In order to investigate the combustion behavior of premixed-spray flames, time-series measurements have been conducted using optical diagnosis techniques that have highly spatial and temporal resolution such PDA, a high-speed camera with laser visualization, a Cassegrain optical probe system. By processing obtained data in these measurements statistically, the detailed structure of premixed-spray flames could be observed. However, they are still not enough to explain the cause of the rapid disappearance of premixed spray named "preferential flame propagation". This paper introduces some of these results and our recent experiments to approach more detailed combustion behavior of spray flames.

View full abstract

The new NOx reduction method, "Expansive Vertical Vortex Combustion (EVVC)" was suggested as follows. A combustion expansive flow developed along the piston bowl can form a strong vertical vortex. This vortex can mix hot burned gas into the cold excess air existing in the center of the piston bowl, which gets burned gas cool rapidly. Therefore, it is possible to reduce NOx which would be produced if burned gas remained hot. In this paper the EVVC effect was verified by CFD analyses and experiments on a 4-cilinder 2.0-liter direct injection diesel engine. As a result, it was found that the EVVC was an effective method, because the stronger vertex could reduce NOx by over 20% without worsening smoke and thermal efficiency.

View full abstract

Tumble Generation Valve (TGV) is possible to improve combustion stability under lean condition by inclining the tumble rotating axis. This was discussed in the authors' previous works (1-2). TGV can also reduce the level of unburned hydrocarbons produced during a cold start significantly. It seems to play a role in permitting only small fuel droplets to flow into a cylinder, so that the evaporation process increases. Authors named this phenomenon "Preferential Fuel Component Dynamics". Additionally, TGV can reduce the amount of fuel required for the engine to start.

View full abstract

Spray characteristics of hypergolic propellant injected by impingement nozzles have been investigated under combusting conditions, in order to clarify the difference of the atomization characteristics between non-reactive and reactive liquid. The atomization process was visualized by a laser sheet and a high-speed camera, and the droplet size distributions were calculated from the scattering intensity. Compared with non-reactive flow, the atomization process of reactive flow is accelerated by the immediate ignition of the hypergolic propellant. The mean droplet diameter of reacting flow is much smaller than that of non-reacting flow. The variation of the mean droplet diameter can be approximated to a function of Weber number based on the linear stability theory, although the empirical coefficients are significantly different.

View full abstract

In the cylinder, combustion stages of fuel vaporization, air fuel mixing, low-temperature oxidation, thermal ignition, reactions toward thermal equilibrium, and bum-up of products, proceed at different timings and rates in local areas. As a result, products in these stages exist at the same time. In the enclosed field filled with a lot of eddies, products in one stage can be mixed with those in other stages. When it is now that thermal ignition is triggered, low-temperature oxidation was in the past, and soot will be in future. In this sense, products at a moment can be mixed with those in the past or future. This mechanism of mixing, dubbed time-domain mixing, is considered essential for describing combustion in the cylinder. For ignition control as new approach to in-cylinder combustion control, it is important to understand influence of time-domain mixing on low-temperature oxidation. Modeling with detailed kinetics of dimethyl ether shows that CH2O entrained by time-domain mixing, acts as an OH scavenger in the initial stage of low-temperature oxidation, or as a thermal-ignition retardant.

View full abstract

Drying process of porous media was analyzed by using experimental visualization of water distribution. The distribution of the moisture content in the drying process can be observed as an image. It is found that the experimental imaging enable us to examine the characteristics of drying phenomenon inside the porous media.

View full abstract

Warm air drying is a popular method in the drying of marine products. However, the warm air drying method need a long drying time, and the quality of a drying product is poor. This has been a technical subject. Then, the purpose of this study is exploring the effective drying method for seafood. We conducted the warm air drying experiment using the scallop and investigated the heat and mass transfer mechanism. It is found that the morphological change of the muscular fiber has an important role in the drying process.

View full abstract

Thermally-developing and fully-developed turbulent flow forced convection in cylindrical packed beds heated at constant wall temperatures are numerically studied. The macroscopic momentum equation considers the effects of turbulence and hydrodynamic dispersion in addition to Darcy-Brinkman-Forchheimer flow resistances, while the effects of thermal radiation, turbulence and thermal dispersion are taken into account in the energy equation. It is found that the coupled hydrodynamic dispersion and turbulence term in the momentum equation affects the pressure gradients in packed beds and that the agreement between the theoretical results of temperature profiles and heat transfer characteristics accounting for thermal radiation and the experimental ones is excellent

View full abstract

An estimation method of the plane directional thermal conductivity of fibrous insulation using both the cyclic heat and transient hot-wire methods is proposed. Namely, the thermal conductivity in the direction of the plane λ_x is shown to be equal toλ_h^2/λ_y, whereλ_y andλ_h are the thermal conductivities in the direction of the thickness and measured using transient hot-wire method, respectively. In this paper, thermal conductivities of rockwool (ρ=76 and 121kg/m^3) are measured in the temperature range 100℃ to 600℃ using the transient hot-wire estimated values onλ_x, it is confirmed that the present simple method can estimate the measured values fairly well even in the case of different bulk density of the same kind of specimen.

View full abstract

Three main kinds of irreversibilities exist in SOFC due to the presence of porous electrodes and electrolyte. Those are concentration overpotential, ohmic overpotential and activation overpotential. Appropriate overpotential model is a fatal factor for the successful modeling of electrical performance, heat and mass transfer of SOFC. In this paper three different activation overpotential models have been compared for tubular SOFC simulation. The results of current density, output power and the temperature distribution within a tubular SOFC unit are discussed in detail.

View full abstract

This paper describes experimental research on two-phase flow of supercritical CO_2 and water in a porous medium. We used a magnetic resonance imaging (MRI) technique to directly visualize the distribution of supercritical CO_2 injected into a packed bed of glass beads containing water. After the CO_2 displaced much of the water, about 20% of water remained in the porous medium under the condition at the depth of 1000m. Supercritical CO_2 moves upward swiftly due to buoyancy.

View full abstract

We carried out the simulating experiments of Carbon Dioxide (CO_2) ocean storage with a large high-pressure tank to measure pH change caused by the dissolution of CO_2 from CO_2 drops covered with CO_2 hydrate films. The CO_2 drops were stored at 30MPa, 3 to 6℃ and 8 to 12℃ for 2 days. The experimental results showed the lowering of pH for both temperature regions, then, the experiment at lower temperatures provided smaller pH change than that at higher temperatures. The difference of pH change between these temperature regions agreed with the temperature dependency in the solubility of CO_2 hydrate.

View full abstract

In this article, we employ a recently introduced numerical technique, known as lattice Boltzmann method (LBM), to numerically simulate immiscible two-phase flow in microscopic models of porous media. This model takes into account the ratio of (dynamic) viscosity, density, interfacial tension, and wettability, . The two-phase flows of supercritical CO_2 and water in a straight channel with a lot of hexagonal cylinders (imitation porous media) were simulated numerically to show the effect of (dynamic) viscosity ratio on the permeability of porous media. The imbibition of wettable liquid into porous media driven by capillary pressure can be simulated successfully.

View full abstract

The distribution and mass transfer of alcohols in water-hydrocarbon interface were studied. Molecular dynamics method was used for this study. We used octane as hydrocarbon and heptanol as alcohol. The position, speed, and potential energy of molecules can be found from this simulation, and various kinds of physical-properties are calculated from these. In low heptanol concentration, heptanol makes a monomolecular layer to water and octane interface. In high heptanol concentration, heptanol that cannot finish going into a monomolecular layer forms clusters in octane layer. Absorption rate of heptanol to water-hydrocarbon interface has peak in modicum heptanol concentration when octane concentration is low. But this peak is diminished when octane concentration is high.

View full abstract

Temperature distribution and mixing rate of materials were numerically investigated during Friction Stir Welding by changing rotation speed, thermal conductivity of material, location of tool, and circular flow velocity. Temperature at advancing side is higher than that at retreating side. The temperature difference is largest when rotation speed of a tool is 300rpm. Circular flow in radial cross section is a key parameter to mix of materials and to avoid causing void defects.

View full abstract

The effect of heat loss on the instability of premixed flames is studied by two-dimensional, unsteady calculations of reactive flows. To obtain the relation between the growth rate and the wave number, i.e., the dispersion relation, a sufficiently small disturbance is superimposed on a planar flame. The superimposed disturbance grows exponentially with time, which is consistent with the prediction of linear analyses. To study the unstable behavior of cellular flames, the disturbance with the linearly most unstable wave number, i.e., the critical wave number, is superimposed. The superimposed disturbance evolves, and the cellular-flame front is formed, owing to intrinsic instability. As the heat loss becomes larger, the cell depth increases and the behavior of cellular flames becomes unstable.

View full abstract

New idea of a distributed temperature measurement, where many isolated temperature sensors can freely move in some objective area getting their locational informations and sending them to a host terminal, will be proposed in this study. As a first step to demonstrate this idea, temperature measurement experiment in some area inside Kyoto city has been conducted using a set of existing portable sensors, compact thermistor-type temperature sensor and a handy-type GPS (Global Positioning System) receiver. Both equipments have no sending function but can sequentially save their data inside their memories. Five persons, each having one set of them as so called a sensor, walked or rode bicycles inside the objective area. Although the obtained data were processed after they were transported to a personal computer, each equipment worked well and the obtained tempearure distributions can rationally be understood. Thus, it was demonstrated that the present measuring method is appricable to the temperature analysis etc. in the city area.

View full abstract

Innovative regenerative combustion technology has been developed in Japan over the past decade and has been applied to industrial furnaces so far like steel mills, heat treatment and non-ferrous melting fields. Typical advantages for the regenerative combustion system compared with conventional combustion and heat recovering system are higher energy saving rate, low NOx and uniform heating capabilities. In the regenerative system, Nippon Furnace Kogyo has succeeded to accomplish both an ultimate waist heat recovery rate of over 80% by adopting ceramic honeycomb as a regenerator and to reduce NOx emission to around 1/3 compared with conventional burner system by using ultra low NOx firing mechanism developed in consideration of High Temperature Air Combustion where preheated air temperature will be over 1000℃. These advantageous results has been arousing further needs for such high performance industrial furnaces as non-oxidized furnaces and hydrogen reformer as examples, so that these application have been commercialized successfully.

View full abstract

High temperature air combustion is one of the promising technologies for its high effective and low pollutant tendency. Many studies have been made on its fundamental behavior especially on NOx emission. It has been showed that low-NOx tendency in high temperature air combustion can be achieved by the flame with high lift and high radiation. As its advantages confirmed, this technology has been applied to high performance industrial furnaces, non-oxidizing heating furnace and exhaust gas deodorization facilities. Recently, new project to use this new technology for solid fuels like pulverized coal and municipal solid wastes has been started. It has been revealed that same low-NOx tendency can be achieved even for the fuel NOx. This paper represents some basic studies on the fundamentals of high temperature air combustion, investigation on application of this new technology to industrial furnaces and gas deodorization process, and also recent studies to adopt this technology for pulverized coal and municipal solid waste combustion.

View full abstract

High-Temperature Air Combustion Technology is an attractive method for producing surplus electric power and reducing environmental disruption materials such as NOx and dioxins especially in combustion process of Municipal Solid Waste (MSW) incinerator. The objective is to develop an energy-saving system for the MSW incinerator and to lower the emission pollutants. The experimental study is carried out systematically with simulated MSW furnaces (500kg-waste/h and commercial plant) to study the thermal degradation and the distributions of temperature and gas concentrations in the furnaces. Blowing the mixture of high temperature air and the flue gas to the primary combustion space brings extremely stable combustion. Moreover, it reduces not only the NOx, CO and the other toxic products, but also more than 20% of the excess air.

View full abstract

In 1999,a national project on the development of an advanced Steam Reformer was indicated. The project's objective is to break through design constraints experienced on conventional Steam Reformer for Hydrogen, Methanol, GTL, DME, Ammonia and other synthesis Gas Plants. This paper describes major results of the project up to August 2003.

View full abstract

According to high level needs such as environmental conservation, simple operation and maintenance, and low cost, importance is increasing more rapidly in recent years in developing a combustion system technology for thermal power stations. One of the reasons is diversity of fuels, i.e., wide range of coal properties and low grade of oil etc.. Hitachi group is trying to raise the technology to correspond to them. This paper describes a compact ring-roller mill with 25% lower mill height and with 30% higher grinding capacity by high grinding energy and high efficient classifier for coal combustion, and the Hitachi low NOx burners with a concept of DeNOx in flame for coal, oil, and gas combustion.

View full abstract

Development of the integrated gasification combined cycle power generation of various gasifying methods has been preceded in the world. The gasified fuels are chiefly characterized by the gasifying agent and the synthetic gas clean-up method, and divided roughly into four types. The calorific value of gasified fuel differs according to the type of gasification agent. On the other hand, to improve the thermal efficiency, it is necessary to use a hot/dry type synthetic gas clean-up, but ammonia originated from nitrogenous compounds in coal is not removed. And then it forms fuel-NOx. For these reasons, the combustion technology for each gasified fuel is important. In this paper, we reviews our developments of the gas turbine combustors for the gasified fuels of three types through numerical analyses, experiments using a small burner and the designed combustors.

View full abstract

A tubular flame can be established in a rotating, axisymmetric, stretched flow field. This flame consists of an inner region of hot burned gas and an outer region of cold unburned gas, between which exists a thin reaction zone of tubular shape. Due to its symmetrical temperature distribution, an almost adiabatic condition can be achieved. In addition, the flame is aerodynamically stable for rotational motion. Thus, the tubular flame has potentialities for practical combustor. This paper reports a recent progress of the tubular flame burner; establishment of a uniform, large-area flame and of very safe, rapid mixing type combustion free from flame flash-back. Various kinds of fuels such as methane, propane, kerosene, heavy-oil, and also blast furnace gas of low caloric value can be burned in tubular flame burners.

View full abstract

In order to make efficient use of energy resources, optimum design and development of new combustors are extremely important. In particular, emission and energy efficiencies are becoming very important considerations. A heating system incorporating a newly developed combustor was used to supply warm air and moisture to the control atmosphere in a greenhouse. We developed a high-performance combustor (80-kw type) which makes use of fuel-air counter flow. We confirmed experimentally that the combustor provided an 17% reduction in fuel cost, as compared to the current fuel-air conical supply combustor. NO_x composition measured in the flue gas was as small as 6ppm. The counter airflow nozzle design method is discussed herein.

View full abstract

Fill-factors of flame on Yamazaki's method wee calculated from exit-gas temperature of boiler-furnaces on combustion with air and oxygen, fill-factors of flame with air were nearly equal with previous data and fill-factors of flame with oxygen were reasonable values because reduce with oxygen-density. Therefore, heat-calculation of boiler-furnace with oxygen becomes be enable by using these fill-factors.

View full abstract

Turbulent burning velocity characteristics of hydrogen mixtures with having the same laminar burning velocity are investigated experimentally in the present study, where the laminar burning velocity S_<L0> and the equivalence ratio Φ are varied extensively. The measured turbulent burning velocity at the same turbulence intensity shows to increase as Φ decreases, regardless of S_<L0>. That, however, becomes to depend on the characteristics chemical time when Φ is as low as around 1.0. This phenomenon is discussed by the estimated mean local burning velocity taking account of the preferential diffusion effect and the obtained turbulent flame images.

View full abstract