Flash Point and Chemical Composition of Aviation Kerosene (Jet A)

The relationship between chemical composition, flash point, and ignition energy was examined for eight samples of aviation kerosene (Jet A) with flash points between 29°C (84°F) and 74°C (165°F). We report the results of liquid characterization by two different laboratories. We use the results of headspace gas chromatography carried out by Woodrow and Seiber to characterize the vapor composition at liquid mass loading fractions of 3 and 400 kg/m^3. The composition data were analyzed to obtain analytical representations of vapor pressure and average molar mass as a function of temperature for each flash point fuel. The relationship between composition and flash point is examined by using two prediction methods. The first method is based on the notion of a critical value of fuel-air mass ratio at the flammability limit. The second method is based on Le Chatelier's rule for flammability limits. Both methods show a reasonable correlation between measured and predicted flash point. The relationship between flash point and ignition temperature threshold at a fixed spark ignition energy was examined for four fuels. A linear correlation was obtained for an ignition energy of 0.3 J. The effect of fuel weathering was examined by determining the flashpoints of seven fuel samples obtained from flight tests. The flash point increased about 8°C for fuel that had been exposed to 5 take-off, cruise, and landing cycles

Predicting Alzheimer's risk: why and how?

Because the pathologic processes that underlie Alzheimer's disease (AD) appear to start 10 to 20 years before symptoms develop, there is currently intense interest in developing techniques to accurately predict which individuals are most likely to become symptomatic. Several AD risk prediction strategies - including identification of biomarkers and neuroimaging techniques and development of risk indices that combine traditional and non-traditional risk factors - are being explored. Most AD risk prediction strategies developed to date have had moderate prognostic accuracy but are limited by two key issues. First, they do not explicitly model mortality along with AD risk and, therefore, do not differentiate individuals who are likely to develop symptomatic AD prior to death from those who are likely to die of other causes. This is critically important so that any preventive treatments can be targeted to maximize the potential benefit and minimize the potential harm. Second, AD risk prediction strategies developed to date have not explored the full range of predictive variables (biomarkers, imaging, and traditional and non-traditional risk factors) over the full preclinical period (10 to 20 years). Sophisticated modeling techniques such as hidden Markov models may enable the development of a more comprehensive AD risk prediction algorithm by combining data from multiple cohorts. As the field moves forward, it will be critically important to develop techniques that simultaneously model the risk of mortality as well as the risk of AD over the full preclinical spectrum and to consider the potential harm as well as the benefit of identifying and treating high-risk older patients

Spark Ignition Measurements in Jet A: part II

An improved system for measuring the ignition energy of liquid fuel was built to perform experiments on aviation kerosene (Jet A). Compared to a previously used system (Shepherd et al. 1998), the present vessel has a more uniform temperature which can be held constant for long periods of time. This ensures thermal equilibrium of the liquid fuel and the vapor inside the vessel. A capacitive spark discharge circuit was used to generate damped sparks and an arrangement of resistors and measurement probes recorded the voltage and current histories during the discharge. This permitted measurement of the energy dissipated in the spark, providing a more reliable, quantitative measure of the ignition spark strength. With this improved system, the ignition energy of Jet A was measured at temperatures from 35C to 50C pressures from 0.300 bar (ambient pressure at 30 kft) to 0.986 bar (ambient pressure near sea level), mass-volume ratios down to 3 kg/m^3, with sparks ranging from 10 mJ to 0.3 J. Special fuel blends with flash points (Tfp) from 29C to 73.5C were also tested. The statistical properties of the ignition threshold energy were investigated using techniques developed for high-explosive testing. Ignition energy measurements at 0.585 bar with high mass-volume ratios (also referred to as mass loadings) showed that the trend of the dependence of ignition energy on temperature was similar for tests using the stored capacitive energy and the measured spark energy. The ignition energy was generally lower with the measured spark energy than with the stored spark energy. The present ignition energy system was capable of clearly resolving the difference in ignition energy between low and high mass-volume ratios. The ignition energy vs. temperature curve for 3 kg/m^3 was shifted approximately 5C higher than the curve for high mass-volume ratios of 35 kg/m^3 or 200 kg/m^3. The ignition energy was subsequently found to depend primarily on the fuel-air mass ratio of the mixture, although systematic effects of the vapor composition are also evident. As expected, the ignition energy increased when the initial pressure was raised from 0.585 bar to 0.986 bar, and decreased when the pressure was decreased to 0.3 bar. Finally, tests on special fuels having flash points different from that of commercial Jet A showed that the minimum ignition temperature at a spark energy of about 0.3 J and a pressure of 0.986 bar depends linearly on the flash point of the fuel

Comparative Aspects of Mating Behavior Patterns in Six Species of Stink Bugs (Heteroptera: Pentatomidae)

Mating sequences were analyzed for six species of stink bugs using video- tapes. The results consisted of qualitative descriptions of the precopulatory activities of the pairs and quantitative analyses of the number and direction of mating sequences, including the latency to and duration of copulatory lock. It was possible to quantitatively characterize each of the six species tested. In addition, certain infrequent behavior patterns, e.g., head butts, were observed for some species and not others. The results extend the previous information on mating activities in stink bugs, particularly for Euschistus. We interpret our findings with regard to reproductive strategies in different species of stink bugs, and consider the use of behavior as a taxonomic tool

Application of NASTRAN to TFTR toroidal field coil structures

The primary applied loads on the TF coils were electromagnetic and thermal. The complex structure and the tremendous applied loads necessitated computer type of solutions for the design problems. In the early stage of the TF coil design, many simplified finite element models were developed for the purpose of investigating the effects of material properties, supporting schemes, and coil case material on the stress levels in the case and in the copper coil. In the more sophisticated models that followed the parametric and scoping studies, the isoparametric elements, such as QUAD4, HEX8, and HEXA, were used. The analysis results from using these finite element models and the NASTRAN system were considered accurate enough to provide timely design information

Jet A Explosion Experiments: Laboratory Testing

This report describes a series of experiments and analyses on the flammability of Jet A (aviation kerosene) in air. This is a progress report on ongoing work. The emphasis so far has been on measuring basic explosion parameters as a function of fuel amount and temperature. These parameters include vapor pressure, flammability limits, peak explosion pressure and pressure as a function of time during the explosion. These measurements were undertaken in order to clear up some fundamental issues with the existing data. The report is organized as follows: First, we give some background with data from previous studies and discuss the fuel weathering issues. Second, we describe the facility used to do combustion experiments, the combustion test procedures and the results of the combustion experiments. Third, we give estimates of peak pressure, review the standard analysis of pressure histories and discuss the application to the present data. Fourth, we review the standard approach to flammability limits and the issues in determining Jet A flammability. Fifth, we discuss the problems associated with measuring vapor pressure and describe our results for Jet A. Sixth, we present a model for Jet A which illustrates the issues in analyzing multicomponent fuels. Finally, we apply these results to TWA 800 and summarize our conclusions to date

Spark Ignition Energy Measurements in Jet A

Experiments have been carried out to measure the spark ignition energy of Jet A vapor in air. A range of ignition energies from 1 mJ to 100 J was examined in these tests. The test method was validated by first measuring ignition energies for lean mixtures of the fuels hexane (C6H6) and propane (C3H8) in air at normal temperature (295 K) and pressure (1 atm). These results agree with existing data and provide new results for compositions between the lean flame limit and stoichiometric mixtures. Jet A (from LAX, flashpoint 45–48 [degress] C) vapor mixtures with air have been tested at temperatures between 30 and 60 [degrees] C at two fuel mass loadings, 3 and 200 kg/m3, in an explosion test vessel with a volume of 1.8 liter. Tests at 40, 50, and 60 [degrees] C have been performed at a mass loading of 3 kg/m3 in an 1180-liter vessel. Experiments with Jet A have been carried out with initial conditions of 0.585 bar pressure to simulate altitude conditions appropriate to the TWA 800 explosion. Ignition energies and peak pressures vary strongly as a function of initial temperature, but are a weak function of mass loading. The minimum ignition energy varies from less than 1 mJ at 60 [degrees] C to over 100 J at 30 [degrees] C. At temperatures less than 30 [degrees] C, ignition was not possible with 100 J or even a neon sign transformer (continuous discharge). The peak pressure between 40 and 55 [degrees] C was approximately 4 bar. Peak pressures in the 1180-liter vessel were slightly lower and the ignition energy was higher than in the 1.8-liter vessel. The following conclusions were reached relative to the TWA 800 crash: (a) spark ignition sources with energies between 5 mJ and 1 J are sufficient to ignite Jet A vapor, resulting in a propagating flame; (b) the peak pressure rise was between 1.5 and 4 bar (20 and 60 psi). (c) a thermal ignition source consisting of a hot filament created by discharging electrical energy into a metal wire is also sufficient to ignite Jet A vapor, resulting in a propagating flame; (d) laminar burning speeds are between 15 and 45 cm/s; and (e) the limited amount of fuel available in the CWT (about 50 gal) did not significantly increase the flammability limit. The rapid decrease in spark ignition energy with increasing temperature demonstrates that hot fuel tanks are significantly more hazardous than cool ones with respect to spark ignition sources. A systematic effort is now needed in order to utilize these results and apply spark ignition energy measurements to future analyses of fuel tank flammability. Some key issues that need to be addressed in future testing are: (a) effect of flashpoint on the ignition energy-temperature relationship; (b) ignition energy vs. temperature as a function of altitude; (c) effect of fuel weathering on ignition energy; and (d) the effect of ignition source type on ignition limits