Interferometric measurement of ionization in a grassfire

Abstract

Grassfire plumes are weakly ionized gas. The ionization in the fire plume is due to thermal and chemiionization of incumbent species, which may include graphitic carbon, alkalis and thermally excited radicals, e.g., methyl. The presence of alkalis (e.g., potassium and sodium) in the fires makes thermal ionization a predominant electron producing mechanism in the combustion zone. Alkalis have low dissociation and ionization potentials and therefore require little energy to thermally decompose and give electrons. Assuming a Maxwellian velocity distribution of flame particles and electron-neutral collision frequency much higher than plasma frequency, the propagation of radio waves through a grassfire is predicted to have attenuation and phase shift. Radio wave propagation measurements were performed in a moderate intensity (554 kW m-1) controlled grassfire at 30-and 151-MHz frequencies on a 44 m path using a radio wave interferometer. The maximum temperature measured in the controlled burn was 1071 K and the observed fire depth was 0.9 m. The radio wave interferometer measured attenuation coefficients of 0.033 and 0.054 dB m-1 for 30-and 151-MHz, respectively. At collision frequency of 1.0 9 10 11 s-1 , maximum electron density was determined to be 5.061 9 10 15 m-3 .

Two Dimensional Axisymmetric Simulation Analysis of Vegetation Combustion Particles Movement in Flame Gap under DC Voltage

“…The main component of vegetation is cellulose, which is similar to hydrocarbons. The process of generating electrons and ions in the reaction of hydrocarbons is shown in Formula (1) [9]. During combustion, alkali metal and alkaline-earth metal salts can react with the combustion byproduct CO to produce electrons and CO 2 , such as in Formula (2).…”

“…There are also many reports in other countries, such as the forest fire in California in November 2018, which caused a considerable area of power supply interruption [4][5][6][7]. The influence of flame on gap breakdown mainly includes flame temperature, charged particles, ashes and so on [8][9][10]. High flame temperature reduces air density and promotes thermal ionization.…”

Study on the breakdown characteristics of the transmission line gap under forest fire conditions

“…Different models of gap breakdown mechanism under fire conditions have been proposed . The main reasons for the decrease of gap insulation strength are as follows: High temperature makes air density reduced, which leads to the decrease of insulation.…”

An Empirical Relation for Vegetation Fuel Flames Breakdown Electric Field Strength

“…These processes are flame temperature dependent and have been identified as thermal and chemi-ionization. tassium-based salts [18]. However, at temperatures lower than 500 K, charcoal is A-AEM atoms according to the following reaction equation (Okuno et al, [19]):…”