Abstract 



A method is presented for the evaluation of the heating efficiency 

 required for ignition as a spreading fire closes with fuel. 



An array of thermocouples was implanted in the fuel ahead of the 

 fire to obtain the heat absorbed by the fuel prior to ignition. The frac- 

 tion absorbed compared to the total that would be absorbed if uniformly 

 heated is the effective heating number. The effective heating number 

 is represented in its final form as decreasing exponentially with the 

 reciprocal of the surface area-to-volume ratio. 



The spreading fire is carried in a regular fuel crib array. Two 

 fuel sizes are used in cross-sectional dimension: 0.6 cm. and 1.3 cm. 

 Isotherms are generated from the temperature field at ignition and 

 presented for both fuel sizes to determine heat absorbed. 



