Yuji Nakamura

Verified

Yuji verified their affiliation via an institutional email.

Learn more

Verified

Yuji verified their affiliation via an institutional email.

Learn more

• Dr. Eng.
• Professor (Full) at Toyohashi University of Technology

In this study, a kerosene-fueled premixed burner system with a thick and large pore-sized ("coarse") porous matrix was developed to achieve less-soot stable premixed combustion with variable combustion loads, i.e., turn-down ratio, TDR, defined as the ratio between the maximum and minimum loads. The present burner system mainly consists of the thic...

An experimental study was made on burning velocity in powder-gas hybrid combustion in order to investigate the determination factor to alter the burning velocity caused by the addition of power in the premixed gas. A burner system was newly developed to visualize the dynamic flame behavior originally stabilized in a stagnation point flow field. Usi...

Evaluating thermal damage of a combustible material, caused by feedback heat fluxes exposed directly below a burning matter, plays essential role in a fundamental study for fire suppression. In this study, we proposed a small wooden crib as a small heat source model, applicable to the lab-scale fire testing. The small crib which measures 100 mm (le...

The fundamentals of inverse droplet combustion for a single droplet of 90 wt.% of hydrogen peroxide (H2O2) suspended in a quiescent nitrogen-balanced methane atmosphere were studied under various ambient mole fractions of methane from 0.55 to 1 at standard conditions (298 K and 0.1 MPa in absolute). Burning behavior of the droplet was recorded with...

This paper provides a feasible way to suppress flame flickering under normal gravity and atmospheric pressure without changing the fuel mass burning rate, thus promoting steady-state combustion. By periodically reciprocating one burner horizontally in a dual burner system, a death mode (namely, amplitude death of flame height oscillation) is genera...

The authors are a team of fire whirl researchers who have been actively studying whirls and large-scale wildland fires by directly observing them through fire-fighting efforts and applying theory, scale modeling, and numerical simulations in fire research. This multidisciplinary research-background team previously conducted scale model experiments...

A striking feature of fire whirls is that they tend to have higher mean flame heights than free buoyant pool fires at the same heat release rates, which has been extensively studied in the past. Different from the mean flame height, the instantaneous flame height of a fire whirl reflects its dynamic nature in time domain, but has received less atte...

This study aims to elucidate the scaling law to provide the critical condition on appearance of the downwash pattern of the hot smoke ejected from a chimney in a turbulent cross flow. A specially designed wind tunnel with an active turbulence generator developed by Makita was adopted to offer a quasi-isotropic turbulence field in a lab-scale test f...

The effect of the internal angle on downward flame spread over a thick folded plate is experimentally investigated in this study. The lateral side of a thermoplastic plate is cut at desired angles and two of these plates are welded to form a single folded sample. All the faces other than the front and two 5-mm areas of the front face from each side...

The combustion structure of a "hybrid fuel", as a mixture of combustible gas and combustible solids (in powder form) was studied experimentally. A combustible fine powder was introduced into the rich-premixed flame. The results showed that the powder underwent high-temperature pyrolysis in the region sandwiched by inner and outer flames to accompli...

Observation of the deformation process of a thermoplastic rod is important because the burning behavior depends on the instantaneous shape. However, the observation is often difficult because the rod, particularly its top, is hidden by the flame. This study proposes a novel imaging technique that visualizes the deformation process of the burning ro...

The Hifukusho-ato fire whirl (HAFW) is a catastrophic fire accident in Tokyo in 1923 and a representative fire whirl phenomenon that occurs over the non-fuel zone around an L-shaped fire source. Previous studies have mainly focused on fire whirls above fire sources, while very limited work reported the HAFW-type fire whirls, which were found to be...

This study aims to study the hot-smoke dispersion behavior ejected from a chimney in a turbulent cross flow experimentally using a lab-scale wind tunnel, which can generate quasi-isotropic turbulence. An active turbulence generator developed by Makita was installed for this purpose. A heated jet with smoke is issued into the cross flow from the ver...

In this work, numerical investigations of burning characteristics of a specimen consisting of polyethylene foam soaked in hydrogen peroxide diluted with water are made. A one-dimensional burning model developed in our previous work is used to predict total mass flux and pressure exponents as a function of fuel porosity, concentration of hydrogen pe...

This study aims to investigate the hot-smoke dispersion behavior released from a chimney in a cross flow experimentally using specially designed wind tunnel. An artificially obtained quasi-isotropic turbulence was generated using an active turbulence generator developed by Makita. A heated jet and an unheated jet with smoke are injected into the cr...

The ability to achieve the optimum design based on specifications is a skill that should be trained in mechanical engineering education. We have developed an engineering educational scheme for designing, creating, and evaluating via the spontaneous participation of students themselves. The most significant feature is to provide experiences such as...

Influence of fiber structure on flame extinction of cellulose materials has been investigated varying oxygen concentration. Filter paper and Washi (Japanese paper) were used as the samples with fiber structure, whereas bacterial cellulose was used as the sample without fiber structure. Thermogravimetric analysis reveals that char production in pyro...

Wire mesh is a useful structural material for combustors, which has the thermal effect of quenching, holding or enhancing a flame. Previous researches mainly focused on the interaction between premixed flame and wire mesh in confined/semi-confined pipes, and the mesh, in addition to the thermal effect on flames, also induced a dynamic resistance to...

With an increasing awareness of environmental concerns (e.g., ozone depletion, acid rain, etc.), “green” propellants replacing into AP-based (ammonium perchlorate, chlorin-origin gunpowder) solid propellants have been of a great interest for sustainable developments [1][2]. In order to reach this goal, explosive, yet stable burning with low-harmful...

Heat flux sensor based on active control of temperature by a thermoelectric module is expected to be a promising instrument for convection-dominated fire tests because it can electrically adjust the temperature to its surrounding and thus enables to reduce systematic measurement error due to installation. Although the idea has already been proposed...

抄録 Experimental investigations of burning characteristics of a tested specimen consisting of a polyethylene foam soaked in 100 wt% hydrogen peroxide are made. All experiments are carried out in a large volume chamber, which newly introduced in our previous work at an initial pressure range from p = 0.1 to p = 0.35 MPa in absolute with various fuel...

Acoustic wave can destabilize the flame and has a potential in firefighting, but the influences of the sound source and its frequency are still poorly understood. This work applies a loudspeaker to extinguish a laminar diffusion propane flame of 5-25 mm high, where the local sound frequency is 50-70 Hz and sound pressure is 0.8-3.2 Pa (92.0-104.1 d...

In this study, we experimentally investigate the successive-burning characteristics of a porous combustible soaked in a liquid oxidizer. Polyethylene foam soaked in hydrogen peroxide is packed in a vertically oriented quartz tube that is considered as a tested combustor in this work. Following forced ignition at the top surface, a successive (stead...

This study numerically investigates the effect of dripping on the ignitability of a vertically-oriented thermoplastic material subjected to localized radiant heating within a 2D domain. Thermoplastic material is modeled as a phase-change material with the prescribed solidification/melting temperature, and its rate of gasification (pyrolysis) proces...

This paper reports experimentally observed characteristics of smoldering and flaming spread along a cellulosic combustible solid. A thin cylindrical sample was burned in a forced oxidizer flow, and quasi-steady, downward opposed-flow spread was observed. The oxidizer velocity and the oxygen concentration were varied, and the spread velocity and the...

Source of error in measurement of heat flux sensor using a Peltier module (PHFS) was experimentally and numerically investigated. A series of measurement tests using a cone heater was carried out. It is confirmed that the estimated heat flux was overestimated when the temperature difference within the module was not zero. It is suggested the excess...

This study presents the effective thermal design concept of exothermic Sabatier reactor, which shall convert carbon dioxide with hydrogen to produce water and methane (so-called “methanation”) assisted by the catalytic activity. Pellet type of Ru-based catalyst is packed in the preheated reactor tube and stoichiometric reactant gas mixture (CO2 and...

The effects of the traveling sound wave generated by the speaker on diffusion flame were investigated experimentally. The sound frequency was varied from 50 to 1000 Hz using two sizes of loudspeakers, whose peak frequency showing the maximum sound pressure amplitude is nearly identical. A spirit lamp was used as the reference (diffusion) flame. Hav...

This work presents an investigation, both experimentally and numerically, of the similarity of the periodic dynamic behavior of buoyant jet-flames. A single buoyant jet-flame exhibits two well-known types of dynamic behavior, namely, axisymmetric (varicose mode) and asymmetric (sinuous mode) motions, whereas the interaction of two adjacent buoyant...

The transition from downwardly (reverse) smoldering to flaming in a low-pressure environment during combustion of a thin-rod biomass stick with low porosity (high density and low permeability) was experimentally investigated to determine the dominant factor affecting the critical condition of this transition. After forced ignition at the top of the...

This paper presents an experimental and theoretical study on limit conditions for smoldering combustion of biomass fuel. A fuel rod was burned in an oxidizer flow in a Tsuji-Yamaoka type, counterflow configuration, and the spread rate and temperature distribution were measured. The spread rate and maximum temperature increased with an increase in o...

The propagation of a glowing combustion front in a packed bed of activated carbon (AC) particles was investigated with particular attention to the role of gas phase oxidation of carbon monoxide (CO). The AC particles were loosely packed in a cylindrical quartz column. A N2/O2 mixture of varying O2 concentration flowed through the bed from the botto...

The dynamic behavior, especially in the transition to oscillation mode (in-phase and anti-phase), of two interacting non-premixed methane-air jet flames was investigated experimentally. A well-controllable experimental system for the present purpose was constructed and key parameters; such as fuel flowrate (Q), burner diameter (d), and burner separ...

The original version of this article unfortunately contained an error in Table 1 and text under Sect. 3.3.

Electrical wires and cables have been identified as a potential source of fire in residential buildings, nuclear power plants, aircraft, and spacecraft. This work reviews the recent understandings of the fundamental combustion processes in wire fire over the last three decades. Based on experimental studies using ideal laboratory wires, physical-ba...

This paper provides alternative methodology to reproduce the smoldering of a 2-mm dia biomass stick in reduced gravity by utilizing a reduced-pressure approach. Since smoldering has been known as an initial process of fire hazard, a deep understanding of its characteristics is an important task to improve fire safety strategy in space. The aim of t...

This paper provides the methodology to achieve pseudo 1-D combustion system of specific polymeric materials without any complex physical effect (e.g., deformation, bubble bursting etc.) by adopting a low pressure technique with a fuel-layered approach. The adopted pressure level in this study is as low as 20 kPa and the size of the specimen is sub-...

Fingering pattern formation of flame spread over a thick solid has been observed recently. Since the oxygen-enriched atmosphere in microgravity promotes the occurrence of fingering and thus it leads to a fire in space, it is important to understand the mechanism. Motivated by this, a previous study attempted to validate a similarity to smoldering f...

The existing extinguishment device used in spacecraft is an inert gas (CO2) extinguisher or water mist which is a promising technique to suppress flames, however, the remained production of fume (harmful) gas in the enclosed space was paid little attention, although its removal from the cabin is not an easy task. We propose novel methodology, which...

Features of one-dimensional combustion-wave propagation of activated carbon particles (~ 1mm) packed in a quartz tube was examined experimentally. Rich oxygen was introduced into the tube to promote the surface oxidation of the activated carbon particles. An oxidizing mixture flows through a vertically placed quartz tube (from bottom to the top). F...

Dynamics of adjacent two burner flames formed over the boundary layers, especially the gap between two burners are very small (< 10 mm) were studied experimentally. Burner system is newly developed with cooling system to ensure the reproducibility. Considered parameters are channel height, air flow velocity, and fuel volume fraction. There are thre...

This paper describes dynamic transition behavior of single buoyant flames and interacting twin jet flames subjected by buoyancy. Single buoyant jet flame exhibits two modes of periodic flame behaviors; such as (axisymmetric) varicose and (asymmetric) sinuous modes. Similar behavior is observed when twin jet flames interacted at certain separation d...

Flame spread over a thin paper-disk in concurrent oxidizer flow within narrow channel was observed. The oxidizer flow rate and channel height were varied from 0.02 to 2 L/min and 2 to 16 mm, respectively. After the ignition, the flame initially spreads in radial direction, then it separates into multiple flamelets like conventional fingering patter...

To identify the occurrence conditions of a symmetry-breaking phenomenon, numerical simulations of flame spread along parallel, combustible plates are performed. Two-dimensional, time-dependent conservation equations for gas-phase with a one-step global reaction coupled to one-dimensional heat conduction for the solid-phase are simultaneously solved...

The smoldering behavior of porous combustibles near the extinction limit was examined under a highly-vacuumed environment at various oxygen concentrations. The considered ambient conditions of the present work is 1.0-90 kPa in absolute pressure filled with a nitrogen-oxygen mixture. A 2-mm-rod-shaped incense stick is considered as the burning speci...

We manipulated oxy-fuel combustion of methane in small scales to study the characteristics of micro counterflow diffusion flames under the gravity field. Methane-oxygen diffusion flames in counterflow burners were observed, where the burner distance was less than or equal to 1.0 mm and the apparent equivalence ratio was unity. The flame thickness a...

Flameless combustion is considered as a flexible and efficient combustion process for low heating value gas fuel. This paper presents numerical simulations of premixed flameless combustion using producer gas as a fuel. Different initial conditions of the premixed fresh reactant (air/fuel mixture) and dilution levels are taken into account for the i...

This paper provides a new methodology for measuring heat flux with “net” heat flux sensor utilizing the Peltier device to enable heat feedback control. The advantages of this sensor are that the removal heat on the cooling surface of the Peltier element shall be controlled electrically, and the surface temperature of the sensor can be controlled ar...

The properties of biomass producer gas are totally different from conventional gas fuel. Using in an ordinary combustion concept, the performance of the combustion process might reduce. Flameless combustion, as a flexible and efficient combustion concept, can be used to mitigate this concern. This paper presents an investigation to determine the re...

Geometrical effects on the flame spread over thermally thick combustibles in a narrow channel were experimentally investigated. Two series of experiments were conducted with two kinds of fuel geometry to form a narrow channel: parallel plates and cylinder. Both channels were made of polymethyl methacrylate, which also served as a combustible specim...

A novel technology to reduce soot is developed utilizing a high-frequency standing wave of 20 kHz applied to a methane-air lifted jet flame base. The amount of soot was measured using the transmitted light attenuation method. A mixing profile of the fuel jet was visualized using acetone planar-laser-induced fluorescence in order to measure the mixi...

This paper numerically investigated the detail process to appear the asymmetrically spreading flames in narrow channel consisted of combustibles. We have successfully reproduced the transient process to form asymmetrically arranged spreading flame first ever in this work. 2-D, time-dependent mass and energy transport process as well as one-step che...

In order to prove the existence of heat-recirculation (through burner wall) assisted flame stabilization mechanism for miniaturized jet diffusion flames, a series of two-dimensional axisymmetric numerical computations are performed for methane?air flames over a sub-millimeter (constant inner diameter of 0.8 mm) jet. A skeletal mechanism including 1...

A modified regression rate formula for the uppermost stage of CAMUI-type hybrid rocket motor is proposed in this study. Assuming a quasi-steady, one-dimensional, an energy balance against a control volume near the fuel surface is considered. Accordingly, the regression rate formula which can calculate the local regression rate by the quenching dist...

This article briefly reviews the recent works related to small-scale combustion and its potential impact into combustion science and engineering is presented. Followed by a simple description of the scale effect on combustion to highlight its “unique” feature, past related works are then summarized. The impact of heat recirculation appearing in com...

A n interacting behaviour of twin flickering diffusion flames at various distances horizontally is investigated experimentally as well as numerically. Flickering methane-air diffusion flames were formed over the round jets and their separation dis¬ tance was varied by using the optical stage, which enables us to control it in a precise manner. Expe...

This paper experimentally examines the heating performance brought by the chemical igniter (used in NASA-STD-6001B and ISO-TS16697) exposed in various oxygen concentrations. Final goal of this study is to discuss about the reliability of the chemical igniter for such material screening test ensuring the fire safeness in space. Prescribed mixture of...

In this study, a comparison of flame base structures of hydrogen/methane–air diffusion flames formed over a tiny-jet is made numerically for both isothermal and thermal conductive burner conditions, in order to clarify the fuel dependent flame stabilization mechanisms. It is found that, unlike a methane flame, the flame base of a hydrogen flame alw...

Flame spreading behavior in narrow gap constituted by parallel combustible thermally thick solid plates was experimentally investigated. Ten millimeter thick PMMA was used as fuel and the gap height was varied from 1 to 4 mm. Pure oxygen was flowing into the channel and the opposed flame spread was attained. It was found that the transition from a...

We studied the near-limiting behavior of various thicknesses of thermoplastic materials under a candle-like burning configuration; followed by an ISO 4589-2 protocol. The motivation for this work is to understand the sensitivity of the sample thickness on the limiting oxygen concentration in the range from 0.5 mm to 10 mm. In the first place, the e...

This paper discusses the interaction between two identical micro-slot diffusion flames. First, it is experimentally found that the burner pitch (distance between burners) influences the flame shapes and the total heat release rate. The total heat release rate, measured by integrating the intensity of CH chemiluminescence, tends to increase with a d...

This paper examines the feasibility of adopting conventional “heat-release-rate prescribed” fire source model to predict the potential fire damage in early (developing) stage of the fire. Numerical experiments are performed to investigate the difference in the time-variation of heat flux onto the ceiling, if any, between following two models; one i...

We theoretically examine the characteristics of a combustion wave of solid fuel in a porous medium. We consider two problems (i) a sample is ignited at one of the either ends and (ii) a sample is ignited around the middle. Depending on the ignition process, forward and opposed modes of a combustion wave are found in the first problem while they sim...

This paper investigated the effect of cell temperature and product species concentration induced by a small jet flame on the power generation performance of a direct flame fuel cell (DFFC). The cell is placed above the small-scale jet flame and the heated product’s gases are impinged toward it. This system is considered to be the simplest and small...

A universal correlation between the flame spread rate and the flame length formed along the electric wire was studied experimentally based on scale modeling concept. In the first place, we studied the burning behavior of researchgraded wire (i.e., controlled wire, polyethylene-coated metal thin rod) in order to examine the precise effect of the tot...

Low-temperature (< 600 K) ignition of dimethyl ether (DME) is investigated both experimentally and numerically with particular attention given to the transition from a cool flame to a hot flame. The premixed DME/air mixture is fed into a laminar flow reactor with prescribed temperature profiles at atmospheric pressure. Periodic behaviors involving...

This volume thoroughly covers scale modeling and serves as the definitive source of information on scale modeling as a powerful simplifying and clarifying tool used by scientists and engineers across many disciplines. The bookelucidates techniques used when it would be too expensive, or too difficult, to test a system of interest in the field. Topi...

This work is devoted to propose the concept of the laboratory-scale test facility to provide a partial-g environment based on slope-sliding method, SSMe. SSMe mainly consists of the experimental rack and the less-frictional slope which enable to set at the prescribed angle against the ground. During the sliding operation, the experimental rack shou...

This paper studies the interaction between two identical micro-slot diffusion flames. Here, we define a micro-slot flame as a slot flame of which the slot width is less than about 1 mm. Because of its smallness, a micro-slot flame has a high heating density and can be used as a small heat source. However, the heat release rate of a single micro-slo...

This paper investigated the effect of cell temperature and product species concentration induced by small-jet flame on the power generation performance of Direct Flame Fuel Cell (DFFC). The cell is placed above the small flame and heated product gas is impinged toward it and this system is the simplest and smallest unit of the power generation devi...

This work is devoted to examine the effect of melting behavior of polymer sample on limiting oxygen index (LOI), whose concept will be utilized to evaluate the safeness of the material bringing into the space environment, currently based on NASA-STD-6001 (TEST 1). Tested samples; PMMA are manufactured by different methods (casting and molding) to s...

The thermal and chemical structure formed in the micro burner potentially leading to the unique stability mechanism of miniaturized jet diffusion flame via excess heat recirculation through the burner wall, is studied numerically. 2-D axis-symmetric heat and mass transport processes with chemical reactions are considered in gas phase, while the hea...

Flame spread and counterflow diffusion flame experiments are widely conducted to investigate the combustibility of solid fuels. Although the use of the gas phase Damkohler number to organize the flame spread rate or regression rate of a solid fuel is effective under constant pressure, some research point out the possibility that the combustion pres...

Methane flames have been successfully established on the 3 x 3 array of micro burners with a burner diameter of 0.07 mm, even though this burner diameter is smaller than the smallest burner diameter to establish a methane flame. This means that the burner pitch of 2.5 mm is close enough to cause flame-flame interaction to get over the limit of burn...

In opposed-flow flame spread over thermally thin solid fuels, an increase in flow velocity eventually leads to flame extinguishment. While the chemical time is independent of the flow velocity, the residence time of the oxidizer at the flame leading edge is inversely proportional to the flow velocity. A competition between the two leads to a situat...

In opposed-flow flame spread over solid fuels, an indefinite increase in flow velocity eventually leads to flame extinguishment. While the chemical time is independent of the flow velocity, the residence time of the oxidizer at the flame leading edge is inversely proportional to the flow velocity and, therefore, a completion between the two leads t...

In this study, a universal model is developed to examine the behavior of combustion wave observed in porous solid matters (e.g., smoldering, self-propagating high-temperature synthesis (SHS), diesel particulate filter (DPF) regeneration process). Analytical expressions of the combustion characters of solid combustible (e.g., diesel particulate matt...

Numerical simulations are carried out in order to predict drop-size and -time of molten polymer during fire. Mass, momentum and energy conservation equations are solved in a 2-D system based on a fixed grid by means of a finite volume method. The Volume of Fluid (VOF) method and the Enthalpy-Porosity method are applied to model the deformable polym...

A microflame, defined in this paper as a diffusion flame established on a burner whose size is less than 1 mm, is used as a small heat source having high heating density. Multiple microflames are often used to achieve a high density and uniform heating performance. However, when the microflames are placed too closely, they merge into a larger flame...

Numerical studies on 1-D, non-sooting counterflow diffusion flames were performed to determine the precision with which the total heat release rate can be calculated using light emission, namely, chemiluminescence, from the reaction zone. A detailed reaction mechanism, incorporating sub-reaction models for excited state radicals (CH* and OH*, where...

Ignition phenomena of electric wires carrying short-term excess electric currents were investigated in microgravity with experiments and calculations. Microgravity experiments were conducted in 100 m and 50 m drop towers and calculations were carried out with a one dimensional cylindrical coordinate system. The experimental results showed that the...

Tests with flames spreading over wire insulation in microgravity were performed at varying external opposed flow conditions to examine the influence of flow velocity in the time dependent volume change of molten insulation. In the experiments, low density polyethylene insulated Nickel-chrome wire specimens were used and the oxygen concentration was...

Fire safety in manned spacecraft or space station is one of the most important requirements for any manned space mission. To prevent fires in space, material flammability tests such as NASA-STD-(I)-6001B standards have been widely employed. The tests are performed in normal gravity environment. Previous research showed material flammability could b...

Time-dependent melting and deforming processes of heated polymeric materials is modeled and direct numerical simulation is performed accordingly. Their main dynamic (mass and heat transfer) behaviors are well-captured and role of deformation is discussed.

It is important to investigate the flammability of circuit subjected to arc discharge in terms of fire safety. In this research, the flammability of electric wire was investigated as a most simplified circuit. Furthermore, stable arc discharge is assumed by using TIG arc welding machine. The electric wire subjected to arc discharge is ignited in an...

This work is devoted to examine the effect of ambient temperature on limiting oxygen index (LOI), whose concept will be utilized to evaluate the safeness of the material bringing into the space environment, currently based on NASA-STD-6001 (TEST 1). For LOI test (= ISO 4589-2), flame spreads toward the downward, whereas for TEST1, flame spreads tow...