The document discusses fuel injection and spray formation in diesel engines. It examines the effects of injection pressure on engine performance and emissions. The results of an experiment showed that brake thermal efficiency peaked at an injection pressure of 200 bars, while brake specific fuel consumption was lowest. CO and smoke emissions decreased with higher injection pressure, while UHC first decreased and then increased as pressure became too high. Optimal injection pressure was found to be 200 bars for a 20% biodiesel blend. Cavitation in the fuel injector nozzle enhances spray atomization and improves combustion. Nozzle geometry and injection conditions can affect cavitation.

1. FUEL INJECTION AND SPRAY
FORMATION
AIN SHAMS UNIVERSITY
FACULTY OF ENGINEERING
SUBMITTED TO:
DR. Mostafa Abdelkhalek
September 26, 2015

2. Pressure injection and its effect
on performance
Injection system is used to optimize the fuel/air ratio that enters the
engine .
The aim of developof fuel injection system is:
1-achieve a high degree of atomization to enable sufficient evaporation in a
very short time
2-achieve sufficient spray penetration to utilize the fuel air charge.
We develop this system to get high injection pressure to get more efficiency.
*When injection pressure decrease, droplets size will enlarge and ignition
delay period (formation of mixing of fuel and air) will increase, so pressure of
piston will increase and efficiency will decrease.
*when injection pressure increase, droplets size will be very small and ignition
period will be better so efficiency will increase.
*when injection pressure extremely increase, droplets size will be very very
small and igniton period will decrease more and more , possibility of
homogenous mixing will decrease and efficiency will decrease again.
There is some results from an experiment was made in india :
The engine is started and run the engine at 1500 rated RPM for 16.5:1
compression ratio.
Experiments are conducted starting with no load at the injection timing of 23 o
b TDC and six different injection pressures of 170,180, 190, 200, 210 and 220
bars. Then the load is increased to 25% load, 50% load, 70% load and full
load with diesel fuel.
Data such as the relation between BTE, BSCF, CO emissions, smoke opacity
and IP .

3. Brake thermalefficiency ( BTE):
Is the break power of a heat engine as a function of the thermal input from
the fuel and used to evaluate how well engine convert the heat from a fuel to
mechanical energy.
It is observed that:
1- as IP decreases, BTE decreases due to coarse spray formation , poor
atomization , poor mixture formation and poor penetration.
2- at BTE at IP of 200 bar for 20BD ,30BD is higher than BTE for diesel.
So 200 bar and 20 BD is the optimum for bio diesel.
Brake specific fuelconsumption (BSFC):
It is the measure of the fuel efficiency and used for comparing the efficiency of
internal combustion engine with shaft output.
It is observed that:
1- when IP increase, BSFC decrease .
2- the lowest BSFC was found at 200 bar and 20 BD =12.67 MJ/KW- hr and it
is better than that for diesel =13.25 MJ/KW-hr.

4. CO emissions:
It is observed that:
1- as IP increases , co emissions increase for all bio diesel blends. may be
due to improper mixing of fuel particles with air, less penetration of fuel
particles and ineffective combustion of the blend at these pressures.
UHC ( un burnt hydrocarbons):
Is the result of incomplete combustion of fuel.

5. It is observed that:
1-when IP increase , UHC decrease. But at IP of 210,220 bar , there is an
increase of UHC emissions cause of finar fuel spray and penetration of the
droplets resulting incomplete combustion.
2- the minimum UHC was at IP of 200 bar and 20BD,100 BD.
Smoke opacity:
It is observed that:
1-the highest smoke opacity for blends at 170 bar.
2- as IP increase , the smoke opacity decrease.
3- all blends have less smoke opacity than diesel. The presence of oxygen in
the blends in addition to good atomization of fuel at higher pressure may be
the reason for lower opacity.
4- the better combustion was at IP of 200 bar.

6. Finally this is the difference between the shape of fuel in diesel and bio diesel:
biodiesel typically produces longer spray tip penetration lengths and narrower
spray angles.

7. CAVITATION
1. INTRODUCTION
One of the important methods in reducing the exhaust emissions from
compression ignition engines at source is by improving the spray break up
and introducing smaller droplets inside the combustion chamber. The flow
inside the fuel injector nozzle has effects on the spray formation. Cavitation
occurs if the local pressure drops below the vapor pressure of the liquid at
local temperature. The high pressure drop across the injection nozzle tends to
accelerate the liquid within the small nozzle holes. This acceleration of liquid
inside the nozzle generates a high level of turbulence. At the sharp edges
inside the nozzle holes, such as the inlet of the nozzle hole, the streamlines
are contracted such that the effective cross section of the flow is reduced
leading to accelerated velocity of the liquid. According to Bernoulli principle,
this causes a reduction in the local static pressure and it can reach value to as
low as the vapor pressure of the liquid. bubbles are formed inside the nozzle
hole because of the cavitation phenomenon. These cavitation bubbles are
swept out of the nozzle into the combustion chamber. As the bubbles are
introduced into combustion chamber pressure, they implode and contribute to
further break up of the spray.This leads to finer droplets of fuel which aids in
faster evaporation of fuel.
2. CAVITATION
Cavitation is the formation of vapor cavities in a liquid that are the
consequence of cavitational forces acting upon the cavitational liquid. It
usually occurs when a liquid is subjected to rapid changes of pressure that
cause the formation of cavities where the pressure is relatively low.When
subjected to higher pressure, the voids implode and can generate an intense
shockwave.
Cavitation is a significant cause of wear in some engineering contexts.
Collapsing voids that implode near to a metal surface cause cyclic stress
through repeated implosion. This result in surface fatigue of the metal causing
a type of wear also called "cavitation". Apart from excessive vibrations,
cavitation drastically alters the flow field, reducing the hydraulic efficiency of
the affected hydraulic components.Even if vibration and erosion problems are
avoided by design or operation, it is likely that the performance of the systems
is sub-optimal because countermeasures by design were needed to prevent
cavitation problems.

8. 3. HYDRODYNAMIC CAVITATION
Hydrodynamic cavitation describes the process of vaporization, bubble
generation and bubble implosion which occurs in a flowing liquid as a result
of a decrease and subsequent increase in local pressure. Cavitation will only
occur if the local pressure declines to some point below the
saturated vaporpressure of the liquid and subsequent recovery above the
vapor pressure. In pipe systems, cavitation typically occurs either as the result
of an increase in the kinetic energy (through an area constriction) or an
increase in the pipe elevation.
Hydrodynamic cavitation can be produced by passing a liquid through a
constricted channel at a specific flowvelocity or by mechanical rotation of an
object through a liquid. In the case of the constricted channel and based on
the specific (or unique) geometry of the system, the combination of pressure
and kinetic energy can create the hydrodynamic cavitation cavern
downstream of the local constriction generating high energy cavitation
bubbles.
The process of bubble generation, and the subsequent growth and collapse of
the cavitation bubbles, results in very high energy densities and in very high
local temperatures and local pressures at the surface of the bubbles for a very
short time. The overall liquid medium environment, therefore, remains at
ambient conditions. When uncontrolled, cavitation is damaging; by controlling
the flow of the cavitation, however, the power can be harnessed and non-
destructive.
Orifices and venturi are reported to be widely used for generating cavitation.
A venturi has an inherent advantage over an orifice because of its smooth
converging and diverging sections, such that that it can generate a higher flow
velocity at the throat for a given pressure drop across it.
4. Cavitation in Automotive Applications
Cavitation is known to occur in various automotive components, where high
fluid velocities and rapid accelerations develop; for example fuel may cavitate
in high pressure fuel injection systems, or lubricant in piston rings and
bearings. As a result cavitation erosion may accumulate, causing damage and
affecting engine durability. Cavitation is also known to alter the composition of
Diesel fuel properties. In large Diesel engines it might be possible the coolant
fluid to cavitate at cylinder walls, due to vibrations produced by the engine
operation.

9. On the other hand, cavitation is believed to enhance atomization, thus
improving combustion and reducing emissions in Diesel engines.
5. FACTORS AFFECTING CAVITATION
According to the flow configuration (shape and relative motion of the walls
limiting the flow field, or physical properties of the liquid), injection condition
and injector geometric structure parameters influence the development of
cavitation in nozzles.
5. DETERMINATION OF THE CAVITATION NUMBER
Typical situations in which cavitation can appear and grow in a liquid flow:
The case of a sharp inlet, where the flow separates at the corner, the flow
experience a vena contracta. A diagram of the sharp entrance flow. Point 1
would be downstream of the injector needle that the local velocity would be
small, such as in the sac ofthe injector. Point c is downstream of the inlet,
where the vena contracta effect is amaximum. In the case of a sufficiently
rounded nozzle this point is nonexistent.For convenience a ratio between the
area at the contraction and the nominalnozzle area, known as the coefficient
of contraction, is defined:

10. (Ac(represents the effective flow area through the contraction and)A
(represents the nominal nozzle area. The value of the contraction coefficient
varies
with the nozzle geometry and cavitation characteristics. For a very rounded
entrance, the flow will not separate and the coefficient of contraction will be
unity.
Another relevant integral property of the flow is the coefficient of discharge,
Cd. The coefficient of discharge represents the efficiency of the nozzle
between points 1 and 2 and thus is a measure of whatever losses occur in the
nozzle The definition of the coefficient of discharge is:
useful cavitation parameter and is referred to as K .
* The shearing between two neighboring flows having very different velocities
entails large turbulentfluctuations of the pressure.

11. Results from experiments
Badock et al. (1999) showed experimentally that increasing the radius of
curvature at the nozzle inlet could reduce cavitation. Desantes et al. (2010)
also reported that the cone angle of the fuel spray was found to be increased
due to the formation of vapor inside the nozzle. Payri et al. (2004 and 2005)
also reported that the spray cone angle and outlet speed increased with the
cavitation .Suh et al. (2008) also studied experimentally and reported that
cavitation enhanced the fuel spray characteristics and the primary fuel
breakup due to the turbulence created inside the nozzle. Recently, bio-diesel
fuels promise clean, alternative and renewable source of energy.
Biodiesels have a number of properties that make it an excellent
alternative fuel for diesel engines, particularly because of its low
emissions compared with the diesel fuel (Buyukkaya, 2010; Moser et al.,
2009). Moreover, the distinct properties of bio-diesel may influence the
cavitation phenomenon in the nozzle hole.

12. DROPLET SIZE
Droplet size measurement
Atomic transmission microscope ATM model JEM-1230 is used for nano
emulsion fuel particle size measurement. It is also used for measuring the
histogram of the obtained nano emulsion blend. Max magnification of the
used ATM is 600Kx with max resolving power about 0.3nm per line. Energy
intensity was in the range from 40kv up to 120kv on steps.
Calorific value determination
The calorific value of the sample was measured in the Egyptian Petroleum
Research Institute using
Parr 6200 calorific value tester.
Determination of viscosity
Brook filed model DV-II+ viscometer was used to determine the viscosity and
sample was kept in the water thermostat bath until it reaches the equilibrium
temperature of 18°C. After reaching the equilibrium temperature, the
viscometer tip was inserted to the sample and the reading was taken from the
controller.
Reaction Mechanism
The above equation presents the estimated slow reaction mechanism of
nonylphenol and oleic acid in which neutralization reaction was obtained
showing the formation of one molecule of water and condensation of
nonylphenol and oleic acid resulting viscous dispersing agent of water in
biodiesel. Also this high viscosity may be is the reason for the long stability of
the obtained biodiesel nanoemulsion fuel.

13. Effect of nonylphenol concentration
Fig.1 shows the effect of nonylphenol surfactant concentration on the ignition
time at biodiesel
concentration 80%, and 1% oleic acid. The results show that as the
nonylphenol concentration increases from 1.82% to 6% no significant change
in ignition time is observed and the ignition times were 15.33, 15, and
15mins., respectively, while at 8% dose nonylphenol no ignition is obtained.
Also the observations showed that as the nonylphenol concentration
increases the flame length decreases and no flame at all was obtained at 8%
nonylphenol concentration. Based on the above results 1.82% nonylphenol
surfactant was selected as the optimum surfactant concentration.
Effect of Water content
The effect of water content on the ignition time of the obtained biodiesel
nanoemulsion fuel at
nonylphenol concentration of 1.82% was illustrated in Fig.2. Biodiesel
percentage normally changed with the variation of water content at 0.5ml oleic
acid was added for each sample. The results showed that as the water
percentage increases the ignition time decreases where it was 18min utes for
5ml raw biodiesel and decreases to 15min., 15min, and 10min. at water
content 15%, 24.5% and 35% respectively. The observation shows that the
flame length was the highest at raw biodiesel and slightly decreases at the
rest of the sample at different water percentages. Based on the above
obtained results water content of 24.5% which is balanced with 72.7%

14. biodiesel was selected as the optimum water concentration.
Nanoemulsion stability
Fig. 3 shows the effect of water content on the observed viscosity of the
obtained biodiesel
nanoemulsion. It was found that as the water content increases the viscosity
of the obtained biodiesel
nanoemulsion increases too. Fig. 4 shows the change of the viscosity of the
optimum selected composition with storage time. Biodiesel nanoemulsion
prepared in this work exhibited good stability without phase separation for
more than 6 months but with dramatic decrease in the viscosity. The results
show that the raw biodiesel has a viscosity of 6.81MP at 18°C, while the
obtained viscosity of prepared nanoemulsion at the beginning of preparation
was decreased to 18 MP at 18°C then after 4 months the viscosity of the
same nano emulsion reached 3.5 MP at 18°C. The decrement of the nano
emulsion fuel viscosity with regard to storage time may be attributed to the
continuous slow decomposition of the reaction product of nonylphenol and
oleic acid.

15. From the above obtained data and according to the emulsion satiability,
ignition time, and flame length, the following composition was selected as the
optimum biodiesel nanoemulsion fuel. This composition was water percentage
24.5%, biodiesel 72.7%, nonylphenol 1.82%, and oleic acid 0.98%. This
sample has a density of 0.92g/mL, viscosity of 3.5MP at 18°C at the beginning
of preparation.

16. ATM and Droplet size results
The optimum sample was subjected to ATM analysis for obtaining the
biodiesel nanoemulsion fuel particle size and its histogram.
Fig.5 shows the ATM analysis for the measurement of selected optimum
composition particle size.
The analysis shows that the obtained particle sizes were ranged from 18nm to
240nm. Fig. 6 shows the
histogram of the optimum sample of biodiesel nanoemulsion fuel prepared
using nonylphenol and oleic acidsurfactant at water percentage of 24.5%.

17. The major particle size was 18nm (73%) and the minor particle size was
124nm (8.5%).
Calorific value
The prepared biodiesel nanoemulsion fuel under optimum conditions was
subjected to calorific value
tester and it is found 35.94KJ/Kg.
CONCLUSIONS
Novel formulation of water in biodiesel nanoemulsion form is successfully
prepared with the
composition of 72.7% biodiesel, 1.82% nonylphenol, and 0.98% oleic acid
with water balance of 24.5%.
Resulted biodiesel nanoemulsion, prepared under optimum conditions, has
major particle size 18nm
and the minor particle size was 124nm, density of 0.92g/mL, viscosity of
3.5MP at 18°C and calorific value of
35.94 KJ/kg.
Recommendations
 It is recommended to decrease surfactant dose to ensure maintaining low
viscosity by time and also
studying the effect of oleic acid concentration.
 Also it is recommended to apply the prepared biodiesel nanoemulsion on
the engine and investigate
its effect on the engine performance, fuel consumption and so o

18. SPRAY FORMATION
Spray Regimes
Diesel engine sprays are usually of the full-cone type. This means that in the
idle mode the fuel is blocked from the upstream side of the nozzle and during
injection the core of the spray is more dense than the outer regions.
The liquid spray can be characterized by distinguishing five regimes. Starting
from the nozzle exit first there is an intact liquid core. A few nozzle diameters
further downstream in the so-called churning flow the liquid consists of
ligaments .These liquid parts are like large droplets with sizes comparable to
the nozzle diameter. Then the ligaments breakup into many smaller droplets
in the thick zone where the volume and mass fraction of the liquid phase is
high. Further downstream the breakup process of droplets goes on and in the
same time more and more of the surrounding gas is entrained into the spray
area. The regimes after the thick zone are the thin zone (low volume but still
high mass fraction of liquid) and the dilute zone (negligible volume and low
mass fraction of liquid), respectively.
Breakup Regimes
The disintegration of liquid jets is described by two main mechanisms. The
First mechanism is the breakup of the intact liquid core into droplets and is
called primary breakup. This mechanism is characterized by the droplet size
and the breakup length, which is defined as the length of the intact liquid core.
The second mechanism is the breakup of droplets into smaller ones, which
is called secondary breakup. Both breakup length and droplet size are
dependent on the properties of the liquid and the surrounding gas. At least as
important is the relative velocity between the liquid and the surrounding gas.
The primary breakup is the most important mechanism in fuel injection
systems, because it determines the size of the droplets that separate from the
liquid core, hence therefore also determines evaporation behavior and it
marks the starting point for further breakup into smaller droplets (secondary
breakup).

19. Primary Breakup
The primary breakup mechanism concerns the breakup of the intact liquid
core and can be divided into four regimes. Namely, the Rayleigh regime, the
first and second wind-induced regimes and last but not least the atomization
regime. In order to make a quantitative classification of the regimes the
Ohnesorge number Oh is introduced:
Herein the Weber number Weland the Reynolds number Relare defined as:
The Weber number is the ratio between inertial (or aerodynamic) and surface
tension forces. The Reynolds number is the ratio between inertial and viscous
forces.
The Ohnesorge number is a ratio between viscous forces and surface tension
forces.
the various regimes can be classified in the space Oh as function of the jet
velocity, or alternatively Rel.In this figure the four regimes and also the
relevant zone for diesel injection applications are indicated.

20. Rayleigh regime Breakup at low jet velocity due to axis symmetric
oscillations initiated by liquid inertia and surface tension forces. (D)
droplet>(D) nozzle, the breakup length L jet is long and by increasing jet
velocity( u) also L jet increases.
First wind-induced regime Liquid inertia and surface tension forces are
amplified by
aerodynamic forces. The relevant Weber number for this regime is:
Here urelis the relative velocity between liquid and surrounding gas and the
subscript g
denotes the gas properties. Ddroplet = Dnozzle, Ljet>Dnozzleand by
increasing jet velocity
uthe breakup length Ljetdecreases.
Second wind-induced regimeThe flow in the nozzle is turbulent.
Ddroplet<Dnozzleand by increasing jet velocity u the breakup length
Ljetdecreases.
Atomization regime Breakup at surface directly at the nozzle hole, so the
intact corelength Ljetgoes to zero. Conical spray develops immediately after
leaving the nozzle. Ddroplet is more less than Dnozzle.

21. Secondary Breakup
The secondary breakup mechanism concerns the breakup of droplets due to
aerodynamic
forces that are induced by the relative velocity between the droplets and the
surrounding gas. Similar to the first wind-induced regime for the liquid core the
gas Weber number is the relevant dimensionless quantity to identify the
process, with the only difference that the nozzle diameter D in equation is
replaced with the droplet diameter before breakup d :
Decreasing the droplet diameter d raises the surface tension force. This
means that the
critical relative velocity, the relative velocity at which breakup takes place,
must be higher.
Wegin equation is used to separate the droplet breakup regimes. The values
at which
transitions from one regime to another occur, are determined experimentally.
In engine sprays all droplet breakup regimes occur at the same time. Near the
nozzle the Weber number is high, so most of the breakup takes place at the
nozzle exit. Further downstream the Weber number is lower due to smaller
droplet diameters and lower relative velocities. Therefore the breakup far from
the nozzle is much less.
Atomization in DieselSprays
Modern injectors for diesel engines have nozzle diameters of 200 Mm or less,
and the length of the nozzle hole is approximately 1 mm. Injection pressures
up to 200 MPa are used and therefore the jet velocity u reaches values of 500
m/s and more.

22. Some possible sources for atomization are shortly treated in the
following.
Aerodynamic shear forces amplify the surface waves created by the
turbulence in the nozzle hole. The waves separate from the jet and form
droplets. There are two reasons why this aerodynamic source is less
important. First, this process is time dependent, but it is known from
experiments that jets break immediately at the exit of the nozzle. Second,
aerodynamic breakup is a surface effect, so it cannot explain disintegration of
the inner structure.
Relaxation of velocity profileAt the wall inside the nozzle a no-slip
boundary conditions exists. When the liquid exits the nozzle, the velocity
profile will transform into a uniform one. In order to realize that the outer
region of the liquid accelerates, which may cause instabilities and ultimately
result in breakup into droplets. However, in modern diesel engines the length
to diameter ratio of the nozzle hole is typically small ([ L/D]nozzle = 5), so
probably the flow in the nozzle has no time to develop.
Turbulence The presence of radial turbulent velocity fluctuations in the jet
results, if strong enough to overcome the surface tension, in formation of
droplets. Turbulence-induced primary breakup is considered one of the most
important mechanisms in high pressure applications.
Fuel Spray Characteristics
The most important diesel fuel spray characteristics may be classified as
• Macroscopic quantities such as:
– Spray tip penetration
– Cone angle
• Microscopic quantities such as:
– Droplet size
All fuel spray characteristics influence the combustion process
and engine performance.
-Fuel spray tip penetration(Lp (is defined as the maximal distance measured
from the injector to the spray tip.
-Spray cone angle(θ) is defined as the angle between two straight lines
originating from the orifice exit of the nozzle and being tangent to the spray
outline. This angle usually ranges from 5 to 30.
-Droplet size is usually measured on an average basis by the medium
diameter of the droplets, called the Sauter mean diameter.

23. Fuel spray penetration is determined by the equilibrium of two factors: the
linear momentum of the injected fuel and the resistance of the working fluid in
the control volume. Due to friction, the kinetic energy of the fuel is transferred
to the working fluid. This energy transfer decreases continuously the kinetic
energy of the droplets until their movement depends solely
on the movement of the working fluid.
Diesel fuel spray penetration depends on injection pressure, fuel
properties, and nozzle geometry. By increasing the injection pressure the fuel
penetration velocity is increased. This means increased fuel momentum and
larger spray penetration. Fuel properties like density, viscosity, and surface
tension also affect spray penetration. However, when making raw estimates,
fuel density is often used as the only influencing property. In this context fuel
density of a given fuel may vary, for example, due to variations in fuel
temperature. An increase of fuel temperature typically reduces the fuel
density, which results in shorter spray penetration.
The cone angle is mainly affected by the geometric characteristics of the
nozzle, the fuel and air density. Furthermore, the cone angle increases by
increasing the injection pressure and by decreasing the working fluid
temperature.
The diameters of the droplets depend on injection pressure, on working
fluid temperature, and on fuel properties. The diameters of the droplets tend
to become smaller as the injection pressure raises. Furthermore, the working
fluid temperature and fuel properties influence the evaporation rate, which
also affects the droplet size. Namely, by increasing the temperature the rate
of evaporation increases. Consequently, the droplets with small diameters
tend to evaporate completely within a quite short time interval. On the other
side, the droplets with greater diameters maintain a stable geometry for some
time until they also evaporate completely.
In a fuel spray, fuel droplets evaporate as they travel away from the nozzle.
The maximal distance, reached by the droplets before they all evaporate,
is called the liquid length. After the liquid length is reached, the evaporated
fuel continues to penetrate the surrounding gas and its range is denoted as
the vapor length. It was found out that the liquid length tends to stabilize after
a short spray
development time and then remains constant. On the other hand, in a typical
diesel injection timeframe (a few milliseconds) the vapor length does not
reach a steady state.

24. Liquid spray formation is a rather sophisticated physical process, starting from
the breakup of the liquid core into droplets, shortly after the nozzle exit, called
the
primary breakup. In the second stage the formed droplets break up into
smaller droplets, which is called the secondary breakup .