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INTRODUCTION
1. The reason of the theme choosing
Depending on the mode of production and use, biofuels can be divided into 4 groups as follows:
BIOFUELS
Biodiesel
Straight Vegetable Oil
Biomass
ETHANOL
Currently, technology of using animal fat and vegetable oil as fuel (with the appropriate rate) for
diesel engines can be classified in two main directions:
(1). Handling chemically to animal fats and vegetable oils have properties similar to diesel oil (DO).
Oil-treated so-called biodiesel
(2). Mechanical and physical handling of vegetable oil to gain some basic requirements of DO fuel.
In this direction, primarily technology can be divided into 2 branches as follows:
- First, Fabricate the converted kit to dual fuel system or fabricate specialized fuel injectors for SVO
as single fuel system.
- Second, create a mixture of vegetable oils with low viscosity solvents (such as kerosene, ethanol,
diesel ...), and additives to reach standard fuel use for diesel engine.
In this topic, The researcher chosen fuel mixture creation because:
- The manufacture and installation of additional the converted kit or specialized injectors SVO able
to use 100% pure vegetable oil but will increase cost of the fuel system, causing the complex to use.
- No need for treatment plant to industrial scale, such as biodiesel, the equipment cost is very high
(30,000 EU for device yield 50lit / batch).
On the other hand, biodiesel is susceptible to infections which reduce the quality of biodiesel
damaging PVC synthetic materials, rubber pipes, washers. Have not found any published works wich have
similar effects when using the mixture technology
Direct use vegetable oil from available oil production plant, especially non-edible oil, creating mixed
with fuel additives and the DO will lower prices on fuel. This solution does not require the use of highly
qualified, well-suited to the conditions of our country.
In the field of Agriculture - Forestry - Fishery and transportation in Vietnam, the diesel engine is
used very common (90%). To 10/2011 there were nearly 500,000 tractors used in agriculture, with a total
capacity of over 5 million horsepower (cv); 580,000 threshing machines; 17,992 harvesting machines of all
kinds ... the end 2008, the number of Vietnam fishing vessels up to 128,000 with a total capacity of over
6,784,000 cv (average 53 cv / unit). In addition, the ship waterway transport, tourism ... also very large
number. So, if we use vegetable oil as alternative fuel for diesel engines would save a large amount of
foreign currency for the country and limit environmental pollution
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Vietnam vegetable oil is processed from the raw materials of plant origin including soya beans,
soybeans, peanuts (peanuts), sesame, coconut, rice bran ... the most common of which is coconut oil.
Coconut oil have lower viscosity, density and flash point, the highest index cetan. This is a significant
advantage when used as alternative fuels, moreever, coconut oil production topped 3 oils popular in
Vietnam. Recently, appeared some non-edible oils such as jatropha curcus oil, algae oil, full of potential ...
but not yet commercial.
From the arguments above, that: "Study on appropriate mixing ratio between coconut oil and
diesel oil used as fuel for diesel engines to improve the economic and the environment indicators" is urgently
needed in the face current situation.
2. The objective of the study subjects:
Study on the effect in proportion of coconut oil mixed with diesel oil to the economy and
environment indicators on the diesel engine, thereby determining the mixture formula as input parameters
for the design of conversion fuel system. To address the goal of the project, the researcher hypothesize:
- A diesel engine can work if using the new fuel properties (mainly viscosity and cetane index)
equivalent conventional fuels.
- The economic and environment criteria of the engine change the nature of the fuel.
3. Study subjects: Alternative fuels for diesel engines
4. Scope of the Study: The mixture of coconut oil, additives and diesel as fuel for diesel engines.
5. The meaning of scientific and practical:
1. In science
- To build the theoretical basis of mixed use coconut oil, diesel oil as fuel for diesel engines;
Establishing formula and building thermodynamic parameters for the fuel mixture: coconut oil, diesel and
additives as fuel for diesel engines;
- Define the simulation conditions (initial conditions and boundary conditions) when using coconut
oil mixed with diesel oil; Identify main adjust factors of the fuel mixture for simulation processing are
injection time and ignition delay through the fuel properties and viscosity cetane index;
- The scientific data of the experimental tests using coconut oil, diesel and additive mixture as fuel
on the specialized AVL test rig.
2. In practical
- Propose solution of using fuel mixture for diesel engines;
- Success Conversion of diesel fuel system to use fuel mixture of coconut oil, and diesel and
additives. Contributing to exploit biofuels for diesel engines to replace a traditional fuel sources are
becoming scarce and reduce environmental
6. Research methods:
1. Theoretical research:
- Study materials on modern theories have been developed in the world for the fuel injection process,
forming the mixture and combustion in diesel engines using alternative fuels.
- Analysis of selected mathematical model reasonably in the application of coconut oil fuel injection
identification compared to diesel fuel as the basis for solutions using mixed fuel.
- Simulation by software using effects of the rate of coconut oil mixed into diesel to the engine
combustion process as a basis for selection of experimental fuel samples
2. Experimental research:
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- Determination of thermal - viscosity correlation of the mixture of fuel samples with different
ratios, which determine a range of reasonable mixture rate
- Compare and verify the performance characteristics, combustion characteristics, economic and the
environment criteria of the engine using diesel fuel with the sample mixture on a specialized test rig.
7. Research content:
1. General comment and study the theoretical basis of using a mixture of coconut oil and diesel oil as
fuel for diesel engines;
2. Selecting mathematical model and simulation by a software of injection and combustion process
of coconut oil - diesel oil mixture in diesel engines;
3. Assessing the impact when changing the ratio of coconut oil into diesel to the economic criteria
and environmental impacts of diesel engines.
8. Thesis Structure
The thesis is structured into four chapters:
1. Overview of the use of biofuels for diesel engines;
2. Theoretical basis using a mixture of coconut oil and diesel oil as fuel for diesel engines;
3. To assess the effects of coconut oil ratio into diesel oil to economic and environmental criteria to
diesel engine by simulation software;
4. Experimental studies the effects of coconut oil ratio into diesel oil to economic and the
environment criteria of diesel engines.
9. Limitations of the Thesis
The thesis has not solved the relevant issues yet, such as molecular formula of the fuel mixture; The
stability of the fuel mix over time and storage conditions.
Chapter 1 - OVERVIEW OF USING BIOFUEL FOR DIESEL ENGINES
Concept as well as processing technology and use of biofuels for diesel engines is quite broad. The
scope of this topic refers only to liquid fuel: biodiesel and SVO.
1.1. Using biodiesel
Biodiesel is a fuel with properties similar to diesel fuel but is produced from vegetable oils or animal
fats. In terms of the chemistry of biodiesel is fatty acid methyl ester. Raw materials for biodiesel producing
from animal fat catfish, catfish, chicken fat, ... even from plants: coconut oil, soybean oil, canola oil,
sunflower oil, sesame oil, peanut oil, ...
The main advantages of being able to use in the common diesel engine without major renovation,
biodiesel fuel blend well with DO.
The main disadvantages of biodiesel are:
- Must be treated chemically, investment technology chain lead to increase the cost of fuel.
- Biodiesel acts as a soluble, so mixed in diesel oil (DO) is not compatible with some sort of
synthetic compounds and natural rubber.
- Biodiesel has a high rate of aging
1.2. Using direct SVO as fuel
Besides biodiesel, there are a lot of research work such as install additional equipment to convert
clusters to diesel engines can operate directly with vegetable oil or a mixture between them with the mixture
without processing into biodiesel. This technology is called "direct use of vegetable oil" (Straight Vegetable
Oil) referred to as SVO.
1.2.1. Using Pure Vegetable Oil
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In this way, vegetable oil can be directly used for diesel engines without the use of additives or
chemical treatment such as biodiesel
SVO to diesel engines in the world are extracted from rapeseed, sunflower, soybean, palm, coconut,
peanuts, ...
Since the 1970s, many research projects to improve the diesel engine to use SVO. Elsbett Company
(Germany) has pioneered this technology, the engine "Elsbett" of this company is the first diesel engine of
the car in the world using SVO.
Summary of studies using SVO conclude: "100% vegetable oils may be unable to handle alternative
fuels reasonable for diesel fuel "
Technology for direct use of vegetable oil is heated primarily associated dilution to achieve the
viscosity of oil equivalent DO fuel. This makes a good quality for oil spray and leads to combustion process
in a engine more complete. Currently, the world has two common types of SVO fuel system: dual fuel
system; only system SVO fuel.
1.2.1.1. Dual fuel system: This system use DO to start and stop the engine with the same use as
traditional diesel fuel. In this sense, the research of Dr. Nguyen Thach - Faculty of Transport Engineering,
HCMC University of Technology gave good results. This solution matches the station Diesel - Generators
with a capacity of medium and large.
1.2.1.2. The system only SVO fuel: The engine has the additional fuel filter can be run with 100%
SVO without the use of diesel. Most of them characterized by a nozzle, additional fuel pump and auxiliary
filter. This solution change deeply structure of the engine , even this direction is only suitable for new
design engine.
1.2.2. Using vegetable oil and solvent mixture .
Research content is handled mechanically-physical of vegetable oil to achieve some basic
requirements of conventional diesel fuel (DO). In this direction, the technology are mainly:
1.2.2.1. Vegetable oil mix with soluble solvent that have low viscosity
This branch has a number of studies:
Linh Ao Hung (2005). Application of coconut oil as fuel for the DS-60R diesel engine.
Tuan Ho Đuc (2008). To study the effect of the rate of ethanol in the coconut oil- Ethanol mixture to
some basic technique specifications of the diesel
The Author has had the works:
The tested study Vietnam vegetable oil as fuel for small diesel engine of the fishing vessel, Research
Projects as Ministry level of the B2006-13-09.
Solvents used in the above projects are the kerosene and ethanol, depending on the ratio in the
mixture, it may need to preheat or not.
1.2.2.2. Blend vegetable oil and additives with diesel oil (DO)
Starting from the theoretical basis for the fuel used in diesel engines; the formation of a combustion
mixture and combustion of the fuel in the engine, the two priority issues to be addressed when using
alternative fuels are:
a / Handling viscosity: 100% fuel system of diesel engine used in the field of agriculture-forestryfishery currently uses low viscosity diesel oil . The system can not operate with viscous higher than standard
DO. Fuel mixture due to the high viscosity of vegetable oil, so the need to:
- First, mixed vegetable oil into diesel oil at the rate of viscosity is small enough to remain within the
limits of standard DO without heating.
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- Second: mixed vegetable oil into diesel fuel at a rate large enough but the technology conversion
engine fuel system is not too complex, non-interference engine texture and acceptable price. Under this
option, the mixture must be heated to a certain temperature to achieve standard viscosity.
b/ Improve the quality of combustion
The Author has had the works:
“Study on conversion technology fuel system of small marine diesel to use coconut oil, additives
and diesel oil mixture”, Research Projects as Ministry level of the B2009-13-42
In summary, from the foregoing comments, prominent research issues to: Define reasonable ratio of
vegetable oil into diesel (with additives) to this mixture can be used as fuel for diesel engines, satisfying the
economic and the environment indicators:
So: “Research on appropriate mixing ratio between coconut oil and diesel oil used as fuel for diesel
engines to improve the economic and the environment indicators” is a topic that researcher will be presented
in this Thesis
Contents of research presented at the Opening
Research process will follow the diagram in Figure 1-2.
FLOWCHARTS RESEARCH PROCESS
B100 (SVO)
Economic indicators
Objectives
T 0C
0
Content of research
ge
ηe
x%+Pg
1
x1
2
3
x2
Environment indicators
B00 (DO)
NOx
K%
HC
COx
%
Hình 1-1. Flowcharts research process
With:
x1%: Lower bounds on the rate of coconut oil mixed diesel oil (not heated) that the viscosity is
located in the upper limit of diesel oil standard
x2%: Upper bounds of the ratio of coconut oil mixed with diesel and heating the mixture to 800C
(above this temperature no significant reduction in viscosity), but the rate of of the mixture is large enough
but the viscosity is still located in the diesel oil standard
x% (x1, x2): percentage of coconut oil mixed with diesel oil and heating are the samples of test fuel.
Pg: Additives;
T(0C): Heating temperature of the mixture
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Chapter 2- THEORETICAL BASIS OF USING COCONUT OIL AND DIESEL
MIXTURE AS FUEL FOR DIESEL ENGINES
With diesel (compression pressure, self-burning fuel) outside the structure characteristics of the
engine, the fuel nature have meaning decisions to spray characteristics, the quality of the mixture, and
combustion and exhaust in the engine. That also means, targets mainly are the economic and the
environment indicators depends on the nature and type of used fuel .
As described in the Overview section, the intention of the researcher when using alternative fuels on
diesel engine is non-interference in engine texture that just adding to a mixture set for the fuel system. And
so, as described in the diagram in Figure 2-1, isolate the engine structural and intake system parameters, the
economic and the environment indicators of the engine only depends on the fuel nature . The study of this
relationship is also the goal of the Thesis.
With such arguments, the theoretical basis will present the basic idea:
- On the basis of the theory of diesel fuel for the parameters to be handled when using coconut oil as
alternative fuel
- Analysis of the effect of the parameters: viscosity, density, surface tension of the fuel to the jet
structure. This effect is described by the diagrams and mathematical formulas, as a basis for analysis of the
jet structure and form solutions using coconut oil as a fuel.
- The next important content is the basis of the theory of mixture formation, combustion and
emissions, including: charts, mathematical descriptions, models ... On this basis, with the support of
computer through a dedicated software to help study the effect of fuel properties on the environmental and
economic indicators by simulation (Chapter 3).
The basis of this theory also allows to explain the results of experimental study of fuel properties
affect the economic and environmental indicators (Chapter 4).
2.1. Fuel for diesel engines
The basic norms of diesel fuel include:
2.1.1. Viscosity
2.1.2. Thermal Treatment
2.1.3. Temperature flash fire and the burning temperature.
2.1.4. Cloudy temperature and the freezing temperature.
2.1.5. Self-ignition of the fuel
To quantify the burning of fuel, can use the quantity:
2.1.5.1. Ignition delay (τi)
2.1.5.2. cetane number
2.1.6. Density
2.1.7. Calculated evaporation
2.1.8. Surface tension.
Surface tension (σ) are important parameters affect the fuel spray structure.
In addition, diesel fuel are also some other properties but no or very little influence on the jet
structure should not be considered here.
2.2. Theory of the fuel injection process and the jet structure of coconut oil fuel in diesel engine
2.2.1. Theory of fuel injection process in diesel engine
2.2.1.1. Breaking mechanism of liquid jets
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Air
Fuel
EGR
Fuel specifications
Boost pressure characteristics
Intake structure
Motion
characteristics of the
air (swirling,
tangled)
Injection system
Injection process Features
(Injection rule, injection time)
Combustion chamber structure
Jet structure (particle distribution, jet
penetration, spray cone angle)
Evaporation characteristics
Fuel mixture, air
Inition delay characteristics
Ignition
Ignition delay
Early combustion a part of fuel air mixture
Combustion process
Diffusion combustion
Diffusion of the
combustion products
Heat transfer
Thermal
efficiency
NOx
Soot
Exhaust
gas
emissions
HC
Figure 2-1. Diagram describing the formation of a mixture
and fuel combustion of diesel engine
Breaking mechanism of liquid jet depends on the relative velocity and the properties of the liquid
and the surrounding gas, the breakdown of liquid jets are regulated by different decay mechanisms. These
mechanisms are usually characterized by the distance between the hole injection to the first point of droplet
formation, called the decay length and the size of the droplets are created. Can be divided into four stages of
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decay jets, Rayleigh phase, primary phase perturbations, secondary phase turbulence and small dispersed
phase particles (mist).
Figure 2-2 is a diagram of Ohnesorge (Ohnesorge W., 1931), in which Z is a function of Re. With
stable conditions, to distinguish the differences between the four jets decay mechanism. However, only
describe the nature of the liquid phase in the above mechanism is not enough, because of the tear to the
particles (mist) can be enhanced by increasing gas density.
Figure 2-2. Ohnesorge diagram: jet break-up regimes
So Reitz (Reitz RD, Bracco FV - 1986) refers to the ratio of the density of gas / liquid and expand
Ohnesorge two-dimensional into three-dimensional diagram as shown in Figure 2-3.
Figure 2-3. Schematic diagram including the effect of gas density on jet break-up
Figure 2-4. Schematic description of jet break-up regimes
2.2.1.2. Breaking mechanism droplet
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Experimental studies indicate that the mechanism of breaking droplets depends on the number of
different Weber. Figure 2-5 shows a summary of the decay mechanism drops, at very low Weber near Weg
value = 12, droplet deformation does not decay. Results of the break-up of drops due to distortions like a
bag. At the surface to form large drops, while the rest of the bags break down into smaller droplets, the result
has two methods size distribution.
Figure 2-5. Drop break-up regimes according to Wierzba (Wierzba A., 1993)
2.2.1.3. The structure of jets in the engine
Figure 2-6. Break-up of a full-cone diesel spray
Immediately after leaving the spray hole, jet spray began to split into spray cone . This is the first
break of the liquid is called the primary decay and as a result large droplets dense distribution near the
injection hole.
In the case of high-pressure spray, the cavitation erosion and disturbance inside the injection hole is
main decay mechanisms. Subsequent decay into smaller-sized droplets is called the secondary decay caused
by aerodynamic forces generated by the relative velocity between the droplet and the surrounding gas, as
described in the previous section.
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The basic experimental and semi-empirical relationships relevant spray parameters of diesel as:
angle cone, jets length, decay length, and the average diameter of the droplets is a function of theboundary
conditions have been made and published by different authors.
2.2.2. Jets structure analysis of coconut oil fuel
Understanding the process of scattering and beam characteristics have important implications for
designing diesel and alternative fuel research, because the combustion in diesel engine dependent on the
quality of fuel injection into the combustion chamber closely. Figure 2-7 shows the main parameters of the
jet fuel. beam length S, decay length Lb for the concept of the beam dispersion. Beam cone angle 2θ and the
average size of the particles as a result of fuel dispersion process..
2.2.2.1. Decay length Lb :
Jet of liquid fuel not decay immediately after out of the injection hole , which experienced a new part
of the beam decays into particles. Length is called the decay length Lb. Length of Lb approximately (20 ÷30)
mm.
Decay length
Injection angle
-
Lb
Fuel droplet size distribution
Depth penetration
S
Figure 2-7. Spray parameters
2.2.2.2. Fuel particle size:
Calculated by Sauter average diameter (D32)
2.2.2.3. Fuel beam length S:
Fuel beam length S proportional to the square root of time from the beginning of fuel injection.
2.2.2.4. Fuel beam cone angle 2θ
To investigate theoretically spray coconut oil fuel compared to diesel, it should be assumed that the
technical condition of the engine does not change, then, calculate the basic parameters of the beam as fuel in
Table 2.1.
With:
d0 – diameter of injection hole
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Cb - coefficient, according to the Levich model Cb = 15.8; model of Reitz and Diwakar or
Kelvin-Helmholz (1987) experiments with high-pressure spray occurs cavitation bubbles, Cb = 10.
D32 - Average Size Sauter, µm;
∆p - difference of pressure , Pa;
ρg - Density of gas, kg/m3;
Q - The amount of jet fuel in a cycle, kg/m3;
Table 2.1: Results of the theoretical calculations of the basic parameters
of the beam fuel for diesel and coconut oil.
The model
Parameters
calculations
Formular calculations
diesel
Cocnut oil
ρl
ρg
26,572
27,799
ρl d 0
ρ g ∆p
1.688
1.848
39.503
39.038
41.989
43.928
43.9415
43.9415
Reitz and Diwakar
Length decay,
or Kelvin-
mm
Helmholz (KH),
Lb = 10d 0
1987
Time decay, ms
Levich, 1962
tb = 29.8d 0
Hiroyasu and
D32 = 2.33.103 ( ∆p )
Kadota, 1974
( ρ ) (Q )
Sauter average
diameter, µm
0.121
−0.135
0.131
g
0 < t < tb
Beam length,
Hiroyasu and Arai,
mm
1980
Beam cone
Hiroyasu and Arai,
angle, degree
1980
S = 0.39t
2∆p
ρl
ρ g ∆pd 02
2θ = 0.05
µ 2
g
0.25
Table 2.1 shows that:
- Deviation decay length Lb of coconut oil with diesel fuel (about 5%).
- Chiều dài Lb của dầu dừa lớn hơn nhiên liệu diesel, như vậy cần tăng áp suất phun pph.
- Thời gian phân rã tb dầu dừa lớn hơn nhiên liệu diesel, đây là thông số ảnh hưởng nhiều đến thời
gian cháy trễ của động cơ, vì vậy cần tăng góc phun sớm của động cơ khi chuyển sang sử dụng dầu dừa làm
nhiên liệu.
- Decay time tb of diesel greater coconut oil near 9%.
- The length of the jet fuel in time t 700C the surface tension of the coconut oil are similar with diesel oil at room
temperature. Thus, the heating the 800C surface tension of the mixture equivalent of diesel oil (Table 2.4).
Relationship surface tension of the mixture and the ratio of coconut oil into diesel is calculated by:
σ = 0.05x + 23.4
(2.3)
Where: σ is the surface tension of the mixture (mN/m); x is the percentage of coconut oil mixed
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2.3.2.6. Density.
When diluting and preheat the density of a mixture of coconut oil - DO approximates diesel.
Relationships mixture density (g/cm3) and the percentage of mixing of coconut oil. is calculated by:
ρ = 0.0008x + 0.836
(2.4)
2.3.2.7. Flash point, cloudy point
Pure coconut oil have quite high cloudy point (> 200C) but when dilute (cloudy point calculation for
mixture <- 40C) and heated to 800C, the problem is solved.
From what just presented we can confirm that:
Diluted coconut oil and additives on diesel at the rate of 10-25%, heated to 800C will create fuel
mixture meets the basic criteria of traditional diesel.
2.4. Solution using a mixture of coconut oil and diesel oil as fuel for diesel engines.
2.4.1. Method mix mixture.
Mixing method manually, the biggest drawback is hard to ensure homogeneous mixture after
mixing.
Mixing method in industrial scale, fuel ratios are prepared in the large-scale plants and is distributed
to the fuel station.
Method of using homogeneous equipment of fuel mixture, hydrodynamic equipment can work on
the principle of cavitation can be applied to handle the fuel mixture.
2.4.2. Method for heating the mixture.
2.4.2.1. Heating by the cooling water.
Fuel preparation systems for water heaters have the advantage to make use of engine coolant
temperature. However, it takes time to heat the fuel to achieve the desired temperature
2.4.2.2. Heating by exhaust gas.
Fuel preparation systems for exhaust gas heaters have the advantage to make use of engine exhaust
heat. Drawback is difficult thermostat, thermal emission at startup period is low, long heating time, not
suitable for small capacity engines..
2.4.2.3. Electric heaters
Fuel preparation systems for electric heaters use DC starting battery.
2.4.3. Choosing of alternative fuel systems
2.4.3.1. Alternative fuel systems for motor cars, small boats:
The solution is to use the automatic mixing and heating fuel mixture by DC power of starting motor.
2.4.3.2. Alternative fuel systems for diesel engines in agriculture:
The common agricultural machines are small, no specialized service systems. So the fuel mixture is
prepared by using a mixed industrial-scale automatically (or manually depending on the conditions of use)
and is heated by the cooling water.
From the analysis above, we have:
(1). Mixing ratio of Vegetable oil and additives in oil DO:
Mix coconut oil into diesel oil (DO) at the rate of turn: 10, 15, 20, 25%
Mixing Nano fuel bosster addtive with fuel mixture which designated by the Manufacturer 1/800
The fuel mixture is denoted from B10 to B25
(2). The interpolation formula from 2.1 to 2.4 are used to:
Assess the compatibility of the physical parameters of the sample of alternative fuels compared to
traditional fuel, thus forming new fuel solutions.
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Declare the parameters, the adjustment of input parameters for simulation studies when switching
fuel types are presented in the next chapter.
DO
SVO
Flter
Throttle
valve DO
Throttle
SVO
Homogeneous Tank
Heating to 800C
stirring
Diesel engine
Residual fuel drain line
Figure 2-8. System principle diagram of mixing equipment use throttle valve
Chapter 3. IMPACT ASSESSMENT OF MIXING RATIO OF COCONUT OIL IN DIESEL OIL TO
ECONOMIC INDICATORS AND ENVIRONMENT BY SIMULATION SOFTWARE.
3.1. Combustion in diesel engines and its model.
Many approaches have been made to create a mathematical model of ch was heterogeneous. The
model that describes the thermodynamics, phenomena and detailed models.
3.1.1. Fuel spray model.
3.1.1.1. Primary decay
a / Blob Method (spherical droplets)
This approach was developed by Reitz and Diwakar (1987).
b/ Distribution Functions
This method assumes that the fuel spray was completely at her mouth of nozzle hole and the droplet
size distribution can be described by mathematical equations.
c/ Decay due to turbulence
Huh and Gosman (1991) published a model of the phenomenon of turbulence generated fog of jets of
diesel engine, it can also be used to predict the spray cone angle. Spray model begins with the spherical
droplet diameter of approximately nozzle hole diameter D. Developing the initial surface wave due to the
relative velocity between gas and drops under the Kelvin-Helmholtz (KH) and decay to create the mist.
d/ The decay due to bubble erosion
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Arcoumanis et al (1997) have developed a model for primary decay of cone jets of diesel engine that
erosion, disturbance and aerodynamic effects are taken into account. Initial droplet decomposition is
modeled using the Kelvin-Helmholtz mechanism, in the case of decay due to the aerodynamic forces, applied
model of Huh KY, Gosman (1991).
e/ The decay due to erosion and disturbance
Nishimura and Assanis (2000) have presented a model of primary decay caused by erosion and
disturbance to the spray cone jets of diesel engines take into account the explosive energy burst bubble
cavitation.
3.1.1.2. Secondary decay
a/ Phenomenon models
Arcoumanis C., Gavaises M., French B. (1997),distinguish the secondary decay mechanism in seven
forms depends on the Weber number.
b/ Decay model is similar to Taylor: PJ O'Rourke, AA Amsden (1987) proposed a decay model
which is similar to Taylor
c/ Drop deformation and decomposition model: Ibrahim EA, Yang HQ, Przekwas AJ (1993),
proposed the droplet deformation and decay model.
d/ Kelvin-Helmholtz Decay model
This model proposed by Reitz RD (1990)
e/ Rayleigh-Taylor decay model
The model based on the theory of GI Taylor (1963)
3.1.2.Turbulent movement of the air and turbulent dispersion
Turbulent movement of air in the cylinder affect the quality of the burning mixture. The detailed
multi-dimensional model (Gosman - 1985, [20]) refers to the swirling cyclone of air speed.The turbulent
dispersion is described by: GM Faeth (1983, 1987) and Gosman A.D., Ioannides E. (1981).
3.1.3. Evaporation of the fuel, self ignition and ignition delay
3.1.3.1. Evaporation of the fuel
3.1.3.2. The self ignition of the fuel
Self-ignition model of the fuel used the most widely is Shell model.
Shell model is the model used the most in the simulation of self ignition of current diesel engine. It is
capable of describing the effects of temperature, pressure and composition of the fuel – air mixture when
combustion is late.
3.1.3.3. Ignition delay time
The two most common criteria are used as pressure increases latency and latency ignition. Effect of
environmental temperature and pressure to ignition delay time was studied by Arai et al (1984).
3.1.4. Heat and heat transfer
3.1.4.1. Heat rate
In the Wiebe model (1956) and Shipinski (1968) apparent heat rate is determined by the simple
relation with the operating parameters of the engine. Austen (1960) and Lyn (1962) scaled volume of fuel in
the injection cycle to create a relationship between the apparent rate of heat and spray process. There are also
a number of researchs of Tanasawa (1953), Shipiski (1970) and Ikegami (1967) describes the relationship
between the speed of injection, the volume of fuel evaporation with rate of the apparent heat.
3.1.4.2. Heat transfer
There are studies measuring the heat transfer cylinder engine and the model was launched. The study
of heat transfer divided into: the process of compression and expansion; combustion; Air change process and
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the entire work cycle. On that basis, the authors have established the empirical formula to estimate the
instantaneous heat transfer rate.
3.1.5. Emissions
3.1.5.1. Nitoric oxide emissions (NOx)
NOx Product create in the high-temperature flame zone, where nitrogen can form a small amount of
a compound of CN, HCN and oxidized to NOx.
3.1.5.2. Particle emissions
The particles in diesel exhaust basically are Carcbon particles with organic compounds of high
molecular weight aggregates into blocks or combined in the form of a string. These particles called coal or
soot.
3.1.6. The numerical models used in the simulation software
Table 3.2: The computational model in the simulation of combustion
Phenomenon
Turbulent flow
The calculation model
Re-Normalisation Group (RNG) k- improvement of Han
and Reitz, 1995
Tear to fuel jet
Wave Breakup of Liu et al, 1993
Ignition delay
Shell Model by Kong et al, 1995
Main combustion
Characteristic-time combustion model of Abraham et al,
1985
Formation of NOx
Extending Zel'dovich mechanism
Soot formation
Soot formation model in several steps of Kazakov and
Foster, 1998
Oxidation of soot
Nagle and Strickland-Constable model, 1962
3.2. Simulation process
3.2.1. Calculation Flowchart in KIVA
All models are integrated into KIVA. The order of calculation is described in Figure 3-14 and Table
3.7 in the thesis.
3.2.2. The simulation conditions
For comparison between experimental and simulation results, the parameters included in the
simulation parameters also correspond to a cylinder research AVL-5402 engine of internal combustion
engine Key Laboratory of the National University Ho Chi Minh City.
In the actual operation of the engine, the load size mode arises most pollutant emissions. Therefore,
the simulation was performed at 80% load mode, at speed of 2000 rpm with 5 different fuel samples: B0 B25
Due to the symmetric nature of the combustion chamber and nozzle spray has 5 holes, the model
simulation is performed on the fifth combustion chamber (72o) instead of the entire combustion chamber to
19
reduce the time of computation.
Combustion chamber to meshing model calculations are presented in Figure 3-15 with 37 cells in the
centripetal direction (x-axis), tangential 36 cells (y-axis) and 31 cells along the vertical axis (z axis). The
calculation is done on a computer fitted with Intel Core 2 Duo processor, the average time is 4 hours to get a
result.
To consider the effect of cetane number and viscosity, a number of input parameters change during
the simulation, while the other parameters the same as in the calculation for diesel. This has been discussed
from Chapter 1
Table 3.3: The main parameters to be adjusted
Shift
Samples
1
B0
2
3
4
5
Adjusted coefficient
follow cetane number:
Ef4
1
B10
B15
B20
B25
0.926
0.974
0.987
1.013
Injection time
Spray time
18o before TDC
10° crankshaft angle
o
18 before TDC
18o before TDC
18o before TDC
18o before TDC
10° crankshaft angle
10° crankshaft angle
9.5° crankshaft angle
9.5° crankshaft angle
3.3. Combustion process analysis and evaluation of the effect of mixture ratio to economic
indicators, environment by simulation software KIVA-3V
3.3.1. Environmental and economic indicators of the Diesel engine
3.3.1.1. Economic indicators
a/ Engine efficiency
b/ Specific fuel consumption (ge)
3.3.1.2. Environmental indicators
a/ Sulfur oxide (SO2)
b/ Carbon oxide (CO)
c/ Carbon dioxide (CO2)
d/ Nitoric oxide (NOx)
e/ Hydrocarbon (HC)
f/ Soot
Soot is particularly important pollutants in diesel exhaust
So:
- To assess economic indicators are: fuel consumption rate ge (g / kW.h).
- Environmental indicators for diesel engines and the most notable are: the amount of NOx and soot
(exhaust gas opacity K%)
3.3.2. Simulation results.
3.3.2.1. The pressure variation
The average pressure rate of the fuel sample is not much difference.
3.3.2.2. Heat rate and temperature variability
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Table 3.4: The value of the average maximum temperature (K)
Value
B0
B10
B15
B20
B25
1.641
1.623
1.613
1.683
1.660
-
-1.09 %
-1.70 %
2.55 %
1.15%
Difference compored
with B0
3.3.2.3. Coconut oil ratio affect NOx emissions
Table 3.5: Volume of NOx emissions at the time of exhaust valve open (g)
Value
B0
B10
B15
B20
B25
0.00112
0.00091
0.00086
0.00107
0.00095
- 18.75%
- 23.21%
- 4.46%
- 15.17%
Difference
compored with B0
3.3.2.4. Coconut oil ratio affect soot emissions
Table 3.6: Amount of soot emissions at the time of exhaust valve opening (g)
Value
B0
B10
B15
B20
B25
7.7 x 10-5
5.6 x 10-5
4.8 x 10-5
5.6 x 10-5
6.6 x 10-5
- 27,3 %
- 37.6 %
- 27.2 %
- 14.2 %
Difference compored
with B0
3.3.2.5. Coconut oil ratio affect capacity and fuel consumption
Table 3.7 introduces engine power when changing the ratio of coconut oil in the fuel from 0% to
25%. While all samples have a slight increase in capacity compared with samples B0, B25 reduce more than
4%.
Table 3.7: Engine power (kW)
Value
B0
B10
B15
B20
B25
5.328
5.354
5.477
5.394
5.108
0.48 %
2.79 %
1.24 %
- 4.12 %
Difference compored
with B0
Specific fuel consumption ge (ISFC) of the sample are presented in Table 3.8. ge has the opposite
trend with capacity. In sample B25, ge increased 4.3%, while other samples decreased slightly with B0.
Table 3.8: Specific fuel consumption ge (g/kWh)
Value
Difference compored
with B0
B0
B10
B15
B20
B25
337.3
334.2
326.9
331.7
349.9
- 0.92 %
- 2.96 %
- 1.51 %
3.76 %
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