Tatsuro Tsukamoto

Characterization of Asian dust and Siberian smoke with multi- wavelength Raman lidar over Tokyo, Japan in spring 2003

[1] In the spring of 2003, we observed lofted Asian dust and Siberian forest-fire smoke plumes in the free troposphere over Tokyo, Japan with a dual-wavelength Raman lidar. These data show clear signatures of the optical characteristics depending on the aerosol type. The Asiandust layer shows that the particle depolarization ratio (PDR) at 532 nm is 20%, and the extinction-to-backscatter ratio (lidar ratio) at 355 nm is 49 sr, which is close to 43 sr measured at 532 nm. On the contrary, the smoke layers show that the PDR is as small as 5–8% or less, and the lidar ratio at 355 nm is 40 sr, which is considerably lower than 65 sr which was measured at 532 nm. We also applied an inversion algorithm for the smoke case. The effective radius was 0.22 mm and the single-scattering albedo at 532 nm was 0.95. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0368 Atmospheric Composition and Structure: Troposphere— constituent transport and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques.

Ignition of blended-fuel droplet in high-temperature atmosphere

Ignition time of a suspended fuel droplet is obtained experimentally with high ambient temperature. A stationary fuel droplet suspended by a fine silica fiber is taken into a furnace moving on rail and is quickly exposed to high ambient temperature. Blended fuels of n-heptane and n-hexadecane are used, and the effects of fuel mixture ratio, initial droplet diameter, and ambient air temperature on ignition time are observed. For pure hexadecane droplets, ignition time increases with the increase in initial droplet diameter. On the other hand, it decreases for pure heptane, especially under lower ambient temperatures. For the case of mixed fuel, the variation of ignition time with the initial droplet diameter has a characteristic feature, namely the results show that an initial droplet diameter exists at which the ignition time has the maximum value and that this diameter increases with a decrease of the heptane concentration or the ambient temperature. The maximum ignition time is also confirmed by the combination of ethylalcohol and decylalcohol.

Mechanism of flame kernel formation produced by short duration sparks

With reference to flame kernel developments in spark ignition of combustible mixtures, the formation process of hot kernels produced by short duration sparks (less than 0.3 μs) in an inert gas is modeled by using a set of partial differential equations with unsteady and two-dimensional cyclindrical coordinates. These equations are solved numerically. The results show that the gas flow pattern governs the kernel configuration and that the kernel shape has some characterized features such as a torus, a torus with a groove and a nontoroidal shape. The simulated results are successfully verified by optical measurements.

Analysis of ignition mechanism of combustible mixtures by composite sparks

Abstract Formation process of flame kernels produced by composite sparks in a quiescent propane-air mixture is numerically simulated by using a set of partial differential equations on two-dimensional cylindrical coordinates. Simulation is done with emphasis on physical effects such as gas movements generated by spark discharge and heat transfer from the flame kernel to spark electrode surfaces. Although chemical reaction is considered only by an overall reaction, the present simulation is found to be useful for understanding of physical effects in the following points: the flow pattern near spark gaps is an important factor that governs the flame kernel structure, the flow pattern is affected by the spark electrode diameter, gap width, and spark duration, and the calculated variation in the minimum ignition energy agrees qualitatively with the experimental variation, and the existence of the optimum spark duration is well confirmed. As for composite sparks, it is found that the superiority in ignition ability of composite sparks over capacitance sparks depends on spark electrode diameter and gap width.

Diffusion-flame extinction of liquid fuel at elevated pressures

Abstract The objective of this study is to determine the effect of pressure on droplet size at extinction of the diffusion flame around the droplet. An analogy between the diffusion flame in a stagnation-point flow on a liquid fuel and that of a droplet is given, and an analytical equation is obtained for the relationship between both diffusion flame extinctions. This equation makes it possible to calculate droplet diameter ( d c ) at extinction without any chemical parameters. In order to obtain extinction velocities, experiments are conducted for the diffusion flame in a stagnation-point flow at elevated pressures. The extinction velocity increases with pressure, but it becomes almost constant at pressures from about 0.3 to 1 MPa. From these data, it is found that the droplet diameter at extinction decreases sharply with pressure: d c = 150 μ m at 0.1 MPa, 46 μm at 0.3 MPa, and 17 μm at 0.8 MPa for heptane in an air environment.

Numerical study on flame propagation of a fuel droplet array in a high-temperature environment under microgravity

A series of numerical simulations was conducted to observe the flame propagation of a fuel droplet array in a high-temperature environment and revealed details of the propagation process. Based on theoretical considerations, various modes of flame propagation were predicted for characteristic parameters that represented the kind of fuel, droplet spacing S , droplet diameter d , and ambient temperature. In the present study, droplet spacing was employed as a control parameter to investigate the effect of time scales among the heat transfer to an unburned droplet, formation of flammable premixed gas, and ignition of premixed gas. A fuel droplet was assumed to be decane with 1 mm initial diameter. The initial ambient temperature was set at 573 K, which was lower than the autoignited temperature of decane. When the spacing was small, the flame front went straight in the premixed gas layer formed at the outer region of a droplet array. When the spacing was relatively large, the flame front traveled through the premixed gas layer between droplets. When spacing was large, the unburned droplet ahead of the flame front was ignited before the front expanded to the premixed layer of the unburned droplet. The ignited region was immediately combined with the propagating flame. Hence, this process was considered as intermediate between premixed propagation and propagation with discontinuous ignition. Also, the trend of flame propagation rate versus S/d was in agreement with the trend of experimental results obtained at room temperature.

Monitoring of the atmospheric boundary layer with lidar, sun photometers, and filter sampling in Tokyo

Since the winter of 1995, we have routinely performed combined measurements with polarization lidar, sun-photometer, and filter-sampling. Such a so-called closer experiment is necessary and useful to cope with the variety of boundary- layer aerosols. The aims of the observation are as follows: (1) study of the dynamics of the atmospheric boundary layer (ABL) by lidar, (2) use of depolarization ratio measurement for the study of the ABL and the characterization of aerosols, (3) to clarify the relationship between depolarization ratio and chemical component of the aerosol in the ABL, (4) comparison between the optical thicknesses derived from the lidar and the sun-photometer measurements, (5) diurnal and seasonal changes of the above items, etc. We will present an overview of the study until now.

Particulate Emissions From a Two-Stroke Marine Diesel Engine Operated With Heavy Fuel Oil

In these years, a problem of air pollution in a global scale becomes a matter of great concern. In such social situation, diesel engines are strongly required to reduce the NOx and particulate emission in the exhaust gas. In this paper, measurements of particulate emissions from a low speed two-stroke marine diesel engine were conducted with several kinds of diesel oil and a heavy fuel oil, to know the characteristics of particulate emissions at the present situation. The effects of engine load and sulfur content of the fuel on the particulate emission have been examined. The particulate emission from the test engine was measured by partial-flow dilution tunnel system, and particulate matter collected on the filter was divided into four components, SOF (soluble organic fraction), sulfate, bound water and dry soot, by Soxlet extraction and ion chromatograph. Results show that the particulate emission from the test engine operated with heavy fuel oil is three times as much as the value with diesel oil and that not only sulfate but SOF and dry soot concentration increase with the increase in fuel sulfur content. It is also found that the conversion rate from sulfur in fuel into sulfate in particulate matter is nearly independent of the sulfur content in the fuel and increases with the increase in the engine load.Copyright

Numerical Simulation of Laminar Flame Propagation in Constant Volume Vessels

Recently, computer technology has advanced to a point, where it is possible to numerically simulated combustion phenomena in the spark ignition engine [1,2], though some numerical difficulties still exist [3]. Such simulation provides a deep understanding of the phenomena and thus offers useful suggestions for engine designers creating new engines of high efficiency and low pollutant emission [4].

Characteristics of Particulate Emission from Two-stroke Marine Diesel Engine

The carbonaceous particulate or soot emission from diesel engines has become one of serious environmental problems in the world. There is no regulation on particulate emission from marine diesel engine at present. In the present report, experimental investigation was conducted with a two-stroke marine diesel engine to know the characteristics of particulate emission. Concentration of particulate emission was measured by three kinds of method, such as direct sampling method, partial-flow dilution tunnel method and Bosch type smoke meter method. The effects of engine load ratio and cylinder oil feed rate have been examined. The experimental results show that the particulate concentration measured by the dilution tunnel method increases with an increase in cylinder oil feed rate. The data points obtained by the direct sampling method and the smoke meter are somewhat scattered and the general tendency is not evident within the limits of this experiment.