Forest Fuel Drying, Pyrolysis and Ignition Processes during Forest Fire: A Review

Forest ecosystems perform several functions that are necessary for maintaining the integrity of the planet’s ecosystem. Forest fires are thus a significant danger to all living things. Forest fire fighting is a foreground task for modern society. Forest fire prediction is one of the most effective ways to solve this urgent issue. Modern prediction systems need to be developed in order to increase the quality of prediction; therefore, it is necessary to generalize knowledge about the processes occurring during a fire. This article discusses the key features of the processes prior to forest fuel ignition (drying and pyrolysis) and the ignition itself, as well as approaches to their experimental and mathematical modeling.

Mathematical Simulation of Forest Fuel Pyrolysis in One-Dimensional Statement Taking into Account Soot Formation

Pyrolysis (thermal decomposition) is considered as the most important stage of a forest fire before direct forest fuel ignition. This process is accompanied by soot particle formation. Such particles have a negative impact on public health in the vicinity of forest fires. The purpose of this article was to investigate the heat and mass transfer process occurring in a typical forest fuel element (birch leaf). The pyrolysis and soot formation processes were taken into account, and various forest fire scenarios were considered. Computational experiments were carried out using the high-level programming language Delphi. Heat and mass transfer processes were described by nonlinear non-stationary differential heat conduction equations with corresponding initial and boundary conditions. The differential equations were solved by the finite difference method. Nonlinearity was resolved using a simple iteration. The main results of the research were (1) physical and mathematical models proposed for modeling forest fuel pyrolysis, taking into account soot formation and conditions corresponding to various forest fires; (2) a computer program coded in the high-level programming language Delphi; (3) the obtained temperature distributions over leaf thickness; (4) volume fractions obtained for various components dependent on time and space coordinates. The qualitative analysis of the dependencies showed that the temperature distributions in the birch leaf structure are similar for all forest fire types and differ only in absolute value. The intensity of the soot formation process directly depends on the forest fire type. The presented results should be useful in predicting and assessing forest fire danger, including near the facilities of the Russian Railways.

Trends in forest fuel accumulation in pine forests of Kyiv Polissya in Ukraine

At present, forest fire research is becoming especially relevant in Ukraine. This study examines patterns of forest fuel accumulation in pine (Pinus sylvestris L.) stands that grow in different soil conditions with different pine stand structure. To estimate the load of forest fuel of different fractions, a combined methodology was used: the weighing method and the FIREMON (fuel load estimation) method. It was found that increase in surface forest fuel loads is not directly proportional to forest stands’ age. Fractional size distribution, capacity and loads of forest fuel depend on several factors, among which the greatest role is played by forestry characteristics of the pine stand. It was determined that in the forest site conditions of type C (fairly rich soils) in Kyiv Polissya, the share of forest litter compared to pine stands that grow in poor soil conditions (A) is smaller, ranging from 41% to 76% of the total forest fuel load. The mass proportion of the duff layer varies from 15% in young forest stands to 43% in mature stands. It was established that changes in forest fuel fractions for 1, 10, 100 and 1000 hours varied insignificantly with age rate. The share of substratum woody debris of 10 and 100 hours was insignificant and depended more on the forestry treatment regime on these sites. The mass proportion of coarse woody debris (1000 hours) was also insignificant, varying from 0% to 5.9% of the total load of surface fuel.

The influence of particle size and density of pelleted samples of forest fuel on thermokinetic characteristics of pyrolysis and oxidation

This paper presents the results of experimental studies of thermokinetic characteristics of pyrolysis and oxidation of pine needles, taking into account the influence of particle size and density of forest fuel in pelleted samples. The sample densities range within 206-955 kgm-3 (i.e. from typical sample densities to average ones for pressed pelleted samples), and the component particle sizes amount to 60-140 ?m. The range of studied temperatures is 20-1000 o?. The particle size and density of the material are found to be important parameters that significantly affect the kinetics of pyrolysis. According to the results of measurements, the activation energy of needles pyrolysis is within the range of 22.8-113.8 kJmol-1, and that of oxidation corresponds to 134.7-211 kJmol-1. Three intervals with significantly different values of activation energy and pre-exponential factor are distinguished in the studied temperature range. Approximation expressions are formulated for the activation energies of pyrolysis and oxidation as functions of forest fuel particle sizes, sample density and temperature.