Experimental study of fire propagation and heat transfer of biomass straw fuel with different stacked diameters and thicknesses

Abstract

The combustion of biomass straw that ignited by a fire point is an important latent danger form of wildfire. The investigation of development of the straw burning are essential for the efficient and safety utilization of biomass straw as a typical fuel. In this paper, the naturally stacked straws with diameters of 60 cm, 90 cm, and 120 cm and thicknesses from 2.0 cm to 12.2 cm were ignited from a point-source fire. The fire propagation and combustion characteristics including propagation stage, flame spreading rate, mass loss rate (MLR), and flame central temperature were measured and analyzed. The results showed that the straw combustion process was divided into four typical stages, namely the center combustion stage, merged annular stage, separated annular stage, and decay stage. The combustion area between the inside and outside flame front forms an annular shape, thus forming a hollow structure in the flame. The outside flame front spreads outward linearly with the spreading rate approximately rising with the increase of diameter and thickness. The peak of MLR is determined by diameter and thickness, hence an MLR quantitative model was constructed as m′/SL̇″h∝Deq2.391 . The exponential function between the dimensionless flame temperature Tf-T∞T∞ and the z-z0ṁ-2/5 was established. The inclined trend was becoming more obvious with a smaller negative slope in the three longitudinal regions.