For the full report and more information please visit: http://matc.unl.edu/research/research_projects.php?researchID=109

1. Diesel-Induced Fires: A Look at Enhancing
Safety with Droplet Science
Albert Ratner, Ph.D.
Associate Professor
University of Iowa

2. Disclaimer
• The contents of this report reflect the view of
the authors, who are responsible for the facts
and the accuracy of the information presented
herein. This document is disseminated under
the sponsorship of the Department of
Transportation university Transportation
Center Program, in the interest of information
exchange. The U.S. Government assumes no
liability for the contents or use thereof.

3. University of Iowa

4. The Need for Fire-Safe Fuels
• The September 11th attacks showed the
severity of mist-triggered explosions
• Ruptured fuel tanks released a fraction
(1000-3000 gallons) of the total fuel in
the fuel tanks throughout the building in
the form of a fine mist
• An ignition source ignited the mist into a
fireball
• Burning fuel was spread throughout the
building
• Pool fires ignited building materials and
began to weaken the structure due to the
extremely high temperatures of the fire
• The structure collapsed

5. Issues with Ground Transportation Vehicles
• Approximately 31 highway fires are responded to every hour,
and one person is killed every day due to vehicle fires in the
US (National Fire Protection Association, 2010)
• Between the years 2003 and 2007, it was estimated that
there were approximately 287,000 vehicle fires, 1525 injuries,
and 480 deaths annually associated with vehicle fires
• Collisions accounted for only 3% of all vehicle fires but for
over half of the deaths (58%)
* From “Crash and burn? Vehicle, collision, and driver factors that influence motor
vehicle collision fires” by T.L. Bunn, S. Slavova, M. Robertson, Accident Analysis
and Prevention 47 (2012) 140– 145

6. Approaches to Inhibit Misting & Fire
• Gelled fuel
• Prevents the ability of fuel to form a fine mist
• Limits the ability of the fuel to be pumped and
to serve in other areas of the fuel system
(hydraulic fluid, coolant, and lubricant)
• Emulsified fuel
• Encapsulates fuel within a thin film of
immiscible, low-flammability liquid
• Typically requires fuel droplets to be
suspended within another fluid
• Polymeric additives
• Allows for increased elongational viscosity
while continuing regular flow through the fuel
system
• Requires mechanical degradation device before
the fuel reaches the combustor

7. Outline
• History/Defining the Problem
• Initial Testing
• Selecting a Workable Lab-Scale Experiment
• Issues with Droplets
• Droplet Testing
• Droplet Modeling
• Research Conclusions
• Future Directions

8. Requirements for an Effective Fire-Safe Fuel
• Effective fire protection under survivable crash conditions
• Can be introduced at the refinery – cost effective quality control
• Effective at low concentration with acceptable flow behavior
• Resistant to unintentional degradation
• Soluble over relevant temperature range (-60 to 120 °F)
• No affinity for water
• Friendly to transportation, storage, and vehicle materials
• Degrades under high pressure and temperature in the combustion
chamber – eliminates need for a mechanical or chemical degrader
• No unwanted engine emissions
• Acceptable cost

9. Main Components of a Fuel System
• Primary fuel tanks
• Boost pumps
• Fuel/Oil heat exchanger
• Fuel hydraulic systems
• Main fuel pump
• Combustor

10. Combustion Chamber
• Fuel enters into the cylinder through spray nozzles
• The fuel enters the nozzle at pressures ranging from 700-1200 psi
• Fuel exits the nozzle at about 30 m/s

11. Additional concerns: Material compatibility
• Fuel Pumps
• Aluminum C355, 2219
• Tool steel or stainless steel
• Fuel Controls
• Aluminum AMS 4225, A201, 2219
• Valves
• Stainless steel 440C
• Actuator
• Aluminum, stainless steel, titanium
• Elastomer Seals
• Nitrile, fluorosilicone, fluorocarbon
Note: Materials both within the fuel tank and on fuel system components
must be compatible with both the fuel and any additives introduced to
the fuel

12. Refinery
• Raw crude oil is sent to distillation tanks to be separated into
various products through boiling
• Fuel is further separated by chemical processes
• Fuel is produced by both distillation and chemical treatment

13. Fuel shipment
• Usually, fuel for commercial use is transported by pipeline and
truck
• Pipelines are generally used for shipments in excess of
400,000 gallons
• Intermediate terminals serve to house fuel for distribution
• During fuel transport, contaminants enter the fuel (such as
water and particulates) which must be removed prior to use
Direct Pipeline
Refinery Intermediate Terminal Retail
Outlet

14. Additional Fuel Requirements
• Fuel must be able to pass through any filtering
• Sit in storage
• Survive all transport methods (shipping, pipeline, and trucking)

15. Problem Definition
• Modified fuel mixture must meet safety needs
• Serve as an effective hydraulic fluid and coolant, and possibly
lubricant
• Easily transported without degradation of the modified fuel
• Compatible with storage facilities
• Cost effective, with little or no modification to current fuel
production methods

16. Initial Testing Procedures

17. Test 1 – Fire Protection at Survivable Crash
Conditions
• A post-polymerization modified polybutadiene (2-3x106 MW)
was tested to gain understanding about the ideal
concentration at which mist-suppression would occur
• For each concentration of polymer/fuel mix, two sticker
concentrations were also tested to find the optimum
concentration that most effectively met the goals of this
project
IGNITER
6 in Diameter
40°
BLOWER WIND TUNNEL 28 m/s
CAMERA

18. 2nd Testing Procedure
• Paint sprayer will be used to produce a very fine mist of fuel
• Modified polymer samples of fuel will be tested for the
purpose of observing the resulting misting

19. Initial Testing Results
• Polymer modified fuel resists misting at a range of velocities
• Pumping or re-circulation of the fuel broke the polymer down
and significantly decrease the fire protection
• Recent lab work has focused on associative polymers

20. Performance at Large Scale
1 inch
1 inch
Jet-A and Unmodified Polybutadiene
California Institute of Technology, July 2004
Poly-Ox and Water
China Lake, September 2002

21. Initial Testing Conclusions
• Polymer modification of fuel works at typical survivable crash
conditions
• Low pressure pumping had no detrimental effect on polymer-
added fuel
• These testing methodologies do not provide the type of
quantitative data that can be used to drive polymer
development
• A simpler, more repeatable experiment is required

22. Developing the Next Round
of Testing Procedures

23. Different Scenarios of Drop impacts
• Outcomes influenced by:
• Drop properties: impact
speed, geometry, surface
tension, viscosity,
roughness, etc.
• Impacted surface: dry or
liquid surface
• Surroundings: at the
normal or higher pressure
Source: Rein, M., Phenomena of liquid drop
impact on solid and liquid surfaces. Fluid
Dynamics Research, 1993. 12: p. 61-93.

24. Drop Impact on a Dry Solid Surface (3 modes)
spreading
splashing
bouncing
Source: Rioboo, R., C. Tropea, and M. Marengo, Outcomes from a drop
impact on solid surfaces. At. Sprays, 2001. 11: p. 155-165

25. Drop Impact on Solid Surfaces
Interplay of capillarity, viscosity and inertia forces
Drop Spreading
• Kinematic phase - Thin lamella formation
• Spreading phase - Deceleration of lamella;
D0
rim formation
• Relaxation phase – Attaining maximum
diameter; change of contact angle
• Equilibrium/Wetting phase
d m ax
Maximum Spread Factor m ax
D0
Splash Threshold – Non-splash to splash
d m ax

26. Four Stages of Drop Impact
Lamella Capillary waves
Kinetic Phase –
Kinetic Energy
Hydrocarbon
drops
Spreading Phase
– Surface Tension
& Viscosity
Relaxing Phase &
Wetting Phase –
Capillary Waves
Source: Rioboo, R., M. Marengo, and C. Tropea, Time evolution of
liquid drop impact onto solid, dry surface. Experiments in Fluids,
2002. 33: p. 112-124.

27. Drop Impact as a Tool
• Non-Newtonian liquids exhibit shear-dependent viscosity
• An impacting drop exhibits strain rates from very high values
to nearly zero.
Idea: Identify non-Newtonian effects in drop impacts by comparing
impact results for a non-Newtonian liquid to a Newtonian liquid
Drawbacks:
• High quality and high speed imaging techniques required
• High strain rates are confined in the thin expanding lamella

28. Experimental Arrangement
• Liquids used: Ethanol, Methanol, cetane, n-propanol, diesel
• Drop sizes: 2.0 mm - 2.6 mm
• Impact speed: 1.5 – 3.5 m/s
• Pressure: 1 – 12 atm.

29. Experimental Procedure
Splashing tests
• Methanol and Ethanol used as test liquids
• At Threshold Pressure first droplets
separated from the main drop at low
angles to the impact surface.
Spreading tests
(a) No splash at 1.4 bars (b) Splash
• Diesel, propanol and Cetane tested from inception at 1.55 bars for impact
speed of 2.15 m/s
constant needle height.
• Ethanol tested at constant impact speed of
1.75 m/s
2 Drop deformation due to
DS
gas drag
Impact speed (m/s)
1.8
1.6 1
DL
2 3
1.4 Deq (DL DH )
1.2
1 d lamella
2 7 12
Chamber Pressure (bars) d contact

30. Computational Modeling

31. Computational Modeling Objectives
• Study the effect of fluid properties and impact characteristics
• Extend the existing theoretical models of drop behaviors from
water to hydrocarbon as applicable
• Develop a new model with lower computational cost & higher
accuracy than those currently available
• Use the model and the experimental results to drive polymer
development

32. Key Modeling Issue Dynamic Contact Angle
Singularity
The moving contact line No-slip boundary condition
Problems
(1) How to describe the behavior (2) How to remove the shear-
of macroscopic contact angle? stress singularity?

33. Experiments: Evolution of Contact Angle
180 120
I II
Dynamic Contact Angle
150 I II
Dynamic Contact Angle
90
120
90 60
60 1.6 m/s
2.40 m/s
1.2 m/s 30
30 2.75 m/s
0.7 m/s
3.05 m/s
0 0
0.01 0.1 1 10 0.1 1 10 100
Non-dimensional Time (tu/D) Non-dimensional Time (tu/D)
(a) Diesel drops (b) Methanol Drops
0.01 0.1 1 10
180 I II III 1.8
Dynamic Contact Angle
150 1.5
120 1.2
d/D
90 0.9
60 0.6
30 4.1 m/s 1.41 m/s 0.3
1.04 m/s d/D
0 0
0.01 0.1 1 10
Non-dimensional Time (tu/D)
(c) Glycerin Drops

34. Experiments: Evolution of Spread Diameter (1)
6
Diesel (u=1.6 m/s)
5 Diesel (u=1.2 m/s)
Spread Factor (d/D)
Diesel (u=0.7 m/s)
4
Methanol (u=2.33 m/s)
3 Methanol (u=2.75 m/s)
Methanol (u=3.05 m/s)
2 Glycerin (u=4.1 m/s)
Glycerin (u=1.4 m/s)
1 Glycerin (u=1.04 m/s)
f=2.8*(t^0.5)
0
0.01 0.1 1 10
Non-dimensional Time (tu/D)
Spread factors of various cases in the kinetic phase
compared with the power law (Rioboo et al., 2002)

35. Experiments: Evolution of Spread Diameter (2)
6
Diesel (u=1.6 m/s, Oh=0.0155)
5
Diesel (u=1.2 m/s, Oh=0.0155)
Spread Factor (d/D)
4 Diesel (u=0.7 m/s, Oh=0.0155)
Methanol (u=2.33 m/s, Oh=0.0027)
3 Methanol (u=2.75 m/s, Oh=0.0027)
Methanol (u=3.05 m/s, Oh=0.0027)
2
Glycerin (u=4.1 m/s, Oh=0.2673)
1 Glycerin (u=1.4 m/s, Oh=0.2673)
Glycerin (u=1.04 m/s, Oh=0.2673)
0
0.1 1 10
Non-dimensional Time (tu/D)
Spread factors of various cases in the spreading phase

36. Experimental/Numerical Comparison
Computer generated images compared with photographs of a diesel
drop impacting a glass surface with an impact velocity of 1.6 m/s

37. Numerical Results
0.01 0.1 1 10 0.01 0.1 1 10
4 Expt. 160 4 Expt. 160
SCA
Spread Factor (d/D)
Spread Factor (d/D)
SCA
SCA-DCA SCA-DCA
3 120 3 Kistler's 120
Kistler's
theta
theta
2 80 2 80
1 40 1 40
0 0 0 0
0.01 0.1 1
Non-dimensional Time (tu/D) 10 0.01 0.1 1
Non-dimensional Time (tu/D) 10
Diesel: u = 1.6 m/s Diesel: u = 0.7 m/s
0.1 1 10 0.01 0.1 1
7 Experiment 120 2 180
Spread Factor (d/D)
SCA-DCA 1.8
Dynamic Contact Angle
Dynamic Contact Angle
6 100
Spreading Factor (d/D)
Kistler's 1.6 144
5 1.7
theta 80
4 1.2 108 1.6
60
3 1.5
0.8 Sikalo's Expt 72
40 1.4
2 SCA-DCA
20 0.4 Sikalo's Simul. 36 1.3
1
theta 0.5
0 0 0 0
0.1 1
Non-dimensional Time (tu/D) 10 0.01 0.1 1
Non-dimensional Time (tu/D)
Methanol: u = 2.33 m/s Glycerin: u = 1.41 m/s

38. Evolution of Strain Rate
Diesel, Impact Speed u = 1.6 m/s

39. Modeling Conclusions

40. Fuels of the Future: Ethanol Mixed Gasoline
• Ethanol is produced from crops (most made from corn in
U.S.).
• Ethanol diluted with gasoline provides a cleaner, more nature
fuel source: economical & environmental benefits.
• 30% of all gasoline consumed in the U.S. is blended with
ethanol.
• Disadvantages: ethanol can form explosive vapors in fuel
tanks.

41. Future Directions
• Examine both higher vapor pressure (Diesel) and lower vapor
pressure (Ethanol) based fuels
• Assess both viscosity and vapor pressure modifying
techniques for making fuel safer.
• Utilize both experimental and computational tools to generate
the maximum insight.
• Expand our collaboration to include more partners, including
Caltech and Princeton

42. CREDITS
Yan Zhang
and
former students Neeraj Mishra & Brett Bathel
Slide design © 2009, Mid-America Transportation Center. All rights reserved.