Fuel Injector Project

1. 0

Heath Headley Vu Danh Nicholas Chua
Tommy Harris Ryan Fontenot
DEPARTMENT OF MECHANICAL ENGINEERING
UNIVERSITY OF LOUISIANA AT LAFAYETTE
PROJECT ADVISOR: DR. LULIN JIANG
Flow-Focusing to
Flow-Blurring Fuel
Injector
MCHE 484 SENIOR DESIGN PROJECT
APRIL 28, 2016

2. Executive Summary

This project involved designing and building a fuel injector that is of the continuous flow
type, and employs the flow-blurring concept. Flow-blurring was invented by Dr. Alfonso Gañán-
Calvo. Flow-blurring involves the use of high speed air flow mixing with fuel flow to atomize
and vaporize any given fuel. This is especially useful if one were to be using an unusually high
viscosity fuel like some thick biofuels, as it would effectively vaporize them for more efficient
combustion.
The team designed and built an injector that can be adjusted to operate in both the flow-
blurring and flow-focusing regimes by adjusting the offset distance. The injector parts were 3-D
printed with ABS plastic. The model that was built performed as expected, working well in both
flow-focusing and flow-blurring regimes. Pictures were taken of the spray patterns that resulted
from various air-liquid ratios and later examined.
The approximate spray angle and air-liquid composition of the injector sprays were both
able to be analyzed visually from the photographs that were taken with a Nikon camera mounted
on a tripod. More exact analysis of spray characteristics, for example droplet size, was not possible
to determine from photographs alone. More sophisticated measuring equipment would be
necessary.

3. Table of Contents

Introduction………………………………………………… ………………..….…………....…..1
Section I: Project Constraints………………………………………………………… .....…..…..3
Section II: Background Research……………………………………………………… ....…..….4
Section III: Design Process……………………………………………… .………………… ...…6
III.1 Design Criteria……………………………………………………………… .…..…6
III.2 Design Evaluation Process…………………………………………………… ..…...7
III.3 Designs Created………………………………………………………………… ......8
Section IV: Final Design Details…………………………………………………………….....16
IV.1 Design Testing and Results…………………………………………………… .….16
IV.1.A Equipment Used…………………………………………………… .…..16
IV.1.B Testing Procedure…………………………………………………… .…16
IV.1.C Testing Results…………………………………………………………. 17
IV.2 Cost Analysis……………………………………………………………………… 20
IV.3 Conclusions……………………………………………………………………….. 21
Appendices……………………………………………………………………………………. .23
Appendix A: Sample Calculations…………………………… ….….………………. 24
Appendix B: Injector Part Drawings…………………………… ………………… ....29
Appendix C: Parts List………………………………………… …………………… .32
Appendix D: Time and Personnel Management…………………………………… ..33

4. 1


Introduction

Flow-blurring fuel injectors would be desirable for use in turbine engine applications that
are running on high viscosity biofuels. They can also be quickly adjusted to operate in the flow-
focusing regime, if desired. High viscosity fuels are not as quick to vaporize as more conventional
fuels like gasoline. A common automotive injector can simply spray gasoline into a combustion
chamber to vaporize and mix with the incoming air quite readily. A thicker fuel is not as easily
vaporized by conventional injectors. This is one way a flow-blurring injector can be useful. When
certain geometrical and flow conditions are met within the injector nozzle and around the exit
orifice, a flow-blurring injector that is operating in the flow-blurring regime can effectively
vaporize even the thickest of fuels, which allows easy mixing with intake air so that efficient
combustion can be achieved.

5. 2

Project Objectives

 Design unique flow-focusing to flow-blurring fuel injector using Solidworks

 3-D print design

 Install leak-proof and reliable fuel and air connections

 Set up test lab with all necessary equipment

 Outline experiment plan for relating spray characteristics to ALR (air-liquid ratio) and
H/D ratio (offset distance to fuel feed tube diameter ratio)

 Conduct experiments and collect desired data

 Organize data into neat and presentable form

 Discuss what has been learned from the experiments

6. 3

Section I
Project Constraints

In this context, project constraints are defined as limitations that prevent the design from
becoming the best it can be. These will include time, cost, and material constraints, among others.
The constraints for this project are as follows:
Material Constraints:
The material is limited to 3-D printable plastic like PLA or ABS.
Size Constraints:
The size of the full assembly must be as small as practicable, while still allowing
installation of a 1/16” NPT compression fitting for liquid and a 3/8” NPT air hose adapter.
Financial Constraints:
An arbitrary budget limit of $500 was set by Dr. Jiang. The Cole-Parmer liquid pump was
$2400 and specifically purchased by Dr. Jiang, so the budget was not affected by this purchase.
Time Constraints:
Approximately 13 weeks was available from the start of project to final presentation on
April 28, 2016.

7. 4

Section II
Background Research

The three main factors for producing a better spray pattern are maximized surface
production, minimized droplet coalescence, and minimized gas expense. All of these are increased
by a new atomization technique called flow-blurring atomization. Flow-blurring atomization was
a concept which was first conceptualized by Dr. Alfonso Gañán-Calvo, a fluid mechanics professor
at the University of Seville in Spain. It was Gañán-Calvo’s idea to create an atomizer that is simple
yet effective. His concept takes advantage of turbulent gas currents in order to create a more
efficient atomization of liquid. In his studies, he observed that at a certain height to diameter ratio,
a backflow of gas is introduced into the fluid stream which acts to break up the fluid. When the
ratio, Ψ= H/D, is greater than 0.25, a pattern termed flow-focusing spray is observed. This pattern
is characterized by a micro-jet, which either can break up in a symmetric or asymmetric pattern
depending on the Weber number. When this ratio Ψ is less than or equal to 0.25, a turbulent
backflow can be observed. Dr. Gañán-Calvo refers to this as flow-blurring. This phenomenon
increases the surface of spray up to fifty times more than standard plain-jet air blast type atomizers
which observe flow-focusing spray. A model of this design can be seen below in Figure 1.

8. 5


Figure 1: Schematic of the Simple Nozzle Geometry Used
One of the advantages of this design is that the effects of viscosity become negligible. This
means that this atomizer can be applied to a variety of fluids and that the material used for
constructing the model is also able to be varied.

9. 6

Section III
Design Process

III.1 Design Criteria
Design criteria are guidelines or rules that must be met when designing the models. The
design criteria for this fuel injector were communicated verbally by the team’s advisor, Dr. Jiang.
Requirements for a flow-blurring injector were also outlined by Dr. Gañán-Calvo in his paper.
1

These criteria are as follows:
 Offset distance (H) must be adjustable, so that H/D can be varied

 Fuel feed tube diameter (D) must be either adjustable or interchangeable

 Injector nozzle must attach to some sort of holder, so that fuel and air lines can be
connected

 All parts must be 3-D printable

 Exit orifice diameter must equal fuel feed tube diameter


1
Gañán-Calvo,Alfonso. Enhanced Liquid Atomization: From flow-focusing to flow-blurring.
Applied Physics Papers 86 2005

10. 7


III.2 Design Evaluation Process
Several models were designed over the course of three months. Once the team outlined
the design criteria and constraints, ideas were brainstormed and then modeled with Solidworks.
Going with the advice of the team’s advisor and client, Dr. Jiang, small changes were made with
each iteration. The ultimate goal was to produce an injector that was suitable for use in a small
turbine engine. Once this final design was satisfactory, it was 3-D printed by Idea Zoo, a company
that specializes in producing parts from CAD designs. Figure 2 shows a morphological chart that
helped with design selection.


Figure 2. Morphological chart

11. 8


III.3 Designs Created
Here, several versions of the injector design are shown as it evolved. Figure 2 shows the
first idea of the injector model.

Figure 3. First idea

12. 9


This first idea was modified to decrease the size and increase the wall thickness of the outer
shell that holds air pressure.
After more team brainstorming sessions and spending more hours into putting these ideas
into Solidworks, an injector holder was designed as well as a new exit orifice cap. These early
ideas are shown in Figures 4, 5, and 6 below.

Figure 4. First exit orifice cap design

13. 10


Figure 5. First injector holder

14. 11


Figure 6. First design of injector and holder assembly

15. 12

After consulting with Dr. Jiang, she suggested we make the parts even smaller and modify
the fuel feed tube. This resulted in the design shown in Figures 7 and 8.

Figure 7. Injector holder

16. 13


Figure 8. Injector holder section view

17. 14

Further modifications were made to this design so that fuel and air attachments could be
installed on the injector holder. This resulted in the design that was 3-D printed, tested, and is still
in use today. This design is shown in Figures 9 and 10.

Figure 9. 3-D printed design

18. 15


Figure 10. 3-D printed design section view

19. 16

Section IV
Final Design Details

IV.1 Design Testing and Results

IV.1.A Equipment used:
 Cole-Parmer water Pump
 Air compressor
 Air flow meter with stand
 Test stand
 Nikon D3100 camera

IV.1.B Testing Procedure
Water is used for liquid and air is used for gas in this experiment. To find the relationship
between Air-Liquid ratio (ALR) and spray angle for each H/D ratio, air flow rate is fixed at 1
SCFM while liquid flow rate is increased from 20 mL/min to 240 mL/min with 20mL/min
increments. This is repeated for two H/D ratios of 0.19 and 0.375. Images of each spray for every
set of conditions were captured with the Nikon digital camera.

20. 17

IV.1.C Testing Results

Graph 1: Comparison of the two flow regimes

21. 18


Graph 2: Flow-blurring regime

22. 19


Graph 3: Flow-focusing regime

The spray angle was measured from the images captured during experimentation. This
was accomplished by using the computer program ImageJ, which has the ability to determine
angles referenced in images. The angles were then plugged into an Excel spreadsheet according
to the GLR which they were tested at. From this Graphs 1-3 above were produced.
Upon observation of the graphs, it appears that as ALR (GLR) increases, the spray angle
decreases. A smaller spray angle correlates to smaller liquid droplets, because larger droplets have
a larger momentum and are thus more likely to escape from the center of the exit orifice. This is
what we would intuitively expect. The air mass flow rate was determined from a flow meter and
recorded. The liquid flow rate was read and recorded from the pump directly.

23. 20

IV.2 Cost Analysis




Table 1: Price List

Total Price: $2900




Each member of the group of five students spent at least 5 hours a week to
work on this project, totaling 65 hours each.

24. 21

IV.3 Conclusions

The team took about six weeks to design a fuel injector with Solidworks that would be
reliable and satisfactory for testing purposes. This final design was 3-D printed by a private
company, Idea Zoo. The cost to make all the fuel injector parts of ABS plastic was $20.
The test lab was set up with an air compressor, which Heath Headley brought from
home. Dr. Jiang bought a Cole-Parmer liquid pump that accurately delivers a desired flow rate.
A test stand was bought that holds the injector during experiments. Dr. Jiang also supplied an air
flow meter that was later attached to a wooden stand.
An experiment plan was outlined. It was desired to relate ALR and H/D to the resulting
spray pattern. Pictures were taken with Heath’s camera, and these pictures were matched with
their respective ALR and H/D values.
When the injector was tested in the flow-blurring regime (H/D=0.19) with an ALR around
1.0-1.5, the water spray appears to fully vaporize with a small spray angle. When the ALR is
around 0.3-0.7, it is clear to see a small micro-jet with a wider spray angle, presumably because
the exit velocity of the air-water mixture is lower. This would indicate a higher droplet size, and
incomplete vaporization. We can conclude from this that a higher ALR is more desirable. An
ALR>1 would be ideal.

25. 22

The injector was also tested in the flow-focusing regime, with H/D=0.38. With a low ALR
of around 0.3-0.7, the liquid micro-jet is clearly visible. With a higher ALR, the micro-jet is still
visible but smaller, and the spray angle is smaller because the exit velocity is higher.
We can conclude that this injector operates as expected when in the flow-blurring mode by
completely vaporizing the water that running through it. If there were more time, it would be
interesting to conduct more precise experiments with more sophisticated equipment. For instance,
we would like to test many values of ALR, while taking pictures with a camera that is fixed in
place. It would also be desirable to measure the droplet size directly, and then produce a graph of
droplet size vs. ALR. It is also possible that this design could be used in a turbine engine if it were
made of steel. This might be feasible if a few small changes were made to the design, so that it
could be made with a lathe and milling machine.

26. 23

Appendices

27. 24

Appendix A
Relevant Equations and Sample Calculations

Theoretical Mass Flow Rate of Air (that could be used in later
experiments)
(Compressible Flow)
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28. 25

Unit Conversions
SCFM (Standard cubic feet per minute)
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temperature and pressure)
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29. 26

How to set offset distance for testing (H)
Threads: M19 x 1.5
Pitch = 1.5 mm/turn D=2mm
=0.375mm/
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30. 27

Matlab program used during testing to calculate ALR






Figure 11. ALR program

31. 28






Figure 12. ALR program code

32. 29

Appendix B
Injector Part Drawings


Drawing 1. Injector Holder

33. 30






Drawing 2. Exit Orifice

34. 31



Drawing 3. Injector nozzle

35. 32

Appendix C
Parts List


 Swagelok compression fitting Part #: SS-400-1-1
 3/8” NPT air hose adapter got from home
 ¼” OD fuel hose Guidry Hardware
 Two air hoses one from home, one bought from Wal-Mart
 3-D printed parts Idea Zoo

36. 33

Appendix D
Time and Personnel Management



Figure 13. Gantt chart

37. 34


Figure 14. Personnel flow chart