SLUTRAPPORT
Datum 2016-12-30
1 (5)
Dnr 2015-007124
Projektnr 34111-2
Energimyndighetens titel på projektet – svenska
Nya analystekniker för mätning av initial upplösning hos bränslesprayer
Energimyndighetens titel på projektet – engelska
New analysis techniques for primary breakup in fuel sprays
Ev. Energimyndighetens program
Tidplan
Energieffektiva vägfordon
2016-01-01 till 2016-12-31
Total projektkostnad
Energimyndighetens andel av kostnaden i %/kr
1 510 000
100%
Universitet/högskola/företag
Avdelning/institution
Chalmers
Förbränning/Tillämpad mekanik
Adress
Organisationsnummer
Hörsalsvägen 7B, 412 96
GÖTEBORG
556479-5598
Namn och e-post - projektledare
Mark Linne, [email protected]
Namn och e-post – Huvudförfattare/ medförfattare/projektdeltagare/doktorander
Zachary Falgout, [email protected]
Sammanfattning
Vårt mål med projektet har varit att bidra till att utveckla mer prediktiva modeller
för förbränning i direktinsprutade motorer. Den svagaste länken är en effektiv
teori för mekaniken i flytande uppdelning nära munstycket på trycket atomiserat
injektorer. Vi fokuserar på det problemet med vår laser teknik som kallas ’ballistic
imaging’. Vi har också utvecklat optiskt transparent munstycke tips så att vi kan
titta in i passager munstycksflödet att korrelera det inre flödet med flytande
uppdelning. Vi har utvecklat optiskt transparent munstycke tips för fartygsmotorer
och nu ska vi utveckla dem för vägfordon. Vi utför dessa experiment under
förhållanden så nära realistisk eftersom den utrustning som gör det möjligt, med
hjälp av högt tryck och temperatur spray kammare på Chalmers. Injektorn vi
studerar är en diesel injektor används i ett globalt samarbete som kallas ’Engine
Combustion Network’ (ECN). Vårt resultat alltså paret till en mycket större
uppsättning data för resten av spray.
Summary
EM2022 W-4.0, 2011-07-15
Our goal for this project has been to help develop more predictive models for
combustion in direct injected engines. The weakest link is a description of the
mechanics of liquid breakup near the nozzle of pressure atomized injectors. We
have focused on that problem using our laser technique called ballistic imaging.
We plan also to look inside the nozzle flow passages to characterize the interior
flow and correlate that with primary breakup. We have recently developing
optically transparent nozzle tips for marine engines and now will design new tips
for Diesel engines in heavy-duty trucks. We perform these experiments under
conditions as close to realistic as the equipment will allow, using the high pressure
Box 310 • 631 04 Eskilstuna • Besöksadress Kungsgatan 43
Telefon 016-544 20 00 • Telefax 016-544 20 99
[email protected]
www.energimyndigheten.se
Org.nr 202100-5000
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Datum 2005-05-15
Projektnr 34111-1
and temperature spray chamber at Chalmers. The injector we have studied is a
specialized diesel injector used in a worldwide collaboration called the Engine
Combustion Network (ECN). Our results thus couples to a much bigger dataset
for the rest of the spray. Unlike the ECN, we have also studied the effect of
changing fuel types by blending with bio-fuels.
Inledning
The fluid mechanics of spray breakup has origins in the transient flow through
passages and holes inside an injector. The fuel then exits into the gas at high speed
and high turbulence intensity. The flow exiting the nozzle controls formation of
the first drops (“primary droplets”) based on how the liquid structures break up
(“primary breakup”). Those first drops, with specific size and momentum, then
control development of the remaining part of the spray including droplet breakup,
vaporization, mixing and combustion.
In this final year of the project, we focused more in interior flow. We developed a
first-of-a-kind optically transmissive injector tip design methodology that allows
operation at higher fuel pressures than other groups have reached, and we have
been using a set of them to generate experimental data to support the development
of a cavitation model at Chalmers.
Main results
This project officially started in January, 2016.
We have recently designed (via finite element analysis, FEA) and built a
specialized marine injector that uses acrylic for the injector passages, but the
acrylic is held by sapphire flats (see Figure 1).
This approach is used because acrylic is well
index matched to fuel, while sapphire provides
structural strength. We chose to start this
optical nozzle development work with a marine
injector because their passages are larger and
easier to manufacture and observe.
Figure 1. Optical nozzle for marine
injector. Fuel supply is from the
bottom and a sac volume pressure
transducer can be mounted at the
top. Sapphire flats hold the inner
acrylic piece shown in
compression.
Recent work has focused on the use of 3-D
FEA on a cluster to analyze failure mechanisms
in these tips once they are subjected to fuel
pressure. Because failure is controlled by the
surface quality inside the nozzle, and that is
controlled by the manufacturing process, a
statistical approach was required. Many tips
were evaluated at fixed fuel pressure, cycling
them until they failed, and the number of cycles
achieved before failure (n) were cataloged. An
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example outcome is presented in Figure 2. In
Case I there were no sapphire clamps
restraining the acrylic piece and it was operated
at 400 bar fuel pressure. In Case II sapphire
clamps were used but they did not compress the
acrylic, and it was operated at 600 bar fuel
pressure. These cases were run in order to
provide the kind of statistical data necessary to
carefully analyze any such design.
Note also that tensile stress scales with size.
This sac volume is roughly 1 mm in size and
the holes are 450 microns, so this tip was much
more susceptible to breakage than a heavy duty
Diesel injector would be.
These results were presented in a much larger
article published in Review of Scientific
Instruments explaining how such injector tips
can be designed, and it was also used to
generate a design for a HD Diesel injector
(Figure 3).
Figure 2. Failure probability
density distribution (ρf) and failure
probability distribution (Pf) for
Cases I and II, where n is the
number of trials to failure.
Since that work, the marine injector has been
used to develop a database to support the
development of a cavitation model at Chalmers. The injector is mounted in a
sealed vessel which allowes the desired back pressures to be applied. This vessel
has windows that allow visual access to the injector.
Figure 3. (a) Illustration of design for road
vehicle Diesel engine injector and (b) close
up of nozzle region.
Backlit imaging is used to capture the
cavity edge in both orifices. An LED
lamp is used to illuminate the nozzle,
and a Vision V7.3 camera with a Nikon
macro lens captures the images with a
framerate of 13,029 fps. An achromatic
lens is placed between the vessel and
the camera to achieve the desired
magnification. In transillumination
imaging, flow interfaces appear dark
due to the large refractive index
gradients across them. Only the outer
edge of cavitation features are visible
with this single line of sight imaging
technique.
For image processing, the area in the
high speed videos corresponding to the
orifices is manually separated from the
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rest of the image area, and then
background-subtracted. The resulting subframes are then averaged over the time
period where the injection pressure was
above the set pressure. The intensity
contours corresponding to 50, 60, 70, and
80% of the maximum intensity of the image
are then superimposed on the background
image, which contains no cavitation
features, to provide a visually
uncomplicated indication of average
probabilities for cavity locations in the flow
during the steady period of injection. The
goal is to generate data that can be easily
modeled.
Projektnr 34111-1
Figure 4. Iso-contours of cavitation
probability for doecane at a cavitation
number of CN = 0.88

P
−P

out
 C N ≡ fuel

High speed images also show that


−
P
P
fuel
vapor


fluctuations in size of the cavitation vapor
cavity and spray width outside of the nozzle
are correlated. The cavity shape is very unsteady.
Preliminary experimental and computational cavitation results were presented at
ILASS-Europe in September 2016, but they have not been published because the
experiments are not finished and there have been some difficulties with
development of a model. The goal is to produce a paper that combines models and
experiments. We anticipate that the experimental database will be completed by
the end of 2016 but the model (funded by another grant) will take longer. When
the model is successfully reproducing the experiments, a paper will be generated.
Zachary Falgout successfully defended his thesis on September 23, 2016. His
thesis is based upon work that was supported by Energimyndigheten within this
and the previous grants. The opponent was Dr. Scott Parrish, from General
Motors Research Lab. The reading committee included Prof. Öivind Andersson
from Lund, Prof. Laszlo Fuchs from KTH, and Dr. Niklas Nordin from Scania.
Reports from this time period:
“Interior Flow and Formation of Plain Orifice Sprays”, Z. Falgout, PhD Thesis,
Chalmers University, (2016).
Journal articles from this time period:
“Novel design for transparent high-pressure fuel injector nozzles”, Z. Falgout and
M. Linne, Review of Scientific Instruments, DOI: 10.1063/1.4960402, (2016).
“Interior flow and near-nozzle spray development in a marine-engine diesel fuelinjector”, J. Hult, P. Simmank, S. Matlok, S. Mayer, Z. Falgout, and M. Linne,
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Experiments in Fluids, Exp Fluids, 57:49, DOI 10.1007/s00348-016-2134-8,
(2016).
Conference papers from this time period:
“LES modelling of cavitation flow in a diesel injector nozzle”, B. Chen, Z.
Falgout, M. Oevermann, and M. Linne, ILASS – Europe 2016, 27th Annual
Conference on Liquid Atomization and Spray Systems, Sep. 4-7, Brighton, UK,
(2016).
Relationship of these results to the main goals
The main goals of this project have been to study the ECN injector by correlating
interior flows to primary breakup under various conditions, and to collaborate
with modelers. These results present logical steps towards those goals. It was
decided that a marine injector provides a simpler geometry for initial development
of an optical tip and for development of a cavitation model. As shown in Figure 3,
a new tip for an ECN type injector has been designed but it will be necessary to
have an industrial partner in order to go further.
Effect on Society
From a 20-year perspective, the goal of basic combustion research is to develop
computer models that are predictive. Fully predictive models do not currently
exist, but if they did engine companies could use them to evaluate ideas and
design devices before cutting any metal. This would make it possible to optimize
combustion engines for minimum CO2 and pollutant emissions.
Implementation
This new optical tip idea has already caught hold in the marine engine
community. A new CERC project includes Winterthur Gas and Diesel as an
industrial partner (with an industrial PhD student, Mr. Reto Balz) and it will
involve the development of an optical tip for their injector. In addition, the
University of Hamburg in Germany is building similar tips for studies of a marine
injector. There are a number of new optical tip concepts now being reported, but
this is the only one that can reach more realistic fuel pressures while allowing
access to both the interior flow and spray formation at the same time.
The supercritical spray work described in the former final report has now
generated a lot of interest within the research community. It has lead to a new
follow-on grant from the US Air Force Office of Scientific Research at the
University of Edinburgh.