A Combined Experimental and Theoretical Study of the Combustion of Live vs. Dead

Leaves

Dallan R. Prince and Thomas H. Fletcher

Figure 1. Flaming leaf after 4 s of heating as viewed from the video and infrared cameras. The leaf is held from a rod which extends through the black backdrop to the mass balance. A glass duct borders the FFB, which is rolled underneath the leaf from

the left. The IR image is taken through a 1-inch hole in the glass.

Leaf thickness profile, dry dead leaf

Figure 2. (Left) schematic of leaf divided into analysis regions, first into equal leaf-area rows, then into equal leaf-area regions on each row; (right) example of a subdivided

leaf (m = 20, n = 10).

Figure 3. Temperature histograms at 3 s of heating averaging all runs for (a) dry dead leaves, (b) rehydrated dead leaves, (c) dehydrated live leaves, and (d) fresh live leaves. Error bars represent 95% CIs on bin temperature (horizontal) and fraction of leaf area

(vertical). Fraction of leaf area is determined by pixel counting of the IR images.

(a) (b)

(c) (d)

Figure 4. Traces of temperature histograms at 2 s, 4 s, 6 s and 8 s, averaging all runs for (a) dry dead leaves, (b) rehydrated dead leaves, (c) dehydrated live leaves, and (d)

fresh live leaves. Each marker represents one histogram bin (see Figure 3).

(a) (b)

(c) (d)

Figure 5. Mode temperatures averaged for each leaf group. Average values (solid with markers) are bounded by 95% CIs (dashed or dotted).

Figure 6. Average normalized mass remaining for each leaf group. Average values (solid with markers) are bounded by 95% CIs (dashed or dotted).

Mass vs. Temperature

Figure 7. IR thermal images of a fresh live manzanita leaf during heating at 2 s intervals. Temperature maps such as these were averaged with other runs to

produce the histograms in Figures 3 and 4.

Figure 8. Modeled and experimental mass release during heating for each leaf group: (a) dry dead, (b) rehydrated dead, (c) dehydrated live and (d) fresh live. The experimental mass curves are bounded by 95% intervals. The data-fit single-

component, model-fit single-component, multicomponent one-step and CPD models are plotted. The TPD model treats water release for all cases.

(a) (b)

(c) (d)

Figure 9. Comparison of TLH, KIN and TPD water release models for (a) a rehydrated dead leaf, (b) a dehydrated live leaf, and (c) a fresh live leaf. The multicomponent one-step model was used to determine a dry mass curve to which each water prediction is

added. Quenching MC data is included with 95% CIs.

(a) (b)

(c)

Pictures vs. Time

2 s

2

Rehydrated

Dehydrated

Fresh

2

6 8 10 12

6 8 10 12

2 6 8 10 12