Jun Fang

A polarization-modulated multichannel Mueller-matrix scatterometer for smoke particle characterization

The polarization properties of scattered light are being exploited to determine the optical and physical information of small particles. In this paper, a scatterometer is developed for simultaneously measuring the Mueller scattering matrix elements as functions of the scattering angle. The scatterometer uses an electro-optic modulator to modulate the polarization state of the incident light, and uses two photomultipliers provided with different polarization optics to consist multichannel polarization-state detector. The instrument takes advantage of combination of the polarizationmodulation technique and division-of -amplitude photopolarimeter, which make for a compact design and substantial increase in measurement throughput and speed. The methods of calibration and alignment using the polarizationmodulated light are established, with which the instrument is calibrated precisely. The methods of data processing and error analysis of the measured Mueller matrix elements are developed. A hybrid experimental/theoretical approach to study the light scattering properties of smoke particles is also presented.

A prediction model of point-type smoke detector response signal variation in high altitude area

The response signal trends of ordinary ionization and photoelectric detectors under high altitude area were predicted using a simple model. The analysis results showed that the response trend varied with the pressure at 2nd power law for ionization detector, and 4th power law for photoelectric detector, which indicates that the signal performance of point-type smoke detector decreased with increasing altitude based on the same test fire source, and the main reason is the influence of air pressure on the burning behavior of material. Pool fires experiments were conducted in Hefei and Lhasa by ISO detector test method, TF 4 and TF 5 experimental results was consistent with the theory well, it means, to achieve the same ability or performantce as normal pressure condition, the engineering parameters such as alarm threshold of smoke detector should be adjusted properly for low pressure condition. While error appeared during small size pool fire test for the weaken of smoke accumulation under ceiling. This simple prediction model could be as a reference in the design of smoke detector for high altitude area.

Study on Burning Characteristics of Small-Scale Ethanol Pool Fire in Closed and Open Space Under Low Air Pressure

This paper presents results of different burning rates of small-scale ethanol pool fires at pressures of 0.6∼1.0 atm in closed and open space. Experiments were performed using a square burner of side length of 4 cm under two different conditions: one was taken in a closed low air pressure cabin (0.5 m3 , the interior pressure ranges from 0.6–1.0 atm); another was taken in open space respectively in Hefei (air pressure: 1.0 atm) and Lhasa (air pressure: 0.66 atm). The pool fire characteristics including the burning rate, the axial temperature and pulsation frequency of flame were measured. In closed space, the burning rate, flame temperature, and pulsation frequency of small-scale ethanol pool fires decreased with the decreasing pressure, while in open space they increased when the air pressure reduced. As a result of different ambient conditions and oxygen depletion, the burning rate, flame temperature and pulsation frequency were lower at lower air pressure in closed space but were higher at higher air pressure in open space.Copyright

Influence of high altitude on the burning behaviour of typical combustibles and the related responses of smoke detectors in compartments

The effect of altitude on typical combustible burning and related smoke detector response signals was investigated by comparison experiments at altitudes of 40 m and 3650 m based on EN54 standard tests. Point-type light scattering photoelectric smoke detectors and ionization smoke detectors were used for four kinds of EN54 fire tests, including two kinds of smouldering fires with wood (test fire no. 2 in EN54 standard or TF2) and cotton (TF3), and two kinds of flaming fires with polyurethane (TF4) and n-heptane (TF5). First, the influence of altitude or ambient pressure on mass loss for smouldering combustion (TF2 or TF3) was insignificant, while a significant decrease in the mass burning rate was found for flaming tests (TF4 and TF5) as reported in our previous studies. Second, for photoelectric smoke detectors in flaming fire tests, the effect of altitude was similar to that of the burning rate, whereas for the ionization smoke detectors, the response signal at high altitudes was shown to be ‘enhanced’ by the detection principle of the ionization chamber, leading to an even larger value than at normal altitude for smouldering conditions. Third, to provide a reference for smoke detector design in high-altitude areas, the differences between signal speed in rising and peak values at two locations are discussed. Also, relationship between ion chamber signals and smoke optical densities are presented by utilization of an ionization smoke detector and smoke concentration meter. Moreover, a hierarchical diagram is illustrated to provide a better understanding of the effects of altitude on combustible burning behaviour and the mechanisms of detector response.

Design of a Real-Time Video-Fire-Detection System Based on DSP

Many methods of fire detection in video have been carried out on PC. Generally it needs long cables to transmit images and processes videos on computers. That system is too dependent on computers, and costs a lot using cables to transmission. We would rather use a portable device to detect fire, which will bring us much more convenience. This paper designed a portable system to detect fire using DSP. The system integrates video acquisition, image processing and fire alarm together in a circuit board. Then we develop algorithms to recognize fire, and transplant them into DSP. Finally put it into use after commissioning test. This portable system can work independently. Users can put into their requirements through user-interface, and system will output the fire pictures and alarm by wireless communication or internet. This system is applicable to various places, such as indoor and outdoor, large and open spaces, forest, etc.