Chihong Liao

Flame-extinguishing concentrations and peak concentrations of N2, Ar, CO2 and their mixtures for hydrocarbon fuels

Fire-extinguishing efficiency of inert gas mixtures was investigated by measuring flame-extinguishing concentrations and peak concentrations for hydrocarbon fuels, because new fire-extinguishing agents composed of inert gas mixtures have been developed as halon alternatives. The flame-extinguishing concentrations of nitrogen, argon, carbon dioxide and their mixtures for n-heptane were measured with the FRI glass cup burner. The peak concentrations of the agents for methane-air and propane-air mixtures were also measured with the tubular flame burner. Chemical equilibrium calculations showed that the adiabatic flame temperatures of the cup burner flames at the extinction condition were almost constant for all the agents. The adiabatic flame temperatures at the flammability limit of the tubular flame for each fuel were also independent of the inert gas agent if the mixtures had the same equivalence ratio. The flame-extinguishing concentrations of the inert gas mixtures were predicted by a simple equation averaging over the flame-extinguishing concentrations of all component gases weighted by mole fraction. The equation has the same form as Le Chateliers law. For the flammability limits of the hydrocarbon-air mixtures, the same relation was also recognized in the effect of the mixed agents. The facts show clearly that this simple equation for the flame extinction concentrations is useful to estimate the fire suppression efficiency of any mixed agents of the inert gases. At the same time, it appears that the flame-extinguishing concentrations and the flammability limits reported in the paper are consistent.

Extinction of counterfiow diffusion flames with halon replacements

Extinction of counter/low diffusion flames on liquid fuels was investigated, to confirm the superiority of the counterflow diffusion flame over the cup burner method for measuring flame extinguishing concentrations of fire suppressants, and to examine the fire suppression effects of halon replacements. The flame extinguishing concentration for the counterflow flame was less sensitive to the burner size than that for the cup burner method. Furthermore, the flow velocity of the fuel vapor had no change when the suppressant concentration in the oxidizer mixture of the counterflow diffusion flame was varied, whereas it changed remarkably in the case of the cup burner flame. The flame extinguishing concentrations of nitrogen, carbon dioxide, halon 1301 (CF3Br), and three kinds of hydrofluorocarbons (HFC) and perfluorocarbon (FC) for n-heptane or ethanol counterflow flames were measured at various strain rates. Adiabatic flame temperatures at the extinction concentrations were calculated using the flame extinguishing concentrations measured for counterflow flames, assuming various equivalence ratios. The results suggest that HFC-23 (CHF3) suppression exhibits a higher contribution to the chemical suppression effect than other HFC or FC.

Flammability limits of combustible gases and vapors measured by a tubular flame method

A tubular flame burner method was employed as a new test method for flammability limits, and repeatable and reliable flammability limits were measured. The data were obtained under well-defined conditions. New data on the flammable regions of mixtures of several hydrocarbons and ethanol with inert gases and halogenated fire suppressants in air are reported and compared with the literature data.

A Study On Extinction Of RDF (Refuse Derived Fuel) Pile

Tests were conducted with the objectives of observing and recording the characteristics of fire growth and extinction of RDF fire, and to establish a tentative basis for the development of safety and fire control requirements. An RDF sample used was a pellet type made from municipal solid waste. A pile of RDF pellets was ignited and burned for predetermined burn time. By applying water mist, flame over the pile was extinguished. When burn time was longer than 30 min, hot area remained on the surface after extinguishing flame. The hot area expanded with time. Smoke was emitted from the hot area. After the pile was cut open for inspection, hot area was found inside the pile. RDF pellets are aggregated by heating since shredded plastics contained in them melt and work as adhesive. By applying water, aggregated pellets are cooled to form a layer which prevents water from soaking inside. RDF pellets remain hot under the layer. If air is supplied to hot RDF pellets under the layer, oxidation continues and heat and smoke are emitted.