LIMITED CONDITIONS FOR BIOFUEL IGNITION AT DIFFERENT HEATING SCHEMES
Authors: Антонов Дмитрий Владимирович , Копылов Сергей Николаевич , Стрижак Павел Александрович 
Published: June 2022

Жидкие биотоплива из отходов растительного происхождения считаются перспективными для энергетического и транспортного секторов. Безопасные и эффективные условия их зажигания при разных схемах нагрева образцов существенно отличаются. Как следствие, нередко регистрируются пожароопасные условия, сопровождающиеся нерегламентированными возгораниями. В настоящей работе приведены результаты экспериментальных исследований критических условий зажигания группы жидких биотоплив при кондуктивной, конвективной, радиационной схемах нагрева. Установлены критические температуры и тепловые потоки, достаточные для зажигания и перехода к стационарному горению. Определена связь этих характеристик с начальными размерами капель и частиц топлива, а также компонентным составом.

Liquid biofuels from plant waste are considered promising for the energy and transport sectors. Safe and efficient conditions for their ignition under different schemes of sample heating differ significantly. As a result, fire hazardous conditions are often recorded. This paper presents the results of experimental studies of the critical conditions for the ignition of a group of liquid biofuels during heating with conductive, convective, and radiation heating schemes. Four typical heating schemes were used. As components there was used water, rapeseed oil, sawdust. The mass concentrations of solid and liquid components in the liquid biofuel composition were varied in the following ranges: solid component (sawdust) - 0…10%; liquid combustible component (rapeseed oil) - 80 ... 90%; liquid non-combustible component (water) - 10%. The Phantom Miro M310 high-speed camera recorded ignition process of liquid biofuels. Video frames were processed using the Phantom Camera Control software. The shooting frequency during the experiments was 1000 frames per second. The experiments carried out made it possible to establish a set of regimes during heating of the studied biofuels and their individual components, in particular: I - evaporation; II - boiling; III - puffing; IV - micro-explosion; V - drying; VI - carbonization; VII - flameless burning; VIII - flame burning. Critical temperatures and heat fluxes sufficient for ignition and transition to stationary combustion have been established. In particular, there has been identified a range from 175 to 200 kW/m, at which the ignition of all studies of composite biofuels with a mass concentration of sawdust up to 10% is consistently realized. The connection of these characteristics with the initial size of fuel droplets and particles as well as component composition is determined. Differences in the critical conditions for ignition of individual biofuel components and droplet compositions are highlighted. It is determined that in the fuel compositions biofuel components are crushed more intensively and decompose into small secondary fragments that ignite at lower temperatures of the heating medium. It is extremely important to take these differences into account for the fire-safe use of components and fuel mixtures at all stages: preparation, storage, transportation, spraying, regrinding, ignition, combustion, utilization and conversion of major emissions.