Zhihua Deng

Experimental study of back-draft in a compartment with openings of different geometries

Abstract This paper presents the results of reduced-scale experimental tests to study back-draft in a reduced-scale compartment (1.2 m × 0.6 m × 0.6 m), fitted with six different geometries for the opening on one end-wall and with two geometries for the opening in the ceiling. The experimental variables included the flow rate, the time during which the fuel was burned, and the geometries of the inlet. The quantities recorded before the back-draft included temperature and the concentrations of oxygen, carbon dioxide, and carbon monoxide. To quantify the effect of back-draft, the gas velocities in the inlet and also the pressures in the compartment were measured. The effects of different inlet geometries on the occurrence of back-draft are discussed. This study shows that the mass fraction of total hydrocarbons (i.e, the un-burned methane in this study), whose critical value varies with the geometry of the inlet, is a key parameter determining the occurrence of back-draft.

Experimental Study on Cross-ventilation Compartment Fire in the Wind Environment

When fire occurs in the rooms of high-rise buildings, the strong ambient wind will play an important role in fire spread and smoke movement behavior. However, wind effect on compartment fire in cross ventilation condition has not been fully studied so far. In the present study, an effort has been made to study crossventilation compartment fire in the wind environment through experimental investigations. The experimental fire was generated by 250ml (10cm×10cm tray burner) or 500ml (20cm×20cm tray burner) nheptane on the floor of a cube enclosure with two opposite vents on the walls. The inside and outside gas temperature profiles at different vertical and horizontal locations were recorded by two thermocouple matrixes. The ambient wind velocity was set to zero, 1.5m/s and 3m/s. It is observed that the ambient wind has two contradictory effects on the compartment fire: promoting fire severity by more oxygen supplying and cooling the fire by heat removing and combustible gases diluting. The spilled-out flame/plume extends horizontally farther with the increase of wind speed. It is found that the compartment fire with 500ml fuel reaches post-flashover stage while that with 250ml doesn’t. The wind effect is obviously observed in larger fires while not significant in smaller fires.

Effects of low atmospheric pressure on combustion characteristics of polyethylene and polymethyl methacrylate

Combustion characteristics of polymers are affected significantly by low atmospheric pressure and oxygen concentration at high altitude. In this study, vertical downward experiments aimed at investigating these characteristics, including mass loss rate (burning rate), flame temperature, flame spread rate, and flame height for polyethylene and polymethyl methacrylate having different thicknesses were conducted at elevations of 2295 m (77.4 kPa) in Xining and 29.5 m (101.8 kPa) in Hefei, China. Experimental results showed that mass loss rate and flame temperature are proportional to the ambient pressure. Power-law progressions of flame height and flame spread rate to pressure were produced, and linear relationships between the exponents and thickness of samples were obtained. The influence of ambient pressure and thickness on flame height is similar to that on flame spread rate for polymethyl methacrylate.

Experimental and Numerical Study of the Effect of Sample Orientation on the Pyrolysis and Ignition of Wood Slabs Exposed to Radiation

The effect of sample orientation (vertical and horizontal) on the pyrolysis and ignition of wood exposed to radiation has been studied with experimental and numerical methods in the present article. Experimental results show that the pyrolysis rate of vertically oriented wood exposed to radiation is higher than for horizontally oriented wood exposed to radiation. Pyrolysis gas significantly dominates the process of pyrolysis of wood exposed to radiation. Accounting for radiation absorption by pyrolysis gas, a numerical model has been developed to simulate the pyrolysis and ignition of wood in horizontal and vertical orientations exposed to radiation.

Attenuation of Incident Heat Flux by Pyrolysis Volatiles when Heated Using Resistance Element Radiant Heater

The attenuation of an incident radiant heat flux by pyrolysis volatiles when heated under a resistance element radiant heater, a phenomenon that is not well understood, is studied by simulated experiment and mathematical models. The radiation attenuation of an incident heat flux when pine or PMMA is heated (6—14%) obviously commences before ignition, although it is not as large as the result reported by Kashiwagi (50—80%) using a laser radiant heater. The calculated results clearly indicate that ignition models must consider radiation attenuation by pyrolysis volatiles.

Experimental Study on the Factors Concerning the Ignition Time and Mass Loss Rate of Timber

The article is concentrated on the ignition time and mass loss rate of timber under different conditions such as the radiation flux, the distance between the sample and the radiation source and the sample obliquity. On the basis of a series of experiments, the result is that the ignition time of timber has a linear relation with the factors mentioned above. And after the timber is ignited, the mass loss rate is accelerated.