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| 1.
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小保方, 富夫 ; 橋本, 徹 ; 五十木, 慎一 ; 柄沢, 隆夫 ; 志賀, 聖一 ; 倉林, 俊雄
概要:
application/pdf<br />Journal Article<br />The swirl and axial components of gas velocity in the disk-type combustion cha
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mber of a firing engine were measured by an LDA. The engine was operated under the conditions of a speed of 1500rpm, η_υ=0.5, φ=1.4 and ignition timing of 30°BTDC. The gas velocities at 9 points on a diameter at midheight of the combustion chamber were analyzed by the cycle-resolved method. The bulk (mean) velocity was determined by the frequency discrimination method with the cut-off frequency of 667Hz. The flame propagation pattern was detected by ionization probes set at 17 points on the piston. It has been observed that, in the case of fired operation, the turbulence intensity is higher, the integral length and micro length scales are longer and the swirl flow is weaker and is eccentrically shifted compared with the case of motored operation. These results show that it should be noted that there are remarkable differences in the gas flow between motored operation and fired opeation.
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| 2.
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高橋, 秀夫 ; 志賀, 聖一 ; 小柴, 英俊 ; 柄沢, 隆夫 ; 倉林, 俊雄
概要:
application/pdf<br />Journal Article<br />The purpose of this study is to clarify the characteristics of diesel spray with higher and unsteady injection pressure under an elevated pressure condition and an elevated pressure and
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temperature condition. A Bosch-type injection system and a rapid compression machine were used. The behavior of the spray until 2 ms after the beginning of injection, which corresponds to the period of the ignition delay of most diesel engines, was observed by high-speed photography. Under the less evaporating condition, the spray penetrations of higher and normal injection pressure are almost the same, whereas, under the evaporating condition, those penetrations are not the same. Thus, the penetration of the normal injection pressure is affected by the ambient temperature, while the penetration of the higher injection pressure is little affected by the evaporation. The same tendency was observed in the behavior of spray cone angle development. It is also shown that the spray generates small eddies and the spray pattern is affected by the growth and dissipation of those eddies.
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| 3.
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高橋, 秀夫 ; 志賀, 聖一 ; 柄沢, 隆夫 ; 倉林, 俊雄
概要:
application/pdf<br />Journal Article<br />A rapid-compression machine is developed for fundamental studies of diesel combustion. Low-pressure compressed air and a stainless-steel membrane are employed to drive the piston. This is
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similar to the principle of a shock tube and is quite simple compared with other machines. The combustion chamber has a 120 mm bore and is 20 mm in depth. These dimensions were determined to avoid the impingement of the spray within 2ms, which seems to be a typical ignition delay period. Compression time and polytropic exponent are about 38ms and 1.30, respectively. High-speed photographs were taken to observe the spray development for both evaporating and non evaporating spray, and the effect of evaporation could be shown clearly. A combustion test was also carried out, and a pressure rise due to combustion was recognized. Thus, it is shown that this machine has sufficient performance for the study of diesel combustion. A simple simulation technique to design the machine is also presented and its availability is verified.
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| 4.
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小保方, 富夫 ; 柄沢, 隆夫 ; 倉林, 俊雄
概要:
application/pdf<br />Journal Article<br />The bulk velocity and turbulence of air swirl flow in the dish type combustion
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chamber of a motored engine were measured by an LDA. The LDA was modified with optical finers for easy operation and was improved to form a smaller measuring space 0.29 mm in length. The engine was operated at a speed of 1 000 rpm. The gas velocity at a mid section of the combustion chamber was analyzed by the stationary time average method. The radial distribution of mean swirl flow and turbulence characteristics such as turbulence intensity (u'), integral time and spacial scale (L_t, L) and micro time and spatial acale (λ_t, λ) were obtained, and time depending properties of such flow data were investigated. It has been revealed that the mean swirl velocity and swirl ratio almost agree with those of previous reports, but u' is higher and scales of turblence are lower than the data given by the hot-wire anemometer.
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| 5.
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小保方, 富夫 ; 花田, 尚喜 ; 桑原, 秀樹 ; 倉林, 俊雄
概要:
application/pdf<br />Journal Article<br />The velocity and turbulence in two-dimensional wedge type engine combustion chambers are measured by a laser Doppler anemometer (LDA) with an optical fiber transmitting system under motored
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and firing conditions. The engine is operated at a speed of 2 500 rpm with propane-air mixtures changing the combustion chamber setting direction to the cylinder, here named normal ""N"" and reverse ""R"" combustion chambers. The preliminary experiment indicates that the flame propagating velocity near the slant ceiling and the indicated mean effective pressure are of a higher level at the R chamber than at the N chamber. The mean velocity U^^-, fluctuation intensity u' and integral time scale of turbulent L_t in both chambers are derived through the stationary time averaged analysis of the measured velocities, and each is compared between both chambers. The results have showed that the flow patterns in both chambers are different and the mean value of the U^^- of the R chamber at the spark timing is large than the other by about 70%. However there is little difference at u' and L_t in both chambers.
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| 6.
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柄沢, 隆夫 ; 川口, 暁生 ; 志賀, 聖一 ; 倉林, 俊雄
概要:
application/pdf<br />Journal Article<br />This paper presents an experimental study being aimed at revealing the ignition assistance effect of a hot surface in an alcohol-fueled diesel engine and its mechanism. A single shot of spray was
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injected into a motored diesel engine. Ignition lag was measured and was split into two regimes, physical lag and chemical lag, by applying a statistical technique presented by S. Kumagai. High-speed direct photographs were also taken. The dependence of those ignition lags were classified into three regions on their Arrhenius plots. In lower hot-surface temperatures, the ignition lags decrease exponentially with increasing the hot-surface temperature. In higher temperature regions, the ignition lags tend to have constant values, passing through the transient region. By combining the high-speed photographs, it is suggested that the hot surface does not initiate flame propagation, but supplies heat to assist the spontaneous ignition as the assistance mechanism.
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| 7.
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小保方, 富夫 ; 花田, 尚喜 ; 倉林, 俊雄
概要:
application/pdf<br />Journal Article<br />The intensity and structure of turbulence in a flame front may be changed by expansion flow due to combustion. Therefore the velocity and turbulence in a combustion chamber of a spark
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ignition engine are measured by mans of a laser Doppler anemometer with fiber-optic pick-up under firing conditions. The engine is operated at a speed of 2500 rpm with propane-air mixtures. Data acquisition window width affects the turbulence intensity (u') and integral time scale of turbulence (Lt) of the analysis. In the experiment, a short (0.67 ms) and long (4 ms) window are selected and compared with each other. In the combustion period, twice the intensity of u' and an increase of 40 % in Lt are observed in the case of short window analysis. A stronger u' and larger Lt are observed in the long window analysis and it is shown that the Lt expands laterally during the compression stroke and vertically during the expansion stroke.
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| 8.
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志賀, 聖一 ; 柄沢, 隆夫 ; 倉林, 俊雄
概要:
application/pdf<br />Journal Article<br />To predict the shape of a flame in a vessel is one of very important problems in the field of combustion. But it is difficult because the shape is strongly influenced by the flow which is affected
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not only by the surrounding walls but also by the expansion of gas due to combustion. The mechanism of formation of a wedge shaped flame in a constant volume combustion chamber has longtime been a target of many researchers since Ellis pointed it out in 1928. Several hypotheses have been proposed but they do not clearly present a complete mechanism. Modern techniques of measurement are giving new data about the combustion gases. In this report, a two dimensional LDV and some other measuring techniques are used to check the hypotheses mentioned above, and a new idea on the mechanism of formation of a wedge shaped flame is proposed.
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| 9.
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小保方, 富夫 ; 花田, 尚喜 ; 倉林, 俊雄
概要:
application/pdf<br />Journal Article<br />To improve the adaptability of LDA (laser Doppler anemometer) for measuring velocities in an engine, an optical fiber system composed of a couple of single mode, polarization-preserving
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optical fibers has been made to transmit the incident beams. Though the total transmitting efficiency of this optical system is about 24 %, it has been confirmed that a fiber-optic LDA system with a 25 mW He-Ne laser is applicable to the real-time measurement of gas velocity in the combustion chamber of a small-sized two-stroke spark ignition engine. The ensemble-averaged mean velocities obtained by using this optical system show that the gas velocity rapidly decreases just before the flame front arrival and suddenly increases after passing of the flame. It is also shown that a new bulk flow is generated in the chamber by the gas expansion due to combustion.
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| 10.
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志賀, 聖一 ; 江原, 秀治 ; 柄沢, 隆夫 ; 倉林, 俊雄
概要:
application/pdf<br />Journal Article<br />This paper presents one of the studies which aim to reveal the capability of controlling diesel combustion by exhaust gas recirculation (EGR). In a previous paper, the effect of EGR on soot emission
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was examined, and it was shown that soot emission is suppressed under the condition that the mass fraction burned by spontaneous (pre-mixed) combustion is increased. In a present paper, diesel knock intensity is defined as a sound pressure distributed over 1-1.5kHz, and the effect of EGR on the diesel knock intensity is examined. The diesel knock intensity is remarkably reduced by EGR under the same operating condition as soot emission is reduced by EGR. By calculating the heat release rate based on the indicated pressure diagram, it was suggested that a reduction of knock intensity originates from the reduced reaction rate in the spontaneous ignition. The quantitative relationship between the diesel knock intensity and the maximum rate of pressure rise is also presented.
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