Fire safety is of particular interest in this work.To identify the target range where polymer additives impart shear-thickening effect on fuels while avoid the normal functioning of the fuel system, the variable shear stress of these fuels needs to be known. The impact of hydrocarbon drops on a solid surfaceis a simple and canonical model to investigate the variable viscosity and shear stress effects in liquid drops. Hence, the dynamics of hydrocarbon drops spreading on a flat smooth surface is studied in this work as a starting point for the investigation of non-Newtonian behavior.
Diesel-Induced Fires: A look at Enhnacing Safety with Droplet Science
Diesel-Induced Fires: A Look at Enhancing Safety with Droplet Science Albert Ratner, Ph.D. Associate Professor University of Iowa
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.
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
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
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
Outline • History/Defining the Problem • Initial Testing • Selecting a Workable Lab-Scale Experiment • Issues with Droplets • Droplet Testing • Droplet Modeling • Research Conclusions • Future Directions
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
Main Components of a Fuel System • Primary fuel tanks • Boost pumps • Fuel/Oil heat exchanger • Fuel hydraulic systems • Main fuel pump • Combustor
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
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
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
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
Additional Fuel Requirements• Fuel must be able to pass through any filtering• Sit in storage• Survive all transport methods (shipping, pipeline, and trucking)
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
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
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
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
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
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
Developing the Next Round of Testing Procedures
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.
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
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
Four Stages of Drop Impact Lamella Capillary waves Kinetic Phase – Kinetic Energy Hydrocarbon drops Spreading Phase – Surface Tension & Viscosity Relaxing Phase & Wetting Phase – Capillary WavesSource: Rioboo, R., M. Marengo, and C. Tropea, Time evolution ofliquid drop impact onto solid, dry surface. Experiments in Fluids,2002. 33: p. 112-124.
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 comparingimpact 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
Experimental ProcedureSplashing 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 dragImpact 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
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
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?
Experiments: Evolution of Contact Angle 180 120 I IIDynamic 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
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)
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.
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