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Aviation Fuels with Improved Fire Safety: A Proceedings Appendix B New Concepts in Fuel Fire Research: Final Summary Report of Short-Term Advisory Services (STAS) Team Frederick L. Dryer (Team Leader) Paul Becher, Melvin Gerstein, David E. Foster, Jerry A. Havens, John H. Johnson, J. Adin Mann, Phillip S. Myers, Otto A. Uyehara, and Charles K. Westbrook 1 Note: This appendix was originally produced in 1984 by Batelle Columbus Laboratories, contract no. DAAG29-81-D0100. It is reprinted here in its original form. 1 The views, opinions, and/or findings contained in this report are those of the authors and should not be construed as an official Department of the Army position, policy, or decision, unless so designated by other documentation.
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Aviation Fuels with Improved Fire Safety: A Proceedings EXECUTIVE SUMMARY This report describes the consensus of results and opinions reached by a STAS team review of proposed development strategies for a new fire-resistant fuel for use in Army vehicles. It was concluded that one of the most limiting issues of previous efforts has been the consideration of fuel and vehicle related modifications as separate issues, and future work should be proposed and carried out on a systems (fuel, fuel system, engine system, deployment) basis. Furthermore, fundamental/engineering issues which are important to optimizing the various methods available for fire hazard mitigation remain unanswered. Future programs should take a more balanced approach (than demonstrated by previous programs) in providing sufficient fundamental knowledge to guide the development of optimum approaches. Constraints for previous research goals were not suitably defined in advance of development or deployment-oriented efforts, and those stated for future program development are unrealistic. Specific, acceptable, and realistic criteria for the program solution must be made before any new program or program continuation is initiated. A critical part of deriving these criteria is a conservative cost-benefit ratio analysis of changes in vehicle performance, range, costs, retrofit, deployment, etc. with fire hazard reduction. Acceptable vehicle/fuel systems modifications criteria need to be established because they are in themselves important and sometimes synergistic to modifications in fuels for reducing fire hazard. In reviewing the proposed approaches the program phase plan for future work, it was concluded that the disadvantages produced for operating combustion systems by the presence of halons outweigh fire hazard advantages which would result from their addition. Techniques to remove additives prior to combustion are limited, and four year development of a successful system based on any use of halons other than in approaches currently under development for compartment deluge on M-1 tanks appears unlikely. Furthermore, implementation as a fuel additive would appear to involve substantial logistics difficulties and performance degradation. An 18-month decision point on the proposed approaches is unrealistic because sufficient fundamental information on which to judge their viability is lacking. In fact, there is such a substantial lack of fundamental understanding available for association polymers that it is unrealistic to consider this approach as a serious candidate for four year development and deployment. Long term fundamental research on both conventional and association antimisting polymers is needed on the physical behavior of these compounds under shear before even a decision point for development research can be made. Recommended additional approaches which are believed to hold potential for development and deployment include fuel flash point modification, fuel cooling, halon compartment deluge, and line closure systems. These approaches are all based on established technology, have significant fire hazard reduction potential, are compatible with the addition of other approaches which involve fuel modification, and do not result in (what appear to be) unacceptable performance or logistics penalties. With fuel cooling and suitable fuel systems modifications, conventional antimisting agents may have some potential for reducing aerosol formation, but again fundamental information to guide successful development is lacking. Techniques to derive liquid/vapor interface dilution such as micro-emulsions and/or co-solvent formulations have substantial promise for producing fire-resistant fuel formulations and should be pursued. Fundamental phase diagram development work is critical to evaluating these approaches and deriving optimum formulations. PREFACE Extending over the past twelve years, the U.S. Army has been involved in several research programs, all of which have been directed at reducing the fire threat resultant from required fuel supplies carried aboard combat vehicles (both air and ground). Both mechanical and vehicular design changes as well as modifications of the fuel itself have been considered. Most recent efforts on fuel modification have been devoted to development of a fire-resistant fuel (FRF) based on water-in-fuel micro-emulsion technology. During the last two years, major difficulties have surfaced in this program, particularly with regard to potential field introduction of the FRF formulation brought forward from this research. At the U.S. Army Materials Development and Readiness and Command level, all research on the current FRF formulation was terminated because of logistical, technical, and organizational problems which would result from field introduction. Subsequently, the Fuels and Lubricants Division has been requested to develop an unconstrained plan that would place a new FRF formulation into the field within four years from initiation of the program. In order to aid the Materials, Fuels and Lubricants Laboratory and the staff of the U.S. Army Fuels and Lubricants Research Laboratory in developing the framework for this new plan, both the Coordinating Research Council Ad Hoc Fire-Resistant Fuel Advisory Group and a Short-Term Advisory Services (STAS) team of eleven academicians and scientists were asked to give assistance in reviewing those approaches which are to be proposed and/or recommending alternatives that might assist in this effort. This summary report describes the consensus of results and opinions reached in a two day working session held by the STAS team on May 8–9, 1984 at the Army Fuels and Lubricants Research Laboratory, Southwest Research Institute, San Antonio, Texas. In addition to ten of the team members, Dr. D. Mann of the U.S. Army Research Office, Mr. F.W. Schaekel, Chief of the Fuels and Lubricants Branch of the Materials, Fuels, and Lubricants Laboratory (Fort Belvoir), and six researchers from the Army Fuels and Lubri
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Aviation Fuels with Improved Fire Safety: A Proceedings cant Research Laboratory (A.A. Johnston, S.J. Lestz, W.D. Weatherford, Jr., B.R. Wright, G.E. Fodor, and M.D. Kanakia) were present to brief and assist the team. The team expresses its gratitude for the briefings given and the clarifications offered by these individuals during the meeting. We also thank Southwest Research Institute for the hospitality shown the team members during the meeting. Finally, the team leader expresses his gratitude for the material contributed to and draft review of this summary report by the team members. INTRODUCTION As part of the work statement (TCN 84-047) under which the STAS team operated, the task objective of the team was to review the proposed development strategy for the new fire-resistant fuel and to recommend any additional approaches and/or concepts having potential merit. More specifically, the team was charged to: Review the pertinent background information summary on the research and development activities completed to date on fuel fire reduction. Review the different approaches for a new fire-resistant fuel being proposed for consideration within the new draft plan and assess the merits of each approach being considered. Recommend any additional approaches for the development of a new fire-resistant fuel not addressed in the plans above. Assess the potential for success within each approach; that is, based upon the existing technology, what is the opportunity for achieving the specific goal. In meeting these charges, the team first spent considerable time in attempting to define the technical aspects of the problem, particularly, the scientific fundamentals, and the systems interactions which are relevant to reducing fire hazard. Summaries of the team discussions on the technical issues and on the various methods for reducing fire hazard are presented in the second section (on technical issues) and third section (on methods for producing fire-resistant fuel properties) below. These sections provide the background for the specific task discussions on the above charges which appear in the fourth section. TECHNICAL ISSUES Fire-Resistant Fuel, The Problem Definition The fire problem associated with liquid fuels stored in vehicles can be fundamentally viewed in terms of the following three principal, but not entirely separable, phenomena: Fuel Spillage The compartment (or compartments) which store the fuel, and/or the fuel delivery system on the vehicle are somehow damaged allowing the fuel to escape. If the fuel is under pressure or the impact which causes the malfunction is severe, the spillage initially results in a fuel aerosol cloud, often followed by further spillage which yields a fuel pool in the vicinity of the vehicle. Ignition The presence of hot surfaces or incendiary fragments in the vicinity of the fuel aerosol cloud and/or fuel spill lead to ignition. Flame Propagation and Pool Ignition Flame propagates through the aerosol cloud, and formation of a large ''flame ball" ensues. The diffusion/mixing limited character of this flame ball yields large amounts of gas phase soot formation and results in substantial continuum radiative heat transfer. For combat scenarios, it appears that the flame ball alone may result in irrevocable consequences to both vehicle and operating personnel. Further, the intensity of radiation is typically severe enough to further involve any fuel pool spill which has occurred, thus causing additional damage from the sustained burning in the vicinity of the vehicle. Tantamount to the fire evolution is the ignition process. If the source of ignition can be effectively removed or the ignition process otherwise inhibited, no fire would follow. There are, however, essentially two "ignition" processes: that which leads to the formation of the flame ball, and that of the spilled pool. Elimination of the flame ball ignition process would be more effective as a hazard control method since the flame ball typically causes severe damage. Furthermore, the flame ball is the more likely ignition source of the pool spill. If ignition of the fireball cannot be prevented, the issue becomes one of controlling the "size" of the flame ball. The "size" is not only a volumetric issues, but is related to the time-integrated radiative heat evolved in comparison to that which will result in harm to personnel, or, more likely, to that which will result in secondary ignition of any fuel pool spill which has resulted. Finally, if neither the aerosol ignition nor flame ball size can be controlled, one must consider prevention of the ignition of the fuel pool spill, or the containment of the pool fire to a small area by limiting the region over which the fuel is spilled or the rate at which the flames spread over the fuel spill. The occurrence of these phenomena are inter-related through the actual fire scenario, the mechanical design of the vehicle, fuel storage, and fuel delivery systems, as well as through the physical and chemical properties of the fuel.
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Aviation Fuels with Improved Fire Safety: A Proceedings Furthermore, the choice of the propulsion system (spark ignition, diesel, turbine) and the fuel storage and delivery system design provide certain limitations in the acceptable ranges over which these fuel properties may vary. These property ranges may be contrary to those which would optimize fuel fire resistance. In order to fully clarify the analysis given in the third section of this report, it is important to summarize here the principal effects of these interrelationships. The bibliography in the fifth section (and the references contained within the literature cited) serve as a reasonable basis from which to derive these interactions. It is appropriate to consider the effects of the base fuel properties first. Effects of Base Fuel Physical Properties One of the most important properties of the fuel is the "flash" point. Fundamentally, the flash point of a fuel is that liquid temperature which results in sufficient fuel vapor pressure at the liquid/air interface to produce a flammable mixture of fuel vapor and air over the surface. Thus, for pure liquids, if one knows the lean flammability limit of the material (i.e., the minimum fuel content in air which will sustain a pre-mixed flame) and the vapor pressure-liquid temperature relationship of the material, a "theoretical" flash temperature can be calculated. In lieu of knowing the flammability limit and in order to account for non-ideal vapor pressure-liquid temperature relationships, particularly for multi-component mixtures such as real fuels, various experimental techniques have been developed to measure the flash point. As a result of diffusive transport near the liquid surface and the positioning as well as the type (flame, spark, etc.) of ignition source used to test for flammable mixture conditions, these techniques typically produce experimental values for the flash temperature which are somewhat higher (a few to 5°C) than values calculated for pure liquids or (even ideal) mixtures. In some cases, the flame produced by passing an ignition source over the surface of a liquid heated to its experimental flash point does not sustain itself after propagating over the surface (hence the term "flash" point). However, if the liquid temperature is raised a few degrees Celsius higher, both flame propagation and sustained combustion result. the liquid temperature at which this condition occurs is termed the "fire" point. It is really this condition which is of interest in terms of fire hazard analysis of liquids, but the flash point serves as a conservative approximation which is more easily measured and interpreted. Fire points for conventional fuels may differ from the reported flash points by as much as 20 to 30°C due to the difficulty in retaining the light ends of the fuel during these tests. It is principally the light volatile fraction of the fuel which determines both of these properties. The flash temperature of a fuel in relation to the ambient temperature is important in identifying what controls the ignition and flame propagation process. If the flash temperatures of a fuel is much lower than the ambient temperature, then even at ambient conditions, a flammable mixture will result over an open spill after a very short time. This time is governed by convective/diffusive transport and evaporation kinetics. Ignition and flame propagation will be controlled entirely by gas phase chemical and physical processes. In fact, open spills will sustain flame propagation (with no turbulence effects) over their surface up to nearly five times the laminar flame velocity (approaching several meters per second) because of the stratified fuel/air mixture which exists over the pool. For low flash point fuels, the ignition process will be dominated by requirements for chemical initiation, and aerosol flame propagation will be found to be relatively independent of the aerosol particle size (although there may be some dependence on particle number density). In the case of liquids which have flash points well above the ambient temperature, the liquid must receive heat in order to create a flammable mixture over the liquid surface. Ignition will require sufficient heat to first generate the flammable mixture and then sufficient energy in the form of enthalpy or radicals to cause chemical initiation of flame. In the case of aerosols, the droplet surface must be heated to near the flash point before a flame can be established. This characteristic "heating time" influences the rate of flame propagation through the aerosol by causing significant dependence on droplet size and number density. Indeed, if droplets are large enough and/or the heat available is insufficient, no flame ball will result. Obviously, the minimum droplet size will be a complex function of the amount the liquid is subcooled below its flash temperature, etc., but unlike the case of low flash temperature fuels, aerosol flame ball development may be inhibited by controlling aerosol formation. Finally, the ignition of a pool spill will require heating of the pool surface to produce flammable conditions, and subsequently, ignition of this flammable mixture. Without significant heating of the pool surface by radiation from the flame ball, propagation over the pool surface will be limited to velocities lower than about 0.1 meters per second. This is because the major method through which the region ahead of the flame is heated to temperatures exceeding the flash point is through liquid-phase convection. Indeed, if the surface on which the fuel is spilled is porous and/or the pool is not sufficiently deep for convection to occur, the flame spread rate may be lower than 0.01 meters per second! It will be seen below that the fuel flash point in relation to ambient conditions (or fuel circulation/compartment storage temperature) will dictate the effectiveness of various methods for producing a fire-resistant fuel. Typical Fuel Systems/Engine Systems Encountered The primary reason for carrying fuel in an Army vehicle is to provide propulsion for the vehicle through combustion.
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Aviation Fuels with Improved Fire Safety: A Proceedings Thus any changes in the fuel properties or the fuel/engine system in the interest of fuel fire safety must also consider the effects of these proposed changes on vehicle performance, range, and environmental operating constraints (ambient temperature range, etc.). Most Army vehicles currently use diesel (D-type) or turbine (JP-type) fuels. Jeep vehicles currently powered by gasoline type fuels are to be gradually replaced by attrition as newer, diesel-fueled jeeps are added to the fleet. With the exception of the M-1 armored tank which uses turbine type fuels, all other tactical ground vehicles use diesel grades of fuel and diesel engines. Typical fuel properties for such fuels are shown in Table B-1. Currently, the diesel engines used are either water-or air-cooled with much of the cooling of the fuel injection nozzle itself provided by circulating up to as much as twice to three times the actual fuel required through the nozzle. The excess fuel is then returned to the fuel storage compartment(s). Steady state, recirculated fuel temperatures typically far exceed the flash points shown in Table B-1 and approach or exceed the fire point of the fuel used. Engines with considerably higher operating temperatures and much lower total heat rejection are under development. However, these engines actually make greater use of both lubricating oil and fuel circulation for cooling purposes than earlier designs. It appears that direct cooling, at least of the fuel, through some sort of air-cooled or refrigerated intercooler will be necessary to prevent fuel degradation and nozzle tip deposits. Fuel is often stored in more than one fuel compartment on the vehicle, and thus the susceptibility of the fuel storage compartments to combat damage ranges from uncontrolled to something less than minimized. METHODS FOR PRODUCING FIRE-RESISTANT FUEL PROPERTIES There are several potential approaches which separately or together might be used to produce fire-resistant fuel characteristics. These include: antimisting agents use of higher flash point fuels/fuel cooling liquid/gas interface dilution halon suppressants gelling agents combinations of these methods The use of these methods may require certain design modifications in the fuel system, engine, or vehicle structure. Each of these approaches and their interactions are briefly discussed below, and the STAS team positions taken on these approaches are detailed. Antimisting Agents When added to the fuel, so-called antimisting agents tend to resist the ligament breakup of fluid sheets (and sometimes even the formation of the liquid sheets) during shear atomization of a fluid, and thus they inhibit the formation of small aerosol droplets. All of the products currently used are proprietary so that little can be said of their actual chemical structure except that they are long chain hydrocarbon and sulfur based polymers with molecular weights in excess of one million. One to two percent added to high flash point aircraft fuels have shown them to be extremely effective in eliminating the fireball hazard which arises from wind shear and ground crash impact of aircraft. Tests have also shown them to be ineffective when used with low flash temperature fuels such as JP-4. This fact clearly establishes that the operating mode of these materials is through formation of aerosol drops too large to be heated to flash point conditions by the available heating/ignition sources. In the case of low flash point fuels, aerosol drops already provide flammable vapor concentrations at the environmental temperature. Antimisting agents show no effect on flame propagation over fuel spills for either low or high flash temperature fuels once the pool fire is initiated. However, for high flash points fuels, pool fire initiation can be prevented by using antimisting agents to inhibit or eliminate the occurrence of a fireball. But modification of the fuel atomization characteristics such that it is difficult to form very small fuel droplets is also detrimental to the fuel combustion properties. The formation of a combustible mixture in the diesel engine cylinder is directly related to the droplet formation from the fuel injector. Thus, the antimisting agent must be degraded before the fuel is injected into the engine. It has been found that high shearing rates existing in either the engine fuel pump and/or the engine fuel injectors reduces the chain length of the polymer. However, this results in fuel recirculated to the fuel storage no longer having antimist character, and any fire-resistant fuel qualities are quickly lost. There are essentially three potential ways to solve this problem and retain the fuel antimisting properties. They are listed here in order of the team-evaluated current technical feasibility. Engine/Fuel System Retrofit Since current engine designs require fuel recirculation to cool the injectors, modify the fuel circulation system such that no fuel is returned to the fuel storage tanks. This modification might include nozzle changes and/or some refrigerated intercooling of the circulation loop (see later discussions in next section). The STAS team does not believe that such system modifications should necessarily eliminate this approach from consideration.
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Aviation Fuels with Improved Fire Safety: A Proceedings TABLE B-1 Reference Fuel Properties Property (Fuel Code) (No. 7225) (No. 8821) (FRF of No. 8821)a (No. 9295) Specification Type MIL-F-46162A(MR)-II Fed. Spec. VV-F-800b-DF-2 — VV-F-800b-DF-A Gravity, ¹API at 15.5°C Density, g/ml at 15.5°C Flash Point, PMCC, °C(°F) Fire Point, °C(°F) Cloud Point, °C(°F) Pour Point, °C(°F) Kinematic Viscosity, cSt at 40°C Accelerated Stability (ASTM D 2274), mg/100mL Total Acid No., mg KOH/g Steam Jet Gum, mg/100 mL Sulfur, wt pet Nitrogen, wt pet Copper Strip Corrosion (ASTM D 130) Carbon, wt pet Hydrogen, wt pet Heat of Combustion (Gross), J/kgx10-6, (Btu/lb) Heat of Combustion (Net), J/kgx10-6, (Btu/lb) 36.1 0.844 60(140) 91(196) -21 (-6) -24 (-11) 2.2 0.6 0.01 3.9 0.35 — 1A 86.8 13.2 45.1 (19,427) 42.5 (18,283) 35.2 0.848 72.(161) 84(183) -1 (30) -10 (14) 3.2 2.7 0.03 3.2 0.47 — 1A 86.7 13.3 45.7 (19,670) 42.8 (18,450) 30.4 0.874 None — — — 5.3 — 1.12 — 0.36 -0.32 — 75.06 12.66 39.29 (16,893) 36.47 (15,679) 0.795 45(113) — -52 (126) -56 (133) 1.2 — — — 0.0 — 1A — — 46.1 (19,810) —(—) Hydrocarbon Types, FIA, vol pet saturates aromatics — — 69.1 29.4 — — 87.3 10.8 Hydrocarbon Types, HPLC, wt pet saturates aromatics 72.5 27.5 74.1 25.9 — — — — Aromatic Ring Carbon, UV, wt pet mononuclear dinuclear trinuclear total 7.1 11.5 0.3 18.9 7.5 6.5 0.4 14.4 — — — — 5.5 2.4 0.0 7.9 Cetane No. 48 51 — 51 Distillation (ASTM D 86), °C(°F) Initial Boiling Point 10% Distilled 50% Distilled 90% Distilled End Point 166 (331) 219 (426) 244 (471) 296 (565) 358 (676) 183 (362) 225 (437) 282 (539) 331 (628) 361 (682) — — — — — 164 (328) 178 (353) 191 (376) 214 (418) 252 (485) a 10 vol pet in 84/6 (v/v) base fuel/surfactant mixture.
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Aviation Fuels with Improved Fire Safety: A Proceedings Rapid Addition of Antimisting Agent to Fuel Tank During Fire Hazard Period Only In this scenario, some system would be retrofitted to the fuel storage compartment to rapidly disperse antimisting agent in the fuel on fuel system rupture. The team concluded that either the approach of jacketing the storage compartment or of rapidly injecting antimisting agent directly into the tanks do not appear to be practicable designs. Association Polymers It has been suggested that another class of polymers, so-called "association polymers," might be substituted for the material conventionally used as antimisting agent to eliminate the shear degradation problem. In this type of polymer, a very high molecular weight is achieved by linking smaller polymer units, which are not shear degraded, by means of hydrogen or ionic bonds, as shown in Figure B-1. The assumption here is that, while shear might temporarily disrupt the bonds, the bonding would reform rapidly. Critical points in judging the utility of such compounds, if they do exist, would be the determination of the range of shear energy under which the bonding would be destroyed (without destroying the bonding of the smaller polymer units) and the time required for the association bonding to reform. For the polymer to be effective, it would likely have to have re-association times the order of milliseconds (if not microseconds), and such short association times might also interface with fuel injector atomization. The possibility of the future use of association polymers was considered by the team to be highly speculative. (See later discussion of similar designs for halon addition to the fuel). It should be pointed out here that there is apparently a lack of fundamental information, even for the behavior of current FIGURE B-1 Hypothetical structure of an "association" polymer. antimisting polymers. While it is clear that these compounds shear degrade, little quantitative information as to the minimum shear that such polymers can sustain is available. The aerosol-forming shear created by impact of an incendiary round is likely to be far greater than that produced by wind shear or impactation during aircraft failure, and it is unclear the level to which antimisting agents perform under such combat-related situations. Indeed, the team was led to believe that antimist performance in tests under such conditions with high flash point fuels may not have been equal to that achieved in aircraft tests. The team therefore concluded that additional fundamental testing of antimisting agent behavior when subjected to varying shear conditions should be obtained before further consideration of their use is made. Higher Flash Point Fuels/Fuel Cooling Without being in the high flash point regime, there is essentially no way of eliminating the fireball hazard if an aerosol is formed and even weak ignition sources are available. Further, any flame propagation which would occur over a fuel pool spill would typically be gas-phase controlled and extremely rapid. Ignition of the fuel pool would also be facilitated by the combustible vapor cloud which would immediately form over the pool. Using a fuel with a flash point well above the range of ambient temperatures to be tolerated is a prerequisite for fuel spills to remain in the high flash point regime over long periods of time. Furthermore, if the fuel is used as a cooling medium for the fuel injectors, (see discussion above), it is clear that keeping the fuel circulation and storage temperatures well below the flash point would be beneficial to fire hazard mitigation. If the circulation temperature approaches the flash and/or fire point of the fuel, then aerosol and spilled fuel fire phenomena will again be gas-phase controlled. In fact, the lower the fuel circulation temperature is kept relative to the flash point, the stronger the ignition phenomena will have to be to initiate the flame ball, and the more intense the fireball must be to ignite a pool fire. Such fuel cooling will have little or no effect in terms of diesel engine performance or vehicle range. Substantial cooling of the fuel could be accommodated with existing technology by placing a refrigerated inter-cooler in the fuel recirculation system or fuel tank(s). As mentioned above, inter-cooling will in any event probably be required in new engine designs, but in the absence of fire considerations, air-cooled systems might be adequate. Refrigerated systems would divert some available engine power, but estimated magnitudes would appear to produce relatively small reductions in range. Furthermore, such systems could be modulated during tactical maneuvers requiring maximum power, and therefore, there would be effectively no degradation in vehicle performance. Finally, increasing fuel flash point and cooling recirculated fuel are approaches which are also compatible
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Aviation Fuels with Improved Fire Safety: A Proceedings with not returning circulated fuel to the fuel storage compartments, a requirement for using current antimisting agent (see previous section). The consensus of the STAS team was that some vehicle modifications will likely be required with almost any effective approach to improving fire-resistance of the vehicle (and fuel), and such modifications should not completely eliminate potential approaches. The relevant question is what level of vehicle modification would be acceptable on a cost-benefit basis. Liquid/Gas Interface Dilution The more recent work on the development of fire-resistant fuels has dealt primarily with the formulation of clear to hazy surfactant stabilized emulsions of small percentages of water-in-diesel fuel. The FRF candidate rejected by the U.S. Army Materials Development and Readiness Command was a mixture of 10 percent (by volume) water, 6 percent surfactant, 6 percent co-solvent (for the surfactant) in diesel oil. This formulation diminished (but did not eliminate) the ability of the base diesel fuel to produce a fireball, and completely prevented pool fires. The mechanism by which the material reduced the fireball problem is apparently through an increase in fuel viscosity and thus a reduced capacity to form small aerosol droplets. It appears that the mechanism through which the pool fire issue is mitigated is through the dilution of the fuel vapor layer over the liquid surface by evaporating water. This liquid surface blanketing with water vapor leads to suppression of chemical initiation (pool fire ignition) as well as provides sufficient heat sink effect to extinguish any existent flame. These effects essentially manifest themselves as a nonflammable mixture of water and fuel vapor over the liquid fuel surface. A minimum neat fuel flash point is defined (about 70°C for the current FRF candidate) above which no flame can be established over an FRF formulated from that fuel until all of the water in the FRF formulation has been depleted by evaporation. These mechanisms of action have been experimentally established in recent work at Southwest Research. The findings are contrary to previous work elsewhere which suggested a mechanism of limiting the fuel liquid surface temperature to the boiling point of water. This hypothesis was based upon the premise that the components of an immiscible mixture such as an emulsion vaporize independently of one another. However, the vapor pressure of FRF micro-emulsions were found to be substantially less than would be predicted for classical water-fuel immiscible mixtures. FRF-type blends containing 6 vol pct surfactant and between 2 and 10 vol pct water as micro-emulsions appear to behave similarly as far as liquid vapor pressure-temperature relationships are concerned, but a formulation containing 6 vol pct surfactant, 6 percent co-solvent to solvate the surfactant in aromatic diesel fuel, and 10 vol pct water was chosen as the prototype FRF composition. These large amounts of materials added significant procurement costs, caused substantial deployment difficulties (since the material was to be prepared in forward supply areas), and reduced the performance and range of the vehicles tested. Stability was also substantially affected by the purity of the water used in the formulation. However, minimal water/surfactant concentrations required for fire-resistant behavior were apparently never defined previous to proposing deployment. Finally the formulated FRF showed difficulties in filter plugging at low ambient temperatures. Part of these difficulties may have been the result of too little fundamental research and development before the selection of the micro-emulsion component structure itself. Micro-emulsions represent a state of matter in which one immiscible liquid is dispersed in another, the particle size of the dispersed phase being of the order of 100 to 200 A.U. The presence of a stabilizer (i.e., surfactant or emulsifier) is required to produce stability of the structure. In the case of micro-emulsions, this surfactant is usually a binary mixture of an appreciably water-soluble surfactant (e.g., sodium dodecyl sulfate) and a less-soluble co-surfactant (e.g., pentanol). The composition of the micro-emulsion (oil/water ratio, surfactant concentration, surfactant/co-surfactant ratio, etc.) is usually critical with regard to maintaining stability over any appreciable range of environmental conditions (e.g., changes in temperature). This is in contrast to macro-emulsions which are characterized by much larger particle sizes, and where the composition is much less critical. On the other hand, micro-emulsions are considered to be thermodynamically stable (similar to true solubilized systems), while macro-emulsions are thermodynamically unstable. From this point of view, micro-emulsions can be viewed as an extension of solubilized systems while macro-emulsions represent a totally different state of matter. The relation among composition properties and the existence of micro-emulsions is best understood in terms of a ternary (three component) phase diagram. This is illustrated in Figure B-2 where the micro-emulsion exists only in the shaded regions (S = surfactant; E = water; H = oil). In this figure, surfactant concentration corresponds to the concentration of surfactant mixture and the surfactant/co-surfactant ratio is constant. A different phase diagram for this system would be engendered by a change in S/co-S ratio. It is also to be noted that the diagram is defined for a specific mixture temperature and would be different for different mixture temperatures. Figure B-3 illustrates the kinds of changes in phase diagram which can occur with change in mixture temperature, in this case from 30 to 40°C. A single region of existence has been transformed to two separated regions, and even more drastic changes can occur for larger changes in mixture temperature. The problem involved in formulating a micro-emulsion fuel is obviously to ensure that the chosen formulation is one which will remain stable over the range of mixture
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Aviation Fuels with Improved Fire Safety: A Proceedings FIGURE B-2 Micro-emulsion system water/K oleate/l-hexanol/hexdecane. S/CS ratio: 3/5. (S = surfactant; E = water; H = oil). temperatures which will be experienced. In the military diesel range, these might range from 0°C to about 80°C. Clearly, if the micro-emulsion FRF used was at times cloudy or clogged filters, stability problems had occurred. Particle sizes the order of 100 to 200 A.U. would not result in such phenomena. Apparently the FRF micro-emulsions used were not formulated properly for stability over the temperature range and diesel fuel property and water purity variations of interest. The STAS team believes that achieving suitable results with a single formulation is not a trivial nor highly probable matter. On the other hand, liquid/vapor-interface dilution could also be accomplished through the use of true solution techniques. Such solutions are likely to be less sensitive to water purity. True solutions are stable to shear forces, are not subject to separation on storage, can have wide ranges of solubility and be maintained over wide ranges of mixture temperature, and can easily be produced in the field. Examples of such FIGURE B-3 Effect of temperature. At 30°C, micro-emulsions exist in area A; at 40°C, the micro-emulsion region has split into two regions, A and B. systems are shown in the ternary diagram of Figure B-4 for several hydrocarbon-water-alcohol co-solvent systems. Apparently, the existence of diesel fuel-water-co-solvent mixtures and their flammability characteristics have not been previously investigated. It is likely that the same flammability characteristics as those observed for micro-emulsion FRF could be generated with such solutions. Furthermore, it is likely that co-solvent alcohols of higher molecular weight than ethanol could be found. Finally, other types of co-solvents such as ketones may also exist. It appears that liquid/vapor interface dilution is itself a feasible technical approach which should be further considered before it is abandoned. Limited storage life and operating temperatures are compelling reasons for rejection of candidate systems, but the STAS team concluded that lower energy content and cetane number of candidate mixtures have less serious impact. Decreased energy content has two implications: the logistics of the fuel supply are made more difficult, and there may be a consequent reduction in engine power (and, for existing vehicles, a reduction in vehicle range). Most fuel injector have some reserve capacity, and furthermore, increased fuel volume requirements do not automatically eliminate a system from consideration if other benefits are perceived to be of sufficient importance (as is evidenced by the adoption of the M-1 tank with a 30 to 100 percent greater fuel consumption than previous designs). Likewise, moderate decreases in cetane number are also tolerable, since starting aids are already required and present. At moderate to full load, turbocharged diesels are relatively insensitive to cetane number and future mini-cooled diesel engines will be even less so once they are at operating temperature. If proper micro-emulsion formulation or co-solvent approaches could lead to appropriate stability characteristics, and amounts of co-solvents and/or surfactants as well as water were held to minimums, the fire safety benefits of this approach might outweigh other performance and range degradations.
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Aviation Fuels with Improved Fire Safety: A Proceedings FIGURE B-4 Ternary water-alcohol-hydrocarbon solutions. (1) Water-methanol-heptane. (2) Water-methanol-hexane. (3) Water-ethanol-heptane. (4) Water-ethanol-hexane. (5) Water-ethanol-toluene. Source: International Critical Tables. Halon Suppressants Halons are compounds which contain carbon, various combinations of halogens (fluorine, chlorine, bromine, or iodine), and, occasionally, hydrogen. For convenience, a system of numbering has been devised for halon compounds which consists of four numbers. The first denotes the number of carbon atoms, the second, the number of fluorine atoms, the third, the number of chlorine atoms, and the fourth, the number of bromine atoms. Iodine has not been included in this numbering system since it has only rarely been considered in the construction of halon compounds. (However, iodine atoms are slightly more effective in fire suppressant character than bromine atoms). The amount of hydrogen atoms contained in the compound is determined by the number of remaining valence bonds needed to saturate the number of carbon atoms. There is a considerable body of literature, both fundamental and practical, on the use of halons for ignition and flame inhibition as well as fire extinguishment. There are also a considerable number of formulated halons of varying physical and chemical properties from which to select. The most often employed halon is currently halon 1301, i.e., trifluoro-bromo-methane (CF3Br). According to the briefings received, the Army already has considerable experience in using halon 1301 as a fire suppressant applied as a deluge surrounding the vicinity of fuel compartments (on the M-1 tank). The briefings described a triggering mechanism which released halon 1301 into the compartment surroundings upon shell impact so rapidly that, although an aerosol cloud of fuel is formed by the impact, no fireball ignition (formation) occurs. These systems are currently reaching the deployment stage, and apparently further work is under way to develop (implement?) systems which would operate under multiple impact conditions (on the M-1). This approach to fire suppression can be accomplished via retrofit on other vehicle systems, and the method does not require modification of the engine/fuel system. As such, no degradation of performance or range should result to the extent that the mass/volume of the fire suppressant system offers unacceptable constraints. The STAS team is fully supportive of additional efforts to further evaluate such possibilities. If the fireball formation can be eliminated, one of the major sources of ignition for any fuel pool spill will have been removed. Compartment environment inerting as described above is very effective in preventing ignition of flammable fuel/air mixtures. Inerting through the use of halons probably results from several fundamental effects. Halons have large specific heats and therefore are very effective absorbers of sensible enthalpy. Second, halogen materials, particularly bromine, scavenge radicals which can lead to ignition. Finally, local oxygen concentrations are decreased by the addition of halons and chemical reactions leading to rapid oxidation will be slowed. The order of 1 to 5 percent concentration of halon in the surrounding air is sufficient to prevent ignition and to extinguish small fires (e.g., smoldering cigarettes, etc.). This concentration of halon 1301 in air also causes no distress to human respiratory systems. However, if a vigorous fire is already present when the halon is added, thermal decomposition of the halon can lead to species which are not only extremely toxic, but actually accelerate the rate of burning. Toxic gaseous products and copious amounts of particulates (soot) are produced. Compartment inerting could also be accomplished using carbon dioxide or nitrogen purges which would not lead to any toxicity difficulties. However, there is no direct chemical inhibition which results from these materials, and much larger dilution ratios are required to be effective. Any rapid admission of fresh air would result in loss of effectiveness sooner in the case of these latter materials. Halons might also be used as fire suppressing agents in ways other than through localized atmospheric inerting. These include: Addition to the Fuel Itself Presence of the halon material in the fuel itself could add an additional mechanism for fire safety protection, i.e., liquid/vapor interface inerting (see discussions above). To obtain this benefit, a halon (or mixture of halons) with the appropriate volatility characteristics in comparison to the fuel must be chosen. Initial investigations of the combustion properties of fuel formulations containing halon 1301 in engines
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Aviation Fuels with Improved Fire Safety: A Proceedings by the Army showed that the combustion products derived from the halon were so corrosive as to severely damage the engine in less than 50 hours of operation. Thus the halon component would have to be removed from the fuel previous to injection into the engine. While this removal is probably technically possible through absorption processes, such approaches may not be feasible for this particular application. It is also highly unlikely that a halon type compound could be derived which would not produce engine corrosion problems. Injection and Mixing in the Fuel Compartments After Impact In this approach, upon threat of a fire incident, i.e., shell impact, etc., halon would be rapidly injected and mixed with the liquid fuel within the fuel compartments. Such a technique would not only require very rapid response systems, but designs which would result in almost instantaneous dispersal within the fuel tank. It should be remarked that the fuel-halon mixture will cause rapid degradation of the engine hardware. While several of the STAS team believed that at least some further conceptual studies of the problem might be worthwhile, the majority opinion was that the success of this approach was unlikely. Jacketing of the Fuel Tank In this approach, the fuel compartments themselves would be constructed in some double-jacketed design with halon in the outer shell. The concept here was that any penetration of the fuel compartments would yield a mixture of halon and fuel leaving the point of penetration. The apparent drawbacks are that the fuel supply system to the engine remains unprotected, the rate of ejection and mixing with the fuel at the point of penetration are uncontrolled, and the system is essentially restricted to protecting a single penetration event. Because of these issues, the fire hazard reduction achievable with this technique is unknown. Liquid Halon Deluge of Fuel Spill The STAS team could not envision any method through which such an approach could be implemented since there is no knowledge as to where the impact will occur nor where the spill will result. In summary, the most appropriate method for using halon fire suppressant technology today appears to be to control ignition of the fireball in the vicinity of the fuel compartment penetration. This will not reduce the possibility of igniting the aerosol produced at locations remote from this region. However, if the flame ball can be prevented, the opportunity to prevent serious pool spill burning is substantially improved. Gelling Agents Gelling agents were one of the earliest methods investigated by the Army for fuel fire hazard reduction. The basic premise of using gelling agents was to achieve performance similar to antimisting agents as well as contain the region of post-impact fuel spillage. All previous formulations studied have had serious manufacturing difficulties (in terms of reproducibility of the gel properties), and performance problems (poor filtering ability, substantial difficulty in emptying fuel ullage, high resistance to pumping, poor thermal stability). Indeed, so many difficulties were identified in previous work that those team members who were aware of the research were surprised by the suggested revival of this approach. There appears to be few benefits which can not be achieved through the other methods reviewed above with much less difficulty and fewer performance effects. The STAS team did not place much promise on the possibility of success of any further work on this method. Combinations of These Methods Some of the above discussions assume certain combinations of the various approaches that were described. For example, the use of antimisting agents is only effective in reducing flame ball formation if a high flash point (relative to ambient) base fuel is used and circulation temperature of the fuel is kept well below the flash temperature. However, combinations of two or more of the types of approaches discussed above may result in synergistic improvements. The STAS team devoted some discussion to combinations of not only fuel modifications, but fuel system/vehicle accessories to reduce fire hazard. In these discussions, priority was given to those areas where existing technologies would be used first, and those technologies which required least developmental work would be combined with them. Systems modifications and base fuel modifications fell in the first category of items. The highest priority issue appears to be retrofit of compartment halon deluge systems similar to those already devised for the M-1 tank, and the addition of fuel line closures which activate upon fuel line fracture. The former modification would eliminate the fireball ignition in the vicinity of a ballistic impact itself, and multiple impact designs should be considered. The latter modification would address much of the fire hazard issue arising from fuel supply system line fractures. Clearly, increasing the base fuel flash point and decreasing the fuel circulation and storage temperature (relative to ambient operating requirements) would in all cases benefit the fire hazard issue. Flame ball and pool spill flame initiation should become more difficult, and pool spill flame spread rate might be reduced to a value such that if the vehicle could still maneuver, it might remove itself from the vicinity of the pool before being enveloped. Indeed, the
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Aviation Fuels with Improved Fire Safety: A Proceedings consensus was that halon compartment deluge and refrigerated cooling would be of greater benefit in fire hazard reduction than the costs in additional accessory power requirements and vehicle retrofit issues. Full scale testing will be required to determine if these methods in themselves suitably control the fire hazard issue, but these steps would only be further benefited by those appearing below. The added use of conventional antimisting agents and fuel vapor interface dilution techniques require additional fundamental questions to be answered, as well as some vehicle design modifications, logistics decisions, and fuel cost procurement decisions to be made. In the case of antimisting agents, the minimum shear required to degrade the agent in comparison to shears experienced under ballistic impact needs to be quantified rather than qualitatively determined. In this regard, association polymers will require considerable fundamental research and development and were therefore given both a very long required lead time and a high risk research rating. Finally, a fuel system modification which would not return circulated fuel to the fuel storage compartments would be required. This may cause the need for some redundancy in fuel inter-cooling systems if both the fuel stored as well as the fuel recirculated needs to be cooled. (The team endorsed the refrigerated cooling of stored fuel to permit modulation of the cooling power during strategic power conditions, but air cooling of the small volume of fuel recirculated might be adequate to provide sufficient injector cooling designs which do not return fuel to storage). The added use of liquid/vapor interface dilution, from either micro-emulsion or co-solvent approaches requires additional fundamental work to determine the optimum formulation(s) with regard to thermal stability. The use of this technology could substantially benefit the pool fire problem. If thermal stability is achieved, no filtering problems will be experienced. This research should also determine the minimum quantities and purities of materials that can be used to obtain successful dilution of the interface. Logistic and cost/benefit results must be quantified, i.e., it is impossible to use these technologies without some additional logistical and/or fuel costs being incurred. Indeed, no technique can meet such inflexible criteria, and acceptable levels must be defined. Finally, in the case of both antimisting agents and liquid/vapor interface dilution, the possibility of formulations defined for specific climates should be further investigated. Such an approach is compatible with existing climatic formulations of diesel fuel itself. Methods which add halon type compounds to the fuel, either by injection on impact or as a supplied fuel component, appear to be long term, high risk approaches. The possibility of protecting engine components from the corrosive compounds which result from combustion of halons under further engine operation is speculative at best, directing and controlling halon dispersal in the region of ballistic impact also seems unlikely. Finally, the use of fuel gelling technology appears to add more technical complications than benefits derived in addition to those available from other techniques. SPECIFIC TASK DISCUSSIONS On the basis of information, analysis and commentary appearing in the previous two sections, this section briefly summarizes the collective opinions of the STAS team on the specifics of the tasks appearing in the work statement detailed above. Background Review Summary Future work should be proposed and carried out on a systems (fuel, fuel system, engine system, deployment) basis. One of the principal issues which the team believes has caused considerable difficulty in reaching a successful result is that previous work has concentrated separately on the formulation of a fire-resistant fuel and vehicle modifications as separate approaches to reducing fire hazard. A "successful" FRF was developed, but the implementation phase uncovered shortcomings, most of which would have been evident much earlier in the program if an integrated approach had been taken. Fundamental/engineering issues which are important to optimizing the various methods available for fire hazard mitigation have remained unanswered. Future programs should take a more balanced approach in obtaining sufficient fundamental knowledge to guide development of optimum approaches. For example, in the case of the recently formulated FRF, the team was briefed that no research was devoted to defining the minimum additive package which would yield effective dilution of the liquid/vapor interface. Yet it was because large amounts of additives were required that substantial deployment difficulties resulted. Clouding and filtering difficulties of the FRF indicate thermal instability of the formulation, but no fundamental research apparently ensued from the point of developing simple phase diagrams for the formulation. Another example is that after substantial work, it appears that there is no quantitative definition of what shear leads to degradation of conventional antimisting agents. Constraints for previous research goals were not suitably defined. Specific, acceptable, and realistic criteria for the program solution must be made before any new program or program continuation is initiated . Specific, acceptable, and realistic criteria which bound the possibilities for solution of the fire hazard issue should have been defined in advance of any development-or deployment-oriented
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Aviation Fuels with Improved Fire Safety: A Proceedings efforts. Fundamental research should have proceeded at some level to identify controlling parameters influencing the effectiveness of various approaches, but applied development efforts had little chance of success without this guidance. A conservative cost-benefit ratio for changes in vehicle performance, range, costs, retrofit, deployment, etc. And fire hazard reduction is needed to guide selection of appropriate program criteria. It is neither useful nor realistic for DARCOM to state that any approach to reducing the fire hazard issue must: not degrade performance, range in particular not generate additional procurement cost contribute significantly to fuel survivability have worldwide use capability be compatible with fuel handling and distribution systems Tests and quantitative definitions must be provided for such issues if a successful program is to result. For example, the STAS team consensus was that possibly a range degradation of 10 percent and a maximum power degradation of 5 percent might be accommodated, since these are comparable to effects derived from changes in altitude, alternate base fuels, temperature, etc. In fact, declutching might result in no power degradation at all. With regard to logistics, worldwide use compatibility equivalent to current military diesel fuel classifications might be considered. Similar approaches could be taken in reframing fuel supply/distribution and stability requirements. Finally, an acceptable procurement adjustment(and vehicle retrofit level) must be identified. These suggestions are meant only to exemplify the kind(s) of guidance this development program must have in order to not repeat the recent problem with FRF. Acceptable vehicle/fuel systems modifications criteria need to be established. Even minor vehicle modifications such as fuel filter heating might have eliminated some of the difficulties encountered with the current FRF. Furthermore, the simple addition of line closure mechanism to close fuel lines upon fracture could substantially reduce any hazards arising from fuel line rupture. As detailed in the previous sections of the report, the STAS team thought certain vehicle modifications can be as important as, and synergistic with, modifications to the fuel in mitigating the fire hazard problem. Review of Proposed Approaches for New Program The commentary below specifically addresses the proposed approaches and program phase plan appearing as Table B-2 and Figure B-5. In each case, the merits of each TABLE B-2 Plan for ''New" Fire-Resistant Fuel (FRF) Three parallel approaches to be considered during initial phase of program • Addition of halon compounds (i.e., low molecular weight compounds containing chlorine and bromine) to diesel fuel. • Addition of associated polymers (i.e., metal-containing organo-complexes) to diesel fuel • Addition of both halon compounds and associated polymers to diesel fuel. Selection of candidate fuel approach and major decision point will occur at first milestone (i.e., after 18 months from program initiation) Interim milestone at ninth month will establish selection criteria for major decision point Plan consists of three phases: • laboratory investigations • full-scale engine/system and field tests • specification development and user's guide FIGURE B-5 Plan for "new" fire-resistant fuel (FRF).
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Aviation Fuels with Improved Fire Safety: A Proceedings approach are summarized, and the potential for success within the time requirements is given. Addition of Halon Compounds to Diesel Fuel As a Fuel Component. The disadvantage produced for operating combustion systems by the presence of halons in the fuel presently outweigh fire hazard advantages which would result from the addition. Co-additives to eliminate the formation of acidic combustion products which are highly toxic and corrosive to engine systems does not appear to be possible. Furthermore, techniques to remove the additive prior to combustion are relatively limited, and successful development of an operating method is doubtful. It is also likely that halons added to the fuel could actually aggravate fireball conditions if the fireball were to be ignited. Four year development of suitable techniques appears unlikely, and implementation will involve logistics difficulties, and performance degradation which must be addressed. By Post-Injection. Post-injection of halons (or surfactant-water) into the fuel storage compartments upon initiation of a fire hazard condition will also result in fuel which has similar combustion difficulties to the fuel which would originally contain the additive. In addition, the response time required for injection/dilution in the stored fuel is unknown and is probably system compartment-geometry dependent. The method will probably be ineffective for fireball mitigation, but would involve little logistics problems, and performance degradation only upon activation. Four year development appears unlikely. Post-Deluge of Spilled Fuel. Post-deluge of spilled fuel, either with halons or halon/surfactant/water mixtures does not appear to be a plausible approach. While the use of compartment jackets to contain the mixture would orient the fuel spill and deluge direction, rates of ejection and mixing would be very difficult to control. Other methods appear to be entirely unacceptable since the spill rate/direction will be scenario dependent. Large amounts of additives are likely to be required for this approach, and fuel storage volumes may be significantly reduced. Successful development of an effective system within a four year period appears unlikely. Addition of Association Polymers to Diesel Fuel There is such a substantial lack of fundamental information available for this approach that it is difficult to consider association polymers seriously even for long range development (10 years). No fundamental guidance is available for the physical behavior of such compounds under shear, and none is available concerning the dynamics of their degradation or re-association. The team considered successful development of this approach unlikely. Co-Addition of Halons and Association Polymers The limitations and inadequacies of such a proposal are adequately covered in the discussions appearing in sections on addition as a fuel component and by post injection above. Milestone Plan and Phases An 18-month decision point to choose among the proposed approaches is unrealistic. In the cases for which any potential for success exists, fundamental information on which to judge their viability is missing. Based upon the emphasis of previous Army research programs on this subject, it is also likely that too little emphasis will be placed on obtaining such information from laboratory research prior to full scale systems and field tests in future programs. Recommended Additional Approaches On the basis of earlier discussions, this section briefly summarizes the STAS team consensus on other potential approaches to mitigating the fire hazard problem. Fuel flash point reduction, fuel cooling, compartment inerting by halon deluge, and line closure systems can all be approached on the basis of existent technology, and are therefore all suitable candidates for a four year development-to-implementation program. The potential success of these collective approaches in reducing the fire hazard are substantial, they are compatible with other approaches considered here which might be added at a later date, and they do not result in (what appear to be) unacceptable performance or logistic penalties. It is recommended that the existing program of studying the effect of vehicle fuel system temperature on fires be accelerated and emphasized so as to provide a better technical basis to define trade-offs for advanced vehicle fuel cooling systems. There is a need to immediately do a design study of several existing vehicles using cooling system computer modeling to determine the hardware requirements, complexity, energy requirements, ambient temperature effects, cost, etc. to cool the fuel in the lines and compartments. With fuel cooling and circulation system modifications, conventional antimisting agents may have some poten
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Aviation Fuels with Improved Fire Safety: A Proceedings tial for mitigating the aerosol formation problem. Additional fundamental information on shear energy effects are apparently required before further development should be considered. The technology here is nearly fully developed, is applicable to high flash point fuels, and does not impose large performance penalties or logistics difficulties. Fuel cooling effects may also be synergistic with the addition of antimisting agents. With the system design modifications and fundamental questions answered which were mentioned above, the development of an antimisting fuel package in an intermediate time (5 to 8 years) is plausible. Techniques which have been derived for producing liquid/vapor interface dilution do not currently meet suggested criteria constraints. However, optimization of micro-emulsion technology for this application appears to have been incomplete, and co-solvent approaches have not been investigated. Four year development and deployment of these techniques were viewed as unlikely because of the current lack of fundamental understanding needed to guide such efforts. One of the team members has revised his assessment since the meeting, and he now considers the probability of successful derivation of a suitable micro-emulsion formulation to be possible in the suggested four year period. In fact, the entire STAS team believes that these methods hold sufficient long term promise such that continued effort should be given to mechanisms for producing liquid/vapor interface dilution. Initial work should be on a fundamental level to identify stability issues based on phase diagram analysis, and to better define minimal additive requirements. Additional systems evaluations should not be contemplated without promising results at this research level. Success Potential The success potential of the various methods has been considered in the sections above. BIBLIOGRAPHY (IN ADDITION TO BRIEFINGS PACKAGES DISTRIBUTED AT MEETING) W.D. Weatherford, Jr. and B.R. Wright, "Status of Research on Anti-mist Aircraft Turbine Engine Fuels in the United States," AGARD/NATO 45th Meeting of the Propulsion and Energetics Panel, Rome, Italy, April 7–11, 1975. I. Glassman and F.L. Dryer, "Flame Spreading Across Liquid Fuels," Fire Safety Journal, 3, 123, 1980. W.D. Weatherford, Jr. and D.W. Naegeli, "Research on Fire Resistant Diesel Fuel Flammability Mitigation Mechanisms," Interim Report No. AD A 130743, AFLRL No. 165, U.S. Army Fuels and Lubricants Research Laboratory, Southwest Research Laboratory, San Antonio, TX, December 1982. W.D. Weatherford, Jr. and D.W. Naegeli, "Study of Pool Burning Self-Extinguishment Mechanisms in Aqueous Diesel Fuel Micro-emulsions," Western States Section Meeting of the Combustion Institute, Pasadena, CA, October 17, 18, 1983. Enclosures per letter from M.E. Lepera, dated March 12, 1984 Summary listings of reports completed to date on Fuel Fire Research. Summary status of Implementation of the Fire-Resistant Fuel. Briefings package on the Fire-Resistant Fuel Presenting Technological, Operational, and Organizational Issues Briefing films on FRF performance and shaped charge issues. STAS TEAM PARTICIPANTS Dr. Frederick L. Dryer (Team Leader) 106 Weldon Way Pennington, NJ 08534 Dr. Paul Becher Paul Becher Associates P.O. Box 7335 Wilmington, DE 19803 Dr. David E. Foster Department of Mechanical Engineering University of Wisconsin-Madison 1513 University Avenue Madison, WI 53706 Dr. Melvin Gerstein 1141 Via Romero Palos Verdes Estates, CA 90274 Dr. Jerry A. Havens 1236 Edgehill Drive Fayetteville, AR 72701 Dr. John H. Johnson P.O. Box 39A Royalwood Addition Houghton, MI 49931
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Aviation Fuels with Improved Fire Safety: A Proceedings Dr. J. Adin Mann, Jr. School of Engineering Chemical Engineering Department Case Western Reserve University Cleveland, OH 44106 Dr. Phillip S. Myers Department of Mechanical Engineering University of Wisconsin-Madison 1513 University Avenue Madison, WI 53706 Dr. Otto A. Uyehara 1610 Waunona Way Madison, WI 53706 Dr. C.K. Westbrook Lawrence Livermore National Laboratories P.O. Box 808 L-71 Livermore, CA 94550 Meeting Attendees Dr. David Mann CDR, U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709 Mr. F.W. Schaekel Fuels and Lubricants Branch Materials, Fuels & Lubricants Laboratory Belvoir R&D Center Fort Belvoir, VA 22060 A. A. Johnson S.J. Lestz W.D. Weatherford, Jr. B.R. Wright G.E. Fodor M.D. Kanakia U.S. Army Fuels & Lubricants Laboratory 8500 Culebra Road San Antonio, TX 78284
Representative terms from entire chapter: