Combustion Flashcards
Photosynthesis
Can be reversed by decay (slow) and fire (fast)
Heat of pre-ignition
Heat required to raise fuel to ignition/kindling temperature (usually 600 degrees F)
Heat of combustion
Heat required to maintain chain reaction of combustion
Heat transfer
Movement of heat energy, occurs when there’s heat difference between or within substances
Types of heat transfer
- Convection
- Radiation
- Conduction
Conduction
By molecular activity
- different substances conduct differently
- only way to get to interior of dense materials
- dense materials conduct better (high heat capacity)
Convection
By movement of liquid/gas
- preheating tree canopies/high shrub layers
- flames of burning gas released during pre-heating of fuels
Radiation
By electromagnetic energy
- function of temperature of radiating body and distance from absorbing object
- firebrands
Phases of combustion
- Preignition
- Ignition
- Combustion
- Extinction
Preignition
- dehydration (removes volatiles/water)
- pyrolysis (thermal degradation of plant compound)
Ignition
Pilot heat ignites fuel cloud produced during pyrolysis
- transition from endothermic reaction (preignition) to exothermic reaction (combustion)
- lightning, humans, volcanoes
Combustion
- rapid release of heat energy stored by photosynthesis
- heat + fuel + oxygen
- flaming combustion (rapid oxidation of gases produced by pyrolysis)
- smoldering/glowing combustion (higher residence time = dangerous, more smoke)
Extinction
- end of combustion
- water and inorganic materials
- moisture of extinction
Moisture of extinction
Fuel moisture content at which fire won’t spread
Combustion efficiency
Ratio of actual CO2 released to max possible CO2
- higher for flaming combustion than smoldering combustion
- higher efficiency = less problematic compounds
