As fundamental research on spray combustion, spontaneous ignition phenomenon is important and research has been conducted by various approaches. The Japan-German joint research program “PHOENIX-2” aims to clarify ignition process accompanying the cool flame around ignition limit by utilizing a TEXUS sounding rocket and it is very important study conjunction with the vaporization and flame spread. The design of the experimental equipment has been carried out by confirming the functions of each part by conducting element prototypes and parabolic flight experiments. At present, the detailed design review has been completed and the production phase is underway.

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流通型反応器で,プロパンを発生温度領域で空気酸化した。実験計画法により,発生温度,反応生成物に対する圧力,接触時間およびプロパン対空気の混合比の効果を解析した。発生温度は320～350℃ の間にあった。発生温度に対する圧力の効果は大きいが,他の二つの因子の効果はあまりなかった。によって得られた最高温度は発生温度より80～150℃ 高かった。発生の結果,管内軸方向に最高100℃ の温度分布を生じた。温度上昇は圧力,流速および酸素濃度が増加すると大きくなった。主生成物はアセトアルデヒド,ホルムアルデヒド,一酸化炭素およびメタンであった。
この報告では,プロパンの酸化反応機構との周期性について議論する。

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Ion forrmation is detected for the first time in cool and blue flames which appear during the preflame period for compression ignition of a heptane / air mixture. A rapid-compression machine is used for mixture compression and an ionization gap is installed in the combustion chamber. Ion current and emission of active species are observed simultaneously. Ions arise at the time the cool flame degenerates, and the ion current itself will degenerate very late in the blue-flame induction time τ₂ just before the blue-flame onset. The behavior of ion-current appearance in a cool flame shows the possibility that the ion is mutually related to the emission of excited oxygen molecules and the generation of olefin. During the blue-flame period the ion current is always detected more definitely. Degeneration of the ion current is often observed late in the blue-flame period. The occurrence of ion-current degeneration after the blue flame comes about can be recognized as a prognostication for the development up to the final real ignition.

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Controlling ignition timing in Homogenous Charge Compression Ignition (HCCI) of Dimethyl Ether by adding methanol has been studied in a motored engine. Reduction of heat release at cool flame and consequent delay of ignition timing with the methanol addition were confirmed. In exhaust gas analysis conducted mainly in single cool flame condition, fuel consumption decreases and formaldehyde formation increases with increasing methanol addition. It was found that these functions are independent of equivalence ratio when the three variables are expressed relative to initial fuel load. These behaviors were well reproduced by simulations using Curran's mechanism, whereas a small extent of underestimation of the cool flame heat release was suggested. A simplified model accounting for the additive effect was constructed by extracting the essential chemical mechanism, in which HCHO+OH and methanol +OH reactions are responsible for the termination of the chain reaction mechanism of DME low temperature oxidation.

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This paper presents the experimental study on the phenomena of evaporation and ignition of the fuel-droplet impinged upon a hot surface. The experiment was made on the seven kinds of fuel. It was revealed that cool flame is generated in η-Heptane and diethyl-Ether at a surface temperature range which is 300-400 K below that of hot flame generation. The surface temperatures at which the cool and hot flames were generated were measured by applying a statistic method. Their delay times were also measured and then divided into physical and chemical delays by applying the statistic technique which was presented by S.Kumagai et al. Based upon these investigations, the natures of both the cool and hot flames were clarified and the difference between the surface temperature of hot flame generation and the ignition temperatures measured by using the crucible method was discussed.

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Furans such as 2-Methylfuran (2-MF) and 2,5-Dimethyulfuran (DMF) are not popular fuels so far. But they can be derived from biomass via sugars and have preferable fuel properties for spark ignition engines. In this work, the effect of furans on knock suppression was investigated. Firstly, auto-ignition delay of 2-MF blend fuel was compared with other biofuel blends such as ethanol and toluene blend known as high octane number fuel by using a rapid compression expansion machine. 2-MF suppressed cool flame reaction most effectively among tested fuels. As the result, auto-ignition delay of 2-MF blend fuel was quite longer than ethanol or toluene blend in spite of the fact that pure 2-MF had lower octane number and higher ignitability. Secondly, the impact of knock suppression was confirmed using a single cylinder research engine. The lower the RON of base fuel was, the higher the blending octane number was, when the base fuel was paraffin mixture.

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In this study, spectroscopic techniques were used to investigate the effects of the residual gas state and fuel octane number on ignition characteristics of a Homogeneous Charge Compression Ignition (HCCI) engine. Spectroscopic measurements were made of light emission spectra and of light absorption spectra. The results revealed that varying the fuel octane number and the residual gas state changed the cool flame magnitude and the duration of the low-temperature reaction period, which substantially altered the ignition characteristics of HCCI combustion. Specifically, when a low-octane fuel was used, the heat release rate waveform for HCCI combustion showed cool flame, which was clearly observed in the light emission spectra and light absorption spectra. The level of absorbance at a wavelength corresponding to the cool flame reaction decreased when the fuel octane number was increased. Additionally, the level of absorbance also decreased when residual gas was applied to HCCI combustion of a low-octane fuel and approached that seen for HCCI combustion of a high-octane fuel. With the application of residual gas, the low-temperature reactions showed less reactivity when low-octane fuels were used, and the reactions were less sensitive to changes in the octane number of the fuel. As a result, the ignition timing tended not to change in relation to variation of the fuel octane number.

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Low-temperature flames established on a flat-flame burner are investigated using rich diethyl ether/air mixtures to acquire a new knowledge of self-ignition processes. Temperature, chemical species and emission spectra are measured along with the burner axis. A series of cool flame, blue flame and a bright yellow column appears in a case of equivalence ratio 2.0. A dark zone demarcates between the blue flame and yellow column. Fuel enrichment causes a yellow column disappearance. Onset temperatures of cool and blue flame are 400 and 850 K respectively, which are independent to the equivalence ratios. Blue flame emission spectra contain an emission ranging from 720 to 810 nm in wave length, which can be estimated to be the H_2O spectrum. Yellow column spectra are similar to that of black bodies; the emission probably from solid carbon particles therewith. The dark zone has similar near-infrared emission spectra and intensity to the blue flame though the visible emission is quite weak. The appearance of blue flame is closely related to an intensive decomposition of fuel, i.e., only when the decomposition reactions complete in the blue flame, the low-temperature oxidation process is raised to the final hot-flame stage.

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Compression-ignition processes of hydrocarbon/oxidizer mixtures are visualized using a combination of an image intensifier and a high-speed camera in wide range of temperatures. Onset images of cool-, blue- and final hot-flames are identified. Three typical regions of low-temperature ignition are classified and characterized. The cool flame onset followed by its degeneration is relatively homogeneous. Spatially nonuniform ignition is emphasized, though it does not always appear first in the vicinity of the cylinder wall as hitherto mentioned. Ignition in the blue flame dominant region, the highest temperature region of the low-temperature ignition, does not come under the category of the high-temperature thermal ignition usually obtained in shock tubes.

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The effect of inert species on low-temperature piston-compression ignition is examined. Pseudo-air is prepared, replacing inert species in the air with pure argon. Lean mixtures are composed of leaded or unleaded gasoline as a fuel and the pseudo-air or real air as an oxidizer. Cool-flame ignition delay τ₁ shows no differences. A distinction between the two oxidizers can be found in blue flame ignition delay τ₂ under considerably lean conditions at equivalence ratios of 0.7. An anti-knock additive, tetramethyl lead, does not seem to be responsible for this distinction. When the pseudo-air is used as an oxidizer, onset of cool and blue flames in a pancake chamber shows a sliced-pineapple-like structure having a central core and a ring portion near the cylinder wall. Only when air is used as an oxidizer, does a blue flame appear in the ring portion in the vicinity of the cylinder wall earlier than in the central core. Inert species, nitrogen or argon, would participate as the third body in elementary chemical reactions appearing in preflame periods. Argon may be quite inert chemically, but nitrogen or nitrogen compounds probably act as a chemical species on the preflame reactions in low-temperature ignitions.

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The transition process from cool flame to thermal flame in homogeneous charge compression ignition is discussed in this paper. It was confirmed in HCCI engine experiments using dimehtyl ether, n-heptane and n-decane as fuels that the heat release rate during transition process from the cool ignition to the thermal ignition exhibits linear shape in an Arrhenius plot, and activation energies are in agreement with that of H₂O₂ thermal decomposition reaction, regardless of the fuels. These features were not affected by methanol addition, which suppresses the cool ignition and retards the ignition timing, although the heat release rates were lowered. The results of simulation, using SENKIN in CHEMKIN II package with reaction mechanisms of Lawrence Livermore National Laboratory, were consistent with the experimental results. The mechanism in this process was explained quantitatively by thermal explosion theory, in which rate determining reaction is H₂O₂ thermal decomposition, assuming this reaction obeys an Arrhenius type rate constant, and considering OH reproduction process and the amount of heat release during fuel and intermediate species oxidation process.

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A novel method for eliminating piston-compression ignition is proposed. Cool-flame degeneration/blue-flame generation is the key factor influencing whether the final hot flame will occur or not. Any late generation of formaldehyde other than from the fuel itself is deduced to be efficient for the retardation of the hot-flame onset. A method devised based on this concept consists of vapor addition to the mixture ; vapor of a low-volatile chemical compound which has very low vapor pressure and higher boiling point than that of the fuel is used. Confirmation experiment is carried out using a rapid-compression machine. Silicone oil (dimethylpolysiloxane) is used as the typical source of vapor. The vapor content of silicone oil does not exceed 0.4 percent of the fuel vapor. Air, when used as the oxidizing agent, is found to efficiently eliminate hot ignition ; this is not so when 21O₂/79Ar is used instead.

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The blue-name reaction is a real issue for the autoignition of hydrocarbon fuel/air mixtures in internal combustion engine cylinders. Once a blue flame has appeared, the following hot-flame onset would be inevitable, except for very special cases. Blue flame generates carbon monoxide briskly, and is the final induction stage of oxidation up to the real hot-flame ignition. Piston-compression ignitions of n-butane/air mixtures conditioned at slightly upper and lower than the lean ignitable pressure limit were compared using a rapid compression machine to elucidate the ignition promoter or ignition trigger to the final hot-flame appearance. Carbon-monoxide concentration is always superior to of the carbon dioxide during the whole induction period and its maximum is caused at the very late stage of blue-flame period. Based on chemical species histories it could be concluded that a carbon-monoxide/dioxide ratio should increase for the hot-flame establishment. A small amount of carbon-monoxide brimming over compared with carbon dioxide production rate during the blue-flame period would be a trigger for the transfer to the final hot-flame ignition.

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急速圧縮機において再現した火花点火機関のノックを,直接およびシュリーレンの高速度撮影によって観察した結果,以下の知見が得られた.すべての混合気が自発点火するときのガス振動の発生は,熱炎発生の不均一性による.自発点火における2段点火の1段めは局部的熱炎発生によるものではなくによるものである.火炎伝ぱをともなう場合の末端ガスの点火現象は,すべての混合気が自発点火する場合の点火過程と同等である.

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A diagnostic method has been developed to detect transient intermediate species in reciprocal engine cycles and applied to homogeneous charge compression ignition (HCCI) processes. In-cylinder gas is sampled into a vacuum chamber through an electrically actuated pulse valve mounted on an engine head and analyzed by a quadrupole mass spectrometer. Based on the observation that the quenched volume near the cylinder wall is sampled within 1 ms from the valve open, a correction scheme extracting the reactive core component is employed. The crank-angle resolved measurement of HCCI with dimethyl ether as a fuel demonstrated that intermediate species such as aldehyde and hydrogen peroxide appear at the first stage cool ignition and disappear at the last stage hot ignition. This result is a validation to the detailed chemistry model predictions for the two-stage ignition.

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A lean n-heptane/air mixture is compressed up to hot ignition using a rapid-compression machine. Attenuation and scattering of an incident laser light are measured to evaluate soot formation in compression ignition processes. Even though the mixture is lean, soot is produced in the post-flame period of compression ignition. The red coloration of combustion products is mostly due to the thermal radiation of the soot. It is also observed that the soot precursor is formed correspoonding to the cool and blue flame onsets during the preflame peried, only in the cases where the compression temperatures for these low-temperature flames belong to those of the negative-temperature coefficient regime. The soot precursor first appears just after the cool fiame has degenerated. Soot-precursor formation is closely related to ion generation, and the behavior of soot formation is deduced to depend on fuel pyrolysis in preflame processes of low-temperature ignition.

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ディーゼル機関の着火は反応が弱くてτ₂期間が長い. この着火の基礎研究を目的として, このような性質をもつイソオクタンを燃料に選んで, その総着火おくれτを急速圧縮機で求め, ついで急速圧縮機の圧縮比を高めて擬似モータリング実験を行い, 圧縮中に生ずる青炎の発生時刻t_eを, 上記τを用いたLivengood-Wu積分∫^te₀(l/τ)dt=1(t:時間, te:青炎発生時刻, τ:着火おくれ)で推定できる可能性を実験的に確かめた.

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n-ブタン-空気混合気の自然発火限界を温度範囲620～973K，圧力範囲0．1～1MPaで注入法により測定した．その結果，620～770Kの温度領域に爆発半島が存在し，その大きさはn-ブタン濃度の増加に 対し減少した，

は870K以下で出現した．誘導時間から求めた

冷炎

の見かけの活性化エネルギーは79～109kJ／mo1であった．また，73％n-ブタン-空気混合気の爆発限界圧力は，673Kにおいて1気圧 であった．

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In this study, we applied luminous spectroscopic analysis and Planar Laser Induced Fluorescence (PLIF) method on lean Homogeneous Charge Compression Ignition (HCCI) combustion to obtain some ideas of ignition timing control and combustion rate control methods in HCCI engines. In the tests, we used an optical access engine and n-C₁₂H₂₆ as a fuel. Inlet air temperatures and inlet oxygen concentrations were changed as the test parameters, and the following conclusions were obtained : (1) After low temperature reaction, LIF signal from hydrocarbon was disappeared. This was because that hydrocarbon was changed to another molecules or per oxides. (2) In high temperature reaction region, OH radical was appeared across a wide area in the combustion chamber.

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