Makoto Mashida

Research of the DI Diesel Spray Characteristics at High Temperature and High Pressure Ambient

乗用車用の小型ディーゼルエンジンにおいて比出 力・静粛性・排気性能等の向上が要求され,これらの 要求に対し,燃料噴射装置にはコモンレール噴射シス テムが採用されている.ディーゼルエンジンでは,そ の噴霧の質がエンジン性能(比出力・静粛性・排気性 能等)に大きく影響するため,エンジン・噴射系開発 において,エンジン筒内または同等環境場での噴霧挙 動の詳細解析(蒸気濃度分布解析,混合気形成過程の 解析など)が求められている.近年それだけでなく, 開発期間の短縮化から,噴霧の定量的な解析によるエ ンジン・噴射系への開発指針,方向性の提案が望まれ ている.ディーゼル噴霧の混合気形成過程の解析とし ては,LIEF(Laser Induced Exciplex Fluorescence) 法を用いた蒸気濃度の定量化があるが,蛍光強度の圧 力・温度依存性や,蛍光剤の熱分解,レーザの減衰等 が精度のよい計測を困難にしている. そこで本研究では,小型ディーゼルエンジンにおけ る混合気形成過程の解明及び,これを考慮したエンジ ン・噴射系への開発指針・方向性提案を目指し,蛍光 強度の圧力・温度依存性を考慮した蒸気濃度の準定量 化手法を構築した.また,定容燃焼容器を用い, エン ジン筒内と同等の環境場での,ディーゼル噴霧の混合 気形成過程について考察を行なった. 2.蒸気濃度検定 2)

Evaluation of cavitation in injector nozzle and correlation with liquid atomization

Present paper describes the correlation between occurrence of cavitation inside injector nozzle and progress of atomization in discharged liquid jet flow. A transparent two-dimensional shape nozzle was designed and it was used for flow visualization. The visualized images both of cavitation and atomization were obtained simultaneously. The cavitation was evaluated by applying image analysis. The quantitative analysis on length, thickness and their fluctuations of cavitation was made, and the correlation with atomization was examined. The authors proposed an evaluation method of atomization in the previous study, and it was combined with evaluation method of cavitation developed in this study. It is found that the change of cavitation and progress of atomization are synchronized, and that a strong correlation between them exists. The best performance of atomization may be obtained by controlling the cavitation inside nozzle, and obtained aspects with this study will be utilized for the design of fuel injection nozzle of internal combustion engines.Graphical abstract

Set-off length reduction by backward flow of hot burned gas surrounding high-pressure diesel spray flame from multi-hole nozzle

The backward flow of the hot burned gas surrounding a diesel flame was found to be one of the factors reducing the set-off length (also called the lift-off length), that is, the distance from a nozzle exit into which a diffusion flame cannot intrude. In the combustion chamber of an actual diesel engine, the entrainment of the surrounding gas into a spray jet injected from a multi-hole nozzle is restricted by the combustion chamber walls and the adjacent spray jets, thus inducing the backward flow of the surrounding gas toward the nozzle exit. The emergence of this backward flow was measured by particle tracking velocimetry in the non-combusting condition. A new momentum theory for calculating the backward flow velocity was established by extending Wakuri’s momentum theory. Shadowgraph imaging in an optical engine successfully visualized the backward flow of the hot burned gas. The hot burned gas is re-entrained into the spray jet in the region of the set-off position and shortens the set-off length in comparison to that of a single free-spray flame which does not induce the backward flow.

PTV analysis of the entrained air into the diesel spray at high-pressure injection

In order to clarify the effect of high-pressure injection on soot reduction in terms of the air entrainment into spray, the air flow surrounding the spray and set-off length indicating the distance from the nozzle tip to the flame region in diffusion diesel combustion were investigated using 300MPa injection of a multi-hole injector. The measurement of the air entrainment flow was carried out at non-evaporating condition using consecutive PTV (particle tracking velocimetry) method with a high-speed camera and a high-frequency pulse YAG laser. The set-off length was measured at highpressure and high-temperature using the combustion bomb of constant volume and optical system of shadow graph method. And the amount of air entrainment into spray until reaching set-off length in diffusion combustion was studied as a factor of soot formation.