論文

Core shell particles comprise a core content and a coating shell of another material. The core shell structure can realize a new functional material that cannot be realized by a particle which has only a single composition. Wet chemical synthesis is commonly used in the fabrication of core–shell particles, but recently, some reports on flame aerosol synthesis of core-shell particles have been published. Flame aerosol synthesis can offer continuous one-step production process including high-temperature treatment, and results in high-purity fine crystalline particles. Therefore, it is expected that flame aerosol synthesis method for core-shell particles will be further developed in the future. In this paper, we explain the details of flame aerosol synthesis method for core-shell particles and give an interpretation of the physical processes.

© IMechE 2020. In order to improve thermal efficiency of spark ignition engine under super-lean burn conditions (excess air ratio (Formula presented.)), thermal stratification technique by in-cylinder water injection toward piston surface (stratified water insulated combustion architecture), in which low temperature water vapor layer is formed on the surface, is proposed. From the water spray visualization using the optically accessible engine, injected water is distributed near the piston top surface at ignition timing and thermal stratification can be achieved in the case that water injection timing (SOIw) is set at earlier stage of a compression stroke. In addition, heat flux on the piston surface measured at the same time is reduced by water injection. The 0.5-L single-cylinder engine test at λ = 2.0 at a constant ignition timing also shows that water injection at earlier stage of a compression stroke makes it possible to mitigate knock without significant increase in combustion instability. On the other hand, part of water is distributed near the spark plug at ignition timing with the water injection at SOIw = −60 °ATDC, resulting in unstable combustion. In addition, the engine test at λ = 2.0 and water/fuel ratio(W/F) = 18% shows that knock mitigation by water injection enables spark advance and following combustion enhancement. As a result, combustion period becomes short and cooling loss decreases, followed by the 1.0-pt improvement of gross indicated thermal efficiency. Moreover, the engine can be operated at minimum spark advance for best torque by increasing W/F up to 35%. Finally, stratified water insulated combustion architecture concept is applied at λ = 1.9 with a higher compression ratio of 17, showing that water injection at SOIw = −120 °ATDC and W/F = 50% enables minimum spark advance for best torque operation, and remarkably high gross indicated that thermal efficiency of 52.63% can be achieved with a sufficiently low knock level and coefficient of variation of indicated mean effective pressure.

The "Innovative Combustion Technology" program, a national project is established under the Cabinet Office, Government of Japan as a part of the" Cross-ministerial Strategic Innovation Promotion Program (SIP)". The "Gasoline Combustion Team" is one of teams of the "Innovative Combustion Technology" program.The "Gasoline Combustion Team" is comprised of Keio University as a Leader university and 29 universities as a Cluster university. Upon agreement with the Japan Science and Technology Agency (JST), we have been conducting the research on the "Super-Lean Burn for Gasoline Engines" with a support of the Research Association of Automotive Internal Combustion Engines (AICE) under the strong industry, academia and government collaboration.This paper introduces both scientific and technological approaches to innovative combustion technologies to realize the "Super- Lean Low Temperature Combustion", targeting a thermal efficiency of 50%.

Responses of stagnating laminar methane/air premixed flames under fuel concentration oscillation, i.c., equivalence ratio oscillation, were numerically investigated using a one-step overall reaction mechanism and a four-step reaction mechanism that included CO and H2 formation. The flame motion was numerically investigated for three different oscillation cases namely: lean, rich and lean-rich crossover case. Methane/air mixtures with sinusoidal equivalence ratio oscillations were issued from the burner exit with uniform 1.0 m/s velocity profiles. In the steady state condition, the one-step overall reaction mechanism and the four-step reaction mechanism had nearly the same characteristics in the lean region, while in the rich region variations in characteristics such as flame location and flame displacement speed for the four-step model were much more significant than those for one-step model. When the equivalence ratio was oscillated, the flame location oscillated. The amplitude of the flame location oscillation did not change with the equivalence ratio oscillation when the frequency of equivalence ratio oscillation was less than 8Hz, while it decreased monotonically when it exceeded 8 Hz. Here 8 Hz corresponds to a Strouhal number (St) of unity. Thus, this result indicates that the flame was in a quasi-steady state when St<1.0 while it became unstable when St>1.0. The variation in flame location and the flame displacement speed did not follow those for the steady state condition and made a limit cycles. This was due to the back support effect. The cycles were significantly inclined at higher frequencies. In the lean condition, the limit cycle was inclined similarly for both the one-step and four-step reaction mechanisms. In the rich condition, however, the limit cycle for the four-step reaction was more inclined than that for the one-step reaction. These results show that the formation of CO and H2 played an important role in the rich condition.

© Asia-Pacific Conference on Combustion, ASPACC 2019.All right reserved. Effect of surfactant, sodium dodecyl sulfate (SDS) on the methane hydrate combustion has been investigated experimentally. Water solution of 0-2300 ppm SDS and methane are used to form the methane hydrate with SDS. Methane hydrate of 30 g was placed in a petri dish with 100 mm inner diameter and 10mm depth. The upper surface is opened to the air and is flushed. The temperature at 1.5 mm below from the upper surface of the petri dish along the centerline was measured by a K-type thermocouple. The petri dish is placed in a vertical flow channel where the honeycomb is installed to stabilize the upward flow due to the natural convection by combustion. When the temperature reaches the ignition temperature, the hydrate is ignited at the center by a pilot burner. The flame motion is recorded by a high-speed video camera with 125 fps and the temperature data from the thermocouple is stored in a data logger. In the case of the methane hydrate with SDS, a large amount of soapy bubble was formed shortly after the ignition over the hydrate surface. The bubbles decrease the heat from the flame to the hydrate surface and then the flame is weakened and extinguished faster than the pure methane hydrate. The bubbles stifle to form an anomalous preservation zone and then the distinct decrease in the flame propagation speed is not observed.

This paper describes the ignition and early flame propagation in a high-tumble SI IC engine under super lean-burn condition (excess air ratio (λ) of 2.0). To elucidate the detail process, a high-tumble optically-accessible SI IC engine operating at super lean and stoichiometric conditions were diagnosed by time-resolved OH-PLIF measurements. The engine was operated 2000 rpm with a port fuel injection of isooctane. The cross-sectional imaging of OH distribution was achieved at 12 kHz resulting in a temporal resolution of 1° crank angle at 2000 rpm. The results show that the OH radical is generated without any heat release by the spark discharge during approximately 15 ° crank angle after ignition timing in the super-lean condition. The OH distribution of these crank angles are scatted into small islandlike areas, and then subsequent flame propagation occurs.

Accurate and reliable temperature measurements are crucial to improve the thermal efficiency and optimize the design of products because temperature is an important parameter to understand heat conduction, convention, radiation, and chemical reactions. The emission properties of phosphors are sensitive to temperature, hence, phosphor thermometry can make remote temperature sensing. Accordingly, phosphor thermometry has received considerable attention as a versatile alternative to conventional temperature measurement techniques. This article describes the principles and fundamental aspects of phosphor thermometry, that is, principles of luminescence, temperature dependences of luminescence characteristics and how to use those dependence characteristics such as life time method and spectral intensity ratio method.

Flame height variations of a laminar stagnating premixed flame with gas component transition between fuel mixture A (methane:92%, ethane:6.7%, propane:1.3%) and B(methane:84%, ethane:13.3%, propane:2.7%), and between A and C (methane:76%, ethane:20.0%, propane:4.0%) are discussed. The estimation of the flame speed and the flame temperature of fuel mixtures A, B and C by the Chemkin-Pro show almost the same values for all fuel mixtures. In experiments, the transition between A and B and between A and C were performed. The transition time changes from 1 s to 10 s, keeping flow velocity and equivalence ratio constant at 0.8 m/s and 0.7 respectively. The flame position was measured by using images taken by a high speed camera with 125 fps. Two transition patterns are examined, keeping the total flow rate of premixed mixture constant. One is the constant flow rate transition, which changes the gas component, keeping the fuel mixture flow rate constant. The other is the constant equivalence ratio transition, keeping the equivalence ratio constant. In the case of the constant flow rate transition, the equivalence ratio changes which results in the variation in the flame speed, the flame temperature and the flame height. It means that the combustion state changes with the transition. On the other hand, in the case of the constant equivalence ratio transition, the flame speed, the flame temperature and the flame height keep almost the same state, which means that the gas component can be changed, keeping the combustion state the same.

Responses of premixed laminar Bunsen flame to transient change in fuel gas composition has been investigated experimentally. Mixture of methane, ethane, and propane is used as a model of natural gas. The volumetric fraction of methane was varied from 92 % to 76 % by 4 %, keeping ethane/propane ratio 5 constant. Transition time of the fuel composition was changed from 1 to 20 sec. The flow velocity at the exit of the burner was 0.8 m/s. The distance between the fuel mixing point and the air and fuel mixing point L was changed from 0 to 1500 mm. A flame motion was recorded by a high speed video camera at 60 fps, and variation of the flame height was measured The flame height temporarily exceeded or fell below the steady flame height during the transition even though the equivalence ratio of mixture before and after the transition set the same. When a density meter was set in the flow channel to detect the fuel composition variation, the temporary flame height be suppressed.

In order to improve thermal efficiency of automobile engine, it is necessary to reduce the cooling loss. A method for analyzing local cooling loss (heat flux) using coaxial type thin film temperature sensor has been developed. Recently, results of heat flux analysis using the sensor composed of thermocouple materials standardized based on ANSI and JIS have been reported, but structure and measurement accuracy of its sensor are not clear enough. In this study, the measurement accuracy of sensor A composed of K type materials and sensor B whose body is combustion chamber material (aluminum alloy) was compared using numerical analysis (two-dimensional coordinate heat conduction equation when the sensor is embedded in combustion chamber). As a result, it was important to use same material as combustion chamber for sensor body to measure wall surface instantaneous temperature with high accuracy. Additionally, results of one-dimensional (axial direction) heat flux analysis when the material of the combustion chamber and the material of the sensor body are different had error, it was considered to effect of heat flow (temperature difference) in radial direction due to different thermal conductivity. Therefore, it was confirmed that newly proposed two-dimensional heat flux analysis method using temperature distribution in axial and radial direction can analyze more accurately than one-dimension. These numerical analysis results showed same tendency as measured verifications results.