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Combustion of wire insulation is important for fire safety in Space. Insulated wire has two unique features, one is sample geometry and another is existence of wire core. In this paper we investigate the effect of core materials on combustion phenomena of insulated wires. An experimental study of flame spread phenomena over polyethylene insulated wires with two different core materials, copper and nichrom, in different O2 concentrations was performed in microgravity. The experiments were performed at the Japan Microgravity Center (JAMIC) 10 s dropshaft. Experiments were performed with different O2 concentration and core material. The results show that the core material strongly affects the flame shape irrespective of gravity level. The flame spread rate is also strongly affected by the core material. Under normal gravity, the flame spread rate with copper cores is faster than that with nichrom cores in any of the tested oxygen concentrations. In microgravity, the effect of the core materials on the flame spread rate changes by oxygen concentration. In 35% O2, flame spread rate with copper wire was faster than that with nichrom core wire, as also seen in the normal gravity case. In 21% O2, the flame spread rate with the nichrom core wire is faster than that with copper core wire. The core heat conduction analysis shows that the thermal conductivity of the core material has an important effect on the flame spread rate. The case of high flame temperatures, the core acts as a heat source and high conductivity material supplies more heat to the insulation. At low temperatures, the core becomes heat sink and high conductivity material causes heat removal from the insulation near the flame front.

Opposed flame spreading over ETFE (ethylene-tetrafluoroethylene co-polymer) insulated wire, which is used for actual wire in space, in low air flow velocity has been investigated under microgravity environment. The experiments were performed with Japan Microgravity Center (JAMIC) 10 s dropshaft and NASA's KC 135 parabolic flight. Experiments were performed with changing O2 concentration, 35 and 40%, external air flow velocity, 0 (quiescent) -22 cm/s and dilution gas, N2, CO2, He. The sample of 0.32 mm inner core diameter with 0.15 mm insulation thickness was used. The results showed that flame spread rate over wire insulation was strongly affected by air flow velocity and the dilution gases. Flame spread with N2 dilution had maximum value in a low flow velocity region. However, CO2 dilution resulted in monotonic increase in flame spread rate with decrease in air flow velocity and the maximum flame spread at Ve=0 cm/s (quiescent). The different dependency of the spread rate on flow velocity with different dilution gas was explained by the reabsorption effect of CO2 gas ahead of flame front. Reabsorption of radiation heat with CO2 gas recovers the radiation heat from the flame and prevent the flame temperature decrease even in very low flow velocity region, which is known as radiation control region for optically thin gas.

An experimental study of flame spread phenomena over ETFE (Ethylene-Tetrafluoroethylene) insulated wire was performed under microgravity to obtain fundamental data on fire safety in space. The effects of the parameters thought dominant for wire combustion in fires-the ambient oxygen concentration, wire initial temperature, Ti, and wire diameter, dω, - were investigated in the microgravity experiments. A series of comparative experiments were also conducted at normal gravity. Flame shape under microgravity changed depending on the state of the molten fuel accumulation. Experimental results showed that there existed a possibility of higher flame spread rates under microgravity than at normal gravity, in spite of lower flame temperature in microgravity. Wire initial temperature, Ti, had a very large influence both on flame spread rates and extinction limit of the wire under microgravity. The degree of flame spread rate decreased with increase in dω and, correspondingly, the increase with decrease in dω under microgravity was higher than at normal gravity.

The flame color method to measure mixture strength in laminar premixed flames was investigated as a new combustion diagnostic technique. Flame colors were quantitatively determined by chromaticity coordinates (x, y) defined by the CIE 1931 standard colorimetric system. Using 12 types of hydrocarbons, the (x, y) of an inner cone in premixed laminar flames held on a circular tube burner were measured with a colorimeter, and the relationship between the (x, y) and the equivalence ratio φ of the mixture was examined in a range of φ=0.9 to 1.4. The experimental results indicated that the equivalence ration could be measured with accuracy of 0.008-0.014 and error due to axial position in the inner cone was less than 0.02-0.05. Humidity of air had almost negligible effects on the accuracy of the measurement. Results also indicated that the effect of back-light could be corrected by introducing the concept of additive mixture of color stimuli.

The color of laminar diffusion flames burning propane, methane and ethylene was determined by chromaticity coordinates (x, y) defined by the CIE 1931 standard colorimetric system. The differences in flame color attributed to burning condition and fuel types were examined with a colorimeter. Spectroscopic measurement and numerical analysis using a simplified radiation model were also carried out to discuss the determining factors of the flame color. The relation between x and y measured on the central axis of the flames was expressed in the experimental equations. The (x, y) in the luminous region plotted on a chromaticity diagram changed along Planckian locus with the burning conditions. The contribution of the thermal radiation of soot particles and the chemiluminescence to the flame color was successfully evaluated by introducing the concept of additive mixture of color stimuli. The (x, y) profiles from the numerical analysis agreed well with the experimental results.

A three-dimensional computer simulation was performed to determine the formaldehyde (HCHO) and methyl nitrite (CH3ONO) levels inside a small garage during the cold start-up of a methanol fueled vehicle (MFV). The garage size was appropriate for one MFV. Two types of garage were considered in order to quantify the ventilation effect. The total amount of pollutants was independent of the ventilation until 70 s after engine start-up, because the pollutants remained concentrated directly behind the vehicle. After 180 s, the pollutant levels in the ventilated model were reduced to half that in the no-ventilated model. However, under such small garage condition, even with one ventilator, at a point 1 m behind the MFV and 1.5 m high, the HCHO concentration reached 9.2 ppm. To reduce the HCHO level to below 5 ppm, the HCHO peak concentration in the emission should be reduced to 0.5 times the present concentration. Although the harmful effects of CH3ONO have not yet been investigated in detail, they should be considered, particularly during cold start-up of MFV in a closed garage.

Methyl nitrite (MN) is identified in the exhaust gases of methanol-fueled vehicles as one of the trace components. However, for a high concentration of methanol at low temperatures, as occurs in start-up conditions, more MN would be emitted due to reaction with the co-exhaust emission of nitrogen dioxide (NO2). In this study, the concentration of MN in the exhaust emission of a methanol-fueled truck was measured during cold start-up. To prevent the secondary formation of MN during the measurement procedure, the best method is thought to be dilution of the sample with hot clean air. Also NO2 measurement methods, including those for high-MN-concentration samples, were studied. The behavior of MN emission is similar to that of other pollutants. The highest concentration occurs about 80 (s) after the engine starts, and MN is never detected after 180 (s). At low temperatures(-5∼5°C), the MN level was more than 5 times higher than that under warm temperature conditions (20°C). It was demonstrated that some NO2 emitted from the engine was converted into MN by the catalyst converter system.

The visualization for analyzing the reaction mechanism of catalytic combustion of methanol/air mixture has been newly attempted. The measurement of formaldehyde distribution above a platinum plate in premixed methanol gas flows was carried out by the LIF (laser-induced fluorescene) method. Formaldehyde has the fluorescence spectra in the range of 340.6∼493.3 nm when it is excited by the thrid-harmonic wavelength of the Nd : YAG laser (355 nm). In this work, formaldehyde was excited by one pulsed laser shot and the fluorescence at wavelength of 412.2 nm was selected. By this laser technique, the time-resolved instantaneous distribution of formadehyde yielded during catalytic combustion of methanol/air mixtures on a platinum plate has been successfully measured. The results show that the distribution of formaldehyde fluorescence above the platinum plate is affected by gas velocity, catalyst temperature, and, in particular, air-fuel ratio. These results show good correspondence with those of other studies of conventional flow-reactor experiments, and con-firm that this measurement is a reliable method for analyzing the reaction mechanism of catalytic combustion.

Experimental studies have been carried out to investigate some problems in the development and practical use of a catalytic combustor using a methanol mixture. For the suppression of undesirable exhaust emission, the possibility of using a catalyst with a higher amount of noble metal than the usual level as a component of the entire catalyst layer is examined. The combustion characteristics of the catalytic combustor with water-containing methanol and with aged catalysts are also investigated. From the results, it was found that undesirable exhaust emission during the startup period was suppressed by use of the higher noble metal loaded catalyst as a component of the catalysts. Formaldehyde emission was increased as the contained water was increased in the range of zero to 15wt%. The reaction region moved downward with the use of the aged catalyst, and the catalyst temperature profile was decreased. This indicates that the emission characteristic on unburned species is degraded.

The secondary photochemical products from alcohol fueled engine exhaust gases were investigated. Sampled exhaust gases from an S. I. engine fueled by methanol or ethanol were introduced into a reactor tube with dilution air at dilution ratios ranging between 10 and 2000. Near ultraviolet rays were irradiated throughout the samples. At high dilution ratios ranging from 1000 to 2000, the resulting photochemical product from both unburned methanol and ethanol was methylnitrate. 3-5% of unburned alcohol was converted to methylnitrate in two or three days. In the case of ethanol emission, methylnitrate seemed to be formed by photochemical reaction passes except for that of ethylnitrate as an intermediate product from ethanol. Intermittent irradiation of ultraviolet rays and coexistence of hydrocarbons in an alcohol engine exhaust had no significant influence on the photochemical reaction mechanism of unburned alcohols.

Air, fuel gas and fuel-air mixture injection into a recirculation zone formed behind a thick burner rim were examined. Flame stability limits, residence times in the recirculation zone and inflow ratios of injected gas were measured. Flame stability limits were widened by fuel or mixture injection. Mixture injection was most effective. The length of the recirculation zone and residence time in the recirculation zone with injection coincided with these without injection. Inflow ratios of the injection gas in the recirculation zone were about 80% irrespective of the injection rate or mixture strength of the injected gas.

The catalytic reduction of NOx by NH3 generated from NOx has been applied to a methanol engine exhaust system. In automotive three-way catalyst (Pt-Rh coated) a large amount of NOx was converted to NH3 in a temperature range of 500550 K and an excess air ratio of 0.91.0. On the other hand, NOx reduction by NH3 in methanol engine exhaust gas was favorably performed under the condition of O2=24%, gas temperature= 450500 K and NH3≥ the stoichiometry of NOx. Finally, about half an amount of NOx was converted to NH3 in a three-way catalyst and the formed NH3 was reached with the NOx left in the exhaust gas. The resulting NOx reduction ratio was around 55%. On the basis of these results, some systems using the application of NOx-NH3 reactions to practical engines were proposed and their potential was discussed.

The mathanol oxidation reaction on the catalysts of Pt, Pd, Rh, Ir and Cu has been investigated to select the suitable catalysts for the purification of methanol engine exhaust gases. On all of these catalysts, the presence of NO showed an inhibitory effect on the methanol oxidation reaction and caused the formation of formaldehyde. By comparison with other exhaust components (CO, H2O, HC), it was found that NO had a stronger effect than other species. Under the presence of NO, the relative activity sequence was also obtained as Pt≒Pd>Rh≒Ir>Cu. The temperature conditions for formaldehyde formation were revealed for each catalyst in the presence of NO, and it was also found that formaldehyde formation was most suppressed by use of the Pd catalyst. Consequently, Pd is one of the advantageous catalysts for reducing unburned methanol.

簡単化した反応動力学モデル(S-モデル)により,排気系でのメタノールの酸化とホルムアルデヒドの生成に対するNOの効果を検討した.排ガス中のメタノールの酸化はNOとO2濃度の増加により速くなり,また,O2の存在はホルムアルデヒドの生成を,NOは消滅を促すことが明らかとなった.理論計算の結果は実験ともよく一致し,NOからNO2への変換反応が末燃両成分の反応挙動に重要な役割をはたしていることが解明された.

一定温度に保持した反応管を用いて,排気ガスの反応実験を行った。アセトアルデヒドおよびホルムアルデヒドはガス温度が750～850 K, 滞留時間が50ms前後において顕著な濃度増加を示す。未燃エタノールの参加に伴い,アセトアルデヒドがホムルアルデヒドよりわずかに速く生成され,HCがそれらに続く。アセトアルデヒドの濃度増加は空燃当量比の影響をほとんど受けないが,ホルムアルデヒドは希薄になるにしたがい増加する。

The stoichiometry of methylnitrite formation in exhaust gases issued from a methanol fueled 4-stroke cycle S.I. engine was investigated. A part of exhaust gas was sampled and introduced into a reactor tube kept at a temperature ranging 20-200°C. Changes in unburned methanol, NO, NO2 and methylnitrite concentrations were measured. With an increasing reacting time, methylnitrite increased in both NOx and O2 rich sample gases. The amount of increase in the concentration of methylnitrite was found to be close to the amount of decrease in the concentration of methanol for any reactor conditions. These observations suggest that methylnitrite is formed by the reaction between unburned methanol and nitrogen dioxide with the same moles of each. Furthermore, in the case of diluting the sampled gas by air to one fifth and one hundredth, a considerable formation of methylnitrite was also observed.