BIODIESEL A RENEWABLE
ALTERNATE CLEAN AND
ENVIRONMENT FRIENDLY FUEL FOR
PETRODIESEL ENGINES: A REVIEW
RASHID ALI
Department of Mechanical Engineering, Z H C E T, Aligarh Muslim University, Aligarh, UP, Pin-202002, India rashid_ali10@rediffmail.com
Abstract:
The paper presented a comparative study of emissions produced by engine using biodiesel as a fuel or in blends with emissions produced by engine using petrodiesel as a fuel. Biodiesel is a renewable fuel that is almost compatible with commercial diesel engines and has clear benefits relative to diesel fuel including enhanced biodegradation, reduced toxicity and lower emission profile. The emissions produced from biodiesel are generally lower than petrodiesel fuel. It can be used either in pure form or as blends on conventional petrodiesel in automobiles without any major modifications. A B20 (refers 20% biodiesel and 80% petrodiesel by volume) blend fuel reduced particulate emissions, carbon mono-oxide and unburned hydrocarbons by 22%, 20% and 30% respectively. Such a blend will give better cold flow properties compared with neat B100 biodiesel (100% biodiesel). A B35 (refers 35% biodiesel and 65% petrodiesel by volume) reduces the amount of particulate matter by about 20%.
Keywords: Biodiesel, Blends, Particulate Matter, Unburned Hydrocarbons, Carbon Mono-oxide, NOx
Emissions
1. Introduction
Biodiesel is a renewable, alternative fuel derived from vegetable oils and variety of fats by a transesterification reaction, thus consisting of the alkyl esters, usually methyl esters, of the fatty acids comprising the parent oil or fat. These methyl esters of fatty acids have some features in common with those components of petroleum-based diesel fuels that make petrodiesel suitable as fuel. Since biodiesel is made entirely from vegetable oil, it does not contain any sulphur, aromatic hydrocarbons, metals or crude oil residues. The absence of sulphur means a reduction in the formation of acid rain by sulphate emissions generating sulphuric acid in our atmosphere. The reduced sulphur in the blend will also decrease the level of corrosive sulphuric acid accumulation in the engine crankcase. The lack of toxic carcinogenic aromatics (benzene, toluene and xylene) in biodiesel means the fuel mixture gases will have reduced impact on human health and the environment. The high cetane rating of biodiesel (49 to 62) is another measure of the additive’s ability to improve combustion efficiency. An engine running on 100% biodiesel would have no aromatic emissions and the biodiesel would be much safer to store and handle, in addition biodiesel blends have reduced emissions of poly aromatic hydrocarbons, another group of potentially carcinogenic substance found in petroleum [1].
and smoke emissions from oxidized and un-oxidized biodiesel. Wang et al. [7] tested eight trucks on pure diesel and with 35% of biodiesel over 5-peak cycle. They found that the trends in NOx emissions were varied with emissions increases or decreases for various trucks. They also found that the particulate matter decreases by about 20%. Similar works also reported by Pramanik [8], Forson et al. [9] and Yuan et al. [10]. Nafis et al. [11] experimentally studied the performance and emission characteristics of a single cylinder diesel engine when fuelled with blends of vegetable oils and diesel oil. They found that the vegetable oils have lower concentrations of nitrogen dioxide and particulate matter for an engine speed of 1500 rev/min.
2. Emission Characteristics of Biodiesel
The use of biodiesel in a conventional diesel engine results in substantial reduction of unburned hydrocarbons, carbon mono-oxide and particulate matter. Emissions of nitrogen dioxide are either slightly reduced or slightly increased depending upon the duty cycle or testing methods. Biodiesel decreases the solid carbon fraction of particulate matter (since the oxygen in the fuel enables more complete combustion to CO2) eliminates the sulphur fraction (as there is no sulphur in the fuel) while the soluble or hydrogen fraction stays the same or increased [12]. Emission results for pure (B100) and mixed biodiesel (B20) compared to conventional diesel are given in Table 1.
Table 1. Biodiesel Emissions Compared to Conventional Diesel
EMISSIONS B 100 B 20
Regulated Emissions
Total Unburned Hydrocarbons - 93 % - 30 % Carbon mono-oxide - 50 % - 20 % Particulate Matter - 30 % - 22 %
NOx + 13 % + 2 %
Sulphates - 100 % - 20 %
Polycyclic Aromatic Hydrocarbons
(PAH) - 80 % - 13 %
Nitrate PAHs (NPAH) - 90 % - 50 % Ozone Potential of Speciated HC - 50 % - 10 %
Life Cycle Emissions
Carbon dioxide (LCA) - 80 % Sulphur Dioxide (LCA) - 100 %
The life cycle production and use of biodiesel produces approximately 80 % less carbon dioxide and almost 100 % less sulphur dioxide compared to conventional diesel. From Table 1 it is clear that biodiesel gives a distinct emission benefit almost for all regulated and non-regulated pollutants when compared to conventional diesel fuel but emissions of NOx appear to increases from biodiesel. NOx increases with the increase in concentration of biodiesel in the mixture of biodiesel and petrodiesel. This increase in NOx may be due to the high temperature generated in the fairly complete combustion process on account of adequate presence of oxygen in the fuel. This increase in NOx emission may be neutralized by the efficient use of NOx control technologies, which fits better with almost nil sulphur biodiesel than conventional diesel containing sulphur.
Number of Cases
P
ar
ti
c
u
lat
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M
at
ter
in
g
m
/B
H
P
-h
r.
0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3
Case I Case II Case III
Figure 1. Shows the particulate matter emissions from the engine for different cases
Number of Cases
C
a
rbon
M
ono-ox
id
e
in
gm/
BH
P
-hr
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0 0.25 0.5 0.75 1 1.25 1.5 1.75 2
Case I Case II Case III
Number of Cases
T
o
ta
l
U
nbu
rn
e
d
H
y
dr
oc
a
rb
ons
in
gm
/B
H
P
-h
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0 0.1 0.2 0.3 0.4 0.5
Case I Case II Case III
Figure 3. Shows the emissions of total unburned hydrocarbons from the engine for different cases
Number of Cases
NO
x
E
m
is
s
ion
in
gm
/B
H
P
-hr
.
4.1 4.2 4.3 4.4 4.5 4.6
Case I Case II Case III
Figure 4. Shows the emissions of NOx from the engine for different cases
concern over particulates arises partly from the potential harmful effects of the soluble fraction, it might be suspected that emissions from biodiesel would be more harmful however data shows no tendency for the mutagenicity of exhaust gas to increase for a vehicle running on 20% biodiesel and 80% diesel blends.
Table 2 gives the comparison of particulate emission of all forms (soluble, fuel soluble, lube soluble and inorganic soluble) from petrodiesel and biodiesel from rapeseed methyl ester.
Table 2. Particulate Composition Diesel vs Biodiesel
Test Fuel Total PM
gm/mile
Insoluble gm/mile
Fuel Soluble gm/mile
Lube Soluble gm/mile
Soluble Inorganic
gm/mile
Cold FTP Difference
Diesel Biodiesel
0.311 0.258 - 17%
0.259 0.118 - 54%
0.021 0.104 + 49%
0.031 0.036 +16%
17 54 + 318% Hot FTP
Difference
Diesel Biodiesel
0.239 0.190 - 21%
0.206 0.101 - 51%
0.012 0.068 +567%
0.021 0.021 0.0%
14 47 + 335% (Source: Concawe Report number 2/95)
4. Emission of Green House Gas
Unlike other “clean fuels” such as compressed natural gas (CNG), biodiesel and other biofuels are produced from renewable agricultural crops that assimilate carbon dioxide from the atmosphere to become plants and vegetable oil.
The carbon dioxide released this year from burning vegetable oil biodiesels, in effect, will be recaptured next year by crops growing in fields to produce more vegetable oil starting material. The global community is under considerable pressure from the international community to take seriously its efforts to reduce carbon dioxide, carbon mono-oxide and other green house gases released in part, by the combustion of fossile fuels in vehicles. Fossile fuel combustion accounts for 70% of the total man made CO2 contribution. Supplementing our dwindling fossile fuel reserves with biomass-based fuels (biodiesel, for petrodiesel, biomass based alcohols or hydrogen for gasoline) helps reduce the accumulation of CO2 [1].Comparative emissions of green house gases for diesel and biodiesel in various stages of life cycle are depicted in Table 3.
Table 3. Emissions of Green House Gases (gm/km)
Diesel Biodiesel
Extraction 15.84 Fertilizer Production 15
Transport 2.74 Fertilizer Application 10
Refining 13.63 Agricultural Machinery 25
Distribution 0.95 Oil Production 3
Vehicle Operation 245 Processing Straw 1
Processing Gas 17
Transport 5
Vehicle Operation 0
Total 278.16 Total (Straw Processing) 59
Total (Gas Processing) 75
Fules G re e n H o us e G a s E m is s ions in gm /k m
0 1 2 3 4 5 6 7 8
0 50 100 150 200 250 300 W at er -D ies el Bi od ie se l E tha n ol (W o od) E th a nol (C om) CNG Di e s e l Ga s o li n e
Figure 5. Shows the life cycle analysis-green house emissions of different fuels
5. Production of Seeds and Oils for the Production of Biodiesel
From the experience in India and elsewhere, a plant density of 2500 per hectare (spacing 2*2) has been found to be optimal, although in rain fed areas on poor soil a lower plant density of 1666 has been felt to be more desirable. In relative poor deserts such as in Kutch (Gujrat) the yield has been reported to be 1 kg per plant. The seeds production in plantation varies between 2.5 tonnes/hectare, depending upon whether the soil is poor or average [13]. India is rich in cultivated land, and is suitable for the production of edible and non-edible oil seeds for the production of biodiesel. Table 4 gives the actual production of different edible and non-edible oil seeds during different years.
Table 4. Status of Edible and Non-edible Oil Seeds (in Lakhs Tonnes)
Vegetable oils 1997-98 1998-99 1999-2000 2000-01 2001-02 2002-03 2003-04 2004-05 Primary Source Ground nut
oil 16.95 20.66 12.09 14.74 16.16 9.48 18.82 16.16 Mustard/Rape
Secondary Oils
Cotton seed
oil 4.20 4.80 5.00 4.60 4.70 4.30 4.30 4.30
Coconut oil 4.50 4.90 4.50 5.60 5.50 5.50 5.50 5.50 Total
Non-Edible Oil 19.20 19.90 18.00 18.00 18.60 18.60 19.90 20.50
All Vegetables
Oils
70.58 79.60 68.15 62.99 54.84 54.84 80.84 85.48
6. Conclusion
In view of environmental considerations biodiesel is considered to be the best fuel for diesel engines because biodiesel has the lowest Green House Emissions on a life cycle basis, carbon monoxide gas is a toxic byproduct of all hydrocarbon combustion and it is reduced by using biodiesel as a fuel. Use of biodiesel as a fuel reduces emissions like hydrocarbons, particulate matter, visible smoke and odour. Using biodiesel in blends or in pure form reduces polyaromatic hydrocarbon emissions. Use of biodiesel as a fuel reduces Particulate Soot Emissions; Soot has adverse health effect in terms of respiratory impairment and related illness. Biodiesel is free from undesirable element like sulphur as compared to petrodiesel, which may have Sulphur content less than or equal to 550 parts per million. This concludes that biodiesel is a clean fuel and also environment friendly fuel, which can replace petrodiesel as a fuel in future.
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