Taku Tsujimura

Biodiesel effects on transient needle motion and near-exit flow characteristics of a high-pressure diesel injector

In this study, biodiesel effects on transient needle motion and near-exit flow characteristics of a single-orifice high-pressure diesel injector were investigated in terms of needle-lift, needle speed, exit velocity and near-exit flow structure under various injection pressures. Ultrafast x-ray phase-contrast imaging technique was employed in this study to analyze the transient needle motion and near-exit flow characteristics. High-energy sub-nanosecond x-ray pulses have a potential to visualize the needle inside the nozzle and near-exit dense supersonic flow which speed reaches over 600 m/s. Transient needle motion and the structure and velocity of near-exit supersonic flows can be obtained by fabricated analysis of the x-ray images regardless of fuel, injection condition and type of injector. High bulk modulus and viscosity of biodiesel normally slow down the needle movement and decrease the flow performance. During opening-transient, sharp increase and following overshoot in needle speed and exit velocity were observed with a concurrent increase in spray width. The biodiesel showed a slower increase in needle speed, exit velocity and spray width but a higher degree of velocity overshoot during opening-transient. At steady-state, the biodiesel showed less turbulent flow structure and smaller spray width than diesel. During closing-transient, an abrupt increase in needle speed and decrease in exit velocity were observed with a concurrent increase in spray width. The biodiesel showed the retarded start of closing-transient and longer total injection duration under same energizing pulse duration. The difference between biodiesel and diesel became insignificant at low injection pressures roughly below 100 MPa.

A Study of Direct Injection Diesel Engine Fueled with Hydrogen

In this study, characteristics of the development and auto-ignition/combustion of hydrogen jets were investigated in a constant-volume vessel. The authors focused on the effects of the jet developing process and thermodynamic states of the ambient gas on auto-ignition delays of hydrogen jets. The results show that the ambient gas temperature and nozzle-hole diameter are significantly effective parameters. By contrast, it is clarified that the ambient gas oxygen concentration has a weak effect on the auto-ignition/combustion of hydrogen jets. Consequently, it is supposed that the mixture formation process is capable of improving the autoignition/combustion of hydrogen jets.

Micro Gas Turbine Firing Kerosene and Ammonia

A demonstration test with the aim to show the potential of ammonia-fired power plant is planned using a micro gas turbine. 50kW class turbine system firing kerosene is selected as a base model. A standard combustor is replaced by a prototype combustor which enables a bi fuel supply of kerosene and ammonia gas. Diffusion combustion is employed in the prototype combustor due to its flame stability. Demonstration test of co-firing of kerosene and ammonia gas was achieved to check the functionality of the each component of the micro gas turbine. The gas turbine started firing kerosene and increased its electric power output. After achievement of stable power output, ammonia gas was started to be supplied and its flow rate increased gradually. 21kW power generation was achieved with 30% decrease of kerosene by supplying ammonia gas. Ammonia gas supply increases NOx in the exhaust gas dramatically. However post-combustion clean-up of the exhaust gas via SCR can reduce NOx successfully.© 2015 ASME

Development of dynamic simulator of alkaline water electrolyzer for optimizing renewable energy systems

In order to analyse dynamic behaviours of hydrogen production by alkaline water electrolysis against fluctuating electric power, we developed a large-scale electrolyzer simulator. The measurement d...

Estimation of equivalence ratio distribution in diesel spray using a computational fluid dynamics

It is important to understand the mechanism of mixing and atomization of the diesel spray. In addition, the computational prediction of mixing behavior and internal structure of a diesel spray is expected to promote the further understanding about a diesel spray and development of the diesel engine including devices for fuel injection. In this study, we predicted the formation of diesel fuel spray with 3D-CFD code and validated the application by comparing experimental results of the fuel spray behavior and the equivalence ratio visualized by Layleigh-scatter imaging under some ambient, injection and fuel conditions. Using the applicable constants of KH-RT model, we can predict the liquid length spray on a quantitative level. under various fuel injection, ambient and fuel conditions. On the other hand, the change of the vapor penetration and the fuel mass fraction and equivalence ratio distribution with change of fuel injection and ambient conditions quantitatively. The 3D-CFD code used in this study predicts the spray cone angle and entrainment of ambient gas are predicted excessively, therefore there is the possibility of the improvement in the prediction accuracy by the refinement of fuel droplets breakup and evaporation model and the quantitative prediction of spray cone angle.

Combustion and Fuel Technologies of Advanced Diesel Engine

ディーゼル機関の熱効率は内燃機関の中で最も高く,世界的 に見ても極めて厳しいポスト新長期排出ガス規制 1) をクリアす るクリーンディーゼル 2) の普及は,大気環境を悪化させず,二 酸化炭素の排出抑制および石油依存度の低減に対して有効と考 えられる。ただし,同排出ガス規制は前規制に比べ窒素酸化物 (nitrogen oxide,NOx),粒子状物質(particulate matter,PM)を ともに約1/3とする厳しいものであり,蓄圧式燃料噴射装置に よる燃料噴射圧力の高圧化および電子制御化が進んだ最新の ディーゼルエンジンにおいても,ディーゼル排気の特徴である NOxおよび PM生成特性のトレードオフ関係の打破が依然とし て課題である。また,エンジンシミュレーション解析からは NOxと燃料消費率(燃費)についてもトレードオフ関係にある ことが指摘されており ,NOx,PM,燃費のトレードオフ関係 を打破し,三者の同時低減を果たすディーゼル燃焼技術および 燃料技術の研究開発が重要視されることになる。近年のディー ゼルエンジンにはディーゼルパティキュレートフィルター (diesel particulate filter,DPF)および NOx浄化装置の搭載が必 須になりつつあり,後処理装置による排気浄化特性を勘案した エンジン燃焼制御ロジックの構築が,燃費改善も含めた燃焼改 善には必須である。 一般に NOx浄化触媒の浄化性能は温度依存性が強く,低温 度条件下で高い浄化性能を得ることは困難であるが,Fig. 1に 示すように NOx浄化触媒の浄化効果が得られ難い低排気温度 となる低負荷運転領域においては予混合圧縮着火(premixed compression ignition,PCI)燃焼法等のクリーン燃焼技術を適用 し,また排気温度が高く NOx浄化触媒による高浄化率が得ら れる中・高負荷運転領域では熱効率または燃費を重視した従来 燃焼を適用するデュアル燃焼コンセプト 4) が排気性状と燃費を 同時に改善する燃焼制御コンセプトであると考えられる。今後 ますます要求されるディーゼルエンジンシステムの省燃費化に 対し,エンジン燃焼の熱効率向上,エンジン排気量のダウンサ イジング化,および高過給化が進むことが予想され,必然的に エンジン排気が低温化することを意味し,触媒浄化に頼らない クリーン燃焼となるエンジン運転領域を拡大することは極めて 重要である。 本研究では,クリーン燃焼運転領域の拡大のため,従来型エ ンジンにおける PCI燃焼等の新燃焼方式の適用だけでなく,可 変動弁機構,超高圧燃料噴射に代表される先進的なエンジン要

Planar Laser Rayleigh Scattering for Analyzing Diesel Spray Characteristics

The developing and mixing characteristics of a diesel spray were investigated, and under circumstances of changing fuel injection and the ambient gas conditions. The mixing measurement in the diesel spray was conducted using planar laser Rayleigh scattering. Experiments were conducted in an optically accessible, constant-volume combustion chamber. The chamber could simulate the ambient conditions of a typical diesel engine. In this study n-heptane was injected into the chamber and the scattered light from the spray was detected by an ICCD camera. A 532 nm Nd: YAG laser was used as a light source. The experimental results show that an injection pressure has a great effect on fuel vaporizing and in the mixing. Also, an increase in the injection pressure could promote a much leaner fuellambient gas mix. The results showed that an ambient temperature and density do have a great effect on the vaporization of fuel droplets and a development of liquid length in the diesel spray.

Distribution of Gaseous Fuel Concentration in Unsteady Jet Measured by Planar Laser-induced Rayleigh Scattering (Quantitative Measurement for Mixture Concentration in a High-pressure Ambient)

In this study, a planar laser-induced Rayleigh scattering (PLIRS) was applied to unsteady gas jets to understand processes of jet development process and ambient gas entrainment in a relatively high pressure ambient. In the verification of PLIRS, Rayleigh scattered light intensities were in proportion as incident light intensities and molar number densities of scatterer. From the results of this study, it is clarified that dense mixtures occupy in the center part of the jet and large-scale vortices exist around the jet axis as a large-hole nozzle is used, that dense mixtures do not clearly appear as a small-hole nozzle is used, and that in volumetric concentrations in the steady portion of jets distribute according to a law of 3/2.

A Study on Underexpanded Jet Structure under High Pressure Ambient

In this study, underexpanded flows of hydrogen injected into high pressure ambient were focused to clarify the effect of the flow structure on jet developing and mixing processes. Flow behaviors of underexpanded jets injected into atmospheric pressure ambient are well known. However there are few works about the flow under high pressure ambient and about the flow injected through relatively small orifice (<1.0 mm). Therefore, in this study, the jet flows near the nozzle exit were observed by shadowgraph photography with changing conditions of injection, ambient, and nozzle configuration. The objectives are to clarify the effects of those experimental conditions on the jet structures and to suppose the effect of the jet structures on mixing and developing processes. The shadowgraph images were used to measure Mach disc diameter, barrel length, jet radial width, and shock spacing which were related to a pressure ratio of injection to ambient and nozzle diameter. The results show that the pressure ratio has significant effects on underexpanded jet structures and as the increase in the pressure ratio, jet structures near the nozzle exit enlarged, and that the injected mass was conserved at where the Mach disc was generated. From the results, it is supposed that the pressure ratio is significantly related to the scale of the eddy generated just near the shock structure and also related to mixing process.