Katsunori Hanamura

Micro- and macroscopic visualization of particulate matter trapping and regeneration processes in wall-flow diesel particulate filters

Abstract Particulate matter trapping and regeneration processes in wall-flow diesel particulate filters (DPFs) without catalysts were investigated through micro- and macroscopic visualization experiment. The vertical walls of a small DPF were polished using a lapping process to create a mirror-like surface on each ceramic particle grain. Using an all-in-focus optical microscope, micro-scale flow pores inside the DPF wall could be clearly observed from the polished surface to a depth of 100 μm. Furthermore, a real-time video with a speed of 30 frames per second could be sharply recorded. Through the microscopic cross-sectional view, transition from depth filtration to surface filtration could be observed clearly. Only surface pores opened on the wall surface were related to the filtration depth, i.e. the penetration depth. During regeneration of the DPF without catalyst, after a particulate (soot) cake was burnt out, the particulates trapped inside the surface pores were oxidized. On the other hand, using a half-cylindrical-shaped, wall-flow DPF, the overall trapping phenomena and regeneration process were clarified through a long-distance focusing lens camera. Diesel particulates were trapped almost uniformly over the entire surface of an inflow channel of the DPF in the direction of the channel flow, while the trapped particulates were not necessarily oxidized uniformly since there was a large temperature difference between the inlet and the outlet of the flow channel. The regeneration patterns were strongly dependent on the initial particulate mass and the inlet temperature of the working gas, including the microscopic phenomena in each location. Consequently, microscopic surface pores played a significant role in the regeneration process as well as in the beginning of trapping. Furthermore, at a macroscopic level, a uniform temperature and wall-flow distributions were found to be significant for quick regeneration.

Nano‐gap TPV Generation of Electricity through Evanescent Wave in Near‐field Above Emitter Surface

Nano‐gap thermophotovoltaic (Nano‐Gap TPV) generation of electricity through evanescent wave existing only in a near‐field above an emitter surface has been investigated experimentally using a GaSb cell. Through the cell, radiation with wavelength less than 1.8μm is converted into electricity. With decreasing gap between the emitter and cell surfaces, the output power, first increases, and then is maintained at constant since the view factor for the propagating radiation becomes close to unity. On further decrease in gap from about 3μm, evanescent effect for long wavelength radiation becomes remarkable, resulting in enhancement only of heat transfer from the emitter to the cell. However, under the condition of the gap less than 1μm, the output power increases with decreasing gap; that is, the evanescent wave for wavelength less than 1.8μm contributes to generation of electricity.

Photovoltaic Generation of Electricity Using Near-Field Radiation

Near-field radiation that has a high intensity of electric field was applied to enhance conversion from thermal energy to electricity in a wavelength range less than 1.1 μm or 1.8 μm. A commercial Si-photovoltaic cell and a thermophotovoltaic cell made of GaSb semiconductors were used to confirm that the near-field radiation effect (the evanescent wave effect) can be applied to enhance generation of electricity. As a result, an increase in output power generation of electricity by the evanescent wave effect was detected and the short-circuit current density increased about 1.3 times for the Si-PV cell and 3.0 times for the GaSb-TPV cell as larger than those obtained by the conventional propagating-wave radiation.Copyright

Spectral Control of Near-Field Radiation Through Surface Plasmon Polariton Interference

Through interference of surface plasmon polaritons (SPPs), near-field radiation transfer between pillar-array-structured surfaces was enhanced compared with that between plane surfaces. Even in nanoscale channels between the pillars, the SPPs could propagate, and then a kind of interference and resonance took place according to the depth of the channel between the pillars. With decreasing pillar height, the frequency at maximum radiation transfer was shifted to the high-frequency side. That is, spectral control of near-field radiation could be achieved using pillar-array-structured surfaces.Copyright

Variation in Catalytic Activity of Carbon Black during Methane Decomposition: Active Site Estimations from Surface Structural Characteristics

The variation in the catalytic activity of carbon black (CB) during methane decomposition was investigated by considering the number of active sites of CB. We demonstrated that the activity variation could be well estimated by assuming the edge length of graphitic sheets evolving from the CB surface. The results suggested that the activity variation originated from surface structural changes due to carbon deposition.Graphical Abstract

Energy Conversion From Fossil Fuel Into Spectral-Controlled Radiation for TPV by Super-Adiabatic Combustion in Porous Quartz Glass

Characteristics of energy conversion from fossil fuel into radiant energy in the energy-recirculated thermophotovoltaic (TPV) generation system with piled porous quartz glass plates have been investigated through numerical simulation. When the total thickness of the quartz glass plates is fixed, it is revealed that the conversion efficiency of the system does not almost depend on a combination of the number of the quartz glass plates and the individual thickness. However, the spectral efficiency with respect to the specific TPV cell may be improved as both the number of the quartz plates is larger and the individual thickness is smaller. As a result, it is suggested that the achievable total efficiency of the TPV system is expected to be over 15% under the condition that the emitter of the system is regarded as gray body and the total thickness of the quartz media is 30mm.Copyright

TPV Power Generation System using Super‐Adiabatic Combustion in Porous Quartz Glass

Electric power was obtained using the super‐adiabatic combustion TPV power generation system. In the system, a porous emitter made of alumina (Ceramic Foam) is installed at the middle. At both sides of the emitter, porous quartz glass plates with many pores are set up. A mixture of air and methane is introduced into the porous media, and flows uniformly across the cross section, where the flow direction changes regularly. Combustion occurs around the surface of the porous emitter. Through energy recirculation, the temperature of the emitter reaches about 1500K under the condition of the equivalence ratio of 0.2. Furthermore, the long‐wavelength components of the radiation emitted from the porous emitter are partially absorbed by the porous quartz glass, then, the short wavelength components are introduced into the TPV cell. Though the view factor was very small and there was multiple‐surface reflection by the quartz glass, we obtained the output power, which was small, using the super‐adiabatic combustion...

Electron microscopic time-lapse visualization of surface pore filtration on particulate matter trapping process.

A scanning electron microscope (SEM) was used to dynamically visualize the particulate matter (PM) trapping process on diesel particulate filter (DPF) walls at a micro scale as ‘time‐lapse’ images corresponding to the increase in pressure drop simultaneously measured through the DPF. This visualization and pressure drop measurement led to the conclusion that the PM trapping in surface pores was driven by PM bridging and stacking at constricted areas in porous channels. This caused a drastic increase in the pressure drop during PM accumulation at the beginning of the PM trapping process. The relationship between the porous structure of the DPF and the depth of the surface pore was investigated in terms of the porosity distribution and PM penetration depth near the wall surface with respect to depth. The pressure drop calculated with an assumed surface pore depth showed a good correspondence to the measured pressure drop.

Energy Conversion from Fossil Fuel into Spectral-controlled Radiation for TPV by Super-Adiabatic Combustion

Characteristics of energy conversion from fossil fuel into radiant energy in the energy-recirculated thermophotovoltaic (TPV) generation system with specific porous quartz media such like piled porous quartz glass plates are investigated through numerical simulation. When the total thickness of the quartz media is fixed, the conversion efficiency of the system depends mainly on the design parameter of coefficient heat transfer and porosity for the porous quartz media. It is suggested that the achievable total efficiency of the TPV system is expected to be over 10% under the condition that the emitter of the system is regarded as gray body and the total thickness of the quartz media is 15mm.

A Feasibility Study on Spectral Control using Piled AR‐coated Quartz Filters for Application to TPV

Piled AR‐coated quartz filters enable to control spectral transmittance for diffuse irradiation without designing the complex multi‐layer coatings. In this study, spectral transmission characteristics of the piling quartz filters with simple double‐layer coat and the optimum condition for TPV application were investigated through Ray Tracing numerical simulation. As a result, it was revealed that the piled quartz filters was very useful to achieve good spectral performance in the ideal energy recirculated TPV system when the number of the filters was enough large and thickness of each filter was enough thin. Then, the achievable spectral efficiency in the TPV system can be expected to exceed 70%. In the filtering method, the most striking feature is that the spectral efficiency can be controlled flexibly by changing the number of the filters and the individual thickness according to the situation.