Hiromichi Yanagihara

A study of DI diesel combustion under uniform higher-dispersed mixture formation

A new concept of combustion system is proposed for the simultaneous reduction of NOx and soot. The injection system is constructed with a new injector driven by a piezo-actuator and mechanical feed pump. The image of combustion was taken by shadow graph method, and an image intensifier was used to detect very weak photic signals in combustion. The level of NOx is about 1/100 that of a conventional Dl diesel engine or lean burn gasoline engine. The mechanism of extremely low NOx and the ignition mechanism are discussed. This system is named the uniform bulky combustion system (UNIBUS). Presently, UNIBUS is only effective under lower load.

Effect of Multi-Injection Strategy on Cavitation Development in Diesel Injector Nozzle Holes

The effect of multiple-injection strategy on nozzle hole cavitation has been investigated both experimentally and numerically. A common-rail Diesel injection system, used by Toyota in passenger car engines, has been employed together with a double-shutter CCD camera in order to visualise cavitation inside a submerged and optically accessible (in one out of the six holes) real-size VCO nozzle. Initially the cavitation development was investigated in single injection events followed by flow images obtained during multiple injections consisting of a pilot and a main injection pulse. In order to identify the effect of pilot injection on cavitation development during the main injection, the dwell time between the injection events was varied between 1.5-5ms for different pilot injection quantities. The extensive test matrix included injection pressures of 400 and 800bar and back pressures ranging from 2.4 up to 41 bar. The results have confirmed that cavitation patterns in the pilot are very similar to those of the main injection, while the effect of the dwell time was present through the variation of the actual injection pressure caused by the pressure wave dynamics within the injection system. The flow inside the VCO nozzle was also simulated using a recently developed cavitation CFD model which takes into account the movement of the needle. Simulations have shown that cavitation inception is very fast and synchronous for both the pilot and the main injection events while its intensity in the sense of spatial extent appears to peak at relatively low needle lifts.

A Study on Friction Materials for Brake Squeal Reduction by Nanotechnology

Brake squeal is caused by dynamic instability, which is influenced by its dynamic unstable structure and small disturbance of friction force variation. Recently, FE Analysis of brake squeal is applied for brake design refinements, which is based on dynamic instability theory. As same as the refinement of brake structure is required for brake squeal reduction, the refinement of pad materials is also required for brake effectiveness and brake squeal reduction. It is well known that friction film, which is composed of polymers like phenol formaldehyde resin and so on, influences for friction coefficient. Therefore it is expected that the refinement of polymers in pad materials enable higher brake effectiveness and less brake squeal. In this paper, Molecular Dynamics is applied for the friction force variation of polymers in pad materials. The MD simulation results suggest the reduction method of friction force variation of polymers. The refinement of pad materials is shown here based on the MD simulation results, which is assured by experiments. This paper shows the possibility of friction materials design with higher performance and less brake squeal.

Flow and Temperature Distribution in an Experimental Engine: LES Studies and Thermographic Imaging

Temperature stratification plays an important role in HCCI combustion. The onsets of auto-ignition and combustion duration are sensitive to the temperature field in the engine cylinder. Numerical simulations of HCCI engine combustion are affected by the use of wall boundary conditions, especially the temperature condition at the cylinder and piston walls. This paper reports on numerical studies and experiments of the temperature field in an optical experimental engine in motored run conditions aiming at improved understanding of the evolution of temperature stratification in the cylinder. The simulations were based on Large-Eddy-Simulation approach which resolves the unsteady energetic large eddy and large scale swirl and tumble structures. Two dimensional temperature experiments were carried out using laser induced phosphorescence with thermographic phosphors seeded to the gas in the cylinder. The results revealed different mechanisms for the development of temperature stratification: intake gas and residual gas mixing, heat transfer in the wall boundary layer, compression of the charge, and large scale flow transport. The sensitivity of LES results to different wall boundary conditions and inflow conditions was analyzed. (Less)