Shuichi Kubo

Effects of exhaust gas recirculation in homogeneous charge compression ignition engines

Abstract Ignition control is an important issue in homogeneous charge compression ignition (HCCI) engines, which have the advantages of low NOx emission and high thermal efficiency. In this study, the effect of the exhaust gas recirculation (EGR) on the ignition control of HCCI engines is discussed using an engine cycle simulation in which a homogeneous mixture is assumed. Auto-ignition of 65 per cent iso-octane + 25 per cent toluene + 10 per cent n-heptane, which is used as a fuel to evaluate the characteristics of a gasoline-like fuel, is represented by a detailed reaction model. The dilution by EGR delays the ignition timing when the charged gas temperature is not changed by EGR. The temperature rise of the charged gas promotes auto-ignition. Based on these characteristics, it was suggested that the ignition timing could be controlled by EGR with temperature control, when the amount of fuel supply is constant. This control method can also be applied to control of the air-fuel ratio (A/F) in the cylinder while maintaining the optimum ignition timing. In spite of the difference in the A/F and the EGR ratios, no significant difference was found in the pressure rise rate at combustion and the NOx emission when the ignition timing was the same.

Computer simulation study on filtration of soot particles in diesel particulate filter

A computational scheme is developed for simulating gas-particle flow in diesel particulate filter (DPF). It is composed of the lattice Boltzmann method for the gas and the Brownian dynamics method for soot particles suspended in the gas. In this scheme, the gas exerts a drag force on each particle, and on the other hand accumulated soot particles obstruct the gas flow by decreasing the gas permeability. Based on the analysis of the overall gas flow through DPF, the developed scheme is applied to simulating the gas-particle flow through a porous structure, which is fabricated by packing powder particles of several tens of micrometer size with the discrete element method so as to mimic the porous wall in SiC-DPF. At the initial stage of the simulation, the filtration efficiency of the porous structure in its clean state is evaluated as a function of diameter of the soot particle, and it is found out that the dominant collection mechanism transfers from the Brownian diffusion to the direct interception around the particle diameter of 300 nm, and the filtration efficiency has the minimum at around this diameter. A coupled simulation of the gas flow and the particle dynamics is executed repeatedly, updating the flow velocity and the gas permeability, until a considerable amount of soot particles accumulates in the porous structure. From this simulation, it is confirmed that the developed scheme can reproduce improvement of the filtration efficiency and deterioration of the back pressure caused by the accumulation of soot particles.

Detailed Surface Reaction Model for Three-Way Catalyst and NOx Storage Reduction Catalyst

In this research we developed surface kinetic model with detailed reaction mechanisms for simulating reaction dynamics of NO x Storage& Reduction (NSR) Catalyst and three-way catalyst (TWC). Simulation results showed that surface site coverage strongly dominates catalytic reaction characteristics especially in transient state. So we confirmed that the surface kinetic model could play important roles in a useful tool for understanding detail reaction dynamics and searching the optimized operating conditions in the development of automotive catalysts which was always exposed to transient conditions. And the detailed reaction mechanisms in TWC and NSR catalyst were discussed on the basis of the calculated surface site coverage.

Der Weg zu einem detaillierten Rußmodell für Verbrennungsmotoren

An der Universitat Cambridge wurde die Rusbildung in einem Verbrennungsmotor, der mit homogener Kompres sionszundung (HCCI) bei fettem Gemisch (Luftzahl 0,52) mit n-Heptan betrieben wird, untersucht. Dies erfolgte experimentell mittels Entnahmeventil und durch Simulation mit einem neu entwickelten „Stochastischen Reaktor Modell“ (SRM), das eine hochgradig detaillierte Beschreibung von Ruspartikeln ermoglicht. Dieses Modell, das bezuglich des Rechenaufwands vergleichsweise geringe Anspruche stellt, liefert auser gemittelten Grosen, wie Masse, Anzahldichte, Volumenanteil, Durchmesser von Ruspartikeln oder Anzahl von Primarteilchen auch Aggregats- und Primarteilchen-Grosenverteilungen sowie detaillierte Informationen uber Morphologie und chemische Zusammensetzung.