Aircraft Fuel Tank Vapor - Assignment Example

Title: Aircraft fuel tank vapor/air explosions Dated: April 21, 2010 Introduction: The aircraft fuel system with fuel tanks allows the crew to manage, store and deliver the fuel to the propulsion system as per requirements of the aircraft. Fuel systems of the aircrafts differ greatly due to varied performance of the aircraft in which these systems are installed for the supply of the fuels to the aircraft. The fuel systems of the aircrafts vary based on the type and size of the aircraft and their working capacities. An aircraft with single engine piston have a very small fuel system while an aircraft like B 707 ,in addition of administrating own fuel will also have the capability of supplying fuel to the receiving aircraft through drogue and probe system or through the boom. Aircraft fuel tank explosions are the result of a variety of internal and external factors and the organizations work for the development of an efficient, reliable and economical method for reducing these explosions with the assistance of a variety of agents with necessary modifications in the aircraft systems. These systems provide safety to the central fuel tank of the normal aircrafts and to the commercial jets. These methods include the ignition source of the explosion, electrical arcing along with electrical wiring, and auto ignition in the terminal wires of the central fuel tank of the aircraft. The explosions in the fuel tanks are the chief threat to the working and physical conditions of the aircraft and need to be lowered with the adoption of plausible options with an objective to maximize the working of the aircraft with normal working of the fuel tanks with all their parts and segments. Optimum use of Explosion Suppressant Foam(ESF) that is reticulated polyurethane foam and is used in the fuel tanks where the possibility of explosion exists. ESF is also called as Safety Foam and the product was invented in the late 1960s and was used by the US Air Force to suppress explosions inside the fuel tanks of the aircrafts. Modifications in the engineering designs in the commercial and corporate business aircrafts have helped in the reduction of the explosions in the fuel tanks of the aircrafts. Changes in all the possible energy sources of the aircrafts could be utilized; however, 100% reduction in the explosions is highly possible. Even if it is possible to remove all the on- board energy sources, it would, however, be impossible to remove the external energy sources as the cause of the explosions in the fuel tanks of the aircrafts. The explosions could be limited through the application of solutions other than designing out energy sources for the aircrafts. These solutions include purging fuel tank ullage areas of dangerous explosive fume vapor through ram air methods and cooling the fuel tank ullage area to decrease flammability potential with the introduction of ram air past the tank. Similarly, the solutions like to reduce the fuel tank ullage area and to reduce fuel tank flammability through cooling fuel tanks with the use of colder fuel for lowering the temperature of the fuel tanks. The understanding of the fuel systems with single engine and twin-engine piston will provide necessary assistance for the understanding of the aircraft fuel tank /vapor explosions and to understand the process of combustion as key area of the whole process. The observance of the recommendations as have been included in the assignment will help in lowering the fire explosions in the fuel tanks of the aircrafts and in the maintenance of vapor-liquid equilibrium with all their thermodynamic values for the execution of the aircraft’s operations in safe modes. Literature Review: The study Aircraft fuel tank vapor/air explosions is completed with the assistance of an experiment and relevant print material on the subject of aircraft fuel tanks, Thermodynamics, Aging aircraft systems ,fuel change ,and cold ambient temperatures as are applied in the working of the aircrafts. The mechanism chiefly based on the major process as are involved in the fuel tank explosions with all there physical impacts on the system and the surroundings. The study has its relationship with the work as completed by Adcock, Sylvia in1998 through "A Quest for Safer Jet Fuel," which has explained the behavior of the Jet Fuel in the normal practices of the air operations. The fuel provides necessary energy for the execution of energy based operations in the aircraft. The importance of wiring in the aircrafts have been discussed by McKenna, James in 1999 through "Debate on Wiring Safety Shifts to Capitol Hill" as an important segment in the explosion process of the aircraft fuel tanks. The aging aircraft systems has also relationship with the aircraft systems especially relating to the explosions of the aircrafts as have been discussed by McKenna, James in 1997 through "Boeing Eyes Fuel Change to Increase Tank Safety". The subject has greatly been discussed in an article as published in the Newsday.com with the title "TWA Flight 800-Graphics" 1996 (www.newsday. com/jet/twamain). Similarly, Tischler, Adelbert O. in article "What Happened to Flight 800" in 1998, has explained the problem. The accumulation of the vapors in side the fuel tanks has been observed and efforts have been made to prevent fuel take explosions through the introduction of inerting gases into the fuel tank ullage area for blocking the accumulation of the fume –vapors there –in. The system has a drawback to these mechanisms are excessive weight penalties and the maintenance requires the high cost and complexities of the system for their execution. The system has developed some safety problems of there own as the displaced unburned hydrocarbons as produced by these methods and have the capacity to create atmospheric pollution. The inerting method proposes the utilization of engine exhaust as the required gases. The major problems as are associated with the system include huge cost of the methods and weight of the system needed to introduce and treat the exhaust gases to the fuel tank and the ability to inherent corrosiveness of the associated exhaust products during the process. The experiment as was completed with the use of cylindrical explosion vessel with a diameter of 0.5 m and a length of 0.5m with the use of a specific pressure for the stimulation of a particular altitude. Different temperatures were generated with the use of the kerosene; however, there was no heating of the air above the fuel in the experiment. The spark was positioned at a distance of 65mm from the surface of the kerosene oil on the centre of the pool for making its impact on the system. The vessel in the experiment was evacuated at the desired pressure and then the fuel had started heating with a value of 15J spark firing. At this stage, the fuel temperature at which the ignition had occurred was determined. A quantity of 68g of aviation kerosene was used in the experiment. The whole experiment was completed with four tests, two with the use of Explosion Suppressant Foam and two without ESF. The results of the experiment has provided a base for the understanding the subject of aircraft fuel tank vapor/air explosions for making significant contributions in the field of air industry and will continue to serve as baseline data in the field of air operations with safety and security of the aircrafts and all other associates of the industry. The combustion process of the fuels as used in the aircrafts affect the process through the rate of reactions. In combustion, the rate of reaction is relatively slow and therefore, needs precise conditions to result in an explosion of a magnitude at the higher rates. If we consider the fuel vapor as the only medium present, there is a possibility that a spark has been generated and has the capacity to initiate fire in that vapors. In such type of situations, the final energy is dissipated and would in turn dependant upon the rate of advance of the reaction through the vapor. This type of reaction would be slow to start and will accelerate as the heat increased in the system. That slows start of the process of course burn any air present in the tank and would eliminate some of the fuel vapor. The reaction would be increased by the confinement as provided within the tank and the tank temperature. The divisions in the tank would block the reaction process as the arrangement has the capacity to restrict movement of heat within the system. The mechanism will occur as in the form of slowing down the chain reactions through the vapors and subsequently build their pressure with the utilization of energy from the eventual explosion. The explosion process requires heat as a source and would have to be a fire, initiated, as proposed by a spark. The heat generated during the process by the fire would vaporize more fuel without the utilization of any additional air in the system. The explosion process and the rate of reaction are in a direct relationship as the start of the process needs an immense quantity of energy as generated during the process for disintegration of the fuel tank. Such type of explosion has transitory effect overall process. Splitting the fuel tank would be one consideration and breaking through the fuselage would be other alternative. The advantages as are associated with the understanding of the explosive mechanism in the fuel tanks of the aircrafts: There are many different conditions from which to approach the issues relating to central fuel tank safety in commercial and other jets. The most common approach recognizes that there must be an ignition source to an explosion to occur. The identification of the ignition source is an important aspect for the whole process. Fuel-air ratio, tank temperature, and fuel flammability are all the relevant issues and have the potential to determine how ignitable the central fuel tank of the aircraft is. Electrical wiring, electrical arcing and auto-ignition are also of significance in the explosion process of the fuel tanks. The identification of the ignition source is of paramount importance for the whole process and has a set of advantages. These advantages as are associated with the identification of the causes of the explosion are listed for their understanding and to examine the process as in comprehensive manner. The advantages are as under: a. The identification of the cause of ignition provides a mechanism for the development of the simplest and most efficient method of removing aircraft fuel tank, maintaining tank temperature to reduce the explosive process and to develop flammability potential within the system, b. To provide a mechanism to reduce an aircrafts fuel tank, explosive potential that can be in expensively retrofitted to the existing air craft systems for the elaboration of the overall process, c. To increase the efficiency of the engine of the aircraft through the enrichment of the engine combustion, intake along with fuel fume vapors, d. The mechanism has provided an arrangement to combust unburned hydrocarbons that were previously vented to the surroundings or atmosphere of the process with its adverse impacts to the physical environment of the area ,therefore ,helps in controlling air pollution, e. To cool fuel tank ullage areas by sketching cooler ambient outside air into the fuel tank while eliminating fuel –fume vapors from the system into the surrounding for normal functioning of the system as per required standards and with the utilization of all the relevant inputs as essential materials for the execution of the system, f. The understanding of the subject provides a mechanism to draw fume vapors from the aircraft's fuel tank and change them with mechanically temperature as conditioned outside air, g. The system helps in the movement of the fume vapors from the fuel tanks connected in series from cooled to the hottest region for the flow of the vapors as are involved in the system, h. The process helps in the understanding of the concept for the suctioning of the vapors continuously while engine is operational. The mechanism provide an arrangement for the comprehension of the complex system in the shape of compartments with all their details, i. The mechanism provides an arrangement for the replacement of the suctioned fumes with a higher altitude cooler air ,cabin air or mechanically conditioned air from the system for normal working of the system as per designed arrangements and for the normal working of the overall system with all its required details, j. The system provides mechanism to use substances other than outside air and to replace fuel tank fume –vapors, and k. To remove and purge fumes and heat fro the fuel tank and fuel tank compartments compartment in a standstill and without any type of movement in the system for the benefit of the overall system. Recommendations: The aircraft fuel tank vapor/air explosions could be reduced with the observance of the recommendations as are relating to minimize ignition sources and to reduce the temperature of the system for the reduction of the probabilities relating to the explosions. These recommendations are as under: A) Recommendations to minimize ignition sources as the cause of the explosions in the mechanism: One important condition causing the fuel to ignite in the central fuel tank is thin and slim but these must be prevented from ever occurring. One important precautionary measure is regular inspection of the wiring in the region. Stripped insulation is helpful in the achievement of the target as per target of the overall mechanism. A cleaner environment should be maintained around the central fuel tank to block the buildup of possible conducting agents for the ignition process. Fuel combustibility needs to be operational as per fuel-air ratio, pressure, temperature and minimum ignition energy for the ignition process. Fuel vapors are the dangerous elements in the fuel tank as these combust easily in the explosive processes. A good fuel-vapor ratio is a good indicator of how easily an explosion can take place. The fuel-air ratio increases as fuel evaporates and mixes with the surrounding air as its part. The two key factors that have the potential to affect the fuel-air ratio in a system with surroundings and the environment are the temperature and the pressure. The temperature is an important factor and its close monitoring helps in the control of the explosive process. Similarly, a close examination of the pressure in the system will also be helpful for avoiding explosions as are associated with the aircraft fuel tanks vapor/air explosions. B. Recommendations to reduce temperature: In the central fuel tanks, a low temperature is essential to keep the fuel-air ratio as low in the central fuel tanks. The main source of heat in the systems are the air- conditioning units and the replacement of the system could be achieved with slight modifications in the designs of the aircrafts as to shift the air-conditioning systems away from the central tanks of the aircrafts and therefore a precautionary measure for lowering the temperature for the overall system. Efficient insulation in the aircraft will drastically reduce the temperature through reduction in the heat transfer to the central fuel tank of the aircraft. The objective of heat reduction could also be achieved through the reduction of air-conditioning timings in the aircrafts. Similarly, large quantity of fuel in the central tank also helps a low temperature in the aircraft. Conclusion: The aircraft fuel system with fuel tanks permits the crew to manage, store and deliver the fuel to the working system as per requirements of the aircraft. Fuel systems play a key role in the explosions of the aircrafts with the required temperature and the pressure. A close examination and vigilance help in the reduction of such incidents, therefore, observance of the recommendations will help in the achievement of the target as per the final objectives that are to operate the aircrafts with security and safety as per required international standards. References: 1. Adcock, Sylvia, "A Quest for Safer Jet Fuel," http://www.newsday.com/jet/year/twa1207.htm (Newsday; New York, December 1998) 2. Deitz, D., "FEA Makes Airframes Safer," http://www.memagazine.org/backissues/january98/features/airframe/airframe.html (American Society of Mechanical Engineers; New York: January1998). 3. McKenna, James T. "Debate on Wiring Safety Shifts to Capitol Hill" Aviation Week & Space Technology, vol. 151, no. 11. (September 13, 1999); p. 57-58. 4. McKenna, James T. "NTSB Sees End to TWA 800 Probe" Aviation Week & Space Technology, vol. 149, no. 3. (July 20, 1998); p. 37. 5. McKenna, James T. "Boeing Eyes Fuel Change to Increase Tank Safety" Aviation Week & Space Technology, vol. 147, no. 24 (December 15, 1997a); p. 33. 6. McKenna, James T. "TWA Probe Targets Aging Aircraft Systems" Aviation Week & Space Technology, vol. 147, no. 24. (December 15, 1997b); p. 30. 7. National Transportation and Safety Board, Public Hearing Exhibit Items - TWA Flight 800 (November 1997 -- October 1999) http://www.ntsb.gov/Events/twa800/exhibit.htm 8. Tischler, Adelbert O. "What Happened to Flight 800" Aerospace America, vol. 36, no. 3. (March 1998); p. 30. 9. Vankin, Jonathan. "How a Quack Becomes a Canard" New York Times Magazine, (November 1996); p. 56-57. 10. http://www.foamengineers.co.uk/manufacturing/explosion-suppressant-foam/ Read More