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DRASTIC IMPROVEMENT OF THERMAL EFFICIENCY BY RAPID PISTON-MOVEMENT NEAR TDC
Moriyoshi, Y.,Sano, M.,Morikawa, K.,Kaneko, M. The Korean Society of Automotive Engineers 2006 International journal of automotive technology Vol.7 No.3
A new combustion method of high compression ratio SI engine was studied and proposed in order to achieve high thermal efficiency, comparable to that of CI engine. Compression ratio of SI engine is generally restricted by the knocking phenomena. A combustion chamber profile and a cranking mechanism were studied to avoid knocking with high compression ratio. Because reducing the end-gas temperature will suppress knocking, a combustion chamber was considered to have a wide surface at the end-gas region. However, wide surface will lead to large heat loss, which may cancel the gain of higher compression ratio operation. Thereby, a special cranking mechanism was adapted which allowed the piston to move rapidly near TDC. Numerical simulations were performed to optimize the cranking mechanism for achieving high thermal efficiency. An elliptic gear system and a leaf-shape gear system were employed in numerical simulations. Livengood-Wu integral, which is widely used to judge knocking occurrence, was calculated to verify the effect for the new concept. As a result, this concept can be operated at compression ratio of fourteen using a regular gasoline. A new single cylinder engine with compression ratio of twelve and TGV(Tumble Generation Valve) to enhance the turbulence and combustion speed was designed and built for proving its performance. The test results verified the predictions. Thermal efficiency was improve over 10% with compression ratio of twelve compared to an original engine with compression ratio of ten when strong turbulence was generated using TGV, leading to a fast combustion speed and reduced heat loss.
DRASTIC IMPROVEMENT OF THERMAL EFFICIENCY BY RAPID PISTON-MOVEMENT NEAR TDC
Y. MORIYOSHI,M. SANO,K. MORIKAWA,M. KANEKO 한국자동차공학회 2006 International journal of automotive technology Vol.7 No.3
A new combustion method of high compression ratio SI engine was studied and proposed in order to achieve high thermal efficiency, comparable to that of CI engine. Compression ratio of SI engine is generally restricted by the knocking phenomena. A combustion chamber profile and a cranking mechanism were studied to avoid knocking with high compression ratio. Because reducing the end-gas temperature will suppress knocking, a combustion chamber was considered to have a wide surface at the end-gas region. However, wide surface will lead to large heat loss, which may cancel the gain of higher compression ratio operation. Thereby, a special cranking mechanism was adapted which allowed the piston to move rapidly near TDC. Numerical simulations were performed to optimize the cranking mechanism for achieving high thermal efficiency. An elliptic gear system and a leaf-shape gear system were employed in numerical simulations. Livengood-Wu integral, which is widely used to judge knocking occurrence, was calculated to verify the effect for the new concept. As a result, this concept can be operated at compression ratio of fourteen using a regular gasoline. A new single cylinder engine with compression ratio of twelve and TGV (Tumble Generation Valve) to enhance the turbulence and combustion speed was designed and built for proving its performance. The test results verified the predictions. Thermal efficiency was improve over 10% with compression ratio of twelve compared to an original engine with compression ratio of ten when strong turbulence was generated using TGV, leading to a fast combustion speed and reduced heat loss.
Two competing soft modes and an unusual phase transition in the stuffed tridymite-type oxideBaAl2O4
Ishii, Y.,Mori, S.,Nakahira, Y.,Moriyoshi, C.,Park, J.,Kim, B. G.,Moriwake, H.,Taniguchi, H.,Kuroiwa, Y. American Physical Society 2016 Physical Review B Vol.93 No.13
<P>We investigated the structural phase transition of BaAl2O4, which has a network structure with corner-sharing AlO4 tetrahedra, via synchrotron x-ray thermal diffuse scattering measurements and first-principles calculations. BaAl2O4 shows the structural phase transition at T-C = 451.4 K from the P6(3)22 parent crystal structure to the low-temperature superstructure with a cell volume of 2a x 2b x c. This phase transition is unusual, in which two energetically competing phonon modes at M and K points soften simultaneously. When approaching T-C from above, the K-point mode appears first. However, this K-point mode is overcome by the later-developed M-point mode. The thermal diffuse scattering intensities from both modes increase sharply at T-C; therefore, both modes soften simultaneously. The first-principles calculations demonstrate that the M-point mode is electrostatically more preferable than the K-point mode and determines the eventual low-temperature structure, although these two modes are competing energetically. This competition is characteristic of BaAl2O4, which is ascribed to the structurally flexible network structure of this compound.</P>
Kim, S.J.,Kim, W.K.,Chan Cho, Y.,Park, S.,Jeong, I.K.,Yang, Y.S.,Kuroiwa, Y.,Moriyoshi, C.,Tanaka, H.,Takata, M.,Jeong, S.Y. Elsevier 2011 CURRENT APPLIED PHYSICS Vol.11 No.3
This study investigated the bonding nature and electrostatic potential of asymmetric Li ionic mobility in Li<SUB>2</SUB>B<SUB>4</SUB>O<SUB>7</SUB> crystals using the maximum entropy method (MEM) combined with Rietveld refinement and Ewald's technique. Compared with the interaction between oxygen and boron, Li<SUP>+</SUP> ions exhibited weak interactions with both oxygen and boron. Furthermore, electrostatic-potential-distribution analysis showed that Li<SUP>+</SUP> ions had a much weaker interaction with the matrix along the c-axis channel, suggesting that higher ionic conductivity occurred along the c-axis than along the a- and b-axes.
Origin of Ultrahigh Dielectric Constants for Barium Titanate Nanoparticles
Satoshi Wada,C Moriyoshi,H. Yasuno,K Kakemoto,K Takizawa,M Ohishi,T Hoshina,T Tsurumi,Y Kuroiwa 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Barium titanate (BaTiO3) nanoparticles with various particle sizes from 17 to 1,000 nm were prepared by using the 2-step thermal decomposition method of barium titanyl oxalate under various degree of vacuum. Various characterizations revealed that these particles were impurity-free, defectfree, dense BaTiO3 nanoparticles. When the degree of vacuum was high (pressure of 150 Pa at 650 C), the dielectric constant of BaTiO3 particles with a size of around 60 nm exhibited a maximum of around 15,000. On the other hand, when the degree of vacuum was low (pressure of 400 Pa at 650 C), no dielectric maximum was observed. To explain this size dependence, we precisely investigated a particle structure by using synchrotron radiation. As a result, the particles were always composed of two layers, i.e., a surface cubic layer and a bulk tetragonal layer, and the thickness of the surface cubic layer decreased with increasing degree of vacuum during the preparation of BaTiO3 nanoparticles. Thus, we confirmed that the surface structure was an important factor in determining the dielectric properties of BaTiO3 nanoparticles.
Park, C.,Kim, C.,Choi, Y.,Won, S.,Moriyoshi, Y. Pergamon Press ; Elsevier Science Ltd 2011 International journal of hydrogen energy Vol.36 No.5
Because blending hydrogen with natural gas can allow the mixture to burn leaner, reducing the emission of nitrogen oxide (NO<SUB>x</SUB>), hydrogen blended with natural gas (HCNG) is a viable alternative to pure fossil fuels because of the effective reduction in total pollutant emissions and the increased engine efficiency. In this research, the performance and emission characteristics of an 11-L heavy duty lean burn engine using HCNG were examined, and an optimization strategy for the control of excess air ratio and of spark advance timing was assessed, in consideration of combustion stability. The thermal efficiency increased with the hydrogen addition, allowing stable combustion under leaner operating conditions. The efficiency of NO<SUB>x</SUB> reduction is closely related to the excess air ratio of the mixture and to the spark advance timing. With the optimization of excess air ratio and spark advance timing, HCNG can effectively reduce NO<SUB>x</SUB> as much as 80%.