1 Introduction
2 Background
2.1 Firebrand/Particle Generation and Transport
2.2 Spot Fire Formation: Ignition (or Non-Ignition) of Fuel Beds After Particle Landing
3 Experiment Description
4 Experimental Results
4.1 Temperature Profiles
4.2 Smolder Spread Rate
4.3 Propensity for Ignition
C1 [m/K] | C2 [K] | |
---|---|---|
Smoldering | 0.0004 | 4862 |
Flaming | 0.0011 | 4264 |
5 Simplified Theoretical Analysis
5.1 Hot Spot Theory
5.2 Application to Present Experiments
Parameter | Value | Units | Reference | Description |
---|---|---|---|---|
k
| 0.1 | W/m · K | Estimated | Thermal conductivity (target) |
ρ
| 200 | kg/m3
| Measured | Density (target) |
c
| 2.0 | kJ/kg · k | Estimated | Specific heat capacity (target) |
ρ
p
| 7833 | kg/m3
| [38] | Density (particle) |
c
p
| 465 | J/kg · K | [38] | Specific heat capacity (particle) |
A
| 1 × 1017a
| s−1
| [39] | Pre-exponential factor |
E
| 222a
| kJ/mol | [39] | Activation energy |
ΔH
| 10b
| MJ/kg | [40] | Heat of combustion |
T
0
| 300 | K | Measured | Initial temperature |
5.3 Assessment of Hot Spot Theory Predictive Capabilities for Present Experiment
6 Concluding Remarks
-
The results show as particle size is reduced, increased temperature is required for ignition. For a particle size of 2.4 mm, temperatures of 1200°C were required for flaming ignition and this was reduced to 650°C for particles of 19.1 mm.
-
Ignition propensity is a function of both particle size and particle temperature.
-
There is not a unique correlation between particle energy and ignition propensity.
-
Hot spot ignition theory provides qualitative agreement with experimental results but is not quantitatively predictive for the present experiments.