Study on the transition mechanism for broadleaf foliage from smoldering to flaming combustion under external radiant hea
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ORIGINAL ARTICLE
Study on the transition mechanism for broadleaf foliage from smoldering to flaming combustion under external radiant heat flux Jun-Jun Tao 1 Received: 4 June 2019 / Revised: 1 August 2019 / Accepted: 12 August 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract This paper explores the behaviors of piloted ignition of fresh broadleaf foliage under external radiant heat flux. A total of 12 plant species were adopted, with volatile matter content varying from 15.4 to 41.4%. Measurements were conducted using a cone calorimeter with the radiant heat flux set at 35, 55, 70, and 85 kW m−2. Under the same radiant heat flux, the samples underwent combustion in two major modes. Some of the samples appeared short time flame and followed by smoldering, whereas the others maintained smoldering throughout the measurements. With an increase in the radiant heat flux or volatile matter content of a sample, the combustion mode of the samples may shift from smoldering to flaming combustion at initial stage of measurement. The critical heat release rate of a sample to form flaming combustion is between 20.9 and 22.5 kW m−2. Further analysis confirmed that the flaming combustion formed at initial stage of measurement mainly relies on the pyrolysis process of the sample surface layer. The initial volatile matter content of a sample and the rate of temperature rise at the surface layer are major factors governing the mass flux of volatiles generated and subsequently determining whether the sample undergoes flaming combustion. Keywords Broadleaf species . Layered fuels . Flaming combustion . Ignition conditions . Plant flammability
1 Introduction Woody plant leaves are the major fuel in wildland fire, especially in crown fire. The combustion characteristics of plant leaves have a direct impact on fire occurrence, burning intensity, and spread rate. For these reasons, studies on the combustion and heat release characteristics of plant leaves have practical value for preventing and controlling crown fire [1]. Existing studies on the combustion characteristics of plant leaf samples can be attributed to the measurements by using standardized cone calorimetric techniques in principal. Measurement results were often applied to assess the ignitibility of samples [1, 2]. By finding the position at which the heat release rate (HRR) underwent a drastic increase, the
* Jun-Jun Tao [email protected] 1
School of Chemistry and Materials Engineering, Changshu Institute of Technology, No. 99rd South Ring Road, Changshu, Suzhou 215500, Jiangsu, People’s Republic of China
ignition delay time was determined and the differences among the ignitibility of the samples were analyzed. In light of the HRR results and the mass change information of a sample during a test, researchers at the Forest Service, Department of Agriculture, determined the effective heat of fuel combustion to evaluate the combustibility of the samples studied [3, 4]. Plant leaf is a type of charring material. Besides the benzene-ethanol extracti
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