川野 大輔

Flash-boiling occurs when fuel in injected into a combustion chamber where the ambient pressure is lower than the saturation pressure of the fuel. In the present study, the sub models of flash-boiling spray are constructed. The sub models consider the bubble nucleation, growth and disruption in a nozzle orifice and injected fuel droplets. Therefore, the model is implemented into KIVA3V and the spray characteristics of multicomponent fuel with and without flashing is numerically investigated. In addition, these numerical results are compared with experimental data which were obtained in the previous study using a constant volume vessel. The flashing spray characteristics from numerical simulation qualitatively show good agreement with the experimental results. Especially, it is confirmed from both the numerical and experimental data that flash-boiling effectively accelerates the atomization and vaporization of fuel droplets.

軽油に高オクタン価成分を混合することにより均一予混合圧縮着火（HCCI）燃焼を実現する手法を提案し、単気筒ディーゼル機関による実験により超低NOxが実現できることを確認した。しかし、THC、CO、可溶性有機成分（SOF）排出量が増加するケースが見られ、混合燃料噴霧モデルを用いた数値解析結果から、液相ペネトレーションを減少させる必要があることがわかった。

燃料温度上昇により得られる低沸点・高沸点混合燃料の減圧沸騰噴霧を定容容器で観察するとともに、混合燃料を単気筒ディーゼル機関にも適用し、初期燃料温度や混合割合の変化による熱発生および排出ガス特性への影響を調査した。その結果、減圧沸騰による微粒化・蒸発過程の改善により、smoke排出量を大きく低減できることが示された。

多成分燃料の物性値や気液平衡を考慮した多成分燃料噴霧モデルを新たに構築し、数値シミュレーションコードKIVA3Vに組み込んだ。本モデルを用いて、多成分燃料の噴霧特性に対する燃料組成の影響を解析した結果、低沸点成分を混合すると、高沸点成分の蒸発が促進されるが、さらに低沸点成分の混合割合が増加すると、逆に高沸点成分の蒸発が抑制されることがわかった。

Alternative fuels, such as gaseous fuels and oxygenated fuels etc., have been used to achieve low exhaust emissions in recent years. In general, most of these alternative fuels have high volatility, and flash-boiling takes place easily in the fuel spray. It is been known that the flashing is a favorable mechanism for atomizing liquid fuels. However, flash-boiling process in a engine is hardly studied. In this study, the sub models for flash-boiling spray of multicomponent fuel which take account for properties, vaporization process, bubble nucleation, growth and disruption in multicomponent fuel droplet were added to KIVA3V. The flashing spray characteristics from numerical simulation qualitatively showed good agreement with the experimental results. In addition, it was confirmed that flash-boiling effectively accelerated the atomization and vaporization of fuel droplets.

Homogeneous Charge Compression Ignition (HCCI) is effective for the simultaneous reduction of soot and NOx emissions from diesel engine. In general, high octane number and volatility fuels (gasoline components or gaseous fuels) are used for HCCI operation, because very lean mixture must be formed during ignition delay of the fuel. However, it is necessary to improve fuel injection systems, when these fuels are used in diesel engine. The purpose of the present study is the achievement of HCCI combustion in DI diesel engine without the large-scale improvements of engine components. Various high octane number fuels are mixed with diesel fuel as a base fuel, and the mixed fuels are directly applied to DI diesel engine. At first, the cylinder pressure and heat release rate of each mixed fuel are analyzed. The ignition delay of HCCI operation decreases with an increase in the operation load, although that of conventional diesel operation does not almost varied. In addition, the mixed fuel containing much high volatility fuel produces the higher peak of heat release rate of premixed combustion. The exhaust emissions (CO, CO2, THC, NOx, PM) in case of each mixed fuel are measured. Low NOx emission can be achieved by HCCI operation using the mixed fuels despite low volatility of base fuel. However, PM emission is relatively high in case of HCCI operation, and then PM is separated into SOF and ISOF. As a result, it can be confirmed that the high PM emission is derived from the increase in SOF, and the high SOF emission results from the base fuel in the mixed fuels. Copyright © 2004 SAE International.

Flash-boiling occurs when a fuel is injected to a combustion chamber where the ambient pressure is lower than the saturation pressure of the fuel. It has been known that flashing is a favorable mechanism for atomizing liquid fuels. On the other hand, alternative fuels, such as gaseous fuels and oxygenated fuels, are used to achieve low exhaust emissions in recent years. In general, most of these alternative fuels have high volatility and flash-boiling takes place easily in fuel spray, when they are injected into the combustion chamber of an internal combustion engine under high pressure. In addition, fuel design concept the multicomponent fuel with high and low volatility fuels has been proposed in the previous study in order to control the spray and combustion processes in internal combustion engine. It is found that the multicomponent fuel produce flash-boiling with an increase in the initial fuel temperature. Therefore, it is important to investigate these flash-boiling processes in fuel spray. In the present study, the sub models of flash-boiling spray are constructed. This sub model considers the bubble nucleation, growth and disruption in nozzle orifice and injected fuel droplets. Therefore, the model is implemented into KIVA3V and the spray characteristics of multicomponent fuel with and w/o flashing are numerically investigated. In addition, these numerical results are compared with experimental data which were obtained in the previous study using a constant volume vessel. The flashing spray characteristics from numerical simulation qualitatively shows good agreement with the experimental results. Especially it is confirmed from both the numerical and experimental data that flash-boiling effectively accelerates the atomization and vaporization of fuel droplets. This means that lean homogeneous mixture can be briefly formed by using flash-boiling in combustion chamber. Copyright © 2004 SAE International.

低沸点・高沸点混合燃料を実機関に適用した場合の機関性能・排気特性を調べた。その結果、低沸点成分の混合により未燃炭化水素（HC）排出量は増加するものの、エネルギー消費率には影響がなく、混合燃料を用いることによる黒煙（smoke）・NOx同時低減の可能性を見出した。

Particulate Matter (PM) from diesel engines is thought to be seriously hazardous for human health. Generally, it is said that the hazard depends on the total number and surface area of particles rather than total mass of PM. In the conventional gravimetric method, only the total mass of PM is measured. Therefore, it is very important to measure not only the mass of PM but also size and number density of particulates. Laser-Induced Incandescence (LII) is a useful diagnostic for transient measurement of soot particulate volume fraction and primary particle size. On the other hand, Scanning Mobility Particle Sizer (SMPS) is also used to measure the size distribution of soot aggregate particulates at a steady state condition. However, the measurement processes and the phenomena used to acquire the information on soot particulate are quite different between the LII and SMPS methods. Therefore, it is necessary to understand the detailed characteristics of both LII and SMPS. In the present study, the size distributions of PM from DI diesel engine are measured by both LII and SMPS simultaneously. In addition, PM mass emission is measured gravimetrically through a dilution tunnel and is separated into SOF and ISOF. The effects of EGR rate and engine load on the results of these particulate measurements are investigated. The different trends in the characteristics of PM emission are shown in each measurement methods for PM. The difference of detailed characteristics between LII and SMPS are illustrated by comparing the measurement results for the particulates. Finally, the problems associated with the measurements using each method are considered and some recommendations have been given for accurate measurement of nanoparticles. Copyright © 2004 SAE International.

減圧沸騰噴霧の発達過程を調べるため、混合燃料の飽和蒸気圧力に関わるパラメータを設定し減圧沸騰噴霧を実現した。この実験的解析から、初期燃料温度の上昇および雰囲気温度の低下によって減圧沸騰が生じ、微粒化・蒸気化が促進されるため、噴霧先端到達距離が短く半径方向に広く分散する噴霧が得られることを確認した。

n-ペンタン・n-トリデカン混合燃料を用いて、レーザ誘起蛍光（LIF）法およびMie散乱光撮影による噴霧の2次元蒸気濃度分布を測定した。その結果、低沸点成分が噴霧上流部で蒸発するため、高沸点成分が噴霧下流部に多く存在し、その液相長さは混合燃料の90%留出温度（T90）で整理できることがわかった。

In this study, the novel fuel design concept has been proposed in order to realize the low emission and combustion control in engine systems. In the fuel design concept, the fuel mixed with high volatility fuel (gasoline or gaseous fuel components) and low volatility fuel (gas oil or fuel oil components) are used to improve the spray characteristics using flash boiling effect. The authors has addressed the combustion processes of the mixed fuel with n-pentane and n-tridecane (n-pentane/n-tridecane) using heat release analysis, shadow photography and two-color method in rapid compression and expansion machine (RCEM). It has been reported the spray characteristics of single component fuel, but that of multicomponent fuels is almost unknown. In the present study, it is reported the results of spray experiments for mixed fuels conducted in RCEM. The liquid and vapor distributions of n-pentane/n-tridecane were analyzed by using Mie scattering and planar laser-induced fluorescence (PLIF). In addition, Mie scattering and laser-induced exciplex fluorescence (LIEF) were applied to investigate the effects of ambient pressure on the spray characteristics of propane/n-tridecane. In the case, pure n-pentane, which has the same transport properties as propane/n-tridecane has, was used to compare the mixture formation of pure n-pentane with that of propane/n-tridecane. From the results of these experiments, it was confirmed that vaporization characteristic of low volatility fuel was improved by mixing high volatility fuel and the effect of flash boiling on liquid-phase penetration and vapor distribution of propane/n-tridecane was obtained at low ambient pressure. Copyright © 2002 Society of Automotive Engineers, Inc.

In this work, we have proposed the novel fuel design concept in order to realize the low emission and combustion control in engine systems. In this concept, we use the reformulated fuels with lower and higher boiling point fuel to obtain the both advantages of their fuels for combustion process. In this paper, ignition characteristics of the mixed fuel were examined for the mixed fuels with n-tridecane and various lower boiling point fuels using RCEM. The results show that the ignition delay of the mixed fuel is depend on ignition characteristics of the higher cetane number component, and is mostly independent of those of the higher octane number component.

本研究では、低沸点・高沸点混合燃料を用いて低エミッション・燃焼制御を実現する燃料設計コンセプトを提案する。混合燃料の相互溶解実験によりパラフィン系炭化水素同士は容易に混合することを確認した。さらに、混合燃料を用いた蒸発および燃焼実験を行い、低沸点・高沸点混合燃料の噴霧燃焼特性を把握した。