This document summarizes a study that used computational fluid dynamics (CFD) software to simulate the properties of fuel droplets inside a multi-hole fuel injector nozzle. A 3D model of a multi-hole fuel injector was created in SOLIDWORKS and imported into ANSYS for CFD analysis. The study varied injection pressure and analyzed its effects on atomization. The CFD results provided insight into improving engine emissions and fuel economy by optimizing fuel droplet atomization patterns in the cylinder.

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Study of fuel droplets from injector using ansys
Mukul K. Badial1
, Shivam Garg2
1
(Student researcher / Department of Mechanical Engineering / SRM Institute of Science and Technology)
2
(Simulation Engineer / FEV India Private Limited / India)
Abstract: The main objective of this study is to simulate the properties of fuel droplets inside the multihole
nozzle fuel injector. A 3D solid model of multihole fuel injector is prepared using SOLIDWORKS and flow
analysis (CFD) is done to check the flow properties of the fuel droplets inside the fuel injector. Variation of
injection pressure on air-fuel mixer is studied in detail in this work.
Scope of this work deals with the improvement of internal combustion engine emissions and fuel economy
performance by proper atomization of droplets into the cylinder.
We are using ANSYS computational fluid dynamics (CFD) software to study the multihole fuel injector to
deliver droplets in just the right spray pattern to optimize engine performance.
Keywords: Multihole nozzle, Atomization, Pressure variation, Combustion, CFD, Simulation
1. INTRODUCTION
The impact a product has on the environment has become increasingly important to the aerospace
industry in the preliminary design phase of jet engines. The study of fuel injection characteristics
within the jet engine can increase our understanding of combustion and therefore improve the
efficiency of engines operation. Accurate computer modeling of the fuel injection spray into the
engine can provide information about future soot and emissions to meet strict environmental
requirements.
The engines combustion chamber is designed around the fuel injector's characteristics. The current
process for estimating the fuel injector's characteristics in the aerospace industry is costly and time
consuming, involving computer and mechanical testing. The process involves creating a model to
study the individual aspect of a nozzle including their sprays distribution and the sprays breakup.
This study involves the use of a numerical model to simulate spray distribution. There are many
characteristics of the spray that must be programmed into the numerical model to accurately create a
realistic simulation. Many of these characteristics are unknown.
This study will examine the relationship between the simulated spray characteristics and results
obtained from experimental results. The results of this study will be useful for
Engineers to tune spray models.
This study demonstrates that each input parameter into the simulation has a unique and dramatic act
on the simulation's output and its correlation with the physical data. However, more importantly, it
was the creation of a realistic simulation, incorporating all the complexities of spray injection that
would result in a good correlation with the physical data.
1.1.FUEL SPRAY
There is a great amount of interest in many industries for the creation of an accurate way to predict
sprays. Some examples of this are, spray coating applications, and re-extinguishing sprays. High-
quality spray coating needs a system that will deliver a constant performance and a high impact
velocity without the worry of overheating. The Computational Fluid Dynamic, (CFD), code Fluent
has been used to simulate the spray of a mist used to extinguish a pool-like gas. The simulation is
modeled based on the stochastic separated ow, with the development and implementations of

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turbulence models for parcels and sub-parcel droplet dispersion, spray collision and spray breakup
models. The results indicated that the approach was successful in providing an accurate and robust
means to solve transport problems dealing with dispersed phase spray for future applications.
2. FUNCTION OF NOZZLE
 It should atomize the fuel droplets. This is a very important function since it is the first phase
in obtaining proper mixing of the fuel and air in the combustion chamber.
 Distribute the fuel in require area within the combustion chamber.
 To prevent fuel from impinging directly on the walls of combustion chamber or piston. This
is necessary because fuel striking the walls decomposes and produces carbon deposits. This
causes smoky exhaust as well as increase in fuel consumption.
 To mix the fuel with air in case of non-turbulent type of combustion chamber.
Fig 1. Different type of fuel injectors
Fig 2. Pintle nozzle
In fig 2, pintle nozzle fuel injector is shown. This type of nozzle the stem of nozzle valve is extended
to from a pin or Pintle which protrudes through the mouth of the nozzle. The size and shape of the

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Pintle can be varied according to the requirement. It provides a spray operating at low injection
pressures of 8-10MPa. The spray cone angle is generally 60 degree. The main advantage of this
nozzle is that it avoids weak injection and dribbling. It prevents the carbon deposition on the nozzle
hole.
Fig 3. Multihole nozzle
The multiple-hole nozzle provides good atomization but less penetration than the pintle nozzle. The
multiple-hole nozzle is used with the open type of combustion chamber in which high atomization is
more important than penetration. The spray pattern of the hole nozzle is dependent on the number and
placement of the holes or orifices. Spray openings, or orifices, are from 0.006 inch up to about 0.033
inch in diameter, and their number may vary from 3 to as many as 18 for large bore engines.
3. METHODOLOGY
 Importing CAD Model
 Meshing is prepared
 Boundary Conditions are applied such as,
- Inlet mass flow rate/ Pressure/temperature applied
- Outlet pressure is applied
 Results are calculated
- Velocity
- Temperature
- flow dynamics
4. SIMULATION SET UP
Generally, the simulation in ANSYS FLUENT involves three main stages which are pre-processing,
solver and post processing. The design of injector used in this study is only focused on the injector
head and combustion chamber. A complete injector has six orifice holes with an angle of 120º between
each other. Figure 1 shows the 3D model of cross section in internal combustion chamber of rapid
compression machine (RCM) while the geometry of injector with orifice 3 holes drawn using
Solidworks software.

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Fig 4. Section view of fuel injector
5. BOUNDARY CONDITIONS
The Mass flow inlet was chosen because it was found to provide a converged solution more easily
than a pressure inlet. The inlet air pressure and mass ow rate was received from experimental data and
the outlet was defined as an outflow with a weighting of 1. The outlet boundary condition is set to this
condition because the details of the flow velocity and the pressure are unknown. This boundary
condition will allow FLUENT to extrapolate the required information from the interior. This boundary
condition can be used in this case because this boundary is a single outflow rather than a split outflow
meaning the flow rate weighting is set to 1. This boundary condition is also useable because the inlet
boundary condition is a mass flow inlet and since the cylindrical control volume is so large, it is safe to
assume the flow will be fully developed once it reaches this point.
Fig 5. Meshing used in chamber Fig 6. Inlet position of mass flow rate
6. RESULTS
The First step in setting up a simulation is to ensure the mesh works, meaning that the mesh is at a
quality that the CFD software can use. This is done by imputing the mesh into the FLUENT software
and running the mesh check. The mesh check will run several checks on the mesh including one to
ensure that the mesh meets the minimum cell skewness limit. This limit was of concern when
creating the mesh for this study because the narrow passages in the complex geometry of the nozzle
skewed the cells of the mesh. To ensure the initial set-up of the simulation within FLUENT was
correct, air was simulated to be passed through the mesh. This is the simplest case possible for this
mesh and therefore included the least amount of possible places for errors.

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The simplest simulation that can be run is a simple arrow through the bottom cylindrical control
volume. Therefore, the nozzle mesh was unselected so that only the bottom cylindrical control
volume remained active. This control volume is a basic cylinder with the inlet at the top of the
cylinder and the outlet at the bottom of the cylinder shown in Figure. After iterating this simulation
it was found that the solution did not easily converge. It was found that there was a great amount of
air re-entering the control volume at the bottom of the cylinder known as reverse ow. To this
problem, a cone was added to the bottom of the cylinder as shown in Figure this reduced the size of
the outlet of the mesh, increasing the pressure the air was exiting with and decreasing the chance of
air entering the bottom of the cylinder. After this change was made, the simulation converged as
expected.
The nozzle mesh was then reactivated so that both the nozzle mesh and the cylindrical mesh would
be active in the simulation. After this mesh was input into FLUENT, FLUENT rejected the mesh. Many
errors were present and the mesh check failed. To solve this problem the geometry was Re-
evaluated. The geometry was combined to include both the nozzle and the cylindrical control
volume. This new geometry was re-meshed and input into FLUENT. The mesh was checked within
FLUENT using its tool and the mesh passed. The simulation that was run at its simplest form passing
only air through the mesh had the boundary conditions
Table 1. Boundary Conditions
This meant that is was very hard to predict the individual initial injection conditions for each of these
flows. Therefore, it was determined that the average of the flows would be injected.
Fig 7. Path line covered by Particle ID
Mass flow rate Air Mass Flow rate 0.071 Kg/sec
Outflow Outlet Flow Rate Weighting 1 Kg/sec

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Fig 8. Path line covered by Particle ID
Fig 9. Axial View of Velocity Magnitude (m/s)
CONCLUSIONS
This study demonstrates that each input parameter into the simulation has a unique and dramatic
effect on the simulation's output and its correlation with the physical data. However, more
importantly, it was the creation of a realistic simulation, incorporating all the complexities of spray
injection that would result in a good correlation with the physical data. A numerical model using the
fluent software was produced to simulate the spray distribution. The results of this model have been
compared to data collected from the mechanical rig. A parametric study has been performed on the
model variables to identify the sensitivities of these parameters on the spray characteristics.

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