the alternative fuels, biodiesel and ethanol are the most widely studied biofuels for diesel

engines and have received considerable attention in recent years. Ethanol, however, is not

a high quality compression ignition fuel. Ethanol can be easily converted, through a

dehydration process, to diethyl ether (DEE), which is an excellent compression ignition

engine fuel with higher energy density and much higher Cetane number ( >125) than

ethanol. DEE has long been known as a cold start aid for engines (Tomoko Kito et al.

(1998), Clothier et al. (1990), but knowledge about using DEE as a significant component

of a blend for biodiesel is limited. The important properties of diethyl ether are given

below in Table 1.2.

Table 1.2 Important Properties of Diethyl Ether

(Source: Bailey et al. 1997)

Properties DEE

Chemical Structure C2H5-O- C2H5

Density(kg/m3) 713

Viscosity(C.P.) mm2/sec (20

0C) 0.23

Auto Ignition point (0 0C) 160

Lowe heating Value(MJ/kg) 33.9

Cetane Number >125

rich

Flammability limit(% vol)

lean

9.5 to 36

1.9

Oxygen content (%Wt) 21

Boiling point (0 0C) 35

Stoichiometric A/F Ratio 11.1

Latent Heat of Vaporization (kJ/kg) 356

To identify the potential of DEE as a transportation fuel a comprehensive literature

review was carried out by Baily et al. (1997) considering the advantages and obstacles of

DEE and Biodiesel. Utilization of their combination in a suitable ratio can amplify their

advantages and over- come their shortcomings. Some researchers have studied the use of

DEE as an ignition improver for diesel fuel (Venkatachalam et al. 2003), added it to

diesel-water emulsions (Subramanian et al. 2002) or with LPG in a diesel engine (Miller

et al. 2006). Mixtures of ethanol-DEE as a fuel have been studied in an alcohol diesel

engine (Gjirja et al. 1998) and in an HCCI engine (Macka et al. 2005). Gjirja et al. (1998)

used DEE as an ignition improver directly by blending or separately fumigating it in an

alcohol diesel engine at different injection timings. The authors had derived the optimum

fraction of ETOH/ETOH+DEE) to be between 40 and 60% and for both techniques the

amount of 50% DEE and 50% ETOH with earlier injection timing led to a shorter ignition

delay and better performance.

Iranmanesh et al. (2008) had carried out a detailed investigation on the effect of

using diesel-DEE blend with 5, 10 and 15% by weight of DEE in a DI diesel engine. The

optimum quantity of DEE, based on the thermal efficiency, along with advanced injection

timing, was found to be 10%. Tests showed that the blend decreased the smoke and CO

level drastically at all loads and increased the brake thermal efficiency at high load

without affecting NOx emissions. It also increased the peak heat-release, peak pressure

and maximum rate of pressure rise. The author has used 2 to 10 vol% DEE as a

supplementary oxygenated fuel with diesel fuel to improve the fuel properties, emission

and combustion characteristics through an experimental investigation earlier. It was found

that 5% DEE-Diesel blend is the most effective combination based on performance and

emission characteristics. It is in agreement with the results obtained by Mohanan et al.

(2003).

Annand et al. (2007) also has achieved the simultaneous reduction of oxides of

nitrogen NOx) and smoke emissions by using 10 to 30% DEE by volume along with 5 to

15% EGR through an experimental investigation on a diesel engine. They found that 5%

EGR operated with 20 vol. % DEE–diesel blend to be favorable. Literature review has

shown that DEE has not been used as a partial substitution in biodiesel to improve

combustion and emission characteristics. The purpose of this investigation is to analyze

the effect of DEE as a supplementary oxygenated fuel along with biodiesel (KOME) on

emission and performance of diesel engine to match the benefits of biodiesel (KOME)

such as its lower HC, CO and smoke emissions and to decrease their NOx productions

which increase in biodiesel fuelled engines. It can also overcome the barriers of biodiesel

utilization like its high viscosity and cold starting problem. It is also desired to find out

optimum amount of DEE to blend with KOME based on performance and emission

characteristics. Biodiesel which is used in this test was a ready-made methyl ester of

Karanja Indian local name oil (KOME). The scientific name is Pongamia Pinnata .It

contains approximately 10% oxygen and its Cetane number varies between 47 and 58 and

it can be adopted as an alternative fuel for the existing conventional diesel engines

without any major modifications (Srivastava et al (2007), Naik et al 2007).

More details about its properties, characterization, oil extraction and trans-

esterification process are mentioned in different references (Agarwal et al. (2007),

Raheman et al(2004), Srivastava et al (2007), Sharma,Y.C et al (2007), Naik, Malaya

(2007) ). Four blends of diethyl ether in KOME were tested, namely, 5% (B-D5), 10% (B-

D10), 15% (B-D15) and 20 % (B-D20) by volume.

Salient features of the conclusions that were drawn based on this experimental

investigations using various KOME- DEE blends are as follows:

Addition of DEE improved the physicochemical properties of KOME with respect

to viscosity, density, boiling point and distillation profile. The heating value of the blends

reduced with addition of DEE. Front-end volatility of the blends improved by addition of

DEE, Which in turn improved the cold starting property. From the various KOME-DEE

blends tested, the 15% KOME-DEE was found to be the optimum blend on the basis of

emission and performance characteristics. Use of DEE addition to KOME increased BTE

in general due to its oxygen content and its effect on lowering the viscosity of the blend,

which led to improved spray formation and finally an improvement in the combustion.

BTE increased 5.5% with 15% KOME-DEE blend. Smoke opacity slightly reduced with

KOME-DEE blends. Addition of 15% DEE gave the lowest level of smoke at no load and

part load conditions; whereas 20% and 10% DEE had the minimum level of smoke at

higher and full load conditions respectively. NOx emission of the DEE blends decreased

drastically. The effect of DEE on NOx reduction was more effective than on other

emissions. Addition of 15% and 20% DEE reduced NOx by 40% and 51% respectively.

CO did not show significant change with DEE blends at no load and part load conditions

but at full load, it rose considerably with 15% and 20% DEE. HC increased with DEE

blend at no load and part load but at full load there was no significant change.

Studies on using biodiesel as fuel in diesel engines have shown greater reduction

in emissions of hydrocarbons, smoke, particulate matter, oxides of sulphur and carbon and

polyaromatics as compared to diesel (Graboski & McCormick, 1997, Wang et al.( 2000),

Agarwal et al.(2001), Kalligeros et al. (2003), Ramadass et al. (2005), Hanumantha Rao

et al. (2009), Hariharan et al. (2009). However, the studies on direct injection diesel

engines have shown an increase in oxides of nitrogen (NOx) (Serdari et al. (2000),

Shailendra et al. (2005), Nabi et al. (2006). The NOx emissions are known to contribute to

the formation of ground level ozone and fine particles that impair visibility. Retarding

fuel injection timing can reduce NOX with a loss of some effectiveness for particulate

matter reduction and a loss of fuel economy. The other approach to reduce NOx emissions

to a level equal to that from conventional diesel engine is to increase the Cetane number

of the fuel. Chemicals such as alkyl nitrates and certain peroxides can serve as Cetane

improvers. Serdari et al. (2000) used iso-octyl nitrate and a combustion improver for

reducing the NOX emissions from a single cylinder diesel engine fuelled with biodiesel.

Szybist et al. (2005) used 2-ethyl hexyl nitrate as fuel additive in B20 blend to combat

the NOx emission.

In the present work, the effect of adding diethyl ether (DEE) to biodiesel blends

was studied. DEE can be produced by dehydration of bio-ethanol, a renewable fuel. DEE

has long been recommended as a cold starting additive in diesel engines and gasoline

engines due to its low auto ignition temperature and high volatility Gupta et al (1988).

The properties of DEE permit it to be used as a fuel for compression ignition engines,

either as a neat fuel or as a blend with diesel. The auto ignition temperature of DEE is

lower than diesel. DEE has a high cetane number of greater than 125. Its heating value is

comparable to that of diesel. The latent heat of vaporization is higher than diesel. DEE is a

liquid at room temperature which reduces handling and storage problems. DEE is also

non-corrosive compared to alcohols. The properties which need concern are its high

flammability and poor storage stability. DEE also poses human health problems due to its

anesthetic effect.

DEE as a fuel additive has shown to offer beneficial effects in terms of both

performance and emissions. Anand et al. (2007) have showed that a 20% DEE in diesel

along with 5% EGR result in the simultaneous reduction of smoke and NOX emission.

Recently, Ramadhas et al. (2008) studied the use of DEE as a fuel additive for reducing

the cold starting problem and to improve the performance and emission characteristics of

a diesel engine fuelled with biodiesel. In the work, pongamia oil derived from the seeds

of Pongamia pinnata is used to produce biodiesel. P. pinnata has been recognized as one

of the most suitable among other plant species such as Jatropha curcus and Madhuca

indica for producing biodiesel. The tree is tolerant to water logging, saline and alkaline

soils and it can withstand harsh climates and planted on degraded boundaries of farmer’s

land or wastelands. It is one of the few nitrogen-fixing trees producing seeds containing

30- 40% oil (Barnwal et al. (2005).

Pugazhvadivu1 et al. (2009), investigated the effect of adding DEE to biodiesel-

diesel blends (B25, B50 and B75) and biodiesel (B100). DEE was added in 10%, 15% and

20% (v/v) to the biodiesel fuels. All the biodiesel blends produced a higher NOx emission

compared to diesel. With B25 blend, the NOx emission was reduced by the addition of

DEE at all load conditions. With B50, B75 and B100 blends, the NOx emission was

lowered by the addition of DEE at low and medium loads. However, at high loads the

NOx emission was higher relative to diesel; but lower compared to the corresponding fuel

blend. The addition of 15% to 20% DEE was more beneficial in reducing NOx compared

to 10% DEE. The biodiesel blends tested showed a significant reduction in smoke

emission. Further improvement in smoke emission was obtained by the addition of DEE.

The addition of DEE resulted in a marginal deterioration of thermal efficiency. It is

concluded that the addition of 15%-20% DEE to biodiesel blends would result in

reduction of both NOx and smoke emission.

Mohamed Y.E. Selim (2009) worked on reducing kinematic viscosity of Jajoba

Methyl ester by heating and by mixing lower viscous fuel like DEE. Y.E.Salim has not

shown any exhaust gas survey in his paper.

But, the author came out with the following conclusions based on the performance

of the engine:

1. Heating the Jojoba methyl ester fuel – with its high viscosity – helped to

reduce the viscosity to its acceptable range for diesel fuel.

2. Adding very low viscosity renewable oil such diethyl ether helped the JME to

reduce its viscosity to the acceptable range.

3. Heating the JME or adding DEE did not change the exhaust gas temperature or

other cycle temperatures.

4. Heating the JME or adding DEE reduced the ignition delay period for the JME.

5. Adding DEE to the JME caused the maximum pressure rise rate to decrease

slightly than pure JME or pure diesel fuel.

6. Heating the JME did not change much the maximum pressure rise rate.

7. The maximum combustion pressure slightly increased for heated JME or when

DEE is added to JME.

8. Heating the JME increased the maximum HRR at all load ranges tested while

adding DEE affected the HRR)max in different ways according to the load output.

9. Adding DEE to the Jojoba Methyl Ester or heating it resulted in an increase in

the indicated mean effective pressure or reducing the mechanical efficiency.

1.6 Application of additive diethyl ether (DEE) with the Mahua methyl ester.

This cetane additive has got advantages of lower boiling point, substantially lower

viscosity and higher cetane number. The Mahua raw vegetable oil has got a mythological

significance since it is used in temples with its remarkable property of emitting lower

smoke levels when used as fuel for temple lighting inside sanctum sanctorum. Our

ancestors may have recognized this as oil which doesn’t create breathing problems. The

oxygen utility of the blends in different proportions is tested by monitoring the

performance, emissions and engine vibration to identify any engine detonation if any and

conclusions were made thereupon.

1.7 Introduction to the Problem

Biodiesel application in diesel engines has reduced the tail pipe emissions to

appreciable extent. But the NOx emission could not be reduced because of the reason that

biodiesel is an oxygenated fuel containing approximately 11% of oxygen. The

temperature of the combustion is also a precursor to the formation of nitrogen oxides.

Injection retardation reduces the NOx formation but leaves more unburned hydrocarbons

in the tail pipe emissions. In fact, the injection will be advancing due to higher bulk

modulus of the biodiesel and the combustion will be assisted by the higher cetane number

of the bio-fuel. In this scenario, biodiesel properties like viscosity, density, latent heat and

volatility play important role in forming combustible mixture before compression pressure

attains peak value. Diluting the mixture with EGR is also one of the attempts made in

controlling combustion temperatures in order to contain NOx formation.

Several scientists have made attempts by blending additives with biodiesel and

reported as explained in the literature. Now there is greater part of oxygen in the blend

because there is contribution from the side of the main fuel and the additive also.

Substantial divergence in the properties of the independent fuels and the presence of

excess molecular oxygen may change the engine out come in all respects and a trail was

made on a DI diesel engine in the laboratory. The investigation yielded different results in

certain zones of operation of the engine with respect to the main fuel equivalence ratio

and the additive proportion.

The molecular structure of biodiesel and acids contained therein will decide the

engine operation in the presence of the additive DEE. The literature has given substantial

positive report about the application of DEE as an additive. It has been reported in general

that there is substantial reduction in smoke emission and more times about the reduction

in CO emission. NOx emission report is varied based on the biodiesel used and the load

and speed condition of the engine along with additive fraction. The objective in this work

is to identify appropriate blend with respect to the load and keeping all other parameters

like, the injection pressure, timing etc. constant to enable comparison comprehensively.

1.8 Selection of Fuel

The main fuel selection itself is crucial one which contributes more to the better

performance and DEE as an additive and cetane improver (Cetane value >125) is the

second choice to reduce blend viscosity to see that there won’t be any injection problems.

This attempt was made with the peers but with different biodiesel fuel. There may be duel

fuel interaction problems with more additive fuel, and being mixed with faster

development of injection plume in the case of additive has got lower evaporation

temperature. With this kind of injection Flame development, the additive will have to be

exposed to colder regions in advance to the main fuel and there by generating more

unburned HC in the exhaust. Since the carbon molecule range is only C4 extent in the case

of DEE and when it occupies 15% by volume in the blend, most of the carbon atoms are

diminished. Because of occupation by DEE, lesser emissions of CO at engine loads were

tested. By and large, there will be also reduction in CO2 green house gas because of

general reduction in carbon molecules.

Excessive oxygen availability will be conducive to smoke reduction and same is

being ascertained with the experimentation. Some of the general equivalence ratios are

acting positively to economize combustion to see that the emissions are reduced

effectively. The results envisage clearly equivalence ratio zone where in the engine

operation is economical. Even though the exhaust gas temperature depends on the

diffusion combustion criteria, there is a marginal temperature decrease in the case of

additive mixing. This may be acclaimed to the lower boiling point and higher latent heat

of DEE. The next Chapter II deals with Biodiesel preparation which is done with utmost

care to retain the properties of biodiesel nearer to the petro-diesel.