Tadashi Konishi

Transient infrared temperature measurements of liquid-fuel surfaces: results of studies of flames spread over liquids

An infrared thermograph technique with an 8-12-microm spectral range was used to measure transient two-dimensional profiles of liquid (1-propanol) surface temperatures. An IR camera was placed over the liquid, allowing us to observe the fuel surface through propanol vapor. To use this technique, one must know the emissivity of the liquid surface and the IR absorption of both the liquid propanol and the propanol vapor. The emissivity of the liquid propanol was determined with a fine thermocouple temperature measurement, IR absorption with the propanol vapor was calibrated with a blackbody source, and IR absorption with a liquid propanol was theoretically estimated. The accuracy of our infrared thermograph technique proved to be better than 97% in detecting the liquid-surface temperature with a temperature sensitivity of 0.1 degrees C and a time response of 30 ms.

Scaling Analysis on Pulsating Flame Spread over Liquids

Scaling analyses based on subsurface layer instability were performed to explore the role of three independent (surface tension, gravity, and viscosity) influences on the mechanism of pulsating flame spread under normal and microgravity conditions. These three influences form two independent pi-numbers: the Marangoni (Ma) number and Grashof (Gr) number, which include the characteristic length scale ratio (depth of subsurface circulation)/(horizontal length of preheated liquid surface). The Prandtl (Pr) number was introduced to compensate for the different thermal diffusivity and kinematic viscosity of different liquids. Also a nondimensional flame spread rate, (= , where is the quenching distance and is the diffusivity of fuel vapor) was introduced. Using these nondimensional parameters, the flame spread mechanism was divided into two separate regimes: for the shallow liquid pool the nondimensional flame spread rate was correlated with , while for the deep liquid pool it was correlated with .

The effect of a cold temperature valley on pulsating flame spread over propanol

The transient three-dimensional structures of velocity and temperature created by a pulsating flame spread over normal propanol were constructed from five independent transient measurements using five different techniques: laser sheet particle tracking (LSPT): smoke tracing (ST); dual wavelength holographic interferometry (DWHI): infrared thermography (IR): and high-speed photography (HSP). These measurements showed that the pulsating flame spread consists of five distinctly different steps. The first step is the onset of pulsation created by the stagnation of flame spread over the liquid, which is followed by the second step, formation of a cold liquid valley near the flames leading edge, and the third step, accumulation of liquid fuel vapor over the liquid surface. In the fourth step, the flame jumps through the formed premixed gas layer, leading to the final step, the cessation of spread. After the fifth step, the process returns to the first step, completing the entire pulsation cycle. Our experimental data confirm the formation of a small gas-phase circulation cell, as predicted by the University of California, Irvine, numerical model, and support the idea that the pulsating spread is triggered by the subsurface liquid convection that affects the gas-phase flow and the fuel vapor concentration. The second result is unique and suggests that a cold temperature valley formed on the liquid surface would play an important role in the mechanism of pulsating spread.

Transient two-dimensional fuel-concentration measurement technique

We propose a nonintrusive experimental technique, the transient fuel-concentration measurement technique (TFMT), that is capable of being used to measure two-dimensional profiles of transient fuel concentrations over an open liquid fuel surface. The TFMT is based on single-wavelength holographic interferometry; its response time is less than 1 mus and spatial resolution is 0.1 mol. %/0.1 mm. It was applied to measure both methanol vapor and n-propanol vapor concentrations. To assess the accuracy of the technique, our results were compared with steady-state methanol and n-propanol fuel-vapor concentrations measured by other researchers with a microsampling technique combined with gas chromatography. We found the TFMT to be accurate for on-line monitoring of two-dimensional profiles of fuel-vapor concentrations.

Simultaneous measurement of temperature and chemical species concentrations with a holographic interferometer and infrared absorption.

What is believed to be a new technique that allows for the simultaneous measurement of 2D temperature and chemical species concentration profiles with high spatial resolution and fast time response was developed and tested successfully by measuring a thin layer of fuel vapor created over a volatile fuel surface. Normal propanol was placed in an open-top rectangular container, and n-propanol fuel vapor was formed over the propanol surface in a quiescent laboratory environment. An IR beam with a wavelength of 8-13 mum emitted from a heated plate and a He-Ne laser beam with a wavelength of 632 nm were combined and passed through the n-propanol vapor layer, and both beams were absorbed by the vapor layer. The absorption of the IR beam was recorded by an IR camera, and the He-Ne laser was used to form a holographic interferogram. Two-dimensional temperature and propanol vapor concentration profiles were, respectively, determined by the IR absorption and the fringe pattern associated with the holographic interferogram. This new measurement technique is a significant improvement over the dual wavelength holographic interferometry that has been used previously to measure temperature and fuel concentration, and it is ready for application under different types of fire and flame conditions.

Scaling Sub-Surface Layer Circulation Induced by Pulsating Flame Spread over Liquid Fuels

The pulsating flame spread over liquid fuels consists of main-pulsation with 0.5 to 2 Hz frequency and sub-pulsation with 5 to 10 Hz frequency. The former originates in existence of a cold temperature valley at the liquid surface ahead of the spreading flame. The cold temperature valley is formed by the surface wave in connection with a sub-surface layer circulation. In this study, the instability analysis for the liquid surface ahead of a flame leading edge was performed to clarify the onset of surface wave. Moreover the effect of gravity on surface wave generation was examined. The theoretical result shows that the onset of surface wave is firstly controlled by Marangoni force and secondary by buoyancy force. The critical condition for onset of surface wave was expressed to the non-dimensional form. Three dimensionless parameters, the Marangoni number, the Weber number and the Froude number include the ratio, ħ/L, of the characteristic length, L, and the depth, ħ, of sub-surface layer circulation (shown in Fig. 1). F1 The circulation scale for seven different thickness of liquid fuel from 2 to 20 mm was measured using a schlieren photograph and thermography. The ratio, ħ/L, decreases with decreasing fuel layer thickness less than 5 mm and consists to μg condition at the fuel layer thickness of 3 mm.

Scale Effects on Flame Structure in Medium-Size Pool Fires

Experiments using a particle-track laser sheet technique (PTLS) combined with a high speed video camera were conducted to reveal the flame structure and flow vector diagram in medium-size pool fires. To improve our understanding of the scale effects on buoyancy controlled flame structure, we employed four different size liquid pool fires whose pan diameters are 10, 20, 30 and 50 cm. These results were compared with numerical analysis previously presented by other researchers. The flow visualization results at the vertical plane along a center axis are in good agreement with numerical results. However, air entrainment through the flame is estimated to be at most 30% larger than that of axis-symmetric smooth flame because of an increase in the reaction surface area and the existing rotational velocity component around the wrinkled flame. For a medium-size pool fire below 20 cm-diameter pan, the flame height and the puffing frequency are close to an assembled small-size pool fire in which 3 cm-diameter pans are lined around a circle. The flame structure below 20 cm-diameter seems to be composed of several flame cells. While the flame structure above 30 cm-diameter is quite different from the aggregate of small-size pool fires. For a 50 cm-diameter pool fire a wrinkled flame having a high frequent disturbance of 12–14 Hz occurs near the base flame zone and grows along the flame surface. A pool fire beyond 50 cm diameter pan becomes a large-scale pool fire having a turbulent flow structure.

Measurement Of A 3-D (Gas And Liquid) Flow Structures Generated By A Spreading Flame Over N-butanol

This paper discusses a new 3-D experimental data that were obtained by a laser-sheetparticle-tracking (LSFT) technique for a spreading flame over n-butanol. The major heattransfer process between the flames leading edge and the liquid is a highly transient phenomenon involving both liquid and gas phases. These interact with each other through exchanges of momentum, heat, and mass. We improved our original 2-D LSPT and made it applicable to study 3-D measurement. Using this new 3-D LSPT we measured a series of velocity profiles in a pulsating flame spread over n-butanol at different distances above or below the liquid surface and obtained 3-D flow visualization in both liquid and gas phases. The new LSPT confirmed the existence of twin vortex flow on the liquid surface and deep in the liquid a few mm below the surface. These vortices gradually disappear as the laser sheet moves down from the liquid surface. A similar twin-vortex structure in the gas phase was also observed for the first time. These results proved that the convective flow in both liquid and gas phases is 3-D in nature in the three trays we have used.

Section B Fire and Explosion - Scale Modeling of Biomass Fire Associated with Hydrogen-Producing Bacteria

This paper details a fundamental study for developing a safe handling system for waste biomass fuels, especially for the prevention of fires and explosions associated with refuse-derived fuels (RDF). Unlike conventional solid fuel, RDF is a living fuel that contains various kinds of bacteria among which flammable gases such as hydrogen and methane may be produced during biological fermentation in the proper circumstances. The RDF storage silo at the Mie prefectural RDF power plant unexpectedly exploded in 2003, and firefighter deaths and injuries were reported. Though flammable gas production was the suspected cause of the explosion, there is disagreement about whether the flammable gas was produced by the biological fermentation or by thermal decomposition of the RDF materials. Due to the difficulties in conducting both the experiments and numerical simulations in a full-scale mock-up silo, the detailed explosion mechanism has not been explained since 2003. On the basis of scale modeling principles, this study begins with determining the physical or chemical laws which govern the phenomena of the accident. For this purpose, flammable gas production tests were conducted using two kinds of RDFs, which were provided from two manufacturers: Kuwana and Sakura. The RDF hydrogen production ability was affected by pH, moisture, and ambient temperature. The microbial colony count method revealed that aerobes occupied a dominant position in RDF on the second or third day from the beginning, whereas anaerobes occupied a dominant position hereafter. Bacillus sp. was superior to Clostridium sp. in Kuwana, whereas Clostridium sp. was superior to Bacillus sp. in Sakura after 3 days of cultivation. Scale effects on the temperature rise of RDF due to biological activities were examined using three different amounts of RDFs. It was found that the higher the amount of RDF, the higher the maximum temperature obtained after 50–85 h cultivation.

Scale Modeling of Air-Dropped Water for Aerial Firefighting Against Urban Fire

In the event of a major earthquake, urban fires would spread unchecked for lack of firefighting water supply due to destruction of roads, hydrant damage, and so on. If aircraft, such as helicopters, could be used under specific conditions, it would be effective for firefighting in these conditions; aircraft can arrive at the fire site quickly and begin firefighting immediately. However, there is not enough research about the fire-extinguishing or fire-deterrent effect of aerial firefighting in urban fires. Until now, full-scale experiments using an actual helicopter have been carried out three times by the National Research Institute of Fire and Disaster. However, it is difficult to carry out full-scale experiments frequently. Therefore, in this research, a scale model experiment was proposed and similarity to a full-scale experiment was verified. Findings about air-spread phenomenon when water was dropped from a bucket and about the impact of water hitting the ground were reproduced.