8th International DAAAM Baltic Conference
"INDUSTRIAL ENGINEERING"
19-21 April 2012, Tallinn, Estonia
THE DEVELOPMENT OF AN ADDITIONAL FUEL SUPPLY
SYSTEM TO AN INTERNAL COMBUSTION ENGINE
Ilves, R.; Küüt. A.; Mikita.V. & Olt. J.
Abstract: The usage of natural resources
such as oil is nowadays gaining more and
more attention. The Estonian national
energy management development plan
foresees increasing the percentage of
renewable
resources
in
energy
consumption by 20 per cent, the
percentage of biofuels in transportation
fuels by 10 per cent. That is the reason
for the increase in using biofuels.
Biofuels are used as engine fuels in many
countries, however, some problems that
hinder using biofuels have not been
solved. One of the greatest problems is
the cost of biofuels which depends on the
raw material, production technologies
and quality of the fuel produced. The
quality of the fuel is important to ensure
the working modes of the engine’s
subsystems on given conditions as well as
the durability guaranteed by the factory.
This particular article provides an
overview of designing and developing an
innovative additional fuel supply system.
For doing so, firstly, the problems
encountered when using biofuels in
engines are discussed, secondly, an
overview of a patent research is given.
The prototype of an innovative additional
fuel supply system is designed, its
development stages as well as the
problems that need to be tackled are
pointed out and discussed.
Key words: combustion engine, liquid
biofuel, fuel supply system, product
development.
1. INTRODUCTION
Biofuels are more and more commonly
used in the world due to decreasing fossil
fuel resources. Biofuels can be divided
into three: 1) solid fuels; 2) liquid fuels;
3) gas fuels. Gas and liquid fuels are used
as engine fuels. Methane produced from
biomass is mostly used as gas fuel.
Liquid fuels can be divided into plant oils
and alcohol. Plant oils include hot and
cold-pressed oils and biodiesel; alcohol
fuels include biomethanol and bioethanol
[1]. There are several problems in using
biofuels as engine fuel. Using plant oils
as engine fuel may cause excessive
sooting and coking of the combustion
chamber and injector nozzle [2]. Idle
engine operation is aggravated because
lots of energy is used for igniting the oil.
Major problem consists in the fluidity of
fuel at low temperatures. Plant oils are
mostly used in compression-ignition
engines. Use of alcohol fuels in
compression-ignition
engines
is
complicated because alcohol fuels need
much more energy for self-ignition than
plant oils or diesel fuel [3]. These alcohol
fuels are mostly used in spark ignition
engines. Their properties cause corrosion
and rapid wear of the components of the
fuel supply system [4]. Another problem
is related to cold-start [5].
In order to use biofuels in spark ignition
and compression-ignition engines, the
engines with two fuel supply systems
have been introduced [6], where main
fuel supply system uses standard fuels as
engine fuel and additional supply system
uses biofuels. In addition to the standard
fuel, also biofuel is channelled tothe
engine
cylinder.
Problems
with
combustion and cold-start occurring in
case of using biofuels are compensated
with standard fuel [7]. The disadvantage
of this system is high cost and complexity
of the engine.
The purpose of this present article is to
provide an overview of the creation and
development of an innovative additional
fuel supply system that uses liquid
biofuels. The advantage of this new
additional fuel supply system is the
opportunity to use different biofuels in
different engines, by ensuring the
durability of fuel supply system and
forming of quality air-fuel mixture.
2. MATERIAL AND METHODS
The additional fuel supply system was
developed based on generally recognized
TRIZ methods [8, 9] which in this case
consisted of the following main steps:
1) identification and definition of the
problem;
2) searching for typical problem
similar to the problem identified;
3) analysis of known solutions;
4) finding the best solution for the
problem in need of solution.
Development of additional fuel supply
system requires examination of the
problems that emerge when using liquid
biofuels and it is also necessary to set the
requirements for creating an innovative
fuel supply system [10]. The two types of
biofuels to be studied include plant oils
and bioethanol (max 96.6 %). The
aforesaid fuels should be usable in spark
ignition engines and compressionignition engines. Forming of air-fuel
mixture by using a single fuel supply
system is a complicated process, because
in case of plant oils great pressure is used
for injection in order to ensure sufficient
fuel quantity and forming of quality airfuel mixture in the cylinder [11]. This is
due to great viscosity of plant oils, which
at the temperature of 27˚C exceeds
30 m2/s [12]. Bioethanol has low
viscosity (~ 2 m2/s). Bioethanol can be
injected by means of injectors with lowinjection pressure and a large nozzle
opening. At the same time the lubricating
properties of bioethanol are significantly
worse than those of plant oils [13]. This
may cause rapid wear and corrosion of
the precise surface finish of the fuel
supply systems intended for plant oils.
Bioethanol does not mix with standard
fuels and plant oils. Therefore they
cannot be mixed inside the fuel supply
system, in order to avoid return of layered
fuel in the fuel tank. Based on these
properties the following requirements
have been prepared for fuel supply
system that describe the properties of
devices in demand and less common on
the market: 1) can be used with several
types of biofuels in one fuel supply
system; 2) ensure production of quality
air-fuel mixture; 3) fuel supply system
can be used in spark ignition engines and
compression-ignition engines; 4) ensure
durability of the fuel supply system.
The most common biofuel-operated fuel
supply systems on the market are either
direct or indirect injection standard
systems. They are generally intended for
one type of biofuel. Pressurised fuel is
forced through the injector to the inlet
manifold or directly into the cylinder.
Main components subject to wear and
tear are precise surfaces in injectors and
fuel pumps (injector needles, CR injector
return valves, plungers). Examples of
some fuel supply systems adjusted for
biofuels can be found in patent
documents EP2208879, US2008202471,
WO2009106647, US20090145403, etc.
Based on the aforesaid description, the
development of a new fuel supply system
requires the reduction of pressure inside
the supply system and exact number of
junctions. At the same time one has to
ensure the highest possible quality of airfuel mixture in the cylinder. One
alternative is to use fuel supply systems
equipped with compressed air, where the
air flow channelled through venturi
nozzle utilises underpressure to suck the
fuel into the injector, where the air and
fuel are then carburized. The advantage
of this system is lack of precise surfaces
and low pressure in the fuel supply
system. In order to allow using the fuel
supply system both in spark ignition and
compression-ignition engines, it has been
placed in the engine inlet manifold.
Fuel supply system has been developed
on experimental basis, i.e. an initial test
device has been built and it has been
improved and modified to solve the
problems emerging in the course of
testing.
injectors
that
ensure
sufficient
productivity of the fuel supply system at
different engine modes. The function of
fuel inlet regulator 2 is to adjust the
quantity of fuel feed from the tank.
Irrespective of the viscosity and density
of fuel, the system allows breaking the
fuel jet into small parts. Implementation
of this concept into an engine fuel supply
system represents a complex process. The
stages of developing the fuel supply
system are listed below.
3. RESULTS AND DISCUSSION
Main parts of fuel supply systems subject
to wear and tear include precise surfaces,
wear and tear of which causes forming of
low-quality air-fuel mixture or reduction
of fuel delivery, which in turn determine
the power characteristics of the engine. In
order to use biofuels, it is recommended
to use fuel supply system that has as few
precise surfaces as possible. One option
is to use pulverizing injectors that operate
on the venturi jet principle (see Figure 1).
5
2
Stage I.
Concept
realisation
and
construction of the test device.
Activities:
1. Carrying out preliminary study:
1.1. Selection of injectors;
1.2. Checking the injection methods,
process modelling.
1.3. Elaboration of the principle of
system construction.
2. CAD modelling.
3. Preparation of 3D drawings.
4. Preparation of control programmes for
CNC benches.
5. Technological mapping.
6. Processing of the details in CNC.
1
3
4
Fig. 1. Basic scheme of the fuel supply
system.
Air flow is drawn through injector 1,
creating underpressure in the fuel supply
line 3 at the end of the injector when
passing through the jet opening. Due to
underpressure the fuel will be sucked
through the fuel supply line into the
injector, where the fuel is carburized. In
casing 4 of fuel supply system the
resulting air-fuel mixture is mixed with
air again and drawn into the cylinder.
Fuel inlet manifold has at least two
Fig. 2. Process modelling.
Stage II. Study of the processes in the
fuel supply system
Activities:
1. Preparation of simplified test device.
2. Monitoring of processes and making
conclusions.
3. Elaboration of enhanced test device
Fig. 3. Simplified test device.
Stage III. Study of the operation of
improved fuel supply system.
Activities:
1. Improving the construction of the test
device.
2. Monitoring the operation process of
the test device and making conclusions.
3. Elaboration of enhanced construction
of prototype devices.
Fig. 4. Improving the construction of the
test device.
Stage III. Designing the prototype
device.
Activities: 1. Preparation of improved
prototype devices.
2. Testing and solving any problems that
might arise.
Fig. 5. Prototype devices.
Stage I: The aim is to find a suitable
construction for implementing the
concept of the fuel supply system. For
that purpose the injection quality and
productivity of different injectors have
been studied in biofuels with varying
viscosity. Injectors are placed in the
casing which is positioned in the inlet
manifold of the engine. Problems found
while testing include condensation of the
injected fuel on casing walls and
adjustment of fuel quantity. In order to
reduce fuel condensation it is necessary
to adjust the quantity of injected fuel so
as to ensure required engine performance
without forming excess air-fuel mixture
in the inlet manifold. Air flow regulator
is used for adjusting the quantity of
injected fuel.
Stage II: Engine testing revealed that the
underpressure generated in the inlet
manifold was high enough to force the
fuel to flow to the manifold through the
injectors. This results in uncontrollable
engine operation, where the fuel flow to
the cylinder increases along with the
increasing rotational speed of crankshaft.
This problem can be solved by
supplementing the system with a fuel
doser that channels the fuel to the
injectors. Doser consists of fuel
distributor, electromagnetic valve and
control module. Doser must be placed as
close to the injector as possible, in order
to reduce the impact of fuel in the fuel
supply line during the work mode of the
engine, when the doser is in closed
position. Dosing effect consists in the
operation of pulse-modulated electromagnetic valve at a fixed frequency by
changing the signal fill factor. Air flow
adjustment is not necessary in case of the
above-mentioned solution.
Stage III: Testing the fuel supply system
equipped with electronic fuel dosing
system revealed excessive forming of airfuel mixture in the inlet manifold. In
order to remove the condensed air-fuel
mixture from the system the position of
the system casing on the engine has been
altered and a return line has been added
which allows directing the condensed
fuel back to the fuel tank.
Stage IV: Prototype device has been
designed in view of the fact that the fuel
must flow out of the casing of the fuel
supply system at various engine
positions. The reason for that comes from
the problem found when testing the
device in spark ignition engine. If the
cylinder is filled with too rich air-fuel
mixture the combustion process will take
a long time, which causes backfire in
inlet manifold when opening the inlet
valve. In case of backfire the condensed
fuel ignited in the inlet manifold. To
solve the problem it is necessary to
supplement the system with a lambda
sensor, the signal of which provides a
basis for controlling the air-fuel mixture
preparation.
As an example of the fuel supply system's
work, graphs of carbon monooxide and
carbon dioxide have been provided (see
figure 6), which have been measured
when using the fuel supply system as an
additional fuel supply system on a
compression ignition engine.
Fig. 6. The carbon monooxide and carbon
dioxide in the exhaust gas of a
compression ignition engine in relation to
the amount of bioethanol fed by the fuel
supply system (DF – diesel fuel).
Diesel engine D120 was used as a test
engine. The fuel used in the supply
system was a 60-per-cent bioethanol. The
rotational speed of the crankshaft on
engine mode was n e = 1300 rpm and
torque T e = 112 Nm. During the test, the
proportion of diesel fuel was gradually
decreased in the air fuel mixture and the
amount of bioethanol was increased to
ensure the stabile engine mode. Using
ethanol in the air fuel mixture reduces the
amount of carbon monooxide and carbon
dioxide in the exhaust fumes. The
bioetahnol added with the fuel supply
system enabled to replace up to 80 per
cent of the diesel fuel on the given mode.
This implies that the efficiency of the
device is comparable to other electronic
additional fuel supply systems.
Using different biofuels in this system
did not cause any problems, which means
that it has great potential as an additional
fuel supply system. The advantage of this
solution consists in lack of precise
surfaces, which allows using different
biofuels without rebuilding the system.
Problems may arise from the complex
control of the air-fuel mixture forming
process.
4. CONCLUSION
There
are
various
development
opportunities for fuel supply systems.
Dosing the amount of fuel may be
considered inaccurate in case of the
innovative solution described in the
article. Thus it is necessary to continue
experimental work for enhancing the
system for using it with biofuels. Further
development of fuel supply system
requires converting the technical solution
provided in the article into a multi-point
injection system, where fuel is injected
into the intake ports just upstream of each
cylinder’s
intake
valve.
Final
improvement would consist in leading the
injectors directly into the combustion
chamber. Such a technical solution
requires highly complex control systems
in order to ensure the resistance of the
fuel supply system to temperature
fluctuations and elevated pressures.
The stages indicated in the article
represent first steps in developing
combined fuel supply system. The
developed
system
allowed
using
bioethanol in spark ignition engine
without the main fuel supply system. It
follows that the produced air-fuel mixture
had the quality suitable for using in an
engine. The purpose of further
development is to improve the efficiency
of the fuel supply system described in
this article.
5. REFERENCES
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6. ADDITIONAL DATA ABOUT
FIRST AUTHOR
Risto Ilves (Phd Student) – Tartu.
Estonian University of Life Sciences,
Institute of Technology, 56 Kreutzwaldi
Street, EE51014, Estonia.
E-mail: [email protected]
Phone: +37258161529.