Osamu Fujita

Bio: Osamu Fujita is an academic researcher from Hokkaido University. The author has contributed to research in topics: Flame spread & Combustion. The author has an hindex of 28, co-authored 169 publications receiving 2124 citations.

Flame spread over electric wire in sub-atmospheric pressure

Abstract: Flame spread along the single wire harness (thin-metal wire with coating of polyethylene film) in sub-atmospheric pressure has been examined experimentally to gain better understandings of the electric fire in the aircraft and space habitats. Two kinds of sample wires, made by nickel-chrome (NiCr) and iron (Fe) as core metal, are used in this study. Ambient gas is fixed as air and total pressure is varied from atmospheric to sub-atmospheric (100–20 kPa). As the pressure decreases, flame shape changes from typical “teardrop” to “oval” and flame becomes less-luminous irrespective of the materials of the wire. It turns out that the dependence of the spread rate on pressure varies with the materials of the wire; when the pressure decreases, the spread rate of NiCr-harness monotonically increases, whereas that of Fe-harness mostly remains as constant. From the simple thermal-length analysis, it is proposed that there are two modes in the spread depending on the controlling factor; one is “wire-driven mode” (the spread is mainly governed by the thermal input through the wire) and the other is “flame-driven mode” (the spread is mainly governed by the thermal input from the flame). Observed two cases (NiCr- and Fe-harness) would be categorized to the latter and former modes, respectively.

Effect of low external flow on flame spread over polyethylene-insulated wire in microgravity

Abstract: An experimental study of flame spread phenomena over polyethylene-insulated wires has been performed in opposed flow under microgravity. The experiments were performed at the Japan Microgravity Center (JAMIC) 10 s drop shaft. Two samples with different insulation thicknesses, 0.075 and 0.15 mm, and with the same inner core diameter, 0.5 mm, were used. Experiments were performed with O 2 concentrations of 21%–50% and external flow velocities 0 (quiescent) to 30 cm/s. The results show that the rate of flame spread is affected by the flow velocity and that the effect is much stronger at high oxygen concentrations. According to the results, flame spread phenomena of wire insulation can be classified into four different regimes based on the flow velocity: (1) an oxygen transport control regimes, (2) a geometrical effect regime, (3) a thermal regime, and (4) a chemical kinetic control regime. A special feature of the flame spread over wire insulation is the existence of the geometrical effect regime and a maximum spread rate between the oxygen transport control and geometrical effect regimes. The mechanism that gives rise to the unique features is discussed based on changes in preheat length, standoff distance, and flame temperature. The importance of the three effects and their relation to sample geometry, enhancement of diffusive oxygen supply, reduction of standoff distance, and logarithmic effect for the heat transfer are discussed.

Experimental study on flame spread over wire insulation in microgravity

Abstract: An experimental study of flame spread phenomena over ETFE (ethylene-tetrafluoroethylene)-insulated wires has been performed in microgravity to obtain basic data on the fire safety of wire insulation. Three samples with different wire diameters, d w (0.32–0.51 mm) and the same insulation thickness, δ (0.15 mm) were investigated. The effects of the parameters thought dominant for wire combustion in fires: the ambient oxygen concentration, wire initial temperature, T i , wire diameter, d w , pressure, and dilution gas were investigated in the microgravity experiments. A series of comparative experiments were also conducted at normal gravity. The results show that flame spread rates in microgravity are higher than vertically downward spread rates at normal gravity when oxygen concentration is greater than 30% O 2 . However, with wire preheating, the spread rate in microgravity is higher than the downward spread rate at normal gravity even at lower O 2 concentrations. The increase in flame spread rates in microgravity became larger with decreases in d w . The effect of pressure on the flame spreading appeared very small, and lower pressure caused extinction of the flames in microgravity. The increase in flame spread rates in microgravity was especially large with CO 2 dilution, and this must be taken into account when selecting extinguisher gas. The microgravity experiments with CO 2 dilution gave rise to a new unsteady flame spread phenomenon for flame spreading over the wire: this phenomenon involves discontinuous flames partly occurring ahead of the spreading flame front.

Flame spread over electric wire with high thermal conductivity metal core at different inclinations

Abstract: This paper reveals experimentally the flame spread rate (FSR) [both upward (concurrently) and downward (opposed)] over electric wire with high thermal conductivity metal core at different inclination angles, which is new in view of that previous works about such inclination effect are mainly focusing on the material (wood, PMMA……) where the conductivity through media itself is not so important. Polyethylene (PE) insulated copper (Cu) wires with inner core diameter (dc) of 0.30 mm, 0.50 mm 0.80 mm and insulation thickness (δp) of 0.15 mm, 0.30 mm are studied with inclination angles ranged from −90° to +90°. Their behaviors are examined in both naturally normal (Hefei city with altitude of 50 m; 100 kPa) and a reduced (Lhasa city with altitude of 3650 m; 64 kPa) ambient pressure atmosphere. Results show that with increase in inclination angles from −90° to 90°, the FSR first decreases and then increases (“U” trend) with its value being lowest at nearly horizontal condition (0°) in both pressures, which is quite different from what we normally know for other materials with low thermal conductivity. Two characteristic lengths, the flame base width (Wf) and the pyrolysis zone length (Lp), are found to account for this special variation behavior with their variation trend with inclination angle being consistent with that of FSR. A simplified heat balance analysis concerning core thermal conduction effect is performed to calculate the FSR in relation to these two characteristic lengths, thermal conductivity of the metal core as well as the effective convection heating of the wire by the flame base. The calculated FSR are shown to be in fairly good agreement with the measured values at different inclination angles for different inner core (wire) diameters in both ambient pressures.

Solid combustion research in microgravity as a basis of fire safety in space

Abstract: This paper introduces fire safety standards for flammability evaluation of solid material intended for use in a spacecraft habitat. Two types of existing standards include material evaluation by pass/fail criteria corresponding to Test 1 of NASA STD 6001B and evaluation by a flammability index such as maximum oxygen concentration (MOC) corresponding to the improved Test 1. The advantage of the latter is the wide applicability of the MOC index to different atmospheres in spacecraft. Additionally, the limiting oxygen index (LOI) method is introduced as a potential alternative index for the evaluation using the improved Test 1 method. When criteria based on an index such as MOC or LOI are applied for material screening, the discrepancy of the index to the actual flammability limit in microgravity such as minimum limiting oxygen concentration (MLOC) is essential information for guaranteeing fire safety in space because material flammability can be higher in microgravity. In this paper, the existing research on the effects of significant parameters on material flammability in microgravity are introduced, and the difference between the limiting value in microgravity and the indices given by the standard test methods on the ground is discussed. Finally, on-going efforts to develop estimation methods of material flammability in microgravity according to normal gravity tests are summarized.

The Self-medication Hypothesis of Substance Use Disorders: A Reconsideration and Recent Applications

Abstract: The self-medication hypothesis of addictive disorders derives primarily from clinical observations of patients with substance use disorders. Individuals discover that the specific actions or effects of each class of drugs relieve or change a range of painful affect states. Self-medication factors occur in a context of self-regulation vulnerabilities--primarily difficulties in regulating affects, self-esteem, relationships, and self-care. Persons with substance use disorders suffer in the extreme with their feelings, either being overwhelmed with painful affects or seeming not to feel their emotions at all. Substances of abuse help such individuals to relieve painful affects or to experience or control emotions when they are absent or confusing. Diagnostic studies provide evidence that variously supports and fails to support a self-medication hypothesis of addictive disorders. The cause-consequence controversy involving psychopathology and substance use/abuse is reviewed and critiqued. In contrast, clinical observations and empirical studies that focus on painful affects and subjective states of distress more consistently suggest that such states of suffering are important psychological determinants in using, becoming dependent upon, and relapsing to addictive substances. Subjective states of distress and suffering involved in motives to self-medicate with substances of abuse are considered with respect to nicotine dependence and to schizophrenia and posttraumatic stress disorder comorbid with a substance use disorder.

Listeria monocytogenes, a food-borne pathogen

Abstract: Listeria monocytogenes is a Gram positive, aerobic, facultative anaerobic and nonacid fast bacterium, which can cause the disease listeriosis in both human and animals. It is widely distributed thoroughout the environment and has been isolated from various plant and animal food products associated with listeriosis outbreaks. Contaminated ready-to-eat food products such as gravad and cold-smoked salmon and rainbow trout have been associated with human listeriosis in Sweden. The aim of this study was to analyse the occurrence and level of L. monocytogenes in gravad and cold-smoked salmon (Salmo salar) products packed under vacuum or modified atmosphere from retail outlets in Sweden. Isolated strains were characterized by serotyping and the diversity of the strains within and between producers were determined with PFGE (Pulsed-field gel electrophoresis). The characterized fish isolates were compared with previously characterized human strains. L. monocytogenes was isolated from 11 (three manufacturers) of 56 products analysed. This included gravad salmon products from three manufacturers and cold-smoked salmon from one manufacturer. The highest level of L. monocytogenes found was 1500 cfu/g from a cold-smoked salmon product but the level was low (<100 cfu/g) in most of the products. Serovar 1/2a was predominant, followed by 4b. Three products of gravad salmon harboured more than one serovar. PFGE typing of the 56 salmon isolates detected five Asc I types: four types were identical to human clinical strains with Asc I and one was identical and one was closely related to human clinical strains with Apa I. Isolation of identical or closely related L. monocytogenes strains from human clinical cases of listeriosis and gravad and cold-smoked salmon suggested that these kinds of products are possible sources of listeriosis in Sweden. Therefore, these products should be considered risk products for human listeriosis.

Dimethyl ether (DME) as an alternative fuel

Abstract: With ever growing concerns on environmental pollution, energy security, and future oil supplies, the global community is seeking non-petroleum based alternative fuels, along with more advanced energy technologies (e.g., fuel cells) to increase the efficiency of energy use. The most promising alternative fuel will be the fuel that has the greatest impact on society. The major impact areas include well-to-wheel greenhouse gas emissions, non-petroleum feed stocks, well-to-wheel efficiencies, fuel versatility, infrastructure, availability, economics, and safety. Compared to some of the other leading alternative fuel candidates (i.e., methane, methanol, ethanol, and Fischer–Tropsch fuels), dimethyl ether appears to have the largest potential impact on society, and should be considered as the fuel of choice for eliminating the dependency on petroleum. DME can be used as a clean high-efficiency compression ignition fuel with reduced NOx, SOx, and particulate matter, it can be efficiently reformed to hydrogen at low temperatures, and does not have large issues with toxicity, production, infrastructure, and transportation as do various other fuels. The literature relevant to DME use is reviewed and summarized to demonstrate the viability of DME as an alternative fuel.