BIOFUEL

Limitation of Using Straight Vegetable Oil and Ethanol as

Transportation Fuel

IBUKUN OLUWOYE

NICOSIA 2012

i

Abstract

The ecological and economic use of Bio-fuels is increasing on daily bases. Basically due to

environmental hazard of the non-sustainability usage of fossil fuel, the European Union had set

a standard for the 2020 most especially in transportation sector.

Major form of bio-fuel remains biodiesel and bioethanol which are produced from vegetable oil

and starchy contents respectively.

All these are only possible if the right physical and chemical processes are being put into

consideration with possibility of blending with fossil fuels because there are limitations in using

vegetable oil and ethanol directly as transportation fuel. In the review paper, such limitations

will be described in detail with necessary engine modification.

ii

Table of Contents

Abstract ……………………………………………………………………………………………………………..i

Table of Content ………………………………………………………………………………………………..ii

1. Introduction …………………………………………………………………………………………..1

2. Limitations of Vegetable in Diesel Engine ………………………………………………2

2.1 limitations based on physical properties

2.2 limitations based on structural and chemical properties

2.3 other limitations

3. Limitations of Ethanol in Gasoline Engine ………………………………………………7

3.1 limitations based on physical and combustion properties

3.2 limitations based on structural and chemical properties

3.3 other limitations

4. Possibilities of Engine Modification ……………………………………………………….10

4.1 Modification of Gasoline engine

4.2 Modification of Diesel engine

5. Conclusions ……………………………………………………………………………………………16

6. References …………………………………………………………………………………………….18

1

1. Introduction

Generally, biofuel are referred to liquid, gas and solid fuels predominantly produced

from biomass. A variety of fuel can be produced from biomass such as ethanol,

methanol, biodiesel, etc [1].

In the transportation industries, the use of biofuel which are basically biodiesel and

bioethanol is increasing on daily bases. The following figure shows the use of biofuel in

different energy mode in transportation.

FIG 1. Global energy use in transport sector (left) and the use of biofuels in different

transport modes (right) in 2050 (BLUE map scenario) [2].

It must be noted that the scenario can only be made possible only and only if the right

physical and/or chemical transformation are made on the biomass; in the case of

biodiesel, we have vegetable oil and in the case of bioethanol, we need blend with 90 %

gasoline.

The question remains: instead of inputting effort into the transformation of the

biomass, is the any possibility of using direct vegetable oil and ethanol?

In the following chapters, the limitation of using direct vegetable oil and ethanol will be

described in full details with possibility of engine modification to suit the direct use if

possible.

2

2. Limitations of Vegetable Oil Compared to Biodiesel.

There are limitations in using straight vegetable oil (SOV) directly in the diesel engine

compared to convectional diesel or biodiesel fuel specifications.

The specification is simply diesel fuel specification ASTM D 975.

2.1 Limitation Based on Physical and Combustional Properties.

The use of straight vegetable oil directly in diesel engine has some limitations based

on the following physical properties.

o Cetane quality: Cetane number is a measure of the ignition quality of the

fuel. Cetane number affects combustion roughness. The minimum cetane

number for diesel fuel (Grades No. 1 and 2) is 40.

As for vegetable oil, the cetane minimum number is 35 which is considered

as poor cetane number [3][4].

Result of Inadequate Cetane Number

Poor Ignition Quality

Long Ignition Delay

Abnormal Combustion

Abnormally High Combustion Pressure

Potential Uneven Thrust on Piston/Cylinder

Louder Engine Knock

Excessive Engine Knock and Smoke at Cold Start

FIG 2. Limitations of vegetable oil due to inadequate cetane number [3].

o Volatility: This is the property of changing readily from liquid to vapor.

According to ASTM D 975, the volatility of normal diesel the range for No. 2

grades of diesel fuel is 282ºC to 338ºC. This limits the level of high boiling

point components that could lead to increased engine deposits.

Vegetable oil has a relatively low volatility which leads to more engine

deposit

3

o Viscosity: The viscosity of diesel fuel is an important property which impacts

the performance of fuel injection systems. ASTM D 975 requires a kinematic

viscosity range of 1.9 minimum to 4.1 maximum mm2/S at 40ºC, for No. 2

diesel fuels (note that the term mm2/S replaces the former term of

centistokes [cst]).

The viscosity of vegetable oil is around 35 cst which is too high for the

engine. It causes too much pump resistance, filter damage and adversely

affect fuel spray patterns.

FIG 3. Viscosity affecting spray pattern [3].

o Flash point: The flashpoint is the lowest fuel temperature at which the vapor

above a fuel sample will momentarily ignite under the prescribed test

conditions. For No. 2 diesel grades, the flashpoint is a minimum of 52ºC. For

vegetable oil, the flash point is 220ºC which is too high.

o Low temperature operability: the cloud point and pour point of a vegetable

oil is high compare to diesel. Therefore, vegetable oil cannot work at low

temperature weather condition.

2.2 Limitations based on chemical and structural properties.

According to chemical and structural composition properties of a vegetable oil, it has

some limitation in using it as alternative fuel for a diesel engine.

Examining Rapeseed and Canola:

4

Oil sample Contamination

Mg/Kg Acid

value mg

KOH/Kg

Oxidation

stability

(1100C) h

Phosphorous

content mg/kg

Ash

Mass % Water

Mass %

Rapeseed 25 2.0 5.0 15 0.01 0.075

TABLE 1: Chemical content of rapeseed [4].

Component Canola Rapeseed Soybean

Triglycerides(%) 94.4- 99.1 91.8 – 99.0 93.0 – 99.2

Phospholipids (%)

Crude oil Up to 2.5 Up to 3.5 Up to 4.0

Water-degummed Up to 0.6 Up to 0.8 Up to 0.4

Acid-degummed Up to 0.1 - Up to 0.2

Free fatty Acid(%) 0.4 -1.2 0.5 – 1.8 0.3 – 1.0

Unsaponifiables(%) 0.5 – 1.2 0.5 – 1.2 0.5 – 1.6

Tocopherols (ppm) 700 - 1200 700 - 1000 1700 - 2200

Chorophylls (ppm) 5 - 35 5 - 35 Trace

Sulfur (ppm) 3 - 15 5 - 25 Nil

TABLE 2: Constituents of Canola, Rapeseed and Soybean Oils [3].

Oil sample phosphorus Iron Calcium Sulfur Zinc Lead

Canola 1190 3.52 296.0 6.5 2.4 0.24

TABLE 3: Simple Mineral Element Content in Canola Oil [3].

It must be noted that all these chemical composition contributes to limitation of

using straight vegetable oil in diesel engine. Details are given in table 4.

5

summary of limitations based of chemical properties

Sulfur content Low, not enough to control emission equipment

Water and Sediment Content Filter plugging, injector wear, increased corrosion

Ash Content Injector and fuel pump wear, piston and ring wear

Engine deposit.

Carbon Residue Fuel system deposit and Combustion Chamber deposit

TABLE 4: Limitations due to chemical properties.

The structural property also evoke limitations

Vegetable oil are composes of Triglycerides which are the main constituents of

vegetable oils and animal fats. Triglycerides have lower densities than water (they

float on water), and at normal room temperatures may be solid or liquid. When

solid, they are called "fats" or "butters" and when liquid they are called "oils".

A triglyceride, also called triacylglycerol (TAG), is a chemical compound formed from

one molecule of glycerol and three fatty acids.

Each triglyceride is composed of fatty acid three long chain fatty acid of 8 -22

carbons attached to a glyceride backbone [1]. This makes the vegetable oil to be

very different form the conventional diesel fuel.

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2.3 Other limitations

The following are some other limitations of straight vegetable oil.

o Carbon Deposits: Excessive carbon deposits and contamination of engine

lubricant both result from SVO's higher boiling point relative to diesel or

blended biodiesel fuels. U.S. Department of Energy studies show prolonged

use dramatically reduces engine life because of this property. The over-

wetting caused by high viscosity exacerbates carbon buildup and lubrication

contamination.

o Catalytic Converter Damage: Modern clean diesel engines use catalytic

converters and fuel traps. SVO's higher boiling point causes saturation of

these components and can poison the catalytic converter with long-term use.

o Clogged Fuel Pumps: Both the increased viscosity and higher boiling points of

SVO lead to fuel pump clogging. While short-term use was deemed effective

in terms of engine performance and emissions, long-term use was deemed a

hazard to the durability of the fuel pump and other fuel system components

[5].

7

3. Limitation of Ethanol in Gasoline Engine

Ethanol is an alcohol-based fuel made by fermenting and distilling starch crops, such as

corn. It can also be made from "cellulosic biomass" such as trees and grasses. The use of

ethanol can reduce our dependence upon foreign oil and reduce greenhouse gas

emissions. A pure ethanol is the one with 95% ethanol.

It must be noted that the 95% cannot be use directly in gasoline engine without been

blended with gasoline (between 10-85 percent value, E10-E85) or necessary engine

modification [6]. This is due to the following limitations.

3.1 Limitations Based on Physical and Combustion Properties.

The following table shows the physical and combustion properties of ethanol

Characteristics of chemically pure fuels.*

Chemical formula Chemical

weight

(lb/mole)

Specific

gravity

Boiling

point

(C)

Latent

heat

(Btu/lb)

Combustion

energy

(Btu/lb)

Vapor

pressure

@100F

(psi)

Solubility

part in

100

parts

H2O

Stoichio-

metric

air-fuel

ratio

Methyl

alcohol

CH3OH 32 0.79 65 503 10,260 4.6 infinite 6.5

Ethyl

alcohol

CH3CH2(OH) 46.1 0.79 78 396 13,160 2.2 infinite 9

Butyl

alcohol

C2H5CH2CH2(OH) 74.1 0.81 117 186 15,770 0.3 9 11.2

Octane C8H18 114 0.70 210 155 20,750 1.72 insoluble 15.2

Hexa-

decane

C16H34 240 0.79 287 -- 20,320 3.46 insoluble 15

*To convert to metrics, use the following conversion factors: 1 pound = 45 kilogram; 1 degree F = degrees C - 32 x

5/9.

TABLE 5: Properties of Ethanol [7].

Based on the above properties the following limitations can be deducted:

o Driving ability of ethanol is lower.

Lower per liter energy value (EV)

Takes more to drive the same distance

Consumers have to fill their cars more often and pay more for ethanol fuel.

8

o Ethanol can absorb water & if water enters the fuel tank

It dilutes ethanol, reducing its value as a fuel;

It causes problems with corrosion and phase separation in the gasoline mixture.

o Ethanol dissolves almost everything.

It absorbs and carries dirt inside the fuel lines and fuel tank, thus contaminating

the car engine system.

o Ethanol is rich in octane content.

It is highly flammable and explosive compared to gasoline.

It requires more attention to handle in daily life.

o Low flash point 13 – 140C

It burns easily

3.2 Limitation Based on Chemical and Structural Properties.

The following are the major chemical properties of ethanol

Molecular formula C2H6O

Molar mass 46.07 g mol−1

Exact mass 46.041864814 g mol−1

Acidity (pKa) 15.9[2]

Basicity (pKb) -1.9

Refractive index (nD) 1.36

Viscosity 0.0012 Pa s (at 20 °C)

Dipole moment 1.69 D

TABLE 6: Some chemical properties of ethanol.

o Ethanol is a reducing agent -- it can be oxidized by strong oxidants, to

acetaldehyde and to acetic acid Ethanol is also weak acid.

Therefore Alcohols may be corrosive to certain materials used in engines.

Generally, methyl alcohol is the most corrosive and butyl alcohol is least

corrosive. Alcohols also can cause injury or physical harm if not used properly.

9

People who use alcohol in motor fuels should observe warning labels and follow

precautions to avoid problems [7].

o Aldehyde, a function of ethanol volume, is a threat to nose, eyes, throat &

possibly causes cancer [8].

3.3 Other Limitations

Other limitation includes:

Instability of the micro-emulsion (separation of ethanol phase

o Another problem is that ethanol has a smaller energy density than gasoline. It

takes about 1.5 times more ethanol than gasoline to travel the same distance.

However, with new technologies and dedicated ethanol-engines, this is expected

to drop to 1.25 times.

o Another problem is that ethanol burning may increase emission of certain types

of pollutants. Like any combustion process, some of the ethanol fuel would come

out the tailpipe unburned. This is not a major problem since ethanol emissions

are relatively non-toxic. However, some of the ethanol will be only partially

oxidized and emitted as acetylaldehyde, which reacts in air to eventually

contribute to the formation of ozone. Current research is investigating means to

reduce acetylaldehyde emissions by decreasing the engine warm-up period [9].

10

4. Possibility of Engine Modification.

In case of using straight vegetable oil or ethanol, necessary engine modifications must

be considered. The following explains the possibilities of modifying an engine for their

usage.

4.1 Gasoline Engine Modification

o MAINJET CHANGES

The first thing to alter is the main metering jet in your carburetor. In most

carburetors, this is a threaded brass plug with a specific-sized hole drilled through

the center of it. This hole is called the main jet orifice, and its diameter dictates how

rich or lean the air/fuel mixture will be when the car is traveling at cruising speeds.

Naturally, the smaller the hole is, the less fuel will blend with the air and the leaner

the mixture will be. As the orifice is enlarged, the mixture gets richer.

Since alcohol requires a richer air/fuel ratio, it's necessary to bore out the main jet

orifice when using ethanol fuel. The standard jet size in MOTHER's alcohol-powered

truck was .056" ... in other words, this was the diameter of the jet orifice. In order to

operate the engine successfully on alcohol fuel, it's necessary to enlarge this opening

by anywhere from 20 to 40%.

o IDLE ORIFICE CHANGES

Most carburetors will require additional idle circuit enlargement in order for the

engine to run at slowest, or idle, speeds. This is because the circuit that's fed by the

main jet operates fully only when the throttle plate within the throat of the

carburetor is opened past the idle position. When the plate is in the idle position,

the air/fuel mixture is allowed to enter the manifold only through the idle orifice

itself ... which, if it isn't large enough, will not provide the needed amount of air/fuel

blend to keep the engine running.

On some engines, it may only be necessary to loosen the idle mixture screw at the

base of the carburetor in order to provide the correct amount of fuel, since this

11

threaded shaft has a tapered tip which allows more mixture to pass as the tip is

backed off. On other engines, it's possible that the seat itself, into which the tapered

screw extends, must be enlarged in order to accomplish the same thing.

In most cases, if the seat has to be bored out, it can be enlarged by 50%, using the

same method of measurement as was detailed in the main jet section. This will allow

a full range of adjustment with the idle mixture screw, even if you should want to go

back to gasoline fuel. (When drilling, be careful not to damage the threads in the

carburetor body.

As a precaution against the idle screw's vibrating loose from its threaded opening,

you can shim the idle mixture screw spring with a couple of small lock washers ...

this will prevent the screw from turning even if it's drawn out farther from the seat

than it normally would be.

o POWER VALVE CHANGES

Most modern auto carburetors have what is known as a power valve that allows

extra fuel to blend with the air/fuel mixture when the accelerator is depressed, in

order to enrich the mixture under load conditions. This vacuum-controlled valve is

spring loaded, and shuts off when it isn't needed in order to conserve fuel.

The power valve used in the carburetor illustrated is somewhat difficult to alter and,

besides, is sufficient for alcohol use in its normal configuration if it's working

properly. However, there are other carburetors - specifically the Holley and Ford

(Autolite or Motorcraft) brands - that have easily replaceable power valves which

are available from auto parts stores in various sizes. If you use a power valve with a

25% or so greater flow capacity than the one that originally came with the

carburetor, your air/alcohol mixture will be sufficiently enriched when your engine

needs more power.

o ACCELERATOR PUMP CHANGES

In addition to a power valve, almost all automotive carburetors utilize an accelerator

pump. This is a mechanically activated plunger or diaphragm that injects a stream of

raw fuel directly down the throat of the carburetor when the accelerator is suddenly

12

depressed. The fuel is injected through a small orifice located in the throat wall at

some point above the carburetor venturi (the point at which the throat narrows).

The reason the accelerator pump is incorporated into modern carburetors is that as

the accelerator is pressed and more air/fuel mixture is drawn into the cylinders,

some of the liquid particles in the blend tend to stick to the walls of the intake

manifold, effectively leaning out the mixture by the time it reaches the combustion

chambers. The extra squirt of fuel that's added by the accelerator pump makes up

for this initial lean condition.

In order to adapt your accelerator pump to use alcohol effectively, you'll probably

have to enlarge the size of the injection orifice slightly (anywhere from 10 to 25% is

fine ... if you go larger than that, you'll risk the possibility of altering the pump

pressure enough either to turn the fuel stream into a dribble or to empty the pump

reservoir before the pump has made a full stroke).

As an alternative to enlarging the hole, you may be able to simply adjust the stroke

length of the pump arm in order to feed more fuel. Most carburetors installed on

Ford products already have a provision for seasonal adjustment, so it's just a matter

of putting the pump on its richest setting. Other carburetors, too, have threaded

rods that can be adjusted to accomplish the same thing.

o CHOKE ALTERATION

Although it's not absolutely necessary to adapt your car's choke system to burn

alcohol fuel, it has been our experience that a manually operated choke is more

desirable on an alcohol-powered car. If your vehicle's engine is already so equipped,

fine. If not, you can purchase - for about $7.00 from any auto parts store - a manual

choke conversion kit that will allow virtually any automatic choke to be adapted for

manual control.

o IGNITION TIMING

In order to take advantage of the great antiknock qualities that alcohol fuel provides,

you'll have to advance the engine's ignition timing by turning the distributor housing

13

opposite to the direction in which the rotor spins (the housing is held in place by a

bolted clamp).

Normally, an engine using gasoline has its timing set so the spark occurs at anywhere

from 8 deg BTDC (Before Top Dead Center) to TDC (Top Dead Center). Since alcohol

has a higher "octane" rating, you can advance the timing considerably more than

this. (In the case of MOTHER's truck, we adjusted it to operate at approximately 22

deg BTDC without any sign of pre-ignition, even under load.) Of course, care should

be taken when you adjust the timing on your vehicle, since a 22 deg advance might

be excessive for your car. Remember, it's not safe to be just short of detonation,

since inaudible knocking can also damage the engine ... the best procedure is to set

the distributor timing at least two degrees retarded from the point of detonation.

o COMPRESSION RATIO CHANGES

Increasing the compression ratio of the engine will be impractical for most people,

because of the expense and work involved ... however, this modification will do a

great deal to improve engine performance and economy. Just like a timing advance,

a compression ratio hike will take advantage of the potential that alcohol has to

offer as a fuel. Optimally, the ratio can be increased to 14- or 15-to-1 ... but even a

nominal increase - to perhaps 12-to-1, a figure that some manufacturers have

already offered in the past for premium gasoline use - will result in a vast

improvement over the standard 8- or 8.5-to-1 that most manufacturers incorporate

into their engines today.

o FUEL PREHEATING

In extremely cold climates, it may be necessary to preheat your alcohol fuel before it

enters the carburetor float bowl. This can be accomplished easily by splicing into the

fuel feed line - near the point where it passes the upper radiator hose - and installing

a fuel heater at this location.

o AIR PREHEATING

Most trucks and autos have air filter housings which are designed to allow heated air

from around the exhaust manifold to channel through a duct and enter the

14

carburetor when the engine first starts from a cold state. As the engine warms up, a

flap within the air cleaner "snorkel" shuts off this supply of warm air and allows

ambient air from the engine compartment to enter in its stead.

This flap is usually either thermostatically or vacuum controlled ... but either way,

you may find it helpful during the winter months to leave this valve closed to the

cold outside air. This can be done either by disconnecting the bimetallic thermostat

spring that controls the flap and installing a small spring of your own that will hold

the valve in the required position, or - if the flap is vacuum activated - by connecting

an existing permanent vacuum line to its control fitting. (You can, of course, remove

the control line entirely, plug it up, and hold the flap closed with a spring if you

wish.)

o THERMOSTAT CHANGE

In order to get maximum efficiency from your engine, you may need to change the

thermostat within the engine block. Thermostats are available in various heat ranges

from 140 to 200 deg F, and these temperatures indicate how hot the engine coolant

will be allowed to get before the thermostat opens to initiate the cooling process. (A

thermostat is designed to hold the coolant within the cylinder head till it achieves

the desired temperature ... at which point the heated liquid is allowed to escape into

the radiator to be cooled, and is replaced by a fresh supply of cool fluid. Depending

on the engine's operating conditions, the thermostat may cycle open and shut

regularly over the span of a few minutes.)

By using a hotter thermostat, you'll be able to warm up the entire engine, including

the intake manifold.

o COLD WEATHER STARTING

Since alcohol doesn't vaporize as easily as does gasoline, cold weather starting can

be a problem ... especially if the engine itself is cold. To alleviate this undesirable

situation, MOTHER's research staff has designed a combination coldstart/dual-fuel

system that'll work with any car.

15

All it requires is a five-gallon fuel storage tank with a fuel filler neck brazed into its

top (we used an old propane bottle), an auxiliary electric fuel pump, some steel

brake or fuel line, neoprene hose, an elbow, a length of copper pipe, a small

metering jet, and several needle valves, tees, and hose barbs. (Details and

illustrations of the installation are shown in the article reprints from MOTHER NOS.

59 and 60, which are included in this workbook.)

The five-gallon tank is mounted in some safe place on the truck or automobile and

used to store gasoline. This cache of petroleum fuel serves a dual role: When it's

needed for cold starting purposes, the electric pump is activated momentarily from

inside the car and a fine stream of gasoline is injected down the throat of the

carburetor. And, in the event that your alcohol supply is unexpectedly depleted on

the highway, the gasoline stored in the small tank can be routed into the carburetor

normally for emergency use.

o FUEL INJECTION SYSTEMS

Since some vehicles are equipped with fuel injection rather than carburetors, we will

briefly touch on the use of alcohol with that system. There are two important factors

in a fuel injection setup: injection timing and control jet diameter. Fortunately - since

many systems now use an electronically controlled timing sequence - injection

timing is not critical in a fuel injected engine. Neither performance nor economy

improve substantially by either advancing or retarding the injection timing process.

Control jet diameter, on the other hand, is an important factor. If you increase the

size of the control jets (which are the equivalent of the metering jets in a

carburetor), the engine will operate well on alcohol fuel. An increase of 15-20% is all

that's necessary to accomplish the conversion. (Ignition timing should, of course, be

advanced as explained previously.)

An interesting feature of the fuel injection system is that it doesn't require any

gasoline during the cold weather starting process to fire the engine up. Since the

fuel is injected at a pressure of about 250 PSI, the alcohol fuel is sufficiently

vaporized to ignite easily within the combustion chamber.

16

[10][11].

4.2 Diesel Engine Modification

To run a diesel engine on straight vegetable oil (SOV) the following modifications

must be considered.

o Preheating the oil, to make it less viscous

o Avoiding injector coking by replacing it often

o Adding extra engine coolant

o Vegetable oil filter

o Fuel filter preheater

o Thermoswitch

o Necessary parts includes

3-port solenoid valves

The fuel return loop

Custom-made heated tank

The hose within hose

Detail information on installation can be found in [12].

17

5. Conclusions

The limitations of using straight vegetable oil or ethanol in diesel engine and gasoline in

respectively have been discoursed. It is clear that they cannot be use directly without an

engine modification which is important or a long term use.

18

References

[1]: ME541-Biofuel- Lecture notes-1, 13/04/2012

[2]: Technology roadmap, Biofuel for Transport, International Energy Agency, page 21.

[3]: http://www.biodiesel.org/docs/ffs-performace_usage/service-technician's-guide-to-diesel-

fuel.pdf?sfvrsn=4

[4]: http://journeytoforever.org/biodiesel_yield2.html

[5]: http://www.ehow.com/list_5783028_disadvantages-using-vegetable-oils-fuel.html

[6]: http://www.fueleconomy.gov/feg/ethanol.shtml

[7]: http://www.ext.colostate.edu/pubs/farmmgt/05010.html

[8]: Advantages and Disadvantages of Using Ethanol: The Consumer Viewpoint, Ngo Anh-Thu and Gale

West, AIEA 2nd International Conference and Workshop, Laval University , Quebec, 2004

[9]: http://science.jrank.org/pages/2576/Ethanol-Disadvantages-ethanol-an-alternative-fuel.html

[10]: http://running_on_alcohol.tripod.com/id32.html

[11]: http://running_on_alcohol.tripod.com/id32.html

[12]:http://www.autonopedia.org/renewable_energy/Biofuels/How_To_Run_Your_Diesel_On_Staight_

Veg_Oil.html