Estimation of Heat Release in Fire Compartment

This paper presents the model to estimate heat release in fire compartment about four fuels, Douglas fir considering char formation and moisture content, methanol, methane and propane, with equivalence ratio Q on the basis of previous work and discusses about the difference of the combustion efficiency of them. As the result, calculated heat release of Douglas fir, methane and propane shows relatively good relation to previous work. By considering the differences of combustion efficiency of fuels, we will be able to conduct the experiments with many fuels to examine heat balance of compartment fire. And the results of combustion efficiency of four fuels show that in Q ~ I, combustion efficiency of Douglas fir. methanol, methane and propane are almost same, but in Q > I as ¢ increases, as combustion efficiency of them differ largely. The reason is considered that heat of reaction is consumed to latent heat of non-reacted fuel in accordance with the amount of non-reacted fuel. NOMENCLATURE L1 H; : heat of formation of completely burned gas of dry fuel (kl/kg) Ll HI' : heat of formation of chemical species i (kJlkg) Ll Hs, : heat of formation of dry fuel (kl/kg) Ll H; : enthalpy of pyrolysis gas (kJlkg weight loss) L1 Hi, : heat of formation of burned gas in arbitrary condition (kl/kg) Ll h; : heat of formation divided in proportion to the amount of oxygen in fuel and air (kl/kg) Qr : heat release in arbitrary condition (kl/kg) Q, : heat of combustion (kl/kg) Q"'7 : heat of combustion except for char and moisture content (kl/kg) Q,,, : heat of combustion except for moisture content (kl/kg) qo: : heat release per gram of oxygen in air consumed (kI/g 0,) xc', XH'. xo'. XN' : mass fractions of C, H, 0 and N (kg/kg dry fuel) 307 Copyright © International Association for Fire Safety Science Xz' : char ratio (kg/kg dry fuel) x-' : moisture content (kg/kg wet fuel) G, b, c. d : mole numbers of C, H, 0 and N of dry fuel (mole) CE : combustion efficiency (-) k : combustion efficiency defined by Hamada (-) L.,' : latent heat of dry fuel (kJlkg weight loss) mi m; : mass rate of fuel and air (kg/s) n : excess air ratio (-) r, s, Pi, p:, ql : the coefficients (-) Q : equivalence ratio (-) Q s : stoichiometric reacting fuel to air ratio (-) INTRODUCTION A lot of studies concerning about compartment fire have been done. Sekine [ I J modeled the temperature in fully developed fire compartment. Then many fire models have been developed. In these models, heat release rate has been evaluated as the product of weight loss rate and heat of combustion of the combustibles [2,3 J or heat release considering empirical combustion efficiency [1 ,4-7J. But little studies have been done about heat release of fuels, such as wood, considering char formation and moisture content to influence them. To study the properties of compartment fire, many experiments using small-scale model had been done. Besides the cellulosic materials, which are the main combustibles of actual fire, liquid and gaseous fuel had been used as the fuel in experiments because of the ease to handle and the definite properties. But it has not been well discussed about the differences among them. This paper presents the results of the estimated heat release of Douglas fir considering char formation and moisture content, methanol, methane and propane, with equivalence ratio on the basis of previous work and discusses about the difference of the combustion efficiency of them. PREVIOUS WORK Recently many plastic materials have come into use in buildings, but it has been reported that the main combustibles were woody materials [8,9J. The summary of previous work concerning about pyrolysis, gas composition of burned gas and heat release of these materials is shown as below. Most part of woody materials consists of cellulose, hemicellulose and lignin, so combustion of cellulose has been studied mainly as that of wood. Although a lot of studies concerning about the combustion of cellulose, related to the problem of energy, incineration of garbage and fire safety, have been done] l O, II], it is not easy to evaluate its combustibility quantitatively. The pyrolysis of cellulose is complicated physically and chemically, and the composition of char, soot and the volatile is influenced by atmospheric condition. Char changes its composition with the increase of temperature and duration of heating, so it is difficult to specify its composition and the nature. The experimental results show that char is formed by a~ 30% weight of initial cellulose [12-15 J . On the point of gas toxity, Beyler [16, 17J studied CO. C02, Hz and 02 yield with equivalence ratio by small scale experiments to burn 13 kinds of fuels under hood steadily. Then Gottuk et al[18] conducted large scale experiments and showed the same property. Zukoski et al ] 19J examined those in transient state. From Beyler's results, Yamada' Tanaka [20J assumed that the normalized yield of